Abstract:The search for alternative plasmonic materials with improved optical properties, easier fabrication and integration capabilities over those of the traditional materials such as silver and gold could ultimately lead to real-life applications for plasmonics and metamaterials. In this work, we show that titanium nitride could perform as an alternative plasmonic material in the visible and near-infrared regions. We demonstrate the excitation of surface-plasmon-polaritons on titanium nitride thin films and discuss the performance of various plasmonic and metamaterial structures with titanium nitride as the plasmonic component. We also show that titanium nitride could provide performance that is comparable to that of gold for plasmonic applications and can significantly outperform gold and silver for transformation-optics and some metamaterial applications in the visible and near-infrared regions. References and links1. W. Barnes, A. Dereux, and T. Ebbesen, "Surface plasmon subwavelength optics," Nature 424, 824-830 (2003). 2. S. Lal, S. Link, and N. Halas, "Nano-optics from sensing to waveguiding," Nat. Photonics 1, 641-648 (2007). 3. D. Smith, J. Pendry, and M. Wiltshire, "Metamaterials and negative refractive index," Science 305, 788-792 (2004). 4. W. Cai and V. Shalaev, Optical Metamaterials: Fundamentals and Applications (Springer Verlag, 2009). 5. J. Pendry, D. Schurig, and D. Smith, "Controlling electromagnetic fields," Science 312, 1780-1782 (2006). 6. C. Soukoulis, S. Linden, and M. Wegener, "Physics: negative refractive index at optical wavelengths," Science 315, 47-49 (2007). 7. V. Shalaev, "Transforming light," Science 322, 384-386 (2008). 8. J. Pendry, "Negative refraction makes a perfect lens," Phys. Rev. Lett. 85, 3966-3969 (2000). 9. Z. Jacob, L. Alekseyev, and E. Narimanov, "Optical Hyperlens: Far-field imaging beyond the diffraction limit,"Opt. Express 14, 8247-8256 (2006). 10. S. Ramakrishna, J. Pendry, M. Wiltshire, and W. Stewart, "Imaging the near field," J. Mod. Opt. 50, 1419-1430 (2003). 11. W. Cai, U. Chettiar, A. Kildishev, and V. Shalaev, "Optical cloaking with metamaterials," Nat. Photonics 1, 224-227 (2007). 12. A. Kildishev and V. Shalaev, "Engineering space for light via transformation optics," Opt. Lett. 33, 43-45 (2008). 13. E. Narimanov and A. Kildishev, "Optical black hole: Broadband omnidirectional light absorber," Appl. Phys.Lett. 95, 041106 (2009). 14. N. Fang, H. Lee, C. Sun, and X. Zhang, "Sub-diffraction-limited optical imaging with a silver superlens," Science 308, 534-537 (2005). (Springer Verlag, 2007). 51. A. Hibbins, J. Sambles, and C. Lawrence, "Surface plasmon-polariton study of the optical dielectric function of titanium nitride," J. Mod. Opt. 45, 2051-2062 (1998). 52. X. Ni, Z. Liu, A. Boltasseva, and A. Kildishev, "The validation of the parallel three-dimensional solver for analysis of optical plasmonic bi-periodic multilayer nanostructures," Appl. Phys. A 100, 365-374 (2010).

The layered cobaltate Ca 3 Co 4 O 9 is of interest for energy-harvesting and heat-conversion applications because of its good thermoelectric properties and the fact that the raw materials Ca and Co are non-toxic, abundantly available, and inexpensive. While single-crystalline Ca 3 Co 4 O 9 exhibits high Seebeck coefficient and low resistivity, its widespread use is hampered by the fact that single crystals are too small and expensive. A promising alternative approach is the growth of highly textured and/or epitaxial Ca 3 Co 4 O 9 thin films with correspondingly anisotropic properties. Here, we present a two-step sputtering/annealing method for the formation of highly textured virtually phase-pure Ca 3 Co 4 O 9 thin films by reactive co-sputtering from Ca and Co targets followed by an annealing process at 730 °C under O 2 -gas flow. The thermally induced phase transformation mechanism was investigated by in-situ time-resolved annealing experiments using synchrotron-based 2D x-ray diffraction as well as ex-situ annealing experiments and standard lab-based x-ray diffraction. By tuning the proportion of initial CaO and CoO phases during film deposition, the method enables synthesis of Ca 3 Co 4 O 9 thin films as well as Ca x CoO 2 . With this method, we demonstrate production of epitaxial Ca 3 Co 4 O 9 thin films with in-plane electrical resistivity of 6.44 mΩcm and a Seebeck coefficient of 118 µVK -1 at 300 K.3

Reduction of cross-plane thermal conductivity and understanding the mechanisms of heat transport in nanostructured metal/semiconductor superlattices are crucial for their potential applications in thermoelectric and thermionic energy conversion devices, thermal management systems, and thermal barrier coatings. We have developed epitaxial (Ti,W)N/(Al,Sc)N metal/semiconductor superlattices with periodicity ranging from 1 nm to 240 nm that show significantly lower thermal conductivity compared to the parent TiN/(Al,Sc)N superlattice system. The (Ti,W)N/(Al,Sc)N superlattices grow with [001] orientation on the MgO(001) substrates with well defined coherent layers and are nominally single crystalline with low densities of extended defects. Cross-plane thermal conductivity (measured by time-domain thermoreflectance (TDTR)) decreases with an increase in the superlattice interface density in a manner that is consistent with incoherent phonon boundary scattering. Thermal conductivity values saturate at 1.7 W/m-K for short superlattice periods possibly due to a delicate balance between long wavelength coherent phonon modes and incoherent phonon scattering from heavy tungsten (W) atomic sites and superlattice interfaces. First-principles density functional theory based calculations are performed to model the vibrational spectrum of the individual component materials and transport models are used to explain the interface thermal conductance (ITC) across the (Ti,W)N/(Al,Sc)N interfaces as a function of periodicity. The long-wavelength coherent phonon modes are expected to play a dominant role in the thermal transport properties of the short-period superlattices. Our analysis of the thermal transport properties of (Ti,W)N/(Al,Sc)N metal/semiconductor superlattices addresses fundamental questions about heat transport in multi-layer materials.