Analytische Chemie
Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (83)
- Vortrag (57)
- Posterpräsentation (36)
- Beitrag zu einem Sammelband (7)
- Sonstiges (7)
- Forschungsbericht (7)
- Beitrag zu einem Tagungsband (4)
- Handbuch (4)
- Forschungsdatensatz (2)
- Corrigendum (1)
Schlagworte
- Nanoparticles (92)
- Electron microscopy (40)
- Nanomaterial (25)
- Particle size distribution (21)
- TiO2 (19)
- SEM (14)
- EPMA (13)
- SEM/EDX (13)
- Nanomaterial classification (12)
- Traceability (11)
Organisationseinheit der BAM
- 6 Materialchemie (137)
- 6.1 Oberflächen- und Dünnschichtanalyse (137)
- 1 Analytische Chemie; Referenzmaterialien (22)
- 6.7 Materialsynthese und Design (10)
- 1.2 Biophotonik (8)
- 1.8 Umweltanalytik (7)
- 1.9 Chemische und optische Sensorik (6)
- 6.3 Strukturanalytik (6)
- 5 Werkstofftechnik (5)
- 5.1 Mikrostruktur Design und Degradation (4)
Paper des Monats
- ja (4)
Eingeladener Vortrag
- nein (57)
In this contribution, two large-area EDS detectors were tested according to the procedure proposed recently by Procop et al. In a first step, the optimal working distance (WD) in the two different SEM chambers was determined by moving the sample stage in the Z direction and monitoring the count rates from a field of view of 25.6 μm. The WD at which the highest intensity was measured was selected as the optimal position. Next the Cu Kα peak was measured at different relative EDS positions while it was partially removed from the fully inserted position. The spectrum at each location was collected for 10 sec using the highest pulse rate and intermediate current (2.3 nA) to minimize pile up effects (13% dead time). The ‘inverse squared normalized intensities vs. relative EDS position’ used to extract the true detector – specimen distance shows a non-linear relationship even at the minimal relative positions, which indicates shadowing due to obstruction or use of an unsuitable and/or off-centered collimator. The normalized count rates measured as a function of the EDS distances, results in a too low GCE (too low true solid angles) for both tested detectors. The search for sources of losses of signal due to possible shadowing effects is in progress.
Evaluation of electron microscopy techniques for the purpose of classification of nanomaterials
(2016)
Electron microscopy techniques such as TEM, STEM, SEM or TSEM (transmission in SEM) are capable of assessing the size of individual nanoparticles accurately. Nevertheless, the challenging aspect is sample preparation from powder or liquid form on the substrate, so that a
homogeneous distribution of well-separated (deagglomerated) particles is attained. The systematic study in this work shows examples where the extraction of the critical, smallest particle dimension - as the decisive particle parameter for the classification as a NM - is possible by analysing the sample after ist simple, dry preparation. The consequences of additional typical issues like loss of information due to screening of smaller particles by larger ones or the (in)ability to access the constituent particles in aggregates are discussed.
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.
CCQM key comparison K-129 for the quantitative analysis of Cu(In,Ga)Se2 (CIGS) films has been performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The objective of this key comparison is to compare the equivalency of the National Metrology Institutes (NMIs) and Designated Institutes (DIs) for the measurement of mole fractions of Cu, In, Ga and Se in a thin CIGS film. The measurand of this key comparison is the average mole fractions of Cu, In, Ga and Se of a test CIGS alloy film in the unit of mole fraction (mol/mol). Mole fraction with the metrological unit of mol/mol can be practically converted to atomic fraction with the unit of at%.
In this key comparison, a CIGS film with certified mole fractions was supplied as a reference specimen to determine the relative sensitivity factors (RSFs) of Cu, In, Ga and Se. The mole fractions of the reference specimen were certified by isotope dilution - inductively coupled plasma/mass spectrometry (ID-ICP/MS) and are traceable to the SI. A total number counting (TNC) method was recommended as a method to determine the signal intensities of the constituent elements acquired in the depth profiles by Secondary Ion Mass Spectrometry (SIMS), X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). Seven NMIs and one DI participated in this key comparison. The mole fractions of the CIGS films were measured by depth profiling based-SIMS, AES and XPS. The mole fractions were also measured by non-destructive X-Ray Fluorescence (XRF) Analysis and Electron Probe Micro Analysis (EPMA) with Energy Dispersive X-ray Spectrometry (EDX).
