Optical reflectance anisotropy of Ag(110): Evidence for contributions from surface-modified bulk band transitions

We report measurements of the optical reflectance anisotropy (RA) of the Ag(110) surface as a function of temperature and we find evidence for contributions to the RA spectrum from bulk band transitions that are modified by the anisotropic (110) surface. A comparison is made between temperature-induced shifts in the energy of RA peaks and thermovariation optical spectroscopy results of the temperature dependence of transition energies between bands at the $L$ symmetry point. A three phase model based on the energy derivative of the bulk dielectric function is found to simulate the RA response from well-ordered and Ar ion bombarded surfaces. We conclude that there is a general trend of surface-modified bulk band contributions to the RA response of the noble metal (110) surfaces.

Figure 1

RA spectra of clean Ag(110) at $300\mathrm{K}$ prepared by annealing at $830\mathrm{K}$ (filled circles) or $1000\mathrm{K}$ (open circles). The main features are labeled A–D. Peak A (thin line) and its absence at $\sim 500\mathrm{K}$ (thick line) are shown on a different vertical scale for clarity.

Figure 2

(Color online) Room temperature STM data of the Ag(110) surface. Upper panel: clean and well ordered, prepared by annealing at $1000\mathrm{K}$ $(200\times 200{\mathrm{nm}}^2)$. Lower panel: $42\min$ Ar ion bombarded surface $(200\times 128{\mathrm{nm}}^2)$. Orientation is the same for both images.

Figure 3

RAS of Ag(110) peak A as a function of temperature. Each spectrum was recorded at the constant temperature stated. Spectra (apart from $570\mathrm{K}$) are offset on the vertical axis for clarity.

Figure 4

RAS of Ag(110) peaks C and D as a function of temperature. Each spectrum was recorded at the constant temperature stated. Spectra are offset on the vertical scale for clarity.

Figure 5

RAS peak position as a function of temperature for peak C (triangles) and peak D (circles). Filled and open symbols refer to the surfaces prepared at 830 and $1000\mathrm{K}$, respectively. Peak positions were measured from RA spectra recorded while the crystal was held at the particular temperature.

Figure 6

The effect on the RA response of Ag(110) upon increasing Ar ion bombardment time. Spectra (apart from $0\min$) are offset on the vertical axis for clarity. The solid lines show the simulated RA spectra of well-ordered (annealed at $1000\mathrm{K}$) and $42\min$ bombarded Ag(110).

Figure 7

Dielectric data for Cu, Ag, and Au. The lower panels show the $A\left(E\right)$ and $B\left(E\right)$ functions, the middle panels show the real and imaginary parts of the energy derivative of the bulk dielectric functions (Refs. 25, 26), while the upper panels show the $X\left(E\right)$ and $Y\left(E\right)$ functions defined by Eqs. (5, 6).