Mobility Enhancement in CVD-Grown Monolayer MoS2 Via Patterned Substrate-Induced Nonuniform Straining.

The extraordinary mechanical properties of two-dimensional transition-metal dichalcogenides make them ideal candidates for investigating strain-induced control of various physical properties. Here we explore the role of nonuniform strain in modulating optical, electronic, and transport properties of semiconducting, chemical vapor deposited monolayer MoS2, on periodically nanostructured substrates. A combination of spatially resolved spectroscopic and electronic properties explore and quantify the differential strain distribution and carrier density on a monolayer, as it conformally drapes over the periodic nanostructures. The observed accumulation in electron density at the strained regions is supported by theoretical calculations which form the likely basis for the ensuing ×60 increase in field effect mobility in strained samples. Though spatially nonuniform, the pattern-induced strain is shown to be readily controlled by changing the periodicity of the nanostructures thus providing a robust yet useful macroscopic control on strain and mobility in these systems.

Heterointerface engineering of cobalt molybdenum suboxide for overall water splitting.

Highly active and earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are of great significance for sustainable hydrogen generation through alkaline water electrolysis. Here, with an aim to enhance the bifunctional electrocatalytic activity of cobalt molybdate towards overall water splitting, we demonstrate a simple method involving the modulation of the cobalt to molybdenum ratio and creation of phase-modulated heterointerfaces. Samples with varying Co/Mo molar ratios are obtained via a microwave-assisted synthesis method using appropriate starting precursors. The synthesis conditions are modified to create a heterointerface involving multiple phases of cobalt molybdenum suboxides (CoO/CoMoO3/Co2Mo3O8) supported on Ni foam (NF). Detailed electrochemical studies reveal that modulating the composition and hence the interface can tweak the bifunctional electrocatalytic activity of the material for HER and OER and thus improve the overall water splitting efficiency with very high durability over 500 h. To further evaluate the practical applicability of the studied catalyst in water splitting, an alkaline electrolyser is fabricated with the optimized cobalt molybdenum suboxide material (CMO-1.25) as a bifunctional electrocatalyst. A current density of 220 mA cm-2 @1.6 V and 670 mA cm-2 @1.8 V was obtained, and the device showed very good long-term durability.