Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Synthetic control over polymorph formation in the d-band semiconductor
  system FeS$_2$   Pyrite, also known as fool's gold is the thermodynamic stable polymorph of
FeS$_2$. It is widely considered as a promising d-band semiconductor for
various applications due to its intriguing physical properties. Marcasite is
the other naturally occurring polymorph of FeS$_2$. Measurements on natural
crystals have shown that it has similarly promising electronic, mechanical, and
optical properties as pyrite. However, it has been only scarcely investigated
so far, because the laboratory-based synthesis of phase-pure samples or
high-quality marcasite single crystal has been a challenge until now. Here, we
report the targeted phase formation via hydrothermal synthesis of marcasite and
pyrite. The formation condition and phase purity of the FeS$_2$ polymorphs are
systematically studied in the form of a comprehensive synthesis map. We,
furthermore, report on a detailed analysis of marcasite single crystal growth
by a space-separated hydrothermal synthesis. We observe that single phase
product of marcasite forms only on the surface under the involvement of H$_2$S
and sulphur vapor. The availability of high-quality crystals of marcasite
allows us to measure the fundamental physical properties, including an allowed
direct optical bandgap of 0.76 eV, temperature independent diamagnetism, an
electronic transport gap of 0.11 eV, and a room-temperature carrier
concentration of 4.14 $\times$ 10$^{18}$ cm$^{-3}$. X-ray absorption/emission
spectroscopy are employed to measure the band gap of the two FeS$_2$ phases. We
find marcasite has a band gap of 0.73 eV, while pyrite has a band gap of 0.87
eV. Our results indicate that marcasite -- that is now synthetically available
in a straightforward fashion -- is as equally promising as pyrite as candidate
for various semiconductor applications based on earth abundant elements.

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The categories of this paper are: atom-ph
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The categories of this paper are: q-alg
16
The categories of this paper are: stat
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The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
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The categories of this paper are: econ
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
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The categories of this paper are: mtrl-th