Designing Nanocomposite Materials for Solid-State Energy Conversion

By Timothy D. Sands

Purdue University

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New materials will be necessary to break through today's performance envelopes for solid-state energy conversion devices ranging from LED-based solid-state white lamps to thermoelectric devices for solid-state refrigeration and electric power generation. The combination of recent materials advances and development of practical 'bottom-up' nanofabrication methods offers to provide the degrees of freedom necessary to design practical nanocomposite-based devices that can eclipse the performance of conventional thin-film or bulk devices. Relaxation of elastic mismatch strain at free surfaces in semiconductor nanorods and nanowires allows the accommodation of a broader range of lattice mismatch and band-lineups in coherent nanostructures than is possible in thin-film heterostructures. This new space for 'bandgap engineering' provides the opportunity to confine and manipulate electrons, phonons and photons at scales that are comparable to their characteristic wavelengths and scattering lengths. Likewise, nanorod, nanowire and multilayer nanocomposites intimately combine materials with disparate functionalities to create fundamentally new materials that do not resemble the constituent materials in their transport properties, anisotropy or crystal structures. In this talk, I will illustrate these new opportunities with our recent work in the design of monolithic phosphor-free white light emitters based on nanorod heterostructures, and metal/semiconductor solid-state thermionic energy converters utilize.


Tim Sands received his Ph.D. in Materials Science at the University of California, Berkeley in 1984. He joined the Purdue faculty in the fall of 2002 after nine years as a faculty member of the Department of Materials Science & Engineering at Berkeley. While at Berkeley, he served as the Chair of the Applied Science & Technology (AS&T) graduate group (97-99). From 1984 to 1993, Sands was a Member of Technical Staff, a District Manager, and a research group Director at Bell Communications Research (Bellcore) in Red Bank, NJ.

He has published over 200 papers and has been granted 11 patents in the areas of metal/semiconductor contacts, heteroepitaxy, thermoelectric materials, ferroelectric and piezoelectric materials and devices, semiconductor nanostructures, laser processing and heterogeneous integration.

Among the most significant of his scientific and technical contributions are i) the understanding of the interface reactions leading to low-resistance, shallow and thermally stable ohmic contacts to compound semiconductors; ii) demonstration of the first stable and epitaxial metal/III-V heterostructures; iii) transfer of the Laser Lift-off process for GaN LED packaging, for which he was a co-inventor, to industry; and iv) leadership of the team that fabricated the first monolithic fluorescence detection microsystems.

His present research efforts are directed toward the development of novel nanocomposite materials for applications in solid-state lighting, direct conversion of heat to electrical power, and thermoelectric refrigeration (see for more information).

Dr. Sands is a recipient of the Materials Research Society (MRS) Von Hippel Award for Graduate Student Research and the Robert Lansing Hardy Gold Medal (The Minerals, Metals and Materials Society). He has served as a Councilor for MRS ('97-'99), as Co-chair for the 1994 Fall MRS Meeting, and as the Chair of the Electronic Materials Committee ('95-'97). Professor Sands is presently the Basil S. Turner Professor of Engineering and a member of the Birck Nanotechnology Center, with joint appointments in the Schools of Materials Engineering and Electrical & Computer Engineering at Purdue.

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Researchers should cite this work as follows:

  • Timothy D. Sands (2005), "Designing Nanocomposite Materials for Solid-State Energy Conversion,"

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