| 1. |
- Chua, C., et al.
(författare)
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Quantum Hall Effect and Quantum Point Contact in Bilayer-Patched Epitaxial Graphene
- 2014
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:6, s. 3369-3373
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Tidskriftsartikel (refereegranskat)abstract
- We study an epitaxial graphene monolayer with bilayer inclusions via magnetotransport measurements and scanning gate microscopy at low temperatures. We find that bilayer inclusions can be metallic or insulating depending on the initial and gated carrier density. The metallic bilayers act as equipotential shorts for edge currents, while closely spaced insulating bilayers guide the flow of electrons in the monolayer constriction, which was locally gated using a scanning gate probe.
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| 2. |
- Lartsev, Arseniy, 1987, et al.
(författare)
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Tuning carrier density across Dirac point in epitaxial graphene on SiC by corona discharge
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:6
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate reversible carrier density control across the Dirac point (Δ n∼ 1013cm-2) in epitaxial graphene on SiC (SiC/G) via high electrostatic potential gating with ions produced by corona discharge. The method is attractive for applications where graphene with a fixed carrier density is needed, such as quantum metrology, and more generally as a simple method of gating 2DEGs formed at semiconductor interfaces and in topological insulators.
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| 3. |
- Yager, Thomas, 1987, et al.
(författare)
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Express Optical Analysis of Epitaxial Graphene on SiC: Impact of Morphology on Quantum Transport
- 2013
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:9, s. 4217-4223
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Tidskriftsartikel (refereegranskat)abstract
- We show that inspection with an optical microscope allows surprisingly simple and accurate identification of single and multilayer graphene domains in epitaxial graphene on silicon carbide (SiC/G) and is informative about nanoscopic details of the SiC topography, making it ideal for rapid and noninvasive quality control of as-grown SiC/G. As an illustration of the power of the method, we apply it to demonstrate the correlations between graphene morphology and its electronic properties by quantum magneto-transport.
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| 4. |
- Yager, Tom, et al.
(författare)
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High mobility epitaxial graphene devices via aqueous-ozone processing
- 2015
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 106:6, s. 063503-
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Tidskriftsartikel (refereegranskat)abstract
- We find that monolayer epitaxial graphene devices exposed to aggressive aqueous-ozone processing and annealing became cleaner from post-fabrication organic resist residuals and, significantly, maintain their high carrier mobility. Additionally, we observe a decrease in carrier density from inherent strong n-type doping to extremely low p-type doping after processing. This transition is explained to be a consequence of the cleaning effect of aqueous-ozone processing and annealing, since the observed removal of resist residuals from SiC/G enables the exposure of the bare graphene to dopants present in ambient conditions. The resulting combination of charge neutrality, high mobility, large area clean surfaces, and susceptibility to environmental species suggest this processed graphene system as an ideal candidate for gas sensing applications.
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| 5. |
- Yager, Thomas, 1987, et al.
(författare)
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Low contact resistance in epitaxial graphene devices for quantum metrology
- 2015
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 5:8, s. 087134-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate Ti/Au contacts to monolayer epitaxial graphene on SiC (0001) for applications in quantum resistance metrology. Using three-terminal measurements in the quantum Hall regime we observed variations in contact resistances ranging from a minimal value of 0.6 Ω up to 11 kΩ. We identify a major source of high-resistance contacts to be due bilayer graphene interruptions to the quantum Hall current, whilst discarding the effects of interface cleanliness and contact geometry for our fabricated devices. Moreover, we experimentally demonstrate methods to improve the reproducibility of low resistance contacts (
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| 6. |
- Yager, Tom, et al.
(författare)
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Wafer-scale homogeneity of transport properties in epitaxial graphene on SiC
- 2015
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 87, s. 409-414
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Tidskriftsartikel (refereegranskat)abstract
- Magnetotransport measurements on Hall bar devices fabricated on purely monolayer epitaxial graphene on silicon carbide (SiC/G) show a very tight spread in carrier concentration and mobility across wafer-size dimensions. In contrast, SiC/G devices containing bilayer graphene domains display variations in their electronic properties linked to the amount of bilayer content. The spread in properties among devices patterned on the same SiC/G wafer can thus be understood by considering the inhomogeneous number of layers often grown on the surface of epitaxial graphene on SiC. (C) 2015 Elsevier Ltd. All rights reserved.
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| 7. |
- Fu, Ying, 1964-, et al.
(författare)
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Time-Resolved FDTD and Experimental FTIR Study of Gold Micropatch Arrays for Wavelength-Selective Mid-Infrared Optical Coupling
- 2021
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Ingår i: Sensors. - Basel : MDPI. - 1424-8220. ; 21:15
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Tidskriftsartikel (refereegranskat)abstract
- Infrared radiation reflection and transmission of a single layer of gold micropatch two-dimensional arrays, of patch length ∼1.0μm and width ∼0.2μm, have been carefully studied by a finite-difference time-domain (FDTD) method, and Fourier-transform infrared spectroscopy (FTIR). Through precision design of the micropatch array structure geometry, we achieve a significantly enhanced reflectance (85%), a substantial diffraction (10%), and a much reduced transmittance (5%) for an array of only 15% surface metal coverage. This results in an efficient far-field optical coupling with promising practical implications for efficient mid-infrared photodetectors. Most importantly we find that the propagating electromagnetic fields are transiently concentrated around the gold micropatch array in a time duration of tens of ns, providing us with a novel efficient near-field optical coupling.
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| 8. |
- Yager, Tom, et al.
(författare)
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Graphene Hybrid Metasurfaces for Mid-Infrared Molecular Sensors
- 2023
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Ingår i: Nanomaterials. - Basel : Multidisciplinary Digital Publishing Institute (MDPI). - 2079-4991. ; 13:14
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Tidskriftsartikel (refereegranskat)abstract
- We integrated graphene with asymmetric metal metasurfaces and optimised the geometry dependent photoresponse towards optoelectronic molecular sensor devices. Through careful tuning and characterisation, combining finite-difference time-domain simulations, electron-beam lithography-based nanofabrication, and micro-Fourier transform infrared spectroscopy, we achieved precise control over the mid-infrared peak response wavelengths, transmittance, and reflectance. Our methods enabled simple, reproducible and targeted mid-infrared molecular sensing over a wide range of geometrical parameters. With ultimate minimization potential down to atomic thicknesses and a diverse range of complimentary nanomaterial combinations, we anticipate a high impact potential of these technologies for environmental monitoring, threat detection, and point of care diagnostics.
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