The quest for efficiency in thermoelectric nanowires

Graham Yelton and Sandia colleagues have developed a single electroforming technique that tailors key factors to better thermoelectric performance: crystal orientation, crystal size and alloy uniformity. The work is outlined a paper, “Using Galvanostatic Electroforming of Bi1-xSbx Nanowires to Control Composition, Crystallinity and Orientation,” in the Jan. 28 edition of the Materials Research Society’s MRS Bulletin. (Photo by Randy Montoya)

by Sue Major Holmes

It’s all about efficiency in the small world of thermoelectric nanowires. Sandia researchers say better materials and manufacturing techniques for the nanowires could let carmakers harvest power from the wasted heat of exhaust systems or lead to more efficient devices to cool computer chips.

Researchers at Sandia’s campuses in New Mexico and California published a paper, “Using Galvanostatic Electroforming of Bi1-xSbx Nanowires to Control Composition, Crystallinity and Orientation,” in the Jan. 28 edition of the Materials Research Society’s MRS Bulletin. The authors are W. Graham Yelton, Steven J. Limmer, Douglas L. Medlin, Michael P. Siegal, Michelle Hekmaty, Jessica L. Lensch-Falk, Kristopher Erickson, and Jamin Pillars.

The work was the first time researchers managed to control crystal orientation, crystal size and alloy uniformity by a single process. All three factors contribute to better thermoelectric performance, Graham says.

“The three together mean a huge gain, and it’s hard to do,” he says. “It’s turning the knobs of the process to get these things to behave.”

Better nanowire geometries can reduce heat conductivity and improve what’s called the thermoelectric figure of merit, a measure of a material’s electrical and thermal conductivity. The higher the electrical conductivity and the lower the thermal conductivity, the higher the figure of merit and, therefore, the more efficient the material. However, the quality of thermoelectric nanowires in the past proved inadequate.

Thermoelectric nanowire use in its infancy

Despite their inefficiency, some thermoelectric materials are already in use. Graham compares their stage of development to the early days of solar photovoltaic cells: Everyone saw the potential, but they were so inefficient they were used only when nothing else worked.

Improved efficiency in nanowires would increase the use of thermoelectric materials. Graham says they’re already used in some sensors, and vehicle manufacturers are looking at their potential to harvest heat from exhaust systems to power vehicle sensor systems. Decreasing the power needed to run a vehicle’s operating system could reduce battery and alternator weight and perhaps eliminate some power-generating equipment, trimming vehicle size and weight.

Sandia’s paper describes how the team created thermoelectric nanowire arrays with uniform composition along the length of the nanowire and across the spread of the nanowire array, which potentially can include hundreds of millions of nanowires. In addition, they created nanowire crystals of uniform size and orientation, or direction. Uniform composition improves efficiency, while orientation is important so electrons, the carriers of energy, flow better.

The team used a cost-effective method called room-temperature electroforming, which is widespread in commercial electroplating. Electroforming deposits the material at a constant rate, which in turn allows nanowires to grow at a steady rate. The method produced wires 70-75 nanometers in diameter and many microns long.

Graham used pulses of controlled current to deposit the thermoelectric material to control composition throughout the wire and the array. “There are little nuances in the technique that I do to allow the orientation, the crystal growth, and the composition to be maintained within a fairly tight range,” he says.

Technique allows control over important facets of nanowire formation

The method produced a fairly large, slightly twisted crystalline wire structure that was almost a single crystal and had the desired orientation. “Without that you couldn’t get good efficiencies,” Graham says.

The chemistry of the material also is important because antimony salts play a major role in crystalline quality and orientation.

Bismuth-antimony (Bi-Sb) alloys have some of the highest thermoelectric performance — acting both as a conductor of electricity and an insulator against heat — among many materials for near-room temperature applications. But existing Bi-Sb materials don’t produce effective solid-state cooling when power is constantly delivered to the device being cooled, such as a computer.

Sandia’s team wanted a compound that behaved like a metal but would not conduct heat. Alloying antimony with bismuth fit the bill, Graham says. Bi-Sb nanowire arrays electroformed with an antimony-iodide-based chemistry lacked the needed qualities, but arrays electroformed from an antimony-chloride-based chemistry produced crystallography and orientation for maximum thermoelectric performance.

“The chemistry allowed us to go from poly-nano-crystalline structure to near single crystals of 2-5 micrometers,” giving better control over uniformity, Graham says.

The next step is more challenging: making an electrical contact and studying the resulting thermoelectric behavior.

“Thermoelectric materials readily form oxides or intermetallics, leading to poor contact connections or higher electrical contact resistance. That reduces the gains achieved in the materials development,” Graham says.

While the Sandia team has been able to get good contact at the bottom of an array, making a connection at the top has proved difficult, he says.

“To make a contact and measure array performance is not trivial,” Graham says.

He and his colleagues are seeking further funding to solve the problem of successfully making contacts, and then to characterize the thermal electric properties of arrays. “If successful at the Labs, we would try to find an industry collaborator to mature the idea,” he says.



