Littérature scientifique sur le sujet « Wulff solid »

Optical vortex array (OVA) containing multiple optical vortices is an optimal candidate for applications of optical communications, complex manipulation of multi-particle systems, and mass-synchronous fabrication. However, the existing OVAs have not been constructed to respond to the application requirements, particularly for micro-/nanomaterial fabrication where the boundary, size, and stability need to be carefully considered. To address this issue, we propose a Gibbs–Wulff OVA (GWOVA) by analogizing the Gibbs–Wulff theorem in solid-state physics. Herein, the Gibbs–Wulff theorem is first generalized to OVA's generation as the condition to confine its growth boundary. The GWOVA, which possesses versatile structures and arrangement modes (simple- and close-packed modes), is successfully generated and grown. It exhibits high stability and perfect symmetry during growth and rotation, which satisfies the symmetric group of D2 s. Owing to its stable structure and growth boundary conditions, the GWOVA has great potential for a wide range of applications, particularly in micro-/nanomaterial fabrication.

A Fortran90 program for the determination of the Wulff construction, starting solely from the directions of the bounding facets (defined by the user), is presented.SOWOSstands for solid of Wulff open source, and the program is distributed freely with no charge to the user, being readily available to the community for immediate use. Its simple algorithm (which will be explained) allows the determination of complex solids with hundreds of facets in just seconds on any machine, requiring only a small amount of memory. It is able to determine even the smallest facets and shortest edges and to distinguish almost adjacent vertices. The output files give a complete range of information about the structure: the coordinates of the vertices and the facets common to them, the extension of the facets and bounding vertices, and the length of the edges and extreme vertices. These details enable the reconstruction of the shape in any other (commercial) software for further processing. Visualization is straightforwardviathe free programgnuplot. A feature for the creation of cubic crystal atomistic models of the resultant solids is included. The program may be a useful tool for crystallography, nanostructures and any other field where crystal facets are involved.

The temperature dependence of the energy of various facets of twin GBs has been measured. For the investigation of GB faceting the Al bicrystals of 99.999% wt. purity were grown by the modified Bridgman technique. One grain in these bicrystals is semi-surrounded by another one. Bicrystals were coated with a layer of Sn–Al alloy and annealed at various temperatures. Contact angles at the junction of a GB and two solid/liquid interfaces have been measured. The ratios of GB energy to solid/liquid interface energy have been calculated. Using these data, the Wulff-Herring plots and GB phase diagrams were constructed. Three different crystallographic facets were observed for the coincidence GB. Two of them are stable at all studied temperatures, the third one becomes metastable below ~ 800K. In GBs with θ = 3° only one facet (symmetric twin GB) is stable.

Abstract The problem of the surface acoustic Rayleigh wave scattering on a deterministic three-dimensional roughness, occupying a finite size rectangular region of an isotropic solid free surface, is solved in the Rayleigh-Born approximation of the perturbation theory in a roughness amplitude. Formula for the displacement field in the scattered Rayleigh wave at a big distance from the roughness, as compared to rough region sizes L1,2 along the x1,2- axes respectively, and asymptotic formulas for this displacement field in the Bragg, i.e. short-wavelength λ≪ L1,2 limit, where λ is the wavelength, are derived. The new laws of scattering are obtained. They are caused by a strong modulation of scattering by the roughness form. They exceed the fundamental physical conception, that a wave scattering in the short-wavelength limit takes place on a medium discontinuities, by the statement, that a wave strongly senses the structure of a medium in the near vicinity of discontinuities as well as the form-factor of the discontinuities lattice. This form-factor is a dependence of the discontinuity amplitude, i.e. of a difference of the left and right limit values of a roughness non-zero derivative, including one of zero order, in coordinate at a point of discontinuity, on a number of this discontinuity in a lattice. This exceeded physical conception violates the classical Laue-Bragg-Wulff laws of scattering.

The all-solid-state lithium-ion battery is a new class of batteries being developed following today’s demand for renewable energy storage, especially for electric cars. The key component of such batteries is the solid-state electrolyte, a technology that promises increased safety and energy density with respect to the traditional liquid electrolytes. In this view, β-Li3PS4 is emerging as a good solid-state electrolyte candidate due to its stability and ionic conductivity. Despite the number of recent studies on this material, there is still much to understand about its atomic structure, and in particular its surface, a topic that becomes of key relevance for ionic diffusion and chemical stability in grain borders and contact with the other device components. In this study, we performed a density functional study of the structural and electronic properties of β-Li3PS4 surfaces. Starting from the bulk, we first verified that the thermodynamically stable structure featured slight distortion to the structure. Then, the surfaces were cut along different crystallographic planes and compared with each other. The (100) surface is confirmed as the most stable at T = 298 K, closely followed by (011), (010), and (210). Finally, from the computed surface energies, the Wulff nanocrystals were obtained and it was verified that the growth along the (100) and (011) directions reasonably reproduces the shape of the experimentally observed nanocrystal. With this study, we demonstrate that there are other surfaces besides (100) that are stable and can form interfaces with other components of the battery as well as facilitate the Li-migration according to their porous structures.

