6 Materialchemie
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Eingeladener Vortrag
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Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals. The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms. We introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. We discuss our recent results investigating the formation of (polymorphic) cocrystals. First investigations of a mechanochemical synthesis under controlled temperature which allow determining the activation barrier are presented.6 Furthermore, X-ray diffraction and in situ Raman spectroscopy coupled with thermography revealed a low temperature increase during milling reactions due to the mechanical impact and clear temperature increases as a result of the reaction heat. Our results indicate that in situ investigation of milling reactions offer a new approach to tune and optimize mechanochemically synthesized compounds.
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 X-ray 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 6 μm thick layer of C, Al, Mn, Cu and Zr deposited on a steel (in case of EDS-TM001) or silicon (in case of EDS-TM002) substrate. The chemical composition of EDS-TM was chosen such as to give nearly equal intensities of the low energy lines in a 10 kV spectrum, thus, making it very sensitive against spectrometer efficiency changes. Meanwhile, about 150 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 the X-ray lines 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.
Windowless detectors have been also tested demonstrating long-term stability after repeated heating and cooling cycles. In this case, the appropriate Background subtraction is decisive for accurate detector characterization. Detailed results will be presented.
It was demonstrated in the past that the electron probe microanalysis (EPMA) can be applied to determine accurately both elemental composition and thickness of thin films by using the dedicated software package for thin film analysis Stratagem. A relatively small number of film materials such as pure metallic films of platinum and nickel, binary alloys of Fe-Ni, and Pt-Ni-Co ternary alloy films has been reported in literature as working successfully. Further, the software can be applied ‘inversely’, i.e., by feeding it with the thickness of the film and using the determined mass coating, one can easily calculate the film density, which for porous layers leads us to the true film porosity.
The present study repeats measurements on an already tested system of 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. Standard-based and standardless EPMA (with EDS) results were used in combination with Stratagem for the quantification.
Further, X-ray fluorescence analysis (XRF) can be used for the determination of elemental composition and thickness of such films as well. In this case, XRF with a μ-focus X-ray source (μ-XRF) attached to a SEM was applied. For quantification, a fundamental parameter (FP) approach has been used to calculate standard-based and standardless results. Compared to EPMA, XRF has a larger information depth and a higher elemental sensitivity because of a generally lower background.
Both thin film systems have been chosen as samples of an international round robin test (RRT) organised in the frame of standardisation technical committee ISO/TC 201 ‘Surface chemical analysis’, under the lead of KRISS. The main objective of the RRT is to compare the results of atomic fractions of Fe1-xNix and Si1-xGex alloy films obtained by different surface Analysis techniques, such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) applied in the depth-profiling operation mode.
Five samples of different atomic fractions of each thin film system, i.e., Fe1-xNix and Si1-xGex, have been grown by ion beam sputter deposition on silicon and Al2O3 wafers, respectively. Reference FeNi and SiGe films with well-known elemental composition and thickness have been also supplied for standard-based analysis. The atomic fractions of all the samples including the references have been certified by RBS (Rutherford backscattering spectrometry) and ICP-AES (inductively coupled plasma atomic emission spectroscopy).
Porous materials play an important role in several fields of technology, especially for energy applications like photovoltaics, electrolysis or batteries. The activity of porous films is affected by properties like porosity, film thickness, chemical composition of the material, as well as the crystallinity of the framework. The complex morphology of such porous films constitutes a challenge even for modern analytical techniques and requires new approaches employing the combination/complementation of data of different analytical methods. In this contribution, we characterise thin mesoporous iridium-titanium mixed oxide film properties by electron probe microanalysis (EPMA) with energy-dispersive X-ray spectroscopy (EDS) at an SEM.
Mesoporous iridium oxide - titanium oxide (IrOx-TiOx) films were prepared via dip-coating of a solution containing a triblock-copolymer as structure-directing agent, an iridium precursor as well as a titanium precursor in ethanol. IrOx-TiOx films were synthesized with different amounts of iridium and calcined in air. The SEM micrographs reveal for all films the achievement of a well-ordered mesoporous structure and homogeneous films with thicknesses between 67 nm and 152 nm.
For the determination of film elemental composition and porosity, EPMA can be used as part of a combined SEM/EDS/STRATAGem analysis. Elemental compositions and mass depositions (in μg cm-2) of IrOx-TiOx films were calculated with the thin film analysis Software STRATAGem via k-values measured with SEM/EDS. Pure bulk Ir, TiO2 and Si were measured as references. The average density of the films was obtained from the mass Deposition and the film thickness as measured by cross-section SEM. The porosity was then extracted from the measured average film density divided by a theoretical bulk density. The latter is calculated from the weight fractions of IrOx and TiOx as determined with STRATAGem and the bulk mass densities of IrO2 and TiO2 (rutil) from literature.
