Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On-Stack Two-Dimensional Conversion of MoS2 into MoO3   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.

1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas