Invited Paper NS-WeM1
2009 Medard Welch Award Lecture - Molecular Interfaces to Nanoscale Materials: Making "Dumb" Materials "Smart"
Wednesday, November 11, 2009, 8:00 am, Room L
Recent years have seen dramatic increases in the ability to synthesize new bulk and nanostructured materials. For many applications, such as sensing and renewable energy, the need for high stability drives a motivation for working with two classes of ‘ultra-stable’ materials: (1) nanoscale carbon, and (2) nanocrystalline metal oxides. While these materials are highly stable they do not provide important properties such as chemical or biological selectivity. Molecular surface chemistry can be used to turn these into “smart” materials by linking molecules that will convey chemical or biological selectivity for sensing or desirable electron-transport properties for applications in renewable energy. We have found that photochemical grafting of alkenes provides a nearly universal method for producing molecular monolayers on a wide range of highly stable materials. Surprisingly, this method works on both wide-bandgap semiconductors such as diamond and TiO2, as well as metallic materials such as carbon nanofibers. Through a series of studies we have identified the underlying mechanism as an internal photoemission process in which ultraviolet light ejects an electron from the material into an adjacent reactive liquid, leaving behind a reactive (and persistent) hole that serves as a reactive site for molecular grafting. With suitable chemistry, this approach can be used to fabricate (bio)molecular interfaces with a high degree of functionality that can be used (for example) to achieve direct biological-to-electronic signal conversion for sensing. Recent work also shows this to be an excellent approach for novel types of electrocatalytic interfaces of interest for applications in renewable energy. In this talk I will discuss some of our efforts in making and understanding “smart” molecular and biomolecular interfaces to nanocrystalline materials, and some of the resulting applications in sensing and in renewable energy.