Raman spectroscopic investigation of radiation damage in carbon implanted diamond

Abstract

Analog and digital structures can be written into thin surface layers of semiconductors by using focused ion beams of submicron dimensions. By inducing the phase transition from the crystalline (c) to the amorphous state (a) optical contrast is generated between areas of different exposure. The aim of this study was to investigate the properties of diamond as a high-density optical recording medium and to determine the corresponding irradiation parameters. To this end, single crystals of diamond were irradiated with self-ions of 75 key energy with fluences between F=0.3-l0xlO15 C/cm2 at about 100 K. The radiation damage, persisting after annealing treatments between 300-1700 K, was studied by Raman measurements, monitoring changes in the atomic bonding arrangements. Since the scattering cross-section of C sp2 bonds is 50x that of C sp3 bonds, this is an extremely sensitive technique in detecting changes in the initially purely sp3 state. The position and linewidth of the characteristic first-order phonon of crystalline diamond at 1332 cm-l reflect crystallinity and stress level, while bands between 1350-1700 cm-l indicate disorder. In utilizing the microscopic resolution of a Raman facility additional information was obtained on the spatial variation of the damage level. The optimum annealing temperature was found to be 1500 K. For F > 3xlO15C/cm2, the damage was irreversible, for F = 3xlO15C/cm2 the damage was only partly repaired after annealing at 1500 K and, for F < 3xlO15C/ cm2, the crystalline/amorphous contrast was reversible. For F < lxl015C/ cm2 Raman spectroscopy was not sensitive enough to detect the incurred damage. Infrared spectroscopy was used to classify the diamond samples according to type.