Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Oxidation dynamics of ultrathin GaSe probed through Raman spectroscopy   Gallium selenide (GaSe) is a 2D material with a thickness-dependent gap,
strong non-linear optical coefficients and uncommon interband optical selection
rules, making it interesting for optoelectronic and spintronic applications. In
this work, we monitor the oxidation dynamics of GaSe with thicknesses ranging
from 10 to 200 nm using Raman spectroscopy. In ambient temperature and humidity
conditions, the intensity of all Raman modes and the luminescence decrease
rapidly with moderate exposure to above-gap illumination. Concurrently, several
oxidation products appear in the Raman spectra: Ga$_2$Se$_3$, Ga$_2$O$_3$ and
amorphous and crystalline selenium. We find that no safe measurement power
exists for optical measurements on ultrathin GaSe in ambient conditions. We
demonstrate that the simultaneous presence of oxygen, humidity, and above-gap
illumination is required to activate this photo-oxidation process, which is
attributed to the transfer of photo-generated charge carriers towards aqueous
oxygen at the sample surface, generating highly reactive superoxide anions that
rapidly degrade the sample and quench the optical response of the material.

19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
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The categories of this paper are: q-fin
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The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
1
The categories of this paper are: cs
3
The categories of this paper are: physics
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga