Enhanced spontaneous nucleation of diamond nuclei in hot and cold microwave plasma systems

摘要

In this work, the diamond nucleation is studied using two different deposition systems: (i) focused microwave plasma (labeled as "hot plasma") and (ii) pulsed-linear antenna microwave plasma ("cold plasma"). For the hot plasma, the influence of CH_4 concentration in the hydrogen rich gas mixture on the self nucleation is investigated. It is found that higher CH_4 concentration leads to increased diamond nucleation density, but also the amount of sp~2 carbon bonds increases within the deposits. In the cold plasma, we investigate the influence of CO_2 addition into CH_4/H_2 and total process pressure. Experimental results reveal a strong dependence of CO_2 and pressure on spontaneous nucleation. The nucleation density (N_d) typical for non-treated substrates (~10~5cm~(-2)) is improved by four orders to 10~9cm~(-2) in cold plasma thanks to increased CH_4 and CO_2 concentrations. The highest nucleation density in the hot plasma system is still one order lower (~4×10~7cm~(-2)). Moreover, in cold plasma a bimodal distribution function of diamond clusters is observed for low ratios of CO_2/H_2. Observed differences in N_d values are attributed to plasma properties and surface chemistry. Based on the experimental results, possible mechanisms contributing to the spontaneous nucleation process are discussed.