In this project, magneto-transport measurements are performed on exfoliated trigonal tantalum disulfide (1T-TaS2) flakes with a top-contact Hall-bar geometry. Transport measurements reveal the...Show moreIn this project, magneto-transport measurements are performed on exfoliated trigonal tantalum disulfide (1T-TaS2) flakes with a top-contact Hall-bar geometry. Transport measurements reveal the presence of charge density waves and therelatednearly-commensuratetocommensuratephasetransition. Thephase transition is shown to depend on both the thickness of the crystal and the cooling rate. The observed critical thickness is approximately 80 nm, relatively large compared to literature. A clear deviation from literature is observed in the resistive behavior during the transition. The increase in resistivity due to the transition is considerably smaller and less abrupt. This deviation may be attributed to partial switching of the crystal, i.e. only some of the layers switching to the commensurate phase. Hall effect measurements in the supercooled phase, i.e. below the suppressed phase transition, reveal large charge carrier density and extremely low mobility, both in agreement with literature. A down-turn is observed in the supercooled phase at low temperatures. This down-turn is also observed in literature, however its origin is not discussed. We propose that this down-turn is caused by weak anti-localization. The phase coherence length, extracted from fitting of the Hikami-Larkin-Nagaoka model (HLN)modeltotheweakanti-localizationpeaks,followsapowerlawwithexponent γ = −0.341±0.03. This exponent suggests that the electron transport is one-dimensional, substantiating the notion that in the nearly-commensurate phase, the electron transport is dominated by the domain boundaries.Show less
In this thesis research is presented into multiple unexplained phase transitions of the two antiferromagnets FePS3 and Fe1-xS (pyrrhotite). X-ray diffraction and resistivity measurements of...Show moreIn this thesis research is presented into multiple unexplained phase transitions of the two antiferromagnets FePS3 and Fe1-xS (pyrrhotite). X-ray diffraction and resistivity measurements of pressurised FePS3 show that this material undergoes at least two crystallographic phase transitions, strongly related to the appearance of an exotic metallic state when pressures over approximately 10GPa are applied. Magnetisation, specific heat and resistivity measurements of Pyrrhotite highlight for the first time the dual nature of the Besnus transition. Compelling evidence is presented that excludes the proposition of extrinsic magnetic coupling between differently ordered vacancy superstructures as the underlying mechanism. Instead the presence of local magnetic domain formation is highlighted.Show less
During this project we have tested and characterized a new cryogenic STM (Scanning Tunneling Microscope) with a uniquely designed coarse XY stage. We have used this STM the perform STM break...Show moreDuring this project we have tested and characterized a new cryogenic STM (Scanning Tunneling Microscope) with a uniquely designed coarse XY stage. We have used this STM the perform STM break junction experiments on both clean gold samples and samples covered by OPE-3 molecules. In the results for the clean gold samples we retrieve the characteristic and well known features of single atom gold wires. For the results of the samples covered by molecules we see faint traces of the molecules in the conductance histogram, although they are not as clear as compared to results in literature. Cryogenic experiments using this STM have proven to be difficult and only partially successful.Show less
Using the notched wire mechanically controllable break junction technique charge transport of a single-molecule junction, containing the OPE3 molecule, is studied at room temperature. By deposition...Show moreUsing the notched wire mechanically controllable break junction technique charge transport of a single-molecule junction, containing the OPE3 molecule, is studied at room temperature. By deposition of molecules from solution between two gold leads we were able to determine the conductance of the OPE3 at (1.6±0.3)·10−4G0. The measurement speed of the LabVIEW control program for this experiment was improved by more than a factor of 7 compared to the previous version.Show less
The structure and conductive behaviour of graphene was studied under breaking. We were able to break and reconnect graphene using the mechanical break junction and observed a change in conductive...Show moreThe structure and conductive behaviour of graphene was studied under breaking. We were able to break and reconnect graphene using the mechanical break junction and observed a change in conductive behaviour from ohmic to non-linear; a possible explanation for the effect was offered. SEM, AFM and Raman spectroscopy determined that no large structural damage was caused by the breaking, nor was a decrease in graphene quality towards the break edge observed up until 1 micron near the edge; graphene was established to be present to within at least 100 nm of the edge. Furthermore, a modified mechanical break junction design for a graphene nanojunction was tested and deemed complicated: it was advised to loosen the requirements for future experiments. Lastly, an approach to electrochemically etching a graphene nanojunction was tested and approached theoretically; it was deemed not feasible using current graphene transfer techniques.Show less
