Analytische Chemie
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The mechanism of action of zirconium permanent modifiers on graphite surfaces was investigated in order to understand its influence on the analytical signal in atomic and molecular absorption spectrometry (AAS/MAS). For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEMEDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. We propose here a mechanism, where ZrO2 acts as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface. No evidence of the formation of zirconium carbide was found. Consequently, as the CaF formation is catalysed by a heterogeneous catalyst, surface modifications with ZrO2 nanoparticles and ZrO xerogels were investigated in order to increase the surface area. Their influence was evaluated in the molecule formation of CaF, CaCl, CaBr, and CaI. Graphite furnace modification with zirconium oxide nanoparticles proves to be the best choice for fluorine analysis with a signal enhancement of more than eleven times with respect a non-coated graphite furnace. However, the influence of zirconium modifications in the analytical signals of Cl, and I is lower than the F signals or even negative in case of the Br. Understanding zirconium modifiers as heterogeneous catalysts offers a new perspective to AAS and MAS, and reveals the potential of surface analytical methods for development of improved permanent modifiers and graphite furnace coatings.
Morphology and structure of TixOy nanoparticles generated by femtosecond laser ablation in water
(2018)
In this work femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated byXRD(two instruments operated in different geometries) and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.
A femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD(two instruments operated in different geometries) and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.
Copper alloys have found widespread application in various fields. The elemental composition determines the properties of the alloys and consequently their application. Therefore, knowing the composition of a copper alloy is very important.
Metrological institutes like the BAM (German Federal Institute for Materials Research and Testing) offer reference materials that can be used to prove the accuracy of the applied analysis method.
The aim of this application note is to demonstrate how Micro-X-ray fluorescence spectroscopy (Micro-XRF) expediently supplements the analysis of copper alloys by
using Bruker’s micro-focus X-ray source XTrace attached to a scanning electron microscope (SEM) and operating with an energy dispersive spectrometer.
Controlled deposition of nanoparticles by electrospray for improved analysis by imaging techniques
(2018)
Of many experimental techniques for measuring particle sizes and size distributions, electron microscopy (EM) is still considered as the gold standard, especially in the nano range (1–100 nm).
Furthermore, high-resolution X-ray spectroscopy (EDX) in conjunction with EM can be applied to individual NPs. Preparation of an EM sample for generic particulate materials is a difficult task. Usually the particles in a suspension are deposited on a support. However, this procedure includes the drying of larger solvent amounts on the substrate itself, and this can affect the spatial distribution of the deposited particles. One possibility to overcome this is the use of an electrospray system, where the suspension of particles is sprayed onto the substrate in charged droplets that are so small that they either dry off on the substrate immediately without affecting the position of particles, or even already during their flight time to the substrate. Additionally, the charging of particles minimizes agglomeration and aggregation, maximizing the collection of the EM grids. The prototype of an electrospray deposition system from RAMEM under its trademark IONER (www.ioner.eu) was tested. Electrospray is theoretically described since a long time, but no dedicated commercial instruments are available for the preparation of TEM grids yet, apart from electrostatic deposition of aerosols.2 Several materials have been sprayed onto TEM grids and the resulting particle distributions were evaluated. 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 (suited to automatic analysis).
The EC Recommendation on the definition of nanomaterial1, based solely on size of the constituent particles, foresees development of harmonised measurement methods ensuring ‘consistent results across materials and over time’. The EU/FP7 large research project NanoDefine (http://www.nanodefine.eu) has been exclusively dedicated to support the implementation of this EC Recommendation for the European Union’s legislation. For the first time, measurement techniques able to determine the size of nanoparticles have been evaluated systematically on a well-defined set of quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity. Particularly based on the analytical performance of the measurement techniques as tested on the challenging real-world particulate materials, it was possible to formulate recommendations for use of a new tiered approach consisting of screening and confirmatory techniques. Thus, a consistent framework of guidance for nanomaterial identification according to the EC Definition has been issued in form of the NanoDefiner e-tool (https://labs.inf.fh-dortmund.de/NanoDefiner), with a transparent decision flow scheme and an extensive user manual. Selected examples of analysis and classification as nano-/non-nanomaterials will be given, highlighting the limits of applicability of the available measurement techniques in dependence on sample properties. On some recent relevant developments in sample preparation – as a crucial part for an accurate analysis - will be also reported.
