**4.2.2 Regular arrays of metallic nano dots**

These are gold or silver hemisphere positioned upon the substrate as to reproduce a regular square lattice. Optical lithography, electron beam lithography, Reactive Ion Etching, evaporation techniques are routinely used for the fabrication of these devices. Differently from the case above, the shape, dimension, position of the dots is deterministic in the limit of the fabrication process. Thereby SERS effects arise from the rational design of the nano

Photonic Crystals for Plasmonics: From Fundamentals to Superhydrophobic Devices 277

solute of Rhodamine at the end of the process of evaporation. The magnification of the images is different: Fig. 4.5A was captured at the low magnification factor of 150, whereby the initial footprint of the drop is clearly visible; Fig. 4.5B and C were acquired setting higher magnification factors as 800 and 1500, respectively. Notice, from these, the solute extremely concentrated to the extent that the Rhodamine is accumulated into a small area clearly bridging the pillars. In any event, the residual solute is smaller than few tens of microns. Considering that the initial diameter of deposition is about 1200 m, while the final deposit is as large as 40 m, the concentration capability of the substrate is, at the very least, in the order of, roughly, (1200/40)2~1000, that is, the problem is scaled down by three orders of

Fig. 4.5. SEM images of a metallic photonic crystal for SERS measurement of Rhodamine.

analysis was performed by referring the band centred at 1650 cm-1.

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

**5. Acknowledgment** 

Fig. 4.5D is a microscope image reporting the deposit of a Rhodamine evaporation process as above. To prove that the identification of the residue as Rhodamine is correct and it is not instead constituted by debris or other refuses, SERS spectroscopy measurements were carried out on the sample. While conventional Raman intensity is directly proportional to the number of molecules probed, in the case of SERS, solely the molecules that are in close proximity of the nano-metallic substrate assure the enhancement of the electric field. In the contour and 3D plot as in Fig. 4.5E and F the SERS intensity signal is consistent with the matter distribution as in Fig. 4.5D, and this would prove the hypothesis above. The mapping

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

magnitude. Notice that this analysis relies upon geometric effects solely.

structure, founding upon the theory of surface plasmon polariton scattering (Fig. 4.4B) (De Angelis et al., 2011).

#### **4.2.3 Adiabatic nanoficusing cones**

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).
