For millennia, materials have mattered-so much so that entire eras have been named for them. From the Stone Age to the Bronze Age to the Iron Age and beyond, breakthroughs in materials have defined what was technologically possible and fueled revolutions in fields as diverse as electronics, construction and medicine.
Today, DARPA is pursuing the next big advances in this fundamentally important domain. Harnessing radical new tools-from ultrafast laser imagers to groundbreaking chemical synthesis approaches-DARPA’s Defense Sciences Office (DSO) is aggressively pursuing the development of novel materials with the potential to boost national security.
“DSO helped launch the modern discipline of materials science and engineering, in part by supporting the first materials-focused interdisciplinary laboratories in the late 1960s and early 1970s,” said DSO Director Stefanie Tompkins. “Since then we’ve stayed at the forefront of the materials revolution, funding seminal work in materials for platforms as diverse as integrated circuits, space-based telescopes, and jet engines. Now, we are moving into an entirely new space, where materials are constructed from atoms on up, to have completely unheard of combinations of properties.”
One major challenge in developing new materials has been the difficulty of retaining and exploiting the unique characteristics that emerge in materials at the nanoscale (a few 10-billionths of a meter). Many materials demonstrate unique and potentially useful electrical, optical and tensile characteristics at these nearly atomic scales, but lose these traits when engineered into millimeter- or centimeter-scale products and systems. DSO’s Atoms to Product (A2P) program aims to cross that divide by developing assembly methods that allow the retention of desirable nanoscale properties in macro-scale materials, components and systems.
“In the past, scientists made most of their new materials through variants of ‘mix, heat and form,'” said DARPA program manager John Main.
“Now we’re taking an entirely different approach, starting with individual atoms, assembling them into nano-structures, then assembling the nano-structures into larger micro-devices. A2P is taking advantage of new methods for controlling nanoscale assembly at very high throughputs to economically build novel micro-devices.”
DARPA is pursuing other approaches to creating new materials with unique properties through its Materials with Controlled Microstructural Architecture (MCMA) program. This program seeks to control the architecture of material microstructures to improve structural efficiency and realize properties that traditionally aren’t achieved together in a single substance, such as the strength of steel and the weight of plastic. The work could also help incorporate other important properties, such as high rates of heat diffusion for thermal management applications and tailorability of thermal expansion to enable joining of normally incompatible materials.
“What if the principles of construction used for large structures could be applied to material microstructures, allowing designers to engineer a material the way civil engineers design skyscrapers and suspension bridges?” asked DARPA program manager Judah Goldwasser. “That would allow us to achieve high-efficiency materials and could lead, for example, to vehicles that are one-tenth their current weight and able to travel ten times farther on a tank of gas.”
One potential benefit of applying control over the internal, nano-architecture of materials is that the materials may then be able to catalyze reactions or perform energy conversions, effectively becoming devices in and of themselves. That’s precisely the goal of DSO’s Materials for Transduction (MATRIX) program. Like A2P, it aims to realize the beneficial properties of new materials at the device or system level-in this case by developing new materials for transduction, the conversion of energy from one form into another.
“Transduction is critical to countless military capabilities on land, under water, in the air and in space,” said DARPA program manager Jim Gimlett, pointing to such examples as communications antennas, which convert radio waves to electrical signals, and thermoelectric generators, which convert heat to electricity.
But research efforts to develop new transductional materials have largely been limited to laboratory demonstrations and have too often failed to translate into functional devices and systems. MATRIX aims to make a difference by speeding the development of significant new capabilities and enabling size and weight reductions for existing military devices and systems.
Getting there will require something that has been central to the success of the materials science field generally since DARPA inaugurated its groundbreaking multidisciplinary laboratories a half-century ago: collaboration among experts in diverse, materials-relevant fields.
The MATRIX program explicitly calls upon representatives from the modeling, design and fabrication communities “to develop a unified research and development effort addressing applications that bridge the material and the device domains.” Anticipated benefits of success include improved energy-harvesting, thermal management, and refrigeration devices and more efficient sensing, actuation, and radio frequency devices.
DSO’s Extended Solids (XSolids) program takes aim at a different class of materials-those that currently can be made and exist only at ultrahigh pressures up to millions of times atmospheric pressure. Many materials subjected to these pressures exhibit dramatic improvements in their physical, mechanical and functional properties. These new “polymorphs” may provide significant performance enhancements in areas as diverse as semiconductor electronics and propulsion, and in structural applications ranging from aerospace to ground vehicles.
“The discovery and fabrication of new materials has long been based on the application of heat,” said Goldwasser. “The development of high-pressure chemistry-or barochemistry-could open up a new era in materials discovery and development featuring an entirely new palette of materials for exploitation.”
Early work already hints at unique materials and properties that may emerge when everyday gasses such as carbon dioxide as well as silicon- and carbon-based solids are compressed under extreme conditions, Goldwasser noted. But because their synthesis and stabilization is so demanding, production of these materials for practical use has proven difficult. So in addition to materials discovery, XSolids is researching processing techniques to make their fabrication practical.
While A2P, MATRIX and XSolids all address in various ways the challenge of scaling innovations from smaller to larger dimensions, another DSO materials program is addressing the challenge of how to add precision to the production of extremely thin films of substances. DSO’s Local Control of Materials Synthesis (LoCo) program seeks to advance thin-film materials and surface coatings, which are used in military applications ranging from optics to advanced electronics.
Despite decades of work, methods to enable atomic through millimeter-scale control over structure and properties of materials deposited on surfaces are still underdeveloped. For example, structural organization of high-value thin films is typically controlled by high-temperature deposition or annealing, but the high temperatures used during thin-film synthesis and deposition exceed the limits of many DoD-relevant substrates, restricting application opportunities. LoCo program researchers are developing new strategies and tools as a first step toward ordered materials deposition at or near room temperature.
“A growing array of technologies, including flexible electronics and even some biological systems such as brain-machine interfaces, depend on thin films with very precise behaviors, including surface mobility, optical clarity and reaction energy. But conventional thin films lose their value if they can be applied only with traditional, high-temperature deposition techniques,” said DARPA program manager Tyler McQuade.
“Because so much of chemistry happens at the surfaces where two materials meet, we’re confident that the development of alternative methods for depositing films on substrates could open up a new world of material possibilities.”
Taken together, Tompkins said, DSO’s materials science portfolio points to a future featuring an exciting array of substances with unprecedented properties and capabilities. “All of these programs reflect a fundamental shift,” she said, “from bulk-process to architected materials-a shift we believe has the potential to introduce a new ‘Designer Age’ of materials development.”