Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Germanene: a novel two-dimensional Germanium allotrope akin to Graphene
  and Silicene   Using a gold (111) surface as a substrate we have grown in situ by molecular
beam epitaxy an atom-thin, ordered, two-dimensional multi-phase film. Its
growth bears strong similarity with the formation of silicene layers on silver
(111) templates. One of the phases, forming large domains, as observed in
Scanning Tunneling Microscopy, shows a clear, nearly flat, honeycomb structure.
Thanks to thorough synchrotron radiation core-level spectroscopy measurements
and advanced Density Functional Theory calculations we can identify it to a
$\sqrt{3}$x$\sqrt{3}$R(30{\deg}) germanene layer in coincidence with a
$\sqrt{7}$x$\sqrt{7}$R(19.1{\deg}) Au(111) supercell, thence, presenting the
first compelling evidence of the birth of a novel synthetic germanium-based
cousin of graphene.

6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th