MEETING DAY 1, Monday, May 9

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The E-MRS 2011 Spring Meeting got off to a great start on Monday at the Acropolis Congress Center in the beautiful city of Nice, France. This year's highlight is the E-MRS/MRS Bilateral Conference on Energy, which comprises 11 of the 27 symposia, and includes three Key Lectures from experts in the energy field. The remaining symposia cover such topics as Thin Films & Nanomaterials; Electronics & Photonics; Materials Fabrication & Characterization; and Organic & Bio-inspired Materials. In addition, a one day workshop entitled "From Semiconductor to New Energy--the PV Value-added Chain" will be held on Wednesday, May 11. This gives the thousands of materials scientists from all over the world who have descended on this wonderful city a chance to learn about the latest research in their field, or perhaps to gain some insight into another field.

 Bilateral Energy Conference First Key Lecture

The Dollar a Watt Initiative
Ramamoorthy Ramesh,Program Manager of the United States Department of Energy's Solar Energy Technologies Program/University of California, Berkeley

In the first of three Key Lectures in the Bilateral Energy Conference, Ramamoorthy Ramesh of the United States Department of Energy (DOE) gave a detailed view of the SunShot Program, whose goal is to produce solar energy at $1 per watt by the end of this decade. The program’s name comes from a comparison with the “MoonShot” program declared by President John F. Kennedy in 1960 to put a man on the moon before the end of that decade. Ramesh said that President Barack Obama’s SunShot initiative was designed to make solar energy cost-competitive with fossil fuels “without subsidies.” To get from solar energy’s current cost of approximately $3.40 per watt to $1 dollar a watt—without subsidies to the solar energy industry— presents challenges that could be considered as great as those faced by the space program.

DOE’s strategy here, as outlined by Ramesh, is to pursue three approaches: (1) Roadmaps, (2) Technology Readiness Levels (TRLs), and (3) Technology Components. The TRLs range from 1 (Basic Research) to 9 (Commercial Implementation); intermediate steps along this spectrum include Photovoltaic Incubators (TRLs 3-5), and Accelerating U.S. Manufacturing (TRLs 7-8). The core funding strategy right now is horizontal technology development, which funds 15 to 18 research programs at various levels, including Basic energy Sciences, Energy Frontier Research Centers, and pipelines to route basic research into applied sciences. This scheme brings together the private sector, universities, and national laboratories to generate ideas that will lead to solutions. Every six months, all participants will meet in what he called “jamborees” to share ideas across all levels and disciplines and to ask questions about what is possible. By 2014, the horizontal strategy will be abandoned in favor of vertical teams that will compete to reach the $1 dollar a watt goal by 2020.

Besides the obvious technological challenges, Ramesh noted that the “balance of system costs” are not dropping nearly as rapidly as the “module costs” in the solar energy field. Balance of system costs are mostly “soft costs” that vary from the utility to the commercial to the residential scales, but include the costs of customer acquisition; financing and contracting; permitting, inspecting, and interconnecting; and installation and performance. It will be essential to gain control of these processes to reduce the soft costs as well as to solve the extreme technological challenges ahead. Materials scientists must play a large role in achieving technical solutions if the SunShot program is to be as successful as the “MoonShot” program.

Bilateral Energy Conference Technical Talks (Symposia Q to ZZ)

Symposium R: Advances in inorganic materials and concepts for photovoltaics

Quo Vadis Photovoltaics 2011
Arnulf Jaeger-Waldau, of the European Commission’s Joint Research Centre (JRC), kicked off the symposium on inorganic photovoltaic materials with an overview of recent progress. He then addressed the remaining challenges facing the implementation of photovoltaics. Despite the impressive 40%, recent yearly growth of photovoltaic cells, much work remains to be done, particularly improving the efficiency of the photovoltaic module and modifying the electric grid to better accommodate decentralized renewable energy sources. Sustained aggressive growth is necessary for photovoltaics to provide a significant portion of the world’s energy consumption, which is predicted to double by 2050. Increasing energy storage capacity is also a research priority necessary for wide-spread implementation of photovoltaics, according to Jaeger-Waldau. On the plus side, all previous estimates on the rate of deployment of photovoltaic installations have been conservative. He believes the future is bright so long as we keep out-performing our previous expectations. Jaeger-Waldau set the stage nicely for the talks to follow in this symposium by concluding that we are at the dawning of the solar age.

Symposium T: Materials for Solar Hydrogen via Photoelectrochemical Production

Doped TiO₂ Nanotubes (and Mesosponges): Modification Approaches for Strongly Enhanced Water Splitting Activity.
Patrik Schmuki and his colleagues at the University of Erlangen, Nuremberg, reported on methods they have developed to control the morphology of doped TiO2 nanotubes on Ti for use in the Fujishima and Honda (1972) electrolytic water splitting technique. The nanotubes grow by self-organization on Ti using an anodization method with an ethylene glycol and HF solution as the electrolyte. By varying the F- concentration from 0.05% to 0.50% and the anode potential from 2 to 20 V, they were able to synthesize amorphous TiO₂ nanotubes with diameters from 10 nm up to a record 800 nm. Furthermore, they were able to control the morphology from bamboo-like structures to branching structures to a highly porous “nano-lace.” These tubes can be modified by surface decoration and by the deposition of metals, semiconductors, or magnetic materials inside the nanotubes, Analysis showed the tubes to be double-walled,V-shaped materials, with thinner walls at the top than at the bottom; the outer shell was pure TiO₂ while the inner shell contained some carbon.

