Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Preserving the 7x7 surface reconstruction of clean Si(111) by graphene
  adsorption
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin