The application of the Kelvin probe in materials science.
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This thesis reports on the application of the Kelvin probe in materials science and in particular on the study of metal and semiconductor surfaces in both ambient and UHV environments. The concept of the work function φ and its importance as a parameter in materials science is discussed in the context of novel technological applications. The various methods to determine the work function are reviewed. The main measurement technique used here – the Kelvin probe - is described in detail. The Kelvin probe measures local work function differences between a conducting sample and a reference tip in a non-contact, truly non-invasive way over a wide temperature range. However, it is an inherently relative technique and does not provide an absolute work function if the work function of the tip (φtip) is not known. Therefore, a novel technique has been developed to measure φtip with the Kelvin probe via the photoelectric effect, thus combining the advantages of both methods to provide the absolute work function of the sample surface. High and low work function surfaces were generated as target materials for a novel ion source based on hyperthermal surface ionisation: oxidised rhenium exhibits the highest work function of 7.15eV at a temperature of ~900K whereas the lowest work function of ~2.54eV was measured on lanthanum hexaboride, LaB6. The process of thermal and hyperthermal surface ionisation (SI, HSI) as well as the generation of hyperthermal molecular beams is discussed and a model of the surface ionisation process is developed to estimate its efficiency. Experimental data of SI and HSI are presented. The application of the Kelvin probe for the detection of defects and impurities in semiconductors, namely iron contamination, is demonstrated via two methods based on the measurement of the surface photovoltage. We find that both methods yield a lower surface potential and surface charge for iron contaminated wafers compared to a clean sample and therefore can be used as an indicator for chemical contamination on semiconductor surfaces.