Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2022 (92) (entfernen)
Dokumenttyp
- Vortrag (92) (entfernen)
Referierte Publikation
- nein (92)
Schlagworte
- Laser-induced periodic surface structures (LIPSS) (9)
- Mechanochemistry (9)
- XPS (9)
- Nanoparticles (8)
- Automation (6)
- HAXPES (5)
- In situ real-time monitoring (5)
- SEM (5)
- Surface functionalization (5)
- VAMAS (5)
Organisationseinheit der BAM
- 6 Materialchemie (92) (entfernen)
Nanoforms with at least one dimension below 100 nm have an important part to play in more and more areas of our daily life. Therefore, risk assessment of these materials is becoming increasingly important. In this context, the European Chemical Agency (ECHA) considered eleven physico-chemical properties as relevant, of which the following six are essential for the registration: chemical composition, crystallinity, particle size, particle shape, surface chemistry and specific surface area. Four of these priority properties can be obtained with electron microscopy and surface analytics like XPS and ToF-SIMS. The reliability of this data must be ensured, especially for their use for grouping and read across approaches. On the other hand, the “reproducibility” crisis has revealed major shortcomings in the reliability of published data.
In a case study, we show how the quality of the data can be ensured by using existing standards and protocols of each step in the workflow of sample characterization. As exemplary samples, two Al-coated TiO2 samples as nanopowders were selected from the JRC repository, capped either with a hydrophilic or a hydrophobic organic ultrathin shell. SEM results provided the size and shape of the nanoparticles, a first overview about the composition was obtained with EDS. XPS and ToF-SIMS supplied the surface chemistry, especially information about the shell and the coating of the particles. Standards and protocols of all steps of the analytical workflow including preparation and data reduction are discussed regarding reliable and reproducible data. Additionally, uncertainties for the different steps are specified.
Only such a detailed description of all these factors allows a comprehensive physico-chemical characterization of the nanoparticles with understanding of their potential risk assessment.
The novel lab-based HAXPES spectrometer (ULVAC-PHI Quantes) gives us the possibility to measure XPS at 1486.6 eV (monochromatic Al Kα source) and HAXPES at 5414.9 eV (monochromatic Cr Kα source) on a sample at the same position. The surface analysis with this spectrometer leads to an information depth of about 10 nm for XPS and in comparison, to an analysis of deeper regions of about 30 nm for HAXPES measurements. This method provides a nondestructive way to distinguish between the near-surface region of the nanoparticles and the whole nanoparticle. Additionally, HAXPES gives access to deeper core levels at higher energy.
An application of this technique is presented using nanoparticles. The results shown were obtained with nanoparticles, that were treated differently by means of sterilization for nanosafety (i.e., before studying their toxicity it is important to establish whether nanomaterials are sterile and, if not, to be treated either via microwave or autoclave sterilisation). As a complementary method, the data is compared with SEM and EDX measurements. All methods demonstrate the influence of sterilization. More specifically, these results show that the sterilization step must be considered in the physical-chemical description of the particles for establishing reliable (quantitative structure-activity) relationships.
The fabrication of laser-generated surface structures on titanium and titanium alloys has recently gained remarkable interests, being technologically relevant for applications in optics, medicine, fluid transport, tribology, and wetting of surfaces. The morphology of these structures, and so their chemistry, is influenced by the different laser processing parameters such as the laser fluence, wavelength, pulse repetition rate, the effective number of laser pulses per beam spot area, etc. A simple way to characterize laser-generated surface structures is by means of optical microscopy (OM) or white light interference microscopy (WLIM). The latter can address the surface topography, while having a lateral resolution limit of ~(lambda)/2 (lambda = illumination wavelength). To resolve morphologies with spatial periods significantly smaller than (lambda)/2, scanning electron microscopy (SEM) is often used, taking benefit of the reduced de Broglie wavelength associated to the electrons of several keV energy. However, all the above-mentioned techniques lack the necessary depth-resolution to reveal and quantify sub-surface material modifications of these laser-generated structures. Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) represents a promising surface analytical technique for studying laser-induced chemical surface alterations since the method combines a high surface sensitivity with the capability to perform a depth-profiling of the laser-affected surface zone. In this study we combine WLIM and high-resolution SEM with ToF-SIMS to fully characterize the evolution of various types of laser-generated micro- and nanostructures formed on Ti-6Al-4V alloys upon irradiation by near infrared ultrashort laser pulses (1030 nm, 925 fs) at different laser fluence levels, effective number of pulses, and at different pulse repetition rates (1 – 400 kHz). We show how this combined surface analytical approach allows to evaluate alterations in the surface chemistry and topography of the laser-generated surface structures depending on the laser processing parameters
In pursuing the automated synthesis of metal nanoparticles (NPs), the capabilities of the “Chemputer” are deployed, for the first time, into the field of inorganic chemistry. Metal NPs have a substantial impact across different fields of science, such as photochemistry, energy conversion, and medicine. Among the commonly used nanoparticles, silver NPs are of special interest due to their antibacterial properties and applications in sensing and catalysis. However, many of the methods used to synthesize Ag NPs often do not result in well-defined products, the main obstacles being high polydispersity or a lack of particle size tunability.
