Laser-enabled localized synthesis of Mo1-xWxS2 alloys with tunable composition

Abstract

Alloying can tailor the optoelectronic properties of two-dimensional transition metal dichalcogenides (2D-TMDC) by bandgap tuning and shallowing of the deep-level defects, leading to enhancement in their photodetection performance. Hence, seeking for a scalable composition-controlled alloy preparation technology is essential. Here, direct laser-synthesis of micro-patterned Mo1-xWxS2 alloys is demonstrated. By irradiating composite single source precursor films of molybdenum and tungsten sulfides with a laser beam at visible wavelengths, photo-thermal decomposition takes place, thus forming high-quality Mo1-xWxS2 alloys in ambient conditions without any need for high-vacuum based environment. The Mo1-xWxS2 alloys composition is simply regulated by adjusting the volume ratio of the partial single source precursor solutions, in the final mixture solution.The stoichiometry, the structural, morphological and optical characteristics of laser-written alloys with different compositions have been investigated. Analysis of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed the formation of the long-range (∼30 nm), few-layered crystals with randomly distributed molybdenum and tungsten metal atoms with no evidence of clustering. A photosensing device has been fabricated from laser-written Mo0·5W0·5S2 alloys to demonstrate the functionality of the material.