Volume 2, Issue 11
Nanoscience's Master Mechanic
This fall, UC Berkeley is launching a new $11.9 million center for researchers to design and test novel motors, sensors, batteries, and other mechanical components. What will set this center apart from most engineering endeavors is that none of the devices built there will be visible without an electron microscope. The Center of Integrated Nanomechanical Systems (COINS) aims to develop a storehouse of mechanical components hundreds of times smaller than the diameter of a human hair. Physics professor Alex Zettl is leading the charge, having recently demonstrated a conveyor belt for ferrying atoms, the world's smallest nanomotor, and an oscillator based on drops of liquid metal that weight just one-quadrillionth of a gram.
Alexander Zettl holds a model of a carbon nanotube, the molecular basis for his nanoscale devices. (courtesy Berkeley Lab)
"We're designing nanoscale building blocks to make them accessible to the point where you could order them like you order lumber at a lumberyard and assemble them," says Zettl, director of COINS and a staff scientist at Lawrence Berkeley National Laboratory.
COINS is one of six Nanoscale Science and Engineering Centers across the country funded by the National Science Foundation. Consisting of more than two dozen researchers from UC Berkeley, UC Merced, Stanford University, and the California Institute of Technology, the Berkeley-based center is unique in that its specific focus is on mechanics at the nanoscale. The COINS Center will directly provide new specialized nanoscience and nanoengineering facilities as well as take advantage of several state-of-the-art nanoscale "machine shops" now under construction, including Lawrence Berkeley National Laboratory's Molecular Foundry, the Nanofabrication Facility in the new headquarters of the Center for Information Technology Research in the Interest of Society (CITRIS), and the Biomolecular Nanotechnology Center at Stanley Hall, future home to the Department of Bioengineering and the California Institute of Quantitative Biomedical Research (QB3).
Zettl's laboratory pioneered what has become quintessential COINS research. Over the last few years, he and his colleagues fabricated pistons, electromechanical switches, and transistors from nanotubes, which are rolled-up crystalline sheets of carbon atoms. The devices, Zettl explains, demonstrate how nanoscience can break down the physical walls faced by engineers trying not only to shrink integrated circuits but also tiny machines. Two decades ago, UC Berkeley led the development of micro-electromechanical system (MEMS) — gears, pumps, and sensors no bigger than the period at the end of this sentence. Now, MEMS are found in everything from automobile airbags to desktop video projectors.
A time series of four transmission electron microscopy (TEM) video images showing one period of oscillator action. The second frame from the left shows the participating liquid metal droplets, labeled I and II. The suspended nanotube substrate, which is visible crossing the images diagonally, is carrying electrical current from the lower left to the upper right corners. In the first frame, the droplet at Position II is barely visible, but by the third frame it has grown to the point where it is nearly touching the droplet at Position I. In the fourth frame, the oscillator is seen directly after the subsequent relaxation event, when the mass distribution has been reset to a condition like that of the first frame. (courtesy Zettl Research Group, Lawrence Berkeley National Laboratory and University of California at Berkeley)
"The machines are quite sophisticated but the materials aren't really well-suited for scaling them down any further," Zettl says. "At the same time, electronic devices have hit their physical limits. But nanotechnology is a nice meeting ground for these fields that have been so well developed at the microscale."
Zettl imagines that MEMS and microelectronics could be integrated with nanostructures to create an entire new breed of devices. For example, a nanoscale cantilever could flex like a diving board when a particular molecule binds to it, enabling the development of a highly sensitive chemical or biological wireless sensor. Or, in the very far future, a nanoscale engine might power a microscale robot traveling through the body to attack a tumor.
"Sometimes it's not just about making a device smaller because you can," Zettl says. "Often, physics on the nanoscale enable devices to work better."
