Ž . Applied Surface Science 130–132 1998 425–430 Bias voltage-dependent scanning tunneling microscopy images of ž / a GaAs 110 surface with small Ag clusters Chun-Sheng Jiang a, ) , Tomonobu Nakayama a , Masakazu Aono a,b a ( ) The Institute of Physical and Chemical Research RIKEN , 2-1 Hirosawa, Wako, Saitama 351-01, Japan b Department of Precision Science and Technology, Osaka UniÕersity, Suita, Osaka 565, Japan Received 1 September 1997; accepted 13 November 1997 Abstract Ž . We report bias voltage-dependent images of scanning tunneling microscopy taken on a GaAs 110 surface with small Ag Ž . clusters. The direction of the observed atom rows changes at certain negative and positive sample bias voltages V . Such s Ž . changes are attributed to the different atoms Ga or As in the case of V -0 and to the different surface states of Ga in the s case of V )0. The images also show a change in contrast with the V . All of these results are explained by tip-induced and s s surface charge-induced band bendings in addition to the fundamental surface states. q 1998 Elsevier Science B.V. All rights reserved. PACS: 61.16.Ch; 68.35.Bs; 73.61.Ey; 73.20.At Ž . Keywords: Scanning tunneling microscopy; GaAs 110 surface; Ag cluster; Band bending; Surface state 1. Introduction Bias voltage-dependent imaging using a scanning Ž . tunneling microscope STM is a powerful method to Ž . study the local density of states LDOS at certain w x electron energies for surfaces 1,2 . For example, Ž . images of the GaAs 110 surface taken at the posi- Ž . tive sample voltages V of q1.2 and q2.6 V show s w x that rows of Ga atoms are aligned along the 001 w x and 110 directions, corresponding to the unoccu- Ž . Ž . pied Ga dangling-bond C and back-bond C 3 4 w x states, respectively 2–5 . However, images taken at negative V show that the As atom rows are aligned s ) Corresponding author. Fax: q81-48-462-4656; e-mail: jiang@postman.riken.go.jp. w x along the 110 direction, irrespective of a smaller Ž . Ž . y0.6 V or larger y1.3 V V corresponding to the s Ž . Ž . occupied As dangling-bond A or back-bond A 5 4 w x states 5–8 . Theoretical LDOS calculations of these Ž . surface states C , C , A , and A agree well with 3 4 5 4 w x the experimentally observed STM images 2,5 . Ž . If we introduce a point charge on the GaAs 110 surface, a flat surface space-charge layer under a Ž . w x clean GaAs 110 surface is locally depleted 9–11 . We recently formed small Ag clusters on the Ž . GaAs 110 surface which trapped negative charges w x 12 . Under a certain condition of a low density of conduction electrons in the space charge layer, an electric field due to a positively-biased STM tip penetrated into the bulk and induced a downward band bending, so that the originally-unoccupied C 3 0169-4332r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0169-4332 98 00095-6