Section 1 Quantum Devices

**Chapter 1**

**Abstract**

**1. Introduction**

**3**

performed using those devices.

Principles and Applications

*Parsoua A. Sohi and Mojtaba Kahrizi*

of Nanoplasmonics in Biological

and Chemical Sensing: A Review

Biosensing requires a highly sensitive real-time detection of the biomolecules. These properties are granted by nanoplasmonic sensing techniques. SPR-based optical sensors have evolved as a sensitive and versatile biosensing tool. A growing number of SPR-based sensing applications in the solution of clinical problems are reported in the recent years. This refers to the point that these sensors provide labelfree detection of the living cells and non-destructive analysis techniques. In this study, we will review the mechanism of the detection in SPR biosensing, followed by the methods used to develop sensors to detect gases and the chemical, biological, and molecular interaction. The device sensitivity improvement based on plasmonic effects is also addressed in this study, and accordingly, the size and material dependence of the resonance frequency are discussed. The reviewed articles are categorized into three groups, depending on the SPR excitation configuration. In the first group of the sensors, the sensitivity of LSPR-based sensors in prism coupler configurations is reviewed. The second group, SPR excitation by optical fiber, slightly improved the sensitivity of the detections. The unique capability of the third group, photonic crystal fiber SPR sensors, in providing greatly improved sensitivity, generated a vast field of researches and applications in biosensing devices.

**Keywords:** surface plasmon resonance, localized surface plasmon resonance, nanoplasmonics, biosensors, extraordinary optical transmission, photonic crystals

For the measurements of chemical and biological quantities in biomedical applications, a variety of methods were available and researched extensively in the last 30 years. In optical sensing, the first chemical sensors were based on the absorption spectrum of species to be measured [1]. Other chemical and biosensors have been developed since that time based on a diversity of optical techniques that involved luminescence, phosphorescence, fluorescence, particle light scattering, Raman scattering, ellipsometry, interferometry, and surface plasmon phenomena. For sensing purposes, measurements of the refractive index and absorbance or fluorescence properties of analyte molecules or a chemo-optical transducing medium were

Among the different techniques developed, the potential of surface plasmon (SP) sensors was clearly recognized due to their great sensitivity, their simple structure,

### **Chapter 1**

## Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review

*Parsoua A. Sohi and Mojtaba Kahrizi*

### **Abstract**

Biosensing requires a highly sensitive real-time detection of the biomolecules. These properties are granted by nanoplasmonic sensing techniques. SPR-based optical sensors have evolved as a sensitive and versatile biosensing tool. A growing number of SPR-based sensing applications in the solution of clinical problems are reported in the recent years. This refers to the point that these sensors provide labelfree detection of the living cells and non-destructive analysis techniques. In this study, we will review the mechanism of the detection in SPR biosensing, followed by the methods used to develop sensors to detect gases and the chemical, biological, and molecular interaction. The device sensitivity improvement based on plasmonic effects is also addressed in this study, and accordingly, the size and material dependence of the resonance frequency are discussed. The reviewed articles are categorized into three groups, depending on the SPR excitation configuration. In the first group of the sensors, the sensitivity of LSPR-based sensors in prism coupler configurations is reviewed. The second group, SPR excitation by optical fiber, slightly improved the sensitivity of the detections. The unique capability of the third group, photonic crystal fiber SPR sensors, in providing greatly improved sensitivity, generated a vast field of researches and applications in biosensing devices.

**Keywords:** surface plasmon resonance, localized surface plasmon resonance, nanoplasmonics, biosensors, extraordinary optical transmission, photonic crystals

### **1. Introduction**

For the measurements of chemical and biological quantities in biomedical applications, a variety of methods were available and researched extensively in the last 30 years. In optical sensing, the first chemical sensors were based on the absorption spectrum of species to be measured [1]. Other chemical and biosensors have been developed since that time based on a diversity of optical techniques that involved luminescence, phosphorescence, fluorescence, particle light scattering, Raman scattering, ellipsometry, interferometry, and surface plasmon phenomena. For sensing purposes, measurements of the refractive index and absorbance or fluorescence properties of analyte molecules or a chemo-optical transducing medium were performed using those devices.

Among the different techniques developed, the potential of surface plasmon (SP) sensors was clearly recognized due to their great sensitivity, their simple structure,

and their capacity in terms of real-time analysis of biospecific interactions without the use of labeled molecules. In fact, SP sensors have been the preferred devices used in real-time analysis situations. They are based on surface plasmon resonance, or collective electron oscillations, that may exist at a metal-dielectric interface. Light is used for excitation of the SP waves, resulting in the transfer of energy into the SP wave. As there is a strong concentration of the electromagnetic field in the dielectric, the propagation constant of the SP wave depends strongly on variations of the optical properties of the dielectric medium surrounding the metallic surface.

Light incident on a smooth metallic surface cannot excite surface plasmons due to the transverse character of the optical wave and the longitudinal character of the SP wave, preventing the coupling between the two. A coupling mechanism is thus necessary, and it can be provided by surface rugosity [2], a grating structure [3], or Kretschmann and Otto prism configurations [4, 5]. Based on this, we can classify the sensors according to the following: (a) sensors using optical prism couplers [4], (b) sensors using grating couplers [6], (c) sensors using optical fibers (SP resonance active metal layer deposited around the fiber core) [7, 8], and (d) sensors using integrated optical waveguides [9]. The sensor characteristics include (a) its sensitivity (derivative of the monitored SP resonance parameter, such as the resonant angle or the wavelength, with respect to the parameter to be determined, such as the refractive index or the overlayer thickness), (b) its resolution (minimum change in the parameter to be determined), and (c) its operating range (range of values of the parameter to be determined). As an example, resolution in the range of <sup>4</sup> <sup>10</sup><sup>5</sup> refractive index unit (RIU) can be generally achieved in sensors using optical prism couplers, while sensors using grating couplers can demonstrate a resolution in the range of 10<sup>6</sup> RIU. Among existing sensing devices, SP sensors using optical fibers presented the best prospect for miniaturization, but it is no longer the case as can be seen below. For their part, sensors based on integrated optical waveguides are promising in the development of multichannel sensing devices, with however limitations on sensitivity performance due to the relatively low concentration of the electromagnetic field achieved in the analyte.

then be coupled to a SP wave which results in a strong absorption at a certain wavelength and angle of incidence. Accordingly there are two types of resonance measurement techniques: angular interrogations (measuring absorption as a function of incident angle) and wavelength interrogations (measuring absorption as a

*SPR electromagnetic wave propagates parallel to the metal-dielectric interface. The evanescent field of SPPs is*

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review*

Surface plasmon resonance (SPR) can be seen as the electromagnetic surface waves that are the solution of Maxwell equation. According to the solution of Maxwell equation, SPR occurs at the interface of a material with a positive dielectric constant with that of a negative dielectric constant (such as noble metals). The waves propagate in the x-y plane along the metal-dielectric interface, and their lateral extensions evanescently decay into both sides of the interface (decay in the z-direction). The penetration length of the evanescent waves is longer for the

S-polarized light (TE polarization) is referred to the polarization state that the electric field is parallel to the surface of the interface. P-polarized (TM polarized) light is the light that the electric field lays on the plane of the incident (the perpendicular plane to the surface of the interface and contains the wavevector of the excitation source). To excite the SPP modes, it is required to have the components of the electric field acting along the metal-dielectric interface. Hence, the oblique incident of the P-polarized light, which has the nonzero perpendicular electric

P-polarized light with a particular wavelength and incident angle induces SPR once the wavevector value of the SP wave is identical to that of the incident light. The dispersion relation of the SPPs can be derived from the solution of wave equation for a P-polarized electromagnetic incident light governed by Maxwell equations subjected to the continuity of the tangential and normal field component as the boundary conditions. The wavevector of the SPP (*KSPP*Þ is determined by the

> ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi *εmε<sup>d</sup> ε<sup>m</sup>* þ *ε<sup>d</sup>*

(1)

r

where ω is the frequency of excitation source, c is velocity of the light, and *ε<sup>m</sup>* and *ε<sup>d</sup>* are dielectric constants of the metal and dielectric material, respectively [12]. As the real part of the *KSPP* for noble metals always falls below the wavevector of the

*KSPP* <sup>¼</sup> *<sup>ω</sup> c*

function of incident wavelength) [10, 11].

*DOI: http://dx.doi.org/10.5772/intechopen.93001*

*decaying in either side of the interface.*

**Figure 1.**

vector component on the z-axis, is required.

following relation:

**5**

dielectric medium compared to the metallic side (**Figure 1**).

Recently, however, the event of ordered periodic nanostructures as well as of photonic crystal configurations has opened a wealth of new opportunities. Although nanoparticles are not new, new tools for their engineering in complex architectures at nanoscale have helped to discover and understand new and exciting phenomena, important not only for fundamental studies but also for device and system. Due to the renewed interest generated by the new fabrication tools (self-assembly methods, electron-beam lithographic methods, nanoimprint methods) and the extraordinary properties exhibited by ordered structures, a new term, "plasmonics," has been coined to describe the study of metallic and metallodielectric nanostructures and plasmon. The promise of highly integrated optical devices with structural elements smaller than the light wavelength made many to refer to it as the "next big thing" in nanotechnology.

### **2. Principle of operation**

Surface plasmon is a charge density wave that exists at the interface between a metal and a dielectric. Surface plasmon polaritons (SPP) is collective oscillation of SPs, which is induced by an electromagnetic wave. This is the interesting optical property of noble metals, as these materials provide the best evidence of SPPs due to possession of high density of electrons free to move. SPs are optically excited at resonance condition. The resonance condition is referred to the condition where the momentum and energy of an incident photon matches that of a SP. Light energy can *Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review DOI: http://dx.doi.org/10.5772/intechopen.93001*

**Figure 1.**

and their capacity in terms of real-time analysis of biospecific interactions without the use of labeled molecules. In fact, SP sensors have been the preferred devices used in real-time analysis situations. They are based on surface plasmon resonance, or collective electron oscillations, that may exist at a metal-dielectric interface. Light is used for excitation of the SP waves, resulting in the transfer of energy into the SP wave. As there is a strong concentration of the electromagnetic field in the dielectric, the propagation constant of the SP wave depends strongly on variations of the optical

Light incident on a smooth metallic surface cannot excite surface plasmons due to the transverse character of the optical wave and the longitudinal character of the SP wave, preventing the coupling between the two. A coupling mechanism is thus necessary, and it can be provided by surface rugosity [2], a grating structure [3], or Kretschmann and Otto prism configurations [4, 5]. Based on this, we can classify the sensors according to the following: (a) sensors using optical prism couplers [4], (b) sensors using grating couplers [6], (c) sensors using optical fibers (SP resonance active metal layer deposited around the fiber core) [7, 8], and (d) sensors using integrated optical waveguides [9]. The sensor characteristics include (a) its sensitivity (derivative of the monitored SP resonance parameter, such as the resonant angle or the wavelength, with respect to the parameter to be determined, such as the refractive index or the overlayer thickness), (b) its resolution (minimum change in the parameter to be determined), and (c) its operating range (range of values of the parameter to be determined). As an example, resolution in the range of <sup>4</sup> <sup>10</sup><sup>5</sup> refractive index unit (RIU) can be generally achieved in sensors using optical prism couplers, while sensors using grating couplers can demonstrate a resolution in the range of 10<sup>6</sup> RIU. Among existing sensing devices, SP sensors using optical fibers presented the best prospect for miniaturization, but it is no longer the case as can be seen below. For their part, sensors based on integrated optical waveguides are promising in the development of multichannel sensing devices, with however limitations on sensitivity performance due to the relatively

properties of the dielectric medium surrounding the metallic surface.

*Recent Advances in Nanophotonics - Fundamentals and Applications*

low concentration of the electromagnetic field achieved in the analyte.

the renewed interest generated by the new fabrication tools (self-assembly methods, electron-beam lithographic methods, nanoimprint methods) and the

"plasmonics," has been coined to describe the study of metallic and metallodielectric nanostructures and plasmon. The promise of highly integrated optical devices with structural elements smaller than the light wavelength made many to

Surface plasmon is a charge density wave that exists at the interface between a metal and a dielectric. Surface plasmon polaritons (SPP) is collective oscillation of SPs, which is induced by an electromagnetic wave. This is the interesting optical property of noble metals, as these materials provide the best evidence of SPPs due to possession of high density of electrons free to move. SPs are optically excited at resonance condition. The resonance condition is referred to the condition where the momentum and energy of an incident photon matches that of a SP. Light energy can

extraordinary properties exhibited by ordered structures, a new term,

refer to it as the "next big thing" in nanotechnology.

**2. Principle of operation**

**4**

Recently, however, the event of ordered periodic nanostructures as well as of photonic crystal configurations has opened a wealth of new opportunities. Although nanoparticles are not new, new tools for their engineering in complex architectures at nanoscale have helped to discover and understand new and exciting phenomena, important not only for fundamental studies but also for device and system. Due to

*SPR electromagnetic wave propagates parallel to the metal-dielectric interface. The evanescent field of SPPs is decaying in either side of the interface.*

then be coupled to a SP wave which results in a strong absorption at a certain wavelength and angle of incidence. Accordingly there are two types of resonance measurement techniques: angular interrogations (measuring absorption as a function of incident angle) and wavelength interrogations (measuring absorption as a function of incident wavelength) [10, 11].

Surface plasmon resonance (SPR) can be seen as the electromagnetic surface waves that are the solution of Maxwell equation. According to the solution of Maxwell equation, SPR occurs at the interface of a material with a positive dielectric constant with that of a negative dielectric constant (such as noble metals). The waves propagate in the x-y plane along the metal-dielectric interface, and their lateral extensions evanescently decay into both sides of the interface (decay in the z-direction). The penetration length of the evanescent waves is longer for the dielectric medium compared to the metallic side (**Figure 1**).

