Second-Harmonic Generation At Semiconductor And Metal Surfaces

Optical second-harmonic generation, although a sophisticated technique, is making a significant contribution to the characterization of surfaces and interfaces. The advantages include: all pressure ranges are accessible; insulators are studied without the problem of charging effects; solid–solid and solid–liquid interfaces are characterized by utilizing the large penetration depth of optical radiation. Single wavelength studies yield information on the crystallographic and magnetic structure of surfaces and interfaces, and are particularly sensitive to symmetry changes. Spectroscopic studies, which have recently become simpler due to the availability of high pulse power, tunable, broadband laser sources, additionally provide electronic structure information, although the interpretation of this may not be simple. In this review examples from well-characterized interfaces are emphasized, and it is shown that the technique is now well understood at the phenomenological level, although theoretical calculations are proving to be difficult. Interfaces not accessible to conventional surface techniques can now be studied with confidence.