Daniel P. Weitekamp
Assistant: Barbara Miralles
The focus of Professor Weitekamp's research is novel spectroscopic phenomena and their application to otherwise inaccessible problems in chemistry and device physics, especially at interfaces. First-principles theory, especially quantum and statistical mechanics, is used to design novel experiments and instruments and interpret the results.
Much of the work involves magnetic resonance - the reorientation of spin angular momenta under the influence of internal and applied fields. The power of magnetic resonance as an analytical method is largely a consequence of the relative isolation of the spin degrees of freedom from the complexity of electronic and nuclear motion. This allows the spins to serve as minimally invasive probes in nearly any material. The photochemical inertness of radiofrequency (rf) photons provides unparalleled freedom in the design of irradiation sequences for spectroscopic finesse. Thus, NMR is the arena for much of the conceptual development in the nonlinear spectroscopy of many-level systems, such as multiple-pulse line narrowing and multidimensional time-domain spectroscopy. The quantitative interpretation of NMR spectra in terms of electronic and molecular structure and motion requires the full power of quantum and statistical mechanics. Our recent discovery of the effect on lineshapes of the nuclear spin dependence of vibrational motion opens the way to calculating NMR spectra to experimental accuracy. New strategies for resolution enhancement are revealing spectroscopically the response of materials to cyclic perturbations, for example the optical and electrical response of epitaxial semiconductor devices.
The most common barrier to making use of magnetic resonance and other spectroscopies in interfacial and nanoscale environments is inadequate sensitivity. Novel ways of coupling molecular spectroscopy to other degrees of freedom are needed. The group continues to develop new ultrasensitive measurement concepts and realize them in prototype instruments. Force-detected spectroscopy of both spin and optical transitions near surfaces are current goals. With such techniques the analytical power of spectroscopy can be brought to bear with unprecedented sensitivity, resolution, and economy, enabling studies of designed or combinatorial libraries of molecular sites and nanostructures.