Computer-generated animation of the "conveyor belt," depicting metal transport from left to right along a single carbon nanotube. (courtesy Zettl Research Group, Lawrence Berkeley National Laboratory and University of California at Berkeley)
The smaller a device, the less power it consumes, Zettl says. Nanodevices could potentially operate for very long periods on very little energy. Meanwhile, small forces that are hardly noticeable at the macroscale become very useful at the nanoscale. Think of the way some insects are capable of walking on water while humans are not. That's because the small insects can take advantage of surface tension, an attractive force exerted on the surface of a liquid by the molecules underneath. Zettl and his research group published a design for a nanoscale oscillator that takes advantage of this same force.
"If I built a regular engine, the surface tension is miniscule," Zettl explains. "But at the nanoscale, that force wins out over everything else."
The oscillator mechanism consists of two separate droplets of liquid metal – one small and one large – on a nanotube. Applying an electrical current to the nanotube causes metal from the larger droplet (Droplet 1) to move to the smaller droplet (Droplet 2). Eventually, Droplet 2 becomes large enough to contact Droplet 1.
A series of scanning electron microscope pictures of the spinning rotor of a nanomotor. The entire electric motor is about 500 nanometers across, 300 times smaller than the diameter of a human hair. (courtesy Zettl Research Group, Lawrence Berkeley National Laboratory and University of California at Berkeley)
"When they touch and the surface tension kicks in, they merge into one droplet and the cycle starts again," Zettl says.
To use the mechanism as an oscillator, a microscale lever could be positioned near Droplet 2 so that when it reaches a certain size it pushes the lever arm. Increasing the electrical voltage across the nanotube moves the metal from droplet to droplet faster, thereby increasing the frequency by which the lever is thrown.
"We tune a nanoscale device just by turning a big knob that controls the electrical current," Zettl says. "It's a real electromechanical coupling between the macro and nanoworld."
The oscillator is based on a nanoscale conveyor belt that Zettl and his colleagues demonstrated last year. In that experiment, they applied a small electrical current to a carbon nanotube laden with indium particles. The voltage caused the metal atoms to scoot along the surface of the nanotube "track" like parts moving along an assembly line. Eventually, the mass conveyor belt could become a key component in the COINS machine shop.
"Right now, we make most nanodevices one at a time, sometimes as laboriously as atom by atom," Zettl says. "That approach can prove a concept, but if you can't scale up then it becomes a curiosity instead of a viable technology. We need automated assembly at the nanoscale."
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Glowing Research on Brain Diseases
Christopher Chang received a prestigious 2005 Beckman Young Investigator award.
Growing old can be scary. An estimated 4.5 million Americans have Alzheimer's disease and two million suffer from Parkinson's disease. As the population ages and life expectancy increases, the number of people with neurodegenerative diseases will skyrocket. For example, the Alzheimer's Association predicts that by 2050, as many as 16 million people could have the disease. UC Berkeley chemistry professor Chris Chang is developing novel optical probes that may shed light on how neurodegenerative diseases slowly devastate the brain. Eventually, these insights could aid in the quest for new treatments.
"We don't know many of the causative reasons for these diseases, but we can see their effect on the brain at the end," Chang says. "We'd like to see from a cellular level what mechanisms are involved in the processes of the disease."
While the symptoms of Alzheimer's, Parkinson's and other neurodegenerative diseases are very different, their pathology is similar. Metals like iron, copper, and zinc are essential nutrients in the brain. However, pools of these metals are found gumming up the brains of patients with Alzheimer's and other diseases. These plaque-like deposits, and also damage from oxidation, are implicated in neurodegenerative diseases.
"If you're healthy, you have a lot of metal ions but they're sequestered and functioning normally," Chang says. "If you have one of these diseases, the metal ion levels are elevated and the associated proteins are not working correctly. Somewhere in the middle though is the black box, and that's the important part to observe."
Last year, the researchers demonstrated a selective, cell-permeable optical probe that fluoresces green in the presence of hydrogen peroxide.
