Nanostructures

Department Head: Dr. Levente Tapasztó

website: www.nanotechnology.hu

The main activity of the Nanostructures Department is the research of two-dimensional (2D) materials. Their research activity covers the synthesis of 2D materials with various techniques, their atomic-scale characterization and modification, as well as exploring their electronic and optical properties. Beyond the investigation of graphene on-going for more than ten years, the focus of attention shifted towards the research of 2D transition metal chalcogenides and topological insulators. The Department is also active in the investigations of biological and bioinspired photonic nanostructures. Their results obtained in 2019:

• In the framework of the ERC Starting Grant they have shown that transition metal chalcogenide single-layers can be used as highly efficient substrates for single-atom catalysts. The substitution of the chalcogenide atoms by various hetero-atoms enables a much higher active site density than previously achieved. They have revealed the main factors influencing the catalytic activity and determined the trends of the activity of various 2D transition metal chalcogenide crystals with substitutional hetero-atom sites.
• Within the framework of the “Lendület” project they have investigated the Pt₂HgSe₃ crystal, employing low temperature scanning tunnelling microscopy and spectroscopy measurements. They have provided both experimental and theoretical evidence on the opening of a topological gap and the corresponding edge states. They have shown that the top layer of such a crystal has a 2D character due to its decoupling from the bulk crystal, and provided a possible explanation for the experimentally observed large doping levels. These results combined, provide compelling evidence of Pt₂HgSe₃ crystals as an air-stable, room temperature topological insulator.
• As part of the Korea-Hungary Joint Nanolaboratory, they have provided the first compelling experimental evidence on the mechanical strain induced direct to indirect bandgap transition in MoS₂ single-layers, by measuring both the optical (photoluminescence) and electronic (tunnelling spectroscopy) bandgap of the same crystal.
• Within the Graphene Flagship project, they have demonstrated the closely epitaxial CVD growth of 2D MoSe₂ layers on graphite substrate. They have shown that for the MoSe₂ lattice, the energetically most favourable configuration is the zero rotation angle relative to the underlying graphite lattice. This enables the relatively simple and cheap growth of large-area 2D MoSe₂ crystals of high structural quality.
• By combination STM measurements and simulations they have revealed the effect of mechanical strain on the periodicity of graphene superlattices. They have developed a theoretical method that enables the determination of the mechanical strain distribution in graphene based on the experimentally measured superlattice morphology.

They have investigated the stability of the blue colour generated by nanostructures on the wing scales of butterflies as a function of location and time. The butterflies were investigated over a time span of 100 years. The location of the investigated butterflies ranged from Western Europe to Eastern Asia. While the structural colour displayed a remarkable stability over time, a clearly detectable colour difference has been observed between butterflies from Europe and Asia.