Modeling the thermoelectric transport properties of nanowires embedded in oriented microporous and mesoporous films

The efficiency of thermoelectric devices has not increased significantly du ring the last 40 years, and currently, the figure-of-merit (ZT) of the best materials is less than one. However, there has been a resurgence of intere st in thermoelectric materials due to recent results that have shown that s ize-effects in nanostructured materials may enable much more efficient ther moelectric devices. Theoretical calculations for isolated single nanowires predict over a 10-fold increase in the figure-of-merit. In order to realize these size-effects, wires must be synthesized with diameters less than the thermal de Broglie wavelength (typically less than 10 nm) which is smaller than is currently accessible by lithographic techniques. Also, in order to transfer meaningful amounts of thermal energy, a practical device must con sist of an array of a large number of nanowires in parallel. One way to pot entially synthesize these nanowire arrays is to use the pores of microporou s and mesoporous materials as a mold to template the diameter and orientati on of wires of suitable thermoelectric materials. Here we provide a review of the relevant physics and derive a model to assess the feasibility of usi ng microporous and mesoporous frameworks in the fabrication of thermoelectr ic devices. The model accounts for the possible deleterious effects of ther mal conduction through the microporous or mesoporous framework and the pres ence of bulk thermoelectric material (that may result from defects in the m icroporous or mesoporous framework) in parallel with the wires on the therm oelectric figure-of-merit. Simulation results are reported for SBA-15, MCM- 41, and zeolites VFI, LTL, and LTA embedded with Bi2Te3 nanowires. The resu lts show that the microporous frameworks may yield figures-of-merit much la rger than one while thermal conduction through most mesoporous frameworks r educes the figure-of-merit below the level of currently available using tra ditional thermoelectric materials. (C) 2001 Elsevier Science B.V. All right s reserved.