Levente Tapasztó and his colleagues at MTA’ Institute for Technical Physics and Materials Science affiliated with MTA’ Research Centre for Natural Sciences managed for the first time to regulate the structural rippling of graphene with an accuracy of less than one nanometer (0.7nm). Compared to the previous 300 nanometer wavelength, it is an immense advancement. This is the second nanotechnology procedure at the institute’s laboratory dedicated to the study of nanostructures, which sets a new record in graphene research.
The mechanics of membranes are most frequently encountered during the study of biological systems, e.g. in cell membranes. Such studies belong to the discipline called soft matter physics, while crystallites belong to solid-state physics. The link between these two distinct study fields could be graphene because of its crystallite structure and also because it is the thinnest possible membrane which behaves as a very soft material to vertical deformations with regard to classical mechanics. These two characteristics co-existing in graphene allow for a controlled modification of its electronic band structure, i.e. its electronic behaviour, through mechanic deformations. This technology is called strain-engineering. Levente Tapasztó and his colleagues could generate nanometer-sized periodic modulation in the atomic structure of suspended graphene nanomembranes in a controlled manner through thermically induced voltage. It is remarkable for two reasons. On one hand, it creates an opportunity to study the mechanic behaviour of membranes in a range where the wavelength of the deformation can be measured against the lattice constant. The researchers established that classic continuum mechanic equations fail in the evaluation of nanoscale graphene deformations, and it is only quantum mechanic models based on the atomic bond mechanisms that can describe the formation of nanoscale graphene rippling. According to classical mechanics there is no membrane from any known material which could endure such structural rippling at such a small wavelength. This achievement is essential in designing graphene-based nano-electromechanical systems (NEMS). By reducing the wave sizes to the nanometer range, structural waves can have a significantly enhanced effect on the band structure. MTA researchers at the ITPMS could generate a superlattice for the first time in graphene, and this could prove to be the foundation for a number of potential applications. This achievement is expected to contribute to the formation of a forbidden band in the band structure of graphene without generating errors (graphene edges). In addition, the spread of charge carriers could be rendered anisotropic in the plane of the graphene, since a slowdown of the electrons heading towards the structural waves could occur. The research phase was conducted at the Joint Korean-Hungarian Nanolaboratory. The graphene samples were compiled jointly under the leadership of the Hungarian laboratory’s coordinator, László Péter Bíró together with the team led by Chanyong Hwang (Korea Research Institute of Standards and Science), while theoretical simulations were carried out in co-operation with theTraian Dumitrica-led team from the University of Minnesota. Before the next Nature Physics issue comes out, the scientists publish their achievements as an Advanced Online Publication (L.Tapasztó, T. Dumitrica, S. J. Kim, P. Nemes-Incze, C. Hwang & L. P. Biró, Breakdown of continuum mechanics for nanometre-wavelength rippling of graphene. Nature Physics, DOI:10.1038/NPHYS238). In the institute’s laboratory dedicated to nanostructrural research this is the second nanotechnology procedure which sets an example in the field of graphene research, since the accuracy of the previously developed STM lithographic nanotailoring procedure (2.5 nm wide graphene ribbon) has not been superseded ever since (L. Tapasztó et al. Nature Nanotechnol. 3, 397 ).