Electronic properties of chemically modified surfaces and nanostructured materials

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The goal of this research program is the development of methods for tuning the electronic properties of surfaces and nanomaterials via chemical modification. Adsorption or covalent attachment of polar molecules at a surface can lead to large changes in the work function of the material. In addition, on semiconductor surfaces, these modifications can have long-range (10-1000nm) effects on the electronic properties due to the penetration of electric fields arising from surface charges which shift energy levels and influence the density of free carriers (a phenomena often called band-bending). These effects can be exploited for electrical detection of chemical and biochemical species as well as in the design of electronic devices such as transistors, photovoltaics, and light emitting diodes. In the proposed work we will continue to learn how chemical modification can be used to induce band bending and control electrical transport on silicon. Functionalization of the surface with organic functional groups of electron donating and withdrawing character will be used to systematically alter the conductivity and form surfaces that selectively respond to different molecular species. Learning how to control and exploit these effects should prove useful in chemical and biochemical detection as well as in the development of a new approach to the formation of nanoscale conducting channels. Studies on planar silicon will be extended to silicon nanowire networks and individual silicon nanowires. Sensitivity of nanowires to adsorption and reaction events will be compared with the planar substrates.