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

Multimetal nanoparticle synthesis: Multicomponent nanoparticles can be difficult to synthesize. Rather than mixing in one type of particle, the compounds often separate and form distinct particles. Using dip-pen lithography, Chen et al. show how adding reactants to very small volumes forces the reactants to form single particles containing various combinations of five different transition metal ions. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy revealed the shapes of the nanoparticles and how metallic composition varied within them. For example, the quinary particle containing gold, silver, cobalt, copper, and nickel consisted of three domains of binary alloys. Science , this issue p. 1565