The surface transient effects in the sputtering yield in amorphous Si layers by 0.5 keV O-2(+) and Ar+ ion bombardments have been studied by MEIS. In the case of O-2(+) ion bombardment, the surface transient effects cause rapid decrease in sputtering yield, even when the grazing incident angle is used, because of oxide layers formed by oxygen ion beam. In the case of Ar+ ion bombardment at the surface normal incidence, implanted Ar atoms, distributed up to 3 run, increase sputtering rate significantly in the surface transition region. For the incident angle of 70degrees, there are little implanted Ar atoms, which suggests that the surface transient effect may be insignificant in sputtering conditions when 0.5 keV A(+) ion bombardment with grazing angle of 70degrees from surface normal incidence was used. (C) 2004 Elsevier B.V. All rights reserved.