With this award, the Chemical Measurement and Imaging program is supporting the research of Chandrasekhar Ramanathan of Dartmouth College to develop new techniques to study and understand the physical and chemical properties of surfaces. A number of important processes occur at the surface of materials. For example, catalysis?such as occurs in solar energy conversion processes or in catalytic converters?takes place on the surface of the catalyst. A detailed understanding of the structure of solid surfaces and their interfaces to other media is critical to the development of new catalysts and other technologies, such as highly sensitive sensors that can be used, for example, to measure groundwater contamination or detect explosives. This research develops methods based on nuclear magnetic resonance (the technology behind magnetic resonance imaging, or MRI) and applies that technique to the study of small-scale materials. The goal is to characterize the structure of these surfaces with high spatial resolution. The resulting information is then used to selectively activate specific sites on the surface to improve on their catalytic or sensing properties. The research is having a broad impact through the development of useful new technologies that will have a variety of applications in many areas. It is having a further impact through programs in local science pubs and cafes designed to communicate the science involved to a broad societal audience.
Nuclear magnetic resonance (NMR) spectroscopic methods are being developed to study the physical and chemical properties of surfaces and interfaces. To compensate for the low sensitivity of NMR, dynamic nuclear polarization techniques (DNP) are being designed and optimized to both maximize the signal enhancements for surface spin species, as well as to obtain information about the local spatial ordering of the spins at nanometer and sub-nanometer length scales. In particular, the use of endogenous and exogenous polarizing agents for DNP of surface functionalized groups in silicon and silica micro- and nano-particles are being compared. Hyperpolarization is being combined with static multiple-pulse NMR techniques such as multiple-quantum spin counting experiments to probe the local ordering of the surface spins in these systems. The newly developed methods are being applied to systems such as nanoparticle surfaces and atomistically-thin layers such as Langmuir-Blodgett or functionalized graphene films, using both endogenous and exogenous polarizing agents. The goal of these studies is to get a better quantitative estimate of the size of the quenched region, the polarization transfer rates and atomic level detail about the local DNP process. A better understanding of these phenomena could, in turn, enable the use of optimal control techniques to selective excite and study certain chemical species, allowing selective maximization of enhancements.
