Hydrogen-related defects in polycrystalline CVD diamond

By simulating the line shapes of a commonly observed S=1/2 electron paramagnetic resonance (EPR) center in polycrystalline chemical vapor deposited (CVD) diamond at 9.8, 14, 20, and 35 GHz, we conclude that the EPR signal, which we label H1, results from a unique defect with a single hydrogen atom similar to 1.9 Angstrom away from the unpaired electronic spin. We report also 14 and 20 GHz studies of an additional hydrogen-related EPR center, labeled H2, which is similar; however, the hydrogen is similar to 2.3 Angstrom away. We propose that, in each case, a hydrogen atom has entered a stretched bond at a grain boundary or other extended misfit region in the CVD material, allowing the carbons to relax backward, one bonding to the hydrogen, the other with an unpaired electron in its dangling bond. These results may provide important insight into the recently discovered phenomenon of hydrogen activation at grain boundaries in silicon.