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Der Mangel an Anwendungsrichtlinien und Validierungsverfahren für struktur-eingebettete faseroptische Dehnungssensoren, insbesondere auf Faser-Bragg-Gitter (FBG)-Basis, führte bislang dazu, dass diese Sensoren trotz ihrer hervorragenden Eigenschaften im Bereich der kommerziellen Material- und Strukturüberwachung nur in geringem Umfange eingesetzt wurden. Fragen zur Degradation der Sensoren unter Beanspruchung, Alterung durch klimatische Einflüsse und Enthaftung infolge Belastung der Struktur konnten bisher nur theoretisch simuliert oder anhand exemplarischer Proben für einzelne einflussnehmende Parameter im Labor untersucht werden. Die Erfassung des Sensorverhaltens im Bauteil unter komplexen Umwelteinflüssen während des Bauteilbetriebes, um damit eine Aussage zur Zuverlässigkeit der Sensormessdaten zu gewinnen, war bisher nicht möglich.
Im Forschungsprojekt FAMOS² wurde deshalb von 2014 bis 2018 die Realisierung eines Autodiagnoseverfahrens für faseroptische Dehnungssensoren erarbeitet, um die Funktionszuverlässigkeit und Langzeitstabilität der Sensoren während des Bauteilbetriebes innerhalb einer Bauteilstruktur bewerten zu können. Im Rahmen des Forschungsprojektes wurde gezeigt, dass ein FBG-Sensor mit einer speziell angepassten magnetostriktiven Schicht magnetisch so angeregt werden kann, dass mit einer zugeschnittenen Messmethodik zu jedem Zeitpunkt eine Bewertung der Sensorzuverlässigkeit unter Betriebsbedingungen möglich ist. Die auf den Sensor aufgebrachte magnetostriktive Schicht erzeugt bei Anregung mit einem passenden Magnetfeld eine gepulste, synthetische Dehnung. Diese Dehnung steht in einem definierten Verhältnis zum anregenden Magnetfeld und wird optisch über die Verschiebung der Bragg-Wellenlänge ausgelesen. Die Konstanz dieses Verhältnisses stellt dann ein Maß für die korrekte Funktionsfähigkeit des Sensors dar. Das Beschichtungs-verfahren, das magnetische Anregungs- und optische Ausleseverfahren, wie auch die Validierung des Sensors unter Berücksichtigung faseroptischer Effekte wurden während des Projekts konzeptionell entwickelt, aufgebaut und charakterisiert. Qualitativ kann mit diesem Verfahren zunächst eine Gut-/Schlecht-Beurteilung des Sensors vorgenommen werden. Perspektivisch bietet das Verfahren jedoch auch die Möglichkeit, verschiedene Versagensmechanismen bestimmen und klassifizieren zu können. Es zeichnete sich schon während des Projektverlaufs ab, dass sich aus den erzielten Ergebnissen über das Autodiagnoseverfahren hinaus weitere Anwendungsmöglichkeiten für den Einsatz des kombinierten magnetostriktiv-faseroptischen Sensorprinzips, beispielsweise als reiner Magnetfeldsensor, ergeben.
Nach Abschluss dieses Forschungsprojekts besteht nun die Möglichkeit, den Funktionszustand faseroptischer Dehnungssensoren jederzeit unabhängig von Alter, Belastung oder Kenntnis eines Referenzzustands zu einem bestimmten Zeitpunkt bestimmen zu können. Aufbauend auf diesen Ergebnissen können weiterführende Forschungen die Messmethodik vertiefend charakterisieren und weitere Anwendungsfälle erschließen.
Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products.
Der Vortrag gibt den aktuellen Stand der Normung im Bereich der Oberflächen-technik insbesondere der Oberflächenanalytik und der Oberflächenmess- und -prüftechnik wider. Vorgestellt wird der Status technischer Berichte, Normenentwürfe und Normen u.a. zur Charakterisierung von funktionellen Glasoberflächen für bioanalytische Anwendungen, zur Messung der Schichtdicke von Nanomaterialien mittels Ellipsometrie, zur Kalibrierung von Interferometern und Interferenzmikroskopen für die Formmessung, zur Rockwelleindringprüfung zur Bewertung der Schicht-haftung, zu den Grundlagen der Ellipsometrie, zur Messung der Schichtdicke mittels Wirbelstromverfahren, zur Schichtpotentialmessung von Mehrfach-Nickelschichten, zu Filtern und Augenschutzgeräten gegen Laserstrahlung sowie zur Bestimmung der Schichthaftung mittels Zugversuch.
The performance of functional coatings and adhesively joined hybrid components relies strongly on the stability of the polymer-metal interface. With the increasing utilization of multi-material structures in the automotive and aerospace industry, it is of great scientific and technical interest to understand the processes leading to interface degradation and to develop novel strategies to increase corrosion and delamination resistance.
The aim of this project is to develop thin epoxy-based films on aluminium alloy AA2024-T3 as a model system and to investigate their interfacial stability under corrosive and coupled corrosive-mechanical load. Electrochemical and spectroscopic methods were used for the characterisation of the film properties and in situ corrosion experiments were performed by means of AFM. The deformation properties of the aluminium alloy and the model coatings were investigated by means of scanning Kelvin probe force microscopy (SKPFM) utilizing the integrated tensile stage.
The presentation will give a brief overview of the capabilities of the new AFM setup to foster future collaborations and summarize our work on the interface stability of model coatings.
The stabilization of crystal phases and nanostructured morphologies is an essential topic in application-driven design of mesoporous materials. Many applications, e.g. catalysis, require high temperature and humidity. Typical metal oxides transform under such conditions from a metastable, low crystal-line material into a thermodynamically more favorable form, i.e. from ferrihy-drite into hematite in the case of iron oxide. The harsh conditions induce also
a growth of the crystallites constituting pore walls, which results in sintering and finally collapse of the porous network. Herein, a new method to stabi-lize mesoporous templated metal oxides against sintering and pore collapse is reported. The method employs atomic layer deposition (ALD) to coat the internal mesopore surface with thin layers of either alumina or silica. The authors demonstrate that silica exerts a very strong influence: It shifts hematite formation from 400 to 600 °C and sintering of hematite from 600 to 900 °C.
Differences between the stabilization via alumina and silica are rationalized by a different interaction strength between the ALD material and the ferrihydrite film.
The presented approach allows to stabilize mesoporous thin films that require a high crystallization temperature, with submonolayer quantity of an ALD material, and to apply mesoporous materials for high temperature applications.
Surface analysis is still gaining importance, as most modern technology is in essence surface and thin film technology. In microelectronics and optics but also in many fields of energy storage and conversion, thin surface layers or structured surfaces are key components. Optical surface measurements are useful because of their reliability, robustness, and scalability – properties, which are especially desirable in a production environment. However, many of these methods take require considerable effort in data analysis. Spectroscopic ellipsometry (SE) is maybe the prime example of this class of methods. To combine the advantages of SE with metrological trueness and traceability, we combine it in a group of other methods, such as electron microscopy, instrumental surface analysis, X-ray diffraction.
This presentation will give an overview on the principles of SE, its available quantities and the general properties of this measurement technique. Several examples from current and past projects of BAM-6.7 will show how a measurement community involving ellipsometry can benefit many fields of interest, from polymer science to energy applications. In the context of creating a “measurement landscape”, standardisation and standard compliance play an important role. The efforts of BAM in standardisation and accrediting of ellipsometry will be shown demonstrating the possible impact on quality assurance in different fields of technology.
UV-curing coatings are nowadays widely used due to their unique advantages. High-quality coatings can be obtained at short curing times and low temperatures so that thermal stress to the substrate is minimised. Photocured Cycloaliphatic-Epoxy Oligosiloxane (CEO) resin was reported to be used as encapsulation material for organic electronics. However, further reinforcement of CEO film properties is desired to achieve requested device lifetime.
In this work we introduced Boehmite nanoparticles (BA) into CEO matrix in order to modify the film properties and study the main changes of the material behaviour with regard to its photocuring kinetics, thermal stability and glass transition. Particular interest was focused on the role of particle surface in nanocomposite properties. Hence, BA particles without (HP14) and with organic surface modifier (OS1) at different loadings (up to 10 wt%) were applied in this study. Morphology investigation with SEM operated in transmission mode showed good BA dispersion forming network-like structure. At the same time, distribution of particles differed for HP14 and OS1 as a result of different interaction in CEO-solvent-particles system. CEO structure obtained via non-hydrolytic sol-gel reaction was verified by 13C and 29Si NMR. In situ monitoring of film curing was performed using RT-IR spectroscopy. No significant modification of final convention degree with particle incorporation was observed in contrast to considerable decrease of curing efficiency reported previously for similar system by Esposito et al.,2008. Further, cured hybrid nanocomposite films were analysed by TGA and DSC, which revealed impact of surface modifier on film thermal properties.
Organic-inorganic nanostructured materials have drawn much attention over the past decade, particularly due to their versatile and outstanding properties. Possessing the properties between those of polymers and those of glasses, siloxane-based resins are non-toxic, easy to synthesize and process hybrid materials, that hold a promising potential in the field of advanced coatings.
