Estimating the range of influence of point defects on Cu (110) surface states

Abstract

By utilizing reflection anisotropy spectroscopy (RAS) and scanning tunneling microscopy (STM) measurements of the ion-bombarded Cu (110) surface at low temperatures, we have developed a simple methodology for estimating the effective surface area over which irradiation-induced defects perturb surface states, leading to a reduction in the intensity of the 2.1 eV RAS peak of this surface. Each composite defect decorating an ion-impact site quenches the RAS signal in proportion to an area equivalent to approximately 170 unit cells. We estimate that an atomic defect has an effective RAS cross section with area approximately equal to that of a circle with a radius of 0.75 nm, an area equivalent to that of around 19 unit cells. Accurate determination of the coverage and spatial distribution of surface defects is a prerequisite for a coherent analytical approach to modeling the RAS data of this system.

Ion bombardment of Ni(110) studied with inverse photoemission spectroscopy and low-energy electron diffraction

“…The larger effective defect radius for a single ion impact revealed in other studies [27] [34] [35] would cause the simulated curves to decrease in intensity for lower sputter doses, and would more quickly approach zero intensity, but these effects do not change our results for the range of sputtering and necessary patch size presented. To verify this, the simulation was also performed assuming 0-2 atom removal per ion collision, effectively decreasing the mean ion damage area in the simulation with little change to the results displayed.…”

“…This is supported by the conclusions of Vasylyev and coworkers in their study of low-energy Ar ion bombardment on low index nickel surfaces [34], where it was suggested that low-dose sputtering on this system likely produces vacancy point defects and adatoms with mean damage area per ion collision of about 5 unit cells. We note, however, that other authors have reported various higher estimates for the yield and damaged area per ion impact [27] [34] [35].…”

“…Recently, Isted, et al [27] investigated Cu(110) under ion bombardment at normal incidence with RAS, STM and a version of the scattering model developed by Poelsema and Comsa [28]. In that study, the authors find close agreement between their integrated RAS signal intensity at various sputtering doses and the simulated fraction of surface cells not contained in circular patches of about 19 unit cells surrounding defects.…”

Optical probe for surface and subsurface defects induced by ion bombardment

“…On the other hand, subsurface defects influence the bulk electronic structure in the near-surface region, with a pronounced effect on the corresponding optical anisotropy. In fact, the sensitivity of RDS to thermally and ion-induced defects on noble metal surfaces has been recognized by several authors in the past 10 – 15 . In particular, a sensitive dependence of the surface-states-related RD signal on the surface defect concentration and distribution has been elucidated 15 – 18 .…”

Micro reflectance difference techniques: Optical probes for surface exploration

“…Reflectance difference (RD/RA) spectroscopy 1–12 is a powerful tool for the optical characterizations of surfaces and interfaces. Among the applications of RD, we can mention the characterization of novel surface processes 13, surface electric fields 14–21, defects, and strain 22–28. The development of the RD spectroscopy as an optical probe for the characterization of surfaces and interfaces has suggested that an extension of the RD spectroscopy to a microscopic scale Micro reflectance difference (µ‐RD) could further increase the potential of the technique.…”