We report on the temperature dependence of in-plane E 2g and out of plane A 1g Raman modes in high quality few layers MoS 2 (FLMS) prepared using a high temperature vapor-phase method.The materials obtained were investigated using transmission electron microscopy. The frequencies of these two phonon modes were found to vary linearly with temperature. The first order temperature coefficients for E 2g and A 1g modes were found to be 1.32×10 -2 and 1.23×10 -2 cm -1 /K, respectively. The thermal conductivity of the suspended FLMS at room temperature was

--------------*rkatiyar@hpcf.upr.edu,

Atomically thin layers of 2D WS2 offer a realization of novel valley-selective electronics and power-efficient optoelectronic device fabrication due to large spin splitting at the top of the valence band and high quantum efficiency. However, the synthesis of the large-area monolayer WS2 film through chemical vapor deposition (CVD) method is in a rudimentary stage. Here we report a modified CVD method to synthesize high-crystalline monolayer WS2 (1L) with uniform size distribution over a large area. The intensity of the second-order Raman modes in 1L WS2 is enhanced, particularly the overtone of the acoustic mode LA(M), when the excitation wavelength is in the vicinity of B exciton. The variation in the intensity profile of the first-order Raman modes for 1L and bulk WS2 in (laser-energy-dependent) resonant Raman scattering processes is discussed within the third-order perturbation theory.

Efficiency of hydrogen evolution via water electrolysis is mainly impeded by the kinetically sluggish oxygen evolution reaction (OER). Thus, it is of great significance to develop highly active and stable OER catalyst for alkaline water electrolysis or to substitute the more kinetically demanding acidic OER with a facile electron-donating reaction such that OER is no longer the bottleneck half-reaction for either acidic or alkaline water electrolysis. Herein, the hierarchical Fe-Ni phosphide shelled with ultrathin carbon networks on Ni foam (FeNiP@C) is reported and shows exceptional OER activity and enhanced chemical stability in 1 M KOH. This unique electrode provides large active sites, facile electron transport pathways, and rapid gas release, resulting in a remarkable OER activity that delivers a current density of 100 mA/cm at an overpotential of 182 mV with a Tafel slope of 56 mV/dec. Combining the hydrogen evolution reaction with organic pollutant (methylene blue) oxidation, a multifunctional electrolyzer for simultaneous cost-effective hydrogen generation and organic pollutant decomposition in acid wastewater is proposed. Our strategies in this work provide attractive opportunities in energy- and environment-related fields.

The two-dimensional (2D) semiconductor molybdenum disulfide (MoS) has attracted widespread attention for its extraordinary electrical-, optical-, spin-, and valley-related properties. Here, we report on spin-polarized tunneling through chemical vapor deposited multilayer MoS (∼7 nm) at room temperature in a vertically fabricated spin-valve device. A tunnel magnetoresistance (TMR) of 0.5-2% has been observed, corresponding to spin polarization of 5-10% in the measured temperature range of 300-75 K. First-principles calculations for ideal junctions result in a TMR up to 8% and a spin polarization of 26%. The detailed measurements at different temperature, bias voltages, and density functional theory calculations provide information about spin transport mechanisms in vertical multilayer MoS spin-valve devices. These findings form a platform for exploring spin functionalities in 2D semiconductors and understanding the basic phenomena that control their performance.