Everyone Starts Small: How Metals Learn to Behave

Watson Lecture Preview

On Wednesday, February 12, Assistant Professor of Aerospace Dennis Kochmann will explain how controlling a material's complex structural details from the atomic scale up can affect its behavior in everyday life. The talk begins at 8:00 p.m. in Caltech's Beckman Auditorium. Admission is free.

Q: What do you do?

A: We study the mechanics of materials. Specifically, we're making computer models that start with collections of individual atoms, and we're trying to extend those models all the way up to the scale of visible objects. We also have a lab where we make new materials and test them to see if they behave the way the models predicted. And eventually, once we have that understanding, we'll try to go back downward—if we want a material with certain properties, how do we make it?

Most innovation nowadays depends on new materials. In energy, in space travel, in biomedicine, many of the challenges involve finding a material that can meet certain conditions or that we can use in an extreme environment. It used to be that whenever you needed a specific material, you would tell your colleagues, "I want a material that has this and this and this property," and they'd look in various handbooks and try to find something that met your conditions. Nowadays we do it online, but it's basically the same process. In the future, we want to be able to tell our computer, "Okay, I want this and this and this," push a button, and an hour later the material is delivered to you. We're far away from this, of course.

It's much more complicated than just looking at the periodic table and throwing atoms together. Getting something on the atomic level is just one challenge. We also need to bridge the scales from atoms to the visible, macroscopic scale that we can see with the naked eye. There are many, many levels in between. Atoms form crystals. The crystals have defects. The defects arrange into networks. So if you put any material under a microscope, as you zoom in closer and closer you'll find that on each level there's a very specific pattern. These very specific structures and the things going on at each level are what give the material its unique properties.


Q: What gets you excited about this?


A: Well, as any researcher would say, it's doing something nobody has ever done before. In our case, making new, peculiar materials, or materials with extreme properties.

For example, we are designing materials that are pretty boring under ambient conditions, but if you tweak the temperature or the electric field the material suddenly gets 100 times stiffer and 100 times better at damping out vibrations. So you can control these properties with the push of a button. Usually, stiffness and damping are mutually exclusive. On the atomic scale, if you want something stiff and strong you need a perfect crystal. If you want high damping, there must be mechanisms at the microscale such as crystal defects that somehow absorb energy. Materials that do both are of great interest in applications such as aerospace—airplanes and spacecraft need materials that can withstand extreme conditions while absorbing vibrations, because there's a lot of vibration going on in them.


Q: How did you get into this line of work?

A: Before I went to college, this was absolutely not my goal. I started playing classical music on the organ when I was a teenager, and so I was trying to decide between music and chemistry. Then someone told me that engineering was a safer career, so I ended up in majoring in mechanical engineering. I wanted to be a design engineer, but by coincidence I was offered a job in solid mechanics, which is the mechanics of materials. By yet another coincidence I ended up at the University of Wisconsin–Madison, where I worked with Roderic Lakes and Walter Drugan—pioneers in the design of extreme materials. So as is often in life, it was many small events and little coincidences.


Q: Do you still play the organ?

A: I do. I'm very lucky. There's a church up in Altadena that lets me go up there every Friday morning for two hours and practice.


Q: Do you plan on giving a recital any time soon?

A: [laughs] No.


Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.


Douglas Smith
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Friday, March 14, 2014
Avery Dining Hall – Avery House

Workshop: Comedy as a Teaching Tool

Caltech's "Secrets" to Success

Everyone who really knows Caltech understands that it is unique among universities around the world. But just what makes Caltech so special? We've asked that question before, and the numbers don't tell the full story. So, is it our focus? Our culture? Our people?

The UK's Times Higher Education magazine recently tackled the topic, asking more specifically, "How does a tiny institution create such an outsized impact?" Caltech faculty share their perspectives in the cover story of the magazine's latest issue.

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Nanoscale Materials and Big Solar Energy: An Interview with Harry Atwater

As a high school student during the oil crisis of the 1970s, Harry Atwater recognized firsthand the impact of energy supply issues. Inspired to contribute to renewable energies, his research at Caltech today works to develop better thin-film photovoltaics—cheaper, lighter, more efficient alternatives to the bulky cells now used in solar panels.

