Quantum chemical molecular dynamics (QM/MD) simulations of ensembles of C2 molecules on the Ni(111) terrace show that, in the absence of a hexagonal template, hydrogen, or step edge, Haeckelite as a metastable intermediate is preferentially nucleated over graphene [1]. The nucleation process is dominated by the swift transition of long carbon chains towards a fully connected sp2 carbon network. Starting from a pentagon as nucleus, pentagons and heptagons condense during ring collapse reactions, which results in zero overall curvature. To the contrary, in the presence of a coronene-like C24 template, hexagonal ring formation is clearly promoted, in agreement with recent suggestions from experiments. In the absence of step edges or molecular templates, graphene nucleation follows Ostwald’s ‘rule of stages’ cascade of metastable states, from linear carbon chains, via Haeckelite islands that finally anneal to graphene. Furthermore, we found similarities between graphene nucleation and other critical phase transition phenomena [2]. Our analysis confirms the existence of a critical nC-C/NC value close to 1.0 (‘H’ model) and 1.1 (‘G’ model), where nC-C is the number of C-C bonds and NC is the number of carbon atoms. As in random graph theory, above this critical value, the further conversion of linear carbon chains to sp2 carbon polygons leads to the emergence of a fully networked carbon structure. Thus we find the theory of selforganized criticality [2] applicable to discuss the sp2 network formation from sp chains in the formation mechanism of graphenes. References: [1] Wang, Y.; Page, A. J.; Nishimoto, Y.; Qian, H.-J.; Morokuma, K., Irle, S.; JACS (just accepted) (2011). [2] Bak, P.; Tang, C.; Wiesenfeld, K., Phys. Rev. Lett. 1998, 59, 381.
Haeckelite and Graphene Formation on a Metal Surface: Evidence for a Phase Transition at the Edge of Criticality Ying Wang, Alister J. Page, Yoshio Nishimoto, Hu-Jun Qian, Keiji Morokuma, Stephan Irle Department of Chemistry, Graduate School of Science, Nagoya University, Japan Fukui Institute for Fundamental Chemistry, Kyoto University, Japan . Kyoto University Nagoya University http://kmweb.fukui.kyoto-u.ac.jp/nano http://qc.chem.nagoya-u.ac.jp Talk XX5.6 2012 Materials Research Society Spring Meeting, San Francisco, CA April 11, 201
Transcript
Haeckelite and Graphene Formation on a Metal Surface: Evidence for a Phase Transition at the Edge of Criticality
Ying Wang, Alister J. Page, Yoshio Nishimoto, Hu-Jun Qian, Keiji Morokuma, Stephan Irle
Department of Chemistry, Graduate School of Science, Nagoya University, JapanFukui Institute for Fundamental Chemistry, Kyoto University, Japan
