Nanocrystalline diamond (NCD) has been grown using a nanodiamond seeding technique, leading to a dense form of this material, with grain sizes around 100 nm. The electrical properties of both intrinsic and lightly boron-doped NCD have been investigated using impedance spectroscopy and Hall effect measurements. For intrinsic material, both grain boundaries and grains themselves initially contribute to the frequency dependant impedance values recorded. However, boundary conduction can be removed and the films become highly resistive. Interestingly, the ac properties of these films are also excellent with a dielectric loss value ∼0.004 for frequencies up to 10 MHz. The dielectric properties of these NCD films are therefore as good as high quality large grain polycrystalline diamond films. In the case of boron-doped material, p-type material with good carrier mobility values (10–50 cm2/V s) can be produced at carrier concentrations around 1017 cm−3.

The use of de-icing chemicals at airport runways has been shown to produce oxides and carbonates of sodium, potassium and calcium which catalyse the oxidation of carbon-carbon composite aircraft brakes leading to an increase of the oxidation rate by an order of magnitude. This review reports on studies that have characterised the catalytic oxidation and discusses the mechanism of the catalytic reaction based on investigations that were carried out with both C-C composites and carbon as a fossil fuel. The alkali metal oxides/carbonates are more active catalysts and in their case, the redox reaction between the monoxides and the peroxides has been identified as the most likely catalysis mechanism. In order to reduce or eliminate the problem of catalysis, doping with boron or phosphorus compounds has been investigated by a number of researchers. The effect of these along with the use of protective coatings is also reviewed.3

The use of diamond as a semiconductor for the realization of transistor structures, which can operate at high temperatures (>700 K), is of increasing interest. In terms of bipolar devices, the growth of n-type phosphorus doped diamond is more efficient on the (111) growth plane; p-type boron-doped diamond growth has been most usually grown in the (100) direction and, hence, this study into the electronic properties, at high temperatures, of boron-doped diamond (111) homoepitaxial layers. It is shown that highly doped layers (hole carrier concentrations as high as 2×1020 cm−3) can be produced without promoting the onset of (unwanted) hopping conduction. The persistence of valance-band conduction in these films enables relatively high mobility values to be measured (∼20 cm2/V s) and, intriguingly, these values are not significantly reduced at high temperatures. The layers also display very low compensation levels, a fact that may explain the high mobility values since compensation is required for hopping conduction. The results are discussed in terms of the potential of these types of layers for use with high temperature compatible diamond transistors.

Nanometer-scale diamonds formed using a detonation process are an interesting class of diamondmaterials. Commercially supplied material is highly aggregated with???5nm diamond crystals forming particles with micron sizes. Previous models have suggested that nondiamond carbon is incorporated between the crystals, which would reduce the electrical and chemical usefulness of this form of diamond. However, using impedance spectroscopy we have shown that at temperatures below350??C the form of detonation nanodiamond being studied is a near to ideal dielectric, implying a full sp 3 form. At temperatures above this the surfaces of the diamond crystals may support some nondiamond carbo