S-polarized light (TE polarization) is referred to the polarization state that the electric field is parallel to the surface of the interface. P-polarized (TM polarized) light is the light that the electric field lays on the plane of the incident (the perpendicular plane to the surface of the interface and contains the wavevector of the excitation source). To excite the SPP modes, it is required to have the components of the electric field acting along the metal-dielectric interface. Hence, the oblique incident of the P-polarized light, which has the nonzero perpendicular electric vector component on the z-axis, is required.

P-polarized light with a particular wavelength and incident angle induces SPR once the wavevector value of the SP wave is identical to that of the incident light. The dispersion relation of the SPPs can be derived from the solution of wave equation for a P-polarized electromagnetic incident light governed by Maxwell equations subjected to the continuity of the tangential and normal field component as the boundary conditions. The wavevector of the SPP (*KSPP*Þ is determined by the following relation:

$$K\_{SPP} = \frac{\alpha}{c} \sqrt{\frac{\varepsilon\_m \varepsilon\_d}{\varepsilon\_m + \varepsilon\_d}} \tag{1}$$

where ω is the frequency of excitation source, c is velocity of the light, and *ε<sup>m</sup>* and *ε<sup>d</sup>* are dielectric constants of the metal and dielectric material, respectively [12]. As the real part of the *KSPP* for noble metals always falls below the wavevector of the incident light *Kx* <sup>¼</sup> <sup>2</sup>*<sup>π</sup> <sup>λ</sup> sin<sup>θ</sup>* � �, to match the wave vectors, specific excitation configuration is required. The prism coupling is a simple and standard technique to induce SPR. The underlying principle of this is to bring down the wavevector of the incident light by passing through a high refractive index prism with nprism > ndielectric in a specific incident angle (θ). The wavevector matching at resonance condition for the prism coupler configuration is defined by

$$K\_{\mathfrak{x}} = K\_{\text{SPP}} \tag{2}$$

In the last many years, numerous researches have involved coupling photons to surface plasmons to study the effect of various materials, structure, and configurations on resonance spectrum. Potential applications extend to new light sources, solar cells, holography, Raman spectroscopy, microscopy, and sensors. In the following sections, the recent advances of SPR sensing applications are explored.

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review*

Numerous useful strategies of protein labeling have been developed for biophysical characterization of proteins including their structure, folding, and interaction with other proteins [18]. Molecular labels, such as biotin, reporter enzymes, fluorophores, and radioactive isotopes, attach covalently to target protein and nucleotides to facilitate identifying and quantifying of labeled target [19]. As the use of the molecular labels may modify the structural configuration and the binding properties of the molecules of interest, a variety of label-free methods have been developed. Among the various sensing methodologies, the SPR-based system is a reliable type of label-free technique for monitoring biomolecular interactions particularly in thermodynamic and kinetic analyses [18–21]. Biosensing application of SPR was first reported in 1983 [22, 23]. As it was mentioned in Section 2, SPR sensors are sensitive to changes in refractive index of the bulk solution in the vicinity of their active surface. Although several techniques are proposed to improve the sensitivity of SPR measurements [5, 24], the sensitivity to monolayers or molecular binding is obtained by the confinement of the plasmonic field in the nanostructured noble metals, which is known as LSPR. The smaller decay length associated with LSPR than that of SPR makes it more sensitive to local refractive index surrounding the nanostructures. **Figure 4a** illustrates the sensitivity of the LSPR spectrum of the functionalized gold nanostructures (shown in **Figure 4b**)

**3. Applications in biological and chemical sensing**

*(a) Waveguide coupler and (b) diffraction grating.*

*DOI: http://dx.doi.org/10.5772/intechopen.93001*

**Figure 3.**

**7**

toward adsorption of amyloid β-derived diffusible ligands (ADDL).

tivities that would be predicted from their aspect ratios alone [12, 26–28].

The impact of the shape and size of the nanostructured noble metals on the device sensitivity is demonstrated by many research groups. Analytical studies revealed that the sharp-tipped structures are reinforcing higher refractive index sensitivity due to the higher electromagnetic fields produced on their sharp edges. Reportedly, particles with sharp tips produce much higher refractive index sensi-

Several geometries have been widely explored in recent years for developing LSPR sensors. Ekinci et al. [29] compared the extinctions spectra of Au, Al, and Ag nanoparticles of the same size. Well-defined ordered nanoparticle arrays were fabricated on quartz substrates. The diameter of the structures varied between 20 and 140 nm. Al nanoparticles with 40 nm diameters exhibit strong and sharp plasmon resonances in the near- and deep-UV ranges. Peaks in visible range were

$$\frac{2\pi}{\lambda}n\_{prim}\sin\theta = \frac{2\pi}{\lambda}\text{ Re}\left\{\sqrt{\frac{\varepsilon\_m\varepsilon\_d}{\varepsilon\_m + \varepsilon\_d}}\right\}\tag{3}$$

where *λ* is the wavelength of the incident light [10]. Equation (3) states that as the refractive index of the dielectric is altered, the propagation constant of the SP mode is altered. This results in changing the coupling conditions between the incident light and SP modes.

**Figure 2** demonstrates the SPR experimental setup using Kretschmann prism coupling [13, 14], which provides proper synchronization between KSPP and Kx. **Figure 2b** shows the dispersion relation for SP in matter. It is seen that by using the prism, it is possible to couple the wavevectors of the SP with that of the incident light.

There are other SPR excitation configurations reported in the literature such as Otto prism coupler [15], waveguide and fiber-optic coupler [16], and diffraction grating [6]. The principal of the waveguide (and fiber-optics) coupler is close to what was explained for prism coupler, except in this configuration it is not possible to interrogate the incident angle (**Figure 3a**). In diffraction grating configuration, the incident electromagnetic radiation is directed toward a medium whose surface has a spatial periodicity (Λ) similar to the wavelength of the radiation. The incident beam is diffracted in different orders producing propagating evanescent modes at the interface. The evanescent modes have wavevectors parallel to the interface similar to the incident radiation but with integer "quanta" of the grating wavevector added or subtracted from it. These modes couple to SP, which run along the interface between the grating and the ambient medium. The diffraction grating is the only configuration that generates the SP in the same side of the metallic layer as the incident light. The only drawback of this configuration is having more than one peak in the resonance spectrum as there are several orders of diffractions in the reflected beam [17].

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review DOI: http://dx.doi.org/10.5772/intechopen.93001*

**Figure 3.**

incident light *Kx* <sup>¼</sup> <sup>2</sup>*<sup>π</sup>*

incident light and SP modes.

reflected beam [17].

**Figure 2.**

**6**

light.

*<sup>λ</sup> sin<sup>θ</sup>* � �, to match the wave vectors, specific excitation config-

*Kx* ¼ *KSPP* (2)

(3)

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi *εmε<sup>d</sup> ε<sup>m</sup>* þ *ε<sup>d</sup>* � � r

uration is required. The prism coupling is a simple and standard technique to induce SPR. The underlying principle of this is to bring down the wavevector of the

*<sup>λ</sup> Re*

where *λ* is the wavelength of the incident light [10]. Equation (3) states that as the refractive index of the dielectric is altered, the propagation constant of the SP mode is altered. This results in changing the coupling conditions between the

**Figure 2** demonstrates the SPR experimental setup using Kretschmann prism coupling [13, 14], which provides proper synchronization between KSPP and Kx. **Figure 2b** shows the dispersion relation for SP in matter. It is seen that by using the prism, it is possible to couple the wavevectors of the SP with that of the incident

There are other SPR excitation configurations reported in the literature such as Otto prism coupler [15], waveguide and fiber-optic coupler [16], and diffraction grating [6]. The principal of the waveguide (and fiber-optics) coupler is close to what was explained for prism coupler, except in this configuration it is not possible to interrogate the incident angle (**Figure 3a**). In diffraction grating configuration, the incident electromagnetic radiation is directed toward a medium whose surface has a spatial periodicity (Λ) similar to the wavelength of the radiation. The incident beam is diffracted in different orders producing propagating evanescent modes at the interface. The evanescent modes have wavevectors parallel to the interface similar to the incident radiation but with integer "quanta" of the grating wavevector added or subtracted from it. These modes couple to SP, which run along the interface between the grating and the ambient medium. The diffraction grating is the only configuration that generates the SP in the same side of the metallic layer as the incident light. The only drawback of this configuration is having more than one peak in the resonance spectrum as there are several orders of diffractions in the

*(a) Prism coupling, Kretschmann configuration, and (b) dispersion relation of incident light coupling SP.*

nprism > ndielectric in a specific incident angle (θ). The wavevector matching at

incident light by passing through a high refractive index prism with

*Recent Advances in Nanophotonics - Fundamentals and Applications*

resonance condition for the prism coupler configuration is defined by

*<sup>λ</sup> nprism* sin *<sup>θ</sup>* <sup>¼</sup> <sup>2</sup>*<sup>π</sup>*

2*π*

*(a) Waveguide coupler and (b) diffraction grating.*

In the last many years, numerous researches have involved coupling photons to surface plasmons to study the effect of various materials, structure, and configurations on resonance spectrum. Potential applications extend to new light sources, solar cells, holography, Raman spectroscopy, microscopy, and sensors. In the following sections, the recent advances of SPR sensing applications are explored.

### **3. Applications in biological and chemical sensing**

Numerous useful strategies of protein labeling have been developed for biophysical characterization of proteins including their structure, folding, and interaction with other proteins [18]. Molecular labels, such as biotin, reporter enzymes, fluorophores, and radioactive isotopes, attach covalently to target protein and nucleotides to facilitate identifying and quantifying of labeled target [19]. As the use of the molecular labels may modify the structural configuration and the binding properties of the molecules of interest, a variety of label-free methods have been developed. Among the various sensing methodologies, the SPR-based system is a reliable type of label-free technique for monitoring biomolecular interactions particularly in thermodynamic and kinetic analyses [18–21]. Biosensing application of SPR was first reported in 1983 [22, 23]. As it was mentioned in Section 2, SPR sensors are sensitive to changes in refractive index of the bulk solution in the vicinity of their active surface. Although several techniques are proposed to improve the sensitivity of SPR measurements [5, 24], the sensitivity to monolayers or molecular binding is obtained by the confinement of the plasmonic field in the nanostructured noble metals, which is known as LSPR. The smaller decay length associated with LSPR than that of SPR makes it more sensitive to local refractive index surrounding the nanostructures. **Figure 4a** illustrates the sensitivity of the LSPR spectrum of the functionalized gold nanostructures (shown in **Figure 4b**) toward adsorption of amyloid β-derived diffusible ligands (ADDL).

The impact of the shape and size of the nanostructured noble metals on the device sensitivity is demonstrated by many research groups. Analytical studies revealed that the sharp-tipped structures are reinforcing higher refractive index sensitivity due to the higher electromagnetic fields produced on their sharp edges. Reportedly, particles with sharp tips produce much higher refractive index sensitivities that would be predicted from their aspect ratios alone [12, 26–28].

Several geometries have been widely explored in recent years for developing LSPR sensors. Ekinci et al. [29] compared the extinctions spectra of Au, Al, and Ag nanoparticles of the same size. Well-defined ordered nanoparticle arrays were fabricated on quartz substrates. The diameter of the structures varied between 20 and 140 nm. Al nanoparticles with 40 nm diameters exhibit strong and sharp plasmon resonances in the near- and deep-UV ranges. Peaks in visible range were

enhancements. Conclusively, in general, LSPR of nanoparticles is more suitable for applications which rely on large local enhancements of electric field, such as surface

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review*

Another form of SPR-based sensors involves extraordinary light transmission (EOT). Periodic structures consisting of a thin metallic film perforated with an array of nanoscale holes exhibit EOT provided that the hole size is in the

subwavelength range. This porous structure can convert light into SPs by providing the necessary momentum conservation for the coupling process. EOT is determined when the transmission spectrum contains a set of peaks with enhanced transmission, although the individual holes are so small that they do not allow propagation of light. Multiple EOT peaks are correlated with excitation of various SPP modes. These peaks are generated by excitation of LSP modes which occurs in the inner

> **Range of λ**

> > NIR

NIR

Vis

Vis

NIR

Au nanorods Experimental 650 NIR 1.34–1.7 LSPR, tunable with size of the

*\*In most reported researches, analytically studied sensors show higher sensitivities than that of the experimental studies.*

Experimental — NIR 1.46, 1.51,

Au nanoring Experimental 880 NIR 1.33–1.4 LSPR. Effect of size is studied [30]

Analytical 1200 NIR 1.33–1.38 LSPR. Effect of ring

**Medium/ RI**

1.357

ADDL fibrinogen AT5G0701

1.63

Experimental 70 Vis 1.32–1.5 LSPR, 30 nm diameter of the

Experimental 300 Vis 1.333–1.35 LSPR. Dielectric spacer layer

**Comment Ref**

[43]

[44]

[10]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

configuration is studied

geometrical parameters

LSPR. In this study protrusive thin films showed higher sensitivity

between plasmonic film and substrate improved the sensitivity

was tuned from 650 to 850 nm by varying the interhole separation

structures. Particles with mean diameters of 18 2 nm

LSPR, refractive indices refer to CCl4, TCE, and CS2

particles

diameter with 500 nm periodicity

particles

1.33–1.36 EOT, holes of 200 nm

LSPR [25]

1–1.6 LSPR. Tuned based on

1–1.5 LSPR. The resonance peak

1–1.658 LSPR. Nonuniform

enhanced Raman scattering.

