Spectroscopic ellipsometry (SE) has been applied to characterize the damaged, amorphous silicon (a-Si) layer created by Ar+-ion bombardment in the ion energy range of 70-2000 eV impinging at 45 degrees angle of incidence on Si(100). The dielectric functions of a-Si during ion bombardment have been determined using the Tauc-Lorentz model for the dielectric functions epsilon(1) and epsilon(2). The dielectric functions resemble literature reports on a-Si-like dielectric functions. The a-Si layer thickness under ion bombardment conditions reaches values from 17 angstrom at 70 eV up to approximate to 95 angstrom at 2000 eV. These values compare reasonably well with SRIM and molecular dynamics simulations. The surface roughness. as determined with SE, is typically 5-15 angstrom during ion bombardment, with a minimum roughness at E-ion = 250 eV. The creation of the amorphous silicon top layer upon 70 eV Ar+-ion bombardment with an ion flux of 0.07 ML s(-1) has been resolved using real-time spectroscopic ellipsometry. The creation of the amorphous layer shows a double exponential ion-dose dependence: a fast, initial period of a-Si creation, with 1/e constant Delta(tau 1) =2 ML, and a slower period, Delta(tau 2) =9 ML, until the matrix is fully amorphous after similar to 30 ML of Ar+ dosing. Relaxation of the a-Si top layer has been observed after the ions are switched off and has been analyzed with a stretched-exponential decay as a function of time, which is characteristic for a defect-controlled relaxation in the bulk a-Si layer. The corresponding time constant tau is found to be similar to 360 s, which is typically observed for self-annealing in amorphous silicon materials., (c) 2006 American Vacuum. Society.