Abstract
Fabrication of nanocone arrays on Si surfaces was demonstrated using grazing incidence irradiation with 1keV Ar+ ions concurrently sputtering the surface and depositing metal impurity atoms on it. Among three materials compared as co-sputtering targets Si, Cu and stainless steel, only steel was found to assist the growth of dense arrays of nanocones at ion fluences between 1018 and 1019ions/cm2. The structural characterization of samples irradiated with these ion fluences using Scanning Electron Microscopy and Atomic Force Microscopy revealed that regions far away from co-sputtering targets are covered with nanoripples, and that nanocones popped-up out of the rippled surfaces when moving closer to co-sputtering targets, with their density gradually increasing and reaching saturation in the regions close to these targets. The characterization of the samples' chemical composition with Total Reflection X-ray Fluorescence Spectrometry and X-ray Photoelectron Spectroscopy revealed that the concentration of metal impurities originating from stainless steel (Fe, Cr and Ni) was relatively high in the regions with high density of nanocones (Fe reaching a few atomic percent) and much lower (factor of 10 or so) in the region of nanoripples. Total Reflection X-ray Fluorescence Spectrometry measurements showed that higher concentrations of these impurities are accumulated under the surface in both regions. X-ray Photoelectron Spectroscopy experiments showed no direct evidence of metal silicide formation occurring on one region only (nanocones or nanoripples) and thus showed that this process could not be the driver of nanocone array formation. Also, these measurements indicated enhancement in oxide formation on regions covered by nanocones. Overall, the results of this study suggest that the difference in concentration of metal impurities in the thin near-surface layer forming under ion irradiation might be responsible for the differences in surface structures.
Highlights
Interest in using low-energy ion-beam irradiation as a tool for nanostructuring and functionalization of the surfaces of various materials has steadily increased over the last four decades [1,2,3,4,5,6,7,8,9,10]
We think of two possible explanations of this observation: (1) under particular conditions of experiments discussed here, either the Ar+ ion fluence or the flux of co-sputtered Cu atoms could be insufficient to trigger any noticeable nanocone formation - if we accept the mechanism of nanocone formation from 1970s [47,48,49,50, 57], and/or (2) Cu atoms did not react with Si surface in the same way and with the same rates as those from stainless steel (SS) (Fe, Cr, and Ni) – if we accept that surface silicide formation played a key role here [9, 25, 40,41,42,43]
We have demonstrated that large nanocone arrays can be fabricated on Si surfaces by grazing incidence irradiation with 1 keV Ar+ ions concurrently sputtering the surface and depositing metal impurity atoms on it
Summary
Interest in using low-energy ion-beam irradiation as a tool for nanostructuring and functionalization of the surfaces of various materials has steadily increased over the last four decades [1,2,3,4,5,6,7,8,9,10] This interest stems in large part from the simplicity and versatility of this technique and its ability to facilitate the fabrication of a rich variety of patterns on solid surfaces [11]. One of the key questions we asked was whether the silicide formation was the primary driver of the surface self-organization in this case, especially in view of others reporting the same structures forming on diamond and other materials irradiated by low energy ions [40, 46, 56]
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