Analytische Chemie
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Modern EBSD systems perform diffraction pattern “quality” (PQ) calculations, essentially measurements of the contrast of the brighter bands in the pattern above background, for every pattern analyzed. Since the calculations are independent of EBSD indexing, data are generated from all points on the analyzed sample surface, regardless of indexability or the state of the material beneath. EBSD maps generated from PQ data are like microstructurally sensitive SEM images, collected at EBSD speeds and grid resolutions, with contrast arising from phase density, crystal structure, crystallographic orientation, grain boundary location, near-surface plastic strain, coating density/thickness, and to some extent topography. Grain boundaries and other aspects of sample microstructure are readily revealed, so the PQ map is a very useful characterization tool in its own right, and serves as a reference for EBSD maps generated from indexing-derived data, such as orientation, grain boundary character, phase distribution and strain maps.
The authors have tested the prototype of an electrospray deposition system developed by the company RAMEM under its trademark IONER. To test the prototype and assess its performance, several materials have been sprayed onto TEM grids and the resulting particle distributions were compared to more traditional sample preparation strategies like the “drop on grid” method. Operation parameters such as the sample flow-rate, capillary – substrate distance, electric field strength and sampling period length have been optimized. It was found that the particles deposited by electrospray generally show a much more homogeneous spatial distribution on the substrate and a substantial increase of the number of single particles, which are much better suited to an automatic image evaluation procedure than the agglomerated particles observed otherwise. The applicability of the technique to a broad range of materials is demonstrated by various examples, but also the influence of the substrate, the choice of the particular TEM grid, on the obtained spatial particle distribution is assessed.
The potential of electrospray deposition, for the controlled preparation of particles for imaging in electron microscopes, is evaluated on various materials: from mono-modal suspensions of spherical particles to multimodal suspensions and to real-world industrial materials. It is shown that agglomeration is reduced substantially on the sample carrier, compared with conventional sample preparation techniques. For the first time, it is possible to assess the number concentration of a tri-modal polystyrene suspension by electron microscopy, due to the high Deposition efficiency of the electrospray. We discovered that some suspension stabilizing surfactants form artifact particles during electrospraying. These can be avoided by optimizing the sprayed suspension.
The potential of electrospray deposition, for the controlled preparation of particles for imaging in electron microscopes, is evaluated on various materials: from mono-modal suspensions of spherical particles to multimodal suspensions and to real-world industrial materials. It is shown that agglomeration is reduced substantially on the sample carrier, compared with conventional sample preparation techniques. For the first time, it is possible to assess the number concentration of a tri-modal polystyrene suspension by electron microscopy, due to the high deposition efficiency of the electrospray. We discovered that some suspension stabilizing surfactants form artifact particles during electrospraying. These can be avoided by optimizing the sprayed suspension.
The potential of electrospray deposition, for the controlled preparation of particles for imaging in electron microscopes, is evaluated on various materials: from mono-modal suspensions of spherical particles to multimodal suspensions and to real-world industrial materials. It is shown that agglomeration is reduced substantially on the sample carrier, compared with conventional sample preparation techniques. For the first time, it is possible to assess the number concentration of a tri-modal polystyrene suspension by electron microscopy, due to the high Deposition efficiency of the electrospray. We discovered that some suspension stabilizing surfactants form artifact particles during electrospraying. These can be avoided by optimizing the sprayed suspension.
The international ISO Standard 20579‐4, dealing with the history and preparation of nano‐objects for surface analysis, has been developed to help address some of the replication and reproducibility issues caused by the fundamental nature of nanoobjects.
Although all types of samples requiring surface analysis need thoughtful preparation, nano‐objects, for which many properties are controlled by their surfaces, present additional challenges in order to avoid variations and artefacts due to the handling and preparation of materials prior to analysis. This international standard is part of a series of standards related to preparation of samples for surface chemical analysis. Parts 1 and 2 of ISO Standard series 20579 address general issues that apply to many samples. Part 3, which is still in development, will focus on biomaterials. Part 4 specifically considers issues that arise due to the inherent nature of nano‐objects.
Because of sensitivity to their environment, the standard indicates the minimum Information that needs to be reported about the handling and preparation of nano‐objects prior to surface analysis. This information should become part of sample provenance information that helps assure the reliability and usefulness of data obtained from surface‐analysis in the context of the synthesis, processing, and analysis history of a batch of material. Application of this standard can help address reproducibility and traceability issues associated with synthesis, processing, and characterization of nano‐objects in research and commercial applications.
A variety of methods used to prepare nano-objects for surface analysis are described along with information about when they might be best applied. Intrinsic properties of NPs which complicate their characterization and need to be considered when planning for surface or other analyses of NPs are identified, including challenges associated with reproducible synthesis and functionalization of the particles as well as their dynamic nature. The relevant information about the sample preparation processes, along with analysis details and data that need to be added to the collection of material provenance information is identified. Examples of protocols that have been successfully used for preparation of nano-objects for surface analysis are included in an annex.
In this chapter sample preparation, image acquisition, and nanoparticle size and shape characterization methods using the scanning electron microscope (SEM) in reflective and transmitted working modes are described. These help in obtaining reliable, highly repeatable results. The best solutions vary case-by-case and depend on the raw (powdered or suspension) nanoparticle material, the required measurement uncertainty and on the performance of the SEM.
Characterization of nanomaterials by transmission electron microscopy - Measurement procedures
(2020)
In this chapter, approaches are proposed for the descriptive and quantitative characterization of nano-objects with nanometer resolution. Measurements are based on the analysis of the characteristics of 2D projections of individual particles visualized on transmission electron micrographs.
Incorporation of spectroscopic methods (EDS and EELS) for elemental analysis of nano-objects is recommended to identify subpopulations of nano-objects in mixtures based on their chemical composition. The focus lies on the determination of physicochemical properties which are essential in a legislatory and regulatory context to define the material as a nanomaterial (NM), and to assess its safety and toxicological potential, using widely accessible equipment.