AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP34
Surface Structures of @beta@-(BEDT-TTF)@sub 2@PF@sub 6@ Induced by Its Polar Surface Characteristics

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: M. Ishida, University of Tsukuba, Japan
Authors: M. Ishida, University of Tsukuba, Japan
T. Mori, Tokyo Institute of Technology, Japan
H. Shigekawa, University of Tsukuba, Japan
Correspondent: Click to Email
Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) based organic compounds, one of the low-dimensional conductors, are distinct from the others due to their polar surface characteristics. For @beta@-(BEDT-TTF)@sub 2@PF@sub 6@, an ordered-defect structure was observed on the anion (PF@sub 6@) surface similarly as the typical reconstructions of the inorganic polar surfaces. And characteristic properties such as superstructures and fluctuation of surface structures were observed on the cation (ET) surface. On the other hand, it is well known that @beta@-(BEDT-TTF)@sub 2@PF@sub 6@ undergoes a metal-insulator transition at 297 K, and formation of the 2x|c| superstructure due to 2k@sub F@ CDW is confirmed by X-ray diffraction. However, several superstructures with considerably longer modulations were observed by STM at 285 K instead of the 2x|c| superstructure. From the results of the STM, AFM, XPS studies, and molecular orbital calculations, the observed cation surface structures were concluded to be influenced by charge localization, relaxation of individual molecules, and symmetry breaking in the molecular relaxation. Concerning the modulated CDW phases, susceptibility @chi@(Q) for the surface layers was calculated in order to investigate the origin of the larger modulations, by taking into account the change in the molecular charge on the polar surface. As a result, the observed STM result were in good agreement with the CDW structure derived from the susceptibility calculation.