Quantitative SIMS depth profiling of diffusion barrier gate-oxynitride structures in TFT-LCDs

Gate oxynitride structures of TFT-LCDs were investigated by SIMS, and successful solutions are demonstrated to overcome difficulties arising due to the charging effects of the multilayer systems, the matrix effect of the method, and the small pattern sizes of the samples. Because of the excellent reproducibility achieved by applying exponential relative sensitivity functions for quantitative analysis, minor differences in the barrier gate-oxynitride composition deposited on molybdenum capped aluminium-neodymium metallisation electrodes were determined between the centre and the edge of the TFT-LCD substrates. No differences were found for molybdenum-tungsten metallisations. Furthermore, at the edge of the glass substrates, aluminium, neodymium, and molybdenum SIMS depth profiles show an exponential trend. With TEM micrographs an inhomogeneous thickness of the molybdenum capping is revealed as the source of this effect, which influences the electrical behaviour of the device.The production process was improved after these results and the aging behaviour of TFT-LCDs was investigated in order to explain the change in control voltage occurring during the lifetime of the displays. SIMS and TEM show an enrichment of neodymium at the interface to the molybdenum layer, confirming good diffusion protection of the molybdenum barrier during accelerated aging. The reason for the shift of the control voltage was finally located by semi-quantitative depth profiling of the sodium diffusion originating from the glass substrate. Molybdenum-tungsten was a much better buffer for the highly-mobile charge carriers than aluminium-neodymium. Best results were achieved with PVD silicon oxynitride as diffusion barrier and gate insulator deposited on aluminium-neodymium metallisation layers.     

Lithiation of 2-chloro- and 2-methoxypyridine with lithium dialkylamides: initial ortho-direction or subsequent lithium ortho-stabilization?

The lithiation pathway of 2-chloro and 2-methoxypyridine with LDA and LTMP has been investigated using deuterated probes. The availability of both H-6 and H-3 protons on the pyridine nucleus was found to be critical to ensure complete C-3 lithiation. We thus concluded that the C-3 lithiation was not a straightforward process. A mechanism involving precomplexation of lithium dialkylamides near the H-6 proton and formation of a 3,6-dilithio pyridine intermediate is proposed.     

Metallation des halogenures d'aryle par le tributylstannyllithium dans le tetrahydrofuranne

The metallation of aryl halides with tributylstannyllithium in THF proceeds via at least three different mechanisms whose relative rates depend on the nature of the halogen, the substrate and the experimental conditions. In the case of aryl bromides, a halogenmetal exchange (major process) is competing with a radical mechanism. With aryl chlorides, an arynic process, a halogenmetal exchange and a radical mechanism are involved. Finally, with aryl fluorides, the arynic process is usual, but it may be strongly competed by a radical mechanism whenever suitable experimental conditions are arranged.     

Towards clustered carbonyl cations [M3(CO)14]2+ (M = Ru,Os): the need for innocent deelectronation

To access the hitherto almost unknown class of clustered transition metal carbonyl cations, the trimetal dodecacarbonyls M₃(CO)₁₂ (M = Ru, Os) were reacted with the oxidant Ag⁺[WCA]⁻, but yielded the silver complexes [Ag{M₃(CO)₁₂}₂]⁺[WCA]⁻ (WCA = [Al(OR^F)₄]⁻, [F{Al(OR^F)₃}₂]⁻; R^F = –OC(CF₃)₃). Addition of further diiodine I₂ to increase the redox potential led for M = Ru non-specifically to divalent mixed iodo-Ru^II-carbonyl cations. With [NO]⁺, even the N–O bond was cleaved and led to the butterfly carbonyl complex cation [Ru₄N(CO)₁₃]⁺ in low yield. Obviously, ionization of M₃(CO)₁₂ with retention of its pseudo-binary composition including only M and CO is difficult and the inorganic reagents did react non-innocently. Yet, the radical cation of the commercially available perhalogenated anthracene derivative 9,10-dichlorooctafluoroanthracene (anthracene^Hal) is a straightforward accessible innocent deelectronator with a half-wave potential E_1/2 of 1.42 V vs. Fc^0/+. It deelectronates M₃(CO)₁₂ under a CO atmosphere and leads to the structurally characterized cluster salts [M₃(CO)₁₄]²⁺([WCA]⁻)₂ including a linear M₃ chain. The structural characterization as well as vibrational and NMR spectroscopies indicate the presence of three electronically independent sets of carbonyl ligands, which almost mimic M(CO)₅, free CO and even [M(CO)₆]²⁺ in one and the same cation.

