AVS 51st International Symposium
    Nanometer-scale Science and Technology Thursday Sessions
       Session NS2-ThM

Paper NS2-ThM2
Ultralong and Portable Semiconductor Nanowire Arrays

Thursday, November 18, 2004, 8:40 am, Room 213D

Session: Nanowires I
Presenter: Q. Li, University of California, Irvine
Authors: Q. Li, University of California, Irvine
E.C. Walter, University of California, Irvine
W. van der Veer, University of California, Irvine
R.M. Penner, University of California, Irvine
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Long semiconductor nanowires, organized into parallel arrays, are desirable for a variety of nanoelectronic applications. Most of the current synthesis methods produce nanowires that are randomly distributed and effort must be expended to organize the nanowires onto solid surface for electronic applications. Here we propose a hybrid electrochemical/chemical method for the synthesis of millimeter-long semiconductor nanowires that are organized into arrays on solid surface. Our method involves two steps: First, electrochemical step edge decoration was adopted to obtain the precursor nanowires on highly oriented pyrolytic graphite (HOPG). Second, the as-deposited nanowires were chemically converted to semiconductor nanowires. MoS@sub 2@ nanowire arrays, a semiconductor material stable in moist air up to 80@super o@C, were synthesized by heating electrodeposited MoO@sub 2@ nanowires in H@sub 2@S at elevated temperatures. The nanowires were characterized by TEM, SEM and XRD. Two discrete structures were observed depending on the conversion temperature. For nanowires annealed at or below 700@super o@C, the MoS@sub 2@ nanowires were composed of randomly distributed 5-10 atomic layer thick MoS@sub 2@ ribbons. For nanowires annealed at 800@super o@C, MoS@sub 2@ atomic layers oriented parallel to the HOPG basal plane. Their diameters were easily controlled by their precursor MoO@sub 2@ nanowires. The electronic and optical properties were probed by transferring the nanowires onto suitable surfaces. Conductivity in both types of wires was thermally activated and the thermal activation energy was tuned from 125meV (700@super o@C annealing) to 25meV (800@super o@C annealing), lower than the reported MoS@sub 2@ thin films. The optical adsorption spectra showed two excitons, which blueshifted as a function of nanowire thickness due to the quantum confinement. Such organized and portable nanowire arrays are promising for nanoelectronics applications.