Bismuth quantum-wire arrays fabricated by a vacuum melting and pressure injection process
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Bismuth quantum-wire arrays fabricated by a vacuum melting and pressure injection process Zhibo Zhang Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307
Jackie Y. Yinga) Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307
Mildred S. Dresselhaus Department of Electrical Engineering and Computer Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (Received 12 September 1997; accepted 13 October 1997)
Ultrafine bismuth nanowire arrays were synthesized by injecting its liquid melt into nanochannels of a porous anodic alumina template. A large area (1 cm 3 1.5 cm) of parallel wires with diameters as small as 13 nm, lengths of 30–50 mm, and packing density as high as 7.1 3 1010 cm22 has been fabricated. X-ray diffraction patterns revealed these nanowires, embedded in the insulating matrix, to be essentially single crystalline and highly oriented. The optical absorption spectra of the nanowire arrays indicate that these bismuth nanowires undergo a semimetal-to-semiconductor transition due to two-dimensional quantum confinement effects.
Highly regular metal and semiconductor nanowire arrays embedded in a dielectric matrix have attracted a great deal of research attention because of their potential applications in electronic and optical devices and promise for studying one-dimensional (1D) quantum properties. The quantum confinement of carriers in two dimensions will significantly change their electronic energy states and make the properties of these 1D systems very different from their bulk counterparts. A promising approach to fabricate nanowire systems is to fill an array of nanochannels with the media of interest. Porous anodic alumina,1–3 which has hexagonally packed nanometer-sized channels, is one such possible host template. Besides its desirable geometry, the wide band gap energy of alumina makes it an excellent host material for quantum wires. Anodic alumina has previously been used to synthesize a variety of metal and semiconductor nanowires, such as Ni, Pd, Au, Pt, and CdS, through chemical or electrochemical processes.4–7 However, the diameters of those nanowires have not reached the quantum confinement regime. In order to exhibit strong quantum confinement characteristics, the wire diameter should be smaller than the exciton diameter, which is h 2 (me21 1 mh21 )ye2 , where e is the given by dex 2e¯ static dielectric constant, and me and mh are the effective masses of electrons and holes, respectively. Bismuth, which is a semimetal and has a very small electron effective mass (me ø 0.014m0 at the band edge along a)
Author to whom correspondence should be addressed. J. Mater. Res., Vol. 13, No. 7, Jul 1998
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the trigonal direction, and me ø 0.0036m0 for heavy electrons along the bisectrix direction), is considered a good candidate to study quantu
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