van der Waals epitaxy of solid C 60 on graphene sheet Akihiro Hashimoto a, ⁎, Kohsuke Iwao a , Satoru Tanaka b , Akio Yamamoto a a Department of Electrical and Electronics Engineering, Fukui University, Japan b Department of Applied Quantum Physics and Nuclear Engineering, Kyusyu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan ABSTRACT ARTICLE INFO Available online 20 March 2008 Keywords: Solid C 60 layer Graphene van der Waals epitaxy We have investigated on the van der Waals epitaxy of a solid C 60 layer on a graphene sheet and have first successfully achieved it. It is expected that the hetero-structures of the solid C 60 layer and the graphene sheet opens new opportunities in the carbon nano-electronics. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Graphene has been a great interest for its peculiar properties due to the ideal 2-dimensional and/or the first discovered massless Dirac fermions system in the condensed matters [1]. Very recently, there are many reports on the peculiar graphene properties such as the anoma- lous quantum Hall effects [2,3], the minimal conductance at the zero gate voltage [2–4], various phonon properties [5], the ballistic transport nature in the FET structure [6] and so on. Moreover, it has been reported that the electronic structures of the graphene are easily modified through the doping. T. Ohta et al. have been reported the controlling the electronic structures of bilayer graphene that the potassium doping accompanied with the graphene bilayer formation process leads to the band gap opening for the gap less electronic structures of the non-doped graphene [7]. Moreover, the theoretical studies of the graphene nano-ribbon have predicted that the excellent electrical properties of the carbon nanotube come from the nan- ometer sized graphene. On the other hand, the solid C 60 layers have the face centered cubic structure at room temperature [8] and show a semiconductor's nature with the band gap energy of about 1.6 eV [9]. Potassium doped solid C 60 layer becomes the superconductor with a rather high critical temperature of 19.8 K [10], and the critical temperature becomes up to 33 K for the RbCsC 60 layer [11]. Moreover, the solid C 60 layer is well known as the n-type organic material with the highest electron mobility [12]. We have already reported that the single crystalline solid C 60 layer with twin defect can be grown on the single AlN crystal layer by the van der Waals epitaxial mechanism under the optimum growth condition [13]. We have also fabricated the solid C 60 FET with Diamond & Related Materials 17 (2008) 1622–1624 ⁎ Corresponding author. E-mail address: hasimoto@fuee.fukui-u.ac.jp (A. Hashimoto). the AlN insulator layer and have investigated on the characteristics of the FET that shows the top-class mobility [14]. The results indicate that the single crystalline interface between the insulator and the active C 60 layers is very important from the device viewpoint. However, it has not been achieved yet any ideal hetero-interface between the insulator and the solid C 60 layer until now. Although the most conventional and studied interface consists of the SiO 2 and the C 60 layers, the interface has a fatal short point as a disorder interface, which comes from the amorphous solid C 60 deposition on the amorphous SiO 2 insulator layer [15], or the damages induced by the gate oxide layer formation [16]. Those research results strongly indicate that the interaction between the graphene sheet and the solid C 60 layer has a meaningful importance from the point of view of the planar type carbon nano-electronics development. Especially, the van der Waals epitaxy of the solid C 60 layer on the graphene sheet and the properties of the interface between them are very interesting. In this paper, we have reported on the first successful growth of a solid C 60 layer on graphene sheet by van der Waals epitaxy. 2. Experiment Graphene sheets were formed by high-temperature sublimation technique of Si from the 6H–SiC substrate in the vacuum [17,18]. The sublimation was performed at 1600 °C for 270 s. The SiC substrate was annealed under the hydrogen ambient at 1650 °C before the sublimation of Si to form the clean and the step-ordering surface. The van der Waals epitaxy of the solid C 60 layer was performed at 100– 160 °C for 1–3 h by the conventional solid source MBE system [19,20]. The pre-annealing of the graphene/SiC substrate at 500 °C was performed for 10 min. The in-situ monitoring of the epitaxial growth process was performed by the reflection high-energy electron diffraction (RHEED) technique and the surface morphology of the grown layer was characterized by atomic force microscope (AFM). 0925-9635/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2008.03.011 Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond