Nonlinear amplitude evolution during spontaneous patterning of ion-bombarded Si(001)

The time evolution of the amplitude of periodic nanoscale ripple patterns f ormed on Ar+ sputtered Si(001) surfaces was examined using a recently devel oped in situ spectroscopic technique. At sufficiently long times, we find t hat the amplitude does not continue to grow exponentially as predicted by t he standard Bradley-Harper sputter rippling model. In accounting for this d iscrepancy, we rule out effects related to the concentration of mobile spec ies, high surface curvature, surface energy anisotropy, and ion-surface int eractions. We observe that for all wavelengths the amplitude ceases to grow when the width of the topmost terrace of the ripples is reduced to approxi mately 25 nm. This observation suggests that a short circuit relaxation mec hanism limits amplitude growth. A strategy for influencing the ultimate rip ple amplitude is discussed. (C) 2000 American Vacuum Society. [S0734-2101(0 0)01001-0].