In this thesis we present and scrutinize a technique to reconstruct the surface profile of a sample using a low energy electron microscope (LEEM). This technique is added to the rich catalogue of...Show moreIn this thesis we present and scrutinize a technique to reconstruct the surface profile of a sample using a low energy electron microscope (LEEM). This technique is added to the rich catalogue of surface analysis techniques available in LEEM.We demonstrate that the surface profile of a sample can be deduced from the local tilt angles. This is done by studying the change in diffraction pattern. The procedure is then applied to two samples: a flake of MoTe2 that has a bump on it and a flake of MoTe2 that has collapsed into a trench. We show that we can correct for lensing effects that are introduced due to a non-flat surface. In these samples we determine the local tilt angle with an accuracy of 0.3°.Show less
In this study, the work function difference between the two terminations of SrTiO3 (STO) is investigated. The two terminations i.e. SrO and TiO2 are formed by annealing the STO sample at 1200°C for...Show moreIn this study, the work function difference between the two terminations of SrTiO3 (STO) is investigated. The two terminations i.e. SrO and TiO2 are formed by annealing the STO sample at 1200°C for 12 hours in air at ambient pressure. To collect more information about this perovskite oxide, we study this material in AFM and LEEM.We distinguish the two terminations, calculate the step heights between the unit cells and record LEEM Multi dark-field images showing different surface reconstructions. To measure the work function difference, three methods are used: Energy-filtered PEEM, Intensity-Voltage curves and the comparison between LEEM real-space data and simulations. All methods showed that the work function difference is lower than predicted by theory.Show less
Van der Waals materials such as graphene are layered materials that can be created in single atom thickness. In most cases there is more than one way to stack subsequent layers, often leading to...Show moreVan der Waals materials such as graphene are layered materials that can be created in single atom thickness. In most cases there is more than one way to stack subsequent layers, often leading to domains of different stackings. In this work stacking domains in few layer stacks of graphene and \mos are studied using Low Energy Electron Microscopy. From dark field LEEM measurements on few layer epitaxial graphene on SiC it is concluded that two different types of domains exists: domains created from nucleation during growth and triangular stress domains induced from lattice mismatch with the underlying SiC. A detailed comparison between epitaxial and quasi-freestanding graphene is made. As part of this comparison deintercalation of the latter to reform the former is performed. The hydrogen diffusion out of the material occurring here is studied and linked to defects in the material and aforementioned stacking domains. For MoS2 no domains were analysed within the scope of this project, but a comparison of flatness for different substrates is made and using muLEED measurements a method to determine the number of layers is demonstrated and the two different orientations of the 2H polytype are experimentally identified.Show less
In medical imaging, model observers are used to define a new method of task based image quality assessment. In this thesis a novel search algorithm is presented that detects possible lesions in a...Show moreIn medical imaging, model observers are used to define a new method of task based image quality assessment. In this thesis a novel search algorithm is presented that detects possible lesions in a digital anthropomorphic 2D and 3D lung phantoms and defines the detectability of the candidate lesions using a non-prewhitening matched filter with an eye filter (NPWE) model observer. Sets of phantom images were simulated for a range of noise levels and two types of noise (Gaussian white noise and CT-like noise). The candidate lesions were classified as true positives and false positives. A proof of concept study showed promising results in the detectability trends the search algorithm described. The trends showed that with increasing noise levels the detectability of true positives decreased. When comparing the detectability indexes of the true positives and false positives, the differences between them became smaller for increasing noise levels. In the future, the algorithm can be applied to the analysis of real CT scans of a lung phantom containing lesions, and used to obtain Free Response Operating Characterisic (FROC) curves.Show less
In this work, we investigate methods to determine the average length for cotunneling in self-assembled gold nanoparticle arrays spaced with alkanethiols. Cotunneling currents can be as low as 10 fA...Show moreIn this work, we investigate methods to determine the average length for cotunneling in self-assembled gold nanoparticle arrays spaced with alkanethiols. Cotunneling currents can be as low as 10 fA, requiring the development of robust measurement techniques to lower the noise floor. We present a comparison of different methods for finding the effective cotunneling length N. Preliminary findings on a variety of arrays indicate the onset of the cotunneling regime, but that there is no distinction in N between choice of alkanethiol in the array.Show less
Combining an applied thermal potential with Conductive Atomic Force Microscopy (C-AFM) enables the measurement of thermoelectric properties of Self-Assembled Monolayers (SAM). Such measurements can...Show moreCombining an applied thermal potential with Conductive Atomic Force Microscopy (C-AFM) enables the measurement of thermoelectric properties of Self-Assembled Monolayers (SAM). Such measurements can be used to show the presence of destructive quantum interference in molecules. To study the feasibility of measuring thermoelectric potentials over SAMs with C-AFM, we have simulated the temperature distribution around the tip in a typical C-AFM setup with finite element simulations in Comsol. These show that a sufficiently large temperature difference can develop across the molecular layer to measure the thermoelectric properties.Show less
Electromigration in bismuth is studied as a way to create bismuth(111) bilayers. Temperature-dependent electromigration measurements have been performed and a model incorporating Joule heating is...Show moreElectromigration in bismuth is studied as a way to create bismuth(111) bilayers. Temperature-dependent electromigration measurements have been performed and a model incorporating Joule heating is used to describe those. An activation energy for diffusion between 100 and 180meV is found. Furthermore, in-situ electromigration experiments have been performed in a scanning electron microscope. This allowed us to link events in the conductance traces of bismuth constrictions during electromigration to visual features. Specifically, remerging of the bismuth electrodes was found to cause increases in conduction.Show less
