Ye, Haitao; (2004) Impedance spectroscopy of diamond films. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Research in the area of CVD diamond thin films has increased significantly during the last decades. The remarkable properties of diamond including its extreme hardness, low coefficient of friction, chemical inertness, high thermal conductivity, transparency and semiconducting properties make it attractive for a number of applications, among which electronic devices is one of the key areas. A detailed knowledge of electrical properties of diamond films is therefore critical. This thesis describes spectroscopic impedance studies of CVD diamond films. Impedance spectroscopy is a powerful technique for investigating the electrical properties of polycrystalline materials, being capable of isolating conduction processes within the grain, grain boundary and electrode regions. Thus it can be used for researching methods for reducing problems within diamond technology that are associated with grain boundaries and poor metallic contacts. Systematic investigations have been carried out on single crystalline, microcrystalline and nanocrystalline diamond films. The influence of film quality variations, such as those found when hot filament CVD grown diamond films are compared to microwave plasma enhanced CVD grown diamond has also been studied. Grain size effects on the dielectric properties of diamond films are discussed in detail. Impedance values and associated equivalent capacitance values enable the conduction paths within the material to be attributed to either grain interiors or grain boundaries. Combined with insight gained from scanning electron microscope images, x-ray diffraction patterns and Raman spectroscopy, a full analysis of all the impedance measurements made are summarized in this thesis. Also reported is the first demonstration of impedance measurements on ultrananocrystalline diamond films. Possible physical mechanisms responsible to the observed phenomena are presented.

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