In addition to his individual research interests in photovoltaic cell development, Atwater is also part of a collaborative effort to advance solar energy research at the Joint Center for Artificial Photosynthesis (JCAP)—a U.S. Department of Energy (DOE) Energy Innovation Hub. JCAP, which is led by a team of researchers from Caltech and partner Lawrence Berkeley National Laboratory, aims to develop cost-effective fuel production methods that require only sunlight, water, and carbon dioxide.

Atwater, who serves as the project leader for the Membrane and Mesoscale Assembly Project at JCAP, recently chatted with us about his research, his background, and why he came to Caltech.

What originally drew you to Caltech?

It was the opportunity to pursue my area of research. I felt that Caltech was the best research environment I could [be in] for mixing fundamental science and engineering technology. Caltech is very developed in its orientation toward engineering and technology, and its connection to technology in many areas like aerospace, photonics, communications, semiconductors and chemistry. It is a great combination—an institutional focus on fundamentals but also a focus on applying those fundamentals to engineer new technologies.

What are your research interests?

My research is at the intersection of solar energy and nanophotonic materials. Nanophotonic materials are materials and structures in which the characteristic length scale of the material is less than the scale of the wavelength of light—meaning that they're so small that they must be visualized with something that has a wavelength much smaller than that of visual light. Half of my research group is focused on the fundamentals of nanophotonic materials. These materials could form the building blocks of a chip-based optical device technology for improved imaging in computing, communications, and for the detection of chemical and biological molecules.

The other half of my group is focused on improving solar energy. We are investigating several approaches to creating very low-cost and ultrahigh-efficiency thin-film photovoltaics, which are an alternative to, and the future of, today's solar cell panels. In our design, we use thin layers of semiconductors for absorbing sunlight. The Joint Center for Artificial Photosynthesis (JCAP) fundamentally focuses on using semiconductor photonic materials and devices to create fuel from solar energy, so it's a really good match for our work.

How do these semiconductors you're working with make thin-film photovoltaics cheaper, thinner, and more efficient?

Most materials cost nearly the same amount when you just think about them on a price-per-atom basis. What makes materials expensive or cheap is the cost of the synthesis and processing methods used to make them with sufficient purity and perfection to enable high performance. Much of what we do is aimed at either designing new syntheses that can yield high-performance materials in a scalable low-cost fashion or designing new structures and devices whose performance is robust against use of impure or defective materials.

How did you first get interested in your field?

I would say that my interest in solar energy dates back to the first big energy crisis in the 1970s, when I was a high school student. I grew up in Pennsylvania, and I remember my school was shut down for a few weeks in the wintertime because there literally was no oil to heat the burner. I thought then that addressing supplies of energy was an important problem. It made a big impression on me. But at that point, I hadn't really thought about how I could contribute to a solution.

But then in graduate school, I got interested in things at the intersection of physics and electrical engineering, which is really where my work lies. As a graduate student at MIT, I began to focus on developing new technologies for thin-film solar cells. At MIT, I worked in one of the first nanostructure fabrication labs in the country, where it became apparent to me that we could make nanostructures and characterize their properties.

You were among the first scientists to study these nanostructures. What was that like?

Nowadays "nano" is sort of pervasive in the ether—nanomaterials are not unusual. At that time, it was as invisible to the general public as the Internet. It became obvious to me that there was a lot of opportunity to use nanofabrication principles and techniques to make new optical materials. Later, around 2001, we ended up playing a pretty significant role in starting another new field called plasmonics, which studies the behavior of the excitations created by light in metals. This new field led to the first serious and widespread efforts to make these kinds of optical devices and optical materials out of metals.

Do you have any hobbies or interests outside of your research?

I'm an avid soccer player, and I play weekly with the graduate students. Until my kids got to an age when I started embarrassing them, I was coaching them every week. That's what I like to do for fun.

Atwater joined the Caltech faculty as an assistant professor of applied physics in 1988, becoming an associate professor in 1994 and a professor in 1999. Now the Howard Hughes Professor of Applied Physics and Materials Science, Atwater has many roles on campus and beyond. These include serving as the director of the Resnick Sustainability Institute, the director of the Department of Energy's "Light-Material Interactions in Energy Conversion" Energy Frontier Research Center (LMI-EFRC), and most recently as the editor-in-chief of a new research journal, ACS Photonics.

