  Dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR)
offers a promising route to studying local atomic environments at the surface
of both crystalline and amorphous materials. We take advantage of unpaired
electrons due to defects close to the surface of the silicon microparticles to
hyperpolarize adjacent $^{1}$H nuclei. At 3.3 T and 4.2 K, we observe the
presence of two proton peaks, each with a linewidth on the order of 5 kHz. Echo
experiments indicate a homogeneous linewidth of $\sim 150-300$ Hz for both
peaks, indicative of a sparse distribution of protons in both environments. The
downfield peak at 10 ppm lies within the typical chemical shift range for
proton NMR, and was found to be relatively stable over repeated measurements.
The upfield peak was found to vary in position between -19 and -37 ppm, well
outside the range of typical proton NMR shifts, and indicative of a high-degree
of chemical shielding. The upfield peak was also found to vary significantly in
intensity across different experimental runs, suggesting a weakly-bound
species. These results suggest that the hydrogen is located in two distinct
microscopic environments on the surface of these Si particles.
