Effects of ion bombardment on the optical and electronic properties of Cu(110)

Abstract

We investigate changes in the optical and electronic properties of Cu͑110͒ upon Ar ion bombardment at room temperature using reflectance anisotropy spectroscopy ͑RAS͒. Using a stepped Cu͑110͒ surface of narrow terraces where transitions between surface states near E F at the Ȳ point do not occur, we observe the return of these transitions upon ion bombardment through the emergence of a RAS peak at 2.08 eV. We relate the return of this RAS peak to a repopulation of the lower-lying surface state on the larger terraces produced by ion bombardment and room-temperature annealing. Further bombardment increases the density of surface vacancies and results in the disruption of the upper surface state leading to a reduction in intensity of the 2.08 eV RAS peak. Changes upon bombardment in the RA response around 4 eV-a region dominated by transitions near the L point in bulk Cu-are simulated in terms of a three-phase model of vacuum, surface, and bulk where the dielectric anisotropy of the surface layer is modeled using the energy derivative of the bulk dielectric function. We conclude that the RA response of Cu͑110͒ is highly sensitive to the occupancy of surface states and the presence of vacancies.

Optical anisotropy of nanostructured noble metal surfaces

“…Energies and strengths of the various contributions to the RAS spectra of the clean (110) noble metal surfaces are summarised in Table 1. The observed temperature dependence of the RAS spectra of all three noble metals have been found to support the assignments given [8][9][10][11]. Values of the derivative model parameters ∆E g and ∆Γ for the L point p→s transitions are also given in the Table. While a comparison of ∆E g and ∆Γ for a particular metal is reliable, the linear scaling of the X(E) and Y(E) functions with d (whose precise values are not known) renders a comparison of derivative model parameters for different metals semi-quantitative.…”

“…2. RAS spectra of the clean and well ordered (solid line) and ion bombarded (dashed line) (110) surfaces of Cu (top) [9], Au (middle) [10] and Ag (bottom) [11] It is satisfying to note that the superficially diverse RAS spectra of the clean (110) noble metal surfaces can be explained within a consistent framework. We now discuss the physical origins of the RAS spectra of modified noble metal surfaces. )…”

Localized subsurface modification of materials using micro-low-energy multiple ion beamlets

“…The interaction of low energy ion beams with matter is quite different from that of high energy ion beams. High energy ion beams are able to sputter, 4 channel, 5 deposit deep inside, and backscatter from substrates 6 etc because of its higher range inside the materials, 7,8 patterning, and generation of internal subsurface excitations [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] etc. Since low energy ion beams cannot penetrate deep inside the substrate therefore its interaction is mainly limited to surface and sub-surface layers.…”

“…of the target material. There can be changes in electrical, [25][26][27] optical, and thermal properties of the materials. However, in all the aforementioned applications people have so far considered mainly single and broad ion beams (diameter ≥ 0.1 -2 cm) where localized phenomena and tailoring of local surfaces and subsurface layers cannot be carried out.…”

Optical anisotropy induced by ion bombardment of Ag(001)

“…This implies that RAS is sensitive to anisotropic structures with a periodicity below the diffraction limit. This technique was already employed by Martin et al 19 to study ion erosion. They limited their study to the effects of ion bombardment on the optical and electronic properties of the intrinsically anisotropic Cu͑110͒.…”