Electronic Structure and Electron Dynamics at Organic-Semiconductor and Organic-Metal Interfaces

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This project addresses issues relevant to the use of organic materials in a range of molecular electronic devices, and also to present day electronic devices such as FETs and LEDs that utilize molecular materials. Two-photon photoemission (2PPE) studies on various organic-metal and organic-semiconductor (Si) surfaces are aimed at characterizing electronic structure and dynamics at such interfaces. Understanding the interfacial electronic structure and electron transfer dynamics is considered a critical step. The primary objective and approach is to systematically establish the electronic structure and electron transfer dynamics at organic-semiconductor and organic-metal interfaces using three well controlled model systems. In the first, simple aromatic molecules will be adsorbed onto or separated from metal surfaces via spacer layers. In the second, aromatic units will be tethered at a particular distance to silicon surfaces in self-assembled monolayers (SAMs). In the third system, thin crystals of conjugating oligomers, particularly oligothiophenes, will be vapor deposited onto metal surfaces. The interfacial electronic structure in all these systems will be characterized by two-photon photoemission (2PPE) for unoccupied electronic states, in conjunction with one-photon photoemission for occupied states. Of particularly importance is 2PPE, which allows direct probing of the ultrafast electron transfer dynamics between unoccupied molecular states and the surface. The experiments on electronic structure and electron transfer dynamics will be closely correlated with surface chemical and structural characterizations using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). %%% The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The studies are expected to improve our fundamental understanding of possible future nanodevice/transistor technologies. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***