Showing papers by "Joshua E. Goldberger published in 2007"

Synthesis and Thermoelectrical Characterization of Lead Chalcogenide Nanowires

Abstract: Thermoelectricity is the phenomenon of conversion between thermal and electrical energy. Compared with other technologies, thermoelectric (TE) devices offer distinct advantages: they have no moving parts, contain no chlorofluorocarbons, and have a long lifetime of reliable operation. However, current TE materials have found limited commercial application due to their low efficiency. TE efficiency is related to a material-dependent coefficient, Z, and is often expressed as the dimensionless figure-of-merit, ZT, given by ZT= rS 2 T/j, where Tis the absolute temperature, r is the electrical conductivity, S is the Seebeck coefficient, and j is the total thermal conductivity. It becomes difficult to improve ZT beyond a certain point since the material properties S, r, and j are inter-dependent. [1] Presently, simple bulk materials have reached an upper limit of ZTat approximately 1. Hicks and Dresselhaus proposed that conversion of bulk materials to low dimensional materials might significantly enhance TE performance through phonon scattering and electron confinement effects. [2] Dimensional reduction has since been shown to increase boundary scattering of phonons and reduce lattice thermal conductivity, [3] possibly without negatively affecting the electrical conductivity or Seebeck coefficient. The positive effects of low-dimensionality on ZT have already been demonstrated through several theoretical [2,4–6] and experimental [7] investigations, a few of which were based on lead chalcogenide systems. [8,9] Harman et al. achieved an especially high ZTof 2.0 at 300 K with PbSeTe/PbTe quantum dot superlattices. [10] Bulk

Method of non-catalytic formation and growth of nanowires

Abstract: A method for the non-catalytic growth of nanowires is provided. The method includes a reaction chamber with the chamber having an inlet end, an exit end and capable of being heated to an elevated temperature. A carrier gas with a flow rate is allowed to enter the reaction chamber through the inlet end and exit the chamber through the exit end. Upon passing through the chamber the carrier gas comes into contact with a precursor which is heated within the reaction chamber. A collection substrate placed downstream from the precursor allows for the formation and growth of nanowires thereon without the use of a catalyst. A second embodiment of the present invention is comprised of a reaction chamber, a carrier gas, a precursor target, a laser beam and a collection substrate. The carrier gas with a flow rate and a gas pressure is allowed to enter the reaction chamber through an inlet end and exit the reaction chamber through the exit end. The laser beam is focused on the precursor target which affords for the evaporation of the precursor material and subsequent formation and growth of nanowires on the collection substrate.