BIAS-DEPENDENCE OF THE APPEARANCE OF SCANNING TUNNELING MICROSCOPE IMAGES OF THE GAAS(001)-(2X4) SURFACE RECONSTRUCTION

The (2 X 4) reconstruction of the (001) surface of GaAs has been studi ed using scanning tunnelling microscopy (STM) and spectroscopy. The im ages, produced at several biases, show coexisting two dimer and three dimer surface unit cell reconstructions. By examining line profiles ac ross the dimers, we find an asymmetry in the two dimer surface unit ce ll reconstruction which changes with the sample bias. The images of th e three dimer surface unit cell reconstruction are also shown to be di fferent at different biases, A spectroscopic spectrum is presented whi ch gives insight into the origin and characteristics of negative and p ositive bias tunnelling. Our results are compared to theoretical studi es of the expected appearance of STM images under different bias condi tions and the implications of the findings are discussed.