The fitting results of the k-values from the STRATAGem software, which are in fair agreement with the measured k-values.
The application of the SEM/EDS/STRATAGem approach for accurate porosity determination on pure mesoporous TiOx films and pure porous IrOx films has been recently demonstrated.
The porosities of pure IrOx, TiOx and mixed IrOx-TiOx films in this study have been determined. The contribution will assess in detail the advantages and limitations of the combined SEM/EDS/STRATAGem analysis for the morphology and porosity of thin metal oxide films. Moreover, the comparison with other measurement techniques and the combination of datasets from multiple measurements will be discussed.
Microbeam analysis data are of continuously improving quality, this owing mainly to developments in instrumentation (hardware and software) and computer performance. The knowledge and skills of the operators must be also kept correspondingly updated. To be deemed as technically competent, the laboratories must be accredited according to an accreditation scheme, mostly following ISO/IEC 17025.
International standards are able to provide requirements, specifications, guidelines or characteristics of methods, instruments or samples with the final goal that these can be used consistently in accredited laboratories. In the field of electron microscopy and microbeam Analysis standardisation and metrology are terms that are encountered rather seldom at major conferences and scientific publications. Several ISO standards already published and used successfully by a large part of the electron microscopy and microbeam analysis community. For example, file formats such as EMSA/MSA for spectral-data exchange or tagged image file format (TIFF) for SEM images; procedures for the specification of X-ray spectrometers, the specification of certified reference materials (CRMs), and for measurement of average grain size by electron backscatter diffraction (EBSD); and guidelines for calibrating image magnification in SEM or TEM. A main task of ISO technical committee TC 202 ‘Microbeam Analysis’ is to identify feasible projects/proposals needed to be developed into new international standards, particularly in respect to recent technology, such the silicon drift detector (SDD).
As far as the metrological aspects are regarded, The International Bureau of Weights and Measures (BIPM) through the Consultative Committee for the Amount of Substance (CCQM) is concerned with the metrological aspect in Chemistry and Biology. In particular, the Surface Analysis Working Group (SAWG) assists in identifying and establishing inter-laboratory work to test the consistency as well as to improve the traceability of spatially resolved chemical surface analysis at the micro and nanoscale. Examples of recent projects on quantitative microbeam analysis at low energies, such as the quantification of light elements such as carbon and nitrogen will be presented.
The significant sources of measurement uncertainty will be emphasized. These are: quality of the unknown and the reference materials used, the quantification model, instrumental parameters like take-off-angle, spectrometer efficiency, and particularly the beam current. The crucial importance of working with uniform and well-defined measurement and data evaluation protocols will be discussed in compliance with the ISO document “Guide to the expression of uncertainty in measurement (GUM)”.
Another international platform where pre-standardisation work can be organised is VAMAS (Versailles Project on Advanced Materials and Standards). International collaborative Projects aim at providing the technical basis for harmonised measurements, testing, specifications, and standards to be further developed at ISO level. One key point of VAMAS activities is constituted by inter-laboratory comparisons for high-quality data. In the field of microbeam analysis, the technical working area (TWA) 37 Quantitative Microstructural Analysis deals with corresponding projects. Good ideas, e.g., on analysis at low energies, are particularly encouraged by directly contacting the author. Support and guidance will be supplied.
The simultaneous detection of different analytes has gained increasing importance in recent years, especially in the fields of environmental and health monitoring. Particularly suitable formats for multiplexing are bead-based assays. The beads employed need to fulfil size and density requirements important for instance for flow cytometry and shall exhibit an as high as possible surface area for anchoring capture probes to allow for low limits of detection. Core/shell particles are ideally suited in this sense because of their modularity in design and adaptability for various (bio)analytical assays. Here, polystyrene particles coated with different kinds of mesoporous silica shells are presented, possessing distinctly higher surface areas in comparison to non-porous core/shell particles. Different factors such as pH and amount and type of mediator salt used during shell preparation were evaluated with shell inspection by scanning/transmission scanning electron microscopy (SEM/tSEM) being key to architecture control of the monodisperse particles.
For a cytometric model assay, the optimized core/shell particles were functionalized with capture oligonucleotides for DNA detection. After covalent attachment of single-stranded DNA to the silane-modified silica surface, a hybridisation assay using labelled t-DNA complementary strands was carried out to demonstrate particle performance, showing how tailoring of the shell’s surface area controls sensitivity and dynamic range of the assay. Finally, a multiplex assay for the determination of DNA from different human papilloma virus (HPV) lines was developed. Using our optimized particles, we were able to detect down to 10 amolμl‒1, which is an improvement of one order of magnitude compared to assays using non-porous particles reported in the literature. In addition, multiplexed detection could successfully be demonstrated.