The researchers performed water-splitting experiments using the TiO₂ nanotubes after annealing the amorphous structures to produce either anatase or rutile crystalline materials. With TiO₂ alone, the maximum solar to hydrogen conversion efficiency was 0.2%. However, they improved this greatly by catalyzing the oxygen evolution reaction using Ru. Starting with a TiRu alloy as the substrate, the anodization reaction produce nanotubes that were essentially Ti doped with Ru. These doped structures produced a five-fold increase in the water splitting efficiency of TiO₂ alone. Ru doping also made the material photostable over long time periods.

Perovskite oxynitride thin films as visible light-sensitive photocatalyst
The ability to use visible light to split water into hydrogen and oxygen would provide a clean and reusable method of energy conversion from solar energy to hydrogen fuel for use in fuel cells. Laurent Le Gendre addressed the challenge of creating a photocatalytic material sensitive to visible light by discussing his research on oxynitride thin films performed at the Université de Rennes, France, and other locations. He began the talk with a look at the various requirements for a photocatalytic material. These include the ability to absorb visible light, chemical stability in water, and a suitable band-gap position for the oxidation and reduction of H₂O. Starting with LaTiO₃ as the base oxide with a band-gap larger than 3 eV, Le Gendre and his colleagues were able to reduce the band-gap below 2.5 eV by adding nitrogen. This was done by sputtering films of LaTiO₂N on Nb-doped SrTiO₃ using both a LaTiO₂N target and thermal nitridation from flowing ammonia. Higher nitrogen plasma content further lowered the film bandgap down to ~2 eV, but this had a detrimental effect on crystallinity. The optimal photocatalytic behavior this research group demonstrated was for epitaxial LaTiO₂N films further modified with a colloidal IrO₂ catalyst, which helped to enhance the photocurrent.

Symposium W: Materials Science for Large Scale Energy Storage

Lithium Solid Electrolyte Thio-LISICON: Properties and Applications to All-Solid-State Lithium Sulfur Battery
In order to meet more stringent mileage standards by 2030, a new type of battery is needed. The Li-ion batteries that power some of the hybrid automobiles today are capable of 70 to 100 Wh/kg, but their theoretical limit is 250 Wh/kg. Standards proposed for the year 2030 will require somewhere in the range of 500 to 700 Wh/kg. Ryoji Kanno and his colleagues at the Tokyo Institute of Technology are trying to develop an all-solid-state battery with very high energy density to meet this challenge. Their focus is on a material they call LISICON for Lithium Super Ionic Conductor. The general formula for this thio-LISICON solid electrolyte material is Li_xM_1-yM’_yS₄, where M can be Si, Ge or P, and M’ can be P, Al, Zn, or Ga. The researchers have determined that a promising electrode for this electrolyte system is a carbon-sulfur composite based on a mesoporous carbon material with sulfur in the pores. They obtained a high energy capacity for an all-solid-state Li battery made with carbon-sulfur composite electrodes in a solid thio-LISICON electrolyte.

DuPont™ Energain™ Battery Separators: an Overview
Joseph Dennes, a researcher with Dupont in Wilmington, Delaware, described the company’s new Energain Battery separator, which is based on a nanofiber/nanowoven polyimide material. This material is made by combining spinning and electroblowing processes to create continuous polymer filaments with diameters between 200 and 1000 nm. This polyimide material was subject to heat curing to produce a battery separator with desirable properties. To characterize the separator, Dennes analyzed the degree of imidization and the crystallinity index. Imidization proved to be complete; crystallinity increased with increasing temperature. The results suggest that increased crystallinity has a significant effect on the mechanical properties and solvent susceptibility of the separator. Dennes also discussed a novel infrared-based method for determination of relative crystallinity in polyimides.

Symposium ZZ: Advances in Thermoelectric Materials & Devices for Energy Applications

Development of optimal thermoelectric measurement protocols
Thermoelectric effects have applications in generating electricity from temperature gradients. The Seebeck coefficient is the figure of merit for thermoelectric materials. Joshua Martin of the U.S. National Institute of Standards and Technology, in Gaithersburg, Maryland, began his talk on Seebeck coefficient metrology by covering the history of thermoelectric measurements and reviewing the basics of the technique. He recommended a recent review article entitled “High temperature Seebeck coefficient metrology" published in the Journal of Applied Physics in 2010. The talk then focused on how a number of elements in thermoelectric measurements may give rise to unexpected uncertainties; Martin encouraged consideration of these elements in order to improve the ability to compare results between different experimental setups. He introduced his experimental setup in which he has minimized potential sources of uncertainty and voltage offsets. He has also simulated many common problems, such as imprecise voltage and temperature measurement coordination, as well as offsets in the sample measurement location, to evaluate the degree to which these uncertainties can influence the determination of the Seebeck coefficient.

