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ABSTRACT: ZnO nanowires (NWs) are emerging as key elements for new lasing, photovoltaic and sensing applications but elucidation of their fundamental electronic properties has been hampered by a dearth of characterization tools capable of probing single nanowires. Herein, ZnO NWs were synthesized in solution and integrated into a low energy photoelectron spectroscopy system, where quantitative optical measurements of the NW work function and Fermi level location within the band gap were collected. Next, the NWs were decorated with several dipolar self-assembled monolayers (SAMs) and control over the electronic properties is demonstrated, yielding a completely tunable hybrid electronic material. Using this new metrology approach, a host of other extraordinary interfacial phenomena could be explored on nanowires such as spatial dopant profiling or heterostructures.
ACS Nano 09/2009; 3(10):3057-62. · 10.77 Impact Factor
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ABSTRACT: Attachment of a simple polar molecule, terpyridine, to the surfaces of Si nanowires with diameters ranging from 7-100 nm was investigated with two terminal conductivity measurements, a unique single nanowire photoelectron spectroscopy, and theoretical analysis. Our experiments reveal the details of molecule-nanowire bonding and charge transfer, diameter dependent Fermi level shifts, and acid attachment leading to conductivity in the cylindrical molecular nanolayer surrounding the nanowire.
Nano Letters 09/2009; 9(9):3165-70. · 13.20 Impact Factor
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ABSTRACT: We have examined the formation of silicon nanowires grown by self-assembly from Si substrates with thin aluminum films. Postgrowth and in situ investigations using various Al deposition and annealing conditions suggest that nanowire growth takes place with a supercooled liquid droplet (i.e., the vapor-liquid-solid system), even though the growth temperatures are below the bulk Al/Si eutectic temperature. Wire morphology as a function of processing conditions is also described. It is shown that when Al environmental exposure is prevented before wire growth a wide process window for wire formation can be achieved. Under optimum growth conditions, it is possible to produce excellent crystal quality nanowires with rapid growth rates, high surface densities, low diameter dispersion, and controlled tapering. Photoelectron spectroscopy measurements indicate that the use of Al leads to active doping levels that depend on the growth temperature in as-grown nanowires and increase when annealed. We suggest that these structural and electronic properties will be relevant to photovoltaic and other applications, where the more common use of Au is believed to be detrimental to performance.
Nano Letters 08/2009; 9(9):3296-301. · 13.20 Impact Factor