Controlled electrospray deposition of nanoparticles for improved analysis by electron microscopy
(2018)
Of many experimental techniques for measuring particle sizes and size distributions, electron microscopy (EM) is considered as the gold standard, especially in the nano range (1–100 nm). Furthermore, high-resolution X-ray spectroscopy (EDX) in conjunction with EM can be applied to individual NPs. Preparation of an EM sample for generic particulate materials is a difficult task. Usually, the particles in a suspension are deposited on a support. However, this procedure includes the drying of larger solvent amounts on the substrate itself, and this can affect the spatial distribution of the deposited particles. One possibility to overcome this is the use of an electrospray system, where the suspension of particles is sprayed onto the substrate in charged droplets that are so small that they either dry off on the substrate immediately without affecting the position of particles, or even already during their flight time to the substrate. Additionally, the charging of particles minimizes agglomeration and aggregation, maximizing the collection of the EM grids. The prototype of an electrospray deposition system from RAMEM under its trademark IONER (www.ioner.eu) was tested.
Electrospray is theoretically described since a long time, but no dedicated commercial instruments are available for the preparation of TEM grids yet, apart from electrostatic deposition of aerosols. Several materials have been sprayed onto TEM grids and the resulting particle distributions were evaluated. 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 (suited to automatic analysis).
The project has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No 604347.
Coming as response to the needs expressed by The European Commission mandating CEN, CENELEC and ETSI to develop European standards for methods that can characterize reliably manufactured nanomaterials, a new European metrology research project ‘nPSize - Improved traceability chain of nanoparticle size measurements’ has received funding for the next three years. The project will develop methods, reference materials and modelling to improve the traceability chain, comparability and compatibility for nanoparticle size measurements to support standardization.
nPSize has selected only those nanoparticle sizing techniques which are able to provide traceable results: electron microscopy (SEM, TSEM and TEM), AFM and SAXS. Metrologists from national metrological or designated institutes (PTB, LNE, LGC, VSL, SMD and BAM) will work together with scientists with know-how in development of new nano reference nanoparticles (CEA, University of Turin, LGC, BAM) and with experts in advanced data processing, e.g. by machine learning (POLLEN). With the support of DIN, the project outcomes will be channelized to standardization bodies such as ISO/TC 229 ‘Nanotechnologies’/JWG 2 ‘Nanoparticle Measurement and Characterization’ (SEM, TSEM and TEM), CEN/TC 352 ‘Nanotechnologies’ (SEM, TSEM and TEM), ISO/TC 201/SC 9 (AFM), ISO/TC 24/SC 4 (SAXS).
Three technical work packages will ensure input for impact to standardization community, nanoparticle manufacturers, instrument manufacturers, and (accredited) service laboratories:
- WP1 Performance and traceability of characterization methods
- WP2 Reference materials - Preparation and Characterization
- WP3 Modelling and development of measurement procedures
Well-defined non-spherical nanoparticles shapes such as cubes, platelets, bipyramids, rods/acicular will be developed, with mono- and polydisperse size distribution, as well as with accurate particle number concentration (by SAXS and isotopically enrichment for ICP-MS).
Physical modelling of the signal for TSEM, SEM, 3D-AFM and SAXS will be used to feed machine learning modeling from a-priori measurement data. Further, data fusion will be developed for hybrid sizing techniques: SEM with TSEM/TEM, SEM/TSEM with AFM, SEM/TSEM with SAXS with the final aim of improving the true shape and size of non-spherical nanoparticles by a better estimation of the measurement uncertainties.
In the second half-time of the project dedicated workshops (focused on method improvement and reference materials development) will be organized to disseminate the gained knowledge to end-users. Further, a data library with relevant tagged measurement data is planned to be organized and made publicly available. Inter-laboratory comparisons based on the newly developed multi-modal nano reference materials will be organized preferably within VAMAS/TWA 34 ‘Nanoparticle populations’.
Extraction of true, 3D shape (and size) of non-spherical nanoparticles (NPs) is associated with errors by conventional 2D electron microscopy using projection images. Significant efforts within the ISO technical committee TC 229 ‘Nanotechnologies’ are aimed at establishing accurate TEM and SEM measurement of NP size and shape as robust, standard procedures. Study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated titania nano-powder for which size and shape distribution of primary crystallites of irregular shape must be measured accurately. To be noticed is e. g. the fact that the measurement procedure allows only manual selection of the particles clearly distinguishable for analysis as well as manual definition of the contour of the imaged NPs.
An inter-laboratory exercise on titania NPs (pure anatase, grown by hydrothermal synthesis) of well-defined non-spherical shape, i.e. bipyramidal has been recently started within ISO/TC 229 under similar conditions as for the irregular shaped titania. Overlapped particles were allowed to be considered, as long as they are clearly distinguishable. One decisive NP selection criterion was to analyze only those NPs with a roundness value below 0.7, i.e. the NPs laying on the support foil and, hence, with projection areas clearly deviating from perfect circles (R=1). The overall evaluation (for 15 labs) of the size descriptors (area, Feret, minFeret, perimeter) and shape descriptors (aspect ratio, roundness, compactness, extent) by analysis of variance is just to be finished and included in ISO/WD 21363 Nanotechnologies -- Protocol for particle size distribution by transmission electron microscopy.
