Electronic Materials and Applications 2017 Plenary Speakers
Sossina Haile, Walter P. Murphy professor of materials science and engineering, Northwestern University
Title: Thermochemistry of redox active oxides and its relevance to solar fuel generation
Abstract: Laboratories around the world are pursuing a variety of promising strategies for converting solar energy into a reliable energy source for on-demand utilization. We describe here a thermochemical approach for achieving this goal using solar heat as the energy source and redox active non-stoichiometric oxides as the reaction medium. Specifically, upon exposure to high temperatures and/or inert gas, the oxide undergoes reduction (without change in crystalline phase) to release oxygen. Upon exposure to H2O (or CO2), the oxide is reoxidized, releasing H2 (or CO). We compare the thermochemical fuel production behavior of a variety of oxides, including those of the fluorite structure-type (ceria and its derivatives) and those of the perovskite structure-type (La1-xSrxMnO3). A shared characteristic of the most promising materials is that bulk oxygen diffusion (chemical diffusion) is fast, such that fuel production rates are limited either by surface reaction kinetics or, at high temperatures, gas-phase mass transfer rates. We develop an analytical model to treat the behavior under gas-phase limited behavior and explore the implications on fuel production rates.
Biography: Sossina M. Haile is the Walter P. Murphy professor of materials science and engineering at Northwestern University, a position she assumed in 2015 after serving 18 years on the faculty at the California Institute of Technology. She earned her Ph.D. in materials science and engineering from the Massachusetts Institute of Technology in 1992. Haile’s research broadly encompasses solid state ionic materials and devices, with particular focus on energy technologies. She has established a new class of fuel cells based on solid acid electrolytes and demonstrated record power densities for solid oxide fuel cells. Her more recent work on water dissociation for solar-fuel generation by thermochemical processes has created new avenues for harnessing sunlight to meet rising energy demands. She has published more than 150 articles and holds more than 15 patents on these and other topics. In 2008, Haile received an American Competitiveness and Innovation (ACI) fellowship from the National Science Foundation in recognition of “her timely and transformative research in the energy field and her dedication to inclusive mentoring, education and outreach across many levels.”
Neil Alford, MBE, FREng., professor of physical electronics and thin film materials, Vice-Dean (research) faculty of engineering, Imperial College London
Title: From ultra-high Q dielectrics to the room temperature maser
Abstract: In this talk, we will look at the problem of dielectric loss (the tan δ) in oxides and specifically, methods to beat the dielectric limit. We do this using a Bragg reflector in which the Bragg layers, which are made of sapphire, are of equal thickness. In this case the Q factor (or the inverse of the tan δ ) saturates to a plateau after approximately 3 layers. Surprisingly, we find that if the layers are aperiodic in thickness, there is no saturation and the Q factor rises quadratically to reach remarkably high values of Q=0.6×106 at 30GHz1. This result suggested that it might be possible to reach the threshold for masing. We recently demonstrated that in P-terphenyl that is doped with pentacene, when located inside a very high Q sapphire resonator, maser action can be observed. This is the first time a solid state maser has been demonstrated at room temperature and in the earth’s magnetic field2. Recent work3 has shown that miniaturization is feasible, and considerable reduction in pumping power is possible by using a strontium titanate resonator, which, by virtue of a higher relative permittivity, leads to a factor of over 5 in size reduction. It is important to note that the Purcell factor, which is the ratio of the Q factor to the mode volume, remains high. This is a key factor in the ability to exceed the threshold for masing.
1 Better than Bragg: Optimizing the quality factor of resonators with aperiodic dielectric reflectors Breeze Jonathan; Oxborrow Mark; Alford Neil McN Applied Physics Letters Volume: 99 Issue: 11 Number: 113515 DOI: 10.1063/1.3639271 SEP 12 2011
2 Room Temperature Maser Nature, 16 August 2012 DOI 10.1038/nature11339 Mark Oxborrow, Jonathan Breeze and Neil Alford (2012)
3 Enhanced magnetic Purcell effect in room-temperature masers Jonathan Breeze, Ke-Jie Tan, Benjamin Richards, Juna Sathian, Mark Oxborrow and Neil Alford Nature Comms DOI 10.1038/ncomms7215 (2015)
Biography: Professor Alford works in the field of materials engineering and has established an international reputation for his achievements in development of high strength cements, viscous polymer processing of ceramics, development of superconducting thick films, and latterly for the development of ultra low dielectric loss microwave dielectrics and ferroelectric thin films for communications.
Recent work is targeted at microwave dielectric materials and successes have been the development of ultra low loss alumina resonators and an understanding of the defect chemistry of TiO2 which has allowed the production of very high Q and high dielectric constant materials. Current activity is in the area of functional thin films for plasmonics and energy materials. His recent work has led to the development of a room temperature, earth’s field MASER which was published in Nature.
He is a fellow of the Royal Academy of Engineering, the Institute of Physics, the Institute of Materials Minerals and Mining, the American Ceramic Society, and a fellow of the Institution of Engineering and Technology. He is an associate editor for the Journal of the American Ceramic Society. In 2012, he was awarded the MBE for services to engineering. He has over 250 journal publications and is the author of 21 patents. He sits on the U.K. government’s advanced materials leadership council.