By Neal Singer
To stretch a supply of salt generally means using it sparingly.
But researchers from Sandia and the University of Pittsburgh were startled when they found they had made the solid actually stretch.
“It’s not supposed to do that,” says Sandia principal investigator Jack Houston (1114). “Unlike, say, gold, which is ductile and deforms under pressure, salt is brittle. Hit it with a hammer, it shatters like glass.”
The research team from Sandia and Pitt was engaged in a preliminary investigation of salt’s properties for desalination studies when the serendipitous discovery was made.
“We were interested in learning what happens when you try to poke salty water through membranes with tiny pores,” says Jack. “So we tried first to characterize the qualities of salt when dry.”
Nathan Moore (1114), investigating with the nanotip of a tool called an interfacial force microscope (IFM) developed by Jack, found with surprise that the brittle substance appeared malleable enough to stay with the tip as it left the surface of the salt, forming shapes that extended into relatively lengthy fingers of separation from the main body.
Examination led by Jianyu Huang (1132) with a transmission electron microscope (TEM) at the Sandia/Los Alamos Center for Integrated Nanotechnologies (CINT) showed that surface salt molecules, like the surface of water when an object is withdrawn, formed a ductile meniscus with the IFM tip as it withdrew from penetrating the cube. But unlike water, the salt meniscus didn’t break from its own weight as the tip was withdrawn. Instead it followed the tip along, slip-sliding away (so to speak) as it thinned and elongated from 580 nanometers to 2191 nm in shapes that resembled nanowires (see image on page 4).
As a possible explanation, offers Jack, “Surface molecules don’t have buddies.” That is, because there’s no atomic lattice above them, they’re more mobile than the internal body of salt molecules forming the salt block.
Another possibility considered was that the TEM electrons (used for viewing the process) break up the salt crystals into tiny grains, allowing rapid atomic diffusion along grain boundaries and permitting nanowires to form and extend. Or the TEM electrons might change sodium from its ionic to its atomic state, where cohesion is weaker and bonding can take place in any direction.
Still, more sparing use of the TEM as an observational tool did not stop the superplastic lengths from occurring. Their lengths increased when the TEM stayed on during the entire experiment, but they were still there and still long when the TEM was used only occasionally and briefly during the process.
While solder creates a liquid-like surface when modestly heated, the fact that salt showed signs of surface mobility at room temperatures was “totally surprising,” says Jack, who had initially intended to study more conventionally interesting characteristics of the one-fourth-inch square, one-eighth-inch-long salt block.
What this means for oceans, quarries, smog, or deer licks is that salt molecules, if forming nanowires rather than remaining inert, might be causing hitherto unobserved but unpleasant effects.
In a paper published in the May Nanoletters, the researchers write that “understanding the deformation of NaCl [common salt] is particularly important for relating laboratory-scale measurements to geotechnical problems, and for understanding the physiochemical reactions of sea salt aerosols. The latter have been implicated in problems as broad as cloud nucleation, smog formation, ozone destruction, and triggering asthmatic responses in humans.”
Other researchers on this work include Junhang Luo and Scott Mao from the University of Pittsburgh.
In unrelated work that also involved a surprisingly mobile surface, Jack with colleagues Matt Goertz (1132), presently a postdoc at CINT, and X.Y. Zhu at the University of Minnesota, followed up on a centuries-old argument about what makes ice so slippery. Their aim: to map the characteristics of the slickness.
A variety of explanations
The original explanation, by dedicated experimentalist Michael Faraday, that a very thin liquid-like layer of water existed at all times atop ice, was rejected by Lord Kelvin, who agreed that water’s presence did make ice slick but announced — apparently more by fiat than experiment — that its presence was the result of pressure-melting of the ice, says Jack. Later work suggested that heat from friction — as an ice skater or car moved over ice — caused water to appear.
Still, says Jack, it was clearly shown that the weight borne by ice, even from skaters was far below that required to produce enough water to maintain the slipperiness of the thin lubricating film.
