Welcome to this autumn's first Linnaeus Physics Colloquium, a series of seminars delivered by renowned researchers in physics.
Lecturer: Rainer Timm, Synchrotron Radiation Research at the Department of Physics and NanoLund, Lund University
Title: Exploring Nanostructures with Scanning Tunneling Microscopy
Place: Kalmar – room N304, Norrgård. Växjö – through link, room D0073, building D. Live – through Adobe Connect, https://connect.sunet.se/cmp-kalmar.
Coffee and buns at 13.45 at Norrgård, room N304.
Illustration: STM image of a InAs nanowire, showing two transitions between the zincblende and wurtzite crystal phases.
Semiconductor nanostructures, such as clusters, quantum dots, or nanowires, are promising candidates for next generation (opto)electronic devices. They combine novel materials science properties, quantum-size effects, and a large flexibility in combining different materials. As an example, III-V semiconductor nanowires with superior charge carrier mobility and direct bandgap can be epitaxially grown on silicon substrates without interfacial defects. Due to the small size and high aspect ratio of most nanostructures, their properties are to a significant extend determined by surface effects. Therefore, detailed surface and interface characterization is crucial for understanding and improving the performance of nanowire-based devices. Scanning tunneling microscopy (STM) has proven to be a powerful tool for exploring surface structure and electronic properties at the atomic scale. However, the finite size, inherent anisotropy, and large aspect ratio of nanostructures are significant challenges for an STM experiment.
Here, I will present our different STM-based approaches for the atomic-scale characterization of III-V semiconductor nanowires in various geometries. We map heterostructures across interfaces between different crystal phases, different doping levels, or different semiconductor materials. By combining STM imaging with scanning tunneling spectroscopy measurements, we correlate the surface structure and local electronic properties at heterostructures with atomically sharp interfaces. Our most recent efforts include in-situ and operando studies, where we investigate nanowires during device performance or while their surface becomes modified. I will show examples of STM results that are relevant for fundamental materials science as well as for future tunnel field effect transistors or solar cells.