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We report the results of a Versailles Project on Advanced Materials and Standards (VAMAS) interlaboratory study on the measurement of the shell thickness and chemistry of nanoparticle coatings. Peptide-coated gold particles were supplied to laboratories in two forms: a colloidal suspension in pure water and particles dried onto a silicon wafer. Participants prepared and analyzed these samples using either X-ray photoelectron spectroscopy (XPS) or low energy ion scattering (LEIS). Careful data analysis revealed some significant sources of discrepancy, particularly for XPS. Degradation during transportation, storage, or sample preparation resulted in a variability in thickness of 53%. The calculation method chosen by XPS participants contributed a variability of 67%. However, variability of 12% was achieved for the samples deposited using a single method and by choosing photoelectron peaks that were not adversely affected by instrumental transmission effects. The study identified a need for more consistency in instrumental transmission functions and relative sensitivity factors since this contributed a variability of 33%. The results from the LEIS participants were more consistent, with variability of less than 10% in thickness, and this is mostly due to a common method of data analysis. The calculation was performed using a model developed for uniform, flat films, and some participants employed a correction factor to account for the sample geometry, which appears warranted based upon a simulation of LEIS data from one of the participants and comparison to the XPS results.
The melting behaviour of metal–organic frameworks (MOFs) has aroused significant research interest in the areas of materials science, condensed matter physics and chemical engineering. This work first introduces a novel method to fabricate a bimetallic MOF glass, through meltquenching of the cobalt-based zeolitic imidazolate Framework (ZIF) [ZIF-62(Co)] with an adsorbed ferric coordination complex. The high-temperature chemically reactive ZIF-62-(Co) liquid facilitates the formation of coordinative bonds between Fe and imidazolate ligands, incorporating Fe nodes into the framework after quenching. The resultant Co–Fe bimetallic MOF glass therefore shows a significantly enhanced oxygen evolution reaction performance. The novel bimetallic MOF glass, when combined with the facile and scalable mechanochemical synthesis technique for both discrete powders and surface coatings on flexible substrates, enables significant opportunities for catalytic device Assembly
A pilot study for the quantitative surface analysis of multi-element alloy films has been performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of this pilot study is to ensure the equivalency in the measurement capability of national metrology institutes for the quantification of multi-element alloy films. A Cu(In,Ga)Se2 (CIGS) film with non-uniform depth distribution was chosen as a representative multi-element alloy film. The atomic fractions of the reference and the test CIGS films were certified by isotope dilution - inductively coupled plasma/mass spectrometry. A total number counting (TNC) method was used as a method to determine the signal intensities of the constituent elements, which are compared with their certified atomic fractions. The atomic fractions of the CIGS films were measured by various methods, such as Secondary Ion Mass Spectrometry (SIMS), Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), X-Ray Fluorescence (XRF) analysis and Electron Probe Micro Analysis (EPMA) with Energy Dispersive X-ray Spectrometry (EDX). Fifteen laboratories from eight National Metrology Institutes (NMIs), one Designated Institute (DI) and six non-NMIs participated in this pilot study. Although the average atomic fractions of 18 data sets showed rather poor relative standard deviations of about 5.5 % to 6.8 %, they were greatly improved to about 1.5 % to 2.2 % by excluding 5 strongly deviating data sets from the average atomic fractions. In this pilot study, the average expanded uncertainties of SIMS, XPS, AES, XRF and EPMA were 3.84%, 3.68%, 3.81%, 2.88% and 2.90%, respectively. These values are much better than those in the key comparison K-67 for composition of a Fe-Ni alloy film. As a result, the quantification of CIGS films using the TNC method was found to be a good candidate as a subject for a CCQM key comparison.
Due to the extremely high specific surface area of nanoparticles and corresponding potential for adsorption, the results of surface analysis can be highly dependent on the history of the particles, particularly regarding sample preparation and storage. The sample preparation method has, therefore, the potential to have a significant influence on the results. This report describes an interlaboratory comparison (ILC) with the aim of assessing which sample preparation methods for ToF-SIMS analysis of nanoparticles provided the most intra- and interlaboratory consistency and the least amount of sample contamination. The BAM reference material BAM-P110 (TiO2 nanoparticles with a mean Feret diameter of 19 nm) was used as a sample representing typical nanoparticles. A total of 11 participants returned ToF-SIMS data,in positive and (optionally) negative polarity, using sample preparation methods of “stick-and-go” as well as optionally “drop-dry” and “spin-coat.” The results showed that the largest sources of variation within the entire data set were caused by adventitious hydrocarbon contamination or insufficient sample coverage, with the spin-coating protocol applied in this ILC showing a tendency toward insufficient sample coverage; the sample preparation method or the participant had a lesser influence on results.
