unprecedented progress of the semiconductor industry and information technology. Yet, we have reached a stage where a simple evolution along established research lines might no longer bear much fruit. Advanced functional materials require increasingly complex and demanding property combinations. Their optimization would thus benefit from novel concepts. In thermoelectrics, which convert waste heat into electricity, for example, materials must show the unusual combination of high electrical and small thermal conductivity. This is demanding since a high electrical conductivity is usually accompanied by a high thermal conductivity. In phase change materials (PCMs) employed for data storage and processing, materials are required which possess a pronounced contrast in optical and/or electrical properties between two different states. Usually one of these states is a metastable one, which is typically amorphous, while the second state is then stable crystalline. The metastable state has to be stable at room temperature and slightly above for 10 years; but it should crystallize, i.e., return to the stable crystalline state in a few nanoseconds if heated to temperatures of typically around 500 °C. The combination of pronounced property contrast and hence presumably different atomic arrangements in the two different phases, yet rapid crystallization is indicative for an unusual correlation of chemical bonding, atomic arrangement, and resulting properties, including crystallization kinetics. Topological insulators, expected to help realize novel electronic functionalities, possess topologically protected spin-polarized surface states with high mobility. These states should govern the sample conductivity, if the bulk is insulating.This raises the question how these demanding requirements can be met and how superior materials can be identified. A number of different approaches have been developed in the past two decades to meet these needs. Combinatorial material synthesis, i.e., the fast preparation of stoichiometric libraries and their efficient analysis to identify superior compounds, has already been promoted over two decades ago. [1,2] While this scheme has indeed been successful in improving certain materials such as metal hydrides for hydrogen storage [3] and benchmarking electrocatalysts for solar water splitting, [4] for many material classes still empirical optimization schemes are employed. Machine learning is an emerging strategy to identify materials with a unique property portfolio. [5][6][7] This novel A unified picture of different application areas for incipient metals is presented. This unconventional material class includes several main-group chalcogenides, such as GeTe, PbTe, Sb 2 Te 3 , Bi 2 Se 3 , AgSbTe 2 and Ge 2 Sb 2 Te 5 . These compounds and related materials show a unique portfolio of physical properties. A novel map is discussed, which helps to explain these properties and separates the different fundamental bonding mechanisms (e.g., ionic, metallic, and covalent). The map also provides evidence ...

AbstractÐA detailed description is given of the microstructure of the top layer of Ti±6Al±4V with SiC particles embedded with a high-power Nd:Yag laser system. Scanning electron microscopy (SEM), as well as conventional, analytical and high-resolution transmission electron microscopy (TEM) were used. An existing controversy about the presence or absence of Ti 3 SiC 2 in the reactive SiC/Ti systems is clari®ed and the ®rst observations of Ti 5 Si 3 precipitation on stacking faults in Si supersaturated TiC are reported. The Si released during the reaction SiC+Ti4TiC+Si results in the formation of Ti 5 Si 3 . If in the reaction layer regions in between the TiC grains become enclosed, the rejected Si content increases locally and Ti 3 SiC 2 plates with dominant (0001) facets nucleate. In the TiC grains particularly of the cellular reaction layer, a high density of widely extending stacking faults of the order of 100 nm is observed and on these faults in many instances small Ti 5 Si 3 precipitates are present. #

Hybrid organic-inorganic perovskites are semiconductors that have great potential for optoelectronic applications such as light-emitting diodes, photodetectors, and solar cells. In such devices, the surface plays a crucial role in the performance and stability, as it strongly influences the recombination rate of excited charge carriers. It is reported that molecular ligands such as benzylamine are capable of reducing the surface trap state density in thin films. In this work, we aim to clarify the mechanisms that govern the surface passivation of hybrid perovskites by benzylamine. We developed a versatile approach to investigate the influence of benzylamine passivation on the well-defined surface of freshly cleaved hybrid perovskite crystals. We show that benzylamine permanently passivates surface trap states in these single crystals, resulting in enhanced photoluminescence and charge carrier lifetimes. Additionally, we show that exposure to benzylamine leads to the replacement of the methylammonium cations by benzylammonium, thereby creating a thermodynamically more stable two-dimensional (2D) perovskite (BA) 2 PbBr 4 on the surface of the three-dimensional crystal. This conversion to a 2D perovskite drives an anisotropic etching of the crystal surface, with the {100} planes being most prone to etching. Initially, square etching pits appear spread over the surface. As time elapses, these etching pits broaden and merge to yield large flat terraces that are oriented normally to the cleaving plane when they form. A thorough understanding of the mechanisms governing the surface passivation is crucially important to optimize and design novel passivation schemes, with the ultimate goal of further advancing the efficiency of optoelectronic devices based on hybrid perovskites.

