The effects of glancing-angle argon ion bombardment on air-contaminated Si(001) surfaces were studied. Bombarding at substrate temperature Ts=730 °C, impingement angle Φ=3–15° relative to the surface plane, ion energy E=1 keV and dose D=3×1015 ions cm-2 gave high-quality reflection high energy electron diffraction (RHEED) patterns and contaminant-free surfaces as observed by ion scattering spectroscopy. Atomic force microscopy images showed roughness value ≤0.5 nm under these conditions, but the roughness increased and RHEED patterns became spotty for higher doses or energies. Secco etching of samples bombarded at Ts=730 °C showed etch pits with a density of 106–107 cm-2 that increased with increasing D and E. Room-temperature bombardment with E=1 keV, D=3×1015 ions cm-2 and Φ=3°, followed by a 730 °C anneal, yielded a lowest roughness value of 0.2 nm. Secco etching showed no resolvable pits, indicating a dislocation density ≪4×104 cm-2. © 1998 American Vacuum Society.