**4. Applications of DNWs**

proved by the stability of DNRs (at 110 direction) synthesized through hydrogen plasma posttreatment of multiwalled CNTs [58], whereas the DNWs at 100 direction seem to be unstable

Tanskanen et al. described the mechanical properties of DNWs through Poisson's ratios, Young's moduli and shear moduli interrogations [66], which proved that (111) DNWs have the highest Young's moduli than the (110) and (111) DNWs. In this report, they suggest that polyicosahedral DNWs have more strain than that of conventional DNWs. In this way, Guo and coworkers presented the mechanical properties of (001) DNWs by means of molecular dynamics simulations [68] and specified that Young's modulus of those DNWs is lower than those of bulk diamond. Similarly, Jiang et al. explored Young's modulus of DNWs in different crystallographic orientations as a function of cross-sectional area [69]. Wherein, Young's modulus has the sequence of (100), (110), (111) and (112) directions and indicated that those

Initially, Dubrovinskaia and Dubrovinsky reported the density of the aggregated diamond nanorods (ADNRs), which were developed from fullerene C60 by multi-anvil apparatus [61]. The X-ray density of ADNRs is about 0.2–0.4% greater than the bulk diamond, which also corresponds to the measured density of 3.532(5) g cm−3. The higher density of ADNRs may arise from the outerlayer contraction leading to shortening of the C-C bonds inside the diamond. In this work, they have also evaluated the compressibility of ADNRs by using the third-order Birch-Murnaghan equation of state, wherein they established the >11% lesser compressibility

Trejo and coworkers reported the optical phonons and Raman-scattering properties of DNWs by using a local bond polarization model based on the displacement–displacement Green's function and the Born potential [70]. Further, they have also studied the electronic band structure of DNWs through a semiempirical tight-binding approach and compared with density functional theory (DFT) studies. From the calculations, they have concluded that phonons and electrons tend to show a clear quantum confinement signature. Moreover, this study also establishes that during the DNWs width increase, the Raman peak shifts to lower frequencies due to the phonon confinement, as reported by our group [71]. Subsequently, the band gap

In general, it is recognized that the thermal conductivity of DNWs may not be incredibly affected by surface functionalization. However, at nanometer scale, dimensions of DNWs may reduce the thermal conductivity than that of bulk diamond as demonstrated by Novikov et al. [72]. In this way, Moreland and coworkers explored that the conductivity of DNW is lower

values are lower than the bulk value and increase with its cross-sectional area.

as reported earlier [67].

**3.2. Mechanical properties of DNWs**

26 Nanowires - Synthesis, Properties and Applications

**3.3. Density and compressibility of DNWs**

of ADNRs than that of usual diamond.

**3.4. Phonon optical modes and electronic properties of DNWs**

**3.5. Thermal conductivity and electrochemical properties of DNWs**

also decreases as the width of the DNWs increases.

Among the applications of DNWs, the following five utilities have been demonstrated strongly. Those applications are (1) field emission applications of DNWs, (2) DNWs in mass analysis of small molecules, (3) DNWs as nanoelectromechanical switches, (4) DNWs as electrochemical sensors and (5) DNWs in ultrasensitive force microscopy.

#### **4.1. Field emission applications of DNWs**

The negative electron affinity of DNWs has been used in field emission studies. Recently, reports on the electron field emission (EFE) properties of CVD-developed ultracrystalline diamond and hybrid diamond-graphite films were reported [78, 79]. In this way, the EFEs of DNWs were also been described by (A) planar DNWs array and (B) single DNW.

(A) Electron field emission of planar DNW array: Lee et al. demonstrated the EFE characteristics of planar diamond film array, which has been developed by CVD techniques [80]. Recently, Sankaran et al. presented the improved EFE applications of graphite-wrapped DNWs [81]. In this path, the above group determined the enhanced electron field emission of vertically aligned ultrananocrystalline diamond needles via ZnO coating to form the heterostructured nanorods [82]. Wherein, it shows a high emission current density of 5.5 mA cm−2 at 4.25 V μm−1 and has a low turn-on field of 2.08 V μm−1 than that of bare Zn-nanorods. This outstanding emission property of planar diamond film arrays seems to be impressive to apply as the electron emitters in flat display panels.

