The initial growth of NiSi, on Si(1 0 0) surfaces with a thin C layer by scanning tunneling microscopy has been investigated. The surface roughening with the formation of epitaxial NiSi2 domains is effectively suppressed even by the introduction of a submonolayer thick C layer. The reduction of an average size of epitaxial NiSi, islands and the increase in the nucleation density of NiSi2 islands are caused by incorporating of C atoms into the surface before the 4.8-monolayer thick Ni deposition. The adsorption condition of C atoms on the surface more strongly influences the density and the average size of epitaxial NiSi2 islands rather than the total amount of deposited C atoms does. (C) 2004 Elsevier B.V. All rights reserved.