Surface Science 207 (1988) 133-141 ~ortb-Hu~~a~d, Amsterdam 133 zyxwvutsrq AZfMUTHAL ~EF~~~~NC~ OF THE ELECTRONK EXCITATIONS IN GaAs(l10) U. DEL PENNING, Maria Grazia BETTI, Carlo MARIANI Dipartimenfo dt Fisica, UniuersitB di Modena, uia Cnmpi 2/3/A. I-41100 Modenu, Italr and I, ABBATI lstttuto di Fisicct, Pobecnico di Miluno, Piazu Leonardo dct Vinci 3-7. 1-20131 Milcmc, Itah Received 12 April 1988: accepted four publication 5 August 1988 An azimuthal dependent study of the electranic properties of the GaAsf110) surface by high resolution electron energy loss spectroscopy is presented. The relative weight of surface and bulk contributions to the loss spectrum is discussed. A minor anisotropy of almost all the identified structures, which are superimposed onto a rather isotropic background of transitions across the zyxwvutsr bulk gap, is found. 1. fntroductiun High resolution electron energy loss spectroscopy (HREELS), being a very surface sensitive technique, is a powerful tool for the investigation of vibra- tional and electronic properties of surfaces [lf. In particular, recently, it has gained a considerable interest for the study of surface electronic excitations of semiconductors [Z-5]. The high energy resolution of this technique allows a careful analysis of those electronic transitions which involve surface states in the range of energy losses of a few electronvolts. Moreover HREELS can enlighten the possible anisotropies of these excita- tions along the main symmetry directions of the surface Brillouin zone. In fact in a HREELS experiment it is possible to discriminate the polarisation of the electronic transition by changing the position of the plane of scattering on the surface and studying the azimuthal dependence of the cross section [3-51. The knowledge of the az,imuthal dependence of the electronic interband transition is an important step to a better understanding of the surface electronic properties and also to discriminate among different structural models. The Si(lll) reconstructed (2 x 1) surface is a typical exampfe. The generally accepted model reconstruction (the “chain model” proposed by Pandey [6]) has been supported, among several spectroscopic techniques [7,8], ~~3~-6~28/88~/$~3.5~ 0 Elsevier Science Publishers B.V. (worth-Holland Physics Publishing Division)