(Funded by the U.S. National Science Foundation and the U.S. Department of Energy)
Scientists from the U.S. Department of Energy’s (DOE) Argonne National Laboratory (ANL) and SLAC National Accelerator Laboratory; the University of Chicago; the University of Vermont; Middlebury College; Brown University; Stanford University; and Northwestern University have observed that when semiconductor nanocrystals called quantum dots were exposed to short bursts of light, the symmetry of the crystal structure changed from a disordered state to a more organized one. The return of symmetry directly affected the electronic properties of the quantum dots by causing a decrease in the bandgap energy, which is the difference in energy that electrons need to jump from one state to another within a semiconductor material. This change can influence how well quantum dots conduct electricity and respond to electric fields. Part of this work was conducted at the Center for Nanoscale Materials, a DOE Office of Science user facility at ANL.

(Funded by the U.S. National Science Foundation)
Researchers at The Ohio State University have developed a new material that, by harnessing the power of sunlight, can clear water of dangerous pollutants. Solar fuel systems that use titanium dioxide nanoparticles can cause significant challenges to implementation, including low efficiency and the need for complex filtration systems. So, the researchers added copper to the nanoparticles, and the new structures, called nanomats, can now absorb enough light energy to break down harmful pollutants in air and water. These lightweight, easy-to-remove fiber mats can float and operate atop any body of water and are even reusable through multiple cleaning cycles. Because the nanomats are so effective, the researchers envision that they could be used to rid water of industrial pollutants in developing countries, turning otherwise contaminated rivers and lakes into sources of clean drinking water.

(Funded by the U.S. Department of Defense and the U.S. National Science Foundation)
Researchers from the City University of New York, Yale University, Caltech, Kansas State University, and international collaborators have discovered a new way of generating phonon-polaritons, a unique type of electromagnetic wave that occurs when light interacts with vibrations in a material’s crystal lattice structure. This advance could pave the way for cheaper, smaller long-wave infrared light sources and more efficient device cooling. The researchers made that discovery by using a thin layer of graphene sandwiched between two hexagonal boron nitride slabs. Until now, exciting and detecting phonon-polariton waves has been expensive – typically involving costly mid-infrared or terahertz lasers and near-field scanning probes – but in this study, the researchers used a cheaper alternative: an electrical current generated by applying an electric field to the graphene.

(Funded by the U.S. Department of Defense, the U.S. Department of Energy and the U.S. National Science Foundation)
Researchers at Caltech have developed an on-chip transducer that converts microwave photons to optical photons. The device involves a tiny silicon beam that vibrates at 5 gigahertz and couples to a microwave resonator – essentially a nanoscale box in which photons bounce around, also at 5 GHz. Using a technique called electrostatic actuation, a microwave photon is converted within that box to a mechanical vibration of the beam, and that mechanical oscillation, with the help of laser light, gets converted by the resonator into an optical photon. Such a conversion could enable the construction of large-scale distributed superconducting quantum computers.

(Funded by the U.S. National Science Foundation)
Researchers from the University of Texas at Dallas, the Massachusetts Institute of Technology, and international collaborators have found that rhombohedral graphene behaves similarly to semiconductors and exhibits novel magnetism and superconductivity, as well as the quantum anomalous Hall effect, at extremely low temperatures. Graphene – a single layer of carbon atoms arranged in a flat honeycomb pattern – can be stacked in two different ways: Hexagonal stacking occurs when even-numbered graphene layers are aligned (with the odd-numbered layers rotated 60 degrees relative to the even layers); in contrast, rhombohedral stacking features a unidirectional 60-degree rotation for each successive layer.