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The development of two metallizations based on the solid-phase regrowth principle is presented, namely Pd/Sb(Zn) and Pd/Ge(Zn) on moderately doped In0.53Ga0.47As (p=4×1018 cm-3). Contact resistivities of 23×10-7 and 67×10-7 ?cm2, respectively, have been achieved, where both systems exhibit an effective contact reaction depth of zero and a Zn diffusion depth below 50 nm. Exhibiting resistivities equivalent to the lowest values of Au-based systems in this doping range, especially Pd/Sb(Zn) contacts are superior to them concerning metallurgical stability and contact penetration. Both metallizations have been successfully applied for contacting the base layer of InP/In0.53Ga0.47As heterojunction bipolar transistors.
One wavelength fits all
(2011)
Structuring of Thin-film Solar Cells with a Single Laser Wavelength Structuring of a PV module into a number of cells is necessary to lower the current and to increase the voltage, and is typically accomplished with nanosecond laser pulses of different wavelengths. Duetothe many available laser sources, complex and expensive scribing Setups are necessary. To overcome this a concept for laser structuring of thin-film PV modules using a single wavelength allows prediction ofthe ablation behaviourfor a given laser pulse energy.
Copolyesters with an alternating sequence of terephthalic acid and aliphatic dicarboxylic acids were prepared with three different methods. First, dicarboxylic acid dichlorides were reacted with bis(2-hydroxyethyl)terephthalate (BHET) in refluxing 1,2-dichlorobenzene. Second, the same monomers were polycondensed at 0-20 °C in the presence of pyridine. Third, dicarboxylic acid dichlorides and silylated BHET were polycondensed in bulk. Only this third method gave satisfactory molecular weights. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that the copolyesters prepared by the pyridine and silyl methods might have contained considerable fractions of cyclic oligoesters and polyesters despite the absence of transesterification and backbiting processes. The alternating sequences and thermal properties were characterized with 1H NMR spectroscopy and differential scanning calorimetry measurements, respectively. In agreement with the alternating sequence, all copolyesters proved to be crystalline, but the crystallization was extremely slow [slower than that of poly(ethylene terephthalate)]. A second series of alternating copolyesters was prepared by the polycondensation of silylated bis(4-hydroxybut- yl)terephthalate with various aliphatic dicarboxylic acid dichlorides. The resulting copolyesters showed significantly higher rates of crystallization, and the melting temperatures were higher than those of the BHET-based copolyesters. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3371-3382, 2001
A magnetically stabilized DC arc device, designed for operation with OES spectrometers was used to determine the elements Ag, Al, B, Ba, Be, Ca, Co, Cr, Cu, Fe, Ga, In, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Si, Sn, Sr, Ti, V, Zr at trace levels of some μg kg−1 up to some 10 mg kg−1 in graphite powders. The coil for the generation of the homogeneous magnetic field was placed outside the closed arc chamber. The time programs of variable current strengths of the magnetic coil (up to 6 A) and of the arc (up to 17 A) which was burning in air were computer controlled. Halogenating gases (mainly CCl2F2, alternatively SF6 and NF3) were used as chemical modifiers to allow an effective release of the carbide forming trace elements. The mass flow controlled modifier gas was led through a special carrier electrode near the arc plasma. The emission radiation was guided by an optical fiber alternatively into two different ICP spectrometers in which the ICP torches were removed. The synergistic interaction of the magnetic field with the halogenating modifier gases resulted in a significant improvement in the analytical performance of the optimized analytical method. All our results for 22 trace elements were in good agreement with the means of an inter-laboratory comparison by BAM for certification of a pure graphite powder material; this holds also for our results for two other graphite materials. The optimized method showed an analytical performance suitable for comprehensive trace analysis of pure graphite. The instrumentation could be integrated into modern DC arc emission spectrometers to improve their analytical capabilities substantially.
In this article, we present two Coptic papyri, P 11934 and P 11935 from the Berlin collection excavated in Ashmunein (ancient Hermopolis) by Otto Rubensohn in 1906. We employ a multi-disciplinary approach that takes into account both their materiality – writing support as well as ink – and their content, as has become ‘best practice’. 1 Material aspects of written documents have traditionally been the purview of papyrologists. Recently developed methods of scientific analysis generate sets of archaeometric data with the potential to improve understanding of the materiality of ancient document production, as well as to yield new evidence for genuine papyrological research questions. To achieve this, a large corpus of comparative data needs to be built. Our contribution offers a first step in this direction. We aim at presenting the papyri, which were selected because of the ink corrosion during conservation work at the Berlin collection, in a format that is exhaustive both for material and textual aspects. The inks from both papyri were analysed using a combination of techniques, contributing to our better understanding of the development of ink technology in Late Antiquity.
