Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effects of Lower Symmetry and Dimensionality on Raman Spectra in 2D WSe2   We report the observation and interpretation of new Raman peaks in few-layer
tungsten diselenide (WSe2), induced by the reduction of symmetry going from 3D
to 2D. In general, Raman frequencies in 2D materials follow quite closely the
frequencies of corresponding eigenmodes in the bulk. However, while the modes
that are Raman active in the bulk are also Raman active in the thin films, the
reverse is not always true due to the reduced symmetry in thin films. Here, we
predict from group theory and density functional calculations that two
intra-layer vibrational modes which are Raman inactive in bulk WSe2 in our
experimental configuration become Raman active in thin film WSe2, due to
reduced symmetry in thin films. This phenomenon explains the Raman peaks we
observe experimentally at ~310 cm-1 and 176 cm-1 in thin film WSe2.
Interestingly, the bulk mode at ~310 cm-1 that is Raman inactive can in fact be
detected in Raman measurements under specific wavelengths of irradiation,
suggesting that in this case, crystal symmetry selection rules may be broken
due to resonant scattering. Both theory and experiment indicate that the and
modes blue-shift with decreasing thickness, which we attribute to surface
effects. Our results shed light on a general understanding of the Raman/IR
activities of the phonon modes in layered transition metal dichalcogenide
materials and their evolution behavior from 3D to 2D.

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The categories of this paper are: alg-geom
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The categories of this paper are: astro-ph
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The categories of this paper are: math
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-fin
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The categories of this paper are: acc-phys
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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: econ
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The categories of this paper are: hep-th