Quantitative depth profiling in glow discharge spectroscopies – A new deconvolution technique to separate effects of an uneven erosion crater shape

An algorithm is presented as a concept for the quantification in direct current and radiofrequency glow discharge (GD) modes for GD optical emission spectroscopy. The algorithm is divided into excitation and sputtering part and thus it is possible to distinguish between the different excitation processes and to consider equivalent sputtering crater formations in both modes. Intensity-time profiles are affected corresponding to the method by several effects. One important effect is that sputtering occurs at a single time in different depths because of curved crater bottoms, this is usually called crater effect. The main purpose is to introduce an iterative deconvolution technique which for the quantification numerically takes into account the curved sputtering crater bottom. Input data for the deconvolution technique are the calibrated mass-time profile, the partial densities of the sample constituents and the measured final shape of the sputtering crater. Using a relatively simple model for ion sputtering the deconvolution technique improves iteratively the calculated layer structure by means of information on crater formation. The mathematical handling is illustrated for the quantification of a depth profile of a multilayer sample of ten 100 nm layers. The resulting concentration-depth profile reflects excellently the real elemental distribution of the multilayer system.     

Characterization of individual atmospheric particles by element mapping in electron probe microanalysis

In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Stereoselektive Synthesen von (Z)-(10-Methoxy-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-4-yliden)essigsäure

Stereoselective Syntheses of (Z)-(10-Methoxy-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-4-ylidene)acetic Acid Two stereoselective syntheses for the antiinflammatory compound 1 ((Z)-isomer) are described. In the first approach (Strategy A, Scheme 1) the stereoselective synthesis of 1 was realized via the bicyclic compound 11 under thermodynamic conditions, followed by a thiophene annelation with retention of the double-bond geometry (Schemes 2–4). Optimized conditions were necessary to avoid (E/Z)-isomerization during annelation. In the second approach (Strategy B, Scheme 1), diastereoisomer 17b was obtained selectively from a mixture of the diastereoisomers 17b and 18b by combining thermodynamic epimerization and solubility differences (Scheme 5). Diastereoisomer 17b was converted into the tricyclic compound 23 using a novel thiophene annelation method which we described recently (Scheme 6). In a final step, a stereospecific ‘syn’-elimination transformed the sulfoxide 24 into the target compound 1 (Scheme 7). To avoid (E/Z)-isomerization, it was necessary to trap the sulfenic acid liberated during the reaction. The key reactions of both approaches are highly stereoselective (> 97:3).     

Kinetic analysis of temperature-programmed surface reactions on porous catalysts

By means of model calculations it could be shown for an irreversible surface reaction of 1st order that the determination of the activation energy of the desorption of the reactant or, respectively, of the surface reaction is possible by application of the method of variation of the heating rate to the desorption curve of the reactant, according to circumstances whether the ratio of the activation energy of the surface reaction and of the desorption of the reactant is greater or smaller than one.The possibilities of the kinetic evaluation are applied to the isomerization of cyclopropane on a NaX-zeolite catalyst. The resulting heat of adsorption of cyclopropane and the activation energy of the reaction agree well with the values of literature obtained by isothermal measurements in a pulse reactor.

---

Zusammenfassung Mit Modellrechnungen für eine irreversible Oberflächenreaktion 1. Ordnung konnte gezeigt werden, daß durch Anwendung der Methode der Variation der Heizgeschwindigkeit auf die Desorptionskurve des Ausgangsstoffes die näherungsweise Bestimmung der Aktivierungsenergie der Desorption des Ausgangsstoffes bzw. der Oberflächenreaktion möglich ist, je nachdem ob das Verhältnis der Aktivierungsenergien für die Oberflächenreaktion und der Desorption des Ausgangsstoffes größer oder kleiner als eins ist.Die Möglichkeiten der kinetischen Auswertung werden auf die isomerisierung von Cyclopropan an einem NaX-Zeoliten angewendet. Die erhaltene Adsorptionswärme für Cyclopropan und die Aktivierungsenergie für die Reaktion stimmen gut mit Literatur-werten von isothermen Messungen im Impulsreaktor überein.

     

Photochemical structuring and fixing of structures in binary polymer brush layers via 2pi+2pi photodimerization

Binary polymer brushes grafted to Si wafers were prepared from hydrophilic and hydrophobic polymer components, which allow switching the surface properties (as revealed by contact angles) by exposure to varying solvents. The hydrophilic component was poly-2-vinylpyridine; the hydrophobic component was a copolymer of styrene and 2-(4-vinylphenyl)indene containing the photodimerizable phenylindene chromophore. The brushes were prepared via thermal and via photochemical grafting-to methods, which led to distinct layer thicknesses. Structural patterns differing in surface properties were produced and fixed via crosslinking the hydrophobic component by 2pi+2pi photodimerization of phenylindene moieties. The patterns were visually observable.     

Assembly and Dissociation of Α-Cyclodextrin [2]Pseudorotaxanes with α,ω-Bis(N-(N,N′-dimethylethylenediamine)alkane Threads

A series of novel bischelate bridging ligands, CH₃NH(CH₂)₂N(CH₃)(CH₂) _n N(CH₃)(CH₂)₂NHCH₃ (n = 9, 10, 11, and 12) were synthesized as hydrochloride salts and characterized by elemental analyses, electrospray mass spectrometry, and ¹H and ¹³C NMR spectroscopy. These ligands form [2]pseudorotaxanes with α-cyclodextrin (α-CD) and the stability constants have been determined from ¹H NMR titrations in D₂O. The kinetics and mechanism of the assembly and dissociation of a [2]pseudorotaxane in which α-CD has been threaded by the CH₃NH₂(CH₂)₂N(CH₃)(CH₂)₁₂N(CH₃)(CH₂)₂NH₂CH ₃ ²⁺ ligand were determined in aqueous solution using ¹H NMR spectroscopy. A weak inclusion of the dimethylethylenediamine end group precedes the passage of the α-CD onto the hydrophobic dodecamethylene chain.     

Der Einfluß von Verhakungen auf das Dehnungsverhalten von vernetzten Polymeren

Colloid and Polymer Science - 20 verschieden stark vernetzte Vulkanisate eines statistischen Butadien-Acrylnitril (18)-Kopolymeren wurden in mehreren Lösungsmitteln gequollen. Dann dehnten wir...     

How Chemistry and Physics Meet in the Solid State

To make sense of the marvelous electronic properties of the solid state, chemists must learn the language of solid-state physics, of band structures. An attempt is made here to demystify that language, drawing explicit parallels to well-known concepts in theoretical chemistry To the joint search of physicists and chemists for understanding of the bonding in extended systems, the chemist brings a great deal of intuition and some simple but powerful notions. Most important among these is the idea of a bond, and the use of frontier-orbital arguments. How to find localized bonds among all those maximally delocalized bands? Interpretative constructs, such as the density of states, the decomposition of these densities, and crystal orbital overlap populations, allow a recovery of bonds, a finding of the frontier orbitals that control structure and reactivity in extended systems as well as discrete molecules.