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1+1= 3, or How I Learned to Stop Worrying and Love Holistic Circuits

Watson Lecture Preview

In a matter of a few decades, silicon chips have transformed the way we live, taking us from typewriters, landlines, and turntables to computers, cell phones, and MP3 players (which by now, are in your cell phone anyway). Today, with the continued development of complementary metal oxide semiconductor (CMOS) technology, literally billions of transistors can be placed on a tiny, inexpensive chip and customized to perform all sorts of marvels. Developing these technologies and exploring potential applications keeps Ali Hajimiri, Thomas G. Myers Professor of Electrical Engineering at Caltech, and everyone in his lab busy. Hajimiri will lecture on integrated circuits and their applications in our daily lives as part of the Earnest C. Watson Lecture Series on Wednesday, January 29, 2014, at 8 p.m. in Caltech's Beckman Auditorium. Admission is free.

What kind of research do you do?

I'm interested in crafting hardware devices for a range of applications, from communications, radars, and sensors to projection, imaging, and medical technologies. My focus is really on coming up with new solutions to interesting problems, using the underlying circuit and device technology we are now capable of developing.

What do you find most exciting about what you do?

Creating something that didn't exist, making a difference. That is what making a difference is—creating something new. In a way it's like having a crystal ball to look into the future, except for the fact that you're making the future.

What is special about today's circuit technology?

CMOS is basically a low-cost technology that's used for making microprocessors. You can have a tiny chip, smaller than your fingernail, and there's a whole city on there. Our chips are manufactured through a lithography process, which basically means that they are made layer by layer. It's like photography, but in the other direction: instead of taking a negative and enlarging it, we take a stencil and make it very tiny.

What can you use these circuits for?

On the commercial side, our lab developed a technology for power amplifiers that go into cellular phones. These chips are smaller, cheaper, and better than those that came before, and now they are in hundreds of millions of cell phones worldwide. We've also developed the world's first radar-on-a-chip. It's an entire self-operating radar system with the antennas and everything on a chip smaller than a dime. It's intended for automotive applications. Eventually it should be able to prevent automobile collisions because your car will automatically detect when, for example, another car is cutting you off, and it will brake or steer your car away.

One of the greatest things about CMOS technology is that these circuits can be made in volume at a very low cost, maybe a dollar or two. This is especially important for medical devices. You can make an amazing diagnostic device, but if they cost $100,000, there won't be very many people who will end up using them. With CMOS, a variety of medical devices can be made available very widely.

When you're coming up with these ideas, are you thinking in terms of a problem you would like to solve, or are you looking at a chip and imagining what you could do with it?

Both. The way I describe it to my students is that you want to expand in both directions. You want to start with the relevant problems, but you also want to say, "These are the technologies that I have at my disposal. What can I do with them?"  They are like two trees, one that goes down and the other that goes up. The multiple branches at some point start meeting each other. When they connect, you've got a way to link an application to a device.

How did you get into this line of work?

My background is in electrical engineering. But even as a boy, I really liked making stuff. When I was in kindergarten, I used to pound rocks and pebbles and stir up different combinations of them. I made cement, essentially. A couple of years later, I invented a device for avoiding afternoon naps. I really didn't like taking afternoon naps, so I made an alarm that I put under the carpet, and when my mom stepped on it, I would hear it buzz, and I could immediately pretend to be asleep.

How long did it take her to catch on?

For some reason she always avoided stepping on that spot.  I think she must have been on to me.

Cynthia Eller
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Monday, May 5, 2014

Teaching Statement Workshop - 2-Part Event

Monday, May 12, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

Teaching Statement Workshop - 2-Part Event

Friday, April 4, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

Spring TA Training

Tuesday, April 1, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

Spring Head TA Lunch

Lessons from the 1994 Northridge Quake

Current Earthquake Research at Caltech

Since the magnitude 6.7 Northridge earthquake 20 years ago (January 17, 1994), researchers at the California Institute of Technology (Caltech) have learned much more about where earthquakes are likely to happen, and how danger to human life and damage to property might be mitigated when they do occur.