Presently, it appears that ice is representative of a self-lubricated material, says Jack. Its thin liquid-like layer of water keeps people, sleds, skates, and other objects sailing above the small but craggy roughnesses of its surface like shaving cream allows a razor to slide above, not on, skin, while mowing down bristles of hair. A wide range of physical exploratory techniques has agreed that this is actually the case. (The term “liquid-like layer” is a technical term used by scientists to describe water that through premelting possesses physical properties between those of water and ice).
Jack and his group confirmed with the IFM yet again that liquid-like water exists atop ice, determining that it creates a kind of capillary-like action with slipperiness that decreases in effectiveness as temperature decreases. The technique gave accurate measurements of the thickness of the aqueous surface layer and the most complete picture to date of its behavior.
This work is currently published in the March 31 issue of the journal Langmuir.
Both research efforts were supported by DOE’s Office of Basic Energy Sciences. The salt research was also supported through the University of Pittsburgh by the National Science Foundation. -- Neal Singer
By Neal Singer
On May 19, student winners of the fifth annual Sandia-sponsored MEMS University Alliance Design Competition, aided by their professors, presented their visions of astonishingly tiny yet productive machines to the scrutiny of Sandia’s seasoned microelectromechanical systems group — arguably one of the most advanced MEMS design and fabrication groups in the world.
The 2009 winner in the “novel device” category was a “microswimmer,” which resembles a tiny fish and is designed to swim like one, its aluminum tail whipping back and forth as it is heated and cooled by periodic bursts of microwave radiation. The design was created by Kevin Bagnall of the University of Oklahoma’s School of Aerospace and Mechanical Engineering, and presented by graduate student Jeff Lantz under the direction of professor Harold Stalford.
“Think Fantastic Voyage,” says Sandia senior microfabrication manager Tom Zipperian (1740), referencing, as a possible future use for the design, the movie that portrayed a vessel shrunken enough to navigate the human body by touring its bloodstream.
A second area of competition — a device to characterize and test the reliability of tiny devices — was won by a design that Texas Tech University students termed a “tribogauge,” used to determine the wear, friction, stiction, and lubrication of moving parts of MEMS devices, on-chip and in situ. (These determinations are called tribological.) The work was presented by student Ganapathy Sivakumar under the direction of associate professor Tim Dallas.
Also participating in this year’s contest were the University of Illinois at Urbana-Champaign, the University of Utah, and the Air Force Institute of Technology.
“This year’s group was again very competitive,” says design contest leader and MEMS Core Technologies team lead Mark Platzbecker (1749). “Each year, the designs get better and the associated white papers more professional.”
Among universities now going through the process to join the alliance but not yet signed up are Cornell and the University of New Mexico. Duke University and the Rose-Hulman Institute of Technology in Terre Haute, Ind., have also expressed interest. More than 20 educational institutions are members of the alliance.
The contest, which took place in a conference room at Sandia’s MESA center, is intended to take students beyond the academic classroom into a world where MEMS devices are of high significance — “a career-altering moment for some student engineers,” says Mark.
The University of Utah’s MEMS team leader and professor Ian Harvey agrees. “I can bleed all over the paper in a classroom,” he says, “but that’s different from being here.” He gestures at the Sandia MEMS personnel and the imposing conference room, with its 30-foot-high ceiling, reserved for the team presentations. “I’m dealing with engineers early in their careers. This can make them passionate about their work.”
From Sandia’s point of view, says Tom, the contest brings in new design ideas, provides impetus to universities to train the next generation of MEMS engineers, permits Sandia engineers the satisfaction of acting as mentors, and allows Sandia to partner on university grants from the National Science Foundation that are ordinarily closed to the national labs.
The program has drawn increased interest from universities, says Mark, perhaps because the latest flat-screen digital light processing — DLP — TVs use MEMS mirrors to switch pixel colors, and MEMS accelerometers provide key sensing elements in popular Wii game controllers.
