Electrical conductivity of thermally hydrogenated nanodiamond powders

Electrical properties of detonation diamond nanoparticles (NDs) with individual diameters of similar to 5 nm are important for many applications. Although diamond is an insulator, it is known that hydrogen-terminated bulk diamond becomes conductive when exposed to water. We show that heating ND in hydrogen gas at 600-900 degrees C resulted in a remarkable decrease in resistivity from 10(7) to 10(5) Omega cm, while the resistivity was essentially unchanged after treatment at 400 degrees C and lower temperatures. Fourier Transform Infrared Spectroscopy and X-ray photoelectron spectroscopy (XPS) studies revealed that hydrogenation of ND occurs at 600-900 degrees C, suggesting that the decrease in resistivity is based on transfer doping at the hydrogenated ND surface. Oxidation of the hydrogenated sample at 300 degrees C recovers resistivity to its original value. The resistivity of treated ND as a function of the O/C atomic ratio showed a transition from resistive (O/C ratio > 0.033) to conductive (O/C ratio < 0.033) state. This is consistent with the idea that the change in the resistivity is caused by the shift of the valence band maximum to above the Fermi level due to the dipole of the C-H bonds leading to transfer doping. (C) 2013 AIP Publishing LLC.