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Ceramic plasmonic components for optical metamaterials

Ceramic plasmonic components for optical metamaterials,Gururaj V. Naik,Alexandra Boltasseva

Ceramic plasmonic components for optical metamaterials  
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The performance of metamaterial and transformation-optics devices is limited by losses in their plasmonic components. We show that ceramics (heavily doped-zinc oxide and titanium nitride) could help in overcoming the loss issue in the optical range. OCIS codes: (250.5403) Plasmonics; (160.3918) Metamaterials; (310.7005) Transparent Conductive Coatings; Ceramic oxides such as zinc oxide and nitrides such as titanium nitride can exhibit metallic properties in the NIR and visible ranges (5-6). These materials can have small negative real permittivity values in the respective wavelength ranges. Heavily doped indium oxide and zinc oxide are good candidates for the NIR and metal nitrides are good choices in the visible range. In Fig. 1, we show the optical properties of Ga-doped ZnO (GZO), Al-doped ZnO (AZO) and titanium nitride. The ellipsometric measurements show that aluminum doping of 3 wt% makes AZO plasmonic for wavelengths longer than 1.73 μm and gallium doping of 5 wt% makes GZO plasmonic for wavelengths longer than 1.9 μm. The losses in this wavelength range are nearly four times smaller than that in silver. The optical properties of titanium nitride film deposited by reactive DC magnetron sputtering shows that TiN is plasmonic for wavelengths longer than 520 nm and has losses slightly larger than that of silver in the visible range. Although losses are slightly larger, the real permittivity is small in magnitude in the visible range which allows useful applications in many TO based devices. In order to evaluate and compare the performance of different MM devices based on these alternative plasmonic materials, we consider metamaterials with hyperbolic dispersion (HMMs). HMMs are important class of plasmonic metamaterials which have wide applications ranging from sub-diffraction imaging (3,4) to quantum-optics (7). One of the simplest ways of realizing HMMs is to stack sub-wavelength-thick, alternating layers of metallic and dielectric materials. The performance of such a device is given by the figure-of-merit (FOM) β'/ β" (8),where β is the propagation vector in the direction normal to the layers. Figure 2 plots the FOM of HMMs formed by many metal/dielectric systems. Clearly, the conventional metal-based systems have FOM barely greater than zero in the visible and NIR ranges. On the other hand, AZO and GZO perform significantly better in the NIR and TiN-based system performs better by more than an order of magnitude in the visible part of the spectrum. Thus, alternative plasmonic materials based on ceramic conductors can serve as better choices for metamaterial building blocks in the visible and NIR ranges.
Published in 2011.
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