Photon and molecular transport enhanced thermionic energy conversion
Thermionic energy conversion uses ions released by a heated material to create a circuit. Robert Nemanich of Arizona State University discussed research using CVD-grown doped diamond thin films in a configuration that allows for high thermionic emission. The diamond thin films were doped with nitrogen, resulting in a significant reduction of the film’s work function. This allowed electrons to be easily emitted from the diamond film surface. Using hydrogen or methane gas also improved the thermionic emission up to a critical pressure where the gas still aided in the charge transfer but did not significantly reduce the mean-free-path. The films exhibited high efficiency in the 500°C range. The application of visible light greatly enhanced the electron emission, suggesting possible applications in photo-assisted thermionic emission energy conversion configurations.

Technical Talks from Other Symposia

Symposium A. MACAN11: Reconciling Atomistic and Continuum Approaches to Interfaces

Multiscale modeling of intermixing in Al/Ni multilayered materials
Vapor deposited multilayered aluminum oxide and bimetallics are promising materials for MEMS technologies as energy carriers; they can also find uses in biology and chemical applications such as smart fuses and microinitiators. Cloé Lanthony of LAAS-CNRS spoke about combining atomistic density functional theory (DFT) calculations with a macroscopic 1D model of chemical kinetics for an Al/Ni system. The DFT calculations described the system as infinite layers stuck together, based on sequential temperature changes and compositional evolution in the Al/Ni system. The researchers were also able to calculate the number of vacancies for the Al/Ni system and discovered a lattice mismatch in the system. Lanthony concluded by emphasizing that vacancies and a lattice mismatch play a significant role in ignition time and temperature. Also, the vacancies allow for the migration of atoms between different layers, thus increasing atomic mixing.

Symposium D: Synthesis & Characterization of Nanoscale Multifunctional Oxide Films

Defects and Strain-dependent Material Properties of Rare Earth Oxides from First Principles
Oxide thin films on silicon have many potential applications, including oxide gate dielectrics and non-volatile oxide-based memory systems. Frank Grosse of the Paul-Drude-Institut für Festkörperelektronik in Berlin, Germany, highlighted recent results on the growth of (La_1-xLu_x)₂O₃ on (111) oriented silicon by molecular beam epitaxy. The oxide films can be grown lattice-matched to Si (111) with an interface that appears defect free. Another experimental approach is to grow superlattices of alternating layers of La₂O₃ and Lu₂O₃. Each of these component layers has a high mismatch to silicon, though in opposite directions. As a superlattice, the material grows epitaxially, with each layer being strained either in biaxial tension or compression. The structure and electronic properties of the random alloy and superlattice were studied and compared using density functional theory (DFT) for hexagonal, perovskite, and cubic phases. DFT provides an excellent tool for predicting and understanding the deviation in structure and electronic properties from the random alloy case to the superlattice case.

Symposium K: Protective Coatings and Thin Films

Evaluation of Composition, Mechanical Properties, and Structure of nc-TiC/a-C:H Coatings Prepared by Balanced Magnetron Sputtering
Pavel Souček and his coworkers at Masaryk University in the Czech Republic have developed nanocomposite nc-TiC/a-C:H coatings with high hardness, high modulus, low friction, and low wear characteristics. Starting with a Ti target in a well-balanced magnetic field, they built up a 70-nm-thick layer of a nanocrystalline Ti adhesive interlayer by magnetron sputtering, then added an amorphous carbon-hydrogen layer using acetylene as the source of carbon and hydrogen. Increasing the flow rate of acetylene led to a linear decrease in Ti content and a linear increase in C, with low oxygen contamination. They achieved a peak Rockwell hardness of 46.2 GPa and a peak Young’s modulus of 414.8 GPa at an acetylene flow of 12 sccm. The composition of the resulting 4–6 micron-thick coating was approximately 38 at.% Ti and 56 at.% C. SEM and TEM analyses of the coating showed a dense columnar structure with elongated grains approximately 15 nm wide.

Symposium P: Bio-inspired and Bio-integrated Materials as New Frontiers Nanomaterials

Point and Stand-off Detection for Water Safety and Security
Water supply chains remain susceptible to contamination with limited means of detection. Asho Vaseashta, Director of the Institute for Advanced Sciences Convergence & International Clean Water Institute in the United States, presented a general overview of detection methods using nanomaterial-based sensors, including point contact and contact-less sensors. Vaseashta described various nanomaterials used as sensors, such as carbon nanotubes and porous silicon. He also discussed thermo-stimulated photoelectron-based sensors and multiple sensors using carbon-polymer systems.

 Scanning the Meeting

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The Meeting Scene e-newsletter of the Materials Research Society (MRS) presents news from MRS and other conferences directly from the conference venue.

This work was partially supported by the IMI Program of the National Science Foundation under Award No. DMR 08-43934. Specifically, the work of Apprentice Science Reporters Charles Brooks and Jean Njoroge was funded under this NSF award, which is managed by the International Center for Materials Research, University of California, Santa Barbara, USA.

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