Seeing nanostructures in an entirely new way
Quantum structures consisting of a few thousand atoms have attracted significant research efforts due to their potential use in quantum information technologies. In particular, self-patterning of semiconductor surfaces by liquid metal droplets has been established for the fabrication of quantum structures with the desired electronic and optical properties. Until recently, however, the structure formed could only be analysed based on snapshots of quenched samples taken with scanning probe microscopies. While these techniques provide valuable information, the actual growth process could only be indirectly inferred. The project TAQUS (Tailored quantum structures) aimed to fill this gap. With EU funding, scientists established the first low-energy electron microscope in Europe. Although it uses electron lenses similar to conventional electron microscopes, it differs from them in the energies that electrons have when they interact with the sample surface. As a result, this unique system is surface sensitive and probing in depth is tuned by varying the electrons' energy. The scientists used the new microscope to acquire real-time movies of quantum structure assembly. Specifically, movies of gallium arsenide quantum ring formation were obtained as they were formed during droplet epitaxy. These observations formed the basis for the development of a theoretical model of how different quantum ring morphologies arise. TAQUS has offered the means to tailor quantum structures from the collective behaviour of atoms to the needs of quantum computing applications. The follow-up focuses on complementing low-energy electron microscopy with imaging techniques, including annular dark-field imaging, to extract additional nanostructural information.
Keywords
Semiconductor, quantum structures, TAQUS, low-energy electron microscope, quantum computing
