Material characterisation by means of alternative scanning tunnelling spectroscopy tools

Ever since its inception in the early 1980s, the Scanning Tunnelling Microscope (STM) has provided surface scientists with a powerful tool for the characterisation of all manner of conductive samples. By harnessing the possibilities of quantum mechanical tunnelling, the STM is capable of imaging and manipulating features down to the single atom scale. In addition to these qualitative tools, the STM also allows for the (semi-)quantitative analysis of samples through the use of Scanning Tunnelling Spectroscopy (STS). A large variety of different types of STS measurements exists, which can be roughly divided into three categories: open-loop, closed-loop and lock-in STS. Through the use of STS, such parameters as the work function, local density of states (LDOS) and band gap of a sample can be probed. While using the STM technique for qualitative measure- ments does not require a thorough understanding of the underlying theory, obtaining accurate quantitative results is often far more involved. Even when considering all con- ventional theoretical contributions to the tunnelling current, spectroscopy experiments occasionally yield unexpected results. As such, the main goal of this thesis is the study of several different spectroscopic configurations and tools in order to further elucidate the underlying mechanisms of the tunnelling process and the common pitfalls of spec- troscopy experiments. The performed measurements and simulations show that using ‘conventional’ formulas for the analysis of acquired spectroscopy data can lead to sig- nificant inaccuracies and deviations outside of a limited parameter range. Additionally, it was found that widely accessible closed-loop measurements can be used as a viable alternative to open-loop measurements which place more demands on the used hardware