Charge Transfer Equilibria Between Diamond and an Aqueous Oxygen Electrochemical Redox Couple

Abstract

Undoped, high-quality diamond is, under almost all circumstances, one of the best insulators known. However, diamond covered with chemically bound hydrogen shows a pronounced conductivity when exposed to air. This conductivity arises from positive-charge carriers (holes) and is confined to a narrow near-surface region. Although several explanations have been proposed, none has received wide acceptance, and the mechanism remains controversial. Here, we report the interactions of hydrogen-terminated, macroscopic diamonds and diamond powders with aqueous solutions of controlled pH and oxygen concentration. We show that electrons transfer between the diamond and an electrochemical reduction/oxidation couple involving oxygen. This charge transfer is responsible for the surface conductivity and also influences contact angles and zeta potentials. The effect is not confined to diamond and may play a previously unrecognized role in other disparate systems.

Microwave purification of large-area horizontally aligned arrays of single-walled carbon nanotubes

“…The discussions above relate the resistance of the SWNTs to the heating power imparted into the SWNTs. Although s-SWNTs are generally more resistive than m-SWNTs, unintentional doping 51,52 and other effects can diminish these differences. Selectivity in such cases can be greatly enhanced by the Schottky barriers that form at the contacts between the antenna metal and the s-SWNT.…”

Generation and transport of photoexcited electrons in single-crystal diamond

“…These results confirm that the photocurrent is proportional to the illuminated volume, which rules out a dominant surface effect. In order to further suppress surface conduction, recently understood to result from a hydrogen terminated diamond surface, 3,4 we either annealed the sample or purged the surface with dry nitrogen during the measurement.…”

Diamond as functional material for bioelectronics and biotechnology

“…As was already mentioned, proteins become denatured on a hydrophobic surface and their hydrophobic core sticks to the surface. Consequently, they can modify the initial equilibrium of the conductive layer, which is a result of the equilibrium of chemical potentials of the diamond and the solution (Chakrapani et al, 2007;Maier et al, 2000). A negative shift occurs as a result of the change of the material properties of diamond (i.e.…”

“…Despite the general chemical stability, diamond surface can be terminated by different atomic species (Rezek et al, 2003) and organic molecules (Rezek, Shin, Uetsuka & Nebel, 2007), which can alter diamond's natural properties and thus open the door for countless new applications. For example, electrical conductance and electron affinity are both significantly influenced by surface termination of diamond by hydrogen or oxygen atoms (Chakrapani et al, 2007;Kawarada, 1996;Maier et al, 2001;Rezek et al, 2003;Ri et al, 1995). The main difference arises from the opposite dipoles of C-H and C-O bonds.…”