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Dislocations, as carriers of plastic deformation, affect important properties in technical materials, e. g., plasticity. The realistic description of plastic deformation caused by dislocations demands the representative measurement of their features, e.g., line direction, slip plane, Burgers vector and density. Bulk deformation of structural and functional alloys requires reliable data from large regions. The filiform nature of dislocations interacting with complex microstructures additionally demands observation and analysis techniques that allow resolving the details of their interactions in space. The use of electron tomography for this purpose is bound to difficult and time consuming experimental setups, which are not always applicable to any material. In this contribution a new tool is presented, which enables the three-dimensional reconstruction, visualization and quantification of dislocation densities and directions from manual tracing of scanning transmission electron microscopy (STEM) stereo-pairs. Examples are shown from samples of a creep-deformed monocrystalline Ni-base superalloy.
The surface chemistry / functionalization of nanomaterials and microparticles largely controls the stability of these materials as well as their solubility and subsequent biofunctionalization and their interactions with biological systems. Moreover, in the case of some nanomaterials like semiconductor quantum dots or lanthanide-based upconversion nanocrystals, the ligand shell strongly affects their optical properties, e.g., via passivation of surface states and traps that favor luminescence quenching or the protection of surface atoms from quenching water molecules. This renders analytical methods for the quantification of surface groups like functionalities very important. Targets of broad interest are here amino, carboxyl, alkine and maleimide groups used for common bioconjugation reactions and typical ligands like thiols and polyethylene glycol (PEG) molecules of varying length, used for the tuning of material hydrophilicity and biocompatibility, minimization of unspecific interactions, prevention of biofouling, and enhancement of blood circulation times as well as surface-bound biomolecules like streptavidin or other biomolecules relevant e.g., for diagnostic assays. Here, we focus on simple optical methods relying on standard laboratory instrumentation, validated by method comparison and/or mass balances and present examples for their use for the characterization of different types of nanomaterials and microparticles.
Luminescence-based detection methods, ranging from fluorescence spectroscopy for photophysical and mechanistic studies over sensing applications, chromatographic separation techniques and the microarray technology with fluorescence detection to fluorescence microscopy, flow cytometry, single molecule spectroscopy, and molecular imaging to integrating sphere spectroscopy, are among the most widely used methods in the life and material sciences. This is due to e.g., their unique sensitivity enabling the detection of single molecules, potential for multiplexing, ease of combination with spatial resolution, and suitability for remote sensing. Many of these advantages are closely linked to the choice of suitable molecular and nanoscale fluorescent reporters, typically required for signal generation. This includes organic dyes without and with sensor function, fluorophore-encoded polymeric and silica nanoparticles as well as nanocrystalline systems like semiconductor quantum dots and upconversion phosphors, emitting in the visible (vis), near-infrared (NIR), and IR (infrared). Current challenges present the environment sensitivity of most fluorophores, rendering fluorescence spectra, measured intensities/fluorescence quantum yields, and fluorescence decay kinetics matrix-dependent, and instrument-specific distortions of measured fluorescence signals that need to be considered for quantification and comparability of data, particularly fluorescence spectra.
Here, current applications of luminescence-based methods and different types of reporters will be presented. In this context, suitable spectroscopic tools for the characteri-zation of the optical properties of fluorescent reporters and fluorophore-encoded microparticles, analytical tools for the determination of the surface chemistry of different types of particles, and different multiplexing strategies will be discussed.
Direct current (DC) fast flow glow discharge mass spectrometry is an important and versatile tool for multielemental trace analysis of conductive solid materials down to the µg/kg level. Special benefits are minimum demands on sample preparation, avoiding losses and contamination, and only short analysis time.
For fast flow GD sources, the quantification strategy based on relative standard sensitivity factors (Standard RSFs) which are independent of matrix is not sufficiently satisfying regarding accuracy for each matrix and element [1]. Therefore matrix-matched calibration samples (MMCS) are required to achieve reliable quantification. In fact, the list of existing certified reference materials (CRM) appropri-ate for calibration in trace analysis is rather short.
Convenient synthesis of homogeneous MMCS, as e.g. easily obtained in liquid sampling spectrometry, can facilitate the application of fast flow GD-MS for quantification of impurities in a variety of matrices.
Pressing of metal powders for the preparation of MMCS for GD-MS was suggested earlier [2], the method was further modified by use of analyte solutions for doping of rather pure metal powders such as Cu and Zn [3], but has not yet been applied Ni matrix.
In the present work we describe the determination of matrix-dependent relative sensitivity factors (RSFs) for Mg, Al, Cr, Mn, Fe, Co, Cu, Zn, Ag, Cd, Tl, Pb and Bi in pure Ni by using the liquid doping approach for the preparation of synthetic pressed Ni-powder samples. A four point-calibration was used applying the fast flow glow discharge mass spectrometer, Element GD (Thermo Fisher). The determined RSF were verified against suitable CRM and compared with the standard RSF given by the supplier of the instrument.
The obtained results demonstrate a satisfying Agreement with the certified values of the CRM and a significant improvement for the quantification of most of the determined elements in comparison with standard RSF.