The EC Recommendation on the definition of nanomaterial, based solely on size of the constituent particles, foresees development of harmonised measurement methods ensuring ‘consistent results across materials and over time’. The EU/FP7 research project NanoDefine has been exclusively dedicated to support the implementation of this EC Recommendation for the European Union’s legislation. For the first time, measurement techniques able to determine the size of nanoparticles have been evaluated systematically on a well-defined set of quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity.
Particularly based on the analytical performance of the measurement techniques as tested on the challenging real-world particulate materials, it was possible to formulate recommendations for use of a new tiered approach consisting of screening and confirmatory techniques. Thus, a consistent framework of guidance for nanomaterial identification according to the EC Definition has been issued in form of the NanoDefiner e-tool, with a transparent decision flow scheme and an extensive user manual. Selected examples of analysis and classification as nano-/non-nanomaterials will be given, highlighting the limits of applicability of the available measurement techniques in dependence on sample properties. On some recent relevant developments in sample preparation – as a crucial part for an accurate analysis - will be also reported. Further, ISO/TC 229 ‘Nanotechnologies’ activities aiming at establishing accurate TEM and SEM measurement of NP size and shape as robust, traceable, standard procedures are highlighted. With participation of BAM, study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated or shape-controlled titania nano-powder for which size and shape distribution of primary particles must be measured accurately.
Many techniques are available for measuring particle size distribution. For ideal materials (spherical particles, well dispersed) it is possible to evaluate the Performance of These methods. The performance of the analytical instrumentation for the purpose of classifying materials according to EC Definition is unknown. In this work the performance of commercially available particle sizing techniques on representative NanoDefine set of real-world testing materials (RTM) and quality control materials (QCM) for the implementation of the Definition is evaluated.
The overall objective of project Improved traceability chain of nanoparticle size measurements is to improve the traceability chain for nanoparticle size measurements. The main impact will be achieved by manifold contributions to standard documents for CEN/TC 352 “Nanotechnologies”, which directly addresses the research needs of CEN, CENELEC and ETSI mandated by EC to develop standards for methods and reference materials to accurately measure the size and size distribution of nanoparticles. This will take place in collaboration with ISO/TC229 ‘Nanotechnologies’, ISO/TC24/SC4 ‘Particle characterization’ and ISO/TC201 ‘Surface analysis’/ SC9 ‘Scanning probe microscopy’.
We discuss the role of the volume specific surface area (VSSA) as determined from the specific surface area measured by the (extended) Brunauer-Emmett-Teller (BET) technique, in the identification process of powdered nano- and non-nanomaterials in line with the EU definition of nanomaterial. Results obtained in the NanoDefine project demonstrate that under appropriate conditions, VSSA can be used as proxy to the number-based particle size distribution. The extent of agreement between nano/non-nano classification by electron microscopy (EM) and classification by VSSA is investigated systematically on a large set of diverse particulate substances, representing most of the cases expected in regulatory practice. Thus, parameters such as particle shape, size polydispersity/multi-modality, and particle (inner or coating) porosity are evaluated. Based on these results, we derive a tiered screening strategy for powders, involving the use of VSSA for the purpose of implementing the definition of nanomaterial, and recommend it for inclusion in a technical guidance for the implementation of the definition.
Extraction of true, 3D shape (and size) of non-spherical nanoparticles (NPs) is associated with errors by conventional 2D electron microscopy using projection images. Significant efforts within the ISO technical committee TC 229 ‘Nanotechnologies’ are aimed at establishing accurate TEM and SEM measurement of NP size and shape as robust, standard procedures. Study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated titania nano-powder for which size and shape distribution of primary crystallites of irregular shape must be measured accurately. To be noticed is e. g. the fact that the measurement procedure allows only manual selection of the particles clearly distinguishable for analysis as well as manual definition of the contour of the imaged NPs.
An inter-laboratory exercise on titania NPs (pure anatase, grown by hydrothermal synthesis) of well-defined non-spherical shape, i.e. bipyramidal has been recently started within ISO/TC 229 under similar conditions as for the irregular shaped titania. Overlapped particles were allowed to be considered, as long as they are clearly distinguishable. One decisive NP selection criterion was to analyze only those NPs with a roundness value below 0.7, i.e. the NPs laying on the support foil and, hence, with projection areas clearly deviating from perfect circles (R=1). The overall evaluation (for 15 labs) of the size descriptors (area, Feret, minFeret, perimeter) and shape descriptors (aspect ratio, roundness, compactness, extent) by analysis of variance is just to be finished and included in ISO/WD 21363 Nanotechnologies -- Protocol for particle size distribution by transmission electron microscopy.
