Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Epitaxial Growth of Large-area Bilayer Graphene on Ru(0001)   Large-area bilayer graphene (BG) is grown epitaxially on Ru(0001) surface and
characterized by low temperature scanning tunneling microscopy. The lattice of
the bottom layer of BG is stretched by 1.2%, while strain is absent from the
top layer. The lattice mismatch between the two layers leads to the formation
of a moire pattern with a periodicity of ~21.5 nm and a mixture of AA- and
AB-stacking. The root3 x root3 superstructure around atomic defects is
attributed to the inter-valley scattering of the delocalized pi-electrons,
demonstrating that the as-grown BG behaves like intrinsic free-standing
graphene.

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The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
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The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
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The categories of this paper are: q-fin
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The categories of this paper are: alg-geom
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The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex