High-resolution transmission electron microscopy and electron energy loss spectrometry were used to characterize the interfacial layer formed between the silicon substrate and the HfO2, thin film grown by atomic layer deposition (ALD) from HfI4 and O-2. The interfacial layer was amorphous and contained SiO2, mixed with a small amount of elemental Si on the atomic level. The interfacial silicon oxide layer was mainly deposited at the beginning of the ALD process since its thickness was insensitive to the number of applied ALD cycles when increased from 50 to 1000. (C) 2004 Elsevier B.V. All rights reserved.