In this article, the diameter distributions of carbon nanotube were theoretically analyzed. The carbon nanotubes were grown by microwave plasma enhanced CVD. For studying the diameter distributions of the carbon nanotubes, the thermodynamic transformation of catalytic films was theoretically considered. Therefore, a process of the formation of stable catalytic islands was supposed, in which the initial continuous catalytic films were first transformed into many critical nuclei and then became stable islands through diffusion of the critical particles, where carbon nanotubes just grew up. The island distribution expression can be derived, and under certain conditions, carbon nanotubes have similar distributions. The nanotubes grown on different catalyst films were analyzed, which showed that the nanotubes over thick films have broad diameter distributions and large mean diameters, while that over thin films have narrow diameter ranges and small diameters on average. The theoretical results were in good agreement with the experimental data.

The process of diamond nucleation by hot filament chemical vapor deposition was investigated by atomic force microscopy. It was observed that a large number of micro-defects (pits) were produced on the surface of the silicon substrate due to ion bombardment under the negative potential and diamond nucleated on the pits. The formation of the pits and their role in diamond nucleation were theoretically approached. The results indicate that the number of the pits increased with increasing potential, the diamond nucleation density and the nucleation rate were functions of the pits, and they were in agreement with the experiment results.

Diamond films have been deposited on AlN substrates using hot filament chemical vapor deposition. By applying a negative bias voltage, a high diamond nucleation density on AlN substrates as high as 10 10 cm-2 has been realized. The appearance of bias current and plasma induced on the AlN surface was found critical for the enhancement of diamond nucleation density. Satisfactory adhesion of the deposited diamond films with the AlN substrates has been achieved for application purposes. q2000 Elsevier Science B.V. All rights reserved.

Nucleation and growth of diamond films on aluminum nitride (ALN) coatings were investigated by scanning electron microscopy, Raman spectroscopy and scratch test. ALN films were grown in a magnetron sputtering deposition. The substrates were Si(111) and tungsten carbide (WC). Chemical vapor deposition (CVD) diamond films were deposited on ALN films by hot filament CVD. The nucleation density of diamond on ALN films was found to be approximately 10 5cm 2, whereas over 10 10cm2 after negative bias pre-treatment for 35min was 320V, and 250mA. The experimental studies have shown that the stresses were greatly minimized between diamond overlay and ALN films as compared with WC substrate. The results obtained have also confirmed that the ALN, as buffer layers, can notably enhance the adhesion force of diamond films on the WC.

The magnetoresistance effect of p-type diamond films has been investigated at different temperature. Diamond films were grown by microwave plasma chemical vapor deposition. Mirror-polished p-type Si(100). was used as a substrate material. The experimental results show that a notable magnetoresistance effect in polycrystalline and heteroepitaxial semiconducting diamond films was observed. The relative changes in the resistivity of the diamond films with magnetic field strongly depended on both boron-doped concentration in the films and geometric form of the samples. The effect of disk structure was greater than that of strip-type samples, also variation in the resistivity of heteroepitaxial diamond films was greater than that of polycrystalline diamond films at same magnetic field. The magnetoresistance of p-type diamond films was decreased with increasing both boron-doped concentration and temperature. The relative changes in resistance of the heteroepitaxial diamond films with the disk structure was increased by 0.85 at room temperature under magnetic intensity of 5T, but only 0.40 for strip-type structure. The results are discussed in detail.