Nanostructuring Of Epitaxial Graphene Layers On Sic By Means Of field-Induced Atomic Force Microscopy Modification

Nanostructuring of epitaxial graphene layers on SiC by means of field-induced atomic force microscopy modification
G. Rius, N. Camara, P. Godignon, and F. Pérez-Muranoa
Instituto de Microelectrónica de Barcelona (IMB-CNM, CSIC), Campus UAB, 08193 Bellaterra, Spain

N. Mestres
Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain

Received 7 July2009; accepted 14 September 2009; published 7 December 2009 Micrometer-size graphene ribbons are generated by epitaxial growth on SiC substrates and contacted by electron beam lithography. The isolated graphene islands are patterned at nanometer scale by atomic force microscopy AFM under the application of an external polarization to the graphene layers. Contrary to previous reports, the patterningcan be made at positive and negative polarizations and using significantly lower absolute voltages. The technique is used to tune the electrical resistance of the graphene ribbons. Combination of graphitization of SiC and AFM nanopatterning is, in consequence, a powerful approach for the fabrication of prototyped graphene-based nanoelectronic devices. © 2009 American Vacuum Society. DOI:10.1116/1.3250208

I. INTRODUCTION Graphene is a promising material with unique physical properties for nanoelectronics.1 Phenomena such as quantum Hall effect or spin transport have been investigated, and the fabrication of electron devices, such as single electron transistors and bilayer transistors, has been demonstrated.2,3 However, the feasibility of practical graphene-based electronics is constrainedby the requirement to completely control the properties, dimensions, and localization of the graphene layers. Epitaxial graphene on SiC is a suitable option for the realization of nanoelectronic devices.4 In this case, the synthesis technique for graphitization consists of Si sublimation of SiC substrates. We have recently demonstrated that this method provides high quality, copious, and largesize graphene layers in a controllable manner.5 Here, we present a new approach to tailor the dimensions and shape of graphene-based devices on SiC substrates by field-induced atomic force microscopy FI-AFM . We have studied the optimal conditions tip-sample bias, AFM operation mode, speed, etc to locally modify graphene layers with nanometer resolution. We show how the combination of this synthesismethod with AFM nanostructuring provides a new tool box for the fabrication of nanoelectronic devices based on graphene. In previous works,6,7 preliminary studies of AFM nanostructuring of graphene layers deposited on silicon oxide by the so-called mechanical cleavage method have been reported. They assume that the modification is attributed to local anodic oxidation.8 In contrast, the experimentalresults that we present in this letter, referred to graphene on SiC, indicate that other mechanisms may be considered. We show that the graphene modification can be performed at positive and negative polarization voltages, and in both cases, applya

ing low absolute values of voltage. Besides the importance from the mechanism point of view, using lower voltages is also interesting regarding toapplication since it should allow a better control of the oxidation process, as well as higher resolution patterning.

II. EXPERIMENT Large, isolated, graphene ribbons grown on the C face of on-axis semi-insulating n-type residual doping of 1015 cm−3 6H-SiC 000–1 wafers are obtained Fig. 1 . Using a graphite cap to cover the SiC sample, we have found that the resulting growth is regular andhomogeneous. After the SiC surface reconstruction, large terraces appear and, on the terraces, very large and uniform isolated graphene ribbons 100 m long and 4 – 5 m wide develop. Optical transmission and Raman spectroscopy performed on the large ribbons evidence unambiguously their graphene monolayer character see Refs. 5 and 9 . The position of the large graphene ribbons synthesized on SiC...