Nanoscale surface optical constants of copper determined by angle-resolvedphotoemission

We study angle-resolved photoemission peak intensities I(psi) on Cu(110) an d Cu(111) surfaces varying the light incidence angle psi of p-polarized lig ht with photon energies between h omega = 8.44 eV and h omega = 21.22 eV. T ransitions out of several initial states are probed, including the well-kno wn surface states at the <(<Gamma>)over bar> and (Y) over bar -point, bulk bands of sp- and d-like orbital character, as well as an oxygen-derived ads orbate state on Cu(110)(2 x 1)O. All data can well be explained within the dipole approximation I(psi) = /(A) over right arrow(psi, epsilon) (.) (P) o ver right arrow (fi)/(2), where (A) over right arrow is the vector potentia l of the photon field and (P) over right arrow (fi) the momentum matrix ele ment. Especially it is not necessary to include "surface photoemission" via a <f/div (A) over right arrow /i) term in the photoemission matrix element s. However, quantitative agreement with experimental data is obtained if an d only if (A) over right arrow is calculated using Fresnel's equations with a modified surface optical constant epsilon (s), which differs drastically from the bulk parameters epsilon (b). Surprisingly independent of h omega all results can be explained using epsilon (s) = (1.0 +/- 0.1) + i(0.1 +/- 0.1), which is much closer to the vacuum value than to epsilon (b). (C) 200 1 Elsevier Science B.V. All rights reserved.