Towards Ultrafast and Ultrasmall: Construction of a THz-STM

Abstract

The combination of high spatial and temporal resolution is still a limiting factor in the field of surface science. Only very recently, a novel experimental approach has been presented that allows versatile access to this regime by combining ultrafast Terahertz (THz) pulses with the extraordinary spatial resolution of scanning tunneling microscopy (STM): The so-called THz-STM. In this device, the THz pulses act as ultrafast transient bias voltage and hence allow to unravel the ultrafast physics of highly localized electronic states via pump-probe experiments. In this thesis, we describe the process of establishing this novel technique in our group. We firstly discuss the new configuration of the designated lab, the design and alignment of our THz-source as well as its characterization using electro-optic sampling. Subsequently we describe the modifications performed on the preexisting STM to facilitate the coupling of THz radiation. The THz-STM was thoroughly tested in different scenarios showcasing its capabilities. We initially present data originating from optical-pump, THz-probe measurements based on photoelectron emission, confirming the successful coupling of ultrashort THz pulses into the STM. Subsequent measurements using field emission resonances show the stability of our system under cryo conditions and using junctions at tunneling distances. Experiments involving Kondo resonances of point defects in MoS2 prove the sensitivity of our THz-STM when used with small nonlinearities and are used to perform exemplary spatially resolved measurements. Finally we present preliminary time-resolved data as part of an outlook.