Inelastic electron tunneling spectroscopy (IETS) is a tool used to research the vibrational modes in a tunneling junction. This report describes the setup of a cryogenic scanning tunneling...Show moreInelastic electron tunneling spectroscopy (IETS) is a tool used to research the vibrational modes in a tunneling junction. This report describes the setup of a cryogenic scanning tunneling microscope (STM). Potentially this STM can be used in the research to the edge modes of graphene edge junctions. Gold samples were used for the calibration of the z stage of the setup by using two different methods (histogram based/line cut based). Experiments at cryogenic temperatures seemed to have difficulties measuring topographic images at 77K. These difficulties are most likely caused by condensation of atmospheric gasses still present in the system. To solve this problem, a heater is required to prevent material condensing on the sample or tip. In order to implement IETS in the system it is proposed to used a combination of a heater and thermometer in order to keep the system clean.Show less
Twisted bilayer graphene at a magic angle might be used to increase our understanding of high temperature superconductivity. Studying 2D-materials with an Atomic Force Microscope (AFM) yields...Show moreTwisted bilayer graphene at a magic angle might be used to increase our understanding of high temperature superconductivity. Studying 2D-materials with an Atomic Force Microscope (AFM) yields information on its surface properties, such as its topography or its conductivity. In this thesis, AFM work has been done on different samples, with the final goal of identifying moiré patterns. AFM tapping mode shows clear roughness decline of a silicon/silicon oxide wafer after annealing 500 degrees for 24 hours. AC mode on layered graphene placed on an identical substrate was able to identify different atomic layers clearly. Sputtered gold, graphite and evaporated gold have been analyzed with current sensing AFM. Finally, I/V-curves have been acquired with AFM contact mode on sputtered gold, corresponding to theoretical expectations. All initial work has been done to measure I/V curves and start conductive AFM measurements on twisted bilayer graphene, in hopes of identifying moiré patterns in the current map.Show less
This thesis describes a part of the first steps towards DNA sequencing via tunneling current measurement though graphene electrodes. The focus lies in particular on the optimization of the...Show moreThis thesis describes a part of the first steps towards DNA sequencing via tunneling current measurement though graphene electrodes. The focus lies in particular on the optimization of the fabrication and the characterization of the graphene electrodes. Progress has been made in the fabrication of atomically sharp graphene edges supported by a Si/SiO2 substrate with prefabricated contact pads. The optimization of reactive ion etching parameters was analyzed using SEM. However some problems were uncovered with the prefabricated wafers, since the contact pads seem to cause to large a step for the graphene to bridge. This leads to the tearing of graphene after some time when unsupported by a protective top layer. The creation of a tunneling junction with two graphene electrodes using a modified STM device confirmed the previously found results. The same hysteresis in the I-Z curve was observed which is likely due to carbon bonds forming between the two graphene electrodes, however more research is necessary to fully analyze the edge composition of the graphene. Knowing fully what the edge of the graphene looks like on the atomic scale is also important for future steps since this is needed to chemically functionalize the graphene edge and to tunneling current measurements more reproducible. The prefabricated wafers in combination with new sample holders with integrated wiring made to fit the STM also made the use of a backgate possible. However this caused some instability in the tunneling current which needs to be resolved before any valuable measurements can be taken. These measurements should also give us information about the composition of the tunneling junction that is formed.Show less
To better understand the LEEM spectra of 2D materials we explored usingtransfer matrices to model them. We applied transfer matrices to find ananalytical expression for the LEEM spectra of graphite...Show moreTo better understand the LEEM spectra of 2D materials we explored usingtransfer matrices to model them. We applied transfer matrices to find ananalytical expression for the LEEM spectra of graphite. We found that itresults in an approximate solution that correctly predicts the position ofthe minima and general shape of the curve in the 0-25 eV range. We alsoapplied transfer matrices to model the spectrum of few-layer grapheneon bulk hexagonal boron nitride. The modeling of graphene on hBN wasdone in a coherent, incoherent and a modified coherent case. We foundthat the model manages to show the 8 eV minima in the coherent case.But the general shape we found is less accurate than for graphite. Theother cases did not model the 8 eV dip of the spectra.Show less
The electronic properties of graphene on silicon carbide have opened up a wide variety of technological applications. During the growth of this graphene, thermal contraction causes strain between...Show moreThe electronic properties of graphene on silicon carbide have opened up a wide variety of technological applications. During the growth of this graphene, thermal contraction causes strain between the graphene layers. This strain induces domains of different crystallographic stacking which influence the electronic properties. The shape and geometry of those domains are given by the local strain and can be seen on images obtained with low-energy electron microscopy. In this research, we extract strain maps from these images to gain more understanding about what drives the formation of these stacking domains. We find that the substrate step edges affect the shape of the domains and therefore provide new parameters to be used for strain engineering.Show less
Motivated by the recent discovery of superconductivity in Magic Angle Twisted Bilayer Graphene, we discuss preparatory work for STM measurements on micrometer-sized graphene flakes. We develop and...Show moreMotivated by the recent discovery of superconductivity in Magic Angle Twisted Bilayer Graphene, we discuss preparatory work for STM measurements on micrometer-sized graphene flakes. We develop and fabricate a dummy sample for testing capacitive navigation in any STM setup with an XY-stage. Furthermore, we calculate the effect of a biased STM tip on the charge distribution in a graphene bilayer. We also estimate the chemical potential shift in a gated graphene sample as a result of the probe tip. All results unambiguously suggest that the STM tip will strongly influence the electrical behavior of the graphene system.Show less
This thesis deals with the use of conducting AFM to image the topography and conducting properties of graphene on SiO2. Specifically,the current image will be used to distinguish graphene from SiO2...Show moreThis thesis deals with the use of conducting AFM to image the topography and conducting properties of graphene on SiO2. Specifically,the current image will be used to distinguish graphene from SiO2 and the height image to identify the edge of the wafer. These together can show how far graphene reaches this edge. For testing the usability of the Conducting AFM module measurements were also made on gold and on graphite. Lastly, specific settings were tested and discussed for optimal current imaging results.Show less
In this thesis, we describe a new sample production method for the graphene nanogap junction of the AMC group. This production method features a new, standardised, sample layout with integrated...Show moreIn this thesis, we describe a new sample production method for the graphene nanogap junction of the AMC group. This production method features a new, standardised, sample layout with integrated metal contacts and a back gate. A large part of the sample production is outsourced commercially. This leads to mass production yielding more reliable samples. We have also introduced some new pieces of equipment that make the rest of the sample production both easier and more efficient. Additionally, we have proposed a design for a new sample holder. This will allow us to perform the experiment in cryogenic environments.Show less
During this study, a device was developed which is capable of measuring the friction coefficient between two macroscopic solid samples for different rotation angles. It is based on an Anton Paar...Show moreDuring this study, a device was developed which is capable of measuring the friction coefficient between two macroscopic solid samples for different rotation angles. It is based on an Anton Paar rheometer. It can measure torques ranging from 10 nNm up to 200 mNm, while controlling the rotation angle with a minimum resolution of 10 nrad. The normal load exerted on the samples can be controlled with mN accuracy. Measurements on HOPG and silicon dioxide have verified that the instrument works and is capable of measuring very low friction coefficients as a function of the rotation angle between the two samples. The obtained friction coefficients are in agreement with values found in literature.Show less