A pilot study for the thickness measurement of HfO2 films was performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of this pilot study was to ensure the equivalency in the measurement capability of national metrology institutes for the thickness measurement of HfO2 films. In this pilot study, the thicknesses of six HfO2 films with nominal thickness from 1 nm to 4 nm were measured by X-ray Photoelectron Spectroscopy (XPS), X-ray Reflectometry(XRR), X-ray Fluorescence Analysis (XRF), Transmission Electron Spectroscopy (TEM), Spectroscopic Ellipsometry (SE) and Rutherford Backscattering Spectrometry (RBS). The reference thicknesses were determined by mutual calibration of a zero-offset method (Medium Energy Ion Scattering Spectroscopy (MEIS) of KRISS) and a method traceable to the length unit (the average thicknesses of three XRR data except the thinnest film). These reference thicknesses are traceable to the length unit because they are based on the traceability of XRR. For the thickness measurement by XPS, the effective attenuation length of Hf 4f electrons was determined. In the cases of XRR and TEM, the offset values were determined from a linear fitting between the reference thicknesses and the individual data by XRR and TEM. The amount of substance of HfO2, expressed as thickness of HfO2 films (in both linear and areal density units), was found to be a good subject for a CCQM key comparison.
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The final report has been peer-reviewed and approved for publication by the CCQM.
CCQM key comparison K-129 for the quantitative analysis of Cu(In,Ga)Se2 (CIGS) films has been performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The objective of this key comparison is to compare the equivalency of the National Metrology Institutes (NMIs) and Designated Institutes (DIs) for the measurement of mole fractions of Cu, In, Ga and Se in a thin CIGS film. The measurand of this key comparison is the average mole fractions of Cu, In, Ga and Se of a test CIGS alloy film in the unit of mole fraction (mol/mol). Mole fraction with the metrological unit of mol/mol can be practically converted to atomic fraction with the unit of at%.
In this key comparison, a CIGS film with certified mole fractions was supplied as a reference specimen to determine the relative sensitivity factors (RSFs) of Cu, In, Ga and Se. The mole fractions of the reference specimen were certified by isotope dilution - inductively coupled plasma/mass spectrometry (ID-ICP/MS) and are traceable to the SI. A total number counting (TNC) method was recommended as a method to determine the signal intensities of the constituent elements acquired in the depth profiles by Secondary Ion Mass Spectrometry (SIMS), X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). Seven NMIs and one DI participated in this key comparison. The mole fractions of the CIGS films were measured by depth profiling based-SIMS, AES and XPS. The mole fractions were also measured by non-destructive X-Ray Fluorescence (XRF) Analysis and Electron Probe Micro Analysis (EPMA) with Energy Dispersive X-ray Spectrometry (EDX).
In this key comparison, the average degrees of equivalence uncertainties for Cu, In, Ga and Se are 0.0093 mol/mol, 0.0123 mol/mol, 0.0047 mol/mol and 0.0228 mol/mol, respectively. These values are much smaller than that of Fe in a Fe-Ni alloy film in CCQM K-67 (0.0330 mol/mol). This means that the quantification of multi-element alloy films is possible by depth profiling analysis using the TNC method.
Our ability to produce and transform engineered materials over the past 150 years is responsible for our high standards of living today, especially in the developed economies. Yet, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of economy, energy, and climate. We are at the point where something must drastically change, and it must change NOW. We must create more sustainable materials alternatives using natural raw materials and inspiration from Nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments based on reliable and relevant data to quantify sustainability.
Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a key comparison, CCQM K55.b, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2010/2011. Nineteen national measurement institutes and the BIPM participated. Participants were required to assign the mass fraction of aldrin present as the main component in the comparison sample for CCQM-K55.b which consisted of technical grade aldrin obtained from the National Measurement Institute Australia that had been subject to serial recrystallization and drying prior to sub-division into the units supplied for the comparison.
Aldrin was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molar mass range 300 Da to 500 Da] and low polarity (pKOW < -2) for which related structure impurities can be quantified by capillary gas phase chromatography (GC).
The key comparison reference value (KCRV) for the aldrin content of the material was 950.8 mg/g with a combined standard uncertainty of 0.85 mg/g. The KCRV was assigned by combination of KCRVs assigned by consensus from participant results for each orthogonal impurity class. The relative expanded uncertainties reported by laboratories having results consistent with the KCRV ranged from 0.3% to 0.6% using a mass balance approach and 0.5% to 1% using a qNMR method.
