STM-electroluminescence probes of metallic and polymeric materials

The STM-electroluminescence technique is shown to be a valuable tool for characterizing optoelectronic properties and understanding structure-function relationships in heterogeneous or disordered materials on nanometer length scales. The intensity of photon emission induced by tunneling electrons from rough Au films is found to depend on the surface feature size. This size-dependent photon emission yield is shown to agree with the theoretically predicted trend based on the inelastic electron tunneling mechanism. Correlated STM "topography" and electroluminescence measurement of polypyridine (PPy) showed electroluminescence almost exclusively results from low conductivity regions of the film. This anomalous correlation between STM topography and photon emission maps of PPy films is interpreted as the consequence of the spatial variation of the carrier mobility. The results have important implications for understanding the underlying physics of electroluminescence of polymer films as well as for development of optoelectronic devices based on polymeric materials.