**5. Acknowledgment**

276 Photonic Crystals – Innovative Systems, Lasers and Waveguides

structure, founding upon the theory of surface plasmon polariton scattering (Fig. 4.4B) (De

These are extremely small conical geometries whereby crystal together with a plasmonic waveguide focuses the excitation laser to the apex of the waveguide, enabling a photon confinement equivalent to the radius of curvature of the nanofabricated tip (De Angelis et al., 2008; De Angelis et al., 2010). The fabrication process is accomplished on the basis of three steps. The grating is milled on the surface of the silicon micropillar by focused ion beam milling. The nanocones are growth on the top of the silicon tapered pillar by employing electron beam induced deposition (EBID) from a Platinum-based gas precursor. A thin layer of silver (40 nm) is finally deposited upon the device by means of thermal evaporation. These devices exploit the surface plasmon polariton adiabatic compression whereby the electro-magnetic field is locally enhanced (Fig. 4.4C) (De Angelis et al., 2011).

The above analysis of SHSs and of the related properties thereof may be summarized as follows: (i) SHSs retain unique properties in terms of wettability, in particular a certain mass of water, in shape of a drop, would be repelled by such surfaces; (ii) SHSs have superior adhesive properties, in the sense that they exhibit vanishing friction coefficients; (iii) a droplet, post upon these surfaces, would accordingly preserve a quasi-spherical shape while evaporates, and the contact area at the interface would thus progressively reduce. Node (iii), above, is the key feature for such surfaces, in that it would enable to concentrate tiny amounts of agents (biomolecules) over micrometric areas. Imagine to deposit a drop of an extremely diluted solution upon a textured, superhydrophobic substrate. The drop would evaporate over time and thus the solution would get more and more concentrated. At the late stage of evaporation, the residual solute would be confined within an incredibly small region of the plane. With an appropriate design, few molecules may be conveniently enforced to confine into the smallest area conceivable, at the limit upon a sole pillar. Nano geometry based biophotonic devices, conveniently tiling these surfaces, would probe/detect the moieties with heretofore

unattainable resolution limits (the process, as a whole, is recapitulated in Fig. 4.1).

identification of proteins or analytes in the single molecule regime.

The devices introduced would perform SERS measurements as well as (and definitely not better than) conventional SERS substrates. Nevertheless, here, the beneficial effects of super hydrophobicity and nanogeometry based spectroscopy are combined and conveyed into a unique platform, and from the combination of the two novel properties arise permitting the

Here, we report briefly on some experiments that would demonstrate the potentials of the method. Small drops of D.I. water containing Rhodamine molecules were gently positioned upon the substrates as in Fig. 4.4A. The evaporation process was followed over time until an irreversible transition to a pinning (Wenzel) state occurred. Few molecules were conveniently enforced to confine into a small area. Solutions were investigated with concentration as small as 10-18 M, that is, in the atto molar range. Figs. from 4.5A to C are SEM images of the residual

Angelis et al., 2011).

**4.3 The device as a whole**

**4.4 Measurements** 

**4.2.3 Adiabatic nanoficusing cones** 

Authors would like to thanks Dr. Marco Salerno for providing APA template.

The authors also gratefully acknowledge support from European Projects SMD FP7-NMP-2008-SMALL-2 proposal No. CP-FP 229375-2 and Nanoantenna FP7-HEALTH-2009, Grant

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**14** 

*India* 

Rajneesh Kumar

**Plasma Photonic Crystal** 

*Indian Institute of Technology Kanpur* 

*Plasmonics and Metamaterials Lab, Department of Physics* 

Recently, there has been a rapid growth in the use of plasma for industrial applications where the use of plasma-based technologies offer distinct advantage over the conventional technologies (Kumar, 2011c). A number of spin-off plasma based technologies have spawned in the area of plasma-microwave interactions and plasma stealth technology. Plasma is the fourth state of matter and its material properties (electric permittivity and magnetic permeability) can be tuned by changing plasma parameters for electromagnetic radiations. As it is well known that electric permittivity () and a magnetic permeability (µ) are the fundamental characteristics which determine the propagation of electromagnetic waves in matter. Here, it may be quite interesting to study the electromagnetic wave propagation in the plasma. Plasma can be used as metamaterials for negative refrction of

Photonic crystals (PCs) are structures with periodic arrangement of dielectrics or metals, which provide the ability to manipulate the propagation of electromagnetic waves. In fact the lattice constant of common materials is 0.2-1 nm, i.e., much shorter than the wavelength of visible light (a few 100 nm). This is the reason why the response of such materials on the electrical and magnetic fields of light wave can be described by macroscopic parameters and µ. In 1987, anomalous refraction properties of PCs were reported based on a numerical analysis with transfer matrix method (Yablonovich, 1987). The light propagation in the PCs can not be considered as an average effect of atoms as in common crystals. In contrary, light propagation in PCs is the result of Bragg diffraction for each atom. Hence the periodic structure of the PCs is very important. The macroscopic constant and µ can not describe the light propagation in PC and the light refraction at the PC boundary. More precisely, light waves in PCs should be considered as the Bloch waves but in the so-called envelope

An effective index of refraction for the crystal is used to describe the overall reflectivity form

*d c dk* 

(1)

electromagnetic waves (Kumar, 2010a; Kumar 2011d).

**2. Photonic crystals (PCs) for negative refraction** 

function approximation they may be considered as plane waves.

**1. Introduction**

the photonic crystal:

Second-harmonic generation in reflection and diffraction by a GaAs photoniccrystal waveguide. *J. Opt. Soc. Am. B*, Vol. 19, No. 9, pp. 2122-2128

