Use of Transmission Electron Microscopy in Combinatorial Studies of Functional Oxides

Summary: The principles of combinatorial methodology are based on high‐throughput properties measurements (HTPM) of multiple compositions in combinatorial libraries, and are recently being increasingly applied in materials research. Nevertheless, the authors' view is that the involvement of detailed but time‐consuming investigation using transmission electron microscopy (TEM) should be an important part of combinatorial materials research. In this paper we present three examples from our combinatorial studies where the TEM investigation was essential in obtaining a detailed picture of microstructures and their relationship with the physical properties. In the study of microwave dielectrics such as BaTiO₃‐SrTiO₃, TEM provides essential information on the type and distribution of defects in the deposited films. In the case of the wide‐band semiconductor ZnO‐MgO, the distribution and morphology of the phases were studied and related to the measured electronic properties. Study of the manganates LaMnO₃‐CaMnO₃ with colossal magneto‐resistive properties showed an anisotropic distribution of the structural domains and the morphology of the film. The distribution of the domains and the absence of epitaxial stresses found are essential in the interpretation of magnetic measurements.

Cross‐sectional TEM (dark field) micrograph taken with the reflection of h‐(Zn,Mg)O at x = 0.5.     

Hamiltonian loops from the ergodic point of view

Let G be the group of Hamiltonian diffeomorphisms of a closed symplectic manifold Y. A loop h:S¹→G is called strictly ergodic if for some irrational number α the associated skew product map T:S¹×Y→S¹×Y defined by T(t,y)=(t+α,h(t)y) is strictly ergodic. In the present paper we address the following question. Which elements of the fundamental group of G can be represented by strictly ergodic loops? We prove existence of contractible strictly ergodic loops for a wide class of symplectic manifolds (for instance for simply connected ones). Further, we find a restriction on the homotopy classes of smooth strictly ergodic loops in the framework of Hofer’s bi-invariant geometry on G. Namely, we prove that their asymptotic Hofer’s norm must vanish. This result provides a link between ergodic theory and symplectic topology. Received July 7, 1998 / final version received September 14, 1998     

Radiative Transport in a Periodic Structure

We derive radiative transport equations for solutions of a Schrödinger equation in a periodic structure with small random inhomogeneities. We use systematically the Wigner transform and the Bloch wave expansion. The streaming part of the radiative transport equations is determined entirely by the Bloch spectrum, and the scattering part by the random fluctuations.     

Heterogeneous Catalysis to Drive the Waste-to-Pharma Concept: From Furanics to Active Pharmaceutical Ingredients

A perspective on the use of heterogeneous catalysis to drive the waste-to-pharma concept is provided in this contribution based on the conversion of furanics to active pharmaceutical ingredients (APIs). The provided overview of the concept in this perspective article has been exemplified for two key molecule examples: Ancarolol and Furosemide.     

Analytical Expressions for Ising Models on High Dimensional Lattices

We use an m-vicinity method to examine Ising models on hypercube lattices of high dimensions d≥3. This method is applicable for both short-range and long-range interactions. We introduce a small parameter, which determines whether the method can be used when calculating the free energy. When we account for interaction with the nearest neighbors only, the value of this parameter depends on the dimension of the lattice d. We obtain an expression for the critical temperature in terms of the interaction constants that is in a good agreement with the results of computer simulations. For d=5,6,7, our theoretical estimates match the numerical results both qualitatively and quantitatively. For d=3,4, our method is sufficiently accurate for the calculation of the critical temperatures; however, it predicts a finite jump of the heat capacity at the critical point. In the case of the three-dimensional lattice (d=3), this contradicts the commonly accepted ideas of the type of the singularity at the critical point. For the four-dimensional lattice (d=4), the character of the singularity is under current discussion. For the dimensions d=1, 2 the m-vicinity method is not applicable.     

Segmentation of Heteropolymer Sequences Specifying Subsequences with Different Composition and Statistical Properties

We have studied the segmentation of two‐letter AB heterosequences composed of subsequences with different composition and distribution of A and B monomer units along the chain. Our approach is based on the segmentation function S(k) introduced in the present work and on the Jensen–Shannon divergence measure determined with respect to the probabilities of the lengths of uniform blocks of A and B monomer units. It is shown that the function S(k) is extremely sensitive to the sequence statistics. Even visual analysis of S(k) allows judgment on some features of sequence statistics. In particular, function S(k) is constant for random copolymers, it is an oscillating function for random block copolymers and shows monotonic growth up to some constant value for proteinlike copolymers. However, due to significant fluctuations observed for short sequences, the function S(k) can be effectively used only for segmentation of a heterosequence composed of very long subsequences. On the other hand, we find that the Jensen–Shannon divergence measure does not allow one to judge the type of statistics, but is extremely efficient for segmentation of a heterosequence. Therefore, the two introduced functions, being mutually complementary, provide an effective approach for recognizing and segmentation of heterosequences. As an example, the methods developed are applied for concatenating sequences of different proteins.