*DOI: http://dx.doi.org/10.5772/intechopen.93001*

**Structure Study\* Sensitivity**

Au nanowell Experimental 1200–1600 Vis-

Double split Au nanoring

Au thin film with cubic nanoholes

Au thin film with circular nanoholes

Au thin film with circular nanoholes

Au nanoparticle

Quantum dots of copper sulfate

Au colloidal nanoparticles

Au thin film with nanoholes

**Table 1.**

**9**

**(nm/RIU)**

Analytical 2000 Vis 1.333 and

Experimental 200 Vis-

Experimental 57 UV-

Experimental 481 Vis-

*Characteristics of several reported SPR-based biological/chemical sensors.*

Au nanoring Experimental — UV-

**Figure 4.**

*(a) UV-VIS spectrum of ADDLs on gold and (b) nanohole/nanoring array prepared with 530 nm polystyrene (PS0 microspheres) and 20 nm Au layer. The inset shows enlarged image of a region where PS spheres were not completely removed. Au nanoparticles are around and on the top of the spheres [25].*

observed for Ag and Au nanoparticles. Increasing the diameter of the nanoparticles for tested materials resulted in a red shift in the peak position.

Considering the feasibility of fabrication, nanoring and nanodisk structures have gained great interest for their biological and chemical sensing properties. Larsson et al. [30] compared the LSPR resonance sensitivity of gold nanorings and nanodisks to refractive index changes of bulk and thin dielectric films with different thicknesses. The sensitivity of nanoring structures was found significantly higher than that of nanodisks with similar diameters in the near-infrared spectrum. Tuning of the LSPR peak wavelength between approximately 1000–1300 nm was obtained by changing the diameter of the nanorings. It is also reported that the extinction spectrum [31] of the nanoring structure is affected by the angle of incidence. By varying the incidence angle from normal to oblique, several higher-energy plasmon resonances appear in the extinction spectrum of the nanoring structures [32].

The mechanism of the enhancement of plasmon resonance in a ring array is analytically studied by Wang et al. [33]. They successfully studied the sensitivity of the device based on the dimension and periodicity of the nanorings. According to their results, increasing the thickness of the nanorings introduces a blue shift in resonance peak wavelength. For the thicknesses above 40 nm, the second resonant peak appears near the short wavelength (below 600 nm). Regarding the periodicity, as the period decreases, a red shift was observed in the position of resonance peak. Sensing characteristics of the optimum sensor was experimentally tested for refractive indices in the range of 1.33–1.4 (obtained from different ratios of glycerol water mixtures). The results also showed a linear relationship of the peak position and refractive index of the medium.

Although biological sensing applications of nanostructure-based LSPR have been reported in several laboratory level studies, commercialized implementation of this technique still requires large improvement regarding reproducibility of the structures in terms of size and shape of nanoparticles. Reproducible structures such as patterned thin films either with perforations or protrusions show a similar plasmonic response [34].

Parsons et al. [35] compared the plasmonic response of nanoparticle and nanohole arrays. They have shown that the spectral response depends on inter-hole separation, while there seems to be little effect of the interparticle spacing. This conclusion is referred to the coupling mechanism of the SPP mode that the thin metal film supports. It was also shown that the resonant spectrum of the thin film perforated with nanohole arrays is qualitatively similar to a particle of approximately the same dimensions and quantitatively shows weaker local field

### *Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review DOI: http://dx.doi.org/10.5772/intechopen.93001*

enhancements. Conclusively, in general, LSPR of nanoparticles is more suitable for applications which rely on large local enhancements of electric field, such as surface enhanced Raman scattering.

Another form of SPR-based sensors involves extraordinary light transmission (EOT). Periodic structures consisting of a thin metallic film perforated with an array of nanoscale holes exhibit EOT provided that the hole size is in the subwavelength range. This porous structure can convert light into SPs by providing the necessary momentum conservation for the coupling process. EOT is determined when the transmission spectrum contains a set of peaks with enhanced transmission, although the individual holes are so small that they do not allow propagation of light. Multiple EOT peaks are correlated with excitation of various SPP modes. These peaks are generated by excitation of LSP modes which occurs in the inner


### **Table 1.**

*Characteristics of several reported SPR-based biological/chemical sensors.*

observed for Ag and Au nanoparticles. Increasing the diameter of the nanoparticles

*(a) UV-VIS spectrum of ADDLs on gold and (b) nanohole/nanoring array prepared with 530 nm polystyrene (PS0 microspheres) and 20 nm Au layer. The inset shows enlarged image of a region where PS spheres were not*

nanodisks to refractive index changes of bulk and thin dielectric films with different thicknesses. The sensitivity of nanoring structures was found significantly higher than that of nanodisks with similar diameters in the near-infrared spectrum. Tuning of the LSPR peak wavelength between approximately 1000–1300 nm was obtained by changing the diameter of the nanorings. It is also reported that the extinction spectrum [31] of the nanoring structure is affected by the angle of incidence. By varying the incidence angle from normal to oblique, several higher-energy plasmon resonances appear in the extinction spectrum of the nanoring structures [32]. The mechanism of the enhancement of plasmon resonance in a ring array is analytically studied by Wang et al. [33]. They successfully studied the sensitivity of the device based on the dimension and periodicity of the nanorings. According to their results, increasing the thickness of the nanorings introduces a blue shift in resonance peak wavelength. For the thicknesses above 40 nm, the second resonant peak appears near the short wavelength (below 600 nm). Regarding the periodicity, as the period decreases, a red shift was observed in the position of resonance peak. Sensing characteristics of the optimum sensor was experimentally tested for refractive indices in the range of 1.33–1.4 (obtained from different ratios of glycerol water mixtures). The results also showed a linear relationship of the peak position and

Although biological sensing applications of nanostructure-based LSPR have been reported in several laboratory level studies, commercialized implementation of this technique still requires large improvement regarding reproducibility of the structures in terms of size and shape of nanoparticles. Reproducible structures such as patterned thin films either with perforations or protrusions show a similar

Parsons et al. [35] compared the plasmonic response of nanoparticle and nanohole arrays. They have shown that the spectral response depends on inter-hole separation, while there seems to be little effect of the interparticle spacing. This conclusion is referred to the coupling mechanism of the SPP mode that the thin metal film supports. It was also shown that the resonant spectrum of the thin film perforated with nanohole arrays is qualitatively similar to a particle of approximately the same dimensions and quantitatively shows weaker local field

Considering the feasibility of fabrication, nanoring and nanodisk structures have gained great interest for their biological and chemical sensing properties. Larsson et al. [30] compared the LSPR resonance sensitivity of gold nanorings and

for tested materials resulted in a red shift in the peak position.

*completely removed. Au nanoparticles are around and on the top of the spheres [25].*

*Recent Advances in Nanophotonics - Fundamentals and Applications*

refractive index of the medium.

plasmonic response [34].

**8**

**Figure 4.**

surface of hole arrays and SPP modes at the surface of the thin film, in the upper and lower rims of the holes [36].

The transmission of electromagnetic waves through a subwavelength hole was investigated by Bethe [37] for the first time. The transmission will occur at specific frequencies imposed by geometrical parameters of the structure, polarization, angle of incident light, and permittivity of the surrounding media. These findings found many applications owing to the simplicity with which their spectral properties can be tuned on.

In several studies [38–41] it was shown that the peak positions are determined by the periodicity of the holes. The periodicity is usually comparable to the wavelength of the incident light. By modifying the film thickness and diameter of the holes, one can control the shape of the peaks in terms of the width and intensity. It was due to these facts that many researchers believe that SPP is responsible for EOT and developed models to explain the phenomena.

The simple structure (perforated thin films) of EOT-based devices is widely studied for potential applications, from optical switches and photolithography masks to sensing applications. Despite this simple structure, the quality of the noble metal film in terms of surface roughness, grain size, and purity is equally important for EOT device application. A single crystalline thin film with atomically smooth surface is required in order to maximize the propagation length of SPP. A smooth surface results in elimination of scattering and loss of the incident light. This improves the transmission spectrum of the device, though it is very challenging to synthesize or grow uniform single crystalline films over a large area [42].

**Table 1** summarizes the reported characteristics of few SPR-, LSPR-, and EOTsupported sensors. As it can be seen, the geometry of the metal film plays an important role in plasmon frequency. As an example, gold has plasmon frequency in the deep ultraviolet; however geometric factors create the possibility to tune the resonance peak wavelength range. The sensitivity (S) of the sensors utilizing the wavelength interrogation is defined as

$$\mathcal{S}\left(\frac{nm}{RIU}\right) = \frac{\delta\lambda\_{rs}}{\delta n\_d} \tag{4}$$

**Structure Study Sensitivity**

*DOI: http://dx.doi.org/10.5772/intechopen.93001*

Single mode, Aucoated core

Tapered fiber, Aucoated

Biconical tapered, Au-coated

Uncladded fiber, Aucoated

**Table 2.**

**Figure 5.**

Gold-coated D-shaped PCF

Two parallel Au-coated D-shaped PCFs

Silvergraphene, Dshaped PCF

PCF externally coated with TiO2-Au

**11**

*(c) D-shaped PCF SPR sensor [56].*

**Structure Study Sensitivity**

Experimental and analytical **(nm/RIU)**

Analytical 23,000 Vis-

46,000 Vis-

**(nm/RIU)**

Experimental 400 Vis-

Experimental 1700 Vis-

*Characteristics of several reported fiber-optic SPR-based sensors.*

Experimental 3200 Vis 1.33–

Experimental 2100 Vis 1.326–

**Range of λ**

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review*

NIR

NIR

*Schematics of PCF-SPR sensors. (a) Analyte-filled cladding holes [54], (b) externally coated PCF [55], and*

**Range of λ**

NIR

NIR

**Medium/ RI**

Analytical 3700 Vis 1.33–1.37 This sensitivity is found for RI

Analytical 13,500 NIR 1.27–1.33 13,500 is the maximum

1.33–1.42 This is the maximum

1.32–1.40 23,000 is the maximum

sensitivity. The average sensitivity of 9800 nm/RIU is reported

of 1.36

sensitivity for RI of 1.32

sensitivity for RI of 1.32

**Medium/ RI**

1.3385

1.375

1.333– 1.35

**Comment Ref**

— [59]

**Comment Ref**

[54]

[61]

[62]

[63]

[57]

[58]

[60]

The sensor is able to detect index changes as low as 4 <sup>10</sup><sup>6</sup> under moderate fiber deformations

and quantitative biochemical detection

Red shift was observed in resonance wavelength of the patterned Au layer

1.35–1.42 The sensor provides qualitative

where *δλres* is the offset of the resonance peak and *δnd* is the change in the refractive index of the dielectric medium.

### **4. SPR sensitivity improvements using photonic crystal fiber**

As mentioned in previous sections, the conventional prism-based Kretschmann setup is widely used for SPR sensors. However, this configuration is bulky due to the required optical measurement components. Furthermore, this configuration is not adequate for remote sensing [7]. The remarked limitations of conventional SPR configurations led to the use of optical fiber instead of the prism. Chemical sensing application of optical fiber configuration was proposed by Jorgenson et al. [52, 53] for the first time, and since then the advantages of various configurations of optical fiber based SPR sensors have drawn a lot of attention. Sensing properties of numerous microstructure optical fiber (MOF)-based SPR have been reported in the last two decades. The sensing properties of some of these sensors are summarized in **Table 2**.

Further improvement in terms of sensitivity and resolution is obtained by photonic crystal fiber-based SPR (PCF SPR). PCFs are similar to conventional optical fiber, but with periodic air holes inside the cladding region. The diameter of the air

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review DOI: http://dx.doi.org/10.5772/intechopen.93001*


### **Table 2.**

surface of hole arrays and SPP modes at the surface of the thin film, in the upper

*Recent Advances in Nanophotonics - Fundamentals and Applications*

The transmission of electromagnetic waves through a subwavelength hole was investigated by Bethe [37] for the first time. The transmission will occur at specific frequencies imposed by geometrical parameters of the structure, polarization, angle of incident light, and permittivity of the surrounding media. These findings found many applications owing to the simplicity with which their spectral properties can

In several studies [38–41] it was shown that the peak positions are determined by the periodicity of the holes. The periodicity is usually comparable to the wavelength of the incident light. By modifying the film thickness and diameter of the holes, one can control the shape of the peaks in terms of the width and intensity. It was due to these facts that many researchers believe that SPP is responsible for EOT

The simple structure (perforated thin films) of EOT-based devices is widely studied for potential applications, from optical switches and photolithography masks to sensing applications. Despite this simple structure, the quality of the noble metal film in terms of surface roughness, grain size, and purity is equally important for EOT device application. A single crystalline thin film with atomically smooth surface is required in order to maximize the propagation length of SPP. A smooth surface results in elimination of scattering and loss of the incident light. This improves the transmission spectrum of the device, though it is very challenging to

**Table 1** summarizes the reported characteristics of few SPR-, LSPR-, and EOT-

<sup>¼</sup> *δλres δnd*

(4)

synthesize or grow uniform single crystalline films over a large area [42].

supported sensors. As it can be seen, the geometry of the metal film plays an important role in plasmon frequency. As an example, gold has plasmon frequency in the deep ultraviolet; however geometric factors create the possibility to tune the resonance peak wavelength range. The sensitivity (S) of the sensors utilizing the

> *<sup>S</sup> nm RIU*

**4. SPR sensitivity improvements using photonic crystal fiber**

where *δλres* is the offset of the resonance peak and *δnd* is the change in the

As mentioned in previous sections, the conventional prism-based Kretschmann setup is widely used for SPR sensors. However, this configuration is bulky due to the required optical measurement components. Furthermore, this configuration is not adequate for remote sensing [7]. The remarked limitations of conventional SPR configurations led to the use of optical fiber instead of the prism. Chemical sensing application of optical fiber configuration was proposed by Jorgenson et al. [52, 53] for the first time, and since then the advantages of various configurations of optical fiber based SPR sensors have drawn a lot of attention. Sensing properties of numerous microstructure optical fiber (MOF)-based SPR have been reported in the last two decades. The sensing properties of some of these sensors are summarized in

Further improvement in terms of sensitivity and resolution is obtained by photonic crystal fiber-based SPR (PCF SPR). PCFs are similar to conventional optical fiber, but with periodic air holes inside the cladding region. The diameter of the air

and lower rims of the holes [36].

and developed models to explain the phenomena.

wavelength interrogation is defined as

refractive index of the dielectric medium.

