Erik Johnson

Atoms on the edge: The atomic edge structure of industrial-style MoS2 nanocatalysts was imaged using single-atom sensitive electron microscopy (see picture). The observed industrial-style edge terminations match predictions of model catalyst studies and thus address the so-called “materials gap” in catalysis.

Au free GaAs nanowires with zinc blende structure, free of twin planes and with remarkable aspect ratios, have been grown on (111) Si substrates by molecular beam epitaxy. Nanowires with diameters down to 20 nm are obtained using a thin native oxide layer on the Si substrates. We discuss how the structural phase distribution along the wire length is controlled by the effective V/III ratio and temperature at the growth interface and explain how to obtain a pure twin plane free zinc blende structure.

Abstract Very high lateral ionic conductivities in epitaxial cubic yttria‐stabilized zirconia (YSZ) synthesized on single‐crystal SrTiO 3 and MgO substrates by reactive direct current magnetron sputtering are reported. Superionic conductivities (i.e., ionic conductivities of the order ∼1 Ω −1 cm −1 ) are observed at 500 °C for 58‐nm‐thick films on MgO. The results indicate a superposition of two parallel contributions – one due to bulk conductivity and one attributable to conduction along the film–substrate interface. Interfacial effects dominate the conductivity at low temperatures (<350 °C), showing more than three orders of magnitude enhancement compared to bulk YSZ. At higher temperatures, a more bulk‐like conductivity is observed. The films have a negligible grain‐boundary network, thus ruling out grain boundaries as a pathway for ionic conduction. The observed enhancement in lateral ionic conductivity is caused by a combination of misfit dislocation density and elastic strain in the interface. These very high ionic conductivities in the temperature range 150–500 °C are of great fundamental importance but may also be technologically relevant for low‐temperature applications.

Thermal hysteresis is observed in x-ray-diffraction studies of the melting and solidification of small crystalline precipitates of lead in aluminum. Reproducible superheating as well as supercooling is present in succesive heating sequences demonstrating that they are intrinsic physical phenomena. For lead precipitates of mean size 140 and 270 A\r{}, the width of the hysteresis loop is 88 and 62 K, respectively. These results are discussed in a phenomenological context considering the lack of free surfaces.