Showing papers by "Peter Blake published in 2006"

Detection of Individual Gas Molecules Absorbed on Graphene

Abstract: The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphenes surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

Graphene Spin Valve Devices

Abstract: Graphene-a single atomic layer of graphite-is a recently found two-dimensional (2-D) form of carbon, which exhibits high crystal quality and ballistic electron transport at room temperature. Soft magnetic NiFe electrodes have been used to inject polarized spins into graphene, and a 10% change in resistance has been observed as the electrodes switch from the parallel to the antiparallel state. This coupled with the fact that a field-effect electrode can modulate the conductivity of these graphene films makes them exciting potential candidates for spin electronic devices

Detection of Individual Gas Molecules by Graphene Sensors

Abstract: The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphenes surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

Graphene Based Spin Valve Devices

Abstract: Graphene is a name given to an atomic layer of carbon atoms densely packed into a benzene-ring structure with a nearest-neighbour distance of ~1.4Aring. This theoretical material is widely used in the description of the crystal structure and properties of graphite, large fullerenes and carbon nanotubes. As a first approximation, graphite is made of graphene layers relatively loosely stacked on top of each other with a fairly large interlayer distance of ~3.4Aring . Carbon nanotubes are usually thought of as graphene layers rolled into hollow cylinders. Graphene films are made by repeated peeling of small (mm-sized) mesas of highly-oriented pyrolytic graphite (HOPG). The exfoliation continues until flakes that are nearly invisible in an optical microscope are obtained. A simple spin valve structure has been fabricated from such films using electron beam lithography. This is based on a symmetrical electrode structure and relies on imperfections in the two ferromagnetic electrodes to give different switching fields for each electrode. Despite this highly non-optimised structure we observed a 10% change in resistance at 300 K as the applied field is swept between +450 G and -450 G. The 10% change in resistance is much larger than can be attributed to MR effects in the individual permalloy electrodes (2.5% maximum), giving confidence that it is due to the spin valve effect with the graphene acting as the non-magnetic conductor. Although spin valve effects have been observed in carbon nanotubes this is the first observation of this effect in planar graphene.