Electrochemistry and in situ Raman spectroelectrochemistry of low and high quality boron doped diamond layers in aqueous electrolyte solution

Abstract

In this work we report on electrochemical and in situ Raman spectroelectrochemical characterization of low quality (LQ) ultrathin nanocrystalline and high quality (HQ) polycrystalline boron doped diamond (BDD) compared especially in terms of the sp2 carbon content. The BDD films were grown by microwave plasma enhanced chemical vapor deposition and doped with various boron concentrations from 250 to 8000ppm (boron/carbon ratio in the gas phase) at different conditions. The quality (presence of graphitic or amorphous phases) and boron doping levels in the BDD films were analyzed by micro-Raman spectroscopy. From the neutron depth profiling, it was found that the boron content in the near surface region (<1μm) was in the range from about 4×1019cm−3 to 58×1020cm−3 for B/C from 250ppm to 8000ppm, respectively. The electrochemical measurements have been performed in aqueous 0.5M H2SO4 in the potential range from −2 to 2.5V vs. Hg/Hg2SO4. Cyclic voltammetry showed that the electrochemical potential window was independent on the boron doping but depended on the film quality, i.e. when the sp2 carbon content increased the width of potential window decreased. The in situ Raman spectroelectrochemistry was performed in aqueous electrolyte solution (0.5M H2SO4) in the potential range from −1.5 to 1.5V vs. Hg/Hg2SO4 using two laser excitations (633nm and 457nm). In the case of films containing high amount of sp2 carbonaceous phase (low quality), the modes belonging to sp2 carbonaceous phases changed their intensities. The intensity of the D, G and D′ Raman peaks increased in cathodic direction, while in anodic direction bleaching of these peaks was observed. The diamond films prepared with very small amount of sp2 carbon (high quality) exhibited no spectroelectrochemical changes in the potential region tested.