"The Northridge quake really heralded the beginning of a new era in earthquake research, not only in southern California, but worldwide," says Michael Gurnis, John E. and Hazel S. Smits Professor of Geophysics, and director of the Seismological Laboratory at Caltech.

In the years just prior to the Northridge earthquake, Caltech launched a program called TERRAscope supported by the Whittier foundations, which placed high-quality seismic sensors near where earthquakes occur. The Northridge earthquake was, in effect, the first test of TERRAscope in which Caltech scientists could infer the distribution of an earthquake rupture on subsurface faults and directly measure the associated motion of the ground with greater accuracy. "With a modern digital seismic network, the potential of measuring ground shaking in real time presented itself," says Gurnis. "The real time view also gave first responders detailed maps of ground shaking so that they could respond to those in need immediately after a quake," adds Egill Hauksson, senior research associate at Caltech.

To give us this new view of earthquakes, Caltech collaborated with the U.S. Geological Survey (USGS) and the California Geological Survey to form TriNet, through which a vastly expanded network of instrumentation was put in place across southern California. Concurrently, a new network of continuously operated GPS stations was permanently deployed by a group of geophysicists under the auspices of the Southern California Earthquake Center, funded by the USGS, NASA, NSF, and the Keck Foundation. GPS data are used to measure displacements as small as 1 millimeter per year between stations at any two locations, making it possible to track motions during, between, and after earthquakes. Similar and even larger networks of seismometers and GPS sensors have now been deployed across the United States, especially EarthScope, supported by the NSF, and in countries around the world by various respective national agencies like the networks deployed by the Japanese government.

Initially, says Gurnis, there were not many large earthquakes to track with the new dense network of broadband seismic instruments and GPS devices. That all changed in December 2004 with the magnitude 9.3 earthquake and resulting tsunami that struck the Indian Ocean off the west coast of Sumatra, Indonesia. Quite abruptly, Caltech scientists had an enormous amount of information coming in from the instrumentation in Indonesia previously deployed by the Caltech Techtonics Observatory with support from the Gordon and Betty Moore Foundation. By the time the magnitude 9.0 Tohoku-Oki earthquake hit northern Japan in 2011, the Seismological Laboratory at Caltech had developed greatly expanded computing power capable of ingesting massive amounts of seismic and geodetic data. Within weeks of the disaster, a team led by Caltech professor of geophysics Mark Simons using data from GPS systems installed by the Japanese had produced extensive measurements of ground motion, as well as earthquake models constrained by this data, that provided new insight into the mechanics of plate tectonics and fault ruptures.

The Tohoku-Oki earthquake was unprecedented: scientists estimate that over 50 meters of slip on the subsurface fault occurred during the devastating earthquake. Currently, scientists at Caltech and the Jet Propulsion Laboratory are prototyping new automated systems for exploiting the wealth of GPS and satellite imaging data to rapidly provide disaster assessment and situational awareness as events occur around the globe. "We are now at a juncture in time where new observational capabilities and available computational power will allow us to provide critical information with unprecedented speed and resolution," says Simons.

Earthquakes are notable—and, for many, particularly upsetting—because they have always come without warning. Earthquakes do in fact happen quickly and unpredictably, but not so much so that early-warning systems are impossible. In a Moore Foundation-supported collaboration with UC Berkeley, the University of Washington, and the USGS, Caltech is developing a prototype early-warning system that may provide seconds to tens of seconds of warning to people in areas about to experience ground shaking, and minutes of warning to people potentially in the path of a tsunami. Japan invested heavily in an earthquake early-warning system after the magnitude 6.9 Kobe earthquake that occurred January 17, 1995, on the one-year anniversary of the Northridge earthquake, and the system performed well during the Tohoku-Oki earthquake. "It was a major scientific and technological accomplishment," says Gurnis. "High-speed rail trains slowed and stopped as earthquake warnings came in, and there were no derailments as a result of the quake."

