Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct observation of ordered configurations of hydrogen adatoms on
  graphene   Ordered configurations of hydrogen adatoms on graphene have long been
proposed, calculated and searched for. Here we report direct observation of
several ordered configurations of H adatoms on graphene by scanning tunneling
microscopy. On the top side of the graphene plane, H atoms in the
configurations appear to stick to carbon atoms in the same sublattice. A gap
larger than 0.6 eV in the local density of states of the configurations was
revealed by scanning tunneling spectroscopy measurements. These findings can be
well explained by density functional theory calculations based on double sided
H configurations. In addition, factors that may influence H ordering are
discussed.

17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg