Bringing together ‘best with best’
Researchers at the AIMR Joint Research Center at Cambridge are making ground-breaking discoveries in materials needed for faster data storage and solar-powered hydrogen generation
Several years of collaboration between the Advanced Institute for Materials Research (AIMR) and the University of Cambridge have yielded some intriguing insights into exotic materials, including chalcogenides, metallic glasses and hydrogen materials. These insights could bring us closer to efficient computer memories that retain information without a power source, and an economy fueled by sunlight and hydrogen.
“Cambridge seeks only ‘best with best’ collaborations, and that is what makes the AIMR such an obvious partner in materials science,” says Alan Lindsay Greer, head of the School of Physical Sciences at Cambridge and a principal investigator at the AIMR who has led the collaborative efforts. In 2012, the AIMR set up the AIMR Joint Research Center (AJC) at Cambridge to formalize a long-standing partnership between the two institutes. This center has acted as a model for two more AJCs: one at the University of California, Santa Barbara, and the other at the Institute of Chemistry, Chinese Academy of Sciences.
Initially focusing on metallurgy, the AJC at Cambridge now covers a wider range of subjects in materials science, chemistry and mathematics. It has hired three full-time research associates and organizes annual workshops to deepen the exchange. “For research institutions to be healthy, the range of research conducted must be wide,” says Greer. “Many of the most exciting developments are at the interfaces between traditional disciplines.”
Rejuvenating metallic glasses
Greer first visited Japan as a postdoctoral fellow in 1981 to attend a conference at Tohoku University. “The visit was more eventful than I had planned,” Greer reminisces. His train journey from Tokyo to Sendai was disrupted by a typhoon and Greer fell ill en route, which forced him to spend three weeks in a Sendai hospital — “among other things, giving me time to learn the Japanese syllabaries hiragana and katakana and to acquire a taste for nattō [gooey fermented soybeans].”
The visit also sowed the seeds for collaboration in the area of metallic glasses, materials that exhibit record-breaking properties in strength and flexibility. “Metallic glasses have been studied for over half a century, yet still provide surprises,” says Greer.
Most recently, Greer has worked closely with AIMR principal investigator Dmitri Louzguine, exploring changes to the structure and properties of metallic glasses exposed to thermomechanical treatments. One such treatment known as thermal annealing takes metallic glasses to ‘aged’ states of lower energy and higher density, which often causes them to become brittle. “Just as for people, it would be desirable to reverse the effects of aging,” says Greer. “Fortunately for metallic glasses, ‘rejuvenation’ is more achievable than for people.”
In August 2015, the joint AIMR–Cambridge team, together with co-workers in China, published a paper in Nature in which they describe an easy route to rejuvenating metallic glasses simply by cycling the materials between room temperature and liquid-nitrogen temperature. This thermal cycling results in glasses that have higher energies and are less relaxed. “The work would simply not have happened without the collaboration,” says Greer. “It demonstrates the advantages of bringing together complementary skills, techniques and instrumentation.”
Glass and not glass
Glasses are formed by cooling liquids in such a way as to prevent the formation of ordered structures known as crystals, which are periodic arrangements of atoms and molecules. Most researchers working on metallic glasses try to find glass-forming liquids that have high resistances to crystallization (or good glass-forming ability) because they can be used to produce glasses in larger dimensions.
Researchers at the AJC, on the other hand, are exploring liquids that have a low resistance to crystallization, such as pure metals and a class of elements known as chalcogenides. “We generally require the worst glass formers,” says Jiri Orava, a research associate who joined the AJC in November 2012 and works closely with Greer, Louzguine and Mingwei Chen, another AIMR principal investigator. Some chalcogenides maintain their glassy state up to 150 degrees Celsius, but rapidly crystallize at higher temperatures. And this fast glass-to-crystal transition is reversible — a phase-changing property that makes these materials attractive for speedier electronic data storage devices. “Effectively, these glasses show extreme rejuvenation,” adds Greer.
More specifically, Orava’s work focuses on studying chalcogenides and their potential for improving the existing range of non-volatile memories, which retain stored information even without a power source. For non-volatile memories to compete with volatile, power-dependent, memories, crystallization needs to happen over nanosecond time scales. Chalcogenides could potentially achieve these crystal growth rates at elevated temperatures, but researchers did not have the means to measure and understand the process.
In 2012, Orava and Greer were the first to quantify the growth rate in a chalcogenide liquid over the operational temperature range; their results were published in Nature Materials. And in July 2015, they characterized the crystal growth behavior of another chalcogenide glass, which responds differently to temperature changes.
Interestingly, the glass-to-crystal transition in chalcogenides can occur in stages, with up to 16 intermediate steps identified so far. “This could allow us to extend the binary recording system of zeros and ones to a hexadecimal system,” says Orava. It could also be exploited in computer systems designed to mimic the behavior of neurons in the human brain.
“The real benefit of being at the AJC has been the freedom I get to do my research,” says Orava. “My ideas can be easily realized by accessing the unique facilities available to me at both organizations.” Over the years, he has been able to gain the trust and friendship of his colleagues. “This might not sound like much, but trusting each other’s research is important when collaborating.”
Trapping solar power in hydrogen
From data to energy storage, Katherine Orchard, another research associate at the AJC, and Erwin Reisner, a principal investigator at the Department of Chemistry in Cambridge, have discovered a more direct route to trapping solar energy in the form of hydrogen fuel.
For renewable energy sources like solar and wind to take a more prominent position in the energy infrastructure, scientists need to find a cheap and easy way of storing energy for later use. One way is to convert it into chemical bonds. Hydrogen is a strong storage contender because it is clean, energy dense, and can be produced from water and sunlight. Semiconductor nanoparticles can facilitate this process of absorbing light to split a water molecule into hydrogen and oxygen. Orchard and Reisner have found a way to improve the activity of these systems by up to 200 times.
By bringing together Reisner’s knowledge of photocatalysis with the nanomaterials expertise of Tadafumi Adschiri, a principal investigator at the AIMR, and the molecular synthesis capabilities of Naoki Asao, a professor at the AIMR, Orchard is trying to immobilize these nanoparticle systems onto electrodes to form light-activated electrodes that can generate hydrogen.
In 2015, Orchard, Reisner and Adschiri, together with researchers at the University of Leeds, created a biohybrid photoelectrode made of titanium oxide nanoparticles assembled onto a protein film. “This work is important as it uses nature’s strategies for transporting electrical charge (conductive proteins) to improve synthetic, fuel-making devices,” says Orchard.
“Having an open line of communication between our labs allows new materials developed in each lab to be explored for new applications fairly rapidly,” she adds. “For example, novel nanomaterials developed for environmental clean-up in Asao’s lab are currently under investigation as catalytic materials in Reisner’s lab.”
“It is clear that the broad range of research being conducted at the AIMR and the University of Cambridge provides an excellent basis for diversifying collaborations between the two institutes more generally,” says AIMR Director Motoko Kotani.