Photocurable resins are nowadays widely used as coatings due to their unique advantages. In particular, cationic ring-opening curing is not inhibited by oxygen, leads to low degree of shrinkage and superior adhesion. The most important, it enables production of high-quality coatings within short exposure times without applying temperature, thus, minimizing the presence of the thermal stress in the substrate. Photocured Cycloaliphatic-Epoxy Oligosiloxane (CEO) resin was reported to be used as encapsulation material for organic electronics. However, further reinforcement of CEO properties is desired to achieve requested device lifetime. One of the common approaches to improve material characteristics is by embedding inorganic nanoparticles into polymer matrix. It has been shown that the resulted nanocomposites exhibit enhanced functional properties included but not limited by optical, mechanical, thermal and barrier ones.
In this work we focused on the incorporation of Boehmite nanoparticles (BA) into CEO matrix as a tool to strengthen the film properties and to study the main changes occurred in the material behavior with regard to its photocuring kinetics, thermal stability and glass transition. Particular interest was focused on the role of particle surface in nanocomposite properties. Hence, BA particles without (HP14) and with organic surface modifier (OS1) at different loadings
(up to 10 wt%) were applied in this study. Morphology investigation with SEM operated in transmission mode showed good BA dispersion forming
network-like structure. At the same time, distribution of particles differed for HP14 and OS1 as a result of different interaction in CEO-solvent-particles system. CEO structure obtained via non-hydrolytic sol-gel reaction was verified by 13C and 29Si NMR. In situ monitoring of film curing was performed using
RT-IR spectroscopy. A slight increase of final convention degree with particle incorporation was observed in contrast to the considerable decrease of curing efficiency reported previously for similar system. Further, the cured hybrid nanocomposite films were analyzed by TGA and DSC, which revealed impact of surface modifier on thermal stability and glass transition temperature.
Many ambient desorption/ionization mass spectrometry (ADI-MS) techniques rely critically on thermal desorption. Meanwhile, the analyte classes that are successfully studied by any particular ADI-MS methods are strongly dependent on the type of ionization source. Generally, spraybased ionization sources favor polar analytes, whereas plasmabased sources can be used for more hydrophobic analytes and are more suitable for molecules with small molar masses. In the present work, classic atmospheric-pressure chemical ionization (APCI) is used. To provide improved desorption performance for APCI, a surface acoustic wave nebulization (SAWN) device was implemented to convert liquid analytes into fine airborne particles. Compared to conventional SAWN that is used solely as an ionization source for liquid samples, the coupling of SAWN and APCI significantly improves ion signal by up to 4 orders of magnitude, reaching comparable ion abundances to those of electrospray ionization (ESI). Additionally, this coupling also extends the applicable mass range of an APCI source, conventionally known for the ionization of small molecules <500 Da. Herein, we discuss cursory evidence of this applicability to a variety of analytes including both polar and nonpolar small molecules and novel peptides that mimic biomolecules upward of 1000 Da. Observed species are similar to ESI-derived ions including doubly charged analyte ions despite presumably different charging mechanisms. SAWN−APCI coupling may thus involve more nuanced ionization pathways in comparison to other ADI approaches.
Uptake and molecular impact of aluminum-containing nanomaterials on human intestinal caco-2 cells
(2018)
Aluminum (Al) is one of the most common elements in the earth crust and increasingly used in food, consumer products and packaging. Its hazard potential for humans is still not completely understood. Besides the metallic form, Al also exists as mineral, including the insoluble oxide, and in soluble ionic forms. Representatives of these three species, namely a metallic and an oxidic species of Al-containing nanoparticles and soluble aluminum chloride, were applied to human intestinal cell lines as models for the intestinal barrier. We characterized physicochemical particle parameters, protein corona composition, ion release and cellular uptake. Different in vitro assays were performed to determine potential effects and molecular modes of Action related to the individual chemical species. For a deeper insight into signaling processes, microarray transcriptome analyses followed by bioinformatic data analysis were employed. The particulate Al species showed different solubility in biological media. Metallic Al nanoparticles released more ions than Al2O3 nanoparticles, while AlCl3 showed a mixture of dissolved and agglomerated particulate entities in biological media. The protein corona composition differed between both nanoparticle species. Cellular uptake, investigated in transwell experiments, occurred predominantly in particulate form, whereas ionic Al was not taken up by intestinal cell lines. Transcellular transport was not observed. None of the Al species showed cytotoxic effects up to 200 mg Al/mL. The transcriptome analysis indicated mainly effects on oxidative stress pathways, xenobiotic metabolism and metal homeostasis. We have shown for the first time that intestinal cellular uptake of Al occurs preferably in the particle form, while toxicological effects appear to be ion-related.
Ferritic high temperature alloys are widely used as boiler tube and heat exchanger materials in coal, biomass and co-fired power plants. All technologies have in common that the applied materials are exposed to different temperatures, process pressures and reactive atmospheres that lead to a change of the material properties and a further degradation of the material. Material changes caused by aging in highly corrosive and toxic gases such as SO2 are mainly studied ex situ after the reaction is finished. The solid material is deposited in the atmosphere for a certain period of time, and material changes are then examined by various microscopic techniques such as optical microscopy (OM), electron microprobe analysis (EMPA), scanning electron microscopy (SEM and TEM) and X-ray diffraction (XRD). Nevertheless, extensive efforts were made to study material changes of high temperature alloys under oxidizing and reducing atmospheres by environmental scanning electron microscopy or in situ TEM techniques However, the possibilities of microscopic in situ techniques are very limited for the use of highly corrosive and toxic gases such as SO2. Since Sulfur induced corrosion at temperatures relevant for coal and biomass fired power plants, which is causing breakaway oxidation and sulfide precipitation at grain boundaries, is still of scientific interest, the current work focuses on the effect of SO2 in an initial stage of corrosion of ferritic alloys. For the analysis of early stages of combined oxidation and sulphidation processes of Fe-Cr model alloys the usage of a light furnace to conduct a rapid reactive annealing experiment is feasible. Previous studies presented distinct results of the influence of chromium on early high temperature corrosion by SO2 by this technique and subsequent classical metallographic analyses. However, it is still not possible to trace the corrosion mechanism in real time by conducting single aging experiments. The current work introduces two different approaches to study the initial stages of high temperature oxidation processes by applying above state of the art X-ray diffraction and spectroscopy methods. One part focuses on the real time observation of the formation of corrosion products such as oxides and sulfides by energy dispersive X-ray diffraction (EDXRD). The potential of this technique to study crystallization and growth processes of thin films in a reactive environment in real time was previously shown for different compound semiconductors. This approach was now applied to follow oxidation and sulphidation processes of ferritic model alloys in SO2 and SO2/H2O environments. The diffraction signals of the X-rays were detected during the corrosion process and the peak area and positions were analyzed as a function of time. This procedure enables monitoring external oxide growth and material loss in real time in an early stage of corrosion.
The other part of the current work presents the possibilities of X-ray absorption near edge structure spectroscopy (XANES) to characterize oxide scales and their growth mechanisms. Precise phase identification and quantification of corrosion products in a multi-phase oxide/sulfide scale is a pre-requisite to understand diffusion paths of metal ions and gas components. It is a challenging task to distinguish structurally similar reaction products such as Fe3O4 and FeCr2O4 especially in thin films with texture effects by diffraction. To illustrate for example Cr-out diffusion of an alloy throughout an inner and external oxide scale the differentiation of Fe3O4 and FeCr2O4 is indispensable. XANES uses the photoionization effect at the metal absorption edge in an aging product and accesses by this structural and chemical information. The current work uses XANES at the Fe-K and Cr-K absorption edge to identify various aging products grown as thin layers on alloys after short time aging experiments. A reaction chamber for combining high temperature oxidation experiments with surface sensitive X-ray absorption near edge structure spectroscopy will be introduced and first results of XANES on scales at high temperatures will be presented.
Ferritic-martensitic alloys with 12-16 % Cr in weight are subject to devices for various energy systems, such as coal power plants and waste incineration plants. These materials are exposed to a highly corrosive environment which lead to a degradation of the material. Especially the simultaneous oxidation and sulfidation is thereby of special interest. Proper spatially resolved measurements that determine not only chemical compositions but phases are rare. However, precise phase identification and quantification of corrosion products within the multi-phase corrosion scales is a key aspect to understand diffusion paths of metal ions and gas ions/molecules. This study investigated Fe-Cr model alloys with Cr contents from 0 to 13 % in weight in 0.5 % SO2 and 99.5 % Ar atmosphere to aim in a fundamental and systematic analysis. Samples were aged at 650 °C for time scales from 12 h to 250 h. The results presented here correspond to depth dependent phase identification of oxide and sulphide phases in the corrosion scales by using X-ray absorption near edge spectroscopy (XANES). Per sample a series of ca. 20 spots (1-5 µm spot size) from scale-gas to scale-metal interface were measured. XANES spectroscopy was performed at the Fe-K edge (7.11 keV) on polished cross sections. The collected spectra were fitted to a combination of reference materials to quantify the present phases at different positions within the scale.The phase distribution differs with Cr content and the Cr diffusion through pure Fe-oxide and mixed Fe-Cr-oxide phases is discussed.
The presence of polycarboxylate ether (PCE) based superplasticizers (SPs) has an enormous influence on the early hydration of cement. The hydration is retarded and the timing of formation and the morphology of hydrates is affected. This short paper presents experimental results about the influence of delayed addition time of PCE SPs on hydration of cement and alite pastes, investigated by isothermal heat flow calorimetry. For cement as well as for alite pastes the hydration is retarded with SP, whereby the high charge PCE has a stronger retarding effect than the low charge PCE. The retardation caused by PCE is much more pronounced for alite than for cement mixes. If PCE is added later to the mix, the induction period is shortened and the hydration is accelerated compared to simultaneous addition. This applies for cement and alite pastes. With delayed PCE addition the alite shows a clearly less retarded setting and main hydration than after simultaneous addition. It is obvious that for alite pastes there is less retardation the later the addition of SP.
