February 14, 2010

Graphene Nanomesh and Ultracold Welding of Gold Nanowires

1. Nature Nanotechnology - Graphene nanomesh transistors support 100 times the current of individual nanoribbons

Graphene has significant potential for application in electronics but cannot be used for effective field-effect transistors operating at room temperature because it is a semimetal with a zero bandgap. Processing graphene sheets into nanoribbons with widths of less than 10 nm can open up a bandgap that is large enough for room-temperature transistor operation but nanoribbon devices often have low driving currents or transconductances. Moreover, practical devices and circuits will require the production of dense arrays of ordered nanoribbons, which remains a significant challenge. Here, we report the production of a new graphene nanostructure—which we call a graphene nanomesh—that can open up a bandgap in a large sheet of graphene to create a semiconducting thin film. The nanomeshes are prepared using block copolymer lithography and can have variable periodicities and neck widths as low as 5 nm. Graphene nanomesh field-effect transistors can support currents nearly 100 times greater than individual graphene nanoribbon devices, and the on–off ratio, which is comparable with the values achieved in individual nanoribbon devices, can be tuned by varying the neck width. The block copolymer lithography approach used to make the nanomesh devices is intrinsically scalable and could allow for the rational design and fabrication of graphene-based devices and circuits with standard semiconductor processing.

5 pages of supplemental information

2. Nature Nanotechnology - Cold welding of ultrathin gold nanowires

The welding of metals at the nanoscale is likely to have an important role in the bottom-up fabrication of electrical and mechanical nanodevices. Existing welding techniques use local heating, requiring precise control of the heating mechanism and introducing the possibility of damage. The welding of metals without heating (or cold welding) has been demonstrated, but only at macroscopic length scales and under large applied pressures. Here, we demonstrate that single-crystalline gold nanowires with diameters between 3 and 10 nm can be cold-welded together within seconds by mechanical contact alone, and under relatively low applied pressures. High-resolution transmission electron microscopy and in situ measurements reveal that the welds are nearly perfect, with the same crystal orientation, strength and electrical conductivity as the rest of the nanowire. The high quality of the welds is attributed to the nanoscale sample dimensions, oriented-attachment mechanisms and mechanically assisted fast surface-atom diffusion. Welds are also demonstrated between gold and silver, and silver and silver, indicating that the technique may be generally applicable.

6 pages of supplemental information

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