On-Stack Two-Dimensional Conversion of MoS2 into MoO3

Abstract

Chemical transformation of existing two-dimensional (2D) materials can be crucial in further expanding the 2D crystal palette required to realize various functional heterostructures. In this work, we demonstrate a 2D 'on-stack' chemical conversion of single-layer crystalline MoS2 into MoO3 with a precise layer control that enables truly 2D MoO3 and MoO3/MoS2 heterostructures. To minimize perturbation of the 2D morphology, a nonthermal oxidation using O2 plasma was employed. The early stage of the reaction was characterized by a defect-induced Raman peak, drastic quenching of photoluminescence (PL) signals and sub-nm protrusions in atomic force microscopy images. As the reaction proceeded from the uppermost layer to the buried layers, PL and optical second harmonic generation signals showed characteristic modulations revealing a layer-by-layer conversion. The plasma-generated 2D oxides, confirmed as MoO3 by x-ray photoelectron spectroscopy, were found to be amorphous but extremely flat with a surface roughness of 0.18 nm, comparable to that of 1L MoS2. The rate of oxidation quantified by Raman spectroscopy decreased very rapidly for buried sulfide layers due to protection by the surface 2D oxides, exhibiting a pseudo-self-limiting behavior. As exemplified in this work, various on-stack chemical transformations can be applied to other 2D materials in forming otherwise unobtainable materials and complex heterostructures, thus expanding the palette of 2D material building blocks.

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Cited by in corpus (9)

• Structural and optical properties of single- and few-layer magnetic semiconductor CrPS4
• Oxide-mediated self-limiting recovery of field effect mobility in plasma-treated MoS${}_2$
• Interface-Confined Doubly Anisotropic Oxidation of Two-Dimensional MoS2
• Second-Harmonic Young Interference in Atom-Thin Heterocrystals
• Variation of photoluminescence spectral line shape of monolayer WS2
• Photoresponsivity enhancement in monolayer MoS${}_2$ by rapid O${}_2$:Ar plasma treatment
• Exciton-Sensitized Second-Harmonic Generation in 2D Heterostructures
• Suppression of the Shear Raman Mode in Defective Bilayer MoS2
• Elucidating the role of electron transfer in the photoluminescence of $\mathrm{Mo}{\mathrm{S}}_2$ quantum dots synthesized by fs-pulse ablation