Graphene Nanoribbon Interconnect Resistivity Comparable to Copper
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wavelengths of light and three different polarization directions. Multiple recording layers may then be combined on a single disk, adding the final spatial dimension, to further increase the storage density. The size and shape of the gold nanorods provide the necessary selectivity for the fivedimensional recording process. The gold nanorods are patterned through a photothermal reshaping process. This reshaping happens when a nanorod absorbs a laser pulse and heats above its melting temperature, which then causes
the nanorod to transform into a spherical particle. The nanorods selectively absorb the laser energy depending on the wavelength and polarization of the light while the threshold for photothermal melting ensures that the writing process is confined within the focal volume of the laser. The aspect ratio and orientation of the nanorods determine the wavelength and polarization sensitivity, respectively. Recordings can be imaged nondestructively using longitudinal surface plasmon resonance mediated by two-photon luminescence.
This nonlinear optical detection mechanism provides much higher angular and wavelength sensitivity compared to linear detection mechanisms used with gold nanoparticles. With the demonstrated ability to record pixel sizes close to the expected diffraction limit and in a manner free from cross-talk, this new optical recording technique has the potential to raise storage density into the terabytes for an optical disk the size of a DVD. CHARLES BROOKS
Graphene Nanoribbon Interconnect Resistivity Comparable to Copper
silicon-based integrated circuit technology. Beyond resistivity improvement, graphene interconnects would offer higher electron mobility, better thermal conductivity, higher mechanical strength, and reduced capacitance coupling between adjacent wires. “Resistivity is normally independent of the dimension—a property inherent to the material,” Murali said. “But as you get into the nanometer-scale domain, the grain sizes of the copper become important and conductance is affected by scattering at the grain boundaries and at the side walls. These add up to increased resistivity, which nearly doubles as the interconnect sizes shrink to 30 nm.” Experimentally, the researchers began with flakes of multi-layered graphene removed from a graphite block and placed onto an oxidized silicon substrate. They used electron beam lithography to construct four electrode contacts on the graphene, then used lithography to fabricate devices consisting of parallel nanoribbons of widths ranging over 18–52 nm. The three-dimensional resistivity of the nanoribbons on 18 different devices was then measured using standard analytical techniques at room temperature. The best of the graphene nanoribbons showed conductivity equal to that predicted for copper interconnects of the same width. Because the comparisons
were between non-optimized graphene and optimistic estimates for copper, the researchers suggest that performance of the new material will ultimately surpass that of the traditional interconnect mat
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