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| Hauptseite > Publikationsdatenbank > Multi-tip scanning tunneling potentiometry on thin bismuth films and topological insulators in a cryogenic system |
| Hauptseite > Publikationsdatenbank > Multi-tip scanning tunneling potentiometry on thin bismuth films and topological insulators in a cryogenic system |
| Dissertation / PhD Thesis | FZJ-2025-04647 |
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2023
RWTH Aachen University
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Please use a persistent id in citations: doi:10.18154/RWTH-2023-07800
Abstract: A multi-tip scanning tunneling microscope (STM) is a great tool to investigate charge transport properties of nanostructured surfaces. This work focuses on the utilization of multi-tip STM implemented scanning tunneling potentiometry (STP) measurements, which allow for the simultaneous acquisition of topography and potential information of the sample under investigation. A detailed insight into the measurement principles and setup as well as theoretical considerations on this measurement method is given in chapter 2. With the means of STP at hand, chapter 3 makes charge transport around nanoscale defects in thin bismuth{012} films, which crystallize in a black phosphorus like structure, the subject of discussion. Potential maps recorded around those defects reveal the formation of transport dipoles, which exhibit different characteristics depending on the underlying transport regime. Comparing the measurement data with numerical calculations and resistor network simulations gives indications for the transition from classical to quantum mechanical charge transport in real space. The results presented in this chapter motivate the need for a new STP setup at cryogenic temperatures, which is introduced in chapter 4. The chapter reports a new four-tip STM seated in a static bath cryostat combined with a scanning electron microscope (SEM) used to monitor the tip movements. Additionally, the STM's and SEM's performance properties are characterized and the ultra-high vacuum chamber and cryostat as well as the vibration isolation system are described. Chapter 5 presents potentiometry measurements in the cryogenic setup. The first part of the chapter discusses thermo voltage signals in thin Bi(001) lms crystallizing in a hexagonal structure. Those measurements illustrate the existence of edge states depending on the step edge type. Furthermore, a performance benchmark for STP measurements in the setup is established. The second part of the chapter characterizes the temperature dependence of one-dimensional crystal defects and step edges in the ternary topological insulator system (Bi1-xSbx)2Te3. It demonstrates a decreased line defect conductivity at lower temperatures, seemingly contradicting an increased suppression of backscattering in topological surface states. A suppressed backscattering can be expected at low temperatures due to less multi-scattering events at crystal defects.
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