**Table 2**.

**10**

be tuned on.

*Characteristics of several reported fiber-optic SPR-based sensors.*

### **Figure 5.**

*Schematics of PCF-SPR sensors. (a) Analyte-filled cladding holes [54], (b) externally coated PCF [55], and (c) D-shaped PCF SPR sensor [56].*



### **Table 3.**

*Characteristics of several reported PCF SPR sensors.*

holes and the separation gap between them defines the light propagation characteristics of PCFs. These sensors own other advantages including small size and flexible structural design over conventional optical fiber and prism coupler SPR sensors. To date, numerous PCF SPR sensors have been demonstrated with different configurations. The schematics of some configurations are shown in **Figure 5**. **Figure 5a** shows the configuration in which the metal layer and the analyte are filled inside the cladding holes. External coatings and D shape PCF are shown in **Figure 5b** and **c** respectively.

The performance of recently reported PCF-based SPR sensors are compared in **Table 3**. Most of the reported sensors are based on theoretical and analytical studies. This is due to the fact that fabrication of these sensors requires a complex process.

### **5. Conclusion**

In this review, the basic principles of SPR and various configurations of SPR excitation are reviewed. Since nanostructures of noble metals have tunable optical properties, they can be applied in nanoplasmonics-based devices and sensors. Nanoplasmonics has proven to be useful in sensing applications, especially for biological uses. Compared to SPR-based sensors, LSPR-based sensors exhibit unique properties, including higher sensitivities and figure of merits (FOM).

**Author details**

**13**

Parsoua A. Sohi and Mojtaba Kahrizi\*

provided the original work is properly cited.

Montreal, Quebec, Canada

Department of Electrical and Computer Engineering, Concordia University,

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review*

*DOI: http://dx.doi.org/10.5772/intechopen.93001*

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: mojtaba.kahrizi@concordia.ca

The researchers' aim to reduce the size of SPR- and LSPR-based sensors led to development of fiber-optic SPR-based sensors. The highest sensitivity reported in the literature allocates to PCF SPR sensors. They have shown their capability in providing high sensitivity as high as 46,000 nm/RIU [54] with respect to small RI changes. However, the majority of reported PCF SPR sensors are based on analytical studies (as it is shown in **Table 3**, most of the researches are only carried out with numerical simulations). This is due to complications of the fabrication process of the PCF SPR sensor. The complication mostly refers to interior metallic coating (into the core or cladding holes). Large interest in PCF SPR sensors among researchers increases the importance of the fabrication technique improvements.

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review DOI: http://dx.doi.org/10.5772/intechopen.93001*

### **Author details**

holes and the separation gap between them defines the light propagation characteristics of PCFs. These sensors own other advantages including small size and flexible structural design over conventional optical fiber and prism coupler SPR sensors. To date, numerous PCF SPR sensors have been demonstrated with different configurations. The schematics of some configurations are shown in **Figure 5**. **Figure 5a** shows the configuration in which the metal layer and the analyte are filled inside the cladding holes. External coatings and D shape PCF are shown in **Figure 5b** and **c**

The performance of recently reported PCF-based SPR sensors are compared in **Table 3**. Most of the reported sensors are based on theoretical and analytical studies. This is due to the fact that fabrication of these sensors requires a complex process.

In this review, the basic principles of SPR and various configurations of SPR excitation are reviewed. Since nanostructures of noble metals have tunable optical properties, they can be applied in nanoplasmonics-based devices and sensors. Nanoplasmonics has proven to be useful in sensing applications, especially for biological uses. Compared to SPR-based sensors, LSPR-based sensors exhibit unique

The researchers' aim to reduce the size of SPR- and LSPR-based sensors led to development of fiber-optic SPR-based sensors. The highest sensitivity reported in the literature allocates to PCF SPR sensors. They have shown their capability in providing high sensitivity as high as 46,000 nm/RIU [54] with respect to small RI changes. However, the majority of reported PCF SPR sensors are based on analytical studies (as it is shown in **Table 3**, most of the researches are only carried out with numerical simulations). This is due to complications of the fabrication process of the PCF SPR sensor. The complication mostly refers to interior metallic coating (into the core or cladding holes). Large interest in PCF SPR sensors among researchers increases the importance of the fabrication technique improvements.

properties, including higher sensitivities and figure of merits (FOM).

respectively.

PCF with Aumetalized microfluidic slots

PCF with Au-coated multichannel

Analyte filled with Au-coated core PCF

**Table 3.**

**Structure Study Sensitivity**

*Characteristics of several reported PCF SPR sensors.*

**(nm/RIU)**

*Recent Advances in Nanophotonics - Fundamentals and Applications*

Analytical 2280 NIR 1.46–

**Range of λ**

**Medium/ RI**

Analytical 2000 Vis 1.33–1.34 The effect of geometrical

Analytical 2400 Vis 1.33–1.34 The effect of geometrical

1.485

**Comment Ref**

[64]

[65]

[66]

parameters is studied. Sensitivity is inversely proportional to gold layer thickness

parameters is studied

Several peaks were observed in the resonance spectrum

**5. Conclusion**

**12**

Parsoua A. Sohi and Mojtaba Kahrizi\* Department of Electrical and Computer Engineering, Concordia University, Montreal, Quebec, Canada

\*Address all correspondence to: mojtaba.kahrizi@concordia.ca

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

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[24] Sathiyamoorthy K, Ramya B, Murukeshan VM, Wei Sun X. Modified two prism SPR sensor configurations to improve the sensitivity of measurement. Sensors and Actuators A: Physical. 2013;

[25] Fida F, Varin L, Badilescu S, Kahrizi M. Gold nanoparticle ring and hole structures for sensing proteins and

antigen–antibody interactions. Plasmonics. 2009;**4**:201-207

film-coupled nanoparticles by evanescent wave excitation. Nano

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[27] Petryayeva E, Krull UJ. Localized

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[10] Dormeny AA, Sohi PA, Kahrizi M. Design and simulation of a refractive index sensor based on SPR and LSPR using gold nanostructures. Results in Physics. 2020;**16**:102869

[11] Fida F. Biosensing Based on Localized Surface Plasmon Resonance of Gold Nanostructures Fabricated by a Novel Nanosphere Lithography Technique. [Thesis]. Concordia University; 2008

[12] Prabowo BA, Purwidyantri A, Liu K-C. Surface plasmon resonance optical sensor: A review on light source technology. Biosensors. 2018;**8**(80):1-27

[13] Kretschmann E, Raether H. Radiative decay of non-radiative surface plasmon excited by light. Zeitschrift für Naturforschung A. 1968;**23**:2135-2136

[14] Roh S, Chung T, Lee B. Overview of the characteristics of micro- and nanostructured surface plasmon resonance sensors. Sensors. 2011;**11**(2):1565-1588

[15] Otto A. Excitation of nonradiative surface plasma waves in silver by the method of frustrated total reflection. Zeitschrift für Physik. 1968;**216**:398-410

[16] Allsop T, Neal R. A review: Evolution and diversity of optical fibre plasmonic sensors. Sensors. 2019; **19**(4874):1-19

[17] Petty CM. Molecular Electronics: From Principle to Practice. Wiley: United States; 2008

[18] Nguyen HH, Park J, Kang S, Kim M. Surface plasmon resonance: A versatile

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review DOI: http://dx.doi.org/10.5772/intechopen.93001*

technique for biosensor applications. Sensors. 2015;**15**:10481-10510

**References**

**30**(7–8):532-533

Optics. 2007;**9**:586-592

2017;**25**(22):254-262

3933-2\_1

**14**

[1] Lubbers DW, Opitz N. The pCO2-/

*Recent Advances in Nanophotonics - Fundamentals and Applications*

[9] Ctyroky J et al. Theory and modelling of optical waveguide sensors utilising surface plasmon resonance. Sensors and Actuators B: Chemical. 1999;**54**(1–2):

[10] Dormeny AA, Sohi PA, Kahrizi M. Design and simulation of a refractive index sensor based on SPR and LSPR using gold nanostructures. Results in

Localized Surface Plasmon Resonance of Gold Nanostructures Fabricated by a Novel Nanosphere Lithography Technique. [Thesis]. Concordia

Physics. 2020;**16**:102869

University; 2008

[11] Fida F. Biosensing Based on

[12] Prabowo BA, Purwidyantri A, Liu K-C. Surface plasmon resonance optical sensor: A review on light source technology. Biosensors. 2018;**8**(80):1-27

[13] Kretschmann E, Raether H.

Radiative decay of non-radiative surface plasmon excited by light. Zeitschrift für Naturforschung A. 1968;**23**:2135-2136

[14] Roh S, Chung T, Lee B. Overview of the characteristics of micro- and nanostructured surface plasmon resonance sensors. Sensors. 2011;**11**(2):1565-1588

[15] Otto A. Excitation of nonradiative surface plasma waves in silver by the method of frustrated total reflection. Zeitschrift für Physik. 1968;**216**:398-410

Evolution and diversity of optical fibre plasmonic sensors. Sensors. 2019;

[17] Petty CM. Molecular Electronics: From Principle to Practice. Wiley:

[18] Nguyen HH, Park J, Kang S, Kim M. Surface plasmon resonance: A versatile

[16] Allsop T, Neal R. A review:

**19**(4874):1-19

United States; 2008

66-73

measurement of pCO2 or pO2 in fluids and gases. Journal of Biosciences. 1975;

[2] Kanso M, Cuenot S, Louarn G. Roughness effect on the SPR measurements for an optical fibre configuration: Experimental and. Journal of Optics A: Pure and Applied

[3] SEO M, LEE J, LEE M. Gratingcoupled surface plasmon resonance on bulk stainless steel. Optics Express.

[4] Svedendahl M, Chen S, Kall M. An Introduction to Plasmonic Refractive Index Sensing. In: Dmitriev A, editor. Nanoplasmonic Sensors. Springer, NY: Integrated Analytical Systems. 2012. Available from: https://link.springer. com/chapter/10.1007/978-1-4614-

[5] Akowuah EK, Gorman T, Haxha S. Design and optimization of a novel surface plasmon resonance biosensor based on Otto configuration. Optics Express. 2009;**17**(26):491-496

[6] Rossi S, Gazzola E, Capaldo P, Borile G, Romanato F. Grating-coupled surface plasmon resonance (GC-SPR) optimization for phase-interrogation biosensing in a microfluidic chamber.

[7] Gupta BD, Verma RK. Surface plasmon resonance-based fiber optic sensors: Principle, probe designs, and some applications. Journal of Sensors. 2009:1-12. DOI: 10.1155/2009/979761

[8] Zhang C, Li Z, Zhen S, Hui C, Cai S, Yu J. U-bent fiber optic SPR sensor based on graphene/AgNPs. Sensors and Actuators B: Chemical. 2017;**251**:127-133

Sensors. 2018;**18**(1621):1-13

pO2-optode: A new probe for

[19] Syahir A, Usui K, Tomizaki K, Kajikawa K, Mihara H. Label and labelfree detection techniques for protein microarrays. Microarrays. 2015;**4**(2): 228-244

[20] Vollmer F, Arnold S. Whisperinggallery-mode biosensing: Label-free detection down to single molecules. Nature Methods. 2008;**5**(7):591-596

[21] Méjard R, Griesser HJ, Thierry B. Optical biosensing for label-free cellular studies. Trends in Analytical Chemistry. 2014;**53**:178-186

[22] Liedberg B, Nylander C, Lundstrm I. Biosensing with surface plasmon resonance—How it all started. Biosensors & Bioelectronics. 1995;**10**:1-9

[23] Liedberg B, Nylander C, Lunstrom I. Surface plasmon resonance for gas detection and biosensing. Sensors and Actuators. 1983;**4**:299-304

[24] Sathiyamoorthy K, Ramya B, Murukeshan VM, Wei Sun X. Modified two prism SPR sensor configurations to improve the sensitivity of measurement. Sensors and Actuators A: Physical. 2013; **191**:73-77

[25] Fida F, Varin L, Badilescu S, Kahrizi M. Gold nanoparticle ring and hole structures for sensing proteins and antigen–antibody interactions. Plasmonics. 2009;**4**:201-207

[26] Mock JJ, Hill RT, Tsai Y, Chilkoti A, Smith DR. Probing dynamically tunable localized surface plasmon resonances of film-coupled nanoparticles by evanescent wave excitation. Nano Letters. 2012;**12**:1757-1764

[27] Petryayeva E, Krull UJ. Localized surface plasmon resonance: Nanostructures, bioassays and

biosensing—A review. Analytica Chimica Acta. 2011;**706**(1):8-24

[28] Tosi D, Poeggel S, Iordachita I, Schena E. Fiber optic sensors for biomedical applications. Opto-Mechanical Fiber Optic Sensors. 2018: 301-333. DOI: 10.1126/science.6422554

