SPEAKER: Prof. Alexey E. Romanov (ITMO university, St. Petersburg, Russia)
TITLE: Disclination ensembles in graphene and pseudo-graphenes
ABSTRACT: In this talk, we consider wedge disclinations as the main structural defects in 2D graphene crystal hexagonal lattice. Disclinations are associated with improper carbon rings, i.e. rings having 4, 5, 7 or 8 members to the contrary of proper 6-member carbon rings constituting ideal 2D graphene crystal lattice. With the help of disclinations, we build the models for grain boundaries and other interfaces in graphene polycrystals as well as for pseudo-graphenes. The pseudo-graphenes are treated as graphene crystals with high density of periodically distributed disclinations with zero total charge. The geometry and energy of disclinated graphene configurations are analyzed with the help of molecular dynamics (MD) simulation technique and in the framework of the theory of defects in elastic continuum. In conclusion, it is argued that studying the properties of disclinations in graphene opens a new direction in graphene science and technology – graphene defect engineering.
IMAGE: Examples of pseudo-graphene crystals with disclination networks (a) 5-7A pseudo-graphene – phagraphene ; 5-7B pseudo-graphene ; 5-8-5D pseudo-graphene – PO graphene ; 4-8 pseudo-graphene . Red circles denote carbon atoms; empty and black triangles denote negative and positive disclinations, respectively.
SPEAKER: Alexey Romanov graduated St. Petersburg Polytechnic University in 1971 with a degree on the physics of metals. In 1981 Alexey defended his PhD thesis in solid state physics and in 1989 he completed a professorial thesis on screened disclinations in solids. He is an author or co-author of over 300 publications with h-index 43. The R&D he is involved in is mainly focused, but not limited to the structure and mechanical properties of solids with emphasis on defects in nanocrystals and thin films. One of his main activities was dedicated to the development of the theory of disclinations in crystals. At the moment Alexey is the Dean of the Faculty of Laser Photonics and Optoelectronics at ITMO University (St. Petersburg, Russia) and the Head of International Research Center of Functional Materials and Devices of Optoelectronics and Electronics. Incidentally, in the period of 2010-2014 Alexey Romanov held a professor position at the Institute of Physics, University of Tartu.
 Zh. Wang, X.-F. Zhou, X. Zhang, Q. Zhu, H. Dong, M. Zhao, A.R. Oganov, Phagraphene: A low-energy graphene allotrope composed of 5–6–7 carbon rings with distorted Dirac cones // NanoLetters 15 (2015) 6182.
 Ch.-P. Tang, Sh.-J. Xiong, A graphene composed of pentagons and octagons // AIP Advances 2 (2012) 042147.
 М.А. Rozhkov, А.L. Kolesnikova, I.S. Yasnikov, А.Е. Romanov, Disclination ensembles in graphene // Low Temperature Physics 44 (2018) 1171.
The current seminar is supported by the Graduate School of Functional materials and technologies receiving funding from the European Regional Development Fund in University of Tartu, Estonia.