The test material EDS-TM001 together with an accompanying software package, “EDX spectrometer check”, have been made available in 2009 by BAM to be employed by EDS (energy dispersive spectrometer) users to check the performance of an EDS attached to the SEM. Particularly for test laboratories operating under accreditation schemes like ISO/IEC 17025, a periodical control of the critical instrumental parameters in end-user laboratories is required. With EDS-TM001 or EDS-TM002 (second generation) test material, this periodical check is simplified to the acquisition of only one 10 kV spectrum. The software “EDX spectrometer check” is destined to evaluate automatically this spectrum and determine the performance of the EDS in terms of energy resolution and calibration as well as possible alteration of low-energy efficiency due to detector contamination. Energy resolution can be compared with the specified values according to the international ISO standard ISO 15632:2012. EDS-TM is a synthetic material consisting of a thick layer of C, Al, Mn, Cu and Zr in a well-defined composition, deposited on a steel (in case of EDS-TM001) or silicon (in case of EDS-TM002) substrate. Meanwhile, more than one hundred laboratories use the EDS-TM001 or EDS-TM002 test material for the periodical check of their EDS. A detailed description of the test material and software together with examples of application was published recently. New results and gained experiences will be presented as well.
When the FWHM of lines appearing in the EDS-TM spectrum are determined, the spectrum background must be subtracted accurately. The applied physical background subtraction procedure is robust and takes into account the transmission of the detector window. While the previous version considers only Moxtek AP windows, the new version includes selection of silicon nitride window and the case of windowless detector. Moreover, the new version allows importing of spectra in Bruker spx format and EMSA/MSA files from EDAX TEAM software.
Grundkenntnisse zum besseren Verständnis der Funktionsweise der Elektronenstrahl-Mikroanalyse (ESMA) werden präsentiert und anhand Beispielen diskutiert.
Das physikalische Messprinzip von ESMA am REM, das Wechselwirkungs- und Informationsvolum und die Anregung der charakteristischen Röntgenlinien werden erklärt. Verschiedene potentielle Artefakte, wie z.B. Heterogenität der Probenzusammensetzung, Oberflächenbeschaffenheit der Probe und Linienüberlagerung werden eingeführt.
Die physikalischen Grenzen der analytischen Methode werden spezifiziert.
In dieser Präsentation werden Aktivitäten im Bereich der 'nano'-Charakterisierung bei der BAM vorgestellt. Beispiele von F&E-Projekten und -Kooperationen im nano-Analytik-Bereich bei der BAM werden genannt. Thematische Kooperations-Möglichkeiten zwischen BAM und dem Netzwerk NanoAnalytik und -Messtechnik in der Produktion werden diskutiert.
The present study repeats electron probe microanalysis (EPMA) measurements with the thin film analysis software Stratagem on an Fe-Ni thin films on silicon and reports - for the first-time – results of analysis on Si-Ge thin films deposited on a non-conductive aluminium oxide substrate.
If the very good EPMA/Stratagem results for the FeNi system were expected due to previous studies, the data obtained for the SiGe films are particularly valuable, because of the challenging insulator substrate of Al2O3. The conductivity of the Si1-xGex surface necessary for charging-free analysis was ensured by applying conductive copper tape onto film surface down to sample stage. Four accelerating voltages, 15, 20, 25 and 30 kV, have been applied, so that the Ge Kα X-ray line at 9.87 keV could be excited.
For the determination of porosity of Ir oxide thin films, electron probe microanalysis (EPMA) can be used as part of a combined SEM/EDS/STRATAGem analysis. The mass deposition (in μg cm-2) of films was calculated with the analysis software STRATAGem via k-values measured with EDS. The average density of coated films was obtained from the mass deposition and the film thickness as measured by the cross-section SEM. The porosity was calculated by dividing the average film density by the bulk (theoretical) density of the film material.
Film porosities were counterchecked by spectroscopic ellipsometry (SE) using the Bruggeman effective medium approximation (BEMA).
The results obtained by both analytical approaches/methods used, SEM/EDS/STRATAGem and SE were in good agreement.
The EC Recommendation on the definition of nanomaterial, based solely on size of the constituent particles, foresees development of harmonised measurement methods ensuring ‘consistent results across materials and over time’. The EU/FP7 research project NanoDefine has been exclusively dedicated to support the implementation of this EC Recommendation for the European Union’s legislation. For the first time, measurement techniques able to determine the size of nanoparticles have been evaluated systematically on a well-defined set of quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity.
