Two-Dimensional Layered Semiconductor Tungsten Disulfide and Molybdenum-Tungsten Disulfide: Synthesis, Materials Properties and Electronic Structure

摘要

Atomically thin two-dimensional tungsten disulfide layers have been synthesized on silicon dioxide substrates via chemical vapor deposition with the assistance of hydrothermally synthesized tungsten trioxide seeds. This seed-assisted chemical vapor deposition approach allows production of highly crystalline semiconductor tungsten disulfide layers with a band gap of 1.94 eV in monolayer form. Photoluminescence spectroscopy measurements in conjunction with ab-initio density functional theory calculations show that bulk tungsten disulfide undergoes a transition from an indirect band gap to a direct one in monolayer limit. We have also synthesized heterogeneous systems of molybdenum disulfide and tungsten disulfide and characterized the layers by Raman and Photoluminescence spectroscopy measurements. The density functional theory calculations verify the modification of the band gap by changing the composition of molybdenum and tungsten in molybdenum-tungsten disulfide heterogeneous layers, pointing to creating a range of band gap values by alloying two-dimensional semiconductors.