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.
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.
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.
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.
Recent scientific advances have opened up new possibilities for material design in the ultrahigh pressure regime (up to three million times higher than atmospheric pressure). Materials formed under ultrahigh pressure, known as extended solids, exhibit dramatic changes in physical, mechanical and functional properties and may offer significant improvements to armor, electronics, propulsion and munitions systems in any aerospace, ground or naval platform.
Despite the dramatic performance improvements—both demonstrated and predicted—for extended solids, the ultrahigh pressures currently required for synthesis and stabilization of such materials prevent scalability for any practical use. DARPA created the Extended Solids (XSolids) program to address the key challenges in synthesis and scale-up necessary for manufacture, through both computational and experimental approaches, with the intention of opening a vast new material design space for the DoD.
Interdisciplinary research teams are working to develop multi-step, barochemical processes that can reduce the peak pressure needed to achieve scalable synthesis of target materials. Performers are working in parallel on computational exploration of high-pressure material structures and properties, and the small-scale synthesis of a variety of materials to experimentally verify their properties.
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.