The aim, Chang explains, is to develop methods for imaging the metal ions and related chemistry within living cells and tissues in real time. Traditional magnetic resonance imaging (MRI) technology used for brain scans can't deliver the cellular resolution necessary to detect the chemical signposts of neurodegenerative disease.
Chang and his colleagues are developing fluorescent chemical probes that act as tags for certain analytes such as metal ions or metabolites that indicate oxidation. The idea is that a physician could inject a patient with a chemical probe that would seek out those targets. Once the probe recognized the specific analyte nearby, a chemical bond would be made or broken, causing the tag's fluorescence to "switch on." Then, an infrared beam of light would reveal the location of the tags in the brain.
"It would be completely non-invasive and the subject wouldn't need to lie perfectly still as they do with MRI to get a good visualization," Chang says.
Already, the researchers have reported success in vitro with a probe that selectively reacts with the oxidant hydrogen peroxide. Their current probes are illuminated using visible light. The next step is to move to infrared wavelengths that can penetrate through bone, skin, and tissue for real world in vivo applications. According to Chang, the long-term goal is to develop a cocktail of probes that can be hit with many wavelengths of light to simultaneously observe a handful of different markers. The ability to image the cellular chemistry of neurodegenerative diseases and correlate those reactions to the progression of symptoms could help unravel mysteries about how the brain works and how it can fail.
"With the population getting older, these are the diseases we need to pay more attention to," Chang says. "Basic research has to start today in order to be ready for these types of problems tomorrow."
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Weathering Climate Variability
When it comes to weather, most of us are only concerned with the forecast. UC Berkeley professor Lynn Ingram is more interested in old news. Very old. She studies how California's climate has changed over thousands of years. Her research could help prepare us for what tomorrow's weather may bring.
Lynn Ingram is a professor of geology, geophysics, and geography.
"We look at the climate's natural variability and the frequency of events like droughts, wet periods, and floods across different regions in the state," says Ingram, a professor of Earth and Planetary Science and of Geography. "With 35 million people depending on the state's water resources, I think it's important to understand what's happened in the recent past regarding the climate here."
Ingram is a paleoclimatologist, which means that her notion of "the recent past" is somewhat different than most. Her research group analyzes sediment, fossils, and archaeological deposits from the Holocene Epoch, a geological period extending back 10,000 years. Hidden within those samples are clues about the temperature, salinity, precipitation, and other climate variables from days long gone.
Most recently, Ingram and her colleagues conducted a large survey of paleoclimate records from across the state. She's integrating data from other research efforts in the Sierra Nevada region with the results from her own group's fieldwork in the San Francisco Bay. Immediately, she was stricken with the dramatic range of the California climate.
"We've only been measuring climate factors like temperature, precipitation, and salinity here for maybe 80 to 100 years," Ingram says. "The longest drought we've observed is six years. But in the paleoclimate records there are droughts that lasted more than a century. That kind of information is desirable for planning purposes because if a shift occurred in the past, it could probably happen again."
The shells of foraminifera hold clues--in the form of oxygen, strontium, and carbon isotopes--about the San Francisco Estuary's salinity over time. (courtesy the researchers)
About once each year, Ingram, Berkeley adjunct professor Doris Sloan, and their students charter a boat into the Bay where they retrieve sediment cores extracted from the floor of the ocean. The sediment layers are like pages in a book, enabling the scientists to look back in time. Once they return to the laboratory, the researchers analyze the fossils and sediments, measuring isotopes of oxygen, carbon, and strontium. These variables are indicative of water salinity, ocean circulation, temperature, and other factors linked to climate events such as precipitation. For example, Ingram explains, the salinity of San Francisco Bay varies in response to rainfall runoff from the entire watershed covering 40 percent of the state.
"That salinity is then recorded in the chemistry of the fossilized shells," Ingram says.