Still, from a university’s point of view in a time of cutbacks, says Harvey, “MEMS is called a boutique course. Administrators ask, ‘Why don’t we just teach the basics? Cover fundamentals? Train people who can find jobs?’”
Harvey says his problem with that outlook is that “a lot of kids are vacillating. They’re not sure what they want to do. Instead of throwing them into a thermodynamics class, we offer a nontraditional class. There are no books or tests. Instead, there’s design, simulations, continuous feedback, and talk about reliability and packaging.”
“It’s the machine shop of the future,” says Tom, “and, here at Sandia, at the most advanced MEMS facility in the world, we have the personnel to help alliance members through problems. But a university has to make a significant investment in tools and education to get its program going.”
The alliance helps by providing classroom teaching materials and licenses for Sandia’s design tools at a very reasonable cost. This makes it possible for a university without its own fabrication facilities to develop a curriculum in MEMS.
No instant gratification here
Contest participation is the opposite of instant gratification. The entire process takes almost nine months. It starts with students developing ideas for a device, followed by creation of an accurate computer model of a design that might work, analysis of the design, and finally, design submission. Sandia’s MEMS experts and university professors review the design and determine the winners.
Sandia’s MESA fabrication facility then creates parts for each of the entrants. Once the parts are fabricated, they’re shipped back to the university students for lengthy tests to determine whether the final product matches the purpose of the original computer simulation.
Among factors of continual interest to MEMS fabricators and designers are friction, stiction, temperature, humidity, and surface topography.
The university alliance coordinates with the Sandia-led National Institute for Nano Engineering (NINE), providing additional opportunities for students to self-direct their engineering education, and the Sandia/Los Alamos Center for Integrated Nanotechnologies (CINT), a DOE Office of Science center with the most up-to-date nano-technology tools.
The University of Oklahoma’s microswimmer is the first known microscale artificial swimmer capable of being produced in batches of 100 by the process known as surface micromachining — the most widespread technique used worldwide to fabricate micromachines, and in which Sandia’s facility is a leader. The swimmer’s free-swinging tail is 40 micrometers in length. The different rates of expansion and contraction of a tail strip with one side aluminum, the other polysilicon, when heated by a cyclically powered microwave, set the tail wagging, propelling the swimmer forward at an average speed of 3.3 micrometers/second. Potential applications include research and drug delivery in the body.
The tribogauge design uses comb drives — interlaid sets of “teeth” that, when electrically charged, attract each other. These normally are used to drive rods that power microgears or latches. Texas Tech student designers propose using this device not only for power but, treating their parallel comb teeth like capacitors, as sensing devices. With this and with pads that extend off the surface of the chip, the gauge will detect wear, friction, stiction (the force needed to break an object out of its stationary position), and lubrication of various MEMS devices in situ, including those actuated by electrostatic and electrothermal means. -- Neal Singer
By Mike Janes
Ordinarily, you don’t see people lining up to test-drive cars, but Thursday, May 28, was not just any day in Livermore. A crowd of more than 100 people gathered downtown for the opportunity to get behind the wheel of hydrogen fuel cell-powered vehicles from major automakers including Honda, Toyota, Nissan, Volkswagen, and GM.
This was the 10th stop on the Hydrogen Road Tour, an eight-day event organized by the California Air Resources Board, California Fuel Cell Partnership, National Hydrogen Association, US Fuel Cell Council, and Powertech Labs (on behalf of British Columbia).
“The purpose is to show the public that hydrogen fuel cell cars are not decades away from market,” says Chris White of the California Fuel Cell Partnership.
Sandia organized the Livermore stop in partnership with the City of Livermore and Livermore Downtown Inc.
“We are honored to be part of this event. Sandia has been involved in hydrogen research for well over 45 years and hydrogen energy since about 1994,” says Jay Keller (8367), hydrogen program manager. “Our hard work has helped put these vehicles on the road today.”
The road tour brought out a diverse crowd that included scientists, auto enthusiasts, and the simply curious. Pleasanton resident Dan Stewart pulled his two sons out of school for a few hours to check out the road tour, and at the urging of 15-year-old Clint, signed up to test-drive one of the cars.
