Epitaxial chemical vapor deposition (CVD) growth of uniform single-layer graphene is demonstrated over Co film crystallized on c-plane sapphire. The single crystalline Co film is realized on the sapphire substrate by optimized high-temperature sputtering and successive H(2) annealing. This crystalline Co film enables the formation of uniform single-layer graphene, while a polycrystalline Co film deposited on a SiO(2)/Si substrate gives a number of graphene flakes with various thicknesses. Moreover, an epitaxial relationship between the as-grown graphene and Co lattice is observed when synthesis occurs at 1000 °C; the direction of the hexagonal lattice of the single-layer graphene completely matches with that of the underneath Co/sapphire substrate. The orientation of graphene depends on the growth temperature and, at 900 °C, the graphene lattice is rotated at 22 ± 8° with respect to the Co lattice direction. Our work expands a possibility of synthesizing single-layer graphene over various metal catalysts. Moreover, our CVD growth gives a graphene film with predefined orientation, and thus can be applied to graphene engineering, such as cutting along a specific crystallographic direction, for future electronics applications.

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...

In this study, we estimated source process of the 2016 Kumamoto earthquake from strong-motion data by using the multiple-time window linear kinematic waveform inversion method to discuss generation of strong motions and to explain crustal deformation pattern with a seismic source inversion model. A four-segment fault model was assumed based on the aftershock distribution, active fault traces, and interferometric synthetic aperture radar data. Three western segments were set to be northwest-dipping planes, and the most eastern segment under the Aso caldera was examined to be a southeast-dipping plane. The velocity structure models used in this study were estimated by using waveform modeling of moderate earthquakes that occurred in the source region. We applied a two-step approach of the inversions of 20 strong-motion datasets observed by K-NET and KiK-net by using band-pass-filtered strong-motion data at 0.05-0.5 Hz and then at 0.05-1.0 Hz. The rupture area of the fault plane was determined by applying the criterion of Somerville et al. (Seismol Res Lett 70:59-80, 1999) to the inverted slip distribution. From the first-step inversion, the fault length was trimmed from 52 to 44 km, whereas the fault width was kept at 18 km. The trimmed rupture area was not changed in the second-step inversion. The source model obtained from the two-step approach indicated 4.7 × 10 19 Nm of the total moment release and 1.8 m average slip of the entire fault with a rupture area of 792 km 2 . Large slip areas were estimated in the seismogenic zone and in the shallow part corresponding to the surface rupture that occurred during the Mj7.3 mainshock. The areas of the high peak moment rate correlated roughly with those of large slip; however, the moment rate functions near the Earth surface have low peak, bell shape, and long duration. These subfaults with long-duration moment release are expected to cause weak short-period ground motions. We confirmed that the southeast dipping of the most eastern segment is more plausible rather than northwest-dipping from the observed subsidence around the central cones of the Aso volcano.

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Dense arrays of aligned graphene nanoribbons (GNRs) are fabricated by substrate-controlled etching of large-area single-layer graphene. An adequate choice of etching substrate and catalyst deposition method allows densities up to 25 nanoribbons μm(-1) to be obtained with average widths of 19 nm. The efficacy of the method is evidenced by the high on/off ratios of back-gated transistors made with these GNRs, which can go up to 5000.