(B) Electron field emission of a single DNW: Recently, Hsu and coworkers presented the electron field emission of a single DNW [57]. Wherein, the threshold field of DNW (1.25 Vμm−1) is four times lower than that of carbon nanotube (5 Vμm−1). This might be due to the electron affinity of DNW and defects existence. In addition, the EFE property of DNW may be attributed to its chemical inertness, high mechanical strength and high thermal conductivity.

glucose biosensing by Zhi et al. [46]. Wherein, the selective determination of glucose has been demonstrated in the presence of ascorbic acid (AA) and uric acid (UA). Meanwhile, BDD NWs were also been efficiently used in the electrochemical identification of tryptophan by Szunerits and coworkers [88]. Alternatively, Lee and Lin collaborators developed a nitrogen incorporated DNW electrode for the amperometric detection of urea and *in situ* detection of dopamine [89]. Here, dopamine determination was well illustrated in the presence of AA and UA. More recently, Peng et al. reported the detection of CO gas by BDD NWs through electrochemical studies [90]. Wherein, the boron-doped ultrananocrystalline diamond (B-UNCD) nanowires (NWs) evidenced greater selectivity to CO gas than that of competitive species.

**Figure 9.** Integration of diamond nanowire tips on ultrasensitive silicon cantilevers. (A) Bare silicon cantilever with a nominal length of 90 μm, a shaft width of 4 μm and a thickness of 135 nm. The scale bar is 10 μm. (B) Batch of DNWs transferred onto an Si substrate for manual pickup. The scale bar is 10 μm. (C, D) zoom-in onto the end region of two different cantilevers where DNW tips had been attached. Scale bars are 10 μm in C and 1 μm in D. Reproduced with

permission from [91].

**Figure 8.** Schematic illumination of the biofunctionalization of vertically aligned diamond nanowires to realize a

Diamond Nanowire Synthesis, Properties and Applications

http://dx.doi.org/10.5772/intechopen.78794

29

nanoscaled spacing between DNA molecules. Reproduced with permission from [86].

## **4.2. DNWs in mass analysis of small molecules**

Firstly, Coffinier et al. described the matrix-free laser desorption/ionization (D/I) mass spectrometric utilization of boron-doped DNWs (BDD NWs) toward small molecular analysis [83], in which the S/N ratios of UDD NWs are very low than that of BDD NWs. Therefore, the potentiality of BDD NWs in mass analysis of small molecules has been proved.

#### **4.3. DNWs as nanoelectromechanical switches**

Recently, researchers tend to develop the diamond-based nanoelectromechanical (NEM) switches as an alternative silicon-based ones due to its exceptional properties such as high Young's modulus, maximum hardness, hydrophobicity, low mass density, greater thermal conductivity, extraordinary corrosion resistance and low toxicity. However, because of existed grain boundaries, impurities, large stress, low electrical conductivity and poor reproducibility, the polycrystalline or nanocrystalline film-based switches seem not to be as impressive candidates [84, 85]. In contrast, the utilization of single-crystalline DNWs as NEM is appraised by Liao and coworkers [29], in which those switches show low leakage current (<0.1 pA) with a high ON/OFF ratio, hence can compete Si-NEMS structures.

#### **4.4. DNWs as electrochemical sensors**

DNWs were effectively applied in many electrochemical sensory studies. For example, Yang and Nebel utilized the vertically aligned diamond nanowires toward DNA detection *via* electrochemical approach [86]. **Figure 8** represents the schematic of biofunctionalized vertically aligned diamond nanowires for the determination of DNA in the abovementioned report.