In this key comparison, the average degrees of equivalence uncertainties for Cu, In, Ga and Se are 0.0093 mol/mol, 0.0123 mol/mol, 0.0047 mol/mol and 0.0228 mol/mol, respectively. These values are much smaller than that of Fe in a Fe-Ni alloy film in CCQM K-67 (0.0330 mol/mol). This means that the quantification of multi-element alloy films is possible by depth profiling analysis using the TNC method.
Scanning Electron Microscopy (SEM) represents the mostly widespread method available in analytical laboratories dedicated to the characterization of physical properties such as morphology of various solid materials from ‘micro-’ down to the nanometre scale. The use of secondary electrons excited by a sharply, nm-focussed primary electron beam enables at any modern SEM to image objects with high in-depth and lateral sensitivity, i.e. with high spatial resolution. Hence, e. g. nanoparticles (NPs) are able to be easily characterized with respect to their individual size and shape, but also to the morphology of their surface.
By preparing the nano-objects on thin membranes as electron transparent samples it is possible to perform electron microscopy in the transmission mode (TEM and TSEM). The corresponding transmission (i.e. mass-thickness) contrast reveals in-depth information, but is also well suited for dimensional measurements in the 2D projection image. Both the surface sensitive mode and the transmission one are meanwhile available at any modern SEM. If an X-ray spectrometer is attached to an electron microscope, it is possible to analyse the characteristic X-rays induced by electron bombardment. Most electron microscopes have attached an energy dispersive X-ray spectrometer (EDX) so that EDX elemental maps can be carried out. Recent technological developments of high throughput EDS detectors and their advantages regarding high-resolution X-ray analysis down to the nm range are reviewed.
High-resolution micrographs (SEM, TSEM, TEM) and corresponding X-ray elemental maps on various representative nanoparticles, but also layered samples prepared in cross-section, will be presented and discussed. The importance of selecting the best suited analysis conditions will be highlighted. Also other, often challenging, topics such as sample preparation and image data processing will be critically addressed by practical examples. Further analytical techniques able to be employed at an electron microscope, like cathodoluminescence (CL) or micro-X-ray fluorescence (µXRF) will be briefly surveyed.
Three types of hybrid modified magnetite (Fe₃O₄) nanoparticles, functionalized with either chitosan, chitosan/iron (II) oxalate or chitosan/iron (III) citrate, were synthesized by chemical precipitation method.
The obtained nanomaterials were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, scanning and Transmission electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometry. The prepared composites were further tested as magnetic catalysts for the removal of bisphenol A (BPA) in aqueous media. The kinetic Degradation experiments were performed at laboratory scale, while the best operational parameters for all three materials were established: 1.00 g L⁻¹ of catalyst, 10 mmol L⁻¹ H₂O₂, under simulated solar light irradiation.
After 15 min of UVA irradiation under the experimental conditions mentioned above, it was possible to decompose up to 99% of the micropollutant over all catalysts. Fe₃O₄/chitosan/iron oxalate catalyst showed the highest and fastest catalytic activity in BPA removal. Catalytic wet peroxide oxidation of non-biodegradable micropollutants on such iron-based hybrid nanoparticles can be a suitable pre-treatment method for wastewater decontamination, as an environment-friendly simplified Approach for water clean-up.
In this contribution, two large-area EDS detectors were tested according to the procedure proposed by Procop et al. (2015). In a first step, the optimal working distance (WD) in the two different SEM chambers was determined by moving the sample stage in the Z direction and monitoring the count rates at a magnification of 10,000 and a field of view of 25.6 µm. The WD at which the highest intensity was measured was selected as the optimal position, corresponding to the crossover between the EDS detector optical axis and electron beam optical axis. Next the Cu Kα peak was measured at different relative EDS positions while it was partially removed from the fully inserted position. The spectrum at each location was collected for 10 sec using the highest pulse rate and intermediate current to minimize pile up effects. The ‘inverse squared normalized intensities vs. relative EDS position’ used to extract the true detector – specimen distance shows a non-linear relationship even at the minimal relative positions, which indicates shadowing due to obstruction or use of an unsuitable and/or off-centered collimator. The normalized count rates measured as a function of the EDS distances, results in a too low GCE (too low true solid angles) for both tested detectors. The source of losses of signal was shadowing caused by collimators.
