Homoepitaxy and controlled oxidation of silicon at low temperatures have been achieved using a dual source, mass-selected, low-energy, ion beam deposition system. For Si homoepitaxy, Si-28(+) ions in the energy range 8-40 eV were used to grow films on Si{100} in the temperature range of 50-750 degrees C. The films were analyzed in situ by reflection high-energy electron diffraction and Auger electron spectroscopy (AES) and ex situ by high-resolution transmission electron microscopy, Rutherford backscattering spectrometry, and atomic force microscopy. For silicon oxidation, films of SiO2 on Si{100} at room temperature were grown by using 25 eV beams of Si-28(+) and O-16(+). Fast switching of the magnetic sectors allows deposition of these ions in alternating pulses. The pulse increments used were 1x10(14) cm(-2) for Si+ and 4X10(14) cm(-2) for O+. Analysis of the oxide films by in situ AES and ex situ x-ray photoelectron spectroscopy show that the films are SiO2, that the suboxides are localized at the interface, and that there is no limitation to the thickness of the oxide films that can be grown. The effects of ion energy and substrate temperature, contamination, and surface damage on the growth mechanism are discussed.