Van der Waals Epitaxial Growth of 2D Metallic Vanadium Diselenide Single Crystals and their Extra‐High Electrical Conductivity

Abstract

2D metallic transition-metal dichalcogenides (MTMDs) have recently emerged as a new class of materials for the engineering of novel electronic phases, 2D superconductors, magnets, as well as novel electronic applications. However, the mechanical exfoliation route is predominantly used to obtain such metallic 2D flakes, but the batch production remains challenging. Herein, the van der Waals epitaxial growth of monocrystalline, 1T-phase, few-layer metallic VSe nanosheets on an atomically flat mica substrate via a "one-step" chemical vapor deposition method is reported. The thickness of the VSe nanosheets is precisely tuned from several nanometers to several tenths of nanometers. More significantly, the 2D VSe single crystals are found to present an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 10 S m , 1-4 orders of magnitude higher than that of various conductive 2D materials. The thickness-dependent charge-density-wave phase transitions are also examined through low-temperature transport measurements, which reveal that the synthesized 2D metallic 1T-VSe nanosheets should serve as good research platforms for the detecting novel many-body states. These results open a new path for the synthesis and property investigations of nanoscale-thickness 2D MTMDs crystals.

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

“…As the temperature changes, an unusual response in resistivity and magnetic susceptibility has been observed in typical CDW material systems, such as 1T-VS2 [21], 1T-VSe2 [4,50,59], 1T-TaS2 [26,37,86] and 1T-TaSe2 [82] which is also an indication of CDW transition.…”

“…CVD involves chemical reactions of gaseous reactants on a heated substrate surface [54,55]. The CVD approach has been used successfully in synthesizing 1T-VS 2 [56,57], 1T-VSe 2 [58,59], 2H-NbS 2 [60], 3R-NbS 2 [60], 2H-NbSe 2 [61], 1T-TaS 2 [62,63], 1T-TiSe 2 [64], and so on. Contamination-free and high crystalline quality samples with potential for scaling-up are the great advantages of the CVD method [65].…”

2D Metallic Transitional Metal Dichalcogenides for Electrochemical Hydrogen Evolution

“…h) OM image of CVD‐synthesized 10 nm thick VSe 2 nanosheets. Reproduced with permission . Copyright 2017, Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…In addition, insulating single crystals (e.g., mica, h‐BN) were also used as alternative substrates to SiO 2 /Si for the CVD growth of MTMDCs. Comparing with traditional heteroepitaxy mode, the van der Waals epitaxy mode can contribute to releasing the strain in the epitaxial layer, since weak van der Waals interaction rather than strong chemical bonding is evolved at the interface.…”

“…However, the controllability of layer thickness and domain size, as well as the batch production possibility for this route is still challenging. To tackle these issues, several scalable methods, including chemical exfoliation, colloidal synthesis, and chemical vapor deposition (CVD), have been developed to synthesize MTMDC nanosheets. Notably, the chemical exfoliation method is compatible with the large‐scale production, and the as‐prepared colloidal nanosheet suspensions can be used to manufacture air‐stable inks for coating and printing .…”