Aufgrund steigender Preise von Wolfram und Kobalt sind die Herstellkosten von Vollhartmetallwerkzeugen durch einen hohen Materialkostenanteil geprägt. Im Forschungsprojekt „Re-Tool 2“ erforscht das Institut für Fertigungstechnik und Werkzeugmaschinen (IFW) zusammen mit der Wulf Schleiftechnik GmbH einen Herstellungsprozess, um verschlissene Werkzeuge als Rohlinge für die Werkzeugherstellung zu verwenden. Durch einen Vergleich der Herstellung von umgeschliffenen und neugeschliffenen VHM-Werkzeugen soll das ökonomische und ökologische Einsparpotenzial der Methode gezeigt werden.   Due to the rising prices of tungsten and cobalt, the manufacturing costs of solid carbide tools are characterized by a high material cost share. In the research project „Re-Tool 2“, the IFW is researching in cooperation with Wulf Schleiftechnik GmbH a manufacturing process to use worn tools as blanks for tool production. By means of a comparison between the manufacturing and re-manufacturing process of tungsten carbide tools, the high economic and ecological savings potential is shown.

By mimicking biomimetic synaptic processes, the success of artificial intelligence (AI) has been astounding with various applications such as driving automation, big data analysis, and natural-language processing.[1-4] Due to a large quantity of data transmission between the separated memory unit and the logic unit, the classical computing system with von Neumann architecture consumes excessive energy and has a significant processing delay.[5] Furthermore, the speed difference between the two units also causes extra delay, which is referred to as the "memory wall".[6, 7] To keep pace with the rapid growth of AI applications, enhanced hardware systems that particularly feature an energy-efficient and high-speed hardware system need to be secured. The novel neuromorphic computing system, an in-memory architecture with low power consumption, has been suggested as an alternative to the conventional system. Memristors with analog-type resistive switching behavior are a promising candidate for implementing the neuromorphic computing system since the devices can modulate the conductance with cycles that act as synaptic weights to process input signals and store information.[8, 9] The memristor has sparked tremendous interest due to its simple two-terminal structure, including top electrode (TE), bottom electrode (BE), and an intermediate resistive switching (RS) layer. Many oxide materials, including HfO2, Ta2O5, and IGZO, have extensively been studied as an RS layer of memristors. Silicon dioxide (SiO2) features 3D structural conformity with the conventional CMOS technology and high wafer-scale homogeneity, which has benefited modern microelectronic devices as dielectric and/or passivation layers. Therefore, the use of SiO2 as a memristor RS layer for neuromorphic computing is expected to be compatible with current Si technology with minimal processing and material-related complexities. In this work, we proposed SiO2-based memristor and investigated switching behaviors metallized with different reduction potentials by applying pure Cu and Ag, and their alloys with varied ratios. Heavily doped p-type silicon was chosen as BE in order to exclude any effects of the BE ions on the memristor performance. We previously reported that the selection of TE is crucial for achieving a high memory window and stable switching performance. According to the study which compares the roles of Cu (switching stabilizer) and Ag (large switching window performer) TEs for oxide memristors, we have selected the TE materials and their alloys to engineer the SiO2-based memristor characteristics. The Ag TE leads to a larger memory window of the SiO2 memristor, but the device shows relatively large variation and less reliability. On the other hand, the Cu TE device presents uniform gradual switching behavior which is in line with our previous report that Cu can be served as a stabilizer, but with small on/off ratio.[9] These distinct performances with Cu and Ag metallization leads us to utilize a Cu/Ag alloy as the TE. Various compositions of Cu/Ag were examined for the optimization of the memristor TEs. With a Cu/Ag alloying TE with optimized ratio, our SiO2 based memristor demonstrates uniform switching behavior and memory window for analog switching applications. Also, it shows ideal potentiation and depression synaptic behavior under the positive/negative spikes (pulse train). In conclusion, the SiO2 memristors with different metallization were established. To tune the property of RS layer, the sputtering conditions of RS were varied. To investigate the influence of TE selections on switching performance of memristor, we integrated Cu, Ag and Cu/Ag alloy as TEs and compared the switch characteristics. Our encouraging results clearly demonstrate that SiO2 with Cu/Ag is a promising memristor device with synaptic switching behavior in neuromorphic computing applications. Acknowledgement This work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 22011044) by KRISS. References [1] Young et al., IEEE Computational Intelligence Magazine, vol. 13, no. 3, pp. 55-75, 2018. [2] Hadsell et al., Journal of Field Robotics, vol. 26, no. 2, pp. 120-144, 2009. [3] Najafabadi et al., Journal of Big Data, vol. 2, no. 1, p. 1, 2015. [4] Zhao et al., Applied Physics Reviews, vol. 7, no. 1, 2020. [5] Zidan et al., Nature Electronics, vol. 1, no. 1, pp. 22-29, 2018. [6] Wulf et al., SIGARCH Comput. Archit. News, vol. 23, no. 1, pp. 20–24, 1995. [7] Wilkes, SIGARCH Comput. Archit. News, vol. 23, no. 4, pp. 4–6, 1995. [8] Ielmini et al., Nature Electronics, vol. 1, no. 6, pp. 333-343, 2018. [9] Chang et al., Nano Letters, vol. 10, no. 4, pp. 1297-1301, 2010. [10] Qin et al., Physica Status Solidi (RRL) - Rapid Research Letters, pssr.202200075R1, In press, 2022.

