Single-crystalline Bi Nanowires Research Articles

자발 성장법으로 성장된 단결정 Bi 단일 나노선의 정상 자기 저항 특성

We report the magneto-transport properties of an individual single crystalline Bi nanowire grown by a spontaneous growth method. We have successfully fabricated a four-terminal device based on an individual 400-nm-diameter nanowire using plasma etching technique to remove an oxide layer forming on the outer surface of the nanowire. The transverse MR (2496% at 110 K) and longitudinal MR ratios (38% at 2 K) for the Bi nanowire were found to be the largest known values in Bi nanowires. This result demonstrates that the Bi nanowires grown by the spontaneous growth method are the highest-quality single crystalline in the literatures ever reported. We find that temperature dependence of Fermi energy () and band overlap () leads to the imbalance between electron concentration () and hole concentration () in the Bi nanowire, which is good agreement with the calculated from the respective density of states, N(E), for electrons and holes. We also find that the imbalance of plays a crucial role in determining magnetoresistance (MR) at T and at T, while mean-free path is responsible for MR at T>75 K for and T>205 K for .

Thermal Properties of Bi Nanowire Arrays with Different Orientations and Diameters

The thermal properties of single-crystalline Bi nanowire arrays with different orientations and diameters were studied by differential scanning calorimeter and in situ high-temperature X-ray diffraction. Bi nanowires were fabricated by a pulsed electrodeposition technique within the porous anodic alumina membrane. The relationships between the orientation and diameter of Bi nanowires and the corresponding thermal properties are deduced solely from experimental results. It is shown that the melting point decreases with decreasing nanowire diameter, and there is an anisotropic thermal expansion property of Bi nanowires with different orientations and diameters. The transition of the thermal expansion coefficient from positive at low temperature to negative at high temperature for Bi nanowire arrays was analyzed and discussed.

Conversion of a Bi Nanowire Array to an Array of Bi–Bi2O3 Core–Shell Nanowires and Bi2O3 Nanotubes

A template-based heat-treatment method has been developed to convert metal nanowire arrays into arrays of metal-metal oxide core-shell nanowires and single-crystalline metal oxide nanotubes. This process is demonstrated by kinetically controlling the conversion of single-crystalline Bi nanowires to Bi-Bi(2)O(3) core-shell nanowires via a multistep, slow oxidation method, and then controlling their further conversion to a single-crystalline Bi(2)O(3) nanotube array via fast oxidation. This process can conveniently be extended to fabricate a free-standing, easily oxidized metal-metal oxide nanowire and metal oxide nanotube array, which may have future applications in nanoscale optics, electronics, and magnetics.

Diameter-depended thermal expansion properties of Bi nanowire arrays

The lattice parameter of bismuth nanowires has been measured using the in situ high-temperature x-ray diffraction method. Single-crystalline Bi nanowire arrays with the diameters from 10nmto250nm have been fabricated within the porous anodic alumina membranes by a pulsed electrodeposition technique. Different temperature dependencies of lattice parameter and thermal expansion coefficient were found for Bi nanowires with different diameters, and there is a transition from positive thermal expansion coefficient at low temperature to negative one at high temperature, and the transition temperature shifts to high temperature with the increase in the diameter of Bi nanowires.

Controlled fabrication of poly- and single-crystalline bismuth nanowires

Poly- and single-crystalline Bi nanowires are fabricated by electrochemical deposition inetched ion-track membranes. Two deposition parameters, voltage and temperature,strongly influence the nanowires’ morphology and texture. X-ray diffraction (XRD) andtransmission electron microscopy (TEM) reveal that potentiostatically deposited nanowiresare textured, the texture increasing for wires deposited at higher temperatures and smaller overpotentials.At T = 60 °C and low overpotentials, single-crystalline wires are produced. Wires deposited with reversepulses exhibit a texture, which is more pronounced for shorter cathodic cycles and higher anodic voltages.They consist of several crystals of size at least .

Fabrication and temperature dependence of the resistance of single-crystalline Bi nanowires

Single-crystalline Bi nanowires with diameters ranging from 20 to 70 nm were prepared by electrodeposition using nanoporous aluminum oxide membranes rather than the more usual track-etched polycarbonate membranes. X-ray diffraction and selected area electron diffraction investigations revealed that the nanowires are essentially single crystalline and highly oriented. The temperature dependence of zero-field resistance of different diameter nanowires indicated that these Bi nanowires undergo a semimetal–semiconductor transition due to two-dimensional quantum confinement effects. The resistance maximum was observed at 50 K in zero magnetic field for 20 nm Bi nanowires, while the resistance minimum at 258 K for 50 nm Bi nanowires, due to the quantum size effect.

Ordered single-crystalline Bi nanowire arrays embedded in nanochannels ofanodic alumina membranes

Single-crystalline Bi nanowire arrays have been assembled into thenanochannels of anodic alumina membranes by electrodeposition. X-raydiffraction and transmission electron microscopy investigations revealed thatthe nanowires with diameter of either 50 nm or 20 nm are essentially singlecrystalline and highly oriented. The magnetotransport properties of the Binanowire arrays were measured, and positive magnetoresistance as high as 45%at 100 K was observed.}\\fnm{3}{Author to whom correspondence should be addressed.

Magnetotransport investigations of ultrafine single-crystalline bismuth nanowire arrays

We have measured the magnetotransport properties of ultrafine single-crystalline Bi nanowire arrays embedded in a dielectric matrix. At low temperatures (T⩽50 K), the wire boundary scattering is shown to be the dominant scattering process for carriers. A reversal in the temperature dependence of the magnetoresistance was observed for wires with 65 nm average diameter relative to those with 109 nm average diameter when T⩽100 K. We attribute this difference to effects due to the quantization of the transverse momentum of the carriers, which results in a semimetal-semiconductor transition for Bi nanowires as the wire diameter becomes sufficiently small.