Metal borides, a class of materials intensively used in industry as superconductors, magnetic materials, or hot cathodes, remain largely unexplored at the nanoscale mainly due to the difficulty in synthesizing single-phase nanocrystals. Recent works have shown that synthetic methods at lower temperatures (<400 °C) yield amorphous polydisperse nanoparticles, while phase purity is an issue at higher temperatures. Among all the metal-rich borides, nickel borides (Ni x B) could be a potential catalyst for a broad range of applications (hydrogenations, electrochemical hydrogen, and oxygen evolution reactions) under challenging conditions (such as high pH or high temperatures). Here, we report a novel solid-state method to synthesize Ni x B nanopowders (with a diameter of approximately 45 nm) and their conversion into colloidal suspensions (inks) through treatment of the nanocrystal surface. For the solid-state synthesis, we used commercially available salts and explored the reaction between the Ni and B sources while varying the synthetic parameters under mild and solvent-free reaction conditions. We show that pure phase Ni3B and Ni2B NCs can be obtained with high yield in the pure phase using as precursors NiCl2 and Ni, respectively. Through extensive mechanistic studies, we show that Ni nanoclusters (1–2 nm) are an intermediate in the boriding process, while the metal co-reactant lowers the decomposition temperature of NaBH4 (used as a reducing agent and B source). Size control can instead be exerted through reaction mediators, as seen from the differential nucleation and growth of Ni (clusters) or Ni x B NCs when employing L- (amine, phosphine) and X-type (carboxylate) mediators. Applying surface engineering methods to our Ni x B NCs, we stabilized them with inorganic (NOBF4) or organic (borane tert-butyl amine, oleylamine) ligands in the appropriate solvent (DMSO, hexane). With this method, we produce stable inks for further solution processing applications. Our results provide tools for further development of catalysts based on Ni x B NCs and pave the way for synthesizing other metal boride colloidal nanostructures.

Analysis of crystal growth in thin films of phase‐change materials can provide deeper insights in the extraordinary phase transformation kinetics of these materials excellently suited for data storage applications. In the present work crystal growth in GexSb100‐x thin films with x = 6, 7, 8, 9, and 10 is studied in detail, demonstrating that the crystallization temperature increases from ∼80 °C for Ge6Sb94 to ∼200 °C for Ge10Sb90 and simultaneously the activation energy for crystal growth also significantly increases from 1.7 eV to 5.5 eV. The most interesting new finding is that in the thin films containing 8, 9, and 10 at% Ge two competing growth modes occur which can have several orders of magnitude difference in growth rate at a single external temperature: an initial mode with isotropic slow growth producing circular crystals with smooth surfaces and growth fronts and a fast growth mode producing crystals with triangular shape having rough surfaces and growth fronts indicative of dendritic‐like growth. The slow‐growth mode becomes increasingly dominant for crystallization at low temperatures when the Ge concentration is increased from 8 to 10 at% Ge. For a certain Ge concentration, the slow growth mode becomes increasingly dominant at lower temperatures and the fast growth mode at higher temperatures. Latent heat produced during crystallization is considered a principal factor explaining the observations. The fast growth mode is associated with (eutectic) decomposition generating more latent heat and instable growth fronts and the slow growth mode is associated with thermodynamically less stable homogeneously alloyed crystals generating less latent heat, but stable growth fronts.