“I think it would be really cool to use hydrogen to power a car,” says Clint, a high school sophomore. “It would be much better for the environment.”
Livermore Police Officer Mony Nop also paid a visit. “I’m really excited to see so many different kinds of cars. I thought it would be just one company,” he says. “These seem like great vehicles. I talked with one guy about how fast he was able to drive — I won’t mention the exact speed to keep him out of trouble.”
Transportation Energy Center 8300 Director Bob Carling, Metal Hydrides Center of Excellence Director Lenny Klebanoff (8367), Terry Johnson (8365), Daniel Dedrick (8365), and other Sandia staff members came out to the road tour. Lenny spent time among the crowd answering questions about hydrogen fuel cells in general and Sandia’s program.
The cars don’t look much different from other cars on the road — which was exactly the point. Larry Goltz, a Livermore insurance agent, pointed out one key distinction. “Look what’s coming out of the tailpipe — water,” he says.
After driving a Honda FCX Clarity for about a quarter-mile around downtown, Goltz was ready to take it home. “I’d buy this car if I could. It’s a quiet, smooth, easy drive, but more important, I think this is our future. We need to stop importing fuel,” he says.
The FCX Clarity is one hydrogen fuel cell car you could very well see on the road, at least in Southern
California. Honda has begun leasing the car to customers in the Torrance, Santa Monica, and Irvine areas at $600 per month, which includes maintenance.
“Right now there is limited infrastructure, so we’re targeting areas with hydrogen refueling stations,” says Kent Dellinger, a government relations manager with Honda. “We’re hoping this tour will get the attention of our legislators, to show that fuel cell vehicles are not the distant future, they are now.”
Honda is not alone in the fuel cell car marketplace. Toyota has said that it will be selling fuel cell cars by 2015, and Hyundai Motor Co. and Daimler AG both have plans for selling hydrogen vehicles to retail customers.
“If you listen to those directly responsible for selling hydrogen fuel cell vehicles to the consumer, it seems clear that commercialization and marketability of these vehicles is moving a lot faster than we anticipated,” says Jay.
Progress in hydrogen R&D is real and significant
According to the California Fuel Cell Partnership, the hydrogen research community has consistently met or exceeded the DOE Hydrogen Program’s ambitious goals for energy efficiency, vehicle range, system durability, and reduced costs. Sandia, says Jay, has been involved in several key advances.
“Through our safety, codes, and standards work, we’ve been instrumental in the National Fire Protection Association’s rewriting of the model codes that local municipalities need to put hydrogen in commercial applications,” he explains. “This is not insignificant, as those agencies now have formal, written safety codes that allow them to work hydrogen into their commercial infrastructure.”
In fact, Jay does not see the infrastructure — refueling stations — as the major obstacle to bringing fuel cell cars to market. He says changing the infrastructure of the fleet poses a bigger challenge.
In addition, DOE’s Metal Hydride Center of Excellence (MHCoE), led by Sandia, continues to make progress finding a suitable new material that can soak up and concentrate hydrogen into a small volume, release the hydrogen when needed, and then repeat this cycle over and over for vehicular applications.
As the lead organization for the MHCoE effort, Sandia coordinates the work of some 18 organizations engaged in several promising areas of research. Sandia also is contributing to materials development work and helping direct research by refining materials theory.
Finally, Sandia’s work on a hydrogen internal combustion engine — considered a transition strategy designed to pave the way toward fuel cell vehicles — is supported by both Ford and BMW.
Road tour grabs media attention
Potential drivers weren’t the only ones lining up to check out the hydrogen fuel cell cars in Livermore — major media outlets also were out in force. Reporters from KQED’s Quest, the Valley Times, and San Francisco Chronicle all took test drives and the event was featured on prime-time news broadcasts on CBS, NBC, and ABC. For more on the Hydrogen Road Tour, visit www.hydrogenroadtour.com. -- Mike Janes