[29] Ekinci Y, Solak HH, Löffler JF. Plasmon resonances of aluminum nanoparticles and nanorods. Journal of Applied Physics. 2008;**104**(083107): 1-6

[30] Larsson EM, Alegret J, Ka M, Sutherland DS. Sensing characteristics of NIR localized surface plasmon resonances in gold nanorings for application as ultrasensitive biosensors. Nano Letters. 2007;**7**(5):1256-1263

[31] Movsesyan AR, Baudrion A-L, Adam P-M. Extinction measurements of metallic nanoparticles arrays as a way to explore the single nanoparticle plasmon resonances. Optics Express. 2018;**26**(5): 2949-2951

[32] Hao F, Larsson EM, Ali TA, Sutherland DS, Nordlander P. Shedding light on dark plasmons in gold nanorings. Chemical Physics Letters. 2008;**458**(4–6):262-266

[33] Wang S, Sun X, Ding M, Peng G. The investigation of an LSPR refractive index sensor based on periodic gold nanorings array. Journal of Physics D: Applied Physics. 2018;**51**(4):045101 (7pp)

[34] Canpean V, Astilean S. Multifunctional plasmonic sensors on low-cost subwavelength metallic nanoholes arrays. Royal Society of Chemistry. 2009;**9**(24):3574-3579

[35] Parsons J, Hendry E, Burrows CP, Auguié B, Sambles JR, Barnes WL. Localized surface-plasmon resonances in periodic nondiffracting metallic

nanoparticle and nanohole arrays. Physical Review B. 2009;**79**(7):1-4

[36] Chen Z, Li P, Zhang S, Chen Y, Liu P. Enhanced extraordinary optical transmission and refractive-index sensing sensitivity in tapered plasmonic nanohole arrays. Nanotechnology. 2019; **30**:335201(9pp)

[37] Bethe H. Theory of diffraction by small holes. Physical Review. 1944;**66** (7–8):163

[38] Hajiaboli A. Optical properties of thick metal nanohole arrays fabricated by electron-beam and nanosphere lithography. Physica Status Solidi A: Applications and Material Science. 2009;**206**(6668):976-979

[39] Rodrigo SG, de León-Pérez F, Martín-Moreno L. Extraordinary optical transmission: Fundamentals and applications. Proceedings of the IEEE. 2016;**104**(12):2288-2306

[40] Motogaito A, Morishita Y, Miyake H, Hiramatsu K. Extraordinary optical transmission exhibited by surface plasmon polaritons in a doublelayer wire grid polarizer. Plasmonics. 2015;**10**(6):1657-1662

[41] Liu H, Lalanne P. Theory of the extraordinary optical transmission. Nature Letters. 2008;**452**:728-731

[42] Zhang J, Irannejad M, Yavuz M, Cui B. Gold nanohole array with sub-1 nm roughness by annealing for sensitivity enhancement of extraordinary optical transmission biosensor. Nanoscale Research Letters. 2015;**10**(238):1-8

[43] Liu S, Yang Z, Liu R, Li X. High sensitivity localized surface plasmon resonance sensing using a double split nanoring cavity. The Journal of Physical Chemistry C. 2011;**115**(50): 24469-24477

[44] Lee SY, Kim S-H, Jang SG, Heo CJ, Shim JW, Yang SM. High-fidelity optofluidic on-chip sensors using welldefined gold nanowell crystals. Analytical Chemistry. 2011;**83**(23): 9174-9180

response to size, shape, and metal composition. Journal of Physical

[52] Jorgenson R, Yee S, Johnson K,

plasmon-resonance-based fiber optic sensor applied to biochemical sensing. In: Fiber Optics Sensors in Medical Diagonistics. 1993. pp. 35-48. DOI:

[53] Jorgenson R, Yee S. A fiber-optic chemical sensor based on surface plasmon resonance. Sensors and Actuators B: Chemical. 1993;**12**(3):

[54] Rifat AA, Ahmed R, Mahdiraji GA, Adikan FRM. Highly sensitive D-shaped photonic crystal fiber-based plasmonic biosensor in visible to near-IR. IEEE Sensors Journal. 2017;**17**(9):2776-2783

[55] Liu C et al. Numerical analysis of a photonic crystal fiber based on a surface plasmon resonance sensor with an annular analyte channel. Optics Communications. 2017;**382**:162-166

[56] Gangwar RK, Singh VK. Highly sensitive surface plasmon resonance based D-shaped photonic crystal fiber refractive index sensor. Plasmonics.

[57] Piliarik M, Homola J. Surface plasmon resonance sensor based on a single-mode polarization-maintaining optical fiber. Sensors and Actuators B:

[58] Lin H-Y, Huang C-H, Cheng G-L, Chen N-K, Chui H-C. Tapered optical fiber sensor based on localized surface plasmon resonance. Optics Express.

Chemical. 2003;**90**:236-242

2012;**20**(19):21693-21701

**17**

[59] Kim Y-C, Peng W, Banerji S, Booksh KS. Tapered fiber optic surface plasmon resonance sensor for analyses of vapor and liquid phases. Optics Letters. 2005;**30**(17):2218-2220

2017;**12**:1367-1372

Compton B. Novel surface-

10.1117/12.144841

213-220

Chemistry B. 2006;**110**(39):19220-19225

*DOI: http://dx.doi.org/10.5772/intechopen.93001*

[60] Antohe I, Spasic D, Delport F, Li J, Lammertyn J. Nanoscale patterning of gold-coated optical fibers for improved plasmonic sensing. Nanotechnology.

[61] Dash JN, Jha R. On the performance of graphene-based D-shaped photonic crystal fibre biosensor using surface plasmon resonance. Plasmonics. 2015;

[62] Wang F, Liu C, Sun Z, Sun T, Liu B. A highly sensitive SPR sensors based on two parallel PCFs for low refractive index detection. IEEE Photonics Journal.

[63] Al Mahfuz M, Hossain MA, Haque E, Hai NH, Namihira Y, Ahmed F. A bimetallic-coated, low propagation loss, photonic crystal fiber based plasmonic refractive index sensor.

Sensors. 2019;**19**(3794):1-12

[65] Azzam SI, Hameed MFO, Shehata R, Heikal A, Obayya SS. Multichannel photonic crystal fiber surface plasmon resonance based sensor. Optical and Quantum Electronics. 2016;**48**(2):1-11

[66] Qin W, Li S, Yao Y, Xin X, Xue J. Analyte-filled core self-calibration microstructured optical fiber based plasmonic sensor for detecting high refractive index aqueous analyte. Optics and Lasers in Engineering. 2014;**58**:1-8

[64] Akowuah EK et al. Numerical analysis of a photonic crystal fiber for biosensing applications. IEEE Journal of Quantum Electronics. 2012;**48**(11):

2017;**28**:215301

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review*

**10**:1123-1131

2018;**10**(4):1-10

1403-1410

[45] Bochenkov VE, Frederiksen M, Sutherland DS. Enhanced refractive index sensitivity of elevated short-range ordered nanohole arrays in optically thin plasmonic Au films. Optics Express. 2013;**21**(12):4428-4433

[46] Brian B, Sepúlveda B, Alaverdyan Y, Lechuga LM, Käll M. Sensitivity enhancement of nanoplasmonic sensors in low refractive index substrates. Optics Express. 2015; **17**(3):2335-2339

[47] Toderas F, Baia M, Baia L, Astilean S. Controlling gold nanoparticle assemblies for efficient surfaceenhanced Raman scattering and localized surface plasmon resonance sensors. Nanotechnology. 2007;**18**: 255702

[48] Luther JM, Jain PK, Ewers T, Alivisatos AP. Localized surface plasmon resonances arising from free carriers in doped quantum dots. Nature Materials. 2011;**10**(4):361-366

[49] Sun Y, Xia Y. Increased sensitivity of surface plasmon resonance of gold nanoshells compared to that of gold solid colloids in response to environmental changes. Analytical Chemistry. 2002;**74**(20):5297-5305

[50] Im H, Sutherland JN, Maynard JA, Oh S. Nanohole-based surface plasmon resonance instruments with improved spectral resolution quantify a broad range of antibody-ligand binding kinetics. Analytical Chemistry. 2012;**84**: 1941-1947

[51] Lee KS, El-Sayed MA. Gold and silver nanoparticles in sensing and imaging: Sensitivity of plasmon

*Principles and Applications of Nanoplasmonics in Biological and Chemical Sensing: A Review DOI: http://dx.doi.org/10.5772/intechopen.93001*

response to size, shape, and metal composition. Journal of Physical Chemistry B. 2006;**110**(39):19220-19225

nanoparticle and nanohole arrays. Physical Review B. 2009;**79**(7):1-4

*Recent Advances in Nanophotonics - Fundamentals and Applications*

[44] Lee SY, Kim S-H, Jang SG, Heo CJ, Shim JW, Yang SM. High-fidelity optofluidic on-chip sensors using well-

defined gold nanowell crystals. Analytical Chemistry. 2011;**83**(23):

2013;**21**(12):4428-4433

[46] Brian B, Sepúlveda B,

Sensitivity enhancement of

[47] Toderas F, Baia M, Baia L,

assemblies for efficient surfaceenhanced Raman scattering and localized surface plasmon resonance sensors. Nanotechnology. 2007;**18**:

[48] Luther JM, Jain PK, Ewers T, Alivisatos AP. Localized surface plasmon resonances arising from free carriers in doped quantum dots. Nature

Materials. 2011;**10**(4):361-366

solid colloids in response to environmental changes. Analytical Chemistry. 2002;**74**(20):5297-5305

[49] Sun Y, Xia Y. Increased sensitivity of surface plasmon resonance of gold nanoshells compared to that of gold

[50] Im H, Sutherland JN, Maynard JA, Oh S. Nanohole-based surface plasmon resonance instruments with improved spectral resolution quantify a broad range of antibody-ligand binding kinetics. Analytical Chemistry. 2012;**84**:

[51] Lee KS, El-Sayed MA. Gold and silver nanoparticles in sensing and imaging: Sensitivity of plasmon

**17**(3):2335-2339

255702

1941-1947

[45] Bochenkov VE, Frederiksen M, Sutherland DS. Enhanced refractive index sensitivity of elevated short-range ordered nanohole arrays in optically thin plasmonic Au films. Optics Express.

Alaverdyan Y, Lechuga LM, Käll M.

nanoplasmonic sensors in low refractive index substrates. Optics Express. 2015;

Astilean S. Controlling gold nanoparticle

9174-9180

[36] Chen Z, Li P, Zhang S, Chen Y, Liu P. Enhanced extraordinary optical transmission and refractive-index sensing sensitivity in tapered plasmonic nanohole arrays. Nanotechnology. 2019;

[37] Bethe H. Theory of diffraction by small holes. Physical Review. 1944;**66**

[38] Hajiaboli A. Optical properties of thick metal nanohole arrays fabricated by electron-beam and nanosphere lithography. Physica Status Solidi A: Applications and Material Science.

2009;**206**(6668):976-979

2016;**104**(12):2288-2306

2015;**10**(6):1657-1662

2015;**10**(238):1-8

24469-24477

**16**

[39] Rodrigo SG, de León-Pérez F, Martín-Moreno L. Extraordinary optical

transmission: Fundamentals and applications. Proceedings of the IEEE.

[40] Motogaito A, Morishita Y,

Miyake H, Hiramatsu K. Extraordinary optical transmission exhibited by surface plasmon polaritons in a doublelayer wire grid polarizer. Plasmonics.

[41] Liu H, Lalanne P. Theory of the extraordinary optical transmission. Nature Letters. 2008;**452**:728-731

[42] Zhang J, Irannejad M, Yavuz M, Cui B. Gold nanohole array with sub-1 nm roughness by annealing for sensitivity enhancement of extraordinary optical transmission biosensor. Nanoscale Research Letters.

[43] Liu S, Yang Z, Liu R, Li X. High sensitivity localized surface plasmon resonance sensing using a double split nanoring cavity. The Journal of Physical Chemistry C. 2011;**115**(50):

**30**:335201(9pp)

(7–8):163

[52] Jorgenson R, Yee S, Johnson K, Compton B. Novel surfaceplasmon-resonance-based fiber optic sensor applied to biochemical sensing. In: Fiber Optics Sensors in Medical Diagonistics. 1993. pp. 35-48. DOI: 10.1117/12.144841

[53] Jorgenson R, Yee S. A fiber-optic chemical sensor based on surface plasmon resonance. Sensors and Actuators B: Chemical. 1993;**12**(3): 213-220

[54] Rifat AA, Ahmed R, Mahdiraji GA, Adikan FRM. Highly sensitive D-shaped photonic crystal fiber-based plasmonic biosensor in visible to near-IR. IEEE Sensors Journal. 2017;**17**(9):2776-2783

[55] Liu C et al. Numerical analysis of a photonic crystal fiber based on a surface plasmon resonance sensor with an annular analyte channel. Optics Communications. 2017;**382**:162-166

[56] Gangwar RK, Singh VK. Highly sensitive surface plasmon resonance based D-shaped photonic crystal fiber refractive index sensor. Plasmonics. 2017;**12**:1367-1372

[57] Piliarik M, Homola J. Surface plasmon resonance sensor based on a single-mode polarization-maintaining optical fiber. Sensors and Actuators B: Chemical. 2003;**90**:236-242

[58] Lin H-Y, Huang C-H, Cheng G-L, Chen N-K, Chui H-C. Tapered optical fiber sensor based on localized surface plasmon resonance. Optics Express. 2012;**20**(19):21693-21701

[59] Kim Y-C, Peng W, Banerji S, Booksh KS. Tapered fiber optic surface plasmon resonance sensor for analyses of vapor and liquid phases. Optics Letters. 2005;**30**(17):2218-2220

[60] Antohe I, Spasic D, Delport F, Li J, Lammertyn J. Nanoscale patterning of gold-coated optical fibers for improved plasmonic sensing. Nanotechnology. 2017;**28**:215301

[61] Dash JN, Jha R. On the performance of graphene-based D-shaped photonic crystal fibre biosensor using surface plasmon resonance. Plasmonics. 2015; **10**:1123-1131

[62] Wang F, Liu C, Sun Z, Sun T, Liu B. A highly sensitive SPR sensors based on two parallel PCFs for low refractive index detection. IEEE Photonics Journal. 2018;**10**(4):1-10

[63] Al Mahfuz M, Hossain MA, Haque E, Hai NH, Namihira Y, Ahmed F. A bimetallic-coated, low propagation loss, photonic crystal fiber based plasmonic refractive index sensor. Sensors. 2019;**19**(3794):1-12

[64] Akowuah EK et al. Numerical analysis of a photonic crystal fiber for biosensing applications. IEEE Journal of Quantum Electronics. 2012;**48**(11): 1403-1410

[65] Azzam SI, Hameed MFO, Shehata R, Heikal A, Obayya SS. Multichannel photonic crystal fiber surface plasmon resonance based sensor. Optical and Quantum Electronics. 2016;**48**(2):1-11

[66] Qin W, Li S, Yao Y, Xin X, Xue J. Analyte-filled core self-calibration microstructured optical fiber based plasmonic sensor for detecting high refractive index aqueous analyte. Optics and Lasers in Engineering. 2014;**58**:1-8

**19**

**Chapter 2**

**Abstract**

Devices

cell and the optical modulation.

