Electroreflectance spectroscopy as a probe of the electronic structure at the metal-electronic interface

The electromagnetic response of a surface is influenced by the surface electronic structure. In particular, the existence of surface states in band gaps can lead to optical absorption below the bulk interband threshold. However, such effects are usually too small to be observed because while surface states are localized within several atomic layers near the surface, light waves can penetrate at least hundreds of layers into the metal. One way to enhance the surface effect for a metallic surface is to make use of electromodulation techniques. When a metal is placed in an electrolyte, an intense electric field (approx. 10 to the 7th volts/cm) can be induced at the metal electrolyte boundary with the application of a bias voltage of less than a volt. Electroreflectance (ER) experiments modulate the bias voltage and measure the resultant modulations in the optical reflectivity. Since the static electric field is highly localized at the interface (the Fermi-Thomas screening length for typical metals is of the order of Angstroms) we expect the ER effect to be highly surface sensitive. Sensitivities in ((DELTA)R/R) up to 10 to the -6th can be achieved in such experiments.