The Scanning Tunneling (STM) and the Atomic Force (AFM) microscopes, due to their high spatial resolution and manipulation capabilities, have greatly contributed to the emergence of Nanoscience and Nanotechnology. The advance has been particularly spectacular in AFM, where the development of the frequency modulation operation mode (FM-AFM) has paved the way for atomic-scale imaging, manipulation and characterization of the tip-sample forces on all kinds of surfaces . In this talk, we focus on the application of these techniques to carbon nanostructures (graphene, carbon nanotubes and fullerenes). The simple honeycomb structure shared by these materials represents both a perfect testing ground and a fundamental challenge for scanning microscopy imaging. STM can achieved atomic resolution in graphite even in ambient conditions but, after 25 years of research, still there is no consensus whether the maxima in the atomic scale images correspond to atoms or to the hollow sites. To tackle this long-standing problem, we have performed complex first-principles calculations of forces and currents between a tip and carbon nanostructures. Our results explain the rich variety of image patterns observed in both AFM and STM experiments in terms of two factors: (i) the tip-sample distance and (ii) the chemical reactivity of the tip . Based on this work, we have explored the electronic properties of epitaxial graphene on metals, both in the case of the pristine layer and in the presence of carbon vacancies, where the calculations help to correlate the structure of the defect with the experimental STM images . These calculations also shed light on the possible magnetic state associated with these defects, predicted but not experimentally confirmed, in graphite . Finally, we'll discuss the microscopic mechanisms behind the different steps involved in our recent proposal for a controlled synthesis of heterofullerenes based on a surface-catalysed cyclo-dehydrogenation process[9,10]. With this approach it is possible to transform with an almost 100% efficiency polycyclic aromatic hydrocarbons like C60H30 and C57N3H33, deposited on Pt(111) surfaces, into C60 fullerenes and triazafullerenes C57N3.
 S. Morita et al, Noncontact Atomic Force Microscopy, 2nd vol. (Springer-Verlag, Berlin, 2010).
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Ruben Perez got his Ph.D. from the Universidad Autonoma de Madrid (UAM) in 1992. After a three-year postdoctoral stay at the Cavendish Lab, University of Cambridge, he returned to the UAM, where he is now a Professor of Condensed Matter Physics and leader of the SPM Theory and Nanomechanics Group. His research focuses on the ab initio modelling of different problems in Materials Science and Nanotechnology that involve forces and currents at the atomic scale, working in close collaboration with experimental groups worldwide.
Invited by G. Cuniberti
Within the nanoSeminar
last modified: 2021.10.02 Sat
Prof. Dr. Gianaurelio Cuniberti
Institute for Materials Science
visitors and courier address:
01062 Dresden, Germany