Controlled Synthesis of Ultrathin PtSe₂ Nanosheets with Thickness-Tunable Electrical and Magnetoelectrical Properties

Thickness-dependent chemical and physical properties have gained tremendous interest since the emergence of two-dimensional (2D) materials. Despite attractive prospects, the thickness-controlled synthesis of ultrathin nanosheets remains an outstanding challenge. Here, a chemical vapor deposition (CVD) route is reported to controllably synthesize high-quality PtSe₂ nanosheets with tunable thickness and explore their thickness-dependent electronic and magnetotransport properties. Raman spectroscopic studies demonstrate all E_g, A_1g, A_2u, and E_u modes are red shift in thicker nanosheets. Electrical measurements demonstrate the 1.7 nm thick nanosheet is a semiconductor with room temperature field-effect mobility of 66 cm² V⁻¹ s⁻¹ and on/off ratio of 10⁶. The 2.3–3.8 nm thick nanosheets show slightly gated modulation with high field-effect mobility up to 324 cm² V⁻¹ s⁻¹ at room-temperature. When the thickness is over 3.8 nm, the nanosheets show metallic behavior with conductivity and breakdown current density up to 6.8 × 10⁵ S m^–1 and 6.9 × 10⁷ A cm⁻², respectively. Interestingly, magnetoresistance (MR) studies reveal magnetic orders exist in this intrinsically non-magnetic material system, as manifested by the thickness-dependent Kondo effect, where both metal to insulator transition and negative MR appear upon cooling. Together, these studies suggest that PtSe₂ is an intriguing system for both developing novel functional electronics and conducting fundamental 2D magnetism study.