This research aims to develop a Scanning Tunneling Microscope (STM) at milli-Kelvin temperatures inside a dry-dilution refrigerator, at the Oosterkamp Group. Getting the STM to operate properly in...Show moreThis research aims to develop a Scanning Tunneling Microscope (STM) at milli-Kelvin temperatures inside a dry-dilution refrigerator, at the Oosterkamp Group. Getting the STM to operate properly in these extreme conditions will allow us to do scanning and spectroscopy measurements with improved resolution. However, these extreme conditions also give rise to challenges. Specifically, we analyse the contributions of the pulse tube, which causes mechanical and acoustical vibrations. We determined that the dominant vibrations entered through microphonics around the I/V- converter and its cables. This gave rise to 30 pARMS noise. By mounting the I/V-converter directly to the cryostat and fixing the cables we success- fully reduced the effect of microphonics to an upper-bound of 4 pARMS, and see potential to improve on this result. Through the feedback system this upper-bound would give rise to 0.02 A ̊ RMS amplitude oscillations of the tip-sample distance. This should not prevent us from achieving step- edge resolution or atomic resolution. Furthermore, we present new scans at room-temperature with significantly improved resolution and a scan at ultra-low temperature with a visible step-edge for the first time since 2014Show less
Scanning Tunneling Microscopy (STM) is a technique that allows its user to make scans of the surface topography of a sample. Via a capacitive approach, a tip is brought in close proximity to the...Show moreScanning Tunneling Microscopy (STM) is a technique that allows its user to make scans of the surface topography of a sample. Via a capacitive approach, a tip is brought in close proximity to the sample, by which eventually a tunneling current is measured that is used to obtain a scan. It can be interesting to do STM experiments at extremely low temperatures (< 4 K), which can be done by placing an STM into a dilution refrigerator. It is difficult to do so in a dry dilution refrigerator, because of the pulse tube system that brings lots of mechanical vibrations. This research shows the performance of the newly developed `PAN-motor' and `linear cryo-walkers', two new types of motors for STM-approaches at extremely low temperatures. The cryo-walkers in particular have allowed for a full approach at millikelvin temperatures due to its low heat dissipation, whereas this approach normally has to be done above 4 K. By realizing dry dilution refrigerator STM, more research at millikelvin temperatures would be made possible, due to these dry dilution refrigerators being closed systems, allowing for time-unlimited measurements. This advancement could allow for experiments with low T_c superconductors, or shot noise experiments with the new Multi-LC circuit, that has shown to enable the measurement of shot noise with a total measuring time of \tau \approx 98 h.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
