Thickness-Independent Semiconducting-to-Metallic Conversion in Wafer-Scale Two-Dimensional PtSe₂ Layers by Plasma-Driven Chalcogen Defect Engineering

Abstract

Platinum diselenide (PtSe2) is an emerging class of two-dimensional (2D) transition-metal dichalcogenide (TMD) crystals recently gaining substantial interest, owing to its extraordinary properties absent in conventional 2D TMD layers. Most interestingly, it exhibits a thickness-dependent semiconducting-to-metallic transition, i.e., thick 2D PtSe2 layers, which are intrinsically metallic, become semiconducting with their thickness reduced below a certain point. Realizing both semiconducting and metallic phases within identical 2D PtSe2 layers in a spatially well-controlled manner offers unprecedented opportunities toward atomically thin tailored electronic junctions, unattainable with conventional materials. In this study, beyond this thickness-dependent intrinsic semiconducting-to-metallic transition of 2D PtSe2 layers, we demonstrate that controlled plasma irradiation can “externally” achieve such tunable carrier transports. We grew wafer-scale very thin (a few nm) 2D PtSe2 layers by a chemical vapor deposition (CVD) method and confirmed their intrinsic semiconducting properties. We then irradiated the material with argon (Ar) plasma, which was intended to make it more semiconducting by thickness reduction. Surprisingly, we discovered a reversed transition of semiconducting to metallic, which is opposite to the prediction concerning their intrinsic thickness-dependent carrier transports. Through extensive structural and chemical characterization, we identified that the plasma irradiation introduces a large concentration of near-atomic defects and selenium (Se) vacancies in initially stoichiometric 2D PtSe2 layers. Furthermore, we performed density functional theory (DFT) calculations and clarified that the band-gap energy of such defective 2D PtSe2 layers gradually decreases with increasing defect concentration and dimensions, accompanying a large number of midgap energy states. This corroborative experimental and theoretical study decisively verifies the fundamental mechanism for this externally controlled semiconducting-to-metallic transition in large-area CVD-grown 2D PtSe2 layers, greatly broadening their versatility for futuristic electronics.

Synthesis of tungsten ditelluride thin films and highly crystalline nanobelts from pre-deposited reactants

“…Furthermore, the overall ratio of W to Te on the surface changes after sputtering, with the sample becoming increasingly deficient in Te. The proposed explanation of these observations is that Te is preferentially sputtered, meaning that the sample becomes more W rich during this process, and WO 3 is not effectively sputtered but rather becoming a substoichiometric WO x [68]. This also correlates with previous reports that indicate the self-limiting nature of WTe 2 oxidation.…”

Two-Dimensional Platinum Diselenide: Synthesis, Emerging Applications, and Future Challenges

“…However, Shawkat et al discovered a reversed transition of semiconducting to metallic as the PtSe 2 film irradiated by plasma. Shawkat et al [ 77 ] realized a semiconductor-to-metallic transition in wafer-scale PtSe 2 film by controlled plasma irradiation. Extensive structural and chemical characterization has proven that large concentration of near atomic defects and selenium vacancies introduced by the plasma irradiations induced the transition of semiconductor to metallic.…”

Excellent HER and OER Catalyzing Performance of Se‐Vacancies in Defects‐Engineered PtSe2: From Simulation to Experiment

“…However, studies on the structure and catalysis capacity of defects, especially multiple ones, in PtSe 2 are still rare. [41][42][43][44][45][46][47][48][49][50][51][52][53] In this paper, the structures, fractions and catalytic performance of various Se vacancies in defective PtSe 2 (d-PtSe 2 ) monolayers were investigated systematically. We indicate the point Se vacancies are quite stable once they are introduced in PtSe 2 .…”