HREELS INVESTIGATION OF THE 1ST STAGE OF INTERACTION OF ATOMIC-HYDROGEN WITH GAAS(1 1 0) SURFACES

The interaction of atomic hydrogen with a cleaved GaAs(110) surface has been investigated by high resolution electron energy loss spectroscopy. This technique, which is extremely surface sensitive, enables the detection of very small amounts of adsorbate and the indication of the adsorption sites. We have exposed a GaAs(110) surface to atomic hydrogen in the 10-10(4) L range. This upper limit corresponds to the onset of the monolayer coverage. The effect of the H exposure is detected in the region of phonon-plasmon losses already at an exposure of 10 L, indicating the occurrence of a band bending. The three layer model for the dielectric function of the GaAs(110) surface had to be adopted to account for the results. At higher loss energies the stretching vibrations of Ga-H and As-H are also detected from the lowest exposures. The possibility that the As-H signal is given by a double loss (Ga-H + phonon) is ruled out for this surface, therefore, it comes out that from the first stage of interaction H bonds to both Ga and As. The intensity of both Ga-H and As-H signal increases faster than the expected number of adsorbed H atoms suggesting that the dynamical dipole drops drastically with increasing exposure.