The major analytical challenge posed by the material proved to be the detection and quantification of a significant amount of oligomeric organic material within the sample and most participants relying on a mass balance approach displayed a positive bias relative to the KCRV (overestimation of aldrin content) in excess of 10 mg/g due to not having adequate procedures in place to detect and quantify the non-volatile content–specifically the non-volatile organics content–of the comparison sample.
There was in general excellent agreement between participants in the identification and the quantification of the total and individual related structure impurities, water content and the residual solvent content of the sample.
The comparison demonstrated the utility of 1H NMR as an independent method for quantitative analysis of high purity compounds. In discussion of the participant results it was noted that while several had access to qNMR estimates for the aldrin content that were inconsistent with their mass balance determination they decided to accept the mass balance result and assumed a hidden bias in their NMR data. By contrast, laboratories that placed greater confidence in their qNMR result were able to resolve the discrepancy through additional studies that provided evidence of the presence of non-volatile organic impurity at the requisite level to bring their mass balance and qNMR estimates into agreement.
Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a key comparison, CCQM K55.a, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2009/2010. Eleven national measurement institutes and the BIPM participated. Participants were required to assign the mass fraction of estradiol present as the main component in the comparison sample (CCQM-K55.a) which consisted of a bulk estradiol hemihydrate material obtained from a commercial supplier that had been extensively but not exhaustively dried prior to sub-division into the units supplied for the comparison.
Estradiol was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molar mass range 300500 Da] and low polarity (pKOW < -2) for which related structure impurities can be quantified by capillary gas phase chromatography (GC) or by high performance liquid chromatography (LC).
The majority of participants used a mass balance approach to determine the estradiol content. The key comparison reference value (KCRV) for estradiol in CCQM-K55.a was assigned by combination of KCRVs assigned by consensus from participant results for each orthogonal impurity class. This allowed participants to demonstrate the efficacy (or otherwise) of their implementation of the mass balance approach and to demonstrate that their assigned value for the main component agreed with the KCRV through use of internally consistent contributing methods.
The KCRV for the estradiol content of the material was 984.3 mg/g with a combined standard uncertainty of 0.42 mg/g. The individual participant results showed that a relative expanded uncertainty for the purity assignment of 0.2% is a reasonable estimate of the best achievable result by an individual laboratory for a material of this complexity available in this amount at this level of purity. The relative expanded uncertainties reported by laboratories having results consistent with the KCRV ranged from 0.2% to 0.8%.
The review of results that were biased from the KCRV showed that two major analytical challenges are posed by the material: the measurement of its water content and controlling for related substance artefact formation during the analysis process. The results displaying a positive bias relative to the KCRV (overestimation of estradiol content) were due to underestimation of the water content of the material, while those with a negative bias (underestimation of estradiol) overestimated the total related substance impurities through a failure to detect and control for artefact formation arising from in situ oxidative dimerization of estradiol in neutral solution prior to analysis. There was however good agreement between all participants in the identification and the quantification of the individual related structure impurities actually present in the sample.
The comparison also demonstrated the utility of high-field 1H NMR for both quantitative and qualitative analysis of high purity compounds. It is noted that all the participants who used qNMR as a major or contributing technique and included it as part of, combined it or confirmed it with a conventional 'mass balance' data estimate, obtained results consistent with the KCRV.
An international comparison study on the accurate determination of the molar mass M(Si) of silicon artificially enriched in 28Si (x(28Si) > 0.9999 mol mol−1) has been completed. The measurements were part of the high level CCQM-P160 pilot study assessing the ability of National Metrology Institutes (NMIs) and Designated Institutes (DIs) to make such measurements at the lowest possible levels of measurement uncertainty and to identify possible difficulties when measuring this kind of sample. This study supports the molar mass measurements critical to disseminating the silicon route to realizing the new definitions for the kilogram and the mole. Measurements were also made by one external research institute and an external company. The different institutes were free to choose their experimental (mass spectrometric) set-ups and equipment, thereby enabling also the comparison of different techniques. The investigated material was a chemically pure, polycrystalline silicon material. The subsequent modified single crystalline secondary product of this material was intended for the production of silicon which was used for two additional spheres in the context of the redetermination of the Avogadro constant NA, required for the revision of the International System of Units (SI) via fundamental constants which came into force from May 2019. The CCQM pilot study was organized by Physikalisch-Technische Bundesanstalt (PTB). Aqueous silicon solutions were shipped to all participating institutions. The data analysis as well as the uncertainty modelling and calculation of the results was predefined. The participants were provided with an uncertainty budget as a GUM Workbench® file as well as a free software license for the duration of the comparison. The agreement of the values of the molar mass (M(Si) = 27.976 942 577 g mol−1) was excellent with ten out of 11 results reported within the range of relative uncertainty of 1 × 10−8 required
for the revision of the SI.