Effective Cleaning of Hexagonal Boron Nitride for Graphene Devices

Garcia, A. G. F.; Neumann, Michael; Amet, François; Williams, James R.; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber‐Gordon, David

doi:10.1021/nl3011726

Cited by 113 publications

(118 citation statements)

References 17 publications

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“…3 (c). To ensure the high quality of the sample, we anneal the h-BN top surfaces in Ar/O2 (90/10%, 500 sccm) at 450 °C for 3 hours and the graphene surfaces in Ar/H2 (90/10%, 500 sccm) at 450 °C for 3 hours before each transfer to remove the polymer residue from previous transfer or lithography 35 . The layer-by-layer transfer approach ensures that both the top and bottom gates extend beyond the bilayer sheet, creating a uniform density profile and ensuring the bulk of the bilayer becomes very insulating in the gapped regime.…”

Section: Methodsmentioning

confidence: 99%

Gate-controlled topological conducting channels in bilayer graphene

et al. 2016

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The existence of inequivalent valleys K and K′ in the momentum space of two-dimensional hexagonal lattices provides a new electronic degree of freedom, the manipulation of which can potentially lead to new types of electronics, in analogy to the role played by electron spin 1-3 . In materials with broken inversion symmetry, such as an electrically gated bilayer graphene 4,5 , the momentum-space Berry curvature  carries opposite sign in the K and K′ valleys. A sign reversal of  along an internal boundary of the sheet gives rise to counterpropagating one-dimensional conducting modes encoded with opposite valley indices. These metallic states are topologically protected against backscattering in the absence of valley-mixing scattering, and thus can carry current ballistically 1,6-11 . In bilayer graphene, the reversal of  can occur at the domain wall of AB and BA stacked domains 12-14 , or at the line junction of two oppositely gated regions 6 . The latter approach can provide a scalable platform to implement valleytronic operations such as valves and waveguides 9,15 , but is technically challenging to realize. Here we fabricate a dual-split-gate structure in bilayer graphene and demonstrate transport evidence of the predicted metallic states. They possess a mean free path of up to a few hundred nanometers in the absence of a magnet field. The application of perpendicular magnetic field suppresses backscattering significantly and enables a 400-nanometer-long junction to exhibit conductance close to the ballistic limit of 4 e 2 /h at 8 Tesla. Our experiment paves the path to the realization of gate-controlled ballistic valley transport and the development of valleytronic applications in atomically thin materials.Exploiting the valley degree of freedom in hexagonal lattices may offer an alternative pathway to achieving low-power-consumption electronics. Experiments have shown that a net valley polarization in the material can be induced by the use of circularly polarized light 2,16,17 or a net bulk current [18][19][20] . However the use of light is not always desirable in electronics and device proposals using bulk valley polarization often put stringent requirements on the size and edge orientation of the active area 3 . Alternatively, electrically created, valley-polarized topological conducting channels in high-mobility bilayer graphene may offer a robust, scalable platform to realize valleytronic operations 1,6,[8][9][10][11][12][13][14][15] . Figure 1a illustrates the dual-split-gating scheme proposed by Martin et al 6 , where an AB-stacked bilayer graphene (BLG) sheet is controlled by two pairs of top and bottom gates separated by a line junction. The device operates in the regime where both the left and the right regions of the BLG sheet are insulating due to a bulk band gap induced by the independently applied displacement fields DL and DR. In the "odd" field configuration, where DLDR < 0, theory predicts the existence of eight conducting modes (referred to as the "kink" states) propagating along the line ...

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Section: Methodsmentioning

confidence: 99%

Gate-controlled topological conducting channels in bilayer graphene

et al. 2016

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“…The h-BN layer with atomically smooth surface free of dangling bonds/charge traps makes it an ideal dielectric substrate for field effect transistor 7 and spacer for novel tunnelling devices 8,9 . The characters of h-BN make it possible to realize ballistic electronics at room temperature 10,11 . Normally, uniform crystalline h-BN flakes are mostly obtained by mechanical exfoliation from h-BN single crystals 7,[11][12][13][14][15] .…”

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“…The characters of h-BN make it possible to realize ballistic electronics at room temperature 10,11 . Normally, uniform crystalline h-BN flakes are mostly obtained by mechanical exfoliation from h-BN single crystals 7,[11][12][13][14][15] . However, the flakes are obtained through a highly skilled manual process-mechanical exfoliation and transferring, which is not a scalable method for practical applications.…”

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confidence: 99%

“…So far, many efforts have been taken on various substrates such as Ni [16][17][18][19][20][21] , Cu 3,[21][22][23][24][25][26][27] , Pt 28,29 , Ru 30,31 and Co 32 to obtain large h-BN crystals via the chemical vapour deposition (CVD) process. However, those grains in h-BN films are very small (usually o50 mm 2 ) because of high nucleation density at the early growth stages 10,11,[15][16][17]19,22 . The small grains lead to high density of grain boundaries and dangling bonds, which are known as structural defects in h-BN 33,34 .…”

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Synthesis of large single-crystal hexagonal boron nitride grains on Cu–Ni alloy

et al. 2015

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Hexagonal boron nitride (h-BN) has attracted significant attention because of its superior properties as well as its potential as an ideal dielectric layer for graphene-based devices. The h-BN films obtained via chemical vapour deposition in earlier reports are always polycrystalline with small grains because of high nucleation density on substrates. Here we report the successful synthesis of large single-crystal h-BN grains on rational designed Cu-Ni alloy foils. It is found that the nucleation density can be greatly reduced to 60 per mm 2 by optimizing Ni ratio in substrates. The strategy enables the growth of single-crystal h-BN grains up to 7,500 mm 2 , approximately two orders larger than that in previous reports. This work not only provides valuable information for understanding h-BN nucleation and growth mechanisms, but also gives an effective alternative to exfoliated h-BN as a high-quality dielectric layer for large-scale nanoelectronic applications.

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“…Gas pressure was kept at ambient, and gas flow rate were 500 sccm Ar and 50 sccm O 2 . The temperature is set to 500˚C with an up-rate of 7˚C/min and typically thermal annealing lasted 2 -3 h [18]. Graphene is exfoliated separately onto a Si substrate coated with a polymer bi-layer consisting of a water-soluble layer (Polyvinyl alcohol) PVA and PMMA using the Scotch Magic tape.…”

Section: Methodsmentioning

confidence: 99%

Transferring Few-Layer Graphene Sheets on Hexagonal Boron Nitride Substrates for Fabrication of Graphene Devices

Leon¹,

Mamani²,

Rahim³

et al. 2014

Graphene

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We have developed a dry transfer method that allows graphene to be transferred from polymerthyl-methacrylate (PMMA)/Si (silicon) substrates on commercially available hexagonal boron nitride (hBN) crystals. With this method we are able to fabricate graphene devices with little wrinkles and bubbles in graphene sheets, but that do not degrade the electronic quality more than the SiO2 substrate does. For hBN to perform the function described above substrate cleanliness is critical to get high quality graphene devices. Using hBN as a substrate, graphene exhibits enhanced mobility, reduced carrier inhomogeneity, and reduced intrinsic doping compared to graphene on SiO2 substrate.

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Effective Cleaning of Hexagonal Boron Nitride for Graphene Devices

Cited by 113 publications

References 17 publications

Gate-controlled topological conducting channels in bilayer graphene

Gate-controlled topological conducting channels in bilayer graphene

Synthesis of large single-crystal hexagonal boron nitride grains on Cu–Ni alloy

Transferring Few-Layer Graphene Sheets on Hexagonal Boron Nitride Substrates for Fabrication of Graphene Devices

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