ATOMIC-SCALE MODIFICATIONS OF HYDROGEN-TERMINATED SILICON 2 X-1 AND 3X-1 (001)SURFACES BY SCANNING TUNNELING MICROSCOPE

Atomic scale desorption and deposition of hydrogen (H) atoms on Si(001 )-(2 x 1)-H and Si(001)-(3 x 1)-H surfaces have been studied using cle an and H covered tips from a scanning tunneling microscope. We report desorption of H atoms from these surfaces at positive and negative sam ple bias voltages with a resolution of one to two atomic rows and atom ic scale phase transitions from 3 x 1 structures to 2 x 1 structures a nd vice versa. At positive sample bias, phase transitions from the 3 x 1 to 2 x 1 structures are accompanied with a large number of dangling bonds on the newly crated 2 x 1 structures, because the desorption of H from the 2 x 1 structure occurs at a lower tunnel current than the formation of the phase transition. At negative sample bias < -5 V, the situation is reversed with the desorption from the 2 x 1 structure oc curring at a larger tunnel current than the formation of the phase tra nsition, and ''clean'' local 2 x 1 structures with few dangling bonds can be achieved. Using H covered tips and increasing the substrate tem peratures of Si(001)-(2 x 1)-H surfaces to approximate to 400 K, oppos ite local phase transitions from 2 x 1 structure to 3 x 1 structures a re also reported, but such phase transitions were only observed at neg ative sample bias. (C) 1998 Elsevier Science B.V. All rights reserved.