[en] Low-energy hydrogen ion beams are shown to clean and rapidly smoothen Ge(001) surfaces that have been subjected to severe oxygen roughening. Characteristic smoothening times of 1000 s are found at 500 degree C for 200 to 600 eV hydrogen ion beams at fluxes of 200 nA/cm². By comparing hydrogen and noble gas ion bombardment at various temperatures, we show that the hydrogen ion smoothening effect consists of both physical and chemical mechanisms which act to free pinned surface sites of contaminants and enable subsequent thermal smoothening of the germanium surface. Such oxygen roughened surfaces can be recovered to a state suitable for epitaxial growth without resorting to high-temperature annealing, keV ion sputtering or additional growth