Nano Focus: Electronic properties of graphene modulated with chemical functionalization
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ing of the BaTiO3 layer, and the tunnel resistance of the junction was shown to strongly depend on the write voltage, as shown in the figure. The magnitude of the OFF/ON ratio was also observed to change by over two orders of magnitude, which corresponds to a nearly 10,000% increase in junction resistance. This is a significant improvement over conventional tunneling magnetoresistive memories, which typically show only a fourfold OFF/ON ratio. The researchers next measured the switching stability of over 50 junctions, and recorded an average switching ratio
of 64 with little variation in I-V behavior over 900 read/write cycles. The power consumption of these devices (~10 fJ/ bit) is also lower than that of other nonvolatile memory technologies, making these junctions appealing for a wide range of memory applications. The research team believes that these devices can be optimized using strain engineering, electrical boundary conditions, and even magnetic electrodes to achieve further improvements in performance and could potentially compete with other nonvolatile memory technologies. Steven Spurgeon
Nano Focus Electronic properties of graphene modulated with chemical functionalization
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raphene, with its two-dimensional, hexagonal honeycomb lattice structure and semimetallic characteristics, has great potential for use in a diverse array of optoelectronic applications, especially now that synthetic routes for its large-scale synthesis have been demonstrated. One route to achieving this goal is through chemical functionalization, which can convert graphene, with its bandgap of zero, to a wide-bandgap semiconductor. In addition, patterned multifunctional regions could be used to form the superlattices required for devices such as chemical sensors and thermoelectrics. Toward these ends, J.M. Tour and colleagues at Rice University and Tianjin University have demonstrated a two-step process to first hydrogenate a pattern on the basal plane of graphene and then convert the hydrogens to a different functionality. As reported in the November 29, 2011 issue of Nature Communications (DOI: 10.1038/ncomms1577), the researchers transferred graphene originally grown on Cu substrates to an insulating substrate (either quartz or SiO2/Si) and then used conventional lithography to expose defined regions of the graphene to atomic hydrogen. Fluorescence quenching microscopy (FQM) was used to image
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MRS BULLETIN
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VOLUME 37 • FEBURARY 2012
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(a) Images of graphane/graphene patterns revealed with fluorescence quenching microscopy (FQM); the scale bars are 200 μm; (b) the fabrication of sp3 C–C exchanged superlattices and subsequent FQM imaging is illustrated with a schematic diagram. Reproduced with permission from Nat. Commun. 2:527, DOI: 10.1038/ncomms1531. © 2011 Macmillan Publishers Ltd.
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NEWS & ANALYSIS RESEARCH/RESEARCHERS the regions of hydrogenated graphene, which are termed graphane; see (a) in the figure. Partial hydrogenation of the graphene was confirmed using Raman spectroscopy. Meas
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