Molecular Beam Epitaxy of Two-Dimensional Vanadium-Molybdenum Diselenide Alloys

Abstract

Two-dimensional (2D) alloys represent a versatile platform that extends the properties of atomically thin transition-metal dichalcogenides. Here, using molecular beam epitaxy, we investigate the growth of 2D vanadium-molybdenum diselenide alloys, V x Mo1–x Se2, on highly oriented pyrolytic graphite and unveil their structural, chemical, and electronic integrities via measurements by scanning tunneling microscopy/spectroscopy, synchrotron X-ray photoemission, and X-ray absorption spectroscopy (XAS). Essentially, we found a critical value of x = ∼0.44, below which phase separation occurs and above which a homogeneous metallic phase is favored. Another observation is an effective increase in the density of mirror twin boundaries of constituting MoSe2 in the low V concentration regime (x ≤ 0.05). Density functional theory calculations support our experimental results on the thermal stability of 2D V x Mo1–x Se2 alloys and suggest an H phase of the homogeneous alloys with alternating parallel V and Mo strips randomly in-plane stacked. Element-specific XAS of the 2D alloys, which clearly indicates quenched atomic multiplets similar to the case of 2H-VSe2, provides strong evidence for the H phase of the 2D alloys. This work provides a comprehensive understanding of the thermal stability, chemical state, and electronic structure of 2D V x Mo1–x Se2 alloys, useful for the future design of 2D electronic devices.

Controllable Thin‐Film Approaches for Doping and Alloying Transition Metal Dichalcogenides Monolayers

“…Reproduced with permission. [ 65 ] Copyright 2020, American Chemical Society. g 1–5 ) Corresponding STS curves to each alloy shown in (f).…”

“…Metal–semiconductor transition in V x Mo 1‐ x Se 2 alloys was recently explored by a combination of MBE, STM/STS, XPS, and DFT calculations. [ 65 ] This type of TMD alloys is of great interest for optoelectronic applications because they could provide a large tunable range of bandgap, such as HfS 2 x Se 2(1− x ), that provide a 0.7 eV tuning range. [ 102 ] Zhang et al.…”

2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

“…To begin with, MBE is easily scalable and versatile for the growth of various 2DLM alloys. Thus far, it has been successfully exploited to synthesize 2D (Bi 1−x Sb x ) 2 Te 3 , [171] (Bi 1−x Sb x ) 2 Se 3 , [172] GaTe x Se 1−x , [173] WSe 2−x Te x , [174] Mo x W 1−x Se 2 , [170] V x Mo 1−x Se 2 , [175] and As x Te 1−x [176] alloys. In addition, by virtue of the precisely modulated supply rate of the molecular beam flux, the thickness of MBE-grown 2DLMs can be readily controlled.…”

“…To begin with, MBE is easily scalable and versatile for the growth of various 2DLM alloys. Thus far, it has been successfully exploited to synthesize 2D (Bi 1− x Sb x ) 2 Te 3 , [ 171 ] (Bi 1− x Sb x ) 2 Se 3 , [ 172 ] GaTe x Se 1− x , [ 173 ] WSe 2− x Te x , [ 174 ] Mo x W 1 −x Se 2 , [ 170 ] V x Mo 1 −x Se 2 , [ 175 ] and As x Te 1 −x [ 176 ] alloys.…”

Optoelectronic Properties of Atomically Thin MoxW(1−x)S2 Nanoflakes Probed by Spatially-Resolved Monochromated EELS

“…when it comes to 2D TMDs, even though bulk TMD alloys have existed for decades now, a wide array of 2D TMD alloys have been synthesised in the past decade [54], thanks to the development in synthesis techniques such as chemical vapor deposition [32], physical vapor deposition [55], chalcogen exchange [32] and colloidal solution synthesis [51,52]. Even so, only a small number of alloys has been achieved so far; most of them ternary alloys based on Mo, W, S, Se and Te [16,24,32,51,52,[55][56][57][58][59][60], although new alloys with different transition metals have also been achieved [33,58,61,62], as well as quaternary alloys [17,[63][64][65][66]. Novel optoelectronic applications have arisen from these new materials [66][67][68][69].…”