Abstract
Four samples of nitrogen-doped carbon microspheres were synthesised using a horizontal chemical vapour deposition process. Characterization of the samples using scanning electron microscopy, Raman spectroscopy and electron paramagnetic resonance spectroscopy showed spherical graphitic carbon microparticles with substitutional nitrogen in the lattice structure. The average diameter of the microspheres was 1.7 μm. Electron paramagnetic resonance spectroscopy was also used as a technique to measure the percentage of substitutional nitrogen in each sample. This was determined to be 3.4% in two of the samples and 1.7% in the other two. Temperature dependent electrical transport measurements were performed on the samples and resistance measurements showed clear semiconducting behaviour in two of the samples and a transition from metallic to semiconducting behaviour in the other two samples. IV characteristics measurements display curves with increasing non-linearity as temperature decreases in two samples and saturation behaviour is seen at higher temperatures in the other two samples. An anomaly is present in the IV characteristics at 300 K in all samples. A combination of fluctuation induced tunnelling and electronphonon scattering is used to model the data. These models provide a satisfactory description of the data for both the IV characteristics and the resistance measurements.
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