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Paper des Monats
- ja (94)
Cross-sectional transmission electron microscopy, in combination with energy dispersive X-ray spectroscopy and focused beam microdiffraction, was applied to study the solid-state reactions taking place during contact formation of the system Ge(115 nm)/Pd(50 nm)In0.53Ga0.47As. In order to get information about the sequence of the different processes, rapid thermal, annealing experiments in the range 225400 °C were performed. The following features were observed: at 225 °C Pd reacted with the substrate forming the quaternary phase PdxIn0.53Ga0.47As (x 4), and with the Ge-layer forming mainly PdGe and Pd2Ge. Between PdxIn0.53Ga0.47As and In0.53Ga0.47As, a 5 nm thick amorphous Pd-In-Ga-As layer remained, indicating that the first reaction step was solid-state amorphization. After annealing at 350 °C, PdxIn0.53Ga0.47As disappeared and regrowth of In0.53Ga0.47As occured. Finally, at 400 °C, residual Ge from the amorphous top layer diffused to the interface and grew epitaxially on the regrown In0.53Ga0.47As, thus separating the IIIV compound semiconductor from the Pd-Ge reaction products. The interface remained flat, while only about 10 nm of the active In0.53Ga0.47As layer had been modified during the annealing processes.
X‑ray emission during the ablative processing of biological materials by ultrashort laser pulses
(2023)
The ablative laser processing with ultrashort pulsed laser beams may cause secondary emission of hazardous X-rays. While the effect has recently been proven to be considered in working safety regulations when processing technical materials, such as metals, the X-ray emission rates during the ablative processing of biological tissue materials are widely unexplored yet.
Therefore, biological materials like water, isotonic saline solution, pig eyes, and human teeth were ablated with ultrashort laser pulses of 1030 nm wavelength, 600 fs pulse duration and 5 kHz pulse repetition rate, aiming to mimic typical surgery situations. Simultaneously, in-situ X-ray dose rate measurements were performed at a short distance from the plasma to display potential X-ray emission. For all four studied biological materials, our measurements prove the secondary emission of laser-induced X-rays.
Powder x-ray diffraction (XRD) defined -Al2O3 has been investigated by x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES). The Au 4f7/2 orbital is used for static charge referencing. This feature originates from well-defined and chemically inert 20 nm highly dispersed gold particles deposited on the sample surface. The particles, with a narrow particle size distribution, were obtained from a highly purified colloidal solution (sodium concentration below 1 mg/l). This procedure allows a determination of gold-referenced XPS and XAES data sets. ©2001 American Vacuum Society.
Yb,Nd,Er-doped upconversion nanoparticles (UCNPs) have attracted considerable interest as luminescent reporters for bioimaging, sensing, energy conversion/shaping, and anticounterfeiting due to their capability to convert multiple near-infrared (NIR) photons into shorter wavelength ultraviolet, visible or NIR luminescence by successive absorption of two or more NIR photons. This enables optical measurements in complex media with very little background and high penetration depths for bioimaging. The use of Nd3+ as substitute for the commonly employed sensitizer Yb3+ or in combination with Yb3+ shifts the excitation wavelength from about 980 nm, where the absorption of water can weaken upconversion luminescence, to about 800 nm, and laser-induced local overheating effects in cells, tissue, and live animal studies can be minimized. To systematically investigate the potential of Nd3+ doping, we assessed the performance of a set of similarly sized Yb3+,Nd3+,Er3+-doped core- and core–shell UCNPs of different particle architecture in water at broadly varied excitation power densities (P) with steady state and time-resolved fluorometry for excitation at 980 nm and 808 nm. As a measure for UCNPs performance, the P-dependent upconversion quantum yield (Φ) and its saturation behavior were used as well as particle brightness (B). Based upon spectroscopic measurements at both excitation wavelengths in water and in a lipid phantom and B-based calculations of signal size at different penetration depths, conditions under which excitation at 808 nm is advantageous are derived and parameters for the further optimization of triple-doped UCNPs are given.
High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid
NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%‒98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%‒40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ~9% and ~25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ~9% (20% Yb3+) to ~7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ~7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.
Young's modulus and Poisson's ratio changes due to machining in porous microcracked cordierite
(2016)
Microstructural changes in porous cordierite caused by machining were characterized using microtensile testing, X-ray computed tomography, and scanning electron microscopy. Young's moduli and Poisson's ratios were determined on similar to 215- to 380-mu m-thick machined samples by combining digital image correlation and microtensile loading. The results provide evidence for an increase in microcrack density and decrease of Young's modulus due to machining of the thin samples extracted from diesel particulate filter honeycombs. This result is in contrast to the known effect of machining on the strength distribution of bulk, monolithic ceramics.
