CAREER: Local Probes of Electronic Disorder in Organic Semiconductors

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Technical: The research component of this CAREER award is to study disorder in thin films of organic semiconductors on metal surfaces at the nanometer scale, using scanning probe techniques. The origin of disorder at metal-organic interfaces is assessed by ultrahigh vacuum scanning tunneling microscopy combined with new quantitative approaches to tunneling spectroscopy in constant current mode that have been explicitly developed for soft materials. The research aims to determine the functional form of the distribution of transport states for prototype disordered organics as well as the spatial correlation between transport states in the plane of the interface. Multilayer films are compared with monolayer films to answer the question of whether interfacial disorder differs significantly from bulk-like disorder. The basic materials research is expected to contribute to organic semiconductor device design capabilities by revealing the major factors governing charge injection at metal-organic interfaces. The research also aims to reveal the spatial disorder in charge transport properties in thick organic semiconductor films by applying conducting atomic force microscopy.Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. The project, if successful, can have impacts on the advancement of organic semiconductors for energy related applications. The research and education activities of the project are integrated. Graduate students are trained in an interdisciplinary environment. New scanning probe experiments will be adapted for the senior level undergraduate physics labs at the North Carolina State University. The plan is to modify the existing scanning tunnel microscopy to permit ballistic electron emission spectroscopy and to use the modified instrument to measure injection barriers at metal-organic interfaces in films grown by students. In addition, computational research project will be developed to allow undergraduates to explore aspects of one-dimensional quantum mechanics relevant to scanning tunneling spectroscopy.