Fabrication and characterization of high quality GeSbSe reflowed and etched ring resonators.

We demonstrate the fabrication of high Q Ge28Sb12Se60 ring resonators in an all chalcogenide platform through electron-beam lithography, lift-off and thermal reflow. We achieve a Q factor of (3.9 ± 0.2) × 105 in the reflowed ring resonators and (2.5 ± 0.2) × 105 in the reactive ion etched ring resonators at 1550 nm. We measure the line roughness of these devices to estimate the scattering loss. We determine the material and scattering losses of the waveguide and find an additional 1.1 dB/cm excess loss from surface absorption. We fabricate Ge23Sb7S70 waveguides with 0.6 dB/cm of losses and show that Ge23Sb7S70 waveguides do not experience the same kind of excess loss when fabricated under the same conditions. This indicates the excess loss is related to the chemical composition of Ge28Sb12Se60 compound.

Core-shell titanium dioxide-titanium nitride nanotube arrays with near-infrared plasmon resonances.

Titanium nitride (TiN) is a ceramic with high electrical conductivity which in nanoparticle form, exhibits localized surface plasmon resonances (LSPRs) in the visible region of the solar spectrum. The ceramic nature of TiN coupled with its dielectric loss factor being comparable to that of gold, render it attractive for CMOS polarizers, refractory plasmonics, surface-enhanced Raman scattering and a whole host of sensing applications. We report core-shell TiO2-TiN nanotube arrays exhibiting LSPR peaks in the range 775-830 nm achieved by a simple, solution-based, low cost, large area-compatible fabrication route that does not involve laser-writing or lithography. Self-organized, highly ordered TiO2 nanotube arrays were grown by electrochemical anodization of Ti thin films on fluorine-doped tin oxide-coated glass substrates and then conformally coated with a thin layer of TiN using atomic layer deposition. The effects of varying the TiN layer thickness and thermal annealing on the LSPR profiles were also investigated. Modeling the TiO2-TiN core-shell nanotube structure using two different approaches, one employing effective medium approximations coupled with Fresnel coefficients, resulted in calculated optical spectra that closely matched the experimentally measured spectra. Modeling provided the insight that the observed near-infrared resonance was not collective in nature, and was mainly attributable to the longitudinal resonance of annular nanotube-like TiN particles redshifted due to the presence of the higher permittivity TiO2 matrix. The resulting TiO2-TiN core-shell nanotube structures also function as visible light responsive photocatalysts, as evidenced by their photoelectrochemical water-splitting performance under light emitting diode illumination using 400, 430 and 500 nm photons.