Some critical discussion of the state of the art of uncertainty evaluationin Instrumented Indentation Testing IIT
Nowadays the Instrumented Indentation Testing (IIT), in the nano range often named as nano indention, is one of the most commonly used methods to determine the mechanical properties of materials in the micro and nano range. This method is already extensive standardized in ISO 14577 part 1-4. In the past, the application of this standard in testing praxis shows that the established values have an excellent precision.If an uncertainty is calculated, the range of values within which the true value is asserted to lie with some level of confidencewill be known. In part 1 of ISO 14577 [1] two methods for evaluation of the uncertainty in IIT are mentioned:
Method 1 for determining uncertainty considers only those uncertainties associated with the overall measurement performance of the testing machine with respect to the reference blocks.
Method 2calculates a combined uncertainty from individual contributions. These may be grouped into random and systematic uncertainties.
Both methods will be described in detail using examples from the dailyexperimental praxis. The comparabilityof both methods will be critically discussed. Finally, it will be showedhow the calculated uncertaintiescan be used for performancetests and product specifications.
Acknowledgement
This work was performed under the support of the EMPIR project 17NRM05Advancing measurement uncertainty̶ comprehensiveexamples for key international standards
References
[1] ISO 14577 part 1 (2017)
In recent years superglassy polymers exhibiting intrinsic microporosity established a new perspective for a number of applications, especially for gas separation membranes as These polymers Combine extremely high permeabilities with attractive selectivities. The essential factor governing the structure Formation in the solid film or layer is either a contorted rigid Backbone (polymers of intrinsic microporosity - PIMs) or extremely bulky side groups (polynorbornenes and polytricyclonenenes).
For a deeper understanding of both types of such high-Performance polymers for gas separation membranes and their further development broadband dielectric spectroscopy (BDS) can provide a substantial contribution.
BDS addresses molecular relaxations characterizing the dynamics of the solid polymer as a major factor determining the gas transport properties but also the physical aging behavior which is an essential issue for such polymers.
BDS is applied on PIMs where fluctuations of molecular dipoles connected to the backbone can be directly monitored. Furthermore, also polynorbornenes were investigated which carry no dipole moment in their repeat unit - the high resolution of modern equipment allows for the detailed analysis also for very small dielectric losses originating from partially oxidized moieties or marginal catalyst residues.
Additionally, from interfacial polarization phenomena, such as Maxwell-Wagner-Sillars (MWS) polarization due to blocking of charge carriers at internal interfacial boundaries on a mesoscopic length scale, valuable information on the intrinsic microporosity and its changes induced by physical aging can be obtained.
Finally, also conductivity can be characterized in detail in such polymeric systems revealing contributions of interactions of aromatic moieties (π-π-stacking) or the drift motion of charge carriers. These features also determine the structure formation in the solid state.
Measurement of elemental composition of Fe1-xNix and Si1-xGex alloy thin films by EMPA and µ-XRF
(2019)
It was demonstrated in the past that the electron probe microanalysis (EPMA) can be applied to determine accurately both elemental composition and thickness of thin films by using the dedicated software package for thin film analysis Stratagem. A relatively small number of film materials such as pure metallic films of platinum and nickel, binary alloys of Fe-Ni, and Pt-Ni-Co ternary alloy films has been reported in literature as working successfully. Further, the software can be applied ‘inversely’, i.e., by feeding it with the thickness of the film and using the determined mass coating, one can easily calculate the film density, which for porous layers leads us to the true film porosity.
The present study repeats measurements on an already tested system of 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. Standard-based and standardless EPMA (with EDS) results were used in combination with Stratagem for the quantification.
Further, X-ray fluorescence analysis (XRF) can be used for the determination of elemental composition and thickness of such films as well. In this case, XRF with a μ-focus X-ray source (μ-XRF) attached to a SEM was applied. For quantification, a fundamental parameter (FP) approach has been used to calculate standard-based and standardless results. Compared to EPMA, XRF has a larger information depth and a higher elemental sensitivity because of a generally lower background.
Both thin film systems have been chosen as samples of an international round robin test (RRT) organised in the frame of standardisation technical committee ISO/TC 201 ‘Surface chemical analysis’, under the lead of KRISS. The main objective of the RRT is to compare the results of atomic fractions of Fe1-xNix and Si1-xGex alloy films obtained by different surface Analysis techniques, such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) applied in the depth-profiling operation mode.
Five samples of different atomic fractions of each thin film system, i.e., Fe1-xNix and Si1-xGex, have been grown by ion beam sputter deposition on silicon and Al2O3 wafers, respectively. Reference FeNi and SiGe films with well-known elemental composition and thickness have been also supplied for standard-based analysis. The atomic fractions of all the samples including the references have been certified by RBS (Rutherford backscattering spectrometry) and ICP-AES (inductively coupled plasma atomic emission spectroscopy).
If the particle size decreases, the ratio of surface area to volume increases considerably. This provides benefits for all surface-driven processes that run faster or at lower temperatures than larger particles. However, handling and characterization of the nanopowders are much more difficult. Particularly polydisperse powders with irregular shape, as grinding products, represent a challenge. Granulometry in the submicron and nanoscale often leads to incorrect results without knowledge of particle morphology.
This presentation demonstrates potentials of using the volume-specific surface area (SV or VSSA) in the granulometric characterization of nanopowders, for instance, correlations between the volume-specific surface area and the median particle size are discussed considering the particle morphology and the model of the logarithmic normal distribution.
Moreover, the presentation deals with the optimal dispersion of nanopowders during sample preparation. Indirect ultrasound device with defined cooling was developed to prevent both contamination by sonotrode abrasion and sample changes by heat.
Successful granulometric characterization of nanopowders demands both improved dispersion technology and very often an effective combination of two or more measurement methods.
The 44th Meeting of the Versailles Project on Advanced Materials and Standards (VAMAS) Steering Committee has just taken place at NIST in Boulder (CO, USA). BAM participates with significant contributions in Technical Working Areas on nanoparticle and surface chemistry characterization, but also has positioned itself to new global material challenges and trends in the developement of advanced materials and their characterization, such as thermal properties, self-healing materials, and micro- and nanoplastic.
Everything SAXS
(2019)
Experimenting on MAUS
(2019)
Metal-organic frameworks (MOFs) are suitable materials for gas storage of small molecules due to their nanoporous, crystalline structure. The extensively studied MOF HKUST-1 consist of Cu(II)-dimers in a paddlewheel structure, with 1,3,5-benzenetricarboxylic acid (BTC) as organic linker. Instability to humidity remains an issue for many types of MOFs, and for HKUST-1, it has been found that exposure to water vapor creates a surface barrier which reduces the gas uptake rate.
Near-ambient pressure XPS (NAP-XPS) is a promising method for investigations of the stability and interaction of HKUST-1 with various gas molecules. The oxidation state of copper can be monitored before, during and after exposure to various gases. This does not only provide information on the stability of the MOFs, but also on the interaction with the gas molecules and the reversibility of the processes.
NAP-XPS measurements of HKUST-1 exposed to methanol, pyridine and water vapor were performed with EnviroESCA, a laboratory NAP-XPS instrument developed by SPECS. Cu 2p, O 1s and C 1s core level spectra were acquired in pressure ranging from 10-5 to 8 mbar to assess the oxidation state of copper and the stability of the organic linker. HKUST-1 does not show interaction with pyridine, but there are indications of copper-reduction upon exposure to methanol and water vapor. Radiation induced damage is considered and two different approaches for determining the ratio of Cu(I) to Cu(II) will be discussed.
Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be observed on almost any material after the irradiation by linearly polarized laser beams, particularly when using ultrashort laser pulses with durations in the femtosecond to picosecond range.
During the past few years significantly increasing research activities have been reported in the field of LIPSS, since their generation in a single-step process provides a simple way of nanostructuring and surface functionalization towards the control of optical, mechanical, biological, or chemical surface properties. In this contribution the mechanisms of formation and current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting properties, the mimicry of the natural texture of animal integuments, the tailoring of surface colonization by bacterial biofilms, the advancement of medical pacemakers, and the improvement of the tribological performance of nanostructured metal surfaces.
It is a well-known story that copolymers beside their molar mass distribution (MMD) can exhibit a functionality type distribution (FTD), a copolymer composition distribution (CCD), a monomer sequence distribution (MSD) and additionally different topologies within one sample. Nowadays a wide range of different analytical separation techniques and multi-detection possibilities are available.
The challenge consists in a clever combination of these techniques coordinated with the heterogeneity to be investigated.
A number of applications will be presented from e.g. topology elucidation of branched EO-PO “academic” copolymers to copolymer composition of partially broadly distributed progressively tailored “industrial relevant” copolymers consisting of e.g. polyamides, polycarbonates and polysiloxanes.
Multidimensional separation techniques will be demonstrated with focus on mass spectrometric detection techniques (ESI-/MALDI-TOF-MS) coupled online or semi-online to prior separation.