The atomic layer deposition (ALD) of tin oxide thin films has been examined using in situ quartz crystal microbalance (QCM) and Fourier transform infrared (FTIR) techniques. The SnOx. films Were deposited using sequential exposures of SnCl4 and H2O2 at temperatures from 150 to 430 degrees C. The linear growth of the tin oxide ALD films was observed by both the mass gain during QCM measurements and the background infrared absorbance increase during FTIR investigations. The FTIR spectra revealed the loss and gain of the O-H stretching vibrations of the hydroxyl group for the SnCl4 and H2O2 exposures, respectively. The background infrared absorbance also oscillated after each SnCl4 and H2O2 exposure. The background absorbance increased after SnCl4 exposure and decreased after H2O2 exposure. QCM measurements were consistent with a tin oxide ALD growth rate of similar to 60 ng cm(-2) per cycle. This mass change corresponds to a growth rate of similar to 0.7 angstrom/cycle at 325 degrees C assuming a SnO2 density of 6.9 g cm(-3). Additional ex situ surface analysis using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) revealed that the SnOx films grown at 325 degrees C were defined by x < 2. Atomic force microscope (AFM) results also showed that the SnOx, ALD films deposited on Si(100) wafers have a very rough surface. Understanding and controlling the growth of tin oxide ALD films should be useful to enhance the sensitivity of SnOx gas sensors. (c) 2005 American Vacuulh Society.