Closer to home, Caltech professor of geophysics Robert Clayton has aided local earthquake detection by distributing wallet-sized seismometers to residents of the greater Pasadena area to keep in their homes. The seismometers are attached to a USB drive on each resident's computer, which is to remain on at all times. The data from these seismometers serve two functions: they record seismic activity on a detailed block-by-block scale, and, in the event of a large earthquake, they can help identify areas that are hardest hit. One lesson learned in the Northridge earthquake was that serious damage can occur far from the epicenter of an earthquake. The presence of many seismometers could help first responders to find the worst-affected areas more quickly after an earthquake strikes.

Caltech scientists have also been playing a leading role in the large multi-institutional Salton Seismic Imaging Project. The project is mapping the San Andreas fault and discovering additional faults by setting off underground explosions and underwater bursts of compressed air and then measuring the transmission of the resulting sound waves and vibrations through sediment. According to Joann Stock, professor of geology and geophysics at Caltech, knowing the geometry of faults and the composition of nearby sediments informs our understanding of the types of earthquakes that will occur in the future, and the reaction of the local sediment to ground shaking.

In addition, Caltech scientists learned much through simulating—via both computer modeling and physical modeling techniques—how earthquakes occur and what they leave in their aftermath.

Computer simulations of how buildings respond during earthquakes recently allowed Caltech professors Thomas Heaton, professor of engineering seismology, and John Hall, professor of civil engineering, to estimate the decrease in building safety caused by the existence of defective welds in steel-frame structures, a problem identified after the Northridge earthquake. Researchers simulated the behavior of different 6- and 20-story building models in a variety of potential earthquake scenarios created by the Southern California Earthquake Center for the Los Angeles and San Francisco areas. The study showed that defective welds make a building significantly more susceptible to collapse and irreparable damage, and also found that stiffer, higher-strength buildings perform better than more flexible, lower-strength designs.

Caltech professor of mechanical engineering and geophysics Nadia Lapusta recently used computer simulations of numerous earthquakes to determine what role "creeping" fault slip might play in earthquake events. It has been known for some time that, in addition to the rapid displacements that trigger earthquakes, land also slips very slowly along fault lines, a process that was thought to stop incoming earthquake rupture. Instead, Lapusta's models show that these "stable segments" may become seismically active in an earthquake, accelerating and even strengthening its motions. Lapusta hypothesizes that this was one factor behind the severity of the 2011 Tohoku-Oki earthquake. Taking advantage of advances in computer modeling, Lapusta and her colleague Jean-Philippe Avouac, Earle C. Anthony Professor of Geology at Caltech, have created a comprehensive model of a fault zone, including both its earthquake activity and its behavior in seismically quiet times.

Physical modeling of earthquakes is carried out at Caltech via collaborative efforts between the Divisions of Geological and Planetary Sciences and of Engineering and Applied Science. A series of experiments conducted by Ares Rosakis, the Theodore von Kármán Professor of Aeronautics and Mechanical Engineering, and collaborators including Lapusta and Hiroo Kanamori, the John E. and Hazel S. Smits Professor of Geophysics, Emeritus, used polymer plates to simulate land masses. Stresses were then created at various angles to the fault lines between the plates to set off earthquake-like activity. The motion in the polymer plates was measured by laser vibrometers while a high-speed camera recorded the movements in detail, yielding unprecedented data on the propagation of seismic waves. Researchers learned that strike-slip faults like the San Andreas may rupture in more than one direction (it was previously believed that these faults had a preferred direction), and that in addition to sliding along a fault, ruptures may occur in a "self-healing" pulselike manner in which a seismic wave "crawls" down a fault line. A third study drew conclusions about how faults will behave—in either a classic cracklike sliding rupture or in a pulselike rupture—depending on the angle at which compression forces strike the fault.

"Northridge was a devastating earthquake for Los Angeles, and there was a massive amount of damage," Gurnis says, "But in some sense, we stepped up to the plate after Northridge to determine what we could do better. And as a result we have ushered in an era of dense, high-fidelity geophysical networks on top of hazardous faults. We've exploited these networks to better understand how earthquakes occur, and we've pushed the limits such that we are now at the dawn of a new era of earthquake early warning in the United States. That's because of Northridge."

Cynthia Eller
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