Islam04 - INSTITUTE OF PHYSICS PUBLISHING Nanotechnology 15...

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I NSTITUTE OF PHYSICS PUBLISHING N ANOTECHNOLOGY Nanotechnology 15 (2004) L5–L8 PII: S0957-4484(04)69293-2 LETTER TO THE EDITOR Ultrahigh-density silicon nanobridges formed between two vertical silicon surfaces MSaif Islam, S Sharma, T I Kamins and R Stanley Williams Quantum Science Research, Hewlett-Packard Laboratories, 1501 Page Mill Road, MS 1123, Palo Alto, CA 94304, USA E-mail: Received 15 September 2003 Published 23 January 2004 Online at (DOI: 10.1088/0957-4484/15/5/L01) Abstract We report simultaneous lateral growth of a high density of highly oriented, metal-catalyzed silicon nanowires ona patterned silicon substrate and bridging of nanowires between two vertical silicon sidewalls, which can be developed into electrodes of an electronic device. After angled deposition of catalytic metal nanoparticles on one of two opposing vertical silicon surfaces, we used a metal-catalyzed chemical vapour deposition process to grow nanowires and eventually form mechanically robust ‘nanobridges’. The growth and bridging of these nanowire arrays can be integrated with existing silicon processes. This method of connecting multiple nanowires between two electrodes offers the high surface-to-volume ratio needed for nanosensor applications. 1. Introduction Free-standing nanostructures are currently being extensively explored [1–4]. They are especially attractive for sensor applications because their high surface-to-volume ratio makes them very sensitive to charged species adsorbed on their surfaces. Lateral growth of carbon nanotubes between two electrodes during chemical vapour deposition (CVD) has been reported [5]; a lateral electric field applied between the electrodes attracts the growing nanotube towards the counter-electrode. Although the potential of carbon nanotubes for applications such as gas-sensing field-effect devices has been demonstrated [6], the difficulty of synthesizing only metallic oronlysemiconductingnanotubes andthe difficulty of modifying nanotube surfaces have limited their development as nanosensors [7]. Lateral growth of GaAs nanowhiskers by metalorganic vapour phase epitaxy (MOVPE) from vertical ridges on a GaAs substrate using Au nanoparticles as the catalyst has also been demonstrated [8, 9]. However, the properties of the mechanical connection between a bridging nanowire and the vertical sidewall have not been reported. Nanowires made of silicon are especially attractive because of silicon’s compatibility with existing IC processes. Moreover, the chemical and physical properties of Si can be controlled to adjust the device sensitivity, and Si nanowires can be selectively grown. Using Si allows the vast knowledge of Si technology to be applied to applications such as sensing.
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Islam04 - INSTITUTE OF PHYSICS PUBLISHING Nanotechnology 15...

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