Clustering of magnetic nanoparticles can drastically change their collective magnetic properties, which in turn may influence their performance in technological or biomedical applications. Here, we investigate a commercial colloidal dispersion (FeraSpinTMR), which contains dense clusters of iron oxide cores (mean size around 9 nm according to neutron diffraction) with varying cluster size (about 18–56 nm according to small angle x-ray diffraction), and its individual size fractions (FeraSpinTMXS, S, M, L, XL, XXL). The magnetic properties of the colloids were characterized by isothermal magnetization, as well as frequency-dependent optomagnetic and AC susceptibility measurements. From these measurements we derive the underlying moment and Relaxation frequency distributions, respectively. Analysis of the distributions shows that the clustering of the initially superparamagnetic cores leads to remanent magnetic moments within the large clusters. At frequencies below 105 rad s−1, the relaxation of the clusters is dominated by Brownian (rotation) relaxation. At higher frequencies, where Brownian relaxation is inhibited due to viscous friction, the clusters still show an appreciable magnetic relaxation due to internal moment relaxation within the clusters. As a result of the internal moment relaxation, the colloids with the large clusters (FSL, XL, XXL) excel in magnetic hyperthermia experiments.
Nowadays, different nanoparticles have been developed for commercial applications. However, since data on toxicity are barely available, their increasing application in cosmetic products, food and their release in the environment might cause severe problems. An accurate separation, identification and characterization of nanoparticles becomes increasingly important1,2.
In this presentation, a two-dimensional separation approach based on AF4 and CE was showed and used to separate NPs with similar sizes but different coatings. Standard reference polystyrene NPs having comparable core sizes but different coatings were investigated. Different migration time and profiles were compared. Separation in either method resulted in non-baseline resolved or non-separated peaks. In contrast, two-dimensional coupling of AF4 and CE resulted in clearly separated regions in their 2 D plots in case of 20 and 50 nm particle mixtures, whereas the 100 nm NP mixture could not be separated. Various factors affecting the separation like hydrodynamic diameter or SDS concentration were discussed.
Future investigations will be focussed on inorganic NPs with differently charged coatings. There, AF4-CE coupling can be coupled with inductively coupled plasma mass spectrometry (ICP-MS) to enhance the sensitivity of this method.
Nowadays, different nanoparticles have been developed for commercial applications. However, since data on toxicity are barely available, their increasing application in cosmetic products, food and their release in the environment might cause severe problems. An accurate separation, identification and characterization of nanoparticles becomes increasingly important.
A common method for nanoparticle separation, which was introduced in 1976 by Giddings, represents asymmetrical field-flow fractionation (AF4). It is a flow based separation method, which can be theoretically used to separate particles range from 1 nm to 50 µm. However, when the particles are smaller than 10 nm, separation with AF4 will become difficult to perform. Because in this case strong separation force, which induces aggregation of particles, should be applied. This will decrease recoveries of analytes and limit its application in accurate quantitative analysis. Capillary electrophoresis (CE) is another well-developed separation technique, in which samples will be separated in relation to their electrophoretic mobility. In recent years, CE has been used to separate different kinds of nanoparticles like, gold colloids or CdSe Quantum dots. However, till now only separation of particles smaller than 50 nm was reported. Because large size distribution of bigger particles will result in strong peak broadening and long separation time.
A two-dimensional coupling of AF4 and CE might provide us a new separation method, which can extend the separation ranges of both methods and be a way to characterise particles with large size distributions.
Nowadays, different nanoparticles have been developed for commercial applications. However, since data on toxicity are barely available, their increasing application in cosmetic products, food and their release in the environment might cause severe problems. An accurate separation, identification and characterization of nanoparticles becomes increasingly important.
A common method for nanoparticle separation, which was introduced in 1976 by Giddings, represents asymmetrical field-flow fractionation (AF4). It is a flow based separation method, which can be theoretically used to separate particles range from 1 nm to 50 µm. However, when the particles are smaller than 10 nm, separation with AF4 will become difficult to perform. Because in this case strong separation force, which induces aggregation of particles, should be applied. This will decrease recoveries of analytes and limit its application in accurate quantitative analysis. Capillary electrophoresis (CE) is another well-developed separation technique, in which samples will be separated in relation to their electrophoretic mobility. In recent years, CE has been used to separate different kinds of nanoparticles like, gold colloids or CdSe Quantum dots. However, till now only separation of particles smaller than 50 nm was reported. Because large size distribution of bigger particles will result in strong peak broadening and long separation time.
A two-dimensional coupling of AF4 and CE might provide us a new separation method, which can extend the separation ranges of both methods and be a way to characterise particles with large size distributions.
The accumulation of plastics leaked into the environment achieve a high perception in the last years. It is uncontroversial that often an uncontrolled, high consumption of plastic products and a poor waste management resulted in plastic findings all over in the environment. However, less is known about the relevant pathways and fate of plastic in the environment. Especially plastic fragments smaller 5 mmm, so called microplastics, achieve a high attention, because their amount and risks arising from these fragments are still unknown. The basic mechanisms of plastic or more precise, of different polymer degradation processes are often not considered, resulting in unrealistic statements.
For generation of fundamental understanding of this problem we developed in the last years a fast thermoanalytical method for identification and mass quantification of microplastics in complex samples. The presentation will also give a short introduction about polymer degradation.
Microbially influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) which act upon the metal by the reactiveness of hydrogen sulfide, and by withdrawal of the available electrons in electrical contact with the metal. Methanogenic archaea can also cause MIC by directly withdrawing electrons from the iron surface for methanogenesis. However, the mechanistic details and kinetics of the overall process are poorly understood. Precipitation of siderite, a by-product of methanogenesis, (4Fe + 5HCO3 + 5H+ 4FeCO3 + CH4 + 3H2O) can lead to an insulating layer on the metal surface and lower the corrosion rate. Still, the extent of FeCO3 precipitation may be significantly influenced by environmental conditions such as pH and advective processes.
The paper presents rheometric results and hydration curves for cementitious systems based on cement mixed with different aqueous phases at solid volume fraction of = 0.45. The varied aqueous phases were deionized water, limewater, the filter residue of a cement paste mixed at w/c = 2.0, and the filtrate of cement paste at solid volume fraction of 0.45. Each cementitious system provided different amounts and sizes of particles formed in the aqueous phase. The pastes were observed with and without polycarboxylate ether based superplasticizer. It was observed that the presence of particles causes higher PCE saturation dosages to achieve a minimum value, but the minimum value is only affected in the case of large particles. In all cases with and without PCE, the presence of small particles causes increased plastic viscosity. In addition, with decreased number and size of hydrates in the aqueous phase the hydration was retarded, which was specifically pronounced in the presence of PCE
To investigate early stage corrosion processes of stainless steel 1.4301 taking place during the biofilm formation of the organism Shewanella putrefaciens electrochemical impedance spectroscopy (EIS) in a multielectrode approach has been used. The multielectrode array consisted of up to 25 electrically isolated electrodes made of stainless steel wires of diameters ranging from 100 µm to 500 µm. They were connected to a multichannel microelectrode analyzer (MMA) electrically coupled through zero resistance ammeters. Current flow between electrodes in the array as well as changes in impedance of individual electrodes over time were recorded and analyzed with respect to the onset of localized corrosion and biofilm formation. The results were complemented by optical microscopy, SEM and AFM images which were taken immediately after the respective experiment. To verify that the multielectrode arrays correctly indicated the initial stages of the corrosion process and of biofilm formation they were introduced in a flow cell reaction vessel containing test specimens made from stainless steel 1.4301, which were checked regularly for signs of localized corrosion and biofilms. Preceding results with the multielectrode array in solutions containing high amounts of chloride ions and hydrogen peroxide at low pH also showed that it is possible with the MMA to monitor individual electrodes becoming local anodes as local corrosion set in, while the remaining electrodes predominantly acted as cathodes.
We report a new method for top-down one-pot, gram-scale production of high-quality nanographene from graphite under mild conditions. The nanographene sheets had a very low oxygen content, comparable to that of nanographene grown by chemical vapor deposition. This method is easily scalable and comparatively mild, opening the door to an environmentally friendly process to produce high-quality nanographenes.
Nanographene sheets were further covalently functionalized using a non-destructive [2+1] cycloaddition reaction that left the π-conjugated system intact.
Near-ambient pressure XPS makes it possible to characterise samples not compatible to ultra-high vacuum, and enables the study of liquid-solid, gas-liquid and gas-solid interfaces. NAP-XPS meas-urements of biofilms, suspended nanoparticles and metal-organic frameworks were performed with EnviroESCA developed by SPECS.
An interesting application is surface characterisation of biofilms, which are bacterial communities embedded in a self-produced polysaccharide matrix. Various model systems ranging from pure polysaccharides of alginate to biofilms harvested directly from the growth medium have been char-acterised in humid conditions[1].
NAP-XPS also makes it possible to characterise nanoparticles in solution. Silver nanoparticles in aqueous solution were characterised and the Ag 3d-spectrum compared to spectra obtained of dried nanoparticles in UHV-conditions[2]. The binding energy of the Ag 3d-core level peak was shifted by 0,6 eV towards higher binding energy for suspended nanoparticles compared to the dried sample measured in UHV. This can be assigned to a change in surface potential at the water-nanoparticle interface.