**1. Introduction**

Graphene-Based Nanophotonic

Graphene is an ideal 2D material that breaks the fundamental properties of size and speed limits by photonics and electronics, respectively. Graphene is also an ideal material for bridging electronic and photonic devices. Graphene offers several functions of modulation, emission, signal transmission, and detection of wideband and short band infrared frequency spectrum. Graphene has improved human life in multiple ways of low-cost display devices and touchscreen structures, energy harvesting devices (solar cells), optical communication components (modulator, polarizer, detector, laser generation). There is numerous literature is available on graphene synthesis, properties, devices, and applications. However, the main interest among the scientist, researchers, and students to start with the numerical and computational process for the graphene-based nanophotonic devices. This chapter also includes the examples of graphene applications in optoelectronics devices, P-N junction diodes, photodiode structure which are fundamental devices for the solar

*Ankur Pandya, Vishal Sorathiya and Sunil Lavadiya*

**Keywords:** Graphene, PN diode, photodetector, modulator, transistor

The scientific community across the globe considered graphene as one of the most revolutionary 2D nanomaterials of the world that possesses zero energy

bandgap [1]. As shown in **Figure 1**, being the monoatomic carbon layer arranged in a honeycomb lattice, graphene possesses unique attractive properties and by the virtue of which it has attracted strong scientific and technological interests [2–5]. Graphene has shown great application potential in many fields, such as nanoelectronics [5, 6], energy storage devices [6–10] and bioelectronic device applications [11–13]. The linear dispersion relation in graphene at the ends of the First Brillouin Zone is shown in **Figure 2** according to which the bandgap at the Dirac point is zero. However, zero energy bandgap limits the applications of pristine graphene on a wide-scale especially in graphene-based nanoelectronics because, in the absence of energy bandgap, it is not possible for pristine graphene-based electronic devices to be operated in ON and OFF states which is desirable for logic gate circuits. To overcome such limitations of pristine graphene and to improve its applicability for designing nanoelectronic devices, the interest also builds up towards the study on doped graphene. Suitable doping with proper concentration can introduce the desired bandgap in graphene that enables graphene to be utilized in electronic circuits at the nanoscale. It has been reported that the hydrogen passivated armchair GNR exhibits direct bandgap at the edges [14]. Moreover, the bandgap can be introduced and tuned by transforming

### **Chapter 2**

## Graphene-Based Nanophotonic Devices

*Ankur Pandya, Vishal Sorathiya and Sunil Lavadiya*

### **Abstract**

Graphene is an ideal 2D material that breaks the fundamental properties of size and speed limits by photonics and electronics, respectively. Graphene is also an ideal material for bridging electronic and photonic devices. Graphene offers several functions of modulation, emission, signal transmission, and detection of wideband and short band infrared frequency spectrum. Graphene has improved human life in multiple ways of low-cost display devices and touchscreen structures, energy harvesting devices (solar cells), optical communication components (modulator, polarizer, detector, laser generation). There is numerous literature is available on graphene synthesis, properties, devices, and applications. However, the main interest among the scientist, researchers, and students to start with the numerical and computational process for the graphene-based nanophotonic devices. This chapter also includes the examples of graphene applications in optoelectronics devices, P-N junction diodes, photodiode structure which are fundamental devices for the solar cell and the optical modulation.

**Keywords:** Graphene, PN diode, photodetector, modulator, transistor

### **1. Introduction**

The scientific community across the globe considered graphene as one of the most revolutionary 2D nanomaterials of the world that possesses zero energy bandgap [1]. As shown in **Figure 1**, being the monoatomic carbon layer arranged in a honeycomb lattice, graphene possesses unique attractive properties and by the virtue of which it has attracted strong scientific and technological interests [2–5]. Graphene has shown great application potential in many fields, such as nanoelectronics [5, 6], energy storage devices [6–10] and bioelectronic device applications [11–13]. The linear dispersion relation in graphene at the ends of the First Brillouin Zone is shown in **Figure 2** according to which the bandgap at the Dirac point is zero. However, zero energy bandgap limits the applications of pristine graphene on a wide-scale especially in graphene-based nanoelectronics because, in the absence of energy bandgap, it is not possible for pristine graphene-based electronic devices to be operated in ON and OFF states which is desirable for logic gate circuits. To overcome such limitations of pristine graphene and to improve its applicability for designing nanoelectronic devices, the interest also builds up towards the study on doped graphene. Suitable doping with proper concentration can introduce the desired bandgap in graphene that enables graphene to be utilized in electronic circuits at the nanoscale. It has been reported that the hydrogen passivated armchair GNR exhibits direct bandgap at the edges [14]. Moreover, the bandgap can be introduced and tuned by transforming

**Figure 1.** *Monolayer graphene nanoribbon [17].*

**Figure 2.**

*The linear dispersion relation in graphene at the ends of First Brillouin Zone [18].*

graphene sheet into its nanoribbon form of finite width i.e. graphene nanoribbon (GNR) [15, 16]. However, the bandgap of graphene nanoribbons shows different magnitudes for three groups i.e. Na =3p, 3p + 1, and 3p + 2 where Na is the number of dimers and p is an integer [15]. The magnitude of bandgap oscillates between these three groups with the number of dimers (N) i.e. ( + + ) ( ) ( ) > > *gp gp gp* 31 3 32 *E EE* . The energy band gap of armchair GNR is determined as a function of the number of dimers wherein the smaller the number of dimer lines, the smaller the nanoribbon width and hence higher the bandgap [15].

The GNRs are narrow strips of graphene nanosheet of finite width possessing structural similarity to that of unrolled carbon nanotube (CNT). GNRs possess mainly two types of structural configurations termed as armchair graphene nanoribbon (A-GNR) and zigzag graphene nanoribbon (Z-GNR). A-GNRs exhibit semiconducting properties whereas Z-GNRs are metallic in nature [15]. This behavior exclusively depends on how the graphene sheet cuts along with its plane (**Figure 1**). As shown in **Figure 3**, the bandgap increases with reducing nanoribbon width in an exponential manner [17–20]. Recently, it has been reported that applying a transverse magnetic field to the ribbon width induce the tunable bandgap i.e. tuning of the bandgap is possible by changing the magnitude of the applied

**21**

bon width.

**Figure 3.**

*Graphene-Based Nanophotonic Devices DOI: http://dx.doi.org/10.5772/intechopen.93853*

magnetic field [21]. The important aspect of a variable bandgap of a material is to develop efficient and flexible optoelectronic devices and sensors that work with the utmost accuracy. Considering this background, the subsequent sections discuss the

Photonic devices are the components that generate or detect the photonic flux that is developed and utilized for either electronic signal or light. The P-N device in the form of a light-emitting diode, photovoltaic cell, and the laser device is the most common type of photonic device. Traditionally these devices are designed and fabricated using Si or Ge due to which limited efficiency, broad bandwidth, high power consumption are few of the major limitations of current electronic devices. These limitations may be overcome by developing the replica of current electronic components at the nanoscale. The main theme of devices at the nanoscale is the smaller the dimensions, the lesser the power consumption, and the higher the efficiency. As mentioned above, though graphene possesses a zero energy bandgap in its nanosheet form, it exhibits a finite bandgap in its nanoribbons form which varies with the width of the nanoribbon. **Figure 3** shows that the bandgap of pristine graphene reduces exponentially with the increase in nanorib-

It is possible to further enhance electronic transport properties of GNR with dopant adatoms [22–26] – that may help to fabricate graphene-based P-N nanodevices [27] as well as the surface acoustic wave sensors [28] at nanoscale. Moreover, it has also been proposed by several research groups that the doping of boron and nitrogen in graphene exhibits the possibility of engineering the graphene-based p-n junction at nanoscale as well as graphene aerogels for oxygen electro-catalysis [29, 30] wherein boron being trivalent and nitrogen being pentavalent impurities introduce the energy bandgap. **Figure 4** shows the boron and nitrogen-doped graphene nanoribbon based forward-biased p-n device. First-principles quantum transport calculations of electronic properties of boron and nitrogen-doped armchair GNR showed that the B-doped p-type GNR based device can exhibit high levels of performance, with high ON/OFF ratios and low subthreshold swing [31].

photonic devices at the nanoscale in the present chapter.

*The energy bandgap varies with nanoribbon width and doping concentration [17].*

**2. Photonic devices at nanoscale**

*Recent Advances in Nanophotonics - Fundamentals and Applications*

graphene sheet into its nanoribbon form of finite width i.e. graphene nanoribbon (GNR) [15, 16]. However, the bandgap of graphene nanoribbons shows different magnitudes for three groups i.e. Na =3p, 3p + 1, and 3p + 2 where Na is the number of dimers and p is an integer [15]. The magnitude of bandgap oscillates between these three groups with the number of dimers (N) i.e. ( + + ) ( ) ( ) > > *gp gp gp* 31 3 32 *E EE* . The energy band gap of armchair GNR is determined as a function of the number of dimers wherein the smaller the number of dimer lines, the smaller the nanoribbon

*The linear dispersion relation in graphene at the ends of First Brillouin Zone [18].*

The GNRs are narrow strips of graphene nanosheet of finite width possessing

structural similarity to that of unrolled carbon nanotube (CNT). GNRs possess mainly two types of structural configurations termed as armchair graphene nanoribbon (A-GNR) and zigzag graphene nanoribbon (Z-GNR). A-GNRs exhibit semiconducting properties whereas Z-GNRs are metallic in nature [15]. This behavior exclusively depends on how the graphene sheet cuts along with its plane (**Figure 1**). As shown in **Figure 3**, the bandgap increases with reducing nanoribbon width in an exponential manner [17–20]. Recently, it has been reported that applying a transverse magnetic field to the ribbon width induce the tunable bandgap i.e. tuning of the bandgap is possible by changing the magnitude of the applied

width and hence higher the bandgap [15].

**20**

**Figure 1.**

**Figure 2.**

*Monolayer graphene nanoribbon [17].*

**Figure 3.** *The energy bandgap varies with nanoribbon width and doping concentration [17].*

magnetic field [21]. The important aspect of a variable bandgap of a material is to develop efficient and flexible optoelectronic devices and sensors that work with the utmost accuracy. Considering this background, the subsequent sections discuss the photonic devices at the nanoscale in the present chapter.

### **2. Photonic devices at nanoscale**

Photonic devices are the components that generate or detect the photonic flux that is developed and utilized for either electronic signal or light. The P-N device in the form of a light-emitting diode, photovoltaic cell, and the laser device is the most common type of photonic device. Traditionally these devices are designed and fabricated using Si or Ge due to which limited efficiency, broad bandwidth, high power consumption are few of the major limitations of current electronic devices. These limitations may be overcome by developing the replica of current electronic components at the nanoscale. The main theme of devices at the nanoscale is the smaller the dimensions, the lesser the power consumption, and the higher the efficiency. As mentioned above, though graphene possesses a zero energy bandgap in its nanosheet form, it exhibits a finite bandgap in its nanoribbons form which varies with the width of the nanoribbon. **Figure 3** shows that the bandgap of pristine graphene reduces exponentially with the increase in nanoribbon width.

It is possible to further enhance electronic transport properties of GNR with dopant adatoms [22–26] – that may help to fabricate graphene-based P-N nanodevices [27] as well as the surface acoustic wave sensors [28] at nanoscale. Moreover, it has also been proposed by several research groups that the doping of boron and nitrogen in graphene exhibits the possibility of engineering the graphene-based p-n junction at nanoscale as well as graphene aerogels for oxygen electro-catalysis [29, 30] wherein boron being trivalent and nitrogen being pentavalent impurities introduce the energy bandgap. **Figure 4** shows the boron and nitrogen-doped graphene nanoribbon based forward-biased p-n device. First-principles quantum transport calculations of electronic properties of boron and nitrogen-doped armchair GNR showed that the B-doped p-type GNR based device can exhibit high levels of performance, with high ON/OFF ratios and low subthreshold swing [31].

