RESEARCH ARTICLE Copyright © 2010 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Computational and Theoretical Nanoscience Vol. 7, 1–4, 2010 Structure and Thermal Stability of Co- and Fe-Intercalated Double Graphene Layers O. V. Mykhailenko 1 , Yu. I. Prylutskyy 1 , D. Matsui 1 , Y. M. Strzhemechny 2 ∗ , F. Le Normand 3 , U. Ritter 4 , and P. Scharff 4 1 Department of Functional Materials Physics, Kyiv National Shevchenko University, Volodymyrska Str., 64, 01601 Kyiv, Ukraine 2 Department of Physics and Astronomy, Texas Christian University, TCU Box 298840, Fort Worth, TX 76129, USA 3 Groupe Surfaces-Interfaces, Institut de Physique et Chimie des Matériaux, 23, rue du Loess, 67034 Strasbourg, France 4 Chemical Laboratory, Technical University of Ilmenau, Weimarer Str., 25, 98684 Ilmenau, Germany We theoretically investigated arrangement of Fe and Co atoms between two graphene planes. We showed that below 690 K Co atoms form stable lattices—hexagonal (with the lattice parameters a = 0354 nm and c = 0406 nm) and cubic (with the lattice parameter of 0.244 nm), whereas Fe atoms form cubic lattice only (with the lattice parameter of 0.281 nm). The system intercalated with Co atoms is stable enough at high temperatures up to 740 K, while the Fe/graphene system is stable only at ∼550–600 K. We also demonstrated that the basic distance between the graphene planes (0.342 nm) increases to 0.566 nm for Fe intercalation and to 0.567 nm for Co intercalation. Keywords: Graphene, Intercalated Metal, Thermal Stability, Quantum-Chemical Calculations. 1. INTRODUCTION Properties of a single or multiple graphene layers were of special interest for the past several years. Graphene’s unique band structure with a zero band gap and a linear energy dispersion for electrons and holes cause the elec- tric charge carriers in graphene behave as relativistic par- ticles with a zero effective mass. 1–2 Anomalous transport and field effects as well as room temperature magnetism make graphene nanostructures very promising for future electronic applications. 3–7 Graphene nanostructures also exhibit a great potential as spintronic materials because of the large mean free path, weak spin-orbital interaction as well as very long spin-scattering times. 8–9 It is natural to expect that new remarkable properties could be obtained upon modification of graphene or nanographene structures. Of special interest is modification of graphene layers by intercalation allowing control of the Fermi level, as well as the relative electron and hole concentrations, without any significant changes of the band structure. Understanding of the structure–property relationship is one of the most fundamental problems of material science, thus the goal of this work is to elucidate the structure of a double graphene layer intercalated with Co and Fe atoms as well as to investigate the thermal stability of this system. ∗ Author to whom correspondence should be addressed. 2. DESCRIPTION OF THE MODEL AND COMPUTATIONAL METHODS Our main object of interest, a double graphene layer, was modeled with 32 carbon atoms in each plane. The distance between the graphene planes was chosen to be 0.342 nm corresponding to the distance between graphene planes in disordered graphite (we selected the AAA order of car- bon atoms between the planes). Graphite intercalation is produced via introduction of the intercalate atoms into the inter-graphene space. As stated above, our goal was to study the system of two graphene planes, with Co or Fe atoms intercalated between them. Of particular interest are the positions of the metal atoms relative to each other and the carbon atoms, mutual positioning of the graphene planes in the presence of the metal intercalates (with or without keeping the AAA order of carbon atoms between the planes), as well as the stability of the system upon thermal treatment. The proposed model for calculating the structure of the metal layer between the two graphene planes was as fol- lows. Interaction between the metal atoms is expected to be caused by a high-energy pair-wise potential of a per- turbed Fe atom 10 described by a well-known Born-Mayer equation. With that, for Co, the inter-atomic distance var- ied between 0 and 0.244 nm obeying the Tersoff-Brener potential 10 with the radius-vector of 0.210 nm. The lengths of the C–C bonds in the graphene planes were chosen to J. Comput. Theor. Nanosci. 2010, Vol. 7, No. 6 1546-1955/2010/7/001/004 doi:10.1166/jctn.2010.1444 1