Research

Optically-pumped Nuclear Magnetic Resonance (OPNMR): The goal of our research is to probe the interplay between dopants, defects, and interfaces and electronic properties of various semiconductors and other optically active materials. To that end, we are developing experimental strategies based on modern solid-state nuclear magnetic resonance (NMR) spectroscopy, which help elucidate the structure and dynamics of complex systems (e.g., thin films, nanoclusters, and amorphous materials).

I. Optically-polarized NMR (OPNMR): OPNMR combines laser excitation with NMR detection. The laser creates polarized electronic spins that couple to nuclear spins. The polarized nuclear spins can then be detected by NMR. We are applying optical pumping techniques to systems of semiconductors to better understand their opto-electronic properties: semiconductor quantum wells, nanoclusters and quantum wires, and opto-electronic devices.

II. Hardware for combined OPNMR and optically-detected NMR (ODNMR): as with OPNMR, ODNMR utilizes laser excitation coupled with NMR where the luminescence is recorded rather than the rf signal. We are designing an integrated system to record both types of information in a single apparatus.

III. NMR of optical switch materials: numerous sys-tems exhibit a structural switch when irradiated with light at a specific wavelength. When this structural change can be reversed with the application of light at a different frequency, an "optical switch" has been created. We are studying systems to observe the structural changes that occur in the material or in composites which house the switch material.

IV. Cluster science and NMR: molecular clusters, nanoclusters, and macroscopic clusters offer unique opportunities for NMR study. We are focusing efforts on several fronts in this arena having to do with the chemical shift values of specific nuclei in these different environments. Much of our work is concerned with ⁷⁷Se NMR and ¹²⁵Te. New ternary II-VI semiconducting nanoclusters (shown in the TEM image) are being fabricated and studied via NMR.

Selected Publications

• S.E. Hayes, S. Mui, K. Ramaswamy "Optically polarized NMR of semiconductors," J. Chem. Phys.special issue, 128, 052203 (2008). doi:10.1063/1.2823131
• S. Mui, K. Ramaswamy, S.E. Hayes "Physical insights from a penetration depth model of optically pumped NMR" J. Chem. Phys.special issue, 128, 052303 (2008). doi:10.1063/1.2831928
• S. Mui, K. Ramaswamy, S.E. Hayes "Effects of optical absorption on ⁷¹Ga optically polarized NMR in semi-insulating GaAs: measurements and simulations," Phys. Rev. B, 75, 195207 (2007). doi: 10.1103/PhysRevB.75.195207
• K. Ramaswamy, E.G. Tulsky, J.R. Long, J. L.-F. Kao, S.E. Hayes, "Determination of ⁷⁷Se-⁷⁷Se and ⁷⁷Se-¹³C J-coupling Parameters for the Selenocyanide Clusters [Re₅OsSe₈(CN)₆]^3- and [Re₄Os₂Se₈(CN)₆]^2-," Inorg. Chem. 46, 1177 (2007). doi:10.1021/ic061571g
• M. Bertmer, R.C. Nieuwendaal, A.B. Barnes, S.E. Hayes "Solid-State Photodimerization Kinetics of alpha-trans-Cinnamic Acid to alpha-Truxillic Acid Studied via Solid-State NMR," J. Phys. Chem. B, 110, 6270 (2006). doi:10.1021/jp057417h