  Stable and metastable metallic nanoparticles exhibit unique properties
compared to the bulk, with potentially important applications for catalysis.
This is in particular the case for the AgPt alloy that can exhibit the ordered
L1$_1$ structure (alternation of pure Ag and Pt (111) planes) in nanometer size
particles. However, for such small systems, the interfaces play an important
role. Therefore, the support used to elaborate the nanoparticles in ultrahigh
vacuum experiments may influence their properties, even in the case of weakly
interacting substrates like amorphous carbon or silica. This work focuses on
the AgPt nanoparticles deposited on silica, and investigates the effect of the
support disorder and roughness on the structure and chemical ordering, in
particular at the interface with the substrate, by Monte Carlo calculations of
the atomic density profiles with semi-empiric potentials.
