We studied the formation of interfaces in W/Si multilayer structures deposited by magnetron sputtering. In vacuo Low Energy Ion Scattering Spectroscopy was used to determine the materials growth profile with a close to atomic resolution. For that purpose, bi-layer structures, W-on-Si and Si-on-W were grown, with Si being deposited using Ar as the sputter gas and W being deposited in either Ar or Kr. The measurements revealed strongly asymmetric interfaces, with W-on-Si being significantly broader than Si-on-W. However, no difference was found in the W-on-Si interface width depending on the sputter gas, Ar or Kr, used for W deposition, suggesting that it is not a ballistic effect of the backscattered gas ions that is responsible for the wider W-on-Si interface. However, strong surface segregation of Si atoms upon the deposition of W in Kr on Si was observed. Mechanisms responsible for the observed effects are discussed.