The (2x4) and (2x1) structures of the clean GaP(001) surface

The surface structure of GaP(001) has been studied using X-ray photoelectron diffraction (XPD), low-energy electron diffraction ( LEED), synchrotron radiation photoemission spectroscopy (SRPES), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). It is confirmed that the clean GaP(001) surface prepared by Ar-ion sputtering and annealing (ISA) exhibits a (2 x 4) reconstruction terminated by gallium. STM images indicate that about 20% of the gallium dimers at the surface are not regularly arranged in the [<1(1)over bar>0] direction. The surface core-level shifts of Ga 3d and P 2p for the (2 x 4) surface, as measured by SRPES, suggest that the surface components S1 and S2 correspond to Ga dimers at the surface and Ga atoms with three-fold coordination in the surface region. respectively. The component S3 is also suggested to be due to P atoms with three-fold coordination. Upon adsorption of t-butylphosphine on the (2 x 4) surface at 350 degrees C, a (2 x 1) structure is observed by LEED and STM. Based on the above results, models of the GaP(001)-(2 x 4) and -(2 x 1) surface structures are proposed. (C) 1999 Elsevier Science B.V. All rights reserved.