(2X4) C(2X8) TO (4X2)/C(8X2) TRANSITION ON GAAS(001) SURFACES/

We present scanning tunneling microscopy data illustrating the evoluti on of the decapped GaAs(001) surface following annealing in stages fro m 450 to 540 degrees C. After annealing at 450 degrees C a (2x4) recon struction is formed by kinked rows of two As dimer unit cells. Followi ng annealing in the 475-500 degrees C range small isolated regions of (4x2) reconstruction are visible, with a considerable increase in diso rder of the remaining (2x4) reconstructed areas. Annealing at higher t emperatures causes the (4x2) structure to become increasingly dominant . We have noted significant differences in the surface morphology as a function of annealing time. Our images of the (4x2) surface are simil ar to those recently reported by other groups but we propose a new str uctural model. (C) 1996 American Vacuum Society.