(Funded by the U.S. Department of Energy and the U.S. National Science Foundation)
The shape of nanoparticles depends on the choice of solvent and temperature during their growth. But the tiny seed particles that form first and that guide the formation of final nanoparticle shapes are too small to measure accurately. With the help of a supercomputer, Penn State researchers have developed computer simulations to model seed particles with 100 to 200 atoms. They found that the shapes of the tiny particles depend on the solvent composition and temperature in unexpected ways. Surprisingly, in some cases the shape of the seed particle changes dramatically when only a single atom is added or removed.

(Funded by the U.S. National Science Foundation and the National Institute of Standards and Technology)
The fractional quantum Hall effect arises when electrons in two-dimensional materials are subject to a strong perpendicular magnetic field at very low temperatures. Researchers from George Mason University, Brown University, and the National Institute of Standards and Technology have shown that fractional quantum Hall states could be better detected using thermopower measurements than with conventional electrical resistivity. (Thermopower is an electrical voltage generated when charge carriers move from the hot side to the cold side of a conducting or semiconducting material.) The researchers performed thermopower measurements on bilayer graphene and observed new fractional quantum Hall states, which had not been previously reported.

(Funded by the U.S. Department of Defense and the U.S. National Science Foundation)
Researchers from Lehigh University, the U.S. Army Research Laboratory, Arizona State University, and Louisiana State University have developed a nanostructured copper alloy with exceptional thermal stability and mechanical strength, making it one of the most resilient copper-based materials ever created. The breakthrough comes from the formation of copper-lithium precipitates, stabilized by a tantalum-rich atomic bilayer complexion. Unlike typical grain boundaries that migrate over time at high temperatures, this complexion acts as a structural stabilizer, maintaining the nanocrystalline structure, preventing grain growth and dramatically improving high-temperature performance. The U.S. Army Research Laboratory was awarded a U.S. patent for the alloy.

(Funded by the U.S. Department of Defense)
Researchers from The University of Texas at Dallas; Texas State University in San Marcos, TX; and Lintec of America in Plano, TX, as well as international collaborators, have invented a new, inexpensive method in which fibers are coiled to make springlike artificial muscles. What’s unique about this method is that it doesn’t make use of a mandrel – a spindle that serves to support or shape the artificial muscles. The mandrel-free fabrication process involves inserting twist into individual fibers, causing them to coil back on themselves, and then plying the twisted fibers to create springlike coils. The researchers used the mandrel-free method to make high-spring-index carbon nanotube yarns, which could be used to harvest mechanical energy or as self-powered strain sensors.

(Funded by the U.S. National Science Foundation)
In a Perspective article published in Nature Materials, two engineers at the Massachusetts Institute of Technology, Carlos Portela and James Surjadi, discuss key hurdles, opportunities, and future applications in the field of mechanical metamaterials. Metamaterials are artificially structured materials with properties not easily found in nature. With engineered three-dimensional geometries at the micro- and nanoscale, metamaterials achieve unique mechanical and physical properties with capabilities beyond those of conventional materials. Over the past decade, metamaterials have emerged as a promising way to address engineering challenges for which other existing materials have lacked success.