Adsorption of CO and NO molecules on a Pt(001)-hex R0.7 degrees surface at
90 K is investigated by scanning tunneling microscopy (STM) in ultra-high v
acuum environments. At an initial stage of adsorption, both molecules are p
referentially adsorbed on the less coordinated Pt atoms of the surface with
hexagonal structure, which act as active sites. Domains of the adsorbates
grow parallel to the stripe structure of the reconstructed surface because
of lower migration energy in this direction. The extra Pt atoms produced fr
om adsorbate-induced restructuring give rise to anisotropic islands on the
(1 x 1) surface. Each of the adsorbed NO molecules at low coverages is atom
ically resolved during STM observation. However, the spots of the adsorbed
CO are invisible. Such a behavior is probably explained in terms of differe
nt interactions between the adsorbates.