A study is reported of the effect of chemisorbed O2 and CO molecules on the properties of structures of the type “nanoscale-ytterbium-film-Si(111) silicon substrate” and, in particular, on the reactions between a metal and silicon. It has been shown that chemisorption of the above molecules on Yb-Si(111) structures initiates partial or total suppression of growth of ytterbium silicide and that the effect of adsorbates on reactions at the metal-silicon interface depends on the thickness of the ytterbium nanolayer. Indeed, at a film thickness of 8 monolayers and higher oxygen doses (360 Langmuir), chemisorbed molecules suppress completely the silicide formation process. With ytterbium films of larger thicknesses (16 monolayers) and higher doses of oxygen (360 Langmuir) or carbon monoxide (480 Langmuir), while the silicide does grow, this apparently takes place only in ytterbium nanofilm layers closest to the substrate. The effect of adsorbed molecules on the silicide formation becomes less pronounced also with decreasing number of these molecules on the surface, i.e., as their dose decreases.