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Organisationseinheit der BAM
- 1 Analytische Chemie; Referenzmaterialien (2)
- 6 Materialchemie (2)
- 6.1 Oberflächen- und Dünnschichtanalyse (2)
- 9 Komponentensicherheit (2)
- 9.4 Integrität von Schweißverbindungen (2)
- 1.1 Anorganische Spurenanalytik (1)
- 1.8 Umweltanalytik (1)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (1)
- 7 Bauwerkssicherheit (1)
- 7.4 Baustofftechnologie (1)
This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries.
The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction. For two typical rapid thermal annealing steps at 750 °C (non-ohmic behaviour) and 850 °C (ohmic behaviour) the intermetallic phases at the metal-semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
A strongly fluorescent organic semiconducting polymer doped with a highly
temperature dependent fluorescent europium(III) complex is converted into a
nanosized material that is capable of optically sensing temperature (T) in the
range from 0 to 50 °C via two-photon excitation at 720 nm. The nanosensors
are prepared from a blue-fluorescent polyfluorene that acts as both a lightharvesting
antenna (to capture two-photon energy) and an energy donor in a
fluorescence resonance energy transfer (FRET) system. The photonic energy
absorbed by the polymer is transferred to the T-sensitive red-luminescent
europium complex contained in the nanoparticles. The close spatial proximity
of the donor and the acceptor warrants efficient FRET. A poly(ethylene glycol)-
co-poly(propylene oxide) block copolymer is also added to render the particles
biocompatible. It is shown that T can be calculated from a) the intensity of
the luminescence of the europium complex, b) the ratio of the intensities of
the red and blue luminescence, or c) the T-dependent luminescence lifetime
of the Eu(III) complex.
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction.
For two typical rapid thermal annealing steps at 750 ◦C (non-ohmic behaviour) and 850 ◦C (ohmic behaviour) the intermetallic phases at the metal–semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
Electron paramagnetic resonance (EPR) of Fe3+ ions in Al2O3 is studied in powder samples prepared by different routes and/or modified by thermal or mechanical treatments, with different doping levels and grain sizes. The measurements are performed in various frequency bands (S, X, K, Q and W) and with bimodal detection in X-band. Simulations of the spectra are achieved with a code designed for computing EPR powder spectra described by any spin Hamiltonian including second-, fourth-and sixth-order ZFS terms (S ? 7/2). The linewidths, intensities and lineshapes are accounted for. The lineshape is Gaussian at low Fe3+ concentration whereas it is Lorentzian for higher concentration. The linewidths are interpreted as the superimposition of three main contributions: intrinsic linewidth, dipolar broadening and broadening due to lattice imperfections. The latter is tentatively interpreted in terms of quadrupolar spin Hamiltonian parameter distributions treated using first-order perturbation theory. Whatever the sample, only the b22 spin Hamiltonian parameter is found to be distributed around a mean zero value which corresponds to rhombic distortions. Angle and bond length distributions are tentatively extracted from the b22 distributions which gives some insight into the local order around the spin probe in relation to the preparation and treatment of the samples.
Methods for the measurement of contact potential differences (CPDs) are discussed from a historical point of view. In addition, a simple experimental setup using common laboratory equipment is presented. Experimental results show, for instance, that the measured CPDs between platinum and nickel can be very close to those obtained using sophisticated equipment. Moreover, it is demonstrated that the implemented method, though very simple, is suitable for surface mapping.
The robust determination of the threshold against fatigue crack propagation DKth is of paramount importance in fracture mechanics based fatigue assessment procedures. The standards ASTM E647 and ISO 12108 introduce operational definitions of DKth based on the crack propagation rate da/dN and suggest linear fits of logarithmic DK– da/dN test data to calculate DKth. Since these fits typically suffer from a poor representation of the actual curvature of the crack propagation curve, a method for evaluating DKth using a nonlinear function is proposed. It is shown that the proposed method reduces the artificial conservativeness induced by the evaluation method as well as the susceptibility to scatter in test data and the influence of test data density.
he main objective of the nPSize project is to improve the measurement capabilities for nanoparticle size based on both measurement methods traceable to SI units and new reference materials. Two basic approaches have been used in order to develop measurement procedures resulting in traceable results of the nanoparticle size distribution: physical modelling for the methods used in the project (TSEM, SEM, AFM and SAXS) and machine learning.
Physical modelling: In this part, the physical models associated with different shape measurements for the techniques TSEM, SEM, AFM and SAXS have been collected and further developed with the aim to simulate the resulting signal as measured by the individual methods. Uncertainties and traceability associated with each model were investigated and evaluated. In the following, the progress on these physical models is reported for each individual method.
Machine Learning modelling: The aim of this part is to use machine learning to enable automatic measurement of nanoparticle shape from expert a-priori information only. No physical model will be used as a-priori information in this task.
The accuracy and traceability of the size results obtained by each technique will be analyzed and compared with the physical modelling. A machine learning database will then be used to create automatic detection algorithms.