Thermoelectric bismuth wire array composites

Bi and its alloys have the largest thermoelectric figure of merit at moderately low temperatures. Composites may perform significantly better than their bulk counterparts for thermoelectric applications because the phonon thermal conductivity is reduced at grain boundaries and interfaces. Also, the figure of merit of low dimensionality systems may be increased over that for bulk because of the increase of the electronic density of states. We have developed a technique that utilizes nanostructured insulators as a matrix for the synthesis of dense composites using high-pressure injection of the semiconductor melt. Using this technique we have prepared Bi wire arrays of diameters of 200 nm and 30 nm in a matrix of anodic porous alumina. The wire array conductivity has been measured as well as its magnetoresistance. Our measurements indicate that the wires are good conductors in the temperature range investigated at zero magnetic field. However, the magnetoresistance is very large, specially for the large nanowires and, in the presence of a magnetic field, we observe a low temperature resistance anomaly