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Antoine Kahn

Our research programs center on the physics and chemistry of semiconductor surfaces and interfaces. Surfaces and interfaces are gateways for electrical or optical communications with the bulk of a solid. In modern thin film electronic devices, they are within a few nanometers of active regions, and thus they occupy an increasingly important place in the physics and technology of semiconductors. Understanding their role and controlling their properties is crucial, and requires extensive investigations of the links between structure and chemistry at the atomic or molecular level, and surface and interface electronic properties.

Part of our present research is directed toward large band gap III-V nitrides, which have a wide range of application in high-temperature electronics and light-emitting devices. This relatively new class of materials brings specific technological issues related to epitaxial growth, fabrication of low-resistivity ohmic contacts, high-temperature interface stability, and negative electron affinity. Our approach to these problems consists in detailed investigations of metal-nitride and nitride-nitride interface atomic geometry, chemistry, and energetics via spectroscopic techniques under highly controlled ultrahigh vacuum conditions (electron diffraction, UV, X-ray, and inverse photoemission spectroscopy), coupled with interface transport measurements.

	Scanning tunneling microscope image of an ordered monolayer of CuPc grown on the (111) surface of gold.

Another important part of our research focuses on electronic organic molecular thin films. This class of materials is being investigated worldwide for its applications in opto- and microelectronics. The structural flexibility due to weak intermolecular bonds, and the endless possibilities for chemical synthesis of new molecules, give molecular systems a unique advantage over inorganic systems for relatively simple fabrication of high-quality films for light-emitting or transport devices. Our research spans from fundamental issues of electron-hole interaction in these molecular systems, to quasi-epitaxial growth of molecular films on a variety of substrates (see figure below), to the chemistry and electronic properties of metal-organic and organic-organic heterojunctions. The all-important problem of electronic structure at, and carrier injection across, organic boundary regions, in particular at metal contacts, is a major focus of our work and is the subject of multitechnique interdisciplinary investigations.