Metal-organic frameworks (MOFs) are suitable materials for gas storage of small molecules due to their nanoporous, crystalline structure. However, instability in humidity remains an issue for many types of MOFs. XPS-measurements of the MOF-structure HKUST-1 were performed in various NAP-conditions to assess the stability of the sample and its interaction with the gas molecules as water, methanol and pyridine.
For years there have been more and more reports on the presence of drugs in the aquatic environment. Due to the demographic change, the consumption of pharmaceuticals has risen sharply. After taking the drugs, they are partly metabolized in the human body. However, the metabolism is not complete so that both the metabolites and non-metabolized amounts of the parent compounds are excreted. These compounds reach the waste water and afterwards the sewage treatment plants. In sewage treatment plants transformation products can be formed by the oxidative conditions during wastewater treatment processes. The transformation products may have a higher toxicity than the actual environmental pollutants and are often only partly removed during the waste water treatment. Since a lot of these compounds are still unknown, the transformation products are not detected by target analysis used in sewage treatment plants and are often released undetected in the aquatic ecosystems. The released substances may be subject to additional transformation processes in the environment. Pharmaceuticals produced in high amounts can be already detected in the μg/L range in water bodies worldwide.
Metformin and its major transformation product guanylurea are one of the main representatives. Metformin is the drug of choice for treating type 2 diabetes. The drug therapy for diabetes mellitus has increased significantly in recent years. In the year 2015 1500 tons of metformin were prescribed in Germany (for statutory insured persons). Metformin is not metabolized in the human body and is excreted unchanged therefore concentrations between 57 μg/L and 129 μg/L are found in German waste water treatment plants influents.
In this work the transformation of the antidiabetic drug metformin is investigated. The degradation of metformin is initialize by commercial water treatment techniques like UV-radiation or noncommercial techniques like heterogenous photocatalysis based on titanium dioxide. The degradation of metformin and resulting transformation products are analyzed by LC-MS/MS and LC-HRMS.
Different strategies for the synthesis of polylactides were presented with special focus on Ring-opening Polymerization (ROP) and simultaneous ROP and Polycondensation (ROPPOC) mechanism. The mechanism of the formation of cyclic Polyesters is discussed in detail and established theories about the formation of cycles in polycondensation reactions are critically reviewed.
We present the synthesis of four mesoporous templated iron oxides: Ferrihydrite, Hematite, Maghemite, Magnetite/Maghemite and the influence of water on the crystallization mechanism and the kinetics. The absence of water stabilize the ferrihydrite structure. By monitoring the dissolution in situ by using a QCMB and ex situ microscopy we got details in the dissolution mechanism of ferrihydrite.
Polynuclear aluminium species (Al13 keggin cluster) find application in different areas like water purification [1], contaminant transport [2], and as pilling clays with high specific surface areas[3], due to their strong binding ability to aggregates and high positive charge.
In the present contribution, we report on the in situ investigation of the Al13 sulfate synthesis by synchrotron wide-angle X-ray scattering (WAXS). Al13 cluster were crystallized by precipitating hydrolyzed aluminum solutions by the addition of sodium sulfate. The measurements were performed using a custom-made acoustic levitator as sample holder. The study provides information about the intermediates during the crystallization process. From the data, a mechanism was derived indicating the influence of the crystallization process.
Micro-concentrator solar cells offer an attractive way to further enhance the efficiency of planar-cell technologies while saving absorber material. Here, two laser-based bottom-up processes for the fabrication of regular arrays of CuInSe2 and Cu(In,Ga)Se2 microabsorber islands are presented, namely one approach based on nucleation and one based on laser-induced forward transfer.
Additionally, a procedure for processing these microabsorbers to functioning micro solar cells connected in parallel is demonstrated. The resulting cells show up to 2.9% efficiency and a significant efficiency enhancement under concentrated Illumination.
The state of fresh concrete is predominantly determined by the rheological properties of the cement paste. In order to control performance spectra and requirements of novel concretes and to better understand macroscopic phenomena, comprehensive knowledge of the material behavior of fresh cement suspensions as well as of the complex relationships of mechanisms at the nano and micro scale are necessary. This work focuses on micro and nano rheology of suspensions of cementitious model systems and the influence of polycarboxylate-based admixtures on the rheology. The phenomena are driven by multiple parameters such as adsorption and particle interactions. Hence, the first part examines the interaction between polycarboxylate ether (PCE) and synthesized clinker phases and hydration products as model systems with regard to early hydration products.
Mechanochemistry is a fast and efficient method applicable for the synthesis of new organic[1], metal-organic[2], and inorganic[3] compounds. The direct monitoring of milling reactions is still challenging. The underlying reaction mechanisms remain often unclear. In the last years, have established a tandem in situ approach for investigating mechanochemical reactions using time-resolved in situ XRD coupled with Raman spectroscopy.[4] Here, we present an in situ coupling of synchrotron XRD, Raman spectroscopy, and thermography allowing the observation of mechanochemical reactions in real time.[5] Information on the crystalline, molecular, and temperature state of the materials during grinding could be collected. The chemical composition of the reaction mixture was found to be directly correlated with changes in the temperature profile of the reaction. Furthermore, the presented setup allows the detection of crystalline, amorphous, eutectic as well as liquid intermediates. The resulting deeper kinetic and thermodynamic understanding of milling processes is the key for future optimization of mechanochemical syntheses.
Mechanochemistry is increasingly used for synthesizing various materials including metal organic compounds and cocrystals. Although this synthesis approach offers a fast and pure synthesis in high yields, there is a lack in understanding the mechanisms of milling reactions. The necessary data can only be obtained in in situ experiments, which were only recently established for milling reactions. Herein, we present a novel setup enabling a combined in situ investigation of mechanochemical reactions using synchrotron XRD and Raman spectroscopy.
Mechanochemistry is a versatile approach for green and fast synthesis of pure substances. The exploration of the chemistry of metal phosphonates has gained considerable interest during the last decades due to their structural diversity. We synthesized manganese phosphonates in milling reactions. The mechanochemical reactions were investigated in situ to reveal the underlying mechanisms.
Mechanochemistry is a fast and efficient method applicable for the synthesis of new organic[1], metal-organic[2], and inorganic[3] compounds. The direct monitoring of milling reactions is still challenging. The underlying reaction mechanisms remain often unclear. In the last years, have established a tandem in situ approach for investigating mechanochemical reactions using time-resolved in situ XRD coupled with Raman spectroscopy.[4] Here, we present an in situ coupling of synchrotron XRD, Raman spectroscopy, and thermography allowing the observation of mechanochemical reactions in real time.[5] Information on the crystalline, molecular, and temperature state of the materials during grinding could be collected. The chemical composition of the reaction mixture was found to be directly correlated with changes in the temperature profile of the reaction. Furthermore, the presented setup allows the detection of crystalline, amorphous, eutectic as well as liquid intermediates. The resulting deeper kinetic and thermodynamic understanding of milling processes is the key for future optimization of mechanochemical syntheses.
The exploration of metal phosphonates chemistry has gained great interest during the last decades, because of their structural diversity. Transition metal phosphonates are promising candidates for an application as electrocatalysts in oxygen evolution reactions (OER).
Here, we present the in situ investigation of mechanochemical syntheses of different manganese phosphonates by synchrotron X-ray diffraction. Nitrilotri(methylenephosphonic acid) and N,N-Bis(phosphonomethyl)glycine were chosen as ligands. The liquid-assisted milling process can be divided into three steps, including an amorphous stage. One of the products has not been obtained by classical solution chemistry before.
These metal phosphonates and/or their derivatives are considered to be active in electrochemical energy conversion. The verification of their applicability is one of the topics of our resent research.
Mechanochemistry is known for short reaction times, nearly quantitative conversions, and decreasing amount of solvents. Among organic syntheses, the Knoevenagel condensation is an important C-C bond forming reaction. We investigated the reaction of benzaldehyde derivates (nitro- and fluoro-derivates) with malononitrile syntheses by a combination of different in situ investigation techniques.
Mechanochemistry is a versatile approach for green and fast synthesis of pure substances. By milling the reactants, various organic, inorganic, and metal-organic compounds can be obtained in high yields. Although mechanochemistry is widely used, the underlying mechanisms are not fully understood making mechanochemical reactions difficult to predict. Metal phosphonates are metal-organic compounds accessible by grinding. Because of their structural diversity, the exploration of the chemistry of metal phosphonates has gained considerable interest during the last decades. Transition metal phosphonates are promising candidates for an application as electrocatalysts in oxygen evolution reaction (OER). Here, we present the in situ investigation of the mechanochemical synthesis of a manganese(II)-phosphonate by synchrotron X-ray diffraction and thermography. The product has not been obtained by classical solution chemistry before and its crystal structure was determined from PXRD data. The milling process can be divided into different steps, with the product crystallization corresponding with the highest temperature rise. The activity of this metal phosphonate towards OER was measured and is presented here.
In this contribution we describe an in-situ study of the crystallization of simvastatin in three solvents. The studies were carried out by solvent evaporation at the µSpot beamline using acoustically levitated solution droplets in combination with simultaneous X-ray diffraction, Raman spectroscopy, and imaging analysis.
