AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA10
Dimer Structure of the Si(001)2x1 Surface Observed below 10K by Scanning Tunneling Microscope

Tuesday, November 4, 2003, 5:00 pm, Room 327

Session: Surfaces and Interfaces of Semiconductors and Compound Materials
Presenter: M. Ono, The University of Tokyo, Japan
Authors: M. Ono, The University of Tokyo, Japan
A. Kamoshida, The University of Tokyo, Japan
E. Ishikawa, The University of Tokyo, Japan
T. Eguchi, The University of Tokyo, Japan
Y. Hasegawa, The University of Tokyo, Japan
Correspondent: Click to Email
The dimer structure of the Si(001) surface has been discussed after recent low-temperature STM observations, which reported symmetric dimers at 5K. Various models to explain the observation contradictory to the previous reports, such as anomalous flip-flop dimer motion and new ground state induced by spin configuration, were proposed. To solve this issue, we studied it using an STM which can be operated under multiple extreme conditions of ultrahigh vacuum (>6x10@super -9@ Pa), low temperature (>2.8K), and high magnetic field (<11T). We observed asymmetric (buckled) dimer structure, locally forming either c(4x2) or p(2x2) periodicity with positive sample bias voltages, while most of the dimer looks symmetric with negative sample bias voltages. Among the apparently symmetric dimers, however, a weak trace of the c(4x2) structure was observed. Our observation suggests that the observed symmetric dimer structure in the filled-state images is not intrinsic; neither static symmetric dimer nor flip-flopped asymmetric dimer, but an artifact induced by STM imaging mechanism. Since a transition temperature between the buckled- and symmetric-dimer imaging, which is found to be 40K, corresponds to the temperature where the carrier density changes dramatically from intrinsic to saturation range, the apparent symmetric-dimer imaging should be related with the reduced carrier density and ensuing charging effect. We also took several STM images under magnetic field up to 10T at 10K. Significant changes are, however, not observed in a structure or arrangement of the dimers.