ABSTRACTIt has been shown that the concepts used to determine the equilibrium shape of crystals can be extended to determine the conditions under which grain boundaries will be fully wetted, partially wetted, or not wetted by a second phase. Recent experimental observations on the equilibrated morphologies of solid or fluid wetting phases along grain boundaries, reveal features that are predicted, and in some cases required, by this construction. Theory distinguishes between cases where surfaces are smoothly curved or where there are facets, edges and corners. In the latter case the conventional comparison of the energy of the original grain boundary with the sum of the surface energy of the two surfaces of the wetting layer leads to erroneous predictions. The correct predictions are obtained by comparing the Wulff shape of the grain boundary (the interfacial energy minimizing shape for a fixed volume of material) with a carefully defined sum of Wulff shapes of the surfaces of the wetting layer. Where orientations that are wetted join with those that are not, there is almost always an abrupt change of orientation. Faceting on two hierarchical levels can occur. Microscopic morphology changes along macroscopically curved surfaces follow well defined rules predicted by theory. The analogy between the thermodynamics of interface faceting and phase transformations allows the well known concepts of phase equilibria to be used to understand the predicted structures. The predictions of the model will be used to identify the nature of the faceting observed in alumina in the presence of a second phase.

Deposition of Ge upon Si substrates is the prototype of the mechanism called Stranski- Krastanov growth, i.e. the self-assembled formation of 3D islands, following the formation of a thin, 2D Wetting Layer. As is shown in Chapter 1, the nucleation of these islands is random and non-uniform when the deposition is performed upon the standard Si(001) substrate. Deposition of SiGe on different substrates of Si can lead, however, to a high degree of uniformity. Some examples are described in Chapters 3 and 4. The aim of this thesis is to supply a quantitative analysis for some peculiar phenomena concerning island nucleation that occurs on these non-standard substrates. This is performed through the evaluation of the internal energy of the island (including also effects on the substrate) as discussed at length in Chapter 2, where the elastic, surface and edge energy contributions are described, focusing particular attention to the second one, that turns out to be quite complicated. Particular attention is devoted to the island nucleation on stepped substrates of Si (Chapter 4). An in-depth analysis of the formation of faceting upon the substrate Si(1 1 10) is carried out in Chapter 5, whereas Chapter 6 deals with the transition from the faceting to three-dimensional islands on this peculiar system. Conclusions are drawn in Chapter 7. Appendices A and B contain some additional information regarding the elastic field and the description of surfaces. In Appendix C an analysis of the strained surface energy is carried out. In Appendix D some preliminary work performed during the PhD period on other impor- tant surfaces for the SiGe system is discussed. Finally at page 203 a Curriculum Vitae is reported.

The energy-related holographic applications such as spectrum-splitting holoconcentrators,1 solar-control Lippmann holowindows,2 heliostat dichroic/polychroic non-Snellian mirrors,3 etc. have unique potential of realizing wavelength/angular selective spatial processing operations. Therefore, the systems with properties such as spectrum-selective Snellian/non-Snellian reflection, deflection concentration, and collimation can be produced by using large-size (1-m2 area), flat or curved thin holographic coatings. In this paper it was shown that only superhigh-efficiency (SHE) holographic technology, based on Bragg reflection Lippmann holograms,3 can satisfy all necessary conditions to be competitive with conventional techniques. These conditions are high diffraction efficiency values close to the theoretical limit, rectangular shape of diffraction efficiency spectral characteristics, low absorption/scattering losses (below1%), low coupling losses (below 5%), and optical efficiency of the compound holographic system close to its average diffraction efficiency within all spectra of interest. In the case of solar applications (inc1uding PV and TPV holoconcentrator systems), the last condition is especially difficult to satisfy because of the relatively wide range of the solar spectrum. To prove the advantages of reflection holograms (compared with transmission holograms) in broadband energy-related applications (solar, chemical, etc.), the wave-tracing kinematic model was applied to 1-D-limited 3-D holographic Bragg structures with a well-defined grating vector. The model was based on the generalized solid-state physics Wulf-Bragg formalism.4