One of the crucial characteristics of functionalized thin films is their porosity (i.e., the ratio between the pore volume and the volume of the whole film). Due to the very low amount of material per coated area corresponding to thin films, it is a challenge for analytics to measure the film porosity. In this work, we present an Approach to determine the porosity of thin films by means of electron probe microanalysis (EPMA) either by wavelength-dispersive X-ray spectrometry (WDX) or by energy-dispersive X-ray spectrometry (EDX) with a scanning electron microscope (SEM). The procedure is based on the calculation of the film mass deposition from electron-excited X-ray spectra. The
mass deposition is converted into film density by division of measured film thickness.
Finally, the film porosity is calculated from the measured film density and the density of bulk, nonporous film material. The general applicability of the procedure to determine the
porosity is demonstrated on thin templated mesoporous TiO₂
films, dip-coated on silicon
wafer, with controlled porosity in the range of 15 to 50%. The high accuracy of the mass deposition as determined from X-ray spectra was validated with independent methods (ICP-OES and weighing). Furthermore, for the validation of the porosity results, ellipsometry, interference fringes method (IFM), and focused ion beam (FIB) cross sectioning were employed as independent techniques. Hence, the approach proposed
in the present study is proven to be suited as a new analytical tool for accurate and relatively fast determination of the porosity of thin films.
Ionic liquids (ILs) are proposed as simple and efficient test materials to evaluate the performance of energy dispersive X-ray spectrometers (EDS) in the low energy range below 1 keV. By only one measurement, C Kα, N Kα, O Kα, and F Kα X-ray lines can be excited. Additionally, the S Kα line at 2.3 keV and, particularly, the S L series at 149 eV complete the picture with X-ray lines offered by the selected ILs. The well-known (certifiable) elemental composition of the ILs selected in the present study can be used to check the accuracy of results produced with the available EDS quantification routines in the low energy range, simultaneously, for several low atomic number elements. A comparison with other reference materials in use for testing the performance of EDS in the low energy range is included.
Currently established and projected regulatory frameworks require the classification of materials (whether nano or non-nano) as specified by respective definitions, most of which are based on the size of the constituent particles. This brings up the question if currently available techniques for particle size determination are capable of reliably classifying materials that potentially fall under these definitions.
In this study, a wide variety of characterisation techniques, including counting, fractionating, and spectroscopic techniques, has been applied to the same set of materials under harmonised conditions.
The selected materials comprised well-defined Quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity. As a result, each technique could be evaluated with respect to the determination of the number-weighted median size. Recommendations on the most appropriate and efficient use of techniques for different types of material are given.
Analytical routines for a comprehensive in-depth morphological, structural, and chemical characterization of functionalized TiO2 films by using different state-of-the-art analytical techniques are presented and discussed with the main objective to identify potential reference TiO2 coating parameters able to be certified at a later stage. TiO2 films fabricated by two different synthetic procedures as representative for two main large-scale applications were selected: (i) pulsed d.c. magnetron sputtering for photocatalytic applications and (ii) screen printing from preformed anatase nanoparticles. The screen-printed films were further loaded with a sensitizing dye for application as a dye-sensitized solar cell. Film properties such as microstructure and crystallographic texture of pulsed d.c. magnetron sputtering synthesized films were systematically studied by means of scanning nanobeam electron diffraction in a transmission electron microscope and the surface and inner morphology by scanning electron microscopy. The dye distribution over the depth of screen-printed TiO2 layers was analyzed before and after dye-loading by means of energy dispersive X-ray spectroscopy at scanning electronmicroscope, Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry. The long-term goal of the present study is the improvement of quality of the TiO2 film parameters as measured by using different types of reference TiO2 coatings having specific parameters certified.
In this contribution the particle sizing techniques evaluated in NanoDefine are presented together with recommendations for their application/implementation on real-world materials. The experimental evaluation is discussed based on examples on NanoDefine materials. A systematic study on volume specific surface area as derived from BET measurements versus electron microscopy on powdered materials is also presented.
k-values (k-ratio, K-value) is defined as ratio of the X-ray photon intensity I measured for a particular characteristic peak from the unknown sample to the value measured for the same X-ray peak from a reference material of known composition under identical conditions of beam energy, spectrometer efficiency and electron dose.