Based on the paleoclimate records, the researchers have already noticed that California appears to have been much wetter 2,500 to 4,000 years ago. Since then, the dryness has only been interrupted by rapid climate changes. The reason remains a mystery, though as the research progresses Ingram hopes climate modelers will shed light on the patterns. Solar phenomena such as sunspots affecting the climate could be one possible cause of the short-term variations, she says.
While the researchers have so far focused on the Holocene, they're beginning to look back further. The deepest sediment core sample they've retrieved came from 100 feet below the ocean floor, providing 120,000 years worth of data. Right now, Ingram explains, the Earth is in an interglacial period, a warm period between ice ages. But the deep core sample reveals that during the last interglacial period, the climate was warmer and sea levels were higher.
This core sample, split lengthwise, reveals the sediment stratigraphy of the San Francisco Bay. (courtesy the researchers)
"That data might provide a good analog of what this area will look like in the future if global warming continues," Ingram says.
Along with cores extracted from below the Bay, Ingram is exploring California's climate history through samples from marshes and shell mounds, prehistoric refuse piles. The former, a collaboration with Berkeley geography professor Roger Byrne and postdoctoral fellow Frances Malamud-Roam, centers on the study of how marsh vegetation has changed in response to salinity shifts. At the shell mounds, Ingram, Byrne, Berkeley anthropologist Kent Lightfoot, and graduate student Peter Schweikhardt examine entire mollusks for hints of seasonal changes that may have affected their growth. For example, California is known for a Mediterranean climate with a wet winter and dry summer. But has that always been the case? The answer lies in the paleoclimate record.
"I enjoy seeing how different things were in the past," Ingram says. "We take San Francisco Bay for granted, but 10,000 years ago it simply didn't exist. We can't think of the world as unchanging."
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Berkeley's Scientific Legacy
Melvin Calvin and Photosynthesis
On September 2, 1945, World War II ended with the Japanese surrender. That day, Ernest Lawrence, Director of UC Berkeley's Radiation Laboratory, suggested to chemistry professor and "Rad Lab" researcher Melvin Calvin that "now is the time to do something useful with radioactive carbon."
Professor Melvin Calvin in the Rad Lab. (courtesy Bancroft Library)
That nudge eventually led Calvin to uncover the secrets of how plants capture energy from the sun. The research earned Calvin the 1961 Nobel Prize in Chemistry.
By the 1930s, scientists were aware that plants took in carbon dioxide and water and released oxygen. That decade, radioactive isotopes were first used as "tags" to trace organic molecules through chemical processes. However, the first radioisotope tracers decayed too quickly to make it through the full photosynthesis reaction. Using the newly-discovered Carbon 14 as a tracer though, Calvin and his colleagues followed the entire path of carbon through photosynthesis. From the absorption of atmospheric carbon dioxide to its sunlight-fueled conversion via chlorophyll into carbohydrates and other compounds, the researchers shed light on the whole photosynthesis question.
That work eventually sparked the US Department of Energy's research into solar energy as a renewable power source.
Green algae, grown in continuous cultures, were placed in the "lollipop" with the light shining on them. Carbon-14 labeled CO2 was injected into the stream of nonradioactive CO2 for a suitable period, at the end of which the algae were killed. The compounds into which the radioactive carbon had entered were analyzed by paper chromatography. (courtesy Bancroft Library)
"If you know how to make chemical or electrical energy out of solar energy the way plants do it – without going through a heat engine – that is certainly a trick," Calvin once said. "And I'm sure we can do it. It's just a question of how long it will take to solve the technical question."
In the early 1960s, Calvin established Lawrence Berkeley National Laboratory's Chemical Biodynamics division and directed it for two decades. Calvin also served on the President's Science Advisory Committee under both Presidents Kennedy and Johnson and was chairman of the Committee on Science and Public Policy at the National Academy of Sciences. He received the National Medal of Science from President George Bush in 1989.
Melvin Calvin died in 1997, but the breakthroughs of Mr. Photosynthesis, as Time magazine nicknamed him, continue to illuminate biology's chemical underpinnings.