Analytical Sciences has developed from Ostwald’s “unentbehrlichen Dienstmagd” to a chemical discipline at the core of many of today’s fundamental and applied scientific problems and innovations. An atomic or molecular understanding of basic processes in chemistry, soft matter physics, materials and life science is enabled only through new analytical methods and instrumentation. Similar observations can be found for pressing sociopolitical conflicts of the future: A rational discussion of global climate change or new energy sources is only possible with reliable analytical results. Progress in Analytical Sciences is only possible if the underlying interdisciplinary character is acknowledged and valued. The talk will illustrate the scope of modern Analytical Science through examples from process analysis relevant to modern process intensification and industry 4.0 to bioanalysis and the use of synchrotron radiation to elucidate fundamental reactions materials.
Synchrotron XPS in the soft-X-ray regime is suitable for the detection of light elements commonly found in biological samples. Various model systems of biofilms have been developed and characterised at synchrotron- and lab-based facilities. By obtaining the chemical composition at various information depths, the vertical distribution of iodine in an artificial biofilm have been determined.
The influence of starting materials and synthesis route on the properties and the structure of cementitious sodium aluminosilicate gels is not fully understood, partly due their amorphous nature and the fact that they often contain residual reactants, which can make the results of single-pulse NMR spectroscopy applied to these materials difficult to interpret or ambiguous. To overcome some of these limitations, 29Si{27Al} TRAPDOR NMR as well as 27Al{29Si} and 27Al{1H} REDOR NMR spectroscopy were applied to materials synthesized by the one-part alkali-activation route from three different amorphous silica starting materials, including rice husk ash. The latter led to formation of a fully amorphous sodium aluminosilicate gel (geopolymer), while the materials produced from the other silicas contained amorphous phase and crystalline zeolites. Application of the double-resonance NMR methods allowed to identify hydrous alumina gel domains in the rice husk ash-based material as well as significantly differing amounts of residual silica in the three cured materials. Four-coordinated Al existed not only in the aluminosilicate gel framework but also in a water-rich chemical environment with only a small amount of Si in proximity, likely in the alumina gel or possibly present as extra-framework Al in the aluminosilicate gel. The results demonstrate how the employment of different silica starting materials determines the phase assemblage of one-part alkali-activated materials, which in turn influences their engineering properties such as the resistance against chemically/biologically aggressive media.
: Simvastatin is one of the most widely used active pharmaceutical ingredients for the treatment of hyperlipidemias. Because the compound is employed as a solid in drug formulations, particular attention should be given to the characterization of different polymorphs, their stability domains, and the nature of the phase transitions that relate them. In this work, the phase transitions delimiting the stability domains of three previously reported simvastatin forms were investigated from structural, energetics, and dynamical points of view based on single crystal X-ray diffraction (SCXRD), hot stage microscopy (HSM), and differential scanning calorimetry (DSC) experiments (conventional scans and heat capacity measurements), complemented with molecular dynamics (MD) simulations. Previous assignments of the crystal forms were confirmed by SCXRD: forms I and II were found to be orthorhombic (P212121, Z′/Z = 1/4) and form III was monoclinic (P21, Z′/Z = 2/4). The obtained results further indicated that (i) the transitions between different forms are observed at 235.9 ± 0.1 K (form III → form II) and at 275.2 ± 0.2 K (form II → form I) in DSC runs carried out at 10 K min−1 and close to these values when other types of techniques are used (e.g., HSM). (ii) They are enantiotropic (i.e., there is a transition temperature relating the two phases before fusion at which the stability order is reversed), fast, reversible, with very little hysteresis between heating and cooling modes, and occur under single crystal to single crystal conditions. (iii) A nucleation and growth mechanism seems to be followed since HSM experiments on single crystals evidenced the propagation of an interface, accompanied by a change of birefringence and crystal contraction or expansion (more subtle in the case of form III → form II), when the phase transitions are triggered. (iv) Consistent with the reversible and small hysteresis nature of the phase transitions, the SCXRD results indicated that the molecular packing is very similar in all forms and the main structural differences are associated with conformational changes of the “ester tail”. (v) The MD simulations further suggested that the tail is essentially “frozen” in two conformations below the III → II transition temperature, becomes progressively less hindered throughout the stability domain of form II, and acquires a large conformational freedom above the II → I transition. Finally, the fact that these transitions were found to be fast and reversible suggests that polymorphism is unlikely to be a problem for pharmaceutical formulations employing crystalline simvastatin because, if present, the III and II forms will readily convert to form I at ambient temperature.
The basics of broadband dielectric spectroscopy were introduced in detail. The analysis of the data was discussed. As application of broadband dielectric spectroscopy the alpha-relaxation (dynamic glass transition) and the chain dynamics of polymers were ilustrated. Further the application of dielectric spectroscopy to polymerbased nanocomposites and high preformance polymers was discussed in detail.
Metal organic frameworks (MOFs) and coordination polymers (CPs) Play an important role in different fields of applications like e.g. catalysis, separations, gas storages, sensors or optoelectronics. Moreover, particularly fluorinated metal-organic frameworks (FMOFs) are in the focus of interest during the last years. Due to the strong electronegativity of fluorine the FMOFs show beside an enhanced thermal stability excellent optical and electrical properties compared to non-fluorinated frameworks. In most cases fluorine is implemented using perfluorinated organic linkers at the synthesis, usually performed by solvothermal synthesis.
However, only few examples are known so far where fluorine is coordinated directly to the metal cation. Recently we reported about successful mechanochemical syntheses and characterization of fluorine-containing coordination polymers of alkaline earth metals by milling M(OH)2 (M: Ca, Sr, Ba) with fluorinated benzene dicarboxylic acids.
In the present study, it was shown that it is possible to connect fluorine directly to Barium using a mechanochemical synthesis route. A new phase pure barium coordination polymer, BaF-benzene-dicarboxylate (BaF(p-BDC)0.5), was synthesized by milling starting either from barium hydroxide or from barium acetate as sources for barium cations. In both cases the second reactant was 1,4-benzenedicarboxylic acid (H2(p-BDC)). Ammonium fluoride was used as fluorinating agent directly at milling. Although single crystals are not accessible so far and the structure was not solved yet, both the 19F MAS NMR spectrum and the FT IR spectrum give strong evidence that fluorine as well as 1,4-benzenedicarboxylate are connected to barium. This is the first mechanochemical synthesis of coordination polymers where fluorine is directly coordinated to the metal cation. The new compound BaF(p-BDC)0.5 was characterized by X-ray powder diffraction, FT IR- and 19F, 1H-13C CP MAS NMR spectroscopies, DTA-TG and elemental analysis.
We present naproxen/proline cocrystals discovered when combining enantiopure and racemic naproxen and proline. Using liquid-assisted grinding as the main method to explore the variety of crystal forms in this system, we found 17 cocrystals, of which the structures of only four of them were previously known. The naproxen/proline system exhibited multiple polymorphs of 1 : 1 stoichiometry as well as more rare cocrystals with 1 : 2 and 2 : 3 stoichiometries, two cocrystal hydrates and one cocrystal solvate. In situ ballmilling, used to monitor liquid-assisted grinding reactions, revealed that the solvent dictates the reaction intermediates even if the final reaction product stays the same. Synchrotron X-ray diffraction data collected in situ upon heating allowed us to monitor directly the phase changes upon heating and gave access to pure diffraction patterns of several cocrystals, thus enabling their structure determination from powder X-ray diffraction data; this method also confirmed the formation of a conglomerate in the RS-naproxen/DL-proline system. Proline in cocrystals kept its ability to form charge-assisted head-to-tail
N-H⋯O hydrogen bonds, typical of pure crystalline amino acids, thus increasing the percentage of strong chargeassisted interactions in the structure and consequently providing some of the cocrystals with higher melting points as compared to pure naproxen. The majority of drugs are chiral, and hence, these data are of importance to the pharmaceutical industry as they provide insight into the challenges of chiral cocrystallization.
The development of quick and simple optical sensing technologies for Endocrine Disrupting Chemicals (EDCs) is needed to facilitate monitoring of these substances to ensure consumer safety. Optical sensing was achieved against phthalates acting as EDC that have host guest interaction with an intercalated Metal-organic framework (MOF), resulting in a fluorescence emission upon excitation. The fluorescent turn-on signal was generated by using a fluorophore with a structural component that has little fluorescence unless excimers are formed. Strategies to engineer functional MOF structures suitable for sensing EDC phthalates were developed, and the characterization of the MOFs with and without present phthalates was done by single crystal XRD, PXRD, RAMAN and Thermogravimetry. Extensive photo-physical characterization of host-guest complexes of different phthalates and the MOF as well as the resulting exciplex fluorescence was performed. Photo physical characterization revealed an analyte specific fluorescence fingerprint that allows discerning even minute changes in chemical structures of the analyte and therefore paving the way for sensing tools in real world analytical applications. The presented capability of MOFs to sense EDCs is envisioned to complement established methods from analytical chemistry such as mass spectrometry based methods which can’t be used on site and are often associated with infrastructural capacity constraints
Due to its low mass and high diffusivity in presence of compositional, thermal and mechanical gradients, hydrogen within a metallic microstructure can result in severe loss in ductility even at low concentrations and might lead eventually to a catastrophic and unpredictable failure of structural components during service. In this context, hydrogen mapping at the microscale is still considered among the most important challenges on the pathway towards a better understanding of the hydrogen transport and assisted cracking phenomena in metals, specifically in structural components, e.g. steels.
Among the very few available techniques to localize hydrogen at the microscale, Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was proven to be a reliable tool. Based on the assumption that deuterium influence the microstructure similarly to hydrogen, in the following contribution ToF-SIMS was applied as the main technique to detect and locally map the deuterium distribution in several alloys: lean 2101 and standard 2205 duplex stainless steel (DSS), AISI 304L austenitic stainless steel and titanium 6Al-4V alloy. These alloys were selected as case studies in this work due to the wide use of them in many applications and environments which frequently provide critical conditions for hydrogen absorption and assisted degradation.