Advances in scanning electron microscopy (SEM) enable the high-resolution imaging of single nanoparticles (NPs) with sizes well below 10 nm. The SEM analysis in transmission mode (T-SEM) of NPs on thin film supports has many benefits when compared to the analysis of NPs on bulk substrates. The enhanced material (mass – thickness) contrast of the T-SEM imaging mode is well suited for in-depth and, particularly valuable, to very accurate, traceable, lateral dimensional measurements of NPs. Compared to samples prepared on bulk substrates, T-SEM with energy dispersive X-ray spectroscopy (EDS) achieves a drastically improved spatial resolution of the emitted X-rays. The poor signal-to-noise ratio of the X-ray spectra emitted by a single nanoparticle (NP) can be improved by the use of high-sensitivity (high collection solid angle) silicon drift (SDD), energy-dispersive X-ray spectrometers (EDS). The EDS spectral imaging of a single NP with a spatial resolution below 10 nm has become possible. This is demonstrated by means of various examples of nanostructures. Advanced data processing of T-SEM/EDS results sets the stage for the automated classification of NPs by feature analysis. This method combines the detection of morphological structures of interest by image processing of T-SEM micrographs with the chemical classification by EDS.
A new method for sampling wear particles directly from the lubricant reservoir has been developed and applied successfully for analyzing wear particles by high-resolution scanning electron microscopy in transmission mode having coupled energy-dispersive X-ray spectroscopy. The lubricated tribological testing was carried out with fully formulated as well as with non-formulated synthetic base oil. It was possible to analyze individual particles with dimensions as small as about 5–30 nm which are likely the 'primary' wear particles. A majority of the particles, however, are agglomerated and, thus, lead to the formation of larger agglomerates of up to a few micrometers. Chemical analysis led to the conclusion that most of the observed particles generated in formulated oil, especially the larger ones, are composed of the additives of the lubricant oil. In non-formulated base oil, the primary particles are of similar dimensions but contain only iron, chromium and oxygen, but most likely stem from the mating materials. This finding points to the fact that the main wear mechanism under lubricated conditions with fully formulated oil is more like a continuous shearing process rather than a catastrophic failure with the generation of larger primary particles. When the oil is non-formulated, however, several wear mechanisms act simultaneously and the wear rate is increased significantly. Generated larger primary particles are milled down to the nanoscale. When the oil is fully formulated, wear mainly takes places at the additive layer or tribofilm; thus, the steel surface is protected.
The combination of complementary characterization techniques such as SEM (Scanning Electron Microscopy), T-SEM (Scanning Electron Microscopy in Transmission Mode), EDX (Energy Dispersive X-ray Spectroscopy) and SAM (Scanning Auger Microscopy) has been proven to be a powerful and relatively quick characterization strategy for comprehensive morphological and chemical characterization of individual silica and titania nanoparticles. The selected real life test materials, silica and titania, are listed in the OECD guidance manual as representative examples because they are often used as commercial nanomaterials. Imaging by high resolution SEM and in the transmission mode by T-SEM allows almost simultaneous surface and in-depth inspection of the same particle using the same instrument. EDX and SAM enable the chemical characterization of bulk and surface of individual nanoparticles. The core–shell properties of silica based materials are addressed as well. Titania nominally coated by silane purchased from an industrial source has been found to be inhomogeneous in terms of chemical composition.
The observation of morphological details down to the nanometer range of the outer surface of micro-, submicro- and nanoparticles in a high-resolution scanning electron microscope (SEM) was extended with in-depth observation by enabling the transmission mode in the SEM, i.e. TSEM. The micro- and nanocapsules characterized in this study were fabricated as depots for protective agents to be embedded in innovative self-healing coatings. By combining the two imaging modes (upper and in-depth observation) complementing each other a better characterisation by a more comprehensive interpretation of the 'consistency' of the challenging specimens, e.g. including details 'hidden' beyond the surface or the real specimen shape at all, has been attained. Furthermore, the preparation of the quasi electron transparent samples onto thin supporting foils enables also elemental imaging by energy dispersive X-ray spectroscopy (EDX) with high spatial resolution. Valuable information on the elemental distribution in individual micro-, submicro- and even nanocapsules completes the '3D' high resolution morphological characterization at the same multimodal SEM/TSEM/EDX system.