The Chemputer is a modular, automated platform developed by the Cronin group for execution of multi-step, solution based organic synthesis. The machine has been further implemented at BAM, where we used this setup to perform automated organic syntheses, autonomously controlled by feedback derived from online NMR. In the Chemputer liquids can be transferred across a backbone, constructed from HPLC selection valves and syringe pumps. The Chemputer operates in a batch mode, common laboratory devices, such as heaters and glassware like round bottom flasks, are connected to the backbone, forming reaction modules. Solutions can be manipulated in these modules, and as all operations are controlled through a software script, reproducibility among individual syntheses is high. Likewise, any adjustments of the synthesis conditions, if required, are straightforward to implement and are documented in the reaction log file and a code versioning system.
We characterised Chemputer-synthesized nanoparticles using small-angle X-ray scattering, dynamic light scattering and further methods, showing that automated synthesis can yield colloids with reproducible and tuneable properties. The approach is an important first step towards the automation of nanoparticle syntheses in a modular, multipurpose platform. The modularity of the Chemputer opens many possibilities for the synthesis of a variety of different NP morphologies and sizes and potentially more complex structures. These advances and further work can help in the general investigations of silver nanoparticles by supplying a reliable and reproducible method of their synthesis and removing tacit knowledge by significantly reducing the experimental bias.
Chemical heuristics are essential to understanding molecules and materials in chemistry. The periodic table, atomic radii, and electronegativities are only a few examples. Initially, they have been developed by a combination of physical insight and a limited amount of data. It is now possible to test these heuristics and generate new ones using automation based on Materials Informatic tools like pymatgen and greater amounts of data from databases such as a Materials Project. In this session, I'll speak about heuristics and design rules based on coordination environments and the concept of chemical bonding. For example, we have tested the Pauling rules which describe the stability of materials based on coordination environments and their connections on 5000 oxides from the Materials Project. In addition, we have created automated processes for analyzing the chemical bonding situation in crystalline materials with Lobster (www.cohp.de) in order to discover new heuristics and design rules.
The processing of laser-induced periodic surface structures (LIPSS) represents a simple and robust way for the nanostructuring of solids that allows creating a wide range of surface functionalities featuring applications in optics, tribology, medicine, energy technologies, etc. While the currently available laser and scanner technology already allows surface processing rates at the m2/min level, industrial applications of LIPSS are sometimes hampered by the complex interplay between the nanoscale surface topography and the specific surface chemistry. This typically manifests in difficulties to control the processing of LIPSS and in limitations to ensure the long-term stability of the created surface functions. This presentation aims to identify some unsolved scientific problems related to LIPSS, discusses the pending technological limitations, and sketches the current state of theoretical modelling. Hereby, it is intended to stimulate further research and developments in the field of LIPSS for overcoming these limitations and for supporting the transfer of the LIPSS technology into industry.
