| 1. |
- Zhan, Zhaoyao, 1983, et al.
(författare)
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Pore-free bubbling delamination of chemical vapor deposited graphene from copper foils
- 2015
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 3:33, s. 8634-8641
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Tidskriftsartikel (refereegranskat)abstract
- The electrolytic bubbling-assisted transfer of graphene from metal catalysts in chemical vapor deposition provides a high efficiency, low cost and environmental benign alternative to the traditional chemical etching method. Despite its high potential, the yield of bubbling delamination is yet low, mainly due to the induced pores in the graphene after the transfer. It is found that water and protons transported through the poly(methyl methacrylate) (PMMA) supporting layer play a critical role in pore formation. Once water and protons reach the PMMA-graphene interface before delamination is finished, the protons permeate the graphene and form trapped hydrogen bubbles between the graphene and the metal. The built-up gas pressure inside the bubbles is high enough to crack the PMMA/graphene sheet, thereby creating pores in the graphene. An optimized PMMA layer not only reduces trapped hydrogen bubble generation, but it is also mechanically stronger preventing cracking. This contributes significantly to the pore-free electrolytic bubbling-assisted delamination of graphene.
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| 2. |
- Lindvall, Niclas, 1985, et al.
(författare)
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Cleaning graphene using atomic force microscope
- 2012
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 111:6, s. Article Number: 064904-
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Tidskriftsartikel (refereegranskat)abstract
- We mechanically clean graphene devices using an atomic force microscope (AFM). By scanning an AFM tip in contact mode in a broom-like way over the sample, resist residues are pushed away from the desired area. We obtain atomically flat graphene with a root mean square (rms) roughness as low as 0.12 nm after this procedure. The cleaning also results in a shift of the charge-neutrality point toward zero gate voltage, as well as an increase in charge carrier mobility.
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| 3. |
- Lindvall, Niclas, 1985, et al.
(författare)
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Measurements of weak localization of graphene in inhomogeneous magnetic fields
- 2015
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Ingår i: JETP Letters. - : Pleiades Publishing Ltd. - 1090-6487 .- 0021-3640. ; 102:6, s. 367-371
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Tidskriftsartikel (refereegranskat)abstract
- Weak localization in graphene is studied in inhomogeneous magnetic fields. To generate the inhomogeneous field, a thin film of type-II superconducting niobium is put in close proximity to graphene. A deviation from the ordinary quadratic weak localization behavior is observed at low fields. We attribute this to the inhomogeneous field caused by vortices in the superconductor. The deviation, which depends on the carrier concentration in graphene, can be tuned by the gate voltage. In addition, collective vortex motion, known as vortex avalanches, is observed through magnetoresistance measurements of graphene.
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| 4. |
- Lindvall, Niclas, 1985, et al.
(författare)
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Towards transfer-free fabrication of graphene NEMS grown by chemical vapour deposition
- 2012
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Ingår i: Micro and Nano Letters. - : Institution of Engineering and Technology (IET). - 1750-0443. ; 7:8, s. 749-752
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Tidskriftsartikel (refereegranskat)abstract
- Graphene, an atomic monolayer of sp(2)-hybridised carbon atoms, is a promising material for future NEMS based on its remarkable electronic and mechanical properties. Through the rapid progress of chemical vapour deposition of large-scale, high-quality graphene, these applications seem to be close to reality. However, issues related to the graphene transfer process limit the reproducibility of such devices. In this Letter, the authors present two different approaches for fabricating suspended graphene devices without any transfer step, using both catalytically and non-catalytically grown graphene. The authors achieve high reproducibility in manufacturing flat and uniform suspended graphene beams. While good mechanical properties are observed, the electrical performance is still poor, requiring improvements.
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| 5. |
- Lindvall, Niclas, 1985, et al.
