The surface and interface sensitive technique of optical second-harmonic generation (SHG) has been applied spectroscopically and time-resolved before, during, and after low energy (70-1000 eV) Ar+-ion bombardment of H-terminated Si(100). The photon energy range of the fundamental radiation was (h) over bar omega = 0.76-1.14 eV. Besides physical sputtering of the silicon, ion bombardment of crystalline silicon damages and amorphizes the top layer of the sample and thereby creates a layered structure of amorphous silicon (a-Si) on crystalline silicon. The SHG radiation, which is sensitive to the Ar+-ion flux, ion energy, and the presence of reactive gas species, originates from the top surface of the sample and from the interface between a-Si and c-Si. From a comparison with the SHG results obtained at a fundamental radiation of (h) over bar omega = 1.3-1.7 eV, it is concluded that the SHG radiation during and after creation of this structure dominantly originates from the tails of electronic transitions in the E-0'/E-1 energy region rather than from silicon dangling bonds. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3305812]