Azimuthally resolved optical second-harmonic generation from hydrogen on nickel (111)

Abstract

We report the first azimuthally resolved measurements of the effect of an adsorbed gas on optical second-harmonic generation (SHG) from a clean, well-ordered metal surface. The second-harmonic intensity from Ni(111) decreases rapidly upon hydrogen adsorption; however, the threefold symmetry with sample rotation about the surface normal is retained. The ${\beta }_1$ and ${\beta }_2$ adsorption states are clearly resolved and their contributions to the second-order susceptibility are determined. For this system, SHG is highly sensitive to local site symmetry and little affected by long-range ordering of adsorbates.