Particularly based on the analytical performance of the measurement techniques as tested on the challenging real-world particulate materials, it was possible to formulate recommendations for use of a new tiered approach consisting of screening and confirmatory techniques. Thus, a consistent framework of guidance for nanomaterial identification according to the EC Definition has been issued in form of the NanoDefiner e-tool, with a transparent decision flow scheme and an extensive user manual. Selected examples of analysis and classification as nano-/non-nanomaterials will be given, highlighting the limits of applicability of the available measurement techniques in dependence on sample properties. On some recent relevant developments in sample preparation – as a crucial part for an accurate analysis - will be also reported.
The main objectives of the new EMPIR project nPSize are to establish EU capability of traceable measurement of NP size and shape, lower uncertainties of NP size measurement by developement of new nano-CRMs, new models (physical and machine learning), 3D method combination, and also by new ISO and CEN standards on accurate NP size measurement and guidance and knowledge transfer. The envisaged outcomes of the project will be presented and their suitability will be discussed to be taken over as pertinent contributions to normative projects within CEN/TC 352 Nanotechnologies.
The test material EDS-TM001 together with an accompanying software package, “EDX spectrometer check”, have been made available in 2009 by BAM to be employed by EDS (energy dispersive spectrometer) users to check the performance of an EDS attached to the SEM. Particularly for test laboratories operating under accreditation schemes like ISO/IEC 17025, a periodical control of the critical instrumental parameters in end-user laboratories is required. With EDS-TM001 or EDS-TM002 (second generation) test material, this periodical check is reduced to the acquisition of only one 10 kV spectrum. The software “EDX spectrometer check” is destined to evaluate automatically this spectrum and determine the performance of the EDS in terms of energy resolution and calibration as well as possible alteration of low-energy efficiency due to detector contamination. Energy resolution can be compared with the specified values according to the international ISO standard ISO 15632:2012. EDS-TM is a synthetic material consisting of a thick layer of C, Al, Mn, Cu and Zr in a well-defined composition, deposited on a steel (in case of EDS-TM001) or silicon (in case of EDS-TM002) substrate. Meanwhile, more than one hundred laboratories (most of them located in Germany) use the EDS-TM001 or EDS-TM002 test material for the periodical check of their EDS. A detailed description of the test material and software together with examples of application was published recently. New results and gained experiences will be presented as well.
A femto-second pulsed laser ablation in liquid (PLAL) procedure for the generation of titanium oxide nanoparticles (NP) is reported with the purpose of understanding morphology and structure of the newly generated NPs. Ablation duration was varied for optimization of NP generation processes between 10 and 90 min. Surface morphology of NPs as well as their size and shape (distribution) were analysed by various complementary electron microscopy techniques, i.e. SEM, TSEM and TEM. The crystalline structure of titanium oxide particles was investigated by XRD and HR-TEM. Concentration of generated titanium oxide NPs in liquid was analysed by ICP-MS. A mix of crystalline (mainly anatase), partly crystalline and amorphous spherical titanium oxide NPs can be reported having a mean size between 10 and 20 nm, which is rather independent of the laser ablation (LA) duration. A second component consisting of irregularly shaped, but crystalline titanium oxide nanostructures is co-generated in the LA water, with more pronounced occurrence at longer LA times. The provenance of this component is assigned to those spherical particles generated in suspension and passing through the converging laser beam, being hence subject to secondary irradiation effects, e. g. fragmentation.
The present study repeats electron probe microanalysis (EPMA) measurements with the thin film analysis software Stratagem on an Fe-Ni thin films on silicon and reports - for the first-time – results of analysis on Si-Ge thin films deposited on a non-conductive aluminium oxide substrate.
If the very good EPMA/Stratagem results for the FeNi system were expected due to previous studies [2], the data obtained for the SiGe films are particularly valuable, because of the challenging insulator substrate of Al2O3. The conductivity of the Si1-xGex surface necessary for charging-free analysis was ensured by applying conductive copper tape onto film surface down to sample stage. Four accelerating voltages, 15, 20, 25 and 30 kV, have been applied, so that the Ge Kα X-ray line at 9.87 keV could be excited.
The test material EDS-TM001 together with an accompanying software package, “EDX spectrometer check”, have been made available in 2009 by BAM to be employed by EDS (energy dispersive spectrometer) users to check the performance of an EDS attached to the SEM. Particularly for test laboratories operating under accreditation schemes like ISO/IEC 17025, a periodical control of the critical instrumental parameters in end-user laboratories is required. With EDS-TM001 or EDS-TM002 (second generation) test material, this periodical check is simplified to the acquisition of only one 10 kV spectrum. The software “EDX spectrometer check” is destined to evaluate automatically this spectrum and determine the performance of the EDS in terms of energy resolution and calibration as well as possible alteration of low-energy efficiency due to detector contamination. Energy resolution can be compared with the specified values according to the international ISO standard ISO 15632:2012. EDS-TM is a synthetic material consisting of a thick layer of C, Al, Mn, Cu and Zr in a well-defined composition, deposited on a steel (in case of EDS-TM001) or silicon (in case of EDS-TM002) substrate. Meanwhile, more than one hundred laboratories use the EDS-TM001 or EDS-TM002 test material for the periodical check of their EDS. A detailed description of the test material and software together with examples of application was published recently. New results and gained experiences will be presented as well.
