Range and mixing distributions of low-energy carbon ions as a base for subplantation growth models

Subplantation was early recognised as being the basic process in low-energy ion growth of diamondlike materials and has also to be considered for the description of bias enhanced diamond nucleation. A number of theories modelling the evolution of diamondlike phases have been proposed. However, the precise details of the subplantation and relaxation processes remain unclear. The problem in testing the complex models is that experimental information other than film structure versus ion energy is missing to a large extent. Mixing and range distributions of low-energy carbon ions are ideal data to model diamond-like film growth. Here we present measurements of range and mixing distributions for carbon ions at energies in the relevant energy range between 12 eV and 692 eV in carbon. The substrates are grown at the identical energies using ¹²C ions by mass separated ion beam deposition. Less than a monolayer of ¹³C was implanted each for the range distributions and as a marker layer for the mixing profiles. The ¹³C depth profiles are measured by high-resolution elastic recoil detection (ERD). These data are directly compared to calculations based on the binary collision approximation (TRIDYN) and to molecular dynamics (MD) simulations which consider atomic interactions on a time scale up to 15 ps including the thermal spike phase. Additionally, mixing distributions are derived from a transport calculation based on the measured range distributions. The measured range profiles show bimodal structures for energies below 200 eV which are significantly broader than the calculated profiles.The mixing profiles are also significantly broader than respective TRIDYN and MD calculations at these low energy. However, mixing profiles are in good agreement with transport calculations based on the measured range profiles showing the relevance of the measured range structures. Three reasons for the observed differences between the measured and theoretical range and mixing distributions are discussed in the paper: thermal induced self diffusion during thermal spike, mobility solely of the deposited ion after the collisional stage and a 3-dimensional surface structure of the carbon films on atomic scale. The experiment allows a crucial test for models of the subplantation scheme and may serve as input for improved calculations.