The innovative design of in-situ and ex-situ experiments enabled us to elucidate the permeation, transport and trapping of deuterium in the microstructure in sub-micron resolution for the first time. In addition to the novel experimental setups, further progress was gained by applying computational multivariate data analysis (MVA) on the raw data and data fusion with high resolution structural characterization methods (scanning electron microscopy and electron back-scattered diffraction – SEM/EBSD). This combination allowed us to correlate the deuterium distribution and the influence on the microstructure.
In the presented research, the high potential and abilities of secondary ion mass spectrometry (ToF-SIMS) to detect and locally map the hydrogen distribution in two types of duplex stainless steels are shown. The research validates certain proposed mechanisms by combining ToF-SIMS with high-resolution scanning electron microscopy and electron-backscattered diffraction. The combination of data from several techniques on the same region was conducted in this field for the first time by applying data treatment of the ToF-SIMS raw data and data fusion approach. This powerful combination of methods allows reviewing of the occurring processes related to hydrogen assisted cracking. The step beyond the state of the art in this field was gained here by developing permeation and mechanical loading experiments within the ToF-SIMS during chemometric imaging of the hydrogen distribution in the microstructure. The research presents the necessary correlation between the hydrogen distribution and the resulted structural changes, the diffusion behavior in a duplex microstructure and stress induced diffusion of hydrogen by applying external load at the microscale.
A promising technology in photovoltaics is based on micro-concentrator solar cells, where the photovoltaic active area is realized as an array of sub-millimeter sized thin-film solar cells. Different approaches to produce micro-sized precursors of CIGSe absorbers on molybdenum are presented using 30-fs laser pulses at 790 nm wavelength. On the one hand, a multi pulse surface structuring of the molybdenum or the underlying glass substrate and a subsequent physical vapor deposition (PVD) process were used for a site-selective aggregation of indium droplets. On the other hand, a single pulse laser-induced forward transfer (LIFT) was utilized to selectively deposit combined copper/indium/gallium precursor pixels on the molybdenum back contact of the solar cell. It was demonstrated that a postprocessing of the laser-generated micro-sized precursors results in an array of working CIGSe solar cells with an efficiency of 2.9% for 1 sun Illumination.
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.
Mechanochemistry is a fast and efficient method applicable for the synthesis of new organic, metal-organic, and inorganic compounds. The direct monitoring of milling reactions is still challenging. The underlying reaction mechanisms often remain unclear. In the last years, we have established a tandem in situ approach for investigating mechanochemical reactions using time-resolved in situ XRD coupled with Raman spectroscopy. A further development is the in situ coupling of synchrotron XRD, Raman spectroscopy, and thermography allowing the observation of mechanochemical reactions in real time. [5] Information on the crystalline, molecular, and temperature state of the materials during grinding could be collected. The chemical composition of the reaction mixture was found to be directly correlated with changes in the temperature profile of the reaction. Furthermore, the presented setup allows the detection of crystalline, amorphous, eutectic as well as liquid intermediates. Based on these data, metastable polymorphs of cocrystals and coordination polymorphs could be isolated and struc-turally characterized. A multi-step diffusion mechanism was identified for most systems. Crystalline phases were obtained intermediately, suggesting that the synthesis is following Ostwald’s rules of stages. The resulting deeper kinetic and thermodynamic understanding of milling processes is the key for future optimization of mechanochemical syntheses.
BAM and Division 6.1
(2018)
Three current research projects performed at BAM’s Division for Surface Analysis and Interfacial Chemistry are presented that tackle important challenges with regard to the characterization of nanomaterials: 1) The characterization at ambient pressure, 2) the investigation of core-shell nanoparticles, and 3) the characterization of non-spherical particles by electron microscopy.
1) Surface analytical techniques such as Photoelectron Spectroscopy (XPS) or Secondary Ion Mass Spectrometry (SIMS) typically require measurements in ultra-high vacuum. However, for many applications (e.g. catalysis and nanotoxicology) it is important to know the surface chemical properties of nanomaterials at ambient conditions. Therefore, near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to investigate nanoparticles in suspension. The used instrumental set-up allows to directly insert nanoparticle suspensions into the analysis chamber and to measure without prior sample preparation. Compared to dry reference samples measured under high-vacuum, a shift towards higher binding energies was observed for silver nanoparticles in water, indicating a change of surface potential at the water-nanoparticle interface.
2) To determine the dimensions of core-shell nanoparticles (shell thickness, core and total diameter), scanning transmission X-ray microscopy (STXM) was used. The analyzed model system consists of a polytetrafluorethylene (PTFE) core surrounded by a polystyrene (PS) shell, providing a strong X-ray absorption contrast at the C K-edge and a well-defined interface. The introduced STXM‐based methodology yields particle dimensions in agreement with scanning electron microscopy (SEM) results and provides additional information such as the position of the particle core, which cannot be extracted from a SEM micrograph.
3) The accurate measurement of size distributions of non-spherically shaped nanoparticles (representing most of the industrial nanoparticulate materials) is a challenging analytical task. High-resolution electron microscopy (TEM and SEM) is best suited to access the shape of individual nanoparticles. To fill the gap between ideal, monodisperse particles of spherical shape and complex real-world samples, BAM has started the work to develop reference nanoparticles of controlled shape, such as TiO2 platelets, bipyramids, and elongated particles. Results of a recent ISO inter-laboratory comparison will be shown with emphasis on the measurement parameters, descriptors and data analysis.
The pathways of plastics, especially of microplastic (MP), in environmental compartments, particularly in aquatic systems, are not well understood. The critical point is the lack of fast, harmonised methods for sampling, sample preparation and sample analysis. These three analytical steps are dependent on one another and must be optimised.
In recent years, we developed a method for representative sampling and fast detection of MP in aqueous systems. The sampling in different freshwater bodies is performed in the field with a fractionated filtration system using mesh sizes of 500, 100 and 50 µm. For water with an intermediate or high content of suspended particular matter a minimum of 1000 L has to be filtered. In the lab, mesh sizes of 10 and 5 µm are used for further filtration. Subsequently, the water filtrates of the different particle size classes are sterilised, dried, weighed and homogenised, if necessary.
Conventional methods for MP analysis are infrared and raman spectroscopy, giving information on the shapes and numbers of individually identified MP particles. Our focus is on the determination of mass contents of various polymers potentially contained in environmental samples. For qualitative and quantitative MP detection TED-GC-MS is used, a two-step method based on gas chromatography-mass spectrometry (GC-MS) with previous thermal extraction. This method not only enables us to screen the samples for characteristic marker-molecules, thus identifying single polymers, but furthermore allows the calculation of mass contents of individual polymers. In the present work, different freshwater compartments were exemplarily studied to identify containing polymers and calculate their mass content in MP particles.
Among the very few techniques to localize hydrogen (H) at the microscale in steels, Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was proven to be a reliable tool. The necessity to detect hydrogen stems from its deleterious effects in metals, that are often used as structural components and to obtain better understanding of the underlying metallurgical mechanisms of hydrogen embrittlement (HE) which are still unclear.
Austenitic stainless steels are nowadays commonly used in a wide variety of application, from hydrogen transport and storage facilities to petrochemical and offshore applications where they are exposed to aggressive environments and therefore prone to HE. One of the greater risks in the austenitic class is the embrittlement of the material due to the instability of the γ austenite and its transformation into a brittle α martensitic phase. This transformation takes place due to the local stresses that are induced by the uptake of hydrogen during service. Nonetheless, it was shown that this transformation can occur as an artefact during SIMS analysis itself where Cs-sputtering is necessary not only to remove surface contaminations but mainly to enhance H/D secondary ion yield.
In the following contribution we show the influence of different sputtering conditions on AISI 304L austenitic stainless steel in order to distinguish the artefact from the hydrogen induced transformation. The material was charged electrochemically in a deuterium based electrolyte. Deuterium (D) must be in these experiments as a replacement for hydrogen which cannot be used because adsorbed hydrogen superimposes hydrogen originating from charging the sample in the SIMS images. ToF-SIMS analyses were conducted by ToF SIMS IV (IONTOF GmbH, Münster, Germany). The experiments were carried out on deuterium charged and non-charged samples. The structural characterization was carried out by SEM and EBSD examinations before and after charging, both with a Leo Gemeni 1530VP field-emission scanning electron microscope and a Zeiss Supra 40 instrument (Carl Zeiss Microscopy GmbH, Oberkochen, Germany). The results showed that the use of 1keV Cs+ beam induces stacking faults while higher sputter beam energies results in γ→α transformation.
The purpose of this study is to shed more light on the transesterification processes in alcohol-initiated and tin(II) 2-ethylhexanoate (SnOct2)-catalyzed polymerizations of lactides at low or moderate temperatures. Ethanol-initiated polymerizations are conducted in concentrated solutions at 80 °C and a strong dependence of even/odd equilibration on the alcohol/Sn ratio. Around or above 120 °C cyclization of poly(l-lactide) via “backbiting” occurs as a third mechanism. However, poly(m-lactide) shows a higher cyclization tendency and yields cyclics even at 100 °C. Combinations of ethanol and certain cyclic dibutyltin(IV) catalysts also yield cyclic oligomers of l-lactide at 80 °C. Reaction conditions allowing for a total suppression of all transesterification reactions are not found, but even-numbered poly(m-lactide)s with a purity >95% are obtained at 70 or 60 °C.
