Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Valence Band Onset and Valence Plasmons of SnO2 and In2-xSnx O3 Thin
  Films   Valence band onset (Ev), valence band tail (VBT) and valence plasmons (VPs)
have been studied as a function of sputtering of SnO2 and In2-xSnxO3 (ITO) thin
films, using ultraviolet photoemission spectroscopy (UPS). Decrease in Ev with
respect to the Fermi level and increase in the density of energy levels of VBT
have been observed after 5 minutes of sputtering using Ar+ ions (500V). Bulk
and surface components of VPs of Sn, SnO and SnO2 in sputtered SnO2 thin films
have been observed in UPS spectra. Similarly, bulk and surface components of
VPs of In, Sn and oxygen deficient ITO in sputtered ITO thin films have been
observed in UPS spectra. Possible roles of Ev and increase in the density of
energy levels of VBT are discussed in the mechanisms of current transport
through heterojunctions of SnO2 with semiconductors.

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The categories of this paper are: acc-phys
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: cs
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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: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: solv-int
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The categories of this paper are: econ
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The categories of this paper are: patt-sol