Efficient simultaneous reverse Monte Carlo modeling of pair-distribution functions and extended x-ray-absorption fine structure spectra of crystalline disordered materials

An efficient implementation of simultaneous reverse Monte Carlo (RMC) modeling of pair distribution function (PDF) and EXAFS spectra is reported. This implementation is an extension of the technique established by Krayzman et al. [J. Appl. Cryst. 42, 867 (2009)] in the sense that it enables simultaneous real-space fitting of x-ray PDF with accurate treatment of Q-dependence of the scattering cross-sections and EXAFS with multiple photoelectron scattering included. The extension also allows for atom swaps during EXAFS fits thereby enabling modeling the effects of chemical disorder, such as migrating atoms and vacancies. Significant acceleration of EXAFS computation is achieved via discretization of effective path lengths and subsequent reduction of operation counts. The validity and accuracy of the approach is illustrated on small atomic clusters and on 5500-9000 atom models of bcc-Fe and α-Fe(2)O(3). The accuracy gains of combined simultaneous EXAFS and PDF fits are pointed out against PDF-only and EXAFS-only RMC fits. Our modeling approach may be widely used in PDF and EXAFS based investigations of disordered materials.     

An unexpected formation of benzoyl benzoin from benzil during the attempted Knoevenagel type condensation with dimethylmalonate (or malononitrile)

An unexpected product, 2-oxo-1,2-diphenylethyl benzoate (benzoyl benzoin), was isolated during the attempted Knoevenagel reaction of benzil and dimethylmalonate (or malononitrile) in the presence of potassium carbonate. The product was confirmed by spectral analysis as well as by single crystal studies and a mechanism is proposed to explain its formation.     

Electrospun Nanofibrous Adsorption Membranes for Wastewater Treatment: Mechanical Strength Enhancement

Functional nanofibrous membranes fabricated by electrospinning technology have attracted much attention in the removal of heavy metal ions from contaminated wastewater. The high specific surface area, high porosity and ease of functionality create an enhanced throughput and high adsorption capacity of the nanofibrous membrane. However, the relatively poor mechanical properties of the membrane with a non-woven nanofibrous structure are one of the major concerns, which can limit the applications in wastewater treatment. Different strategies and methodologies were explored to address the problems and were reviewed in this work, highlighting the possibilities of overcoming the poor mechanical properties of the nanofibrous membrane and to ensure the recyclability and reusability of the membrane during the adsorption process.     

Structure and Reactivity of Al−O(H)−Al Moieties in Siloxide Frameworks: Solution and Gas‐Phase Model Studies

Even though aluminas and aluminosilicates have found widespread application, a consistent molecular understanding of their surface heterogeneity and the behavior of defects resulting from hydroxylation/dehydroxylation remains unclear. Here, we study the well‐defined molecular model compound, [Al₃(μ₂‐OH)₃(THF)₃(PhSi(OSiPh₂O)₃)₂], 1 , to gain insight into the acid–base reactivity of cyclic trinuclear Al₃(μ₂‐OH)₃ moieties at the atomic level. We find that, like zeolites, they are sufficiently acidic to catalyze the isomerization of olefins. DFT and gas phase vibrational spectroscopy on solvent‐free and deprotonated 1 show that the six‐membered ring structure of its Al₃(μ₂‐OH)₃ core is unstable with respect to deprotonation of one of its hydroxy groups and rearranges into two edge‐sharing four‐membered rings. This renders Al_IV?O(H)?Al_IV units strong acid sites, and all results together suggest that their acidity is similar to that of zeolitic Si_IV?O(H)?Al_IV groups.     

Line broadening studies in low energy plasma focus

Optical emission spectroscopic studies were carried out to characterise the plasma leading to the estimation of two plasma parameters, electron density and temperature. These experiments were conducted on a 2 kJ plasma device which is equipped with squirrel cage electrode configuration enclosed in a glass vacuum chamber filled with hydrogen at a pressure of 5 mbar. Spectral emissions obtained from each flash were photographed in the region of 4000–6000 Å using one metre Czerny-Turner spectrograph cum monochromator. Detailed examination of the observed features showed that theH _β andH _λ lines of hydrogen showed significant broadening of the order of 35 Å FWHM which is due to Stark effect expected in high density plasmas. Further several atomic lines of Cu and Zn from the electrode material (brass) showed broadening which was due to quadratic Stark effect. A comparative study of the broadening of lines obtained in DC arc, hollow cathode and plasma focus was made. Electron density from Stark broadened hydrogen lines and quadratic Stark Coefficient C₄ for the CuI and ZnI lines were evaluated. The excitation temperature was determined from the line intensity ratio method using CuI lines.     

