Anomalous deep ion-induced modification of HOPG

Abstract

The temperature dependences ion-induced processes of HOPG (UPV-1T) basal plane modification under high-fluence (1018ion/cm2) 10–30keV Ar+ ion irradiation have been studied in temperature range from room temperature to 400°C. The RBS has been applied to estimate the modified layer depth. The morphology changes have been studied by SEM. It has been found that at sufficiently high ion energy the modified layer depth can be ten times more then the ion projected range Rp. The two different effects of deep modification with depth >1000nm are observed. Firstly, at the temperatures smaller then the temperature of ion-induced texture transition T <Tt≈150°C and the topography is not significantly changed from initial one and modified layer becomes in polycrystalline state according to RBS in channelling geometry. Secondly, at Tt<T<400°C when the SEM shows the development of needle and ridge-like elements and deep argon incorporation takes place. The ion irradiation at temperature of texture transition Tt, as the irradiation at sufficiently high T⩾400°C, does not lead to deep modification effect and the depth h of disordered layer is about Rp. There are the energy thresholds of deep modification which correspond to threshold mean values of stationary level of radiation damage – about 50 and 65 displacements per atom accordingly for deep modification at RT and at T∼250°C.