Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen
  ambient - a summary of ab initio data   Adsorption of ammonia at NH3/NH2/H covered GaN(0001) surface was analyzed
using results of ab initio calculations. The whole configuration space of
partially NH3/NH2/H covered GaN(0001) surface was divided into zones
differently pinned Fermi level: at Ga broken bond state for dominantly bare
surface (region I), at VBM for NH2 and H covered (region II), and at CBM for
NH3 covered surface (region III). The extensive ab intio calculations show
validity of electron counting rule (ECR) for all mixed coverage, for bordering
these three regions. The adsorption was analyzed using newly identified
dependence of the adsorption energy on the charge transfer at the surface. For
region I and II ammonia adsorb dissociatively, disintegrating into H adatom and
HN2 radical for large fraction of vacant sites while for high coverage the
ammonia adsorption is molecular. The dissociative adsorption energy strongly
depends on the Fermi level at the surface (pinned) and in the bulk (unpinned)
while the molecular adsorption energy is determined by bonding to surface only,
in accordance to the recently published theory. The molecular adsorption is
determined by the energy of covalent bonding to the surface. Ammonia adsorption
in region III (Fermi level pinned at CBM) leads to unstable configuration both
molecular and dissociative which is explained by the fact that Ga-broken bond
sites are doubly occupied by electrons. The adsorbing ammonia brings 8
electrons to the surface, necessitating transfer of the electrons from
Ga-broken bond state to Fermi level, energetically costly process. Adsorption
of ammonia at H-covered site leads to creation of NH2 radical at the surface
and escape of H2 molecule. The process energy is close to 0.12 eV, thus not
large, but the inverse process is not possible due to escape of the hydrogen
molecule.

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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga
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The categories of this paper are: math
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The categories of this paper are: eess
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The categories of this paper are: math-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg