Robert H. Havlin

NMR study of InP quantum dots: Surface structure and size effects

We report the results of 31P NMR measurements on trioctylphosphine oxide (TOPO) passivated InP quantum dots. The spectra show distinct surface-capping sites, implying a manifold of crystal–ligand bonding configurations. Two In 31P surface components are resolved and related to different electronic surroundings. With decreasing particle size the In 31P core resonance reveals an increasing upfield chemical shift related to the overall size dependence of the InP electronic structure.

NMR of supercritical laser-polarized xenon

Abstract The feasibility of producing supercritical laser-polarized xenon for nuclear magnetic resonance (NMR) investigations was studied. Using a high-pressure capillary tube, a supercritical xenon sample (52°C, 65 atm) was produced with a 129 Xe polarization approximately 140 times the equilibrium value. The polarization was observed to last for hundreds of seconds, in agreement with previous studies. These preliminary results suggest that supercritical laser-polarized xenon may be used as a polarizing solvent for numerous NMR applications.

Creating isotropic dipolar spectra for a pair of dipole coupled spins in high-field

In the absence of a strong magnetic field, the dipolar interaction between two nuclear spins is independent of orientation leading to sharp lines. However, in high magnetic fields the Zeeman interaction breaks the symmetry of space and spin producing an anisotropic dipolar spectra. In the following Letter, a method that yields isotropic dipolar spectra for a pair of dipole-coupled spins is presented. This is accomplished through a suitable choice of coherence pathways and average Hamiltonians. We present a theoretical explanation as well as an experimental verification for this novel methodology.

Isotropic proton-detected local-field nuclear magnetic resonance in solids

A nuclear magnetic resonance method is presented which produces linear, isotropic proton-detected local-field spectra for INS spin systems in powdered samples. The method, heteronuclear isotropic evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways. The theory behind HETIE is presented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for use in structure determination in the solid state are discussed.