-- Sue Major Holmes

Back to top of page

DOE launches pilot entrepreneur boot camp

Innovation is all about the network needed to bring an idea to reality, said Andrew Hargadon, director of the Child Family Institute for Innovation and Entrepreneurship and a UC Davis professor of technology management, at the Livermore Valley Lab-Corps kick-off.           (Photo by Julie Russell, LLNL)

by Patti Koning

I nterest in entrepreneurship is alive and kicking in the Livermore Valley, if attendance at a recent meeting on the topic is any indication. In a Livermore Valley Open Campus room set up for 60, it was standing-room only as staff from Sandia and Lawrence Livermore national labs gathered on Jan. 21, to learn about Lab-Corps, a new DOE-funded “boot camp” on transitioning lab technologies to the market.

The two national labs, the UC Davis Graduate School of Management, and the Livermore-based

i-GATE Innovation Hub garnered a highly competitive $350,000 grant from the DOE’s Office of Energy Efficiency and Renewable Energy (EERE) to help launch Lab-Corps, now in its pilot year.

“Throughout the national labs, we see an incredible commitment to our national security missions. Now, we’re aiming to foster an equally deep commitment to expanding the societal impact of our results. Essentially, the Lab-Corps program will provide the tools the labs need to meet our obligation to be outstanding stewards of taxpayer-funded R&D,” said Sandia/California site VP Stephen Rottler in his introduction at the meeting.

Putting experience to work

A key Lab-Corps strategy is to help the teams learn from the experiences of others. As a first taste of this strategy, meeting attendees listened to a panel of three entrepreneurs who had left the national labs to successfully market new products.

Each of the panelists encountered different ups and downs. For example, former Sandian Don Arnold, who helped found a company that was purchased by leading mass spectrometry supplier AB SCIEX, obtained funding for his venture after only one pitch. Greg Sommer, also a former Sandian, gave at least 150 pitches before finding investors for his point-of-care medical testing company, Sandstone Diagnostics.

Nonetheless, the three stressed several common themes.

“I really began to understand the importance of personal relationships,” said Greg. “All of a sudden, life became a contact sport. I realized that people were not judging my idea — they were judging me and my team. Did we have the dedication to pull this off?”

Don agreed and added, “It’s really important to be adaptable. After listening to potential customers, you’ll probably find that you need to create a very different product than what you’d originally envisioned.”

The third panelist, Lloyd Hackel, a former LLNL scientist who helped start the Metal Improvement Co., which was originally funded and then bought by advanced technology supplier Curtiss-Wright, offered this advice: “Do your homework, but don’t be afraid of the unknown. You won’t have all the answers when you start out — but you have to move forward anyway.”

Entrepreneurial insights shared

Two others also spoke. Professor Andrew Hargadon, founder of the UC Davis Child Family Institute for Innovation and Entrepreneurship and author of “How Breakthroughs Happen: The Surprising Truth About How Companies Innovate,” stated that innovation isn’t about an idea, but rather about the network needed to bring an idea to the market.

Tracing the trajectory of penicillin to illustrate his point, Hargadon noted that several 19th century scientists, among them Lister and Pasteur, had isolated molds and understood their therapeutic benefits before the 1928 “discovery” of penicillin by Sir Alexander Fleming. It wasn’t until Howard Florey in the early 1940s built a multi-faceted team with drug manufacturing and other expertise that penicillin came into use as a life-saving drug.

Jim Presley, managing director of Pacific Private Capital who has volunteered his time as a mentor and chair for the Lab-Corps Industrial Advisory Board, introduced attendees to the business canvas. This one-page business plan tool requires research into nine key areas — including value proposition, channels, and customer relations — with the most intense focus on listening to and understanding customers.

Tech transition boot camp

Lab-Corps will provide extensive training and resources to two teams selected competitively in late March 2015 from the Livermore Valley Site pilot program, along with two teams each from four other national labs. The objective of the pilot is to determine if training can enhance researchers’ understanding of methods that would allow a wider audience to benefit from government investments in the national labs. If successful, the pilot could be expanded and funded for several years to meet the DOE goal of encouraging lab-wide entrepreneurial skills and bring a greater number of lab technologies to market.

Teams selected for Lab-Corps, will consist of a principal investigator, an entrepreneurial lead, and an industry adviser, and receive $75,000 to attend entrepreneur training and collect direct customer feedback on a potentially marketable technology in an area of interest to EERE. 

At the end of 5–7 weeks of intensive training, market research, and networking over the summer, the teams will gain the information and know-how needed to complete and present the business canvas. Experience from the National Science Foundation’s I-Corps program — the model for Lab-Corps — suggests that teams will need to talk to about 100 potential customers to complete their business canvas.

In essence, the teams will apply the scientific process to refine and validate their hypotheses — summarized as value propositions — about their product. The teams will gain a keen sense of their product’s commercial potential and of the resources and teams needed to transition the product to the market, whether through industry partnerships, licensing agreements, startups, or other business opportunities.

Next Steps

Carrie Burchard of Sandia and Christine Hartmann of LLNL outlined steps for staff wishing to join the competition — or simply learn more about entrepreneurship.

