The initial surface chemical reactions that lead to the chemical vapor deposition (CVD) of tungsten on aluminum, PtSi, and TiN using WF 6/SiH4 mixtures have been studied in an ultrahigh vacuum system using x-ray photoemission and mass spectrometry. In all these cases, tungsten deposition can be initiated by initial deposition of a tungsten or silicon seed layer. Aluminum was found to react with WF6 at elevated temperatures to deposit a seed metallic tungsten layer with the formation of volatile aluminum subfluoride. SiH4 then reacted with the tungsten seed layer to provide silicon to sustain the CVD reaction. The silicon atoms in PtSi, similar to the case of a silicon substrate, initiated the deposition process by reacting with WF6. TiN, on the other hand, was decomposed by both WF6 and SiH4 to deposit the necessary tungsten and silicon seed layers, respectively, for the deposition reaction. Deposition reactions on an oxygen-contaminated technical TiN surface were also investigated.