When the FWHM of lines appearing in the EDS-TM spectrum are determined, the spectrum background must be subtracted accurately. The applied physical background subtraction procedure is robust and takes into account the transmission of the detector window. While the previous version considers only Moxtek AP windows, the new version includes selection of silicon nitride window and the case of windowless detector. Moreover, the new version allows importing of spectra in Bruker spx format and EMSA/MSA files from EDAX TEAM software.
Extraction of true, 3D shape (and size) of non-spherical nanoparticles (NPs) is associated with errors by conventional 2D electron microscopy using projection images. Significant efforts within the ISO technical committee TC 229 ‘Nanotechnologies’ are aimed at establishing accurate TEM and SEM measurement of NP size and shape as robust, standard procedures. Study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated titania nano-powder for which size and shape distribution of primary crystallites of irregular shape must be measured accurately. To be noticed is e. g. the fact that the measurement procedure allows only manual selection of the particles clearly distinguishable for analysis as well as manual definition of the contour of the imaged NPs.
An inter-laboratory exercise on titania NPs (pure anatase, grown by hydrothermal synthesis) of well-defined non-spherical shape, i.e. bipyramidal has been recently started within ISO/TC 229 under similar conditions as for the irregular shaped titania. Overlapped particles were allowed to be considered, as long as they are clearly distinguishable. One decisive NP selection criterion was to analyze only those NPs with a roundness value below 0.7, i.e. the NPs laying on the support foil and, hence, with projection areas clearly deviating from perfect circles (R=1). The overall evaluation (for 15 labs) of the size descriptors (area, Feret, minFeret, perimeter) and shape descriptors (aspect ratio, roundness, compactness, extent) by analysis of variance is just to be finished and included in ISO/WD 21363 Nanotechnologies -- Protocol for particle size distribution by transmission electron microscopy.
Titanium dioxide is one of the most studied metal oxides due to its chemical, surface, electronic and (photo)catalytic properties, providing this material of multisectorial applications ranging from healthcare, photocatalysis, smart materials with self cleaning and self sterilizing properties and solar energy harvesting. However it is difficult to correlate the functional properties of TiO2 nanomaterials to the properties at single nanoparticle level due to the high polydispersity in shape, size and surface features of the currently available TiO2 nanoparticles (NPs). Although intensive experimental and theoretical studies have been conducted on the reactivity of different surfaces of metal oxides such as TiO2 much less attention is paid on the dependence of functional properties, like photocatalytic activity, dye adsorption, open circuit potential and fill factor in dye sensitized solar cells, on crystal facets in different orientations. One of the goal of SETNanoMetro project was the development of design rules to tune crystal facets of TiO2 NPs in order to optimize and control functional properties. In the present work we have developed a series of design rules in order to obtain sets of anatase TiO2 NPs with low polydispersity and to tune their shape and size by hydrothermal processing of Ti(IV)-Triethanolamine complex in presence of different shape controllers. Through a careful experimental design, a predictive soft model was developed. The model is able to predict the synthesis outcome allowing to tune the shape factor from 5 (prisms) to 1.5 (bipyramids) to 0.2 (platelets). This allows to control the main crystal facets exposed ranging from (100) to (001). Due to the dependence of functional properties of nanomaterials on shape distribution and not only size, the availability of NPs sets with uniform and well defined and tunable shapes can be of paramount relevance in order to produce reference nanomaterials for shape measurement.
TiO2 anatase nanoparticles are among the relevant players in the field of light-responsive semiconductor nanomaterials used to face environmental and energy issues. In particular, shape-engineered TiO2 anatase nanosheets with dominant {001} basal facets gained momentum because of the possibility to exploit different and/or improved functional behaviors with respect to usual bipyramidal TiO2 anatase nanoparticles, mainly exposing {101} facets. Nevertheless, such behavior depends in a significant extent on the physicochemical features of surfaces exposed by nanosheets.
They can vary in dependence on the presence or removal degree of capping agents, namely, fluorides, used for shape-engineering, and experimental investigations in this respect are still a few. Here we report on the evolution of interfacial/ surface features of TiO2 anatase nanosheets with dominant {001} facets from pristine nanoparticles fluorinated both in the bulk and at their surface to nanoparticles with F− free surfaces by treatment in a basic solution and to totally F− free nanoparticles by calcination at 873 K.