Segmentation function S(k, l, x) as a function of parameter k and starting number x of “window” for a sequence composed of elastin and ribonuclease sequences.     

Potassium 3‐cyano‐4‐(dicyanomethylene)‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate

The crystal structure of the title potassium salt, K⁺·C₈HN₄O₂⁻, of the organic anion 3‐cyano‐4‐(di­cyano­methyl­ene)‐5‐oxo‐4,5‐di­hydro‐1H‐pyrrol‐2‐olate shows that the di­cyano­methyl­ene moiety is able to accept an electron in the same way as does tetra­cyano­ethyl­ene, to yield the novel product. The organic anion is nearly planar, with deviations caused by steric crowding among the exocyclic cyano groups. The K⁺ cations lie within tricapped trigonal prisms that stack to form channels. The three‐dimensional structure is completed by the formation of hydrogen‐bonded chains by the anions.     

Reactions of Polyfluoroarenes with MenE‐MMe3 Reagents (MenE = Me2As,Me2P,Me2N,and MeS; M = Si,Sn): Synthesis of Polyfluoroaryl MenE Compounds

Trimethylsilyldimethylarsane Me₃SiAsMe₂ was used as a reagent for the substitution of fluorine in polyfluoroarenes C₆F₅X (X = F, H, Cl) and C₅NF₅ by the Me₂As group. The reactions occur between 50 — 180 °C, either in benzene or without solvent, to give as a rule 4‐X‐1‐(dimethylarsano)tetrafluorobenzenes XC₆F₄AsMe₂, ( 1—3 ) and 4‐dimethylarsano‐tetrafluoropyridine C₅NF₄AsMe₂ ( 4 ), respectively, in yields between 43 and 94 %. In the case of C₆F₆, also double substitution is observed affording 1, 4‐bis(dimethylarsano)tetrafluorobenzene 5 in addition to the monosubstituted derivative. The time and temperature dependencies of the reactions increase in the sequence: C₆F₆< C₆F₅H < C₆F₅Cl < C₅NF₅. The arsanes 1 and 4 were transformed to the potentially valuable bidentate ligands 1‐(dimethylarsano)‐4‐(dimethylphosphano)tetrafluorobenzene 6 and 4‐(dimethylarsano)‐2‐(dimethylphosphano)trifluoropyridine 8 by reaction with trimethylsilyl‐dimethylphosphane Me₃SiPMe₂. 6 reacts with oxygen to yield the corresponding phosphane oxide 7 . Trimethylsilyl‐dimethylamine Me₃SiNMe₂ also was successfully tested as a reagent for the dimethylamination of polyfluoroarenes C₆F₅X [X = F, H, Cl, CF₃, P(S)Me₂], 1‐P(S)Me₂‐4‐H‐C₆F₄ and 4‐X‐C₅NF₄ [X = F, PMe₂, P(S)Me₂]. Sulfuration of the new Me₂P derivatives 8 and 20 leads to the corresponding thiophosphanes 9 and 21 (Schemes 2 and 3). Furthermore, the recently reported very efficient one‐pot synthesis of Me₂P substituted polyfluoroarenes (e.g. XC₆F₄PMe₂ with X = F, Me₂PC₆F₄) was extended to the preparation of Me₂As and MeS derivatives of pentafluoropyridine using a mixture of Me₃SnH, As₂Me₄ (or S₂Me₂) and C₅NF₅ as precursors for the one‐pot reaction. The expected products 4‐(dimethylarsano)tetrafluoropyridine 4 and 4‐(methylthio)tetrafluoropyridine 22 , respectively, were obtained in 84 and 82 % isolated yields. The novel compounds were characterized by spectroscopic (NMR, MS) and analytical data. Compounds 5 , 7 , 9 and 21 could be isolated in form of single crystals and their structures have been studied by X‐ray diffraction.     

Double-Lattice Magnetoplasmonic Structures Based on BIG and Perforated Gold Films

Physics of the Solid State - A method of manufacturing double-lattice magnetoplasmonic crystals with the structure (Au/BIG)2, in which the plasmon gold lattices are displaced relative to each other...