Date of Award

8-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Materials Science and Engineering

Advisor

Rao, Apparao M

Abstract

Bismuth in the bulk form is a semimetal with a rhombohedral structure. It has a small band overlap between the conduction and valence bands and a highly anisotropic electron effective-mass tensor. Thermoelectric materials, in which one of the three dimensions is in the nanometer regime, exhibit unique quantum confinement properties and have generated much interest in recent years. Theoretical investigations have suggested that nanowires with diameters <10 nm will possess a figure-of-merit ZT>2. Prior to this research, it has been shown by the Dresselhaus group at MIT that Bi nanowires with small enough diameters (~50 nm), prepared via the template-method, undergo a transition from a semimetal with a small band overlap to a semiconductor with a small indirect band gap. Infrared absorption, temperature-dependent electrical resistance and magneto-resistance measurements were used to confirm this semimetal-to-semiconductor phase transition.
In this thesis, we report the synthesis of ~10 nm diameter Bi nanorods using a pulsed laser vaporization method that was previously developed for preparing single-wall carbon nanotubes. The high resolution transmission electron microscopy images of our Bi nanorods show a crystalline Bi core oriented along <012> direction, and coated with a thin amorphous bismuth oxide layer. The infrared absorption and the surface plasmon peaks in our Bi nanorods are blue-shifted in energy when compared to the corresponding spectra in bulk Bi, and relative to those reported by the Dresselhaus group in 45 - 200 nm diameter Bi nanowires.

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