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Ponomarenko L.A.,University of Manchester | Geim A.K.,University of Manchester | Geim A.K.,Manchester Center for Mesoscience and Nanotechnology | Zhukov A.A.,Manchester Center for Mesoscience and Nanotechnology | And 11 more authors.
Nature Physics | Year: 2011

Disordered conductors with resistivity above the resistance quantum h/e 2 should exhibit an insulating behaviour at low temperatures, a universal phenomenon known as a strong (Anderson) localization. Observed in a multitude of materials, including damaged graphene and its disordered chemical derivatives, Anderson localization has not been seen in generic graphene, despite its resistivity near the neutrality point reaching ‰h/e 2 per carrier type. It has remained a puzzle why graphene is such an exception. Here we report a strong localization and the corresponding metal-insulator transition in ultra-high-quality graphene. The transition is controlled externally, by changing the carrier density in another graphene layer placed at a distance of several nm and decoupled electrically. The entire behaviour is explained by electron-hole puddles that disallow localization in standard devices but can be screened out in double-layer graphene. The localization that occurs with decreasing rather than increasing disorder is a unique occurrence, and the reported double-layer heterostructures presents a new experimental system that invites further studies. © 2011 Macmillan Publishers Limited. All rights reserved.


Moldt T.,Free University of Berlin | Eckmann A.,University of Manchester | Klar P.,Free University of Berlin | Morozov S.V.,Institute for Microelectronics Technology | And 4 more authors.
ACS Nano | Year: 2011

We report large-yield production of graphene flakes on glass by anodic bonding. Under optimum conditions, we counted several tens of flakes with lateral size around 20-30 μm and a few tens of flakes with larger size. About 60-70% of the flakes have a negligible D peak. We show that it is possible to easily transfer the flakes by the wedging technique. The transfer on silicon does not damage graphene and lowers the doping. The charge mobility of the transferred flakes on silicon is on the order of 6000 cm2/V s (at a carrier concentration of 1012 cm-2), which is typical for devices prepared on this substrate with exfoliated graphene. © 2011 American Chemical Society.


Wang L.,Wuhan University | Lin B.,Wuhan University | Zhou L.,Wuhan University | Shang Y.X.,Wuhan University | And 3 more authors.
Materials Letters | Year: 2012

ZnO is a wide band-gap material with excellent optical properties for optoelectronics applications. However, device fabrication has been hampered by difficulties in p-type doping. Nitrogen-doped ZnO nanorods were synthesized through thermal diffusion of nitrogen in an aqueous solution at 90 °C. Low-temperature photoluminescence measured at 10 K showed two peaks located at 3.353 and 3.242 eV, which were assigned to the acceptor-bound excitons and donor-acceptor pairs, respectively. The conductance of the nitrogen-doped ZnO nanorods increased 1.5 times compared with Al-doped samples and 5.8 times compared with undoped ZnO nanorods. The results show hydrothermal process to be an attractive technique for preparation of p-type nitrogen-doped ZnO nanorods. © 2012 Elsevier B.V. All rights reserved.


Nair R.R.,University of Manchester | Blake P.,University of Manchester | Blake J.R.,University of Manchester | Zan R.,University of Manchester | And 7 more authors.
Applied Physics Letters | Year: 2010

We demonstrate the application of graphene as a support for imaging individual biological molecules in transmission electron microscope (TEM). A simple procedure to produce free-standing graphene membranes has been designed. Such membranes are extremely robust and can support practically any submicrometer object. Tobacco mosaic virus has been deposited on graphene samples and observed in a TEM. High contrast has been achieved even though no staining has been applied. © 2010 American Institute of Physics.


Mayorov A.S.,University of Manchester | Gorbachev R.V.,University of Manchester | Morozov S.V.,University of Manchester | Morozov S.V.,Institute for Microelectronics Technology | And 8 more authors.
Nano Letters | Year: 2011

Devices made from graphene encapsulated in hexagonal boron-nitride exhibit pronounced negative bend resistance and an anomalous Hall effect, which are a direct consequence of room-temperature ballistic transport at a micrometer scale for a wide range of carrier concentrations. The encapsulation makes graphene practically insusceptible to the ambient atmosphere and, simultaneously, allows the use of boron nitride as an ultrathin top gate dielectric. © 2011 American Chemical Society.

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