The nanoparticles fluorine content and its subsequent evolution is determined by complementary techniques (ion chromatography, TOF-SIMS, XPS, AES, SEM-EDX), probing different depths. In parallel, the evolution of the electronic properties and the Ti valence state is monitored by UV−vis spectroscopy and XPS. The calcination treatment results in {001} facets poorly hydroxylated, hydrated, and hydrophilic, which appear as surface features consequent to the expected (1 × 4) reconstruction. Moreover, IR spectroscopy of CO adsorbed as probe molecule indicates that the Lewis acidity of Ti4+ sites exposed on (1 × 4) reconstructed {001} facets of calcined TiO2 nanosheets is weaker than that of cationic centers on {101} facets of bipyramidal TiO2 anatase nanoparticles. The samples have also been tested in phenol photodegradation highlighting that differences in surface hydration, hydroxylation, and Lewis acidity between TiO2 nanoparticles with nanosheet (freed by F− by calcination at 873 K) and bipyramidal shape have a strong impact on the photocatalytic activity that is found to be quite limited for the nanoparticles mainly exposing (1 × 4) reconstructed {001} facets.
Singlet oxygen generation potential of two novel free-base-porphyrin photocatalysts was investigated. The freebase-porphyrin-sensitized Fe3O4 magnetic nanoparticles (MNPs) were tested for the degradation of the model pollutant Bisphenol A (BPA) in aqueous solution, for the first time. MNPs with either cubic or spherical shape were synthesized using the sonochemical approach, followed by sensitizing with photoactive 4,4′,4′′,4′′′- (Porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid) (TCPP). The resulted photocatalysts were characterized in detail by scanning and transmission electron microscopy, Brunauer–Emmett–Teller analysis, spectral techniques and vibrating sample magnetometry. The electron spin resonance experiments have confirmed the high activity of the photocatalysts through the efficient formation of singlet oxygen in solution. The optimum operational parameters for BPA degradation were established as follows: 1.0 μmol L−1 BPA, 1.0 g L−1 of photocatalyst, 100 μmol L−1 H2O2, under UVA irradiation. In these conditions, the results for both photocatalysts revealed that after only 10 min of reaction, over 64% and ca. 90% of BPA have been removed from solution in the absence and presence of H2O2, respectively. Whereas after 60 minutes of treatment, only 24% of BPA in real wastewater effluent samples were removed under UVA irradiation in the absence of H2O2, showing the high complexity of real wastewater. Moreover, both photocatalysts were successfully used for BPA removal in three consecutive runs, without significant loss of catalytic features.
Cost-effective water cleaning approaches using improved Treatment technologies, for instance based on catalytic processes with high activity catalysts, are urgently needed. The aim of our study was to synthesize efficient Fenton-like photo-catalysts for rapid degradation of persistent organic micropollutants in aqueous medium. Iron-based nanomaterials were chemically synthesized through simple procedures by immobilization of either iron(II) oxalate (FeO) or iron(III) citrate (FeC) on magnetite (M) nanoparticles stabilized with polyethylene glycol (PEG). Various investigation techniques were performed in order to characterize the freshly prepared catalysts. By applying advanced oxidation processes, the effect of catalyst dosage, hydrogen peroxide concentration and UV-A light exposure were examined for Bisphenol A (BPA) conversion, at laboratory scale, in mild conditions. The obtained results revealed that BPA degradation was rapidly enhanced in the presence of low-concentration H2O2, as well as under UV-A light, and is highly dependent on the surface characteristics of the catalyst. Complete photo-degradation of BPA was achieved over the M/PEG/FeO catalyst in less than 15 minutes. Based on the catalytic performance, a hierarchy of the tested catalysts was established: M/PEG/FeO > M/PEG/FeC > M/PEG. The results of cytotoxicity assay using MCF-7 cells indicated that the aqueous samples after treatment are less cytotoxic.
Control of functionalization of supports for subsequent assembly of titania nanoparticle films
(2018)
For self‐assembling of TiO2 nanoparticles in multiple layers by layer‐by‐layer deposition to be applied to TiO2 thin films with defined and homogeneous thickness for large‐scale applications, the proper functionalization of substrate surface is a prerequisite to guarantee sufficient adhesion.
The substrates selected and tested in the present paper were conductive, fluorine‐doped tin oxide (FTO) glass, nonconductive silica glass, and titanium alloy. The current study focusses on the analytical control of the stepwise functionalization of the substrates with 3‐aminopropyltriethoxysilane and glutaraldehyde (GA) for both the FTO glass and silica glass and with 3‐aminepropyl phosphonic acid and GA for Ti alloy. The analyses have been conducted by means of surface sensitive methods, X‐ray photoelectron spectroscopy, Auger electron spectroscopy, and time‐of‐flight secondary ions mass spectrometry. Chemical composition of surface of functionalized substrates shows differences in the degree and type of modification in dependence on substrate. It could be demonstrated that the best functionalized substrates were the conductive FTO glasses. The analysis of the functionalized Ti substrates has revealed that the surface coverage with 3‐aminepropyl phosphonic acid and GA molecules is an inhomogeneous one, and further optimization of the two‐step functionalization on the Ti alloy substrate is necessary.