Trimeric M₃(CO)₁₂ (M = Ru, Os) reacts with typical inorganic oxidants to unwanted side products. Yet, the 9,10-dichlorooctafluoroanthracene radical cation deelectronates these under CO pressure to give the first homotrimetallic [M₃(CO)₁₄]²⁺ salts.     

Probing the substrate specificity of the catalytically self-sufficient cytochrome P450 RhF from a Rhodococcus sp

Analysis of the substrate specificity of the self-sufficient cytochrome P450 RhF revealed that the enzyme tends to catalyse the dealkylation of substituted alkyl-aryl ethers with shorter alkyl moieties more readily than equivalent compounds with longer alkyl groups.     

Direct structure determination using residual dipolar couplings: reaction-site conformation of methionine sulfoxide reductase in solution

Residual dipolar couplings (RDC) from partially aligned molecules provide long-range structural data and are thus particularly well adapted to rapid structure validation or protein fold recognition. Extensive measurements in two alignment media can also provide precise de novo structure from RDC alone. We have applied a novel combination of these approaches to the study of methionine sulfoxide reductase (MsrA) from Erwinia chrysanthemi, a 27 kDa enzyme essential for repairing oxidative stress damage. The tertiary fold was initially validated by comparing backbone RDC to expected values from the crystal structure of the homologous MsrA from Escherichia coli. Good agreement was found throughout the chain, verifying the overall topology of the molecule, with the exception of the catalytically important peptide P196-L202, where strong and systematic RDC violation was observed. No evidence for local differential mobility in this region was detected, implying that the structure of the strand differs in the two molecules. We have therefore applied the de novo approach meccano to determine the conformation of this peptide using only RDC. A single conformation is found that is in agreement with all measured data. The aligned peptide can be docked onto the expected covalence of the rest of the template molecule while respecting its strictly defined relative orientation. In contrast to the structure of MsrA from E. coli, the reactive side chain of Cys200 is oriented toward the interior of the molecule and therefore closer to the catalytic Cys53, obviating the need for previously proposed conformational reorganization prior to formation of this disulfide intermediate. This analysis requires only backbone assignment and uses unambiguously assigned and readily measurable structural data, thereby greatly economizing investigation time compared to established nuclear Overhauser effect- (nOe-) based structure calculation methods.     

Determination of 13C/12C-ratios of anthropogenic organic contaminants in river water samples by GC-irmMS

This study describes the application of a common analytical procedure adapted for compound-specific stable carbon isotope analyses of riverine contaminants. To evaluate the sensitivity of the analytical method and the precision of the isotopic data obtained, a set of numerous substances at different concentration levels were measured. For most of the anthropogenic contaminants investigated (including chlorinated aliphatics and aromatics, musk fragrances, phthalate-based plasticizers and tetrabutyl tin) acceptable carbon isotope analyses could be obtained down to amounts of approximately 5?ng absolutely applied to the gas chromatograph. These amounts correspond to concentrations in water samples at a natural abundance level of approximately 50–200?ng?L^?1 (low to medium contaminated river systems). However, it has to be considered that the precision and the sensitivity of the analytical method depend partially on the chemical properties of the substances measured. Five recovery experiments were conducted to assess changes in carbon isotope ratios during sample preparation and measurement. The compounds selected for these experiments are known riverine contaminants. Isotopic shifts or higher variations of the isotope ratios as a result of the analytical procedures applied were observed only for a couple of contaminants. Furthermore, compound-specific carbon isotope analyses were performed on eight water extracts of the Rhine river. By comparing the variation of the data of several individual compounds with the deviations obtained from the recovery experiments, it was possible to differentiate contaminants with unaffected isotope ratios and substances with significant alterations of the δ¹³C-values.