| 1. |
- Zhan, Zhaoyao, 1983, et al.
(author)
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Pore-free bubbling delamination of chemical vapor deposited graphene from copper foils
- 2015
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In: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 3:33, s. 8634-8641
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Journal article (peer-reviewed)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. |
- Cagliani, A., et al.
(author)
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Defect/oxygen assisted direct write technique for nanopatterning graphene
- 2015
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:14, s. 6271-6277
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Journal article (peer-reviewed)abstract
- High resolution nanopatterning of graphene enables manipulation of electronic, optical and sensing properties of graphene. In this work we present a straightforward technique that does not require any lithographic mask to etch nanopatterns into graphene. The technique relies on the damaged graphene to be etched selectively in an oxygen rich environment with respect to non-damaged graphene. Sub-40 nm features were etched into graphene by selectively exposing it to a 100 keV electron beam and then etching the damaged areas away in a conventional oven. Raman spectroscopy was used to evaluate the extent of damage induced by the electron beam as well as the effects of the selective oxidative etching on the remaining graphene.
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| 3. |
- Lindvall, Niclas, 1985
(author)
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Fabrication and characterization of graphene-superconductor devices
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Graphene is the first single-atom-thick two-dimensional material and exhibits a large set of interesting properties. This thesis consists of two parts. The first regards the growth of large-area graphene using chemical vapor deposition (CVD). Graphene is grown using CVD on copper catalyst showing high quality with charge carrier mobility exceeding 3000 cm2/Vs.Wet chemical etching is used to transfer graphene to insulating substrates. Cu is removed using either diluted HNO3 or diluted HCl with a small amount of added H2O2. To allow for faster transfer and avoid consuming copper, a hydrogen-bubbling method is developed to delaminate graphene from Cu. Graphene transferred this way shows properties similar to those of graphene transferred using wet etching.To avoid transfer-related issues, graphene is grown non-catalytically directly on insulating substrates such as SiO2, Al2O3, and Si3N4. The grain size is only ~10 nm due to the lack of catalytic activity during growth. Such graphene shows inferior electronic properties with mobility in the order of ~tens of cm2/Vs. Despite that, sheet resistance around kΩ, the possibility to grow several layer thick films, and optical properties similar to those of pristine graphene make it an interesting material.A method for cleaning graphene mechanically using atomic force microscopy (AFM) is developed. By appropriate choice of the applied force, atomically smooth (roughness
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| 4. |
- Lindvall, Niclas, 1985, et al.
(author)
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Measurements of weak localization of graphene in inhomogeneous magnetic fields
- 2015
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In: JETP Letters. - : Pleiades Publishing Ltd. - 1090-6487 .- 0021-3640. ; 102:6, s. 367-371
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Journal article (peer-reviewed)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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| 5. |
- Skoblin, Grigory, 1991, et al.
(author)
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A hybrid-type CVD system for graphene growth
- 2015
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In: Chemical Vapor Deposition. - : Wiley. - 1521-3862 .- 0948-1907. ; 21:7-9, s. 176-180
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Journal article (peer-reviewed)abstract
- A cold-wall CVD system for graphene growth on metal foils is converted to an effectively hot-wall one by merely adding another heater, sandwiching the foil in between the heaters. This simple design demonstrates both an improved temperature uniformity characteristic for hot-wall systems, and a high responsivity distinctive for cold-wall ones. This beneficial combination allows for a much better control of graphene growth kinetics. An effectively hot-wall system for graphene growth is made from a cold-wall one by encapsulating the metal foil in between two heaters. This simple conversion demonstrates improved temperature control and high temperature ramping rate. It also allows reaching lower nucleation density and provides better control of growth kinetics.
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