Herbert Gleiter

Nanostructured materials: basic concepts and microstructure☆

Abstract Nanostructured Materials (NsM) are materials with a microstructure the characteristic length scale of which is on the order of a few (typically 1–10) nanometers. NsM may be in or far away from thermodynamic equilibrium. NsM synthesized by supramolecular chemistry are examples of NsM in thermodynamic equilibrium. NsM consisting of nanometer-sized crystallites (e.g. of Au or NaCl) with different crystallographic orientations and/or chemical compositions are far away from thermodynamic equilibrium. The properties of NsM deviate from those of single crystals (or coarse-grained polycrystals) and/or glasses with the same average chemical composition. This deviation results from the reduced size and/or dimensionality of the nanometer-sized crystallites as well as from the numerous interfaces between adjacent crystallites. An attempt is made to summarize the basic physical concepts and the microstructural features of equilibrium and non-equilibrium NsM.

On the validity of the hall-petch relationship in nanocrystalline materials

Etude experimentale de la variation de la durete en fonction de la grosseur de grain pour des materiaux nanocristallins. En contraste avec la relation de Hall-Petch, cette analyse, realisee sur le cuivre et le palladium a la temperature ambiante, montre un decroissement de la durete lorsque la grosseur de grain decroit. Ces resultats sont expliques en termes dapparition dun fluage diffusionnel, a la temperature ambiante, dans les materiaux a grains ultrafins

Point defect annihilation at grain boundaries in gold

On essaie declaircir linfluence de la structure atomique des joints de grains sur leur efficiacite en tant que puits et source de defauts ponctuels pour les concentrations elevees de defauts ponctuels

Structure and properties of nanometer-sized materials

Abstract Nanometer-sized materials are solids which may be considered as a dense ensemble of atomic clusters with a diameter of a few nanometers. Depending on whether the individual clusters have a crystalline or a glassy structure, nanocrystalline materials or nanometer-sized glasses are formed. Nanocrystalline materials (NCM) are single or multiphase ploy-crystals, the crystal size of which is in the order of a few (typically 1 to 10) nanometers. These materials are of interest for the following three reasons: i. NCM seem to exhibit an atomic structure which differs from the crystalline state (with long range order) and the glassy state (with short range order). NCM seem to represent a new type of solid state structure. ii. The properties of NCM differ (in some cases by several orders of magnitude) from the properties of glasses and/or crystals with the same chemical composition. iii. NCM seem to permit the alloying of conventionally immiscible components such as metals and ceramics. The resulting alloy...

STM/AFM study of grain boundary migration in nanostructured solids

Abstract Nanostructured materials were directly imaged by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Images suggested that nanostructured palladium (Pd) consisted of equiaxed crystals of ≈ 10 nm diameter joined together by grain boundaries. Migration of the grain boundaries in nanostructured Pd was stimulated by STM (but not AFM), resulting in a preferential alignment of the nanometer-sized grains.

The effect of the electronic structure on the behaviour of grain boundaries in metals

Mesure de lenergie des joints de grains dans differents alliages Cu-Ni pour evaluer linfluence de la structure electronique des metaux sur lenergie des joints. Si on compare les alliages Cu-Ni avec Ni pur et Cu on peut dire que la structure electronique evolue de facon continue dune structure de metal de transition vers une structure de metal noble sans que cela affecte la cristallographie

Is the impact velocity of vacuum-deposited atoms of significance for the film structure?

Abstract Our goal in this study was to investigate the effect of the impact velocity of the atoms on the structure of thin films generated by vacuum deposition. For that purpose all atoms faster or slower than a pre-selected velocity u were removed with a velocity filter from a beam of gold atoms obtained by thermal evaporation in vacuum (10 −5 Pa). The residual atoms with a velocity u were deposited onto gold (80K) glass substrates. The annealing behaviour of the films studied by means of d.c. resistance measurements indicates a correlation between film structure and impact velocity in the sense that films generated by means of low velocity atoms have a non-equilibrium structure which does not exist in films prepared by conventional vacuum deposition.

Dislocation annealing in interfaces between crystals and glasses

Etude experimentale du verre metallique 37,5% at. Fe-37,5% at. Ni-2,5% at. B prepare par filage a letat liquide. Par recuit, on obtient un alliage partiellement cristallise. On observe par microscopie electronique levolution au cours du chauffage des dislocations aux interfaces cristal-cristal et cristal-verre

Adaptive intelligent control of economic flows by stochastic dynamics

With development of industry and information, the time subjected to daily economical situations has come. By artificial intervention such as to derive an economic catastrophe, economic bubbles in the world can burst out instantaneously. To protect such situations, the establishment of how to intelligently adaptive control economical flows by means of modern stochastic and computing-economical methods is needed. Using typical model-systems we construct the simulation systems and theoretical frameworks and derive some kind of adaptive intelligent control methods for the analysis, evaluation and control of economical flows.

Visualization of microstructures of economic flows and adaptive control

Economic flows are modeled based on the microscopic particle pictures, and studied by renormalized stochastic dynamics and simulations. From the universal behavior obtained, every catastrophic behavior of the flows may be understood, as well as which sub-system is concerned and how to avoid it by suitable control measures.