Study of the tungsten filament alloying processes with different precursor molecules shows that silicidation occurs when using silacycobutane (SCB) and carburization with 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSCB). The difference in the decomposition chemistry with the two molecules is responsible for the observation. Comparison of the depth profile and temperature distribution of the Si or C content in the alloyed filament illustrates the interplay among the Si or C deposition onto, evaporation from, and diffusion into the filament. Examination of the time distribution of key products from secondary gas-phase reactions at various filament temperatures demonstrates that gas-phase reactions dominate only at low temperatures. Silicidation or carburization is the dominant process at high temperatures, which contributes to a large consumption rate of precursor gas and a reduction in formation rate of the gas-phase reaction products. (C) 2011 Elsevier B.V. All rights reserved.