Substrate-Directed Deposition of 3R–NbS2 Nanocrystals with a Bottom-Up Approach

Abstract

Niobium disulfide is a member of the metallic two-dimensional layered transition metal dichalcogenides (TMDs) family with a thermodynamically stable 3R-structure. Despite the difficulties involved in controlling the growth of NbS₂ crystals with a well-defined structure, a rational approach of bottom-up synthesis of NbS₂ nanostructures was performed to achieve this. The parameters of the synthesis by chemical vapor transport (CVT) were derived by thermodynamic simulations of the reaction pathway according to TRAGMIN. High-quality 3R NbS₂ nanocrystals were successfully deposited directly on thermal-oxidized Si/SiO₂ (100) and thermal-oxidized C-plane sapphire substrates. By using short time vapor transport (0.5 h) and addition of iodine in the temperature range between 600 and 800 °C, a thickness down to 7 nm (∼12 layers) was achieved. The high-crystallinity morphology of the deposited nanocrystals was confirmed by high-resolution transmission electron microscopy, selected area electron diffraction, and atomic force microscopy as well as double-polarized Raman spectroscopy. Our work explores an important synthesis route to obtain a well-determined phase structure, which is a crucial factor to be considered if practical applications should be realized in the future.

Thermodynamically controlled growth of high-quality, phase-pure 3R–NbS₂ nanocrystals via chemical vapor transport enables advances in two-dimensional materials applications.