COMBINED REFLECTANCE ANISOTROPY AND PHOTOEMISSION SPECTROSCOPIES OF CS GAAS(001) INTERFACE FORMATION/

We have investigated the adsorption of cesium on GaAs(001) using synch rotron radiation excited photoemission spectroscopy and also by monito ring the optical transitions related to gallium dimers and arsenic dim ers using reflectance anisotropy spectroscopy (RAS). Cesium adsorption has little effect on the Ga 3d core level shape. In sharp contrast, w e observe modifications of the RA signal related to gallium dimers, in duced by the modification of the electronic states involved in the cor responding surface optical transitions, The changes of the RA. spectru m reveal two adsorption phases at Cs coverages above and below 0.5 mon olayers. The origin for the strong sensitivity of RAS to semiconductor /alkali metal interface formation is discussed. (C) 1997 American Vacu um Society.