The structure of molten elemental (Si, Ge) or binary (III-V, II-VI) semiconductors is well known, and has been shown to depend on the average number of valence s-and p-electrons (N sp ) [1] However, studies on binary systems have been limited to stoichiometric compounds, corresponding to a discrete set of N sp values. Studying ternary compounds allows us to investigate homogeneous liquids with varying average valenceelectron numbers. These materials have the additional advantage of often having lower melting temperatures, which renders them experimentally feasible for studies in an accessible temperature range. Among these ternary systems, a subset of Sb-and Te-based alloys shows a unique combination of properties. On the one hand, their electrical resistivity and optical reflectivity change dramatically with the transition between amorphous and crystalline states, indicating significant structural differences between these two phases. On the other hand, re-crystallization of the amorphous phase using laser or current pulses at temperatures between the glass transition (T g ) and melting (T m ) temperatures is fast, and proceeds in less than 10 ns. These properties are used in phase-change memories, [2,3] with a number of suitable materials for optical and electronic phase-change storage having been identified by trial and error.

Silver nanoparticles embedded in titanium oxide change their color upon irradiation with visible light. Here we investigate the origin of this photochromic effect. The color change is found to result chiefly from a reduction of the optical extinction peak of the photoexcited particle plasmons. From a comparison with x-ray diffraction experiments, we conclude that this reduction is caused by a photoinduced decrease of the mean size of the silver nanocrystals.

Ex situ transmission electron microscopy (TEM) was used to study the crystal morphology in sputtered amorphous Ge4Sb1Te5, Ge2Sb2Te5, and Ag0.055In0.065Sb0.59Te0.29 thin films used for phase change recording. Tilting of plan view samples revealed that each crystallized growth formation is a bent single crystal. Cross-sectional TEM showed that crystals only nucleate heterogeneously at the (naturally oxidized) film surface. These findings allow the determination of nucleation parameters around 150°C from earlier experiments [J. Kalb, F. Spaepen, and M. Wuttig, Appl. Phys. Lett. 84, 5240 (2004)]. The time lag for nucleation has an activation energy of (2.74±0.13)eV for Ge2Sb2Te5 and (2.33±0.18)eV for Ag0.055In0.065Sb0.59Te0.29. The activation energies for the steady-state nucleation rate were (4.09±0.20)eV for Ge4Sb1Te5 and (3.50±0.17)eV for Ge2Sb2Te5. With the activation energy for the crystal-growth velocity found in the earlier article the critical work for formation of the nucleus was found to be (1.35±0.23)eV for Ge4Sb1Te5 and (1.15±0.22)eV for Ge2Sb2Te5. These values are lower limits for homogeneous nucleation.

High-resolution photoelectron spectroscopy of in situ prepared films of GeSb2Te4 reveals significant differences in electronic and chemical structure between the amorphous and the crystalline phase. Evidence for two different chemical environments of Ge and Sb in the amorphous structure is found. This observation can explain the pronounced property contrast between both phases and provides new insight into the formation of the amorphous state.