Dresden 2003 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 22: POSTER C

CPP 22.1: Poster

Donnerstag, 27. März 2003, 12:00–14:00, ZEU/250

Correlations Between E-Field and Pressure Effects on Single-Molecule Spectra at Low Temperatures — •Markus Bauer and Lothar Kador — University of Bayreuth, Institute of Physics and Bayreuther Institut für Makromolekülforschung (BIMF), 95440 Bayreuth

The line shifts of single dye molecules in the amorphous polymer polyisobutylene (PIB) due to external electric fields and pressure were investigated. Both shift parameters are subject to broad distributions, which is typical for disordered matrices. Between Stark and pressure shift, strong correlations were found with a cross-correlation coefficient of 0.51. In Monte Carlo simulations, a coefficient of this magnitude could only be reproduced, if the static dipole moments of the dye molecules are not only caused by electrostatic polarization but contain contributions from short-range interactions with the matrix units, leading to geometrical distortion. Spectral jumps due to the interaction with matrix TLS showed that the TLS parameters can be affected by external electric fields.

Application of the electric field by interdigitating electrodes covered with a thin silicon carbide (SiC) layer led to continuous slow spectral creeping of the single-molecule lines after sudden changes of the field strength. The proposed mechanism involves movements of charge carriers in the SiC, when nanometer-scale regions of strongly different conductivity are present. AFM and REM images support this picture.