Atomic layer growth of hafnium dioxide from HfCl4 and H2O has been studied at substrate temperatures ranging From 180-600 degrees C. A quartz crystal microbalance was used for the real-time investigation of deposition kinetics and processes affecting the growth rate. It was shown that the layer-by-layer growth was self-limited at temperatures above 180 degrees C. The data of ex situ measurements revealed that the structure. density and optical properties of the films depended on the growth temperature. The absorption coefficient of amorphous films grown at 225 degrees C was below 40 mm(-1) in the spectral range of 260-850 nm. The refractive index of the films grown at 225 degrees C was 2.2 and 2.0 at 260 and 580 nm, respectively. The polycrystalline films with monoclinic structure grown at 500 degrees C had about 5% higher refractive index but more than an order of magnitude higher optical losses caused by light absorption and/or scattering.