Step-edge sputtering through grazing incidence ions investigated by scanning tunneling microscopy and molecular dynamics simulations

Abstract

Scanning tunneling microscopy is used to quantify step-edge sputtering of Pt͑111͒ at 550 K by grazing incidence ion bombardment with 5 keV Ar + ions. For bombardment conditions causing negligible erosion on terraces, damage features associated with step bombardment allow us to visualize step retraction and thus to quantify the step-edge sputtering yield. An alternative method for step-edge yield determination, which is applicable under more general conditions, is the analysis of the concentration of ascending steps together with the removed amount as a function of ion fluence. Interestingly, the azimuthal direction of the impinging ions with respect to the surface significantly changes the sputtering yield at step edges. This change is attributed to the orientation dependence of subsurface channeling. Atomistic insight into step-edge sputtering and its azimuthal dependence is given by molecular dynamics simulations of ion impacts at 0 and 550 K. The simulations also demonstrate a strong dependence of the step-edge sputtering yield on temperature.

Sputtering at grazing ion incidence: Influence of adatom islands

“…The interatomic interaction potential has been employed previously for sputtering simulations, and showed fair agreement with experiment, both for normal and glancing ion incidence angles. 3,19 Before the start of the simulation, we put adatom islands containing N adatoms on the surface. In this investigation, we choose sizes of N =7,19,37; in these special cases, the island forms a regular hexagon on the ͑111͒ surface.…”

“…The cases of a single isolated adatom ͑N =1͒ and of a densepacked surface step ͑corresponding to N = ϱ͒ have been simulated previously. [1][2][3][4]6,10,21 The adatoms are put on stable fcc sites on top of the crystallite. The island position, as well as that of all surface atoms are relaxed.…”

“…In simulation, for an impact azimuth of ͓110͔, sputter yields decrease by roughly 50% in simulation compared to the ͓112͔ azimuth; in experiment the reduction amounts to 40%. 3 This strong reduction has been attributed mainly to the fact that the ͑111͒ terrace appears more corrugated for an ion incident along the ͓110͔ azimuth. We include this reduction in sputter yield for the ͓110͔ azimuth in our calculation of the sputter coefficient by reducing the result of Eq.…”

“…The effect of surface steps has been analyzed in detail. [1][2][3][4] It was shown that if the ion impact point is in the vicinity of an ascending step edge, an ion may sputter as many atoms as for normal incidence. The sputter yield of a stepped surface is thus primarily governed by the step density.…”

“…We note that we investigated previously the effects of a varied incidence angle on sputtering from surface steps and found qualitatively similar results. For the 5 keV Ar impact at 83°i ncidence onto the Pt ͑111͒ surface, where already a considerable body of information on the sputtering behavior both from experiment and simulation is available, [1][2][3][4][5][6][7] we perform dedicated experiments. Here, the Pt surface is initially covered by Pt adatom islands which have been deposited on the surface prior to ion bombardment.…”