Electrical and electrochemical characterisation of single crystal diamond

Abstract

The overall aim of this thesis is to examine the electrical and electrochemical properties of single crystal intrinsic and boron doped diamond grown by chemical vapour deposition. Techniques such as AFM, C-AFM, FE-SEM, PL imaging, in air and in solution Hall and resistivity measurements, FET, cyclic voltammetry and SECM have been employed. The results from studying single crystal intrinsic H-terminated diamond with different surface preparations are reported. In air and in solution measurements suggest a similar behaviour for polished surfaces. Different mechanisms (for in air or in solution experiments) have to be applied in order to interpret the electrical transport data correctly. Electrochemistry of H-terminated single crystal diamond with well defined redox couples has been proven, but the electron transfer rates are relatively slow. Initial SECM experiments indicate that the surface is homogeneously active, but can be easily damaged. Single crystal boron doped diamonds with moderate (< 1020 cm-3 boron) doping levels have been examined. PL imaging and C-AFM highlighted regions with different doping level and different conductivity even though the material is single crystal. In air electrical measurements demonstrated that the bulk mobility and carrier concentration are independent of the surface termination (O- or H-). No redox activity (or very little) was observed when the samples were O-terminated; quasi-reversible behaviour and sluggish electron transfer kinetics was observed for H-terminated surfaces. The properties of a as-grown single crystal boron doped diamond with high (> 1020 cm-3 boron) doping levels have also been investigated. Electrical studies confirmed that the diamond behaved like a metallic conductor. Large background currents were observed when CVs were used to study the O-terminated sample in FcTMA+, but the origin of this signal are not clear. For both Ru(NH3)6 3+ and FcTMA+ the metallic boron doped single crystal diamond electrode showed quasi-reversible behaviour. The peak to peak separation is smaller for the H-termination than for the O-termination. Preliminary SECM studies showed that the electrode’s surface was homogeneously active