Transition metal thiophosphates Nb4P2S21: New kind of 2D materials for multi-functional sensors

Highlights: • Synthesis of 2D transition metal thiophosphates Nb₄P₂S₂₁. • Bulk to few nanometer scale separation of Nb₄P₂S₂₁ using mechanical exfoliation. • Multi-functional sensing application in photodetector and gas sensor. -- Abstract: A new of 2D transition metal thiophosphates, Nb₄P₂S₂₁, was synthesized through a vapor transport reaction. High purity and centimeter-scale large Nb₄P₂S₂₁ crystals were obtained by controlling the growth temperature and stoichiometric ratio between niobium, phosphorus, and sulfur (using excess sulfur condition, Nb: P: S = 4: 2: 23). It was confirmed that large Nb₄P₂S₂₁ crystals could be separated to a nanometer scale through mechanical exfoliation, and the exfoliated Nb₄P₂S₂₁ layer exhibits semiconducting characteristics by measuring the change in electrical conductivity with temperature (increased conductivity with temperature in the range of 93–333 K). Furthermore, the device characteristics for detecting visible ray laser (635 nm) and NO₂ gas molecules were verified. Based on these characteristics, the synthesized 2D material is expected to be a potential candidate for additional 2D materials and in multi-functional sensor devices, including optoelectronics and gas sensing applications.