Manufacturing of new perovskite layered solar cells with constant high light conversion Efficiency over time may be hampered by the loss of efficiency caused by structural and/or chemical alterations of the complex layered system. SEM/EDX combined with XPS were chosen as an appropriate methodical approach to characterize perovskite laboratory cells in depth and at surface, before and after light exposure. The layered perovskite system investigated here is based on glass covered with fluorine doped tin oxide, followed by thin films of TiO2, ZrO2, and a thick monolithic carbon. TiO2 film is subdivided into a dense layer covered by porous one constituted of nanoparticles of truncated bipyramidal shape. This layered system serves as the matrix for the perovskite. EDX spectral maps on cross sections of specimen have shown that Pb and I are distributed homogeneously throughout the porous layers C, ZrO2, and TiO2. SEM/EDX data show that 20 weeks of ambient daylight did not change significantly the in‐depth distribution of the elemental composition of Pb and I throughout the entire solar cell system. It was confirmed with EDX that nanoparticles identified in high‐resolution SEM micrographs contain mainly Pb and I, indicating these to be the perovskite crystals. However, a compositional and chemical altering began in the near‐surface region of the outermost ~10 nm after 2 months of illumination which was observed with XPS.
The European Commission's recommendation on the definition of nanomaterial [2011/696/EU] is broadly applicable across different regulatory sectors and requires the quantitative size determination of constituent particles in samples down to 1 nm. A material is a nanomaterial if 50 % or more of the particles are in the size range 1-100 nm. The implementation of the definition in a regulatory context challenges measurement methods to reliably identify nanomaterials and ideally also non-nanomaterials as substance or product ingredient as well as in various matrices.
The EU FP7 NanoDefine project [www.nanodefine.eu] addressed these challenges by developing a robust, readily implementable and cost-effective measurement strategy to decide for the widest possible range of materials whether it is a nanomaterial or not. It is based on existing and emerging particle measurement techniques evaluated against harmonized, material-dependent performance criteria and by intra- and inter-lab comparisons. Procedures were established to reliably measure the size of particles within 1-100 nm, and beyond, taking into account different shapes, coatings and chemical compositions in industrial materials and consumer products. Case studies prove their applicability for various sectors, including food, pigments and cosmetics.
A main outcome is the establishment of an integrated tiered approach including rapid screening (tier 1) and confirmatory methods (tier 2), a decision support flow scheme and a user manual to guide end-users, such as manufacturers, in selecting appropriate methods. Another main product is the “NanoDefiner” e-Tool which implements the flow scheme in a user-friendly software and guides the user in a semi-automated way through the entire decision procedure. It allows a cost-effective selection of appropriate methods for material classification according to the EC's nanomaterial definition and provides a comprehensive report with extensive explanation of all decision steps to arrive at a transparent identification of nanomaterials as well as non-nanomaterials for regulatory purposes.
The project has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No 604347.
For the determination of porosity of Ir oxide thin films, electron probe microanalysis (EPMA) can be used as part of a combined SEM/EDS/STRATAGem analysis. The mass deposition (in μg cm-2) of films was calculated with the analysis software STRATAGem via k-values measured with EDS. The average density of coated films was obtained from the mass deposition and the film thickness as measured by the cross-section SEM. The porosity was calculated by dividing the average film density by the bulk (theoretical) density of the film material.
Film porosities were counterchecked by spectroscopic ellipsometry (SE) using the Bruggeman effective medium approximation (BEMA).
The results obtained by both analytical approaches/methods used, SEM/EDS/STRATAGem and SE were in good agreement.
The accurate EDS microanalysis of light elements such as boron and carbon by spectrum imaging will be demonstrated using a sintered hard ceramic material composed of the three major phases titanium boride (TiB2), titanium carbide (TiC), silicon carbide (SiC) and minor phases, sub-μm in size.
The combination of these three materials leads to improved mechanical and tribological properties. Silicon carbide is a material used for mechanical seals. It has the disadvantage of reduced failsafe running functions, causing increased wear when running dry. The added titanium components (TiC and TiB2) improve the failsafe running functions. This technology has already been transferred to industrial applications.
Quantitative analysis of a bulk sample requires that the
composition of the sample is homogeneous over the analyzed
volume. For inhomogenous samples the calculation of
the matrix effects is not correct and this can lead to wrong results in the element concentrations. For samples containing a layer structure a different quantitative evaluation has to be applied. This can be provided with the standard-based analysis in ESPRIT in combination with the STRATAGem software.