Electronic transport properties of a bismuth microwire array in a magnetic field

Abstract

The magneto-Seebeck coefficient and magnetoresistivity of a polycrystalline bismuth microwire array were measured under magnetic fields of 0–2T and at temperatures of 50–300K. To avoid the influence of contact resistance between the wire array and the electrodes, bulk bismuth was used for the electrodes. In the absence of a magnetic field, the Seebeck coefficient and resistivity were −76μV∕K and 1.8μΩm at 300K, respectively. The magneto-Seebeck coefficient for the wire array increased with the application of an external magnetic field, attributable to the precise control of impurities and carrier scattering process in the fabrication of the wire array. The phonon drag effect was observed below 100K, with a corresponding increase in the magneto-Seebeck coefficient under high magnetic fields. However, the magnetoresistivity was also raised under higher magnetic fields, detracting from the thermoelectric properties. Through analysis of the power factor, the optimum magnetic field was determined for each temperature, revealing a trend for the optimum magnetic field to increase with temperature. The power factor was improved by a maximum factor of 1.12, achieved at 200K and 0.25T. Further improvements appear to be possible by eliminating the bulk bismuth employed for the electrodes.

Thermoelectric Properties of Bismuth Micro/Nanowire Array Elements Pressured into a Quartz Template Mold

“…The residual resistance ratio (RRR) is approximately 3. Bulk bismuth and microwire arrays were found to have different temperature dependences [5][6][7][8][9][10][11] ; for example, the RRR of a single crystal of bismuth is more than 90, 15 depending on its impurity content and crystal orientation. Figure 3 shows a plot of the resistance of a micro/nanowire array and the resistivity of a bulk sample with scales chosen such that the two lines converge at 300 K. Below 250 K, the two lines diverge significantly.…”

“…After injection had been completed, the bismuth was recrystallized by cooling it from 370°C to 250°C over a period of 24 h. This fabrication method is similar to the one we used to produce microwire arrays. [5][6][7][8][9] Figure 2 shows a photograph of an array produced from a bismuth ingot. The quartz template appears very promising for fabricating nanowires.…”

“…Thus, the transport properties may resemble those of a bulk bismuth sample or a microwire array. [6][7][8][9] Unfortunately, the wire diameter distribution was not measured. In the future, we intend to determine the contributions of micro-and nanowires, by either completely controlling the hole diameters in templates or by preparing single-hole templates with hole diameters ranging from nanometers to microns.…”

“…[5][6][7][8][9] Quantum effects are not expected in microsized wires since the wire diameter is much larger than the mean free path of carriers (i.e., electrons and holes) in bismuth. 10 A major challenge that still remains even for microwire arrays is how to eliminate the contact resistance in order to estimate the resistivity, rather than the resistance.…”

Thermoelectric Properties of a 593-nm Individual Bismuth Nanowire Prepared Using a Quartz Template

“…[10][11][12][13][14][15][16][17][18][19] The resistivity and the Seebeck coefficient of an 850-nm-diameter bismuth nanowire were measured and found to be approximately 1.31 lX m and À57 lV/K at 300 K, respectively. 17 These values were quite similar to those of a bulk sample at 300 K; however, the temperature dependence of the resistivity was quite different from that of bulk bismuth, which always exhibits a positive temperature coefficient.…”