Fabrication of graphene nanoribbon by local anodic oxidation lithography using atomic force microscope

Abstract

We conducted local anodic oxidation (LAO) lithography in single-layer, bilayer, and multilayer graphene using tapping-mode atomic force microscope. The width of insulating oxidized area depends systematically on the number of graphene layers. An 800-nm-wide bar-shaped device fabricated in single-layer graphene exhibits the half-integer quantum Hall effect. We also fabricated a 55-nm-wide graphene nanoribbon (GNR). The conductance of the GNR at the charge neutrality point was suppressed at low temperature, which suggests the opening of an energy gap due to lateral confinement of charge carriers. These results show that LAO lithography is an effective technique for the fabrication of graphene nanodevices. PACS numbers:Graphene, a single atomic layer of graphite, has a unique band structure [1,2] and exceptionally high carrier mobility [3]. Therefore, it has been used to develop carbon-based electronic devices [4]. To date, graphene nanodevices such as quantum dots [5,6], AharonovBohm rings [7], and nanoribbons [8,9] have been fabricated by conventional electron-beam lithography combined with plasma etching. However, plasma etching introduces defects in graphene [3,7,10], which causes localization of charge carriers [7,10]. Further, this technique cannot be used to control the edge structure of graphene, which is expected to have significant effects on its electronic properties [8]. Therefore, in order to fabricate high-quality devices, we need a new lithography technique that will allow us to perform high-resolution patterning without damaging the graphene layer.Local anodic oxidation (LAO) lithography using atomic force microscope (AFM) is a promising technique for the fabrication of graphene nanodevices. This is because LAO lithography has been successfully used for fabricating nanodevices based on semiconductors [11,12,13,14,15]. The confinement of charge carriers obtained by LAO is highly specular [16] than that obtained by plasma etching [17], i.e. the charge carriers conserve their momentum along the normal to the confinement. Recently, Weng et al. produced insulating trenches in graphene flakes with a thickness of 1-2 atomic layers using tapping-mode AFM [18]. However, in their experiment, the number of graphene layers was not determined, though the LAO conditions such as the width of oxidized area are expected to be totally different for single-layer, bilayer, and multilayer graphene. Geisbers et al. used contact-mode AFM to produce an insulating trench on single-layer graphene [19]. However, * Electronic address: msatoru@iis.u-tokyo.ac.jp † Electronic address: tmachida@iis.u-tokyo.ac.jp the contact-mode AFM cantilever can damage the fabricated device [20]. Further, the transport phenomena of Dirac fermions were not demonstrated clearly in either experiment above [18,19]. In this letter, we describe LAO lithography experiments that were conducted in single-layer, bilayer, and multilayer graphene using tapping-mode AFM. We show that the width of oxidized area depends on the number of graphene layers. We hav...

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