  The electronic structure of Au-Sn intermetallic layers of different
compositions grown on Au(111) to the thickness of several nanometers has been
studied in this work. The layer, interface and the substrate related components
in the Au 4$f$ and Sn 4$d$ core-level spectra obtained using x-ray
photoelectron spectroscopy (XPS) vary with deposition parameters to reveal the
details of the Au-Sn formation. While AuSn is grown by deposition at room
temperature, Au rich compounds form as a result of heat treatment through inter
diffusion of Au and Sn. Deposition at high temperature forms more Au rich
compositions compared to post annealing at the same temperature due to the
kinetic energy of the impinging Sn atoms in the former case. Post annealing, on
the other hand, stabilizes the bulk phases such as AuSn and Au$_5$Sn and
exhibits an activated behavior for transition from the former to the latter
with increasing temperature. The XPS valence band spectra of AuSn and
Au$_{5}$Sn layers show good agreement with the density functional theory
calculation, indicating that these have the bulk structure reported in
literature. However, the influence of anti-site defects is observed in
Au$_5$Sn. Low energy electron diffraction study reveals that although the AuSn
layer is ordered, its top surface is disordered at room temperature. Surface
order is obtained by annealing or deposition at elevated temperatures and
dispersing bands are observed by angle resolved photoemission spectroscopy.
Both electron-like and hole-like bands are evident for the
($\sqrt{3}$$\times$$\sqrt{3}$)R30$^{\circ}$ phase, while a nearly free
electron-like parabolic surface state is observed for the
p(3$\times$3)R15$^{\circ}$ phase.
