HYDROGEN ADSORPTION ON THE GAAS(001)-(2X4) SURFACE - A SCANNING-TUNNELING-MICROSCOPY STUDY

Using scanning tunneling microscopy (STM) we have investigated the pro cess of hydrogen adsorption on the GaAs(001)-(2x4) surface. Stepwise h ydrogen-induced changes in the atomic structure of the surface are rev ealed in the STM images. In a first step, one or two hydrogen atoms bo nd per As atom, giving rise to localized protrusions within the As dim er rows. In a second step, after adsorption of a third H atom per As a tom, AsH3 forms and desorbs, resulting in depressions and thus a degra dation of the As dimer rows. Finally, at high exposures a disordered s urface develops.