**Figure 4.** *Graphene-based P-N device [17].*

### **2.1 Graphene-based P-N device and field effect transistor**

The P-N device is one of the fundamental devices of an electronic circuit that controls the charge carrier (electron) current in the circuit manufactured from semiconducting materials such as silicon (Si) and germanium (Ge). It has a positive (p) region and negative (n) region created via doping semiconductor material by trivalent and pentavalent impurities respectively. Since AGNR exhibits semiconducting properties it is possible to design P-N device at the nanoscale using AGNR configuration. This type of P-N device will be having better electronic transport properties compared to traditional one because armchair graphene is not only a semiconductor but transparent and flexible also due to which it can be placed in nanoelectronic circuit. In addition to this, according to the recent article on graphene-based terahertz frequency detection, it is possible to design and fabricate graphene p-n junction based nano-antenna (bolometer) using the photo-thermoelectric effect wherein it is reported that with the dual gated dipolar antenna of the gap of 100 nm it is possible to concentrate the incident radiation for better photoresponse [32]. Graphene based field-effect transistors (GFET) are being investigated for more than a decade [33, 34].

There are several reasons behind this hunt such as limited electronic transport parameters of current electronics materials (Si, Ge) i.e. electron mobility and hence conductivity, poor heat dissipation rate of Si and Ge, and their tensile strength, failure of Moore's law, etc. In this context, graphene possesses superiority among all the materials known to researchers because graphene exhibits better electrical, mechanical, thermal, and optical properties in comparison with Si and Ge which are listed as follows: electrical conductivity of graphene is 107 S/m [35] whereas for Si it is 103 S/m, the electrical mobility of graphene is 105 cm2 /Vs [36] whereas for Si it is 103 cm2 /Vs, and 4 × 103 cm2 /Vs for Ge, Young's modulus of graphene is around 1.2 TPa [37] whereas that for both Si and Ge is 1 MPa, the thermal conductivity of graphene is around 5000 W/mK [37] whereas it is 1300 W/mK for Si and

**23**

*Graphene-Based Nanophotonic Devices DOI: http://dx.doi.org/10.5772/intechopen.93853*

580 W/mK for Ge. Considering these values of various parameters, it is obvious that graphene as a material is far better than the traditional semiconductors Si and Ge. In addition to this, graphene is a flexible transparent conducting thin film, unlike Si and Ge, due to which graphene can be used to develop flexible and transparent

The field effect transistor (FET) is one of the most important and fundamental electronic device that uses electric field to control the current and possesses three electrodes source, drain, and gate. A semiconductor channel is connecting source and drain and the third one i.e. gate controls the current. Implementation of graphene field effect transistors (GFET) in sensors has large number of benefits over the bulk FET made from Si. As the silicon is bulk semiconductor, the charge carriers at the channel interface have difficulty to penetrate into the device which limits response sensitivity of the device. On the other hand, as the graphene possesses two dimensional structure, the sensitive channel is itself the surface that ultimately improves the surface sensitivity. In addition to this, the carrier scattering rate through graphene is much lower than that in the case of bulk semiconductors. Therefore, the carrier energy loss also much lower than that for the bulk semiconductors. The fabrication of GFET is possible on Si/SiO2 substrate with metal contacts via chemical vapor deposition (CVD) technique. G. Fiori et al. explored the possibility of tunable gap GFET considering bandgap opening by applying vertical electric field and using atomistic simulations based on the self-consistent solution of the Poisson and Schrödinger equations within the non-equilibrium Green's function formalism [38]. The chemical and biological sensors based on GFET were investigated to show their sensitivity towards detection of protein of different charge types [39]. Such sensors are having relatively higher sensitivities for biomolecules. On the other hand, GFET based high temperature sensor has been reported that works up to 600°C with utmost accuracy wherein researchers calculated the resistivity of the device using semi-classical transport Equations [40]. Graphene succeeded to implant itself in the broad field of organic light emitting diode

(OLED) which is one of the important parts of optoelectronics [41–43]. Traditional OLEDs have their applications in screens of computer, mobile phones and cameras. In general, indium tin oxide (ITO) is used as transparent conductive thin film which is brittle and not flexible. In addition to this, indium may diffuse into active layers of OLEDs [44]. These limitations may be overcome using graphene instead of ITO

Photodetectors are significant optoelectronic devices that detect the optical flux by converting the absorbed optical energy into the electronic current. They are part of remote control, televisions and DVD players. The spectrum responded by detectors is entirely depends on the bandgap of the material of detector. The traditional photodetectors consist of IV or III-IV semiconducting materials that are suffering from longwavelength limits because these materials do not respond to the optical energy if its energy is less than the bandgap. Hence, the particular material becomes transparent for that radiation. As a solution of this problem, the implementation of graphene is the better option as graphene absorbs from ultraviolet to terahertz range [45, 46]. Since, the response time of a photodetector depends on the carrier mobility, graphene based photodetectors (GPDs) can be ultrafast because graphene exhibits very high carrier mobility. It is also possible to utilize photo-thermoelectric effect for efficient GPDs. In photo-thermoelectric effect, the photon energy converts into the heat followed by photocurrent generation. This is an important attribute to the fields of graphene based optoelectronics, photo-thermocouple devices and photovoltaic applications [47].

because the work function of both the materials is same (4.5 eV).

**2.2 Graphene-based photodetector and photovoltaic devices**

electronic devices that are base of wearable electronics [37].

### *Graphene-Based Nanophotonic Devices DOI: http://dx.doi.org/10.5772/intechopen.93853*

*Recent Advances in Nanophotonics - Fundamentals and Applications*

**2.1 Graphene-based P-N device and field effect transistor**

are listed as follows: electrical conductivity of graphene is 107

/Vs, and 4 × 103

S/m, the electrical mobility of graphene is 105

around 1.2 TPa [37] whereas that for both Si and Ge is 1 MPa, the thermal conductivity of graphene is around 5000 W/mK [37] whereas it is 1300 W/mK for Si and

cm2

S/m [35] whereas

/Vs [36] whereas

cm2

/Vs for Ge, Young's modulus of graphene is

The P-N device is one of the fundamental devices of an electronic circuit that controls the charge carrier (electron) current in the circuit manufactured from semiconducting materials such as silicon (Si) and germanium (Ge). It has a positive (p) region and negative (n) region created via doping semiconductor material by trivalent and pentavalent impurities respectively. Since AGNR exhibits semiconducting properties it is possible to design P-N device at the nanoscale using AGNR configuration. This type of P-N device will be having better electronic transport properties compared to traditional one because armchair graphene is not only a semiconductor but transparent and flexible also due to which it can be placed in nanoelectronic circuit. In addition to this, according to the recent article on graphene-based terahertz frequency detection, it is possible to design and fabricate graphene p-n junction based nano-antenna (bolometer) using the photo-thermoelectric effect wherein it is reported that with the dual gated dipolar antenna of the gap of 100 nm it is possible to concentrate the incident radiation for better photoresponse [32]. Graphene based field-effect transistors (GFET) are being investigated for more than a decade [33, 34]. There are several reasons behind this hunt such as limited electronic transport parameters of current electronics materials (Si, Ge) i.e. electron mobility and hence conductivity, poor heat dissipation rate of Si and Ge, and their tensile strength, failure of Moore's law, etc. In this context, graphene possesses superiority among all the materials known to researchers because graphene exhibits better electrical, mechanical, thermal, and optical properties in comparison with Si and Ge which

**22**

for Si it is 103

**Figure 4.**

*Graphene-based P-N device [17].*

for Si it is 103

cm2

580 W/mK for Ge. Considering these values of various parameters, it is obvious that graphene as a material is far better than the traditional semiconductors Si and Ge. In addition to this, graphene is a flexible transparent conducting thin film, unlike Si and Ge, due to which graphene can be used to develop flexible and transparent electronic devices that are base of wearable electronics [37].

The field effect transistor (FET) is one of the most important and fundamental electronic device that uses electric field to control the current and possesses three electrodes source, drain, and gate. A semiconductor channel is connecting source and drain and the third one i.e. gate controls the current. Implementation of graphene field effect transistors (GFET) in sensors has large number of benefits over the bulk FET made from Si. As the silicon is bulk semiconductor, the charge carriers at the channel interface have difficulty to penetrate into the device which limits response sensitivity of the device. On the other hand, as the graphene possesses two dimensional structure, the sensitive channel is itself the surface that ultimately improves the surface sensitivity. In addition to this, the carrier scattering rate through graphene is much lower than that in the case of bulk semiconductors. Therefore, the carrier energy loss also much lower than that for the bulk semiconductors. The fabrication of GFET is possible on Si/SiO2 substrate with metal contacts via chemical vapor deposition (CVD) technique. G. Fiori et al. explored the possibility of tunable gap GFET considering bandgap opening by applying vertical electric field and using atomistic simulations based on the self-consistent solution of the Poisson and Schrödinger equations within the non-equilibrium Green's function formalism [38]. The chemical and biological sensors based on GFET were investigated to show their sensitivity towards detection of protein of different charge types [39]. Such sensors are having relatively higher sensitivities for biomolecules. On the other hand, GFET based high temperature sensor has been reported that works up to 600°C with utmost accuracy wherein researchers calculated the resistivity of the device using semi-classical transport Equations [40]. Graphene succeeded to implant itself in the broad field of organic light emitting diode (OLED) which is one of the important parts of optoelectronics [41–43]. Traditional OLEDs have their applications in screens of computer, mobile phones and cameras. In general, indium tin oxide (ITO) is used as transparent conductive thin film which is brittle and not flexible. In addition to this, indium may diffuse into active layers of OLEDs [44]. These limitations may be overcome using graphene instead of ITO because the work function of both the materials is same (4.5 eV).

### **2.2 Graphene-based photodetector and photovoltaic devices**

Photodetectors are significant optoelectronic devices that detect the optical flux by converting the absorbed optical energy into the electronic current. They are part of remote control, televisions and DVD players. The spectrum responded by detectors is entirely depends on the bandgap of the material of detector. The traditional photodetectors consist of IV or III-IV semiconducting materials that are suffering from longwavelength limits because these materials do not respond to the optical energy if its energy is less than the bandgap. Hence, the particular material becomes transparent for that radiation. As a solution of this problem, the implementation of graphene is the better option as graphene absorbs from ultraviolet to terahertz range [45, 46]. Since, the response time of a photodetector depends on the carrier mobility, graphene based photodetectors (GPDs) can be ultrafast because graphene exhibits very high carrier mobility. It is also possible to utilize photo-thermoelectric effect for efficient GPDs. In photo-thermoelectric effect, the photon energy converts into the heat followed by photocurrent generation. This is an important attribute to the fields of graphene based optoelectronics, photo-thermocouple devices and photovoltaic applications [47].

Graphene based touch screen is an emerging field as well because graphene is transparent and conducting too. This is the reason why graphene transparent conducting films (GTCFs) are promising layers for touch screens of electronic device displays. Graphene being mechanically strong, with high chemical durability, non-toxic, and cheap is one of the ideal materials for displays. Traditional displays consist of ITO which is costly, wear-resistant, brittle and has limited chemical durability. Graphenebased touch panel display can be grown by screen printing by the CVD technique [48]. Thus, GTCF may be an important part of future flexible and efficient touch screens.

For decades, it is known to us that photovoltaic (PV) cells convert light into electricity which is the main theme of traditional solar panels that are using silicon (Si) or germanium (Ge). The energy conversion efficiency of these materials is limited to around 25% [49]. Moreover, since Si and Ge are not flexible materials it limits the flexible solar cells or panels which are important components of futuristic wearable electronics. These limitations can be overcome by using graphene-based PV cells for this aspect. Graphene plays multiple roles in a photovoltaic cell i.e. photoactive material, transparent as well as conducting (TC) layer, charge transport layer, and catalyst. Among all these exciting and promising applications of graphene, the terahertz (THz) photonics based on graphene is a promising field of research as well which is capable to develop high-performance terahertz devices operated in the region between 300 GHz to 10 THz. at 300 K [50].

### **3. Graphene-based metamaterial**

The modern form of artificial substance Metamaterials (MMs) has recently been examined for their electromagnetic properties that are missing in typical natural materials [51, 52]. The different results such as negative refractive index [53], perfect lensing [54], bolometer [55] etc. are discovered when utilizing these properties. From the other horizon, owing to its exceptional electrical, electronics and optical properties, such as strong thermal power, wide carrier mobility, and extremely young module [56], have acquired considerable attention in the domain of the thin and lightweight metamaterial research. Graphene is a 2-dimensional, radioactive medium that offers electrical and optical control across a large spectrum of frequencies, such as THz [57–59] and GHz [60]. The graphene's conductivity can be managed by various parameters such as temperature, duration, dispersion rate, and chemical potential [58]. Several devices are suggested for complete absorption [59, 61–63] polarization-insensitive [64–67], broad-angle [64–68], tunability [69–72]. For the Terahertz area and the Microwave, others are examined. **Figure 5** shows the example of the graphene-based squared shaped spiral metamaterial design for the polarization application. It is very much essential to discuss the refractive index parameters to identify the effect of metamaterial and negative refraction. The effective refractive index parameters can be identified by considering the transmittance and reflectance values of any two-port devices. The negative index behavior of any structure realized the overall effect of the metamaterial at a specific resonance frequency. The Schematic shown in **Figure 5** was numerically investigated to identify the reflection and transmission behavior of the THz wave. According to the results of transmittance and reflectance values, the effective refractive index was calculated for the band of 1 THz to 3 THz frequency region using the mathematical formula given in [73]. The negative refractive index response of the structure has been shown in **Figure 6**. **Figure 6** was derived for the different modes of excitation applied to the structure as shown in **Figure 5**. The effective refractive index of the normal and complimentary structure shows that the metamaterial effect was observed at the different resonance points for range 1 THz to 3 THz range. The proposed metamaterial

**25**

**Figure 6.**

*excited mode [74].*

**Figure 5.**

*structure (SSSG – C) [73].*

behavior can help with different applications such as absorber, polarizer, superlens, etc. **Figure 6** also shows that for the different mode of the excitation (TE or TM) does not affect to the resonance behavior due to the squared spiral symmetric structure of

*The real part of the effective refractive index response of the proposed metamaterial structure for the TE and TM mode of the excitation over 1 THz to 3 THz frequency (structure shown in Figure 5). The response is derived for the different chemical potential varied from 0.1 eV to 0.9 eV. (A) SSSG – N with TE excited mode, (B) SSSG – C with TE excited mode, (C) SSSG – N with TM excited mode and (D) SSSG – C with TM* 

*Schematic of the squared spiral-shaped graphene metamaterial structure. (A) 3D view of the squared spiral-shaped graphene normal structure (SSSG – N), (B) squared spiral-shaped graphene complementary* 

the top graphene layer as shown in **Figure 5**.

