Saturday, February 22, 2014

Nanoscale pillars could radically improve conversion of heat to electricity, say CU-Boulder researchers

February 20, 2014 • Natural Sciences, Engineering, Energy • Discovery & Innovation University of Colorado Boulder scientists have found a creative way to radically improve thermoelectric materials, a finding that could one day lead to the development of improved solar panels, more energy-efficient cooling equipment, and even the creation of new devices that could turn the vast amounts of heat wasted at power plants into more electricity. The technique—building an array of tiny pillars on top of a sheet of thermoelectric material—represents an entirely new way of attacking a century-old problem, said Mahmoud Hussein, an assistant professor of aerospace engineering sciences who pioneered the discovery. The thermoelectric effect, first discovered in the 1800s, refers to the ability to generate an electric current from a temperature difference between one side of a material and the other. Conversely, applying an electric voltage to a thermoelectric material can cause one side of the material to heat up while the other stays cool, or, alternatively, one side to cool down while the other stays hot. - See more at:
In a paper published in the journal Physical Review Letters, Hussein and Bruce Davis demonstrate a Nanophonic Metamaterial: 
Phys. Rev. Lett. 112, 055505 – Published 7 February 2014
Bruce L. Davis and Mahmoud I. Hussein


We present the concept of a locally resonant nanophononic metamaterial for thermoelectric energy conversion. Our configuration, which is based on a silicon thin film with a periodic array of pillars erected on one or two of the free surfaces, qualitatively alters the base thin-film phonon spectrum due to a hybridization mechanism between the pillar local resonances and the underlying atomic lattice dispersion. Using an experimentally fitted lattice-dynamics-based model, we conservatively predict the metamaterial thermal conductivity to be as low as 50% of the corresponding uniform thin-film value despite the fact that the pillars add more phonon modes to the spectrum.
Comparison of the phonon dispersion and thermal conductivity of a pillared silicon thin film with a corresponding uniform thin film. The dispersion curves are colored to represent the modal contribution to the cumulative thermal conductivity, normalized with respect to the highest modal contribution in either configuration. The full spectrum is shown in (a) and the 0≤ω≤2.5  THz portion is shown in (b). Phonon DOS and the thermal conductivity, in both differential and cumulative forms, are also shown. The gray regions represent the difference in quantity of interest between the two configurations. The introduction of the pillar in the unit cell causes striking changes to all these quantities. [from online abstract: Phys. Rev. Lett. 112, 055505 – Published 7 February 2014]