Copper metallization for ULSL and beyond

The investigation of copper for use as an interconnection metal in the ultra large-scale integration (ULSI) era of silicon integrated circuits has accelerated in the past several years. The obvious advantages for using copper to replace currently used Al are related to its lower resistivity (1.7 μΩ-cm vs. 2.7 μω-cm for Al) and its higher electromigration resistance (several orders of magnitude higher compared with Al). The goal of this review is to examine the properties of copper and its applicability as the interconnection metal. A comparison of electromigration behavior of various possible interconnection metal in standard “bulk” state is made. This is followed by a review of the calculations made comparing (a) the RC (resistance × capacitance) time constants of various material systems and (b) the joule heating of the interconnection materials. A comparative study of various metal systems for the application as the interconnect metal is then made. These discussions will clearly establish the superiority of copper over other metals despite certain limitations of copper. We then review the properties, both physical and chemical, and materials science of copper. The concept of using alloys of copper with a minimal sacrifice on resistivity to gain reliability is also discussed. This is followed by the review of the deposition, pattern definition and etching. passivation, need of the diffusion barrier (DB) and adhesion promoter (AP), planarization and dual damascene process using chemical mechanical planarization, and reliability. This review shows that copper will satisfy the needs of the future integrated circuits and provide high performance and reliability as long as we provide an appropriate barrier to diffusion in the underlying devices and the dielectric.     

Factors which influence the formation of oxadiazoles from anthranilhydrazides and other benzoylhydrazines

The cyclization of o-aminobenzoylhydrazine ( 1a ) and its 5-methyl derivative 1b with four equivalents and with one equivalent of triethyl orthoacetate (TEOA) was studied. 3-Amino-2-methyl-4(3H)-quinazolinone ( 2a ), 3,4-dihydro-2-methyl-5H-1,3,4-benzotriazepin-5-one ( 3a ) and an imino ether derivative of 2a , N-[2-methyl-4-oxo-3(4H)quinazolinyl]ethanimidic acid ethyl ester ( 4a ) were obtained from the reaction of 1a with four equivalents of TEOA. These results were compared with those of Merour [1] who isolated 2a and 3a using the same conditions. When 1a was treated with one equivalent of TEOA, 2a, 3a , and a new product, 2-(5-methyl-1,3,4-oxadiazol-2-yl)benzenamine ( 5a ) were produced, and 4a was not. Similar results were obtained with the reactions of 1b with TEOA. Authentic samples of oxadiazoles 5a and b were prepared by alternate routes. Novel acid-catalyzed rearrangements of benzotriazepinones 3a and b , to mixtures of aminoquinazolinones 2a and b and oxadiazoles 5a and b , respectively, were found. The different relative amounts of aminoquinazolinones 2 and oxadiazoles 5 which were produced from these rearrangements allowed us to choose between two potential mechanisms for these interesting rearrangements. Treatment of 5-nitrobenzoylhydrazine ( 37 ) with four equivalents of TEOA gave three products which were characterized, but did not lead to benzotriazepinone formation.     

On biunitary permutation matrices and some subfactors of index 9

This paper is devoted to a study of the subfactors arising from vertex models constructed out of `biunitary' matrices which happen to be permutation matrices. After a discussion on the computation of the higher relative commutants of the associated subfactor (in the members of the tower of Jones' basic construction), we discuss the principal graphs of these subfactors for small sizes of the vertex model. Of the 18 possibly inequivalent such biunitary matrices when , we compute the principal graphs completely in 15 cases, all of which turn out to be finite. In the last section, we prove that two of the three remaining cases lead to subfactors of infinite depth and discuss their principal graphs.