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- EPMA (4)
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- Electron probe microanalysis (EPMA) (2)
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The characteristics of TiO2 coatings can greatly influence their final performance in large-scale applications. In the present study self-assembly of TiO2 nanoparticles (NPs) in multiple layers was selected as a deposition procedure on various substrates. For this, the main prerequisite constitutes the surface modification of both NPs and substrate with e.g. silane coupling agents. A set of functionalized TiO2 NPs has been produced by reaction with either (3- aminopropyl)triethoxysilane (APTES) or (3-aminopropyl)phosphonic acid (APPA) to functionalize the NP surface with free amino-groups. Then, the complementary functionalized NP set can be obtained from an aliquot of the first one, through the conversion of free surface amino-groups to aldehydes by reaction with glutaraldehyde (GA). Several types of TiO2 NPs differing in size, shape and specific surface area have been functionalized. FTIR, TGA, SEM/EDS, XPS, Auger electron spectroscopy (AES) and ToF-SIMS analyses have been carried out to evaluate the degree of functionalization, all the analytical methods employed demonstrating successful functionalization of TiO2 NP surface with APTES or APPA and GA.
The present study reports on measurements on thin Fe-Ni films on silicon and first-time results of analysis on Si-Ge thin films deposited on a non-conductive aluminium oxide Substrate by electron probe microanalysis (EPMA). Standard-based and standardless EPMA (with EDS) results were used in combination with the thin film analysis software 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.
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. An excellent agreement has been obtained between the atomic fractions determined by EPMA and µ-XRF with the KRISS certified values.
Analysis of elemental composition of Fe1-xNix and Si1-xGex alloy thin films by EPMA and µ-XRF
(2019)
The present study reports on measurements on thin Fe-Ni films on silicon and first-time results of analysis on Si-Ge thin films deposited on a non-conductive aluminium oxide Substrate by electron probe microanalysis (EPMA). Standard-based and standardless EPMA (with EDS) results were used in combination with the thin film analysis software 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.
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. An excellent agreement has been obtained between the atomic fractions determined by EPMA and µ-XRF with the KRISS certified values.
Secondary fluorescence is an inevitable effect that has to be taken into account in any algorithm for quantitative electron probe microanalysis (EPMA) as an additional correction. Moreover, secondary fluorescence worsens spatial resolution of EPMA, as discussed once more in two recent papers. Secondary fluorescence is excited both by characteristic radiation and by the X-ray continuum. In most cases the correction is small. There are, however, cases, e.g. the determination of low heavy metal concentration in a light matrix, where the contribution of secondary fluorescence exceeds 10% of the measured X-ray line intensity.
For secondary fluorescence correction the measured X-ray line intensity has to be divided by the correction factor (1+I_flchar/I_p +I_flcont/I_p )≈(1+I_flchar/I_p )(1+I_flcont/I_p ) in order to get those intensity I_p, which is excited only by the primary electrons and enables the determination of specimen composition. I_flchar and I_flcont mean the calculated characteristic and continuums fluorescence intensities. In order to get the intensity of fluorescence radiation, the absorption of the exciting radiation in the specimen, the photoionization probability and the self-absorption of the emitted line must be calculated. This can be performed in a straightforward way. The critical quantity is the X-ray yield of the exciting atoms in case of fluorescence by characteristic radiation and the bremsstrahlung yield of the specimen in case of continuum fluorescence. In the former case it is reasonable to apply the same physical model to calculate I_flchar and I_p.
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.
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.
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).
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.