Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct observation of the basic mechanisms of Pd island nucleation on
  Au(111)   The formation mechanisms of evaporated Pd islands on the reconstructed
Au(111) $22 /times /sqrt{3}$ herringbone surface have been here studied by
Scanning Tunneling Microscopy (STM) at room temperature. Atomically resolved
STM images at the very early stages of growth provide a direct observation of
the mechanisms involved in preferential Pd islands nucleation at the elbows of
the herringbone structure. At low Pd coverage the Au(111) herringbone structure
remains substantially unperturbed and isolated Pd atoms settled in hollow sites
between Au atoms are found nearby the elbows and the distortions of the
reconstructed surface. In the same regions, at extremely low coverage (0.003
ML), substituted Pd atoms in lattice sites of the Au(111) surface are also
observed, revealing the occurrence of a place exchange mechanism. Substitution
seems to play a fundamental role in the nucleation process, forming aggregation
centers for incoming atoms and thus leading to the ordered growth of Pd islands
on Au(111). Atomically resolved STM images of Pd islands reveal a close-packed
arrangement with lattice parameter close to the interatomic distance between
gold atoms in the fcc regions of the Au(111) surface. Distortion of the
herringbone structure for Pd coverages higher than 0.25 ML indicates strong
interaction between the growing islands and the topmost Au(111) layer.

32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph