By tapping the latest advances in nanoscience, Kavli ENSI researchers plan to unravel the most intimate details of nature's energy secrets.
NATURE EXPENDS ENERGY LAVISHLY, but rarely squanders it. From photosynthesis and building proteins to virus replication and muscle contraction, her processes are efficient, some remarkably so. Yet they occur so quickly and at such infinitesimally small scales that until recently, researchers could discern only their barest outlines.
The Kavli Energy NanoSciences Institute (Kavli ENSI) at the University of California, Berkeley and the Lawrence Berkeley National Laboratory (Berkeley Lab) was founded to bring these details into the sharpest focus. By tapping the latest advances in nanoscience, Kavli ENSI researchers plan to unravel the most intimate details of nature's energy secrets and use them to build fundamentally new types of energy systems. In fact, they have already begun.
Roundtable Discussion: A Talk with the Kavli ENSI Directors
Paul Alivisatos, Director of the Kavli ENSI (Credit: Lawrence Berkeley National Lab - Roy Kaltschmidt, photographer)
The Kavli ENSI brings together many of the world's leading experts in energy and nanoscience. This starts with Kavli ENSI director Paul Alivisatos. He is also director of Lawrence Berkeley National Laboratory, where he has led the drive to apply nanotechnology to photovoltaic cells. As a professor of chemistry and materials science at UC Berkeley, Alivisatos pioneered the synthesis of nanoscale crystals and quantum dot technology.
Omar Yaghi, one of the institute's two co-directors, invented metal-organic frameworks (MOFs), a flexible and highly porous nanomaterial that could be used for catalysis and to store hydrogen and natural gas. Peidong Yang, Kavli ENSI's other co-director, recently reported the world's first fully integrated artificial nanoscale photosynthesis system. Like Alivisatos, Yaghi and Yang are chemistry professors at Berkeley. According to Thomson Reuters, all three ranked among the past decade's 10 most influential chemists, as measured by the number of times their research was cited by other researchers.
The institute has 14 other members, many with global reputations. They include chemists, materials scientists, physicists, engineers, and biologists. Some are experimentalists, others develop new types of measurements, and some are theorists. The caliber of their contributions and their diverse approaches make them an unusual team. But what really distinguishes Kavli ENSI is the way they think about energy at the nanoscale.
Diverse Research Realigning Toward Common Goals
Many Kavli ENSI members have worked on nanoscience projects as varied as photosynthesis, nanomachine-enabled virus reproduction, nanotube motors and devices, engineered nanostructures, and ways to manipulate the movement of heat. They often collaborate with their peers, and sometimes with researchers in other disciples. Yet their collaborations tend to focus on the same types of problems. Someone working on nanotubes will collaborate with someone else working on nanotubes.
At Kavli ENSI, that nanotube researcher has the opportunity to interact with researchers who work on biological nanomachine motors. Researchers who want to control the flow of heat in nanoscopic devices get to talk with scientists who have faced similar challenges building devices to control the flow of light and electrical charges.
“These problems appear so different from one another, we did not at first realize that we shared common concerns. Kavli ENSI brings us together so we can share our insights and methods. By working with one another, we will be able to tackle problems we could never solve alone,” Alivisatos said.
Kavli ENSI member Jeff Neaton, director of Lawrence Berkeley's Molecular Foundry and a professor of physics at Berkeley, agreed.
"Collaborating with so many different creative experts across disciplines is the real opportunity here. We're putting a critical mass of knowledge in one place. There is a real qualitative change in what we can do when we bring together such a diverse set of strengths," he explained.
Kavli ENSI’s cross-disciplinary work is vitally important because world needs energy to raise living standards. As a result, most research focuses on such urgent near-term needs as improving the efficiency and emissions performance of existing technologies. While this is important, Kavli ENSI plans to conduct long-term research into the ways nature manipulates energy at the nanoscale. Ultimately, Alivisatos believes this will lead to fundamentally new ways to capture, store, and convert energy.
Such long-term fundamental research would have yielded scarce results a decade ago. Today, however, advances in measurement and matter manipulation are making new breakthroughs possible. In fact, Alivisatos said, they are already showing us that matter interacts with energy very differently at the nanoscale.
"In our ‘macro’ world, where we measure things in meters, we have developed well defined ways to convert one form of energy into another. For example, we use systems with two zones. When we heat one of them, the heat moves from the hot zone to the cold zone. You can use that heat to fire a boiler or push a piston in an engine. The laws of thermodynamics define precisely how much energy you can extract that way," Alivisatos said.
At the nanoscale, where molecules are tens of thousands of times smaller than the width of a human hair, things are very different. "Instead of hot and cold zones, the energy in nature's molecules fluctuates up and down all the time and molecules are always jumping around. Sure, we see solid matter and steady temperatures, but this is because when there is enough matter, all those fluctuations average out," he continued.
"This really shows up when you try to make tiny molecular motors. They start to do funny things. Their parts are moving randomly in addition to motion you want, so you have to think about those fluctuations as well. The laws of thermodynamics still apply, but nature exploits those principles differently than humans do."
Unraveling Mysteries with Game-Changing Technologies
Alivisatos wants to discover those principles, and advances in measuring tools are making this possible. As an example, he pointed to work by Kavli ENSI member Graham Fleming, Berkeley's vice chancellor for research, on chlorophyll, the light-absorbing molecule in photosynthesis.
"Researchers knew that the parts of the chlorophyll molecule that absorbed light were always organized in beautiful circles and other intricate arrangements. Yet they didn't understand why. Graham showed that these patterns took advantage of quantum principles to funnel energy very efficiently in a particular direction. That's something we would like to mimic in our photovoltaic systems," Alivisatos explained.
Fleming was able to unravel this mystery by using a technique called multidimensional spectroscopy. It pulses laser beams at molecules to make them resonate, the way a mallet makes a gong ring. The resonance enabled Fleming to determine the shape of the molecules. By measuring resonance changes in femtoseconds (one millionth of one billionth of a second), Fleming could trace the flow of energy through the molecules by observing how they shifted shape when a charge raced through them.
Naomi Ginsberg, a Kavli ENSI researcher who previously worked in Fleming's lab, hopes to shrink those time scales even further. She is an assistant professor of chemistry and physics at Berkeley and a faculty scientist at the Lawrence Berkeley's Physical Sciences Division.
Ginsberg is interested in the first moments of photosynthesis, when the plant's chlorophyll captures a photon's energy, stores it as an excited electron, and begins transferring its energy to other molecules. The molecules that do this show no apparent pattern, yet they are nearly 100 percent efficient.
"In my lab, we study this by using synthetic molecules that transfer energy in ways similar to chlorophyll molecules. They form crystals, but not perfect crystals. When we look at these very small imperfections, they tell us a lot about what happens in those first femtoseconds," Ginsberg said.
To make even finer measurements, Ginsberg must find a way around a serious roadblock: The light waves she uses are bigger than the molecules in the crystal. Using light to measure imperfections is like using a baseball bat to locate the holes in a pasta colander. Ginsberg hopes to overcome this problem by taking advantage of plasmons, fluid fields of electronic charges that move along a material’s surface.
“Light excites too much of the sample at a time,” Ginsberg explained. “Using the field created by the plasmons, we can excite much smaller areas. This gives us much better resolution to observe details, and we can do it at femtosecond speeds.”
Another Kavli ENSI researcher, Carlos Bustamante, uses advanced measurement equipment to study the physical properties of molecules in cells. The biophysicist is also a professor of chemistry, physics and molecular and cell biology at Berkeley.
"In the past 20 years, biologists have changed how they look at cells. We used to think of them as small bags of proteins and DNA that underwent reactions with each other," Bustamante said.
"Today, we see them as small factories filled with molecular machines that use chemical energy to perform mechanical tasks. These nanodevices have evolved over eons into precise, highly coordinated machines. It is impossible to think about how energy flows at the nanoscopic level without thinking about how nature solved this problem in cells."
An example, Bustamante said, is myosin, a motor protein that changes its shape like a spring. Binding with one molecule stretches it; binding with another snaps it back to its original shape. Because myosin is organized into muscle filaments, these nanoscale snaps work together to create large muscle contractions.
Bustamante also studies the reproduction of viruses. Viruses are essentially DNA inside a protein capsule. Once one enters a cell, it releases its DNA, which begins building more capsules and replicating more DNA. The empty capsules contain a molecular motor that drags the new DNA inside to form a complete virus.
To understand how the motor works, Bustamante used a device called an optical tweezers. First Bustamante attached plastic beads to a strand of DNA. When he shined the optical tweezers on the beads, it produced the barest of forces.
"We take an empty capsule and a single strand of DNA. When the motor grabs the DNA and starts pulling, we use the optical tweezers to pull back. So we're playing tug-of-war. From that game, we have learned how the motor works and how it converts ATP [the molecule that provides energy to cells] into mechanical work," Bustamante said.
The motor consists of a tiny ring of five ATPase molecules, which change shape when they bind to ATP molecules. One of the five ATPases coordinates the movement of the other four. When it grabs a passing DNA, it orders the other four molecules -- in sequence -- to burn their ATP and change back to their original shape. This shape change is enough to yank some of the DNA into the capsule. Each time the cycle repeats, the motor pulls in more DNA.
"The motor is more than 65 percent efficient. The great mystery is why it is so efficient. That is what we want to understand," Bustamante said.
Learning How Nature Manipulates Matter
Other Kavli ENSI members have used their ability to custom engineer chemistry to build other types of nanomotors and complex molecules. Alex Zettl, a Berkeley professor of condensed matter physics and materials science, built the world's smallest synthetic motor. It consists of a paddle that drives one perfectly smooth nanotube inside another. He has also built a radio from a nanotube.
"Gadgets like the radio are not just gimmicks, they involve real scientific challenges," Zettl said.
"We couldn't copy a conventional radio design. It was too complicated to connect the antenna, tuner, amplifier, and demodulator. So we came up with this crazy idea to make one nanotube serve all those functions simultaneously. It had to be able to vibrate and let a current pass through it. Once we saw that it could be done, it was easy to build. The design is beautifully simple and sophisticated," he said.
Zettl is excited to learn about biomolecular motors from Bustamante. "But we're not going to take our ideas and just bolt them together," he said. "We're going to want to design something elegant that will behave the way we want. I can't begin to think about this myself, I don't know enough biology. But Carlos does," he said.
Kavli ENSI co-director Yaghi is also a master of nanoscale matter manipulation. He is the father of metal-organic frameworks (MOFs), combinations of organic and inorganic units linked by strong bonds. They form very precise structures that look a bit like endlessly repeating Tinkertoys. Like Tinkertoys, they are very porous. In fact, a single gram of MOF powder (the weight of a paper clip) has nearly as much surface area as two football fields.
Because MOFs are so porous, they can actually hold more gas than an empty cylinder. Because MOFs have such high surface area, gases that "stick" to their surface actually take up less space than they would in any empty cylinder, pressure and temperature being equal.
"A vehicle that runs on natural gas today could travel two to three times further if we filled its cylinders with MOFs," Yaghi said. MOFs could also hold more hydrogen for fuel cells, or strip carbon dioxide from emissions.
What really attracts Yaghi, however, is the ability to customize his molecular Tinkertoys by attaching catalysts and other molecules to their repeating structure. He noted that photosynthesis makes sugars by placing an enzyme between two nanoscale chambers, one that attracts water and the other that attracts carbon dioxide. He believes he can create porous networks that mimic this, and perhaps learn to use sunlight to convert water into hydrogen or methane into methanol fuel -- without unwanted byproducts.
Fine-Tuning Theories and Engineering New Materials
Kavli ENSI's experimentalists and measurement experts will work with outstanding theorists and engineers. One is Berkeley Molecular Foundry director Neaton, a theorist who has a reputation for working closely with experimentalists.
"I'm driven by the challenge of connecting the structure and chemical composition of materials in complex environments to their behavior, particularly energy conversion. When you start increasing chemical and structural complexity, things get complicated quickly. That makes it really interesting. I want to develop theories that guide experimentalists in the design of materials at the atomic level in order to precisely control the flow of energy," Neaton said.
Neaton hopes to work with Kavli ENSI materials experts like Alivisatos, Yaghi, Yang, Zettl, and Felix Fischer, an assistant professor of chemistry. He also hopes to collaborate with physics professor Michael Crommie, whose ability to manipulate the shape, atomic configuration, and composition of materials should provide the precise feedback he needs to fine-tune his theories. He is also working with Ginsberg on understanding why plants capture energy from sunlight so efficiently, with the aim of developing design rules for new materials that might mimic this behavior.
Mechanical engineering professor Xiang Zhang has developed materials that bend light in ways never seen in nature. His materials would enable a stationary solar cell to capture nearly as much light as one that that moved to track the sun. The coating also traps light in cavities, where it could be converted into electricity by conventional photovoltaic materials. The same approach could also improve photosynthetic and photonic systems being developed by other Kavli ENSI researchers.
Zhang is also interested in working with Zettl on controlling the flow of heat the same way we control the flow of electricity.
"Electrical components heat up when they run, but they don't do anything with that waste heat. We envision heat circuits that could move heat only in the direction we want it to go, so we can use it the way we use electricity in conventional circuits. Then we could integrate in some type of superchip that uses electricity, heat, and light," Zettl.
Perhaps Zettl will one day build that superchip with Zhang, and exchange ideas on nanomotors with Bustamante. Alivisatos, Yaghi, and Yang have a lot to talk about in terms of synthesizing materials. Ginsberg has collaborated with Fleming and is already working with Neaton to understand the first moments of photosynthesis.
A Conversation That’s Just Beginning
Kavli ENSI makes these and many more conversations possible. Alivisatos is already thinking about ways to stir the mix even more, with talks, retreats, colloquia, and graduate student exchanges. With so many of the world's experts on energy nanoscience in one place, the new institute is certain to continue to chip away at the fundamental science behind nature's energy secrets.
Zettl agrees. "The nano world is not just smaller, but fundamentally different. The principles of physics we discovered in the laboratory still apply, but they apply very differently. It is not obvious to one person in one narrow field how to take advantage of this. That's why the institute is so important. It brings ideas together and you go, 'Wow, I didn't know that.' And now we can work together and take advantage of these new ideas to do new things at this size scale," he said.
Researchers have just begun to unravel the intimate details of nature’s nanoscopic energy secrets. Over the past decade, they have developed and mastered the sophisticated nanoscience tools needed to measure and manipulate matter at the nanoscale. Alone, many scientists have made enormous progress. By bringing them together – and encouraging them to think about energy conversion and control as a common concern – Kavli ENSI is ready to tackle scientific challenges none of its researchers could have undertaken alone.
— Summer 2013