We studied in situ the initial stages of atomic layer deposition (ALD) of HfO2 by an ultra high vacuum atomic force microscope working in frequency-modulation mode. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf and water as precursors, were performed on the Si(001)/SiO2 substrate maintained at 230 degrees C. After each AID cycle we studied the influence of the HfO2 growth on the surface height histogram, the root mean square roughness, the surface fractal dimension and the autocorrelation function. This detailed analysis of the surface topography allowed us to confirm the completion of the first HfO2 layer after four ALD cycles. (C) 2009 Elsevier B.V. All rights reserved.