title: Is keV ion-induced pattern formation on Si(001) caused by metal impurities?
abstract: We present ion beam erosion experiments performed in ultrahigh vacuum using a differentially pumped ion source and taking care that the ion beam hits the Si(001) sample only. Under these conditions no ion beam patterns form on Si for angles theta < or = 45 degrees with respect to the global surface normal using 2 keV Kr+ and fluences of approximately 2 x 10(22) ions m(-2). In fact, the ion beam induces a smoothening of preformed patterns. Simultaneous sputter deposition of stainless steel in this angular range creates a variety of patterns, similar to those previously ascribed to clean ion-beam-induced destabilization of the surface profile. Only for grazing incidence with 60 degrees < or = theta < or = 83 degrees do pronounced ion beam patterns form. It appears that the angular-dependent stability of Si(001) against pattern formation under clean ion beam erosion conditions is related to the angular dependence of the sputtering yield, and not primarily to a curvature-dependent yield as invoked frequently in continuum theory models.
authors.affiliation: II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, D-50937 Cologne, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Macko
authors.forename: Frank
authors.initials: F
authors.lastname: Frost
authors.forename: Bashkim
authors.initials: B
authors.lastname: Ziberi
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Förster
authors.forename: Thomas
authors.initials: T
authors.lastname: Michely