Surface-sensitive NMR in optically pumped semiconductors

Abstract

We present a scheme of surface-sensitive nuclear magnetic resonance in optically pumped semiconductors, where an NMR signal from a part of the surface of a bulk compound semiconductor is detected apart from the bulk signal. It utilizes optically oriented nuclei with a long spin-lattice relaxation time as a polarization reservoir for the second (target) nuclei to be detected. It provides a basis for the nuclear spin polarizer [IEEE Trans. Appl. Supercond. 14, 1635 (2004)], which is a polarization reservoir at a surface of the optically pumped semiconductor that polarizes nuclear spins in a target material in contact through the nanostructured interfaces.Comment: 4 pages, 5 figure

Radical-free dynamic nuclear polarization using electronic defects in silicon

“…Alternatively, the source of polarization may be physically separated from the material to be polarized. It has been shown that the large nuclear spin polarizations present in optically pumped noble gases and semiconductors can be transferred to a variety of materials using a Hartmann-Hahn cross-polarization sequence [24][25][26][27] or, in the case of gases, via a direct nuclear dipole-dipole interaction [28]. Surface defects in porous carbon chars have also been shown to polarize 1 H nuclei in solution at room temperature via a contact hyperfine interaction [29].In this Letter, we demonstrate that naturally occurring paramagnetic defects at the surface of silicon nanoparticles (SiNP) can directly polarize 1 H nuclei in a bulk frozen matrix near the surface of the particle as well as the 29 Si nuclei in the particles.…”

Interface-sensitive nuclear magnetic resonance at a semiconductor heterojunction using hyperpolarization

“…Here, we demonstrate a direct observation of NMR signals from the minute heterojunction region without special treatment of the sample. The scheme utilizes nuclear hyperpolarization created and localized at a part of semiconducting nanostructure [1], which is to be called "hyperpolarization labelling". This study is along the lines of recent efforts for the spatial control of hyperpolarization in optical pumping NMR [2][3][4].The implementation of this scheme requires the following: (1) creation, (2) localization, and (3) selective detection of hyperpolarization at a heterojunction.…”

Nuclear polarization by optical pumping in InP:Fe above liquid nitrogen temperature

“…Optical pumping in semiconductors such as GaAs and InP has resulted in nuclear polarization that is enhanced by a factor of 100 over the thermal equilibrium [2,3,5]. Semiconductor substrates have been suggested as spin reservoirs to transfer hyperpolarized nuclear spins to extrinsic substances such as biological or chemical materials deposited on the surface, a procedure referred to as 'Transferred optically-pumped NMR' (TOPNMR) [1,8,9]. InP was considered to be a good candidate for TOPNMR for the following reasons: (1) 100% natural abundance of 31 P nucleus, (2) nuclear spin-lattice relaxation time T 1 long enough to store hyperpolarized nuclear spins, and (3) efficient spin diffusion despite surface-induced electric field gradients since there is no quadrupole splitting.…”