HfO2 was deposited by chemical vapor deposition on Si, native SiO2, and borosilicate glass surfaces using hafnium (IV) tert butoxide in a mesoscale flow reactor. Undulating thin film topographies were observed by atomic force microscopy on all substrates with peak-to-peak periods between 10 and 25 nm in the presence of a temperature gradient perpendicular to flow of 25 degrees C/mm. A computational fluid dynamic model suggests the phenomenon originates from buoyancy driven roll type flow. The thickness uniformity and roughness of the films depended on the flow rate, reactor temperature, and the substrate type. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 2989-2996, 2011