  a-Nb(x)Si(1-x) thin films with thicknesses down to 25 {\AA} have been
structurally characterized by TEM (Transmission Electron Microscopy)
measurements. As-deposited or annealed films are shown to be continuous and
homogeneous in composition and thickness, up to an annealing temperature of
500{\deg}C. We have carried out low temperature transport measurements on these
films close to the superconductor-to-insulator transition (SIT), and shown a
qualitative difference between the effect of annealing or composition, and a
reduction of the film thickness on the superconducting properties of a-NbSi.
These results question the pertinence of the sheet resistance R_square as the
relevant parameter to describe the SIT.