(författare)
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Transfer-free fabrication of suspended graphene grown by chemical vapor deposition
- 2012
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Ingår i: 7th IEEE International Conference on Nano/Micro Engineered and Molecular Systems. NEMS 2012, Kyoto, 5 - 8 March 2012. - 9781467311243 ; , s. 19-22
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Konferensbidrag (refereegranskat)abstract
- Graphene, a true two-dimensional material with extraordinary mechanical- and electronic properties, is thought to be ideal for nanoelectromechanical systems (NEMS), like mass- and force sensors. Here, we present two different ways to fabricate suspended graphene for the intended use in future NEMS applications. The fabrication schemes do not require transfer of graphene from a catalyst where the graphene is grown on to another supporting substrate. The transfer is a source of several issues causing irreproducibility in large-scale production of graphene devices. We obtain suspended graphene membranes by locally removing the copper thin film on top of which the graphene is catalytically grown. The membranes are uniform and exhibit mechanical properties similar to those of exfoliated graphene. Also, suspended graphene beams with electrical interconnects are fabricated from non-catalytically grown graphene on SiO 2. Both approaches represent the first steps towards transfer-free fabrication of suspended graphene for NEMS applications.
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| 6. |
- Lockhart de la Rosa, César Javier, 1987, et al.
(författare)
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Frame assisted H2O electrolysis induced H2 bubbling transfer of large area graphene grown by chemical vapor deposition on Cu
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:2
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Tidskriftsartikel (refereegranskat)abstract
- An improved technique for transferring large area graphene grown by chemical vapor deposition on copper is presented. It is based on mechanical separation of the graphene/copper by H-2 bubbles during H2O electrolysis, which only takes a few tens of seconds while leaving the copper cathode intact. A semi-rigid plastic frame in combination with thin polymer layer span on graphene gives a convenient way of handling-and avoiding wrinkles and holes in graphene. Optical and electrical characterizations prove the graphene quality is better than that obtained by traditional wet etching transfer. This technique appears to be highly reproducible and cost efficient.
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| 7. |
- Nam, Youngwoo, 1983, et al.
(författare)
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Graphene p-n-p junctions controlled by local gates made of naturally oxidized thin aluminium films
- 2012
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 50:5, s. 1987-1992
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Tidskriftsartikel (refereegranskat)abstract
- Graphene structures with both top- and bottom-electrostatic gates are studied. The top gate is made of thin aluminium (Al) film deposited directly onto graphene, with no prior dielectric layer in between. Natural oxidation of Al at the interface with graphene results in an insulating barrier proving useful in making top gates to graphene. For electrically disconnected top gate, graphene resistance as a function of the slowly-varying back-gate voltage shows hysteresis which reveals dielectric properties of the barrier. The estimated barrier thickness is only 2 nm allowing for very sharp profiles of the electric field in graphene devices. By applying voltages to both back- and top gates, effective p–n–p junctions with sharp interfaces can be created.
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| 8. |
- Nam, Youngwoo, 1983, et al.
(författare)
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Quantum Hall effect in graphene decorated with disordered multilayer patches
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:233, s. 233110-
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Tidskriftsartikel (refereegranskat)abstract
- Quantum Hall effect (QHE) is observed in graphene grown by chemical vapour deposition using platinum catalyst. The QHE is even seen in samples which are irregularly decorated with disordered multilayer graphene patches and have very low mobility (
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| 9. |
- Nam, Youngwoo, 1983, et al.
(författare)
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The Aharonov-Bohm effect in graphene rings with metal mirrors
- 2012
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 50:15, s. 5562-5568
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Tidskriftsartikel (refereegranskat)abstract
- We measured the Aharonov-Bohm (AB) effect in graphene rings with superconducting-(Al) and normal-metal (Au) mirrors. The mirrors were deposited either on additional stubs connected to the rings in the transverse direction or on the ring bias lines. A significant enhancement of the visible phase coherence was observed in the latter case, in which we observed even the third harmonic of the AB oscillations. The superconductivity of the mirrors appears to be unimportant for the improved coherence in graphene. A large Fermi energy mismatch between graphene and the mirror material is sufficient for this effect. In addition, a transport gap was observed in our graphene structures at the gate voltage close to the Dirac point. The value of the gap can be reproduced by assuming the occurrence of Coulomb blockade effects in graphene.
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| 10. |
- Nam, Youngwoo, 1983, et al.
(författare)
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Unusual thermopower of inhomogeneous graphene grown by chemical vapor deposition
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:2, s. 021902 -
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Tidskriftsartikel (refereegranskat)abstract
- We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone.
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