Investigating point defects in irradiated boron-doped diamond films by temperature-dependent electrical properties and scanning tunneling microscopy and spectroscopy

We report temperature-dependent electrical resistivity (or dc conductivity, sigma(dc)) down to 4 K for pristine and gamma-irradiated microwave plasma-assisted chemical vapor-deposited boron-doped diamond films with [B]/[C](gas) = 4000 ppm to gain insights into the nature of conduction mechanism, distribution, and kinetics of point defects generated due to gamma irradiation prompted by the article [Gupta et al., J. Mater. Res. 24, 1498 (2009)]. The pristine samples exhibit typical metallic conduction up to 50 K and with reduction in temperature to 25 K, the sigma(dc) decreases monotonically followed by saturation at 4 K, suggesting disordered metal or localized behavior. For irradiated films, continuous increasing resistivity with decreasing temperature demonstrates semiconducting behavior with thermal activation/hopping conduction phenomena. It is intriguing to propose that irradiation leads to substantial hydrogen redistribution leading to unexpected low-temperature resistivity behavior. Scanning tunneling microscopy/spectroscopy helped to illustrate local grain and grain boundary effects.