Diamond electrodes carrier concentration

FIG. 6. Carrier concentrations and mobilities (holes) in boron-doped nanocrystalline diamond thin-film electrodes as a function of the B2H6 concentration added to the source gas mixture. The measurements were made in a van der Pauw geometry with Ti contacts by Dr. Toshihiro Ando at NIMS. The limit of the temperature measurements was approximately 500 K. 

More precisely, the potential drop in the Helmholtz layer in a redox electrolyte increases with increasing doping. Therefore, the reaction rate reflects the Helmholtz potential drop, rather than the charge carrier concentration. This is the reason why the behavior of semiconductor diamond is far from ideal in particular, no current rectification is typically observed on (rather heavily doped) diamond electrodes, as mentioned above. 

Owing to its extraordinary chemical stability, diamond is a prospective electrode material for use in theoretical and applied electrochemistry. In this work studies performed during the last decade on boron-doped diamond electrochemistry are reviewed. Depending on the doping level, diamond exhibits properties either of a superwide-gap semiconductor or a semimetal. In the first case, electrochemical, photoelectrochemical and impedance-spectroscopy studies make the determination of properties of the semiconductor diamond possible. Among them are the resistivity, the acceptor concentration, the minority carrier diffusion length, the flat-band potential, electron phototransition energies, etc. In the second case, the metal-like diamond appears to be a corrosion-stable electrode that is efficient in the electrosyntheses (e.g., in the electroreduction of hard to reduce compounds) and electroanalysis. Kinetic characteristics of many outer-sphere... 

At first glance, the proportionality between Rf and p reflects the fundamental law of the electrochemical kinetics at semiconductor electrodes, namely, the exchange current of a semiconductor electrode must be proportional to the surface concentration of charge carriers participating in the redox reaction. However, a closer look into the problem, based on reference [14], allows one to conclude that it is the potential distribution at the diamond/redox electrolyte solution interface, rather than the surface concentration of the charge carriers, that depends on the diamond doping level, the more so, for more heavily doped samples. 

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