Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nature of resonant Raman scattering in ZnCoO films under sub-band
  excitation   Using the methods of scanning electron (SEM) and atom force microscopy (AFM)
as well as photoluminescence (PL) and Raman micro-spectroscopy, we investigated
$Zn_{1-x}Co_xO$ films ($x=5$ and $15\%$) grown by molecular beam epitaxy on
sapphire substrates. It is found that the films have a nanocrystalline
structure with the grain size decreased from $\sim150$ down to $28$ nm at
changing the $Co$ concentration from $5$ to $15\%$. High-resolution SEM images
of $Zn_{0.85}Co_{0.15}O$ film have been interpreted as inhomogeneous lateral
distribution of $Co$ atoms. Two broad emission bands observed in spectra of
band-to-band PL are ascribed to emission from $Zn_{1-x}Co_xO$ nano-regions
enriched and depleted with $Co$. In low-temperature PL spectra under sub-band
excitation of $Zn_{1-x}Co_xO$ films, there observed are intra-center optical
transitions due to $Co^{2+}$ center: $^2E(G)$, $^2A_1(G)$, $^2T_1(G)$,
$^4T_1(P)$, $^2T_2(G)$ $\longrightarrow$ $^4A_2(F)$. Offered is a new approach
to interpretation of resonant enhancement observed in multi-phonon scattering
by $LO$ phonons in $Zn_{1-x}Co_xO$ under sub-bandgap excitation combined with
the extrinsic Fr\"{o}hlich interaction mediated via a localized exciton bound
to the isoelectronic impurity in which the electron is strongly localized at
the magnetic $Co^{2+}$ ion. This conclusion is confirmed by the dependence of
Raman spectra on the quantum energy of exciting radiation. It assumes formation
of intermediated sub-band electron excited states of isoelectron $Co$ dopant,
they are also referred to as charge transfer processes.

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The categories of this paper are: astro-ph
1
The categories of this paper are: cs
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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: q-fin
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The categories of this paper are: supr-con
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The categories of this paper are: math
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
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The categories of this paper are: nlin