Further, they have protracted those diamond nanowires in electrochemical gene sensors [87]. Akin to vertically aligned nanowires, BDD NWs were applied in nonenzymatic amperometric

diamond and hybrid diamond-graphite films were reported [78, 79]. In this way, the EFEs of

(A) Electron field emission of planar DNW array: Lee et al. demonstrated the EFE characteristics of planar diamond film array, which has been developed by CVD techniques [80]. Recently, Sankaran et al. presented the improved EFE applications of graphite-wrapped DNWs [81]. In this path, the above group determined the enhanced electron field emission of vertically aligned ultrananocrystalline diamond needles via ZnO coating to form the heterostructured nanorods [82]. Wherein, it shows a high emission current density of 5.5 mA cm−2 at 4.25 V μm−1 and has a low turn-on field of 2.08 V μm−1 than that of bare Zn-nanorods. This outstanding emission property of planar diamond film arrays seems to be impressive to apply

(B) Electron field emission of a single DNW: Recently, Hsu and coworkers presented the electron field emission of a single DNW [57]. Wherein, the threshold field of DNW (1.25 Vμm−1) is four times lower than that of carbon nanotube (5 Vμm−1). This might be due to the electron affinity of DNW and defects existence. In addition, the EFE property of DNW may be attributed to its chemical inertness, high mechanical strength and high thermal conductivity.

Firstly, Coffinier et al. described the matrix-free laser desorption/ionization (D/I) mass spectrometric utilization of boron-doped DNWs (BDD NWs) toward small molecular analysis [83], in which the S/N ratios of UDD NWs are very low than that of BDD NWs. Therefore, the

Recently, researchers tend to develop the diamond-based nanoelectromechanical (NEM) switches as an alternative silicon-based ones due to its exceptional properties such as high Young's modulus, maximum hardness, hydrophobicity, low mass density, greater thermal conductivity, extraordinary corrosion resistance and low toxicity. However, because of existed grain boundaries, impurities, large stress, low electrical conductivity and poor reproducibility, the polycrystalline or nanocrystalline film-based switches seem not to be as impressive candidates [84, 85]. In contrast, the utilization of single-crystalline DNWs as NEM is appraised by Liao and coworkers [29], in which those switches show low leakage current

DNWs were effectively applied in many electrochemical sensory studies. For example, Yang and Nebel utilized the vertically aligned diamond nanowires toward DNA detection *via* electrochemical approach [86]. **Figure 8** represents the schematic of biofunctionalized vertically aligned diamond nanowires for the determination of DNA in the abovementioned report.

Further, they have protracted those diamond nanowires in electrochemical gene sensors [87]. Akin to vertically aligned nanowires, BDD NWs were applied in nonenzymatic amperometric

potentiality of BDD NWs in mass analysis of small molecules has been proved.

(<0.1 pA) with a high ON/OFF ratio, hence can compete Si-NEMS structures.

DNWs were also been described by (A) planar DNWs array and (B) single DNW.

as the electron emitters in flat display panels.

28 Nanowires - Synthesis, Properties and Applications

**4.2. DNWs in mass analysis of small molecules**

**4.3. DNWs as nanoelectromechanical switches**

**4.4. DNWs as electrochemical sensors**

**Figure 8.** Schematic illumination of the biofunctionalization of vertically aligned diamond nanowires to realize a nanoscaled spacing between DNA molecules. Reproduced with permission from [86].

glucose biosensing by Zhi et al. [46]. Wherein, the selective determination of glucose has been demonstrated in the presence of ascorbic acid (AA) and uric acid (UA). Meanwhile, BDD NWs were also been efficiently used in the electrochemical identification of tryptophan by Szunerits and coworkers [88]. Alternatively, Lee and Lin collaborators developed a nitrogen incorporated DNW electrode for the amperometric detection of urea and *in situ* detection of dopamine [89]. Here, dopamine determination was well illustrated in the presence of AA and UA. More recently, Peng et al. reported the detection of CO gas by BDD NWs through electrochemical studies [90]. Wherein, the boron-doped ultrananocrystalline diamond (B-UNCD) nanowires (NWs) evidenced greater selectivity to CO gas than that of competitive species.

