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Spring 2015

Layers and Meaning: An Introduction

Robert L. Sacci

"What could we do with layered structures with just the right layers? What would the properties of materials be if we could really arrange the atoms the way we want them? They would be very interesting to investigate theoretically. I can't see exactly what would happen, but I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do." ~Richard P. Feynman, Lecture "There's Plenty of Room at the Bottom," 1959

At the advent of powerful atomic probing and layered material synthesis techniques, Nobel Laureate Richard Feynman speculated on the breadth of new materials and chemistries that could now be discovered. Fifty-five years later, Energy Frontier Research Centers (EFRCs) are behind some of the major advances in producing and studying layered materials and interfacial chemistry. Layered materials demonstrate intriguing properties that can be tuned to accommodate particular applications and are becoming increasingly important in energy science. In this issue, we highlight EFRC research that focuses on layered materials and interfacial chemistry.

Controlling what happens at surfaces and interfaces is as challenging as it is important for human societies. Interfacial science has played an important role in human technology since antiquity. In primitive societies, examples of interfacial control could be found in the weatherproofing of clothing and building materials. In today's societies, we tune interfacial properties of materials in solar cells to enhance the conversion of sunlight to clean sustainable electricity, and the properties of electrodes to efficiently store and deliver that electricity when needed.

The study of surfaces and interfacial phenomena formally began in the 1930s with the Nobel Prize-winning work of Langmuir and Hinshelwood, which focused on the surface reactivity of catalysts. Scientists are continuing to build upon this research, expanding from the study of smooth surfaces to real-world surfaces that are rough and contain many defects. Today's scientists are also working to develop next-generation catalytic surfaces for applications such as fertilizer manufacturing and removing pollutants from automobile and refinery exhausts.

The control that Feynman dreamed of in his speech is possible at the molecular level by using molecular building blocks and controlling layered structures. Using sophisticated computer simulations and novel synthetic techniques, materials can now be custom designed and developed to have a two-dimensional layered structure, enhanced catalytic activity, improved gas binding, large energy storage capacity, and high electronic conductivity, for example.

Scientists at the EFRCs use various techniques to control and study surface and bulk or interior properties of new materials. This issue showcases examples of these techniques beginning with atomic layer deposition, particularly its atomic-level control for producing novel catalysts in biofuel processing, and the controlled assembly of metal-organic frameworks (MOF) for reactive oxygen production and semi-conductor applications.

The research highlights of this issue extend to surface interactions and emphasize the importance of interfacial chemistry. The EFRCs foster high-level, cross-disciplinary collaboration that has enabled the fabrication of nano-engineered surfaces that gather energy from atmospheric dew, a process originally envisioned by Lord Kelvin in 1867, but until recently, no group could effectively demonstrate it. Another example of nano-surface engineering is tuning showcased by the zinc-doped metallic surfaces that exhibit enhanced activity toward biomass conversion for renewable energy sources.

Interfacial chemistry is shown to have far reaching effects in curtailing carbon dioxide emissions from fossil fuel use. For example, storing carbon dioxide for millennia in geologic structures is controlled by the physical properties of the rocks and brine levels in underlying aquifers. Looking more deeply into materials, scientists are investigating how a new computational method could be used to predict which materials are the most energy efficient for carbon capture.

Computational simulations are showing how molecular and even atomic building blocks can be arranged to produce better catalysts, more efficient solar cells, and better energy storage materials. For example, the use of multiple nano- to micron-sized layers was predicted to allow greater collection efficiencies in high-voltage solar cells. Also, simulations and neutron scattering have shown that increasing the number of nano-sized carbon tunnels in energy storage materials increase power density.

While there is still much work to be done to realize Feynman's dream, EFRC scientists are tirelessly seeking new methods to design, build, and study next-generation materials and surface chemistries. The multidisciplinary nature of the EFRCs facilitate the research necessary for providing clean energy solutions, combating adverse environmental impacts of fossil fuels, and discovering new frontiers of energy sciences.

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Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.