Nanostructuring of crystalline grains of natural diamond using ionizing radiation

Abstract

Crystalline grains of type IIa natural diamond (the average grain mass is ~1 mg) are studied after their irradiation with neutrons in a nuclear reactor at a neutron fluence of ~10²¹ cm^-2. The irradiation is found to bring about a decrease in the macroscopic density of the grains by 40%. A quadrature signal of electron spin resonance (ESR) with a g factor equal to 2.00006 and a paramagnetic-relaxation time > 10^-5 s is detected for the first time. Metastable uncompensated electron spins residing at the inner surface of the nanovoids may be the cause of the appearance of this signal. A similar signal is also observed for C₆₀ fullerite powder. The results of an ESR spectroscopy study of the irradiated diamonds are consistent with data obtained from Raman scattering spectroscopy (the appearance of an anomalously broad band peaked at 950 cm^-1 instead of a narrow single line at 1332 cm^-1 in the initial sample) and electron microscopy (the appearance of nanostructuring). It is established that nanostructuring of diamond under the effect of ionizing radiation brings about the appearance of dc electrical conductivity with an activation energy of 0.17 eV in the temperature range 30 to 300°C.