Creating Optical Near-Field Orbital Angular Momentum in a Gold Metasurface

Nanocavities inscribed in a gold thin film are optimized and designed to form a metasurface. We demonstrate both numerically and experimentally the creation of surface plasmon (SP) vortex carrying orbital angular momentum in the metasurface under linearly polarized optical excitation that carries no optical angular momentum. Moreover, depending on the orientation of the exciting linearly polarized light, we show that the metasurface is capable of providing dynamic switching between SP vortex formation or SP subwavelength focusing. The resulting SP intensities are experimentally measured using a near-field scanning optical microscope and are found in excellent quantitative agreements as compared to the numerical results

Creating Optical Near-Field Orbital Angular Momentum in a Gold Metasurface

Nanocavities inscribed in a gold thin film are optimized and designed to form a metasurface. We demonstrate both numerically and experimentally the creation of surface plasmon (SP) vortex carrying orbital angular momentum in the metasurface under linearly polarized optical excitation that carries no optical angular momentum. Moreover, depending on the orientation of the exciting linearly polarized light, we show that the metasurface is capable of providing dynamic switching between SP vortex formation or SP subwavelength focusing. The resulting SP intensities are experimentally measured using a near-field scanning optical microscope and are found in excellent quantitative agreements as compared to the numerical results

Wafer-Scale Growth of WSe₂ Monolayers Toward Phase-Engineered Hybrid WO_<i>x</i>/WSe₂ Films with Sub-ppb NO_<i>x</i> Gas Sensing by a Low-Temperature Plasma-Assisted Selenization Process

An inductively coupled plasma (ICP) process was used to synthesize transition metal dichalcogenides (TMDs) through a plasma-assisted selenization process of metal oxide (MO_<i>x</i>) at a temperature as low as 250 °C. In comparison with other CVD processes, the use of ICP facilitates the decomposition of the precursors at low temperatures. Therefore, the temperature required for the formation of TMDs can be drastically reduced. WSe₂ was chosen as a model material system due to its technological importance as a p-type inorganic semiconductor with an excellent hole mobility. Large-area synthesis of WSe₂ on polyimide (30 × 40 cm²) flexible substrates and 8 in. silicon wafers with good uniformity was demonstrated at the formation temperature of 250 °C confirmed by Raman and X-ray photoelectron (XPS) spectroscopy. Furthermore, by controlling different H₂/N₂ ratios, hybrid WO_<i>x</i>/WSe₂ films can be formed at the formation temperature of 250 °C confirmed by TEM and XPS. Remarkably, hybrid films composed of partially reduced WO_<i>x</i> and small domains of WSe₂ with a thickness of ∼5 nm show a sensitivity of 20% at 25 ppb at room temperature, and an estimated detection limit of 0.3 ppb with a <i>S</i>/<i>N</i> > 10 for the potential development of a low-cost plastic/wearable sensor with high sensitivity