Lab employees are invited to attend two free training programs: a series of weekly entrepreneur information sessions at the I-GATE Innovation Hub in downtown Livermore on Wednesdays at 4 p.m. and UC Davis entrepreneur training sessions held Thursday evenings. To sign up, members of the workforce can go to and submit a request. Lab staff members who want to compete to be selected as a Lab-Corps team should contact Craig  Smith ( to learn more.


-- Patti Koning

Back to top of page

Best Man: BEYA award winner listened to his parents and excelled in materials science

Jon Madison (1814) says a key to his academic and professional success was listening to the adults in his life. “I don’t pretend to know everything,” he says. “I listened to the people who had my best interests at heart: my parents, my teachers, my mentors. I might not have understood or agreed with them, but just hearing what they were telling me provided opportunities later in life.” (Photo by Randy Montoya)

by Nancy Salem

Growing up in Kansas, Jon Madison had a strong sense of who he was and where he was going. “I wasn’t an average kid,” he says. “Whatever my peers were doing, chances are I wasn’t doing it. After school and weekends I helped with my family’s business. When it came to performing academically and taking an intellectual route, I always went my own way.”

Jon (1814) followed a path to advanced degrees in mechanical engineering and materials science and a career at Sandia. He mentors interns at the Labs and young people in the community.

He recently was named winner of a Black Engineer of the Year Award (BEYA) for Most Promising Scientist. “This is a high point in my career,” Jon says. “I was excited to win and to represent Sandia in this way.”

BEYA is a program of the national Career Communications Group, an advocate for corporate diversity, and is part of its STEM achievement program. The awards annually recognize the nation’s best and brightest engineers, scientists, and technology experts. Jon will receive his award at the 29th BEYA conference Feb. 5-7 in Washington, D.C. The event precedes National Engineers Week.

Aimed for a career in science

Jon’s parents were painting contractors who encouraged him to excel. “They didn’t push me into any one field or direction,” he says. “They said whatever you do, do your best, and that stuck with me.”

He worked in the family business and decided it wasn’t for him. He wanted a career in science. But math didn’t come easy, so his sister tutored him every day throughout his first few years of high school. “She got me on the path to learning and understanding math,” he says.

Jon went to Clark Atlanta University, a historically black university, where he earned a bachelor’s degree in engineering science. He then headed to the University of Michigan to complete his master’s and PhD in materials science and engineering.

Jon was in the Louis Stokes Alliance for Minority Participation (AMP) initiative, a STEM scholarship program of the National Science Foundation. “They said from day one that I would go to grad school,” he says. “The expectations were high.”

He did summer internships at the Naval Research Laboratory in Washington, D.C., Washington State University, and the Massachusetts Institute of Technology. “I was looking for mechanical engineering internships but ended up in materials research programs,” he says. “I got a lot of exposure and opportunity to see materials science in different ways. That’s when it clicked for me I would like to pursue materials science as a career.”

Jon began looking at the job market as he finished his dissertation, focusing on industry rather than academia. A conversation with his mentor, George Spanos, technical director of the Minerals, Metals & Materials Society (TMS), changed all that. Jon recalls Spanos asking him what was most important to him. What were the things he really, really wanted to do in his career? “I boiled it down to three things. I wanted to mentor students, do fundamental research, and be involved in professional societies,” Jon says. “George responded by saying it sounded like I was looking for a national lab. That had never even entered my mind.”

That was the summer of 2009, and in 2010 Jon joined Sandia. “I talked to many of the labs, but Sandia was always the frontrunner,” he says.

An advocate for diversity

Jon’s work centers on destructive and non-destructive techniques to understand microstructure in three dimensions, and using that information in experiments and simulations. He’s also helping to develop a materials database that can be used across the Labs. “I get a tremendous sense of satisfaction from accomplishing things,” he says. “I like to see something come together in a complete way.”

Duane Dimos, director of Pulsed Power Sciences Center 1600, nominated Jon for the BEYA award, saying his research skills “are differentiated from many peers by a mastery of both experimental and modeling expertise with a focus on quantification of defects in materials microstructures.”

“Jon is a tireless advocate for ensuring diversity within his professional field and at work,” Duane says. “He serves as a role model for aspiring young African American students.”

Jon is an Executive Fellowship mentor and works with interns from around the country. “I take mentoring really seriously,” he says. “It is our responsibility as scientists to mentor the next generation. It’s close to my heart because I was groomed by mentors.”

He and his wife volunteer with Big Brothers Big Sisters of Central New Mexico. And Jon is a life member of the National Society of Black Engineers and the NAACP. He is also area director of the service fraternity Alpha Phi Alpha, which had Dr. Martin Luther King Jr. as a member.

In his spare time, Jon plays video games, reads, and watches movies. He also takes on the occasional painting job around the house, a nod to the family business. “It tends to be on my to-do list,” he smiles.

Jon’s message to young people is the same one he received as a kid from his parents. “It doesn’t matter what you choose to do, just strive to do your best,” he says. “The better you perform now, the more doors will open for you later. You don’t want to close those doors before you have a chance to look through them. You never know what opportunities are around the corner.”

-- Nancy Salem

Back to top of page

Download Lab News February 6, 2015 (PDF, 2MB)