Structural transformation of diamond induced by 1-keV Ar-ion irradiation as studied by Auger and secondary-electron spectroscopies and total-secondary-electron-yield measurements

Abstract

Secondary-electron emission and Auger spectroscopies and total-secondary-electron-yield measurements have been employed to monitor the transformation of type-IIa diamond (110) induced by 1-keV Ar irradiation for a dose range between 7×${10}^{12}$ and 6.2×${10}^{17}$ ions/${\mathrm{cm}}^2$. The irradiations and the analysis were carried out in situ in a UHV chamber. The C(KLL) Auger line shape provides evidence of the increasing graphitelike nature of the surface as a function of the ion dose. The total secondary-electron yield was found to decrease from the unirradiated value of 0.9 to a value of 0.58 for doses exceeding 1×${10}^{16}$ ions/${\mathrm{cm}}^2$. The most unusual result was the observation of an abrupt and extreme charging of the surface [as measured by a shift in the C(KLL) line position] which occurred at a critical dose of between 1.7×${10}^{15}$ and 2.5×${10}^{15}$ ions/${\mathrm{cm}}^2$. Above this critical dose, the charging was observed to decrease gradually over about a decade of ion dose. This unusual charging can be understood in terms of the production of an amorphous, but still insulating layer at the critical dose, which upon further irradiation gradually transforms into a graphitelike structure. The results are consistent with a model for the ion-beam-induced transformation of diamond involving three distinct dose regimes. Below a certain critical dose, the diamond remains essentially single crystalline, albeit with increasing levels of disorder. At the critical dose, the damaged structure suddenly transforms into an amorphous, but still highly insulating material whose properties appear to be similar to those of amorphous carbon with local tetrahedral (i.e., ${\mathit{sp}}^3$) bonding but without any long-range order. Further irradiation results in the transformation of ${\mathit{sp}}^3$ to ${\mathit{sp}}^2$ bonds with a concomitant rise in the conductivity. At very high doses, there is spectroscopic evidence for the formation of ${\mathit{sp}}^2$-bonded microcrystallites.