The initial stages of titanium nitride atomic layer deposition using sequential additions of TiCl4 and NH3 on fumed silica powder were investigated using in situ Fourier transform infrared spectroscopy techniques. After the first stage, the primary active surface species for the formation of TiN were determined to be TiCl, and Ti2NH. After six complete atomic layer deposition cycles the infrared spectrum indicated a strong TiN band that was verified by diffuse reflectance infrared spectroscopy recorded on pure TiN powder. Incomplete surface reactions were also observed. (c) 2006 Elsevier B.V. All rights reserved.