Borophene: Boron in two dimensions: Although bulk allotropes of carbon and boron differ greatly, small clusters of these elements show remarkable similarities. Boron analogs of two-dimensional carbon allotropes such as graphene have been predicted. Now Mannix et al. report the formation of two-dimensional boron by depositing the elemental boron onto a silver surface under ultrahigh-vacuum conditions (see the Perspective by Sachdev). The graphene-like structure was buckled, weakly bonded to the substrate, and metallic. Science , this issue p. 1513 ; see also p. 1468

We report on the observation of nanoscale conduction at ferroelectric domain walls in hexagonal ${\mathrm{HoMnO}}_3$ protected by the topology of multiferroic vortices using in situ conductive atomic force microscopy, piezoresponse force microscopy, and Kelvin-probe force microscopy at low temperatures. In addition to previously observed Schottky-like rectification at low bias [ Phys. Rev. Lett. 104, 217601 (2010)], conductance spectra reveal that negatively charged tail-to-tail walls exhibit enhanced conduction at high forward bias, while positively charged head-to-head walls exhibit suppressed conduction at high reverse bias. Our results pave the way for understanding the semiconducting properties of the domains and domain walls in small-gap ferroelectrics.

Significance: Few-layered phosphorene, which is isolated through exfoliation from black phosphorus, has attracted great interest due to its unique electronic and optical properties. Although solution-based exfoliation methods have been developed for black phosphorus, these techniques have thus far used anhydrous organic solvents. This approach minimizes exposure to known oxidizing species, but at the cost of limited exfoliation yield and relatively thick flakes. Here, we overcome these limitations by using stabilizing surfactants in deoxygenated water, which results in phosphorene down to the monolayer limit. The resulting aqueous phosphorene dispersions show layer-dependent photoluminescence and enable high-performance field-effect transistors. Overall, this approach holds promise for the solution-phase production of few-layered phosphorene in emerging large-volume applications including electronics and optoelectronics.