AN ISS STUDY OF GA-DIMER ARRANGEMENT IN THE GAP(001)-(4 X-2) SURFACE

A GaP(001) Ga-rich surface produced by ion sputtering followed by anne aling exhibited a 4 x 2 LEED pattern with half streaks in the [110] di rection. We have studied the structure of this surface by low-energy i on-scattering spectroscopy (ISS) using alkali ions (Na+). We have foun d a unit cell of the 4 x 2 structure consisting of two Ga dimers plus two dimer vacancies from the measured incidence-angle dependence of th e scattered-ion intensity in the [1 (1) over bar 0] surface azimuth an d an atomic separation in the Ga dimer being about 0.27 nm from that i n the [110] surface azimuth. Evidence is presented showing the unit st ructures being arranged irregularly in the [1 (1) over bar 0] directio n around the twofold positions.