**Figure 9.** Integration of diamond nanowire tips on ultrasensitive silicon cantilevers. (A) Bare silicon cantilever with a nominal length of 90 μm, a shaft width of 4 μm and a thickness of 135 nm. The scale bar is 10 μm. (B) Batch of DNWs transferred onto an Si substrate for manual pickup. The scale bar is 10 μm. (C, D) zoom-in onto the end region of two different cantilevers where DNW tips had been attached. Scale bars are 10 μm in C and 1 μm in D. Reproduced with permission from [91].

#### **4.5. DNWs in ultrasensitive force microscopy**

Recently, Tao et al. described the utility of DNWs as tips for ultrasensitive force microscopy experiments [91]. Wherein, they have fabricated two types of tips using the upper and lower halves of a DNW by means of a top-down plasma etching technique and from a single-crystalline substrate. **Figure 9** demonstrates the integration of diamond nanowire tips on ultrasensitive silicon cantilevers. The typical lengths of those DNWs lie in few micrometers with diameters around 100 nm. Moreover, the tip radii were at the order of 10 nm, hence becoming suitable for scanning probe applications [32].

**Author details**

Muthaiah Shellaiah1

**References**

C5LC01306B

10.1002/adma.201402710

DOI: 10.1021/ar9700365

10.1038/nbt1138

and Kien Wen Sun1,2\*

1 Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan

2 Department of Electronics Engineering, National Chiao Tung University, Hsinchu, Taiwan

Diamond Nanowire Synthesis, Properties and Applications

http://dx.doi.org/10.5772/intechopen.78794

31

[1] Cheng C, Fan HJ. Branched nanowires: Synthesis and energy applications. Nano Today.

[2] Liu H, Li L, Scofield ME, Wong SS. Research update: Synthesis, properties, and applications of ultrathin metallic nanowires and associated heterostructures. APL Materials.

[3] Rahong S, Yasui T, Kaji N, Baba Y. Recent developments in nanowires for bio-applications from molecular to cellular levels. Lab on a Chip. 2016;**16**:1126-1138. DOI: 10.1039/

[4] Ye S, Rathmell AR, Chen Z, Stewart IE, Wiley BJ. Metal nanowire networks: The next generation of transparent conductors. Advanced Materials. 2014;**26**:6670-6687. DOI:

[5] Lei Y, Deng P, Li J, Lin M, Zhu F, Ng T-W, et al. Solution-processed donor-acceptor polymer nanowire network semiconductors for high-performance field-effect transis-

[6] Li W, Xia F, Qu J, Li P, Chen D, Chen Z, et al. Versatile inorganic-organic hybrid WO x -ethylenediamine nanowires: Synthesis, mechanism and application in heavy metal ion adsorption and catalysis. Nano Research. 2014;**7**:903-916. DOI: 10.1007/s12274-014-0452-9

[7] Wei L, Charles ML. Semiconductor nanowires. Journal of Physics D: Applied Physics.

[8] Hu J, Odom TW, Lieber CM. Chemistry and physics in one dimension: Synthesis and properties of nanowires and nanotubes. Accounts of Chemical Research. 1999;**32**:435-445.

[9] Zheng G, Patolsky F, Cui Y, Wang WU, Lieber CM. Multiplexed electrical detection of cancer markers with nanowire sensor arrays. Nature Biotechnology. 2005;**23**:1294. DOI:

tors. Scientific Reports. 2016;**6**:24476. DOI: 10.1038/srep24476

2006;**39**:R387. DOI: 10.1088/0022-3727/39/21/R01

\*Address all correspondence to: kwsun@mail.nctu.edu.tw

2012;**7**:327-343. DOI: 10.1016/j.nantod. 2012.06.002

2015;**3**:080701. DOI: 10.1063/1.4927797
