Structural switch for fast switching: Phase-change materials are important for computer memory. They can quickly switch from glassy to crystalline using a thermal pulse and then lock in that structure for a long time at lower temperature. Zalden et al. probed the underlying atomic structure of two phase-change materials during this switching using ultrafast x-rays and simulations (see the Perspective by Rao et al. ). A liquid-liquid phase transition in both materials allowed fast switching at high temperatures. The lower-temperature glass locks in the structure, allowing for long-term memory storage. Science , this issue p. 1062 ; see also p. 1032

Oxide nanowire networks or oxide nanonets leverage some of the exceptional functionalities of one-dimensional nanomaterials along with the fault tolerance and flexibility of interconnected nanowires to creating exciting opportunities in large-area electronics as well as green energy systems. This paper reviews the electronic and optoelectronic properties of these networks and highlights their potential applications in field-effect transistors, optoelectronic devices, and solar cells. Techniques to grow nanowires and their subsequent integration into networks using contact printing and electrospinning are described. Electrical properties of field-effect transistors fabricated from contact printed nanowire networks are discussed, and means of integration of the nanowire networks of heterogenous materials that enable ambipolar device operation are outlined. Photocurrent properties of these nanowires are described, including the dye sensitization of large-bandgap SnO₂ nanowires. The final section deals with the advantages of employing nanowire networks in dye-sensitized solar cells and the dependence of solar cell performance on morphology and surface area.

Copper oxides (Cu_xO) thin films were deposited using radio frequency (RF) sputtering on glass substrates. By tuning the argon (Ar) partial pressure during deposition, cuprous oxide (Cu₂O), cupric oxide (CuO), or their mixed phase could be achieved. Drastic variations in the Hall mobility, hole density, and resistivity of the samples were observed due to the presence of different phases in the films. Kelvin probe studies indicate that the photo-generated carriers have lower recombination rate in pure Cu₂O phase. This was further validated by transient absorption measurements, where the estimated carrier lifetime for Cu₂O was much larger that other phases.

Spatially resolved x-ray fluorescence maps are presented that show the introduction and the evolution of oxygen vacancies in chromium-doped strontium titanate during an electric-field-driven insulator-to-metal transition. The vacancies are introduced at the anode and diffuse through the crystal toward the cathode. The spatial distribution of vacancies is explained by a model describing the electrical breakdown as a percolation process. Strong differences in the vacancy distribution were found when the transition took place in air and in a hydrogen-enriched atmosphere. In air, the vacancies disappeared from the surface, whereas in the reducing hydrogen atmosphere, they remained at the surface.