Polymers at interfaces play a major role in a broad variety of applications ranging from engineering purposes (for instance polymer based nanocomposites) to high tech implications (for instance light emitting diodes).
Here, thin films with thicknesses down to few nanometers are prepared on different substrates as model systems for polymer composites. The thin films are investigated by a combination of surface analytical and volume sensitive methods. As surface analytical methods atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements (CAM) are employed. As volume sensitive broadband dielectric spectroscopy (BDS), specific heat spectroscopy (SHS), and ellipsometry are used. Especially attention is paid to understand the glass transition behavior of thin films because the glass transition is the key phenomenon determines the application of polymers also in thin films.
To understand the glass transition behavior of thin films, which is controversially discussed in literature, a three layer model is discussed. Firstly, a mobile surface layer is assumed at polymer air interface of the film due to missing of segment/segment interactions. Secondly, in the middle of the film a bulk-like layer should be expected. Thirdly, for polymers having non-repulsive interactions with the substrate an irreversibly adsorbed layer is expected to be formed. Due the adsorption the molecular mobility of the segments in this layer is slowed down. What is measured for the glass transition of thin films is a complicated average of all of these effects. The different layers are hardly to address separately. Therefore, in the presentation especially model systems are selected and investigated to verify the layer model.
Der Vortrag stellt spektroskopische und neue thermoanalytische Verfahren zum Nachweis von Mikroplastik in Umweltproben vor. Ein spezieller Fokus liegt auf dem neu entwickelten Verfahren der TED-GC-MS. Zusätzlich wird gezeigt, wie die TED-GC-MS eingesetzt werden kann, um Reifen in der Umwelt zu bestimmen.
A facile and convenient approach for the synthesis of core–shell particles via emulsion polymerization is presented. The shell consists of poly(vinylidene fluoride) (PVDF) and the core of poly(methyl methacrylate) (PMMA), poly(glycidyl methacrylate) (PGMA) or poly(methyl acrylate) (PMA). In a first step, a non-fluorinated (meth)acrylate monomer is polymerized in the emulsion to produce poly(meth)acrylate core particles. Secondly, vinylidene fluoride (VDF) is directly added to the reactor and polymerized for shell formation. Small-angle X-ray scattering (SAXS) was employed to characterize the structure of the core–shell particles. Interestingly, the particles’ core contains fluorinated and non-fluorinated polymers, whereas the shell of the particles consists only of PVDF. The resulting particles with a diameter of around 40 nm show a significantly higher PVDF β phase content than the PVDF homopolymer obtained by emulsion polymerization
To investigate the attachment behavior of bacteria, tailored surfaces are needed. Differences in the chemical charge of the substrate are varied by -COO-, -CH3, -OH, -NH3 terminated functional groups. Regular patterns of them on the surfaces enable bacteria to choose their preferred attachment sides. Tools to tailor the samples are µ-contact printing, self-assembled monolayers and physical vapor deposition. The same concept of preferred sides in patterned surfaces is transferred to the nano- and microroughness which is accomplished by using zinc oxide nanorods synthesis.
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.
This presentation explains the outline and scientific content of the ISO technical report 23173 "Measurement of the thickness and nature of nanoparticle coatings using electron spectroscopies". This technical report deals with those electron spectroscopy methods that are able to determine the coating thickness of nanoparticles. This specifically includes X-ray photoelectron spectroscopy (XPS), energy-resolved X-Ray photoelectron spectroscopy (ERXPS) using synchrotron radiation, near abient pressure photoelectron spectroscopy (NAPXPS) and Auger electron spectroscopy (AES).
The proposed ISO Technical Report provides a description of a variety of physical methods of analytical chemistry by which bacteria and biofilms can be analysed. The state of the art, sample requirements and strengths associated with each method are identified. Presented at the DIN-meeting for NA 062-08-16 AA „Chemische Oberflächenanalyse und Rastersondenmikroskopie“
MALDI time-of-flight mass spectrometry (MALDI-TOF MS) has become a widely used tool for the classification of biological samples. The complex chemical composition of pollen grains leads to highly specific, fingerprint-like mass spectra, with respect to the pollen species. Beyond the species-specific composition, the variances in pollen chemistry can be hierarchically structured, including the level of different populations, of environmental conditions or different genotypes. We demonstrate here the sensitivity of MALDI-TOF MS regarding the adaption of the chemical composition of three Poaceae (grass) pollen for different populations of parent plants by analyzing the mass spectra with partial least squares discriminant analysis (PLS-DA) and principal component analysis (PCA). Thereby, variances in species, population and specific growth conditions of the plants were observed simultaneously. In particular, the chemical pattern revealed by the MALDI spectra enabled discrimination of the different populations of one species. Specifically, the role of environmental changes and their effect on the pollen chemistry of three different grass species is discussed. Analysis of the Group formation within the respective populations showed a varying influence of plant genotype on the classification, depending on the species, and permits conclusions regarding the respective rigidity or plasticity towards environmental changes.
Over the past decades, the growing industry working for lightweight constructions has demanded materials exhibiting improved properties such as higher mechanical modulus and strength, better chemical resistance and lower costs of production.
It is known that especially nanofibers tend to enhance the mechanical, thermal and electrical properties of polymers. Therefore, some types of nanofibers are already being used embedded in polymeric matrix of sports equipment, aircraft parts and automobile components. However, nanofibers are a relatively new material category, the consequences of which for mankind are not yet fully known. Nanofibers detached from polymeric materials can be released into the environment during, e.g., processing and aging. The risks in dealing with such nanofibers are generally unknown, even if further studies of health aspects are being carried out. Problems always arise when the fibers can penetrate the cells, thus the mechanical rigidity of nanofibers is a key factor in assessing the risks. Common methods describe the geometry of nanofibers. These methods are necessary, but not sufficient to describe the mechanical properties, as for during manufacture and aging these properties may change; the modulus and strength values may differ from those of the original fibers.
Different experimental techniques for nanomechanical testing have been studied using the atomic force microscope, the scanning electron microscope and transmission electron microscope, showing promising results.
This project aims to evaluate the bending stiffness of CNTs with an experimental setup within the Dynamic Scanning Electron Microscope. Based on the Euller-Bernoulli beam theory, the Young’s modulus of CNTs can be obtained using the resonance frequency of mechanically excited nanofibers, its dimensions and density. The resonance frequency is acquired by extracting the signals of the secondary electrons when the nanofibers show significant vibration movement, also possible to be seen on the microscope images. The electronic signals of the secondary electrons are filtered and treated by a lock-in amplifier, so the corresponding amplitude and phase values can be evaluated. This method could be applied to any nanofiber that has the shape similar to a symmetric beam.
Die Rasterkraftmikroskopie (AFM) hat sich in den letzten Jahren als eine vielseitige Abbildungstechnik von Oberflächen mit einer sehr hohen Ortsauflösung etabliert. Über die Untersuchung der reinen Oberflächentopographie sind erweiterte Modi in der Lage, gleichzeitig Informationen über die elektrischen und magnetischen Eigenschaften sowie Adhäsionsprozesse auf Oberflächen zu liefern. Interessanter wird es, wenn das AFM mit geeigneten Messzellen für in-situ-Untersuchungen in kontrollierten Atmosphären oder in Elektrolyten unter elektrochemischer Kontrolle ausgestattet ist. Dies ermöglicht die Untersuchung von Korrosions- und Adhäsionsprozessen unter Bedingungen, die die Betriebsumgebung repräsentieren.
Ein aktueller Forschungsschwerpunkt unseres Fachbereiches liegt in den Untersuchungen der Deformationseigenschaften von Funktionsschichten auf Leichtmetalllegierungen, sowie in situ Untersuchungen des Korrosionsverhaltens unter kombinierter korrosiver und mechanischer Beanspruchung mittels AFM. Durch die Integrierung eines Zug-Druckmoduls in den Probentisch des Rasterkraftmikroskops haben wir jetzt die Möglichkeit, verschiedene Materialien uniaxialen Umformversuchen mit bis zu 5 kN Kraft zu unterziehen. Dabei können unter anderem auch zyklische Belastungen genutzt werden, um Ermüdungsprozesse zu simulieren. Da die Messungen in situ ohne die De- und Remontage der Probe durchgeführt werden, ermöglicht der Aufbau nicht nur Messungen mit präziser Positionssteuerung, sondern auch die Untersuchung von Prozessen im elastischen Bereich, die für die Aufklärung der Mechanismen, die zu Ermüdungsversagen führen, entscheidend sind.
Die Posterpräsentation wird detaillierte Informationen zum neuen AFM-Setup liefern und unsere aktuellen Ergebnisse zur Verformung dünner Schutzschichten auf AA2024-T3 zusammenfassen.
The performance of adhesively joined hybrid components relies strongly on the stability of the adhesive-material interface. With the increasing utilization of multi-material structures in the automotive and aerospace industry, it is of great scientific and technical interest to understand the processes leading to adhesive failure and to develop novel strategies to increase corrosion and delamination resistance of adhesive joints.
