Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence for 2-D pi-bonded Surface Reconstructions on Si(111)   A silicene-like polymorph of the Si111 7x7 surface is proposed that resolves
numerous experimental paradoxes and inconsistencies arising over the past 34
years. An analysis of the three established surface state charge densities from
atom resolved spectroscopic imaging, including the 'forgotten' surface state at
~ -0.4 eV, shows features that are consistent with well studied 2-D silicenes.
The bonding in this new structure as well as its physical nature are
fundamentally different from the covalent surface bonding that is widely
accepted. From its structural characteristics, this polymorph arises from
significant sp2-sp3 hybridization in the top layer that creates a 'faulted'
honeycomb motif of Si atoms. This top layer has an unusual periodic p-orbital
structure that can inter-digitate with the terminal bulk 'dangling bonds' to
create a 2-D pi-bonded structure. This unusual bonding and new structure is
important in understanding the nature of 2-D silicenes and 1-D honeycomb
structures, as well as the conversion of the 1-D pi-bonded chains of the 2x1
structure to the 2-D pi-bonded 5x5 or 7x7 structures. Such extended pi-bonded
structures can lead to non-covalent dispersion interactions that have not been
accurately included in previous semiconductor surface calculations.

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The categories of this paper are: cs
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: math
19
The categories of this paper are: eess
5
The categories of this paper are: gr-qc