Low-Temperature Chemical Vapor Deposition of Copper(II) Sulfide Crystals and its Nonlinear Optical Response

The need for novel multifunctional nanomaterials capable of meeting new demands in the realm of nanotechnology coupled with versatility of chemical vapor deposition (CVD) technique (in large-area growth of crystals), encourages innovative methods for synthesis of untried two-dimensional (2D) crystals. While there exist reports on both top-down and bottom-up synthesis methodologies of different Cu2S-based nanostructures, CVD-based synthesis of 2D crystals of copper(II) sulfide (CuS) has not been investigated. This work represents details of CVD method in systematic growth of highly crystalline 2D CuS sheets as thin as ~ 6 nm with lateral sizes exceeding 60 {\mu}m, at a relatively low temperature of 560 {\deg}C in ambient pressure. Samples were characterized via X-ray diffraction, Raman, atomic force microscopy, and high-resolution transmission electron microscopy. SAED revealed a 6-fold symmetric structure and identical atomic ratio of copper:sulphur was corroborated from the energy-dispersive X-ray spectroscopy. The as-prepared 2D CuS sheets were successfully utilized in second harmonic generation (SHG) and their strong response was found to be highly polarization angle-sensitive as well. The CVD-synthesized 2D CuS crystals in this study are considered to be of great significance in a diverse range of future applications, as in energy storage, next-generation solar cells, nonlinear optoelectronic-related devices, and even bioelectronics pursuits.