Zeolite synthesis was studied using two silica rich filtration residues (FR 1 and FR 2) as Si-source
and sodium aluminate in a direct synthesis at 60°C at strong alkaline conditions (8 M - 16 M NaOH).
In addition to these one-pot syntheses, a two-step process was investigated. Here, an alkaline digestion
of FR at 60°C was followed by gel precipitation with sodium aluminate and gel crystallization
under usual conditions of 80°C - 90°C. The results show that the substitution of chemical
reagent sodium silicate by a waste material like FR as Si-source is possible but requires fine tuning
of the reaction conditions as zeolite crystallization is a process under kinetic control. The
solubility behaviour and impurities of the inserted filtration residues strongly influenced the
course of reaction. Thus zeolites like hydrosodalite or intermediate zeolite between cancrinite
and sodalite, or zeolite NaA or Z-21 in cocrystallization with hydrosodalite could be observed in
the one pot syntheses already in a short time interval between 1 - 4 h depending on the alkalinity.
The two step process yield to zeolites NaA and NaX in very good quality. The reaction process of FR
in both reaction methods was characterized by chemical analyses, X-ray powder diffraction,
Fourier transform infrared spectroscopy as well as scanning electron microscopy. Surface area
and water content of selected products were further characterized by the BET-method and by
thermogravimetry. Summing up the results, we can show that zeolite formation from filtration residues
is possible by several reaction procedures as model cases for a re-use of industrial waste
materials. Beside the importance for environmental protection, the reactions are of interest for
zeolite chemistry as the re-use of FR is possible under economically conditions of low energy consumption
at 60°C and short reaction periods.
An approach to achieve 'zero leakage' is discussed with respect to experience in Germany, where strict regulations for landfill lining and capping Systems have been developed and issued because of large environmental Problems related to landfills that accumulated in the 1970s and 1980s. Using a thick, high-quality high-density Polyethylene (HDPE) geomembrane (GM) that is installed free of residual waves and wrinkles in intimate contact with a compacted clay liner or geosynthetic clay liner of very low permeability, by a qualified, experienced, well-equipped and properly third-party-controlled installer, and which is protected by heavy protection layers designed with respect to the long-term performance of the GM may result in a liner or capping system of practically no leakage. This is demonstrated by analysing results of measurements obtained from permanently installed leak-detection Systems in combination with HDPE GMs. The survey was based on 32 German landfills with 1.276.500 m² of installed GMs.
Zero wear (Null Verschleiß)
(2013)
The purpose of this paper is to underline the future need for OEMs to receive lowSAP, polymer- and metal-free engine oils with high-viscosity indices and to illuminate for other OEMs the technical feasibility for application of alternative engine oils based on esters or blends of hydrocarbons with esters or polyglycols.
Design/methodology/approach The strategic goal depends technically on the use of intrinsic properties of alternative base fluids, thus substituing some additives, like anti-wear, extreme pressure and viscosity index improvers. The prone wear resistance of novel triboactive/-reactive materials enables higher portions of mixed/boundary lubrication generated by oils with a lower viscosity.
Findings Overall, the different bionotox and low-ash prototype engine oils with reduced additive contents displayed isoperformance regarding the tribological behaviour against cast iron and triboreactive materials. APS-Tin-2Cr2O2n-1 displayed an overall wear resistance comparable with grey cast iron with high-carbon content and liner wear reduction of one order of magnitude when mated with Mo-based rings. Both tests confirmed the potential for substituing molybdenum-based rings by APS-Tin-2Cr2O2n-1. The most significant reduction in system wear down to zero wear was demonstrated by mating the APS-Tin-2Cr2O2n-1 coated piston rings with smooth machined HVOF-(Ti,Mo)(C,N) liner coatings.
Research limitations/implications As lubricants are today not part of the core business of automotive OEMs, the next steps have to be proposed by the petrochemical suppliers. It is recalled here that some OEMs in their history developed and produced lubricants.
Practical implications The customer will appreciate any increase in longevity resulting in reduced maintenance. The OEM now owns, under increased solicitations, now a future-oriented tool box in order to respond to environmental and CAFÉ demands with reasonable cost management.
Originality/value This OEM report displays the complete methodology in order to adopt alternative engine oils in existing engine architectures.