The aim of this study is to develop thin epoxy based films and their carbon nanofiller loaded composites on aluminium alloy AA2024-T3 and to investigate their interfacial stability under corrosive and coupled corrosive-mechanical load. Spin coating was used for the layer-by-layer deposition of poly[(o-cresyl glycidyl ether)-co-formaldehyde] and poly-(ethylenimine) bi-layers. Carbon nanofillers are introduced either by mixing into the coating components or in between individual layers. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis was performed to investigate the porosity and water uptake of the model films, respectively. Atomic force microscopy (AFM) results indicated a very homogeneous and dense film with low surface roughness. The bi-layer thickness ranged between 30 to 40 nm. Electrochemical measurements show a higher corrosion resistance with the increase of the bi-layer number.
The main novelty of this contribution is the in-situ AFM investigations under coupled corrosive-mechanical load. For this purpose, a tensile module capable of uniaxial stretching and compression with up to 5 kN force was integrated into the AFM stage. Stretching experiments were performed to investigate the mechanical properties and adhesion of the films, as well as structural changes of the film morphology during uniaxial deformation. The contribution will provide detailed information on the new AFM setup and summarize our results on the stability of model epoxy and nanocomposite films on AA2024-T3.
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 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.
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.
Spirocyclic phenoxides of germanium, zirconium, and tin were prepared from 2,20-dihydroxybiphenyl and 2,20-dihydroxy-1,10-binaphthyl. Ring-expansion polymerizations of L-lactide are mainly studied at 160 or 180 °C. The reactivity of the catalysts increases in the order: Zr < Ge < Sn. Regardless of catalyst, the weight-average molecular weights (Mw) never exceed 50,000 g mol−1. The resulting poly(L-lactide)s are optically pure and have a cyclic architecture. Decreasing temperature and time favor Formation of even-numbered cycles, and at 102 ° cyclics, almost free of odd-numbered rings are obtained. Analogous polymerizations of meso-lactide give similar results >120 °C, but different results at 100 or 80 °C. Surprisingly, bell-shaped narrow molecular weight distributions are obtained <140 °C, resembling the pattern of living polymerizations found for alcohol-initiated polymerizations. An unusual transesterification mechanism yielding narrow distributions of odd-numbered cycles is discovered too.
The characteristics of different molecules chosen as representatives for specific functionalities in conditioning layers play an important role on attachment behavior and later biofilm formation of bacteria. The chemical composition is a major component influencing the attachment but there is a conglomerate of influences.
Graphene is a two-dimensional carbon network with unique properties. However, its low solubility, poor reactivity and the limited accessibility of a well-defined basal plane are major challenges for applications. An ideal method to overcome these problems is the covalent attachment of functional molecules to its surface which enable further reactive modifications for specific applications. There are several technologies for surface functionalization of graphene and related CNT materials. To get control on the functionalization process and to optimize the performance of the modified surfaces analytical tools for surface chemical characterization are required. X-ray absorption (NEXAFS) and photoelectron spectroscopy (XPS) have been identified to be rather powerful here [1-3]. Specifically, NEXAFS spectroscopy underpinned by quantum chemical spectrum simulations [4] is unique in a way to address changes of aromaticity and defect formation at the graphene surface during functionalization.
For relevant surface modification technologies, we present examples on how NEXAFS and XPS can do a good job. All presented modifications aim on the production of platforms for defined functional 2D nanomaterials, as for example multifunctional hybrid architectures. In detail, we investigated:
• A wet chemical method for covalent functionalization of graphene sheets by a one-pot nitrene [2+1] cycloaddition reaction under mild conditions. Here a reaction between 2,4,6-trichloro-1,3,5-triazine and sodium azide with thermally reduced graphene oxide (TRGO) results in defined dichlorotriazine-functionalized graphene sheets.
• Graphene and carbon nanotube functionalized by Vacuum-Ultraviolet (VUV) induced photochemical or r.f. cw low pressure plasma processes to introduce amino, hydroxy or brominated functionalities.
To underpin finger-print information delivered by C K-edge NEXAFS we studied the effects of selected point and line defects as well as chemical modifications for a single graphene layer model by density functional theory based spectrum simulations.
References
[1] P.-L. Girard-Lauriault et al., Appl. Surf. Sci., 258 2012 8448-8454, DOI: 10.1016/j.apsusc.2012.03.012
[2] A. Lippitz et al., Surf. Sci., 611 2013 L1-L7, DOI: 10.1016/j.susc.2013.01.020
[3] A. Faghani et al., Angew. Chemie (International ed.), 56 2017 2675-2679, DOI:10.1002/anie.201612422
[4] C. Ehlert, et al., Phys.Chem.Chem.Phys., 16 2014 14083-14095, DOI: 10.1039/c4cp01106f
In this talk sample prep/handling, instrument calibration and data acquisition methods with examples from XPS, Auger and SIMS will be addressed in terms of their contributions to the reproducibility of data delivered by the methods.
Active parties in the field are VAMAS TWA 2 “Surface chemical analysis” (http://www.vamas.org/twa2/index.html), ISO/TC 201 “Surface chemical analysis” (https://www.iso.org/committee/54618.html) and the Surface Analysis Working Group (SAWG) at the International Meter Convention (https://www.bipm.org/en/ committees/cc/wg/sawg.html). The tools to improve the reproducibility of spectra, depth profiles and images at these international platforms are inter-laboratory comparisons, validated SOPs, standards and certified reference materials (CRM) as well as uncertainty budgets and establishment of traceability chains. The last point is of specific importance because all the methods, XPS, Auger and SIMS, are not primary methods.
To address quantitative XPS, AES and SIMS results of relevant inter-laboratory comparisons organized by SAWG considering measurands as alloy surface composition and thickness of thin films will be introduced. These comparisons delivered results which are viewed to be benchmarking, some of them resulted in ISO/TC 201 standards. For quantitative XPS and AES the principal outline of an uncertainty budget will be discussed together with the audience. Another issue of quantitative XPS which definitely needs consideration are valid methods for a determination of the transmission function of the instruments and even for the emission angle in the respective experiments.
Concerning the field of depth profiling it has to be investigated together with the audience whether the ISO (or ASTM) standards we have are sufficient to guarantee comparable results. Having in mind the number of different sputter ion species available today and range of samples of interest (metals, semiconductors, organic films) this might be questionable. And, how do depth profiling by AR-XPS and variable excitation energy XPS compete here?
For imaging surface chemical analysis, the characterization of the imaging system is an issue to be investigated. Here the determination of lateral resolution is a relevant topic.
Finally, the future needs to develop metrology for new applications e.g., ambient-pressure XPS, bio samples, and core-shell nanoparticles, will be issues raised for a discussion with the audience.
The occurrence of small particles consisting of organic polymers, so-called microplastic (MP), in aquatic Environments attracts increasing interest in both public and science. Recent sampling campaigns in surface Waters revealed substantial numbers of particles in the size range from a few micrometers to a few millimeters. In order to validate sample preparation, identification and quantification and to investigate the behavior of MP particles and potential toxic effects on organisms, defined MP model particles are needed. Many studies use spherical compounds that probably behave differently compared to irregularly shaped MP found in environmental samples.
However, preparation and handling of MP particles are challenging tasks and have been systematically investigated in the present study. Polystyrene (PS) as a commonly found polymer with a density slightly above that of water was selected as polymer type for milling and fractionation studies. A cryogenic ball mill proved to be practical and effective to produce particles in the size range from 1 to 200 μm. The yield of small particles increased with increasing pre-cooling and milling durations. Depending on the concentration and the size, PS particles do not completely disperse in water and particles partly creep vertically up along glass walls. Stabilized MP suspensions without use of surfactants that might harm organisms are needed for toxicological studies. The stabilization of PS particle suspensions with ozone treatment reduced the wall effect and increased the number of dispersed PS particles but increased the dissolved organic carbon concentration and changed the size Distribution of the particles.
Analysis of microplastic particles (MP) in environmental samples needs sophisticated techniques and is time intensive due to sample preparation and detection. An alternative to the most common (micro ) spectroscopic techniques, FTIR or Raman spectroscopy, are the thermoanalytical methods, where specific decomposition products can be analyzed as marker compounds for different kind of plastics types and mass contents. Thermal extraction desorption gas chromatography mass spectrometry (TED-GC-MS) allows the fast identification and quantification of MP in environmental samples without sample preparation. Whereas up to now only the analysis of thermoplastic polymers was realized, this is the first time that even the analysis of tire wear (TW) content in environmental samples is possible. Various marker compounds for TW were identified. They include characteristic decomposition products of elastomers, antioxidants and vulcanization agents. Advantages and drawbacks of these marker substances were evaluated. Environmental samples from street run off were exemplarily investigated and presented.
Gold ist eines der sieben schon im Altertum bekannten Metalle und wurde wg. seines Glanzes und seiner Seltenheit von alters her als Tauschmittel und zur Herstellung von Schmuck benutzt. Außerdem ist es einfach bearbeitbar und weitestgehend gegen chemische Einflüsse resistent. Die Untersuchungen von Gold mit synchrotronstrahlungsangeregter Röntgenfluoreszenzanalyse sind zerstörungsfrei und geben Auskunft über die in der untersuchten Probe vorhandenen chemischen Elemente. Bei den hier vorgestellten Untersuchungen an der BAMline stehen Fragestellungen wie Herkunft, Herstellungsverfahren und Zusammengehörigkeit von Goldfunden im Vordergrund. Die verschiedenen Fragestellungen werden an einer Reihe von Beispielen erläutert die vom Wikingerschatz aus Hiddensee über die Himmelsscheibe von Nebra bis hin zu Funden aus Ägypten langen. Zusätzlich werden die modernen Messmethoden vorgestellt, die am Synchrotron heutzutage zur Verfügung stehen.