In many bacteria, the biofilm-promoting second messenger c-di-GMP is produced and degraded by multiple diguanylate cyclases (DGC) and phosphodiesterases (PDE), respectively. High target specificity of some of these enzymes has led to theoretical concepts of "local" c-di-GMP signaling. In Escherichia coli K-12, which has 12 DGCs and 13 PDEs, a single DGC, DgcC, is specifically required for the biosynthesis of the biofilm exopolysaccharide pEtN-cellulose without affecting the cellular c-di-GMP pool, but the mechanistic basis of this target specificity has remained obscure. DGC activity of membrane-associated DgcC, which is demonstrated in vitro in nanodiscs, is shown to be necessary and sufficient to specifically activate cellulose biosynthesis in vivo. DgcC and a particular PDE, PdeK (encoded right next to the cellulose operon), directly interact with cellulose synthase subunit BcsB and with each other, thus establishing physical proximity between cellulose synthase and a local source and sink of c-di-GMP. This arrangement provides a localized, yet open source of c-di-GMP right next to cellulose synthase subunit BcsA, which needs allosteric activation by c-di-GMP. Through mathematical modeling and simulation, we demonstrate that BcsA binding from the low cytosolic c-di-GMP pool in E. coli is negligible, whereas a single c-di-GMP molecule that is produced and released in direct proximity to cellulose synthase increases the probability of c-di-GMP binding to BcsA several hundred-fold. This local c-di-GMP signaling could provide a blueprint for target-specific second messenger signaling also in other bacteria where multiple second messenger producing and degrading enzymes exist.
Bacterial biofilms pose serious problems in medical and industrial settings. One of the major societal challenges lies in the increasing resistance of bacteria against biocides used in antimicrobial treatments, e.g., via overabundant use in medicine, industry, and agriculture or cleaning and disinfection in private households. Hence, new efficient bacteria-repellent strategies avoiding the use of biocides are strongly desired. One promising route to achieve bacteria-repellent surfaces lies in the contactless and aseptic large-area laser-processing of technical surfaces. Tailored surface textures, enabled by different laser-processing strategies that result in topographic scales ranging from nanometers to micrometers may provide a solution to this challenge. This article presents a current state-of-the-art review of laser-surface subtractive texturing approaches for controlling the biofilm formation for different bacterial strains and in different environments. Based on specific properties of bacteria and laser-processed surfaces, the challenges of anti-microbial surface designs are discussed, and future directions will be outlined.
Millions of measurements are performed each year by liquid based analytical atomic spectrometry to support healthcare, diagnostic tests, environmental monitoring, material assay, product development and safety. Despite the effort to develop absolute methods, most methods still depend on calibration solutions, which are gravimetric mixtures of high purity solvents and high purity (source material) metals or compounds. As in the real world ideal purity does not exist, the impurity of the solvent and the purity of the source material needs to be known. The impurity of a solvent with respect to one analyte can be measured rather easily and with low limits of determination. In contrast the measurement of the purity of the source material, i.e., the mass fraction of the main constituent in a high purity metal, is more difficult to determine. It becomes even more difficult when the source material is not a pure metal but a compound since problems regarding stoichiometry arise additionally. Although the major producers of calibration solutions make a special effort to determine the purity of the source material, the actual purity statement is often incomplete or not demonstrated. The main reason for this situation is the complexity and high effort necessary to fully characterize such a material. This problem holds to a very wide extent also for the primary standards for element determination at the National Metrology Institutes and Designated Institutes (NMIs and DIs). It is the task of the NMIs and DIs to realise and disseminate primary standards for providing traceability to the International System of Units (SI). The primary elemental standards at the NMIs should provide the link to secondary standards produced by commercial producers and other independently prepared standards for element determination. Without such primary standards, elemental calibration solutions may vary and, depending on the uncertainty required, comparability of measurement in time and space results cannot be achieved.
It has been successfully demonstrated that ceramic materials can be joined in the green
state without a second phase by using low pressure injection molded parts. The investigation of the
joining interface revealed that a high quality interface can be achieved by carefully adjusting the
different manufacturing steps. The use of monomodal particle size distribution in the used powder
CT3000SG is inferior to a broader particle size distribution obtained by replacing 33% of the finer
alumina powder by coarser CT1200SG. In this way the dewaxing process is significantly improved
when the wall thickness of the part exceeds 3 mm. The investigation of the mechanical properties of
the joined and sintered parts revealed, that the bending strength of the joined specimens achieved
about 80 % of the unjoined, monolithic specimens.
High- and medium-entropy alloys (HEAs) are a quite new class of materials. They have a high potential for applications from low to high temperatures due to the excellent combination of their structural properties.
Concerning their application as components; processing properties, such as machinability, have hardly been investigated so far. Hence, machinability analyses with a focus on the influence of the milling process and its basic parameters (cutting speed, feed per cutting edge) on the resulting surface integrity of specimens from an equiatomic high- (CoCrFeMnNi) and a medium- (CoCrNi) entropy alloy have been carried out. A highly innovative milling process with ultrasonic assistance (USAM) was compared to conventional milling processes.
Recent studies have shown that USAM has a high potential to significantly reduce the mechanical load on the tool and workpiece surface during milling. In this study, the basic machining and ultrasonic parameters were systematically varied. After machining, the surface integrity of the alloys was analyzed in terms of topography, defects, subsurface damage, and residual stresses. It was observed that USAM reduces the cutting forces and increases the surface integrity in terms of lower tensile residual stresses and defect density near the surfaces for the CoCrFeMnNi alloy. It was shown that the cutting forces and the metallurgical influence in the sub surface region are reduced by increasing the cutting speed and reducing the feed rate per cutting edge. With the CoCrNi alloy, the tool revealed severe wear. As a result, for this alloy no influence of the parameters on the machinability could be determined.