Ultraslow single- and multicharged ions (USMCI) have small kinetic energy compared with their potential energies. They can be used for surface preparation at room temperature, to engineer the top atomic layers of surfaces without modifying the substrate below, in processes such as ultrathin film growths, etching, deposition, or nanostructures fabrication. The energy for the reaction is brought to the surface through the USMCI potential energy, which can be controlled by varying the ion charge. The USMCI kinetic energy is so small that they do not penetrate below the surface. We have used various USMCI under low pressures of O-2 (between 10(-9) and 5 x 10(-6) Torr) to grow ultrathin films of SiO2 on Si wafers, from 0.3 to 2.3 nm with a resolution of 0.1 nm and a uniformity of +/-0.1 nm. To evaluate the layers and optimise this process, we have analysed the surfaces by Fourier transform infrared spectroscopy, Auger electron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, X-ray photoelectron spectroscopy and surface charge analysis. (C) 2002 Elsevier Science Ltd. All rights reserved.