*Graphene-Based Nanophotonic Devices DOI: http://dx.doi.org/10.5772/intechopen.93853*

### **Figure 5.**

*Recent Advances in Nanophotonics - Fundamentals and Applications*

region between 300 GHz to 10 THz. at 300 K [50].

**3. Graphene-based metamaterial**

Graphene based touch screen is an emerging field as well because graphene is transparent and conducting too. This is the reason why graphene transparent conducting films (GTCFs) are promising layers for touch screens of electronic device displays. Graphene being mechanically strong, with high chemical durability, non-toxic, and cheap is one of the ideal materials for displays. Traditional displays consist of ITO which is costly, wear-resistant, brittle and has limited chemical durability. Graphenebased touch panel display can be grown by screen printing by the CVD technique [48]. Thus, GTCF may be an important part of future flexible and efficient touch screens. For decades, it is known to us that photovoltaic (PV) cells convert light into electricity which is the main theme of traditional solar panels that are using silicon (Si) or germanium (Ge). The energy conversion efficiency of these materials is limited to around 25% [49]. Moreover, since Si and Ge are not flexible materials it limits the flexible solar cells or panels which are important components of futuristic wearable electronics. These limitations can be overcome by using graphene-based PV cells for this aspect. Graphene plays multiple roles in a photovoltaic cell i.e. photoactive material, transparent as well as conducting (TC) layer, charge transport layer, and catalyst. Among all these exciting and promising applications of graphene, the terahertz (THz) photonics based on graphene is a promising field of research as well which is capable to develop high-performance terahertz devices operated in the

The modern form of artificial substance Metamaterials (MMs) has recently been examined for their electromagnetic properties that are missing in typical natural materials [51, 52]. The different results such as negative refractive index [53], perfect lensing [54], bolometer [55] etc. are discovered when utilizing these properties. From the other horizon, owing to its exceptional electrical, electronics and optical properties, such as strong thermal power, wide carrier mobility, and extremely young module [56], have acquired considerable attention in the domain of the thin and lightweight metamaterial research. Graphene is a 2-dimensional, radioactive medium that offers electrical and optical control across a large spectrum of frequencies, such as THz [57–59] and GHz [60]. The graphene's conductivity can be managed by various parameters such as temperature, duration, dispersion rate, and chemical potential [58]. Several devices are suggested for complete absorption [59, 61–63] polarization-insensitive [64–67], broad-angle [64–68], tunability [69–72]. For the Terahertz area and the Microwave, others are examined. **Figure 5** shows the example of the graphene-based squared shaped spiral metamaterial design for the polarization application. It is very much essential to discuss the refractive index parameters to identify the effect of metamaterial and negative refraction. The effective refractive index parameters can be identified by considering the transmittance and reflectance values of any two-port devices. The negative index behavior of any structure realized the overall effect of the metamaterial at a specific resonance frequency. The Schematic shown in **Figure 5** was numerically investigated to identify the reflection and transmission behavior of the THz wave. According to the results of transmittance and reflectance values, the effective refractive index was calculated for the band of 1 THz to 3 THz frequency region using the mathematical formula given in [73]. The negative refractive index response of the structure has been shown in **Figure 6**. **Figure 6** was derived for the different modes of excitation applied to the structure as shown in **Figure 5**. The effective refractive index of the normal and complimentary structure shows that the metamaterial effect was observed at the different resonance points for range 1 THz to 3 THz range. The proposed metamaterial

**24**

*Schematic of the squared spiral-shaped graphene metamaterial structure. (A) 3D view of the squared spiral-shaped graphene normal structure (SSSG – N), (B) squared spiral-shaped graphene complementary structure (SSSG – C) [73].*

### **Figure 6.**

*The real part of the effective refractive index response of the proposed metamaterial structure for the TE and TM mode of the excitation over 1 THz to 3 THz frequency (structure shown in Figure 5). The response is derived for the different chemical potential varied from 0.1 eV to 0.9 eV. (A) SSSG – N with TE excited mode, (B) SSSG – C with TE excited mode, (C) SSSG – N with TM excited mode and (D) SSSG – C with TM excited mode [74].*

behavior can help with different applications such as absorber, polarizer, superlens, etc. **Figure 6** also shows that for the different mode of the excitation (TE or TM) does not affect to the resonance behavior due to the squared spiral symmetric structure of the top graphene layer as shown in **Figure 5**.

### **4. Graphene surface conductivity model**

Graphene-based photonics devices need to be analyzed by the specific mathematical characteristic before implementing it to the fabrication stage. It is important to identify the behavior of the graphene for the different external parameters such as temperature, frequency, external potential. Graphene can be modeled as one atom thick infinitesimally thin and two-sided surface. This model of the graphene can characterize by the surface conductivity model. Complex permittivity of the graphene sheet [75] is expressed by ε ω( ) as expressed in Eq. 1, where the conductivity of the graphene σ *<sup>s</sup>* expressed from Kubo formula as mentioned in Eqs. (2)–(4) [76]. Graphene conductivity is depending on the various parameters such as temperature, scattering rate, frequency and external chemical potential.

$$\varepsilon\left(\phi\right) = \mathbb{1} + \frac{\sigma\_s}{\varepsilon\_0 a \Delta} \tag{1}$$

$$\sigma\_{\text{intra}} = \frac{-j e^2 k\_B T}{\pi \hbar^2 \left(\alpha - j2\Gamma\right)} \left(\frac{\mu\_c}{k\_B T} + 2 \ln\left(e^{-\frac{\mu\_c}{k\_B T}} + 1\right)\right) \tag{2}$$

$$\sigma\_{inter} = \frac{-j e^2}{4 \pi \hbar} \ln \left( \frac{2 \left| \mu\_\epsilon \right| - \left( \phi - j2\Gamma \right) \hbar}{2 \left| \mu\_\epsilon \right| + \left( \phi - j2\Gamma \right) \hbar} \right) \tag{3}$$

$$
\sigma\_s = \sigma\_{\text{outer}} + \sigma\_{\text{intra}} \tag{4}
$$

**27**

**Author details**

Ankur Pandya1

Ahmedabad, Gujarat, India

University, Rajkot, India

\*, Vishal Sorathiya2

provided the original work is properly cited.

1 Department of Electronics and Communication, Nirma University,

\*Address all correspondence to: ankur.pandya@nirmauni.ac.in

2 Department of Information and Communication Technology, Marwadi

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Sunil Lavadiya<sup>2</sup>

replacing traditional semiconductors by graphene. Being a flexible, optically transparent, electrically as well as thermally conducting nanomaterial, graphene, in its nanosheet and nanoribbons forms, can be implanted into the current optoelectronic devices to overcome their existing limitations. However, the synthesis and insertion of graphene and its allotropes into the devices require state-of-the-art and is challenging too. We propose that the inclusion of graphene in traditional devices will take the current electronic devices to new horizons and will open up new frontiers

*Graphene-Based Nanophotonic Devices DOI: http://dx.doi.org/10.5772/intechopen.93853*

of optoelectronic sensor technologies.

Here, <sup>0</sup> ε is the vacuum permittivity, σ *<sup>s</sup>* is the monolayer conductivity, e is the fundamental electron charge value, ω is angular frequency, *kB* is the Boltzmann's constant and is the reduced Planck's constant. In this work, the chemical potential of graphene µ*c* is varied between 0.1 eV to 0.6 eV, electron relaxation time <sup>−</sup><sup>1</sup> τ = 10-13 s, Γ is phenomenological scattering rate, graphene sheet thickness ∆ = 0.34 nm and temperature T = 300 K. Carrier concentration of the whole graphene sheet will be controlled by field-effect, which can be indicated as: = <sup>0</sup> / *n V et s dg d* ε ε [77], where 0 ε , *<sup>d</sup>* ε = 2.25 and td = 2 μm are free space permittivity, permittivity of silica and thickness of silica layer respectively. Vg is gate voltage applied to graphene surface. Many research works have been used the graphene conductivity formula as it is easy to define in the computational studies with finite element method (FEM) of finite difference time domain method (FDTD). Simplified graphene conductivity module can be used also to identify the behavior of the entire structure for different physical parameters. It is also available several software packages that help the researchers to characterize the graphene material using mathematical modeling. RF module of the COMSOL Multiphysics provides the 2D and 3D analysis of the graphene-based devices for the photonics applications [77–79].

### **5. Conclusion**

In summary, the present chapter discusses the current and future possibilities to incorporate wonder material graphene into the current photonic devices to enhance their performance in terms of efficiency, and sensitivity of sensors at the nanoscale

### *Graphene-Based Nanophotonic Devices DOI: http://dx.doi.org/10.5772/intechopen.93853*

*Recent Advances in Nanophotonics - Fundamentals and Applications*

σ

Graphene-based photonics devices need to be analyzed by the specific mathematical characteristic before implementing it to the fabrication stage. It is important to identify the behavior of the graphene for the different external parameters such as temperature, frequency, external potential. Graphene can be modeled as one atom thick infinitesimally thin and two-sided surface. This model of the

graphene can characterize by the surface conductivity model. Complex permittivity

Eqs. (2)–(4) [76]. Graphene conductivity is depending on the various parameters such as temperature, scattering rate, frequency and external chemical potential.

= +

( )

ε ω

2

π

be controlled by field-effect, which can be indicated as: = <sup>0</sup> / *n V et s dg d*

( )

2

ln

σσ

ε ω

σ

− <sup>−</sup> = ++ − Γ

*B c k TB*

 ω

 <sup>2</sup> 2 2

> σ

*c* is varied between 0.1 eV to 0.6 eV, electron relaxation time <sup>−</sup><sup>1</sup>

<sup>2</sup> 2ln 1

<sup>0</sup> ∆

ε ω

µ

*B je k T <sup>e</sup>*

µ

42 2 *c*

*c je j*

<sup>−</sup> − −Γ <sup>=</sup> + −Γ

 µω

σ

10-13 s, Γ is phenomenological scattering rate, graphene sheet thickness ∆ = 0.34 nm and temperature T = 300 K. Carrier concentration of the whole graphene sheet will

 = 2.25 and td = 2 μm are free space permittivity, permittivity of silica and thickness of silica layer respectively. Vg is gate voltage applied to graphene surface. Many research works have been used the graphene conductivity formula as it is easy to define in the computational studies with finite element method (FEM) of finite difference time domain method (FDTD). Simplified graphene conductivity module can be used also to identify the behavior of the entire structure for different physical parameters. It is also available several software packages that help the researchers to characterize the graphene material using mathematical modeling. RF module of the COMSOL Multiphysics provides the 2D and 3D analysis of the graphene-based

In summary, the present chapter discusses the current and future possibilities to incorporate wonder material graphene into the current photonic devices to enhance their performance in terms of efficiency, and sensitivity of sensors at the nanoscale

fundamental electron charge value, ω is angular frequency, *kB* is the Boltzmann's constant and is the reduced Planck's constant. In this work, the chemical potential

( ) as expressed in Eq. 1, where the

1 *<sup>s</sup>* (1)

*<sup>s</sup>* expressed from Kubo formula as mentioned in

µ

( ) ( ) *c*

*s inter intra* = + (4)

*<sup>s</sup>* is the monolayer conductivity, e is the

ε ε

*j kT* (2)

*<sup>j</sup>* (3)

τ=

[77], where

**4. Graphene surface conductivity model**

of the graphene sheet [75] is expressed by

σ

*intra*

π ω

σ

is the vacuum permittivity,

devices for the photonics applications [77–79].

*inter*

conductivity of the graphene

Here, <sup>0</sup> ε

of graphene

0 ε , *<sup>d</sup>* ε

µ

**26**

**5. Conclusion**

replacing traditional semiconductors by graphene. Being a flexible, optically transparent, electrically as well as thermally conducting nanomaterial, graphene, in its nanosheet and nanoribbons forms, can be implanted into the current optoelectronic devices to overcome their existing limitations. However, the synthesis and insertion of graphene and its allotropes into the devices require state-of-the-art and is challenging too. We propose that the inclusion of graphene in traditional devices will take the current electronic devices to new horizons and will open up new frontiers of optoelectronic sensor technologies.

### **Author details**

Ankur Pandya1 \*, Vishal Sorathiya2 and Sunil Lavadiya<sup>2</sup>

1 Department of Electronics and Communication, Nirma University, Ahmedabad, Gujarat, India

2 Department of Information and Communication Technology, Marwadi University, Rajkot, India

\*Address all correspondence to: ankur.pandya@nirmauni.ac.in

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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*Graphene-Based Nanophotonic Devices DOI: http://dx.doi.org/10.5772/intechopen.93853*

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Section 2

Photonic Devices

**33**

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