Influence of a single adatom on sputtering at grazing incidence – A molecular-dynamics case study of 5keV Ar impact on Pt (111)

Abstract

a b s t r a c tGrazing incidence ion impact on a flat terrace lets the projectile reflect specularly off the surface, leading to little or no damage production or sputtering. The presence of isolated surface defects may change this behaviour drastically. We investigate this phenomenon for the specific case of 5 keV Ar ions impinging at 83°towards the surface normal onto the Pt (1 1 1) surface. Molecular-dynamics simulations allow to study the influence of isolated adatoms in detail. The scattering of the projectile from the adatom can redirect the projectile, or let the adatom recoil, such that either of them deposits considerable energy in the target surface, leading to abundant damage production and sputtering. Two distinct collision zones are identified: (i) When the projectile hits the surface in front of the adatom, it may collide with the adatom indirectly (after being specularly reflected off the surface); (ii) alternatively, it may hit the adatom directly. We quantify our results by measuring the zone of influence (ffi 13 Å 2 ) around the adatom, into which the projectile must hit in order to collide with the adatom, and by the sputter cross section of roughly 110 Å 2 . The data compare well with previous simulation results of sputtering from an atomically rough surface.

Sputtering at grazing ion incidence: Influence of adatom islands

“…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.…”

“…Similarly, the influence of single adatoms on a surface was analyzed and it was found that for small coverages, the sputter yield is linear in the adatom coverage. [5][6][7] Real surfaces may be covered by adatom ͑and vacancy͒ islands as well, and the question arises how the sputter yield is influenced by these islands. One might think that adatom islands simply interpolate between the effects of isolated adatoms and straight step edges.…”

“…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.…”

Grazing incidence ion erosion in the presence of adsorbates

“…Adatoms and adatom clusters are elevations exposed to the ion beam. Thus, they are efficiently sputtered through the large-angle scattering processes of impinging ions [26]. Also larger vacancy clusters expose an illuminated step to the ion beam allowing impinging ions to transfer kinetic energy to the substrate through large-angle scattering processes, which cause sputtering.…”

“…Our simulations give cross sections of σ S = 11.3 Å 2 , σ O = 32.6 Å 2 ; the cross section for damage creation amounts to σ ad = 48.8 Å 2 , and the cross section for adsorbate implantation is σ impl = 43.8 Å 2 (see table 1 To link experimental and simulation results we made use of the linear relations (3) and (6) connecting the single adsorbate properties σ O and σ S with properties resulting from an ensemble of adsorbates ( O , Y O and Y S ). From our previous work with isolated Pt adatoms on a Pt(111) surface [26], we could derive a criterion for the maximum coverage lin for which the single adatom results could be extrapolated linearly to finite coverages, Cross sections for sputtering, adatom formation, oxygen desorption and oxygen implantation on a Pt(111) surface covered with a single adsorbate atom (5 keV Ar impact at 85.5…”