Using nanofiber-like cell appendages, secreted proteins and sugars, bacteria can establish initial surface contact followed by irreversible adhesion and the formation of multicellular biofilms. Here, the stabilizing extracellular biofilm matrix together with physiological changes on the single cell level leads to an increased resilience towards harsh environmental conditions, antimicrobials, the host immune response and established cleaning procedures. Persistent microbial adhesion on e.g., medical implants, in water supply networks or food-processing industry is often associated with chronic inflammation, nosocomial and foodborne infections, enhanced biofouling and product contamination. To prevent persistent microbial colonization, antibacterial surface strategies often target the initial steps of biofilm formation and impede adhesion of single cells before a mature biofilm is being formed. While chemical coatings have been widely used, their restricted biocompatibility for eukaryotic cells and attenuated antibacterial-effects due to compound release limit their areas of application and alternative strategies focus on modified surfaces topographies to impede bacterial adhesion. In this work, we used ns-UV laser treatment (wavelength 248 nm and a pulse duration of 20 ns) to generate laser-induced periodic surface structures (LIPSS) with different submicrometric periods ranging from ~210 to ~610 nm on commercial poly(ethylene terephthalate) (PET) foils. Following structurally and chemically analyses, PET samples were subjected to bacterial colonization studies with Escherichia coli TG1, a bacterial test strain with a strong biofilm formation capacity due to the formation of nanofiber-like cell-appendages (pili). Bacterial adhesion tests revealed that E. coli repellence decisively depends on the spatial periods of the LIPSS with the strongest reduction (~91%) in cell adhesion observed for LIPSS periods of 214 nm. Scanning electron microscopy and additional biofilm studies using a pili-deficient E. coli TG1 strain revealed the importance of extracellular appendages in the bacterial repellence observed here, thus, pointing out new antibiotics-free strategies for antibacterial surfaces by impeding nanofiber-mediated bacterial adhesion.
Due to its large strength-to-weight ratio and excellent biocompatibility, titanium materials are of paramount importance for medical applications, e.g. as implant material for protheses. In this work, the evolution of various types of laser-induced micro- and nanostructures emerging on titanium or titanium alloys upon irradiation by near-infrared ultrashort laser pulses (925 fs, 1030 nm) in air environment is studied for various laser fluence levels, effective number of pulses and at different pulse repetition rates (1 – 400 kHz). The morphologies of the processed surfaces were systematically characterized by optical and scanning electron microscopy (OM, SEM). Complementary white-light interference microscopy (WLIM) revealed the corresponding surface topographies. Chemical and structural changes were analysed through depth-profiling time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray diffraction (XRD) analyses. The results point towards a remarkable influence of the laser processing parameters on the surface topography, while simultaneously altering the near-surface chemistry via laser-induced oxidation effects. Consequences for medical applications are outlined.
Calcium sulfate minerals are abundant in natural and engineered environments and they exist in the form of three hydrates: gypsum (CaSO4·2H2O), bassanite (CaSO4·0.5H2O), and anhydrite (CaSO4). Due to their relevance in natural and industrial processes, the formation pathways of these calcium sulfate phases from aqueous solution have been the subject of intensive research1.
The state-of-the-art of the calcium sulfate formation mechanisms builds upon and goes beyond what we have come to appreciate in the astounding intricacy of other mineral formation processes from ions in aqueous solutions. The original, and rather naive, 'textbook' image of these phenomena, stemming from the adaptation of classical nucleation and growth theories, has increased in complexity due to the discovery of a variety of precursor and intermediate species2. These include solute clusters (e.g. prenucleation clusters, PNCs), liquid(-like) phases, as well as amorphous and nanocrystalline solids etc.. In this context, a number of studies have already revealed that nucleation in the CaSO4-H2O system is non-classical, where the formation of the different crystalline phases involves several steps including a common amorphous precursor1, 3, 4.
In this contribution we show that the formation of the amorphous phase involves the aggregation of small primary particles into larger disordered aggregates exhibiting a "brick-in-the-wall" structure5, 6. The actual crystallization occurs by the restructuring and coalescence of the particles ("bricks") into a given calcium sulfate phase depending on the physicochemical conditions of the solution. Importantly, the rearrangement process does not continue until a (nearly-)perfect homogeneous single crystal is obtained. Instead it comes to a stop, or at least significantly slows down. Such a process thus yields a final imperfect mesocrystal, composed of smaller domains rather than a continuous crystal structure, within which the domains are separated by an amorphous (i.e. less ordered) calcium sulfate phase.
Hence, the non-classical crystallization process of CaSO4 yields a final imperfect mesocrystal with an overall morphology resembling that of a single crystal, yet composed of smaller nano-domains. Importantly, these observations reveal that organic-free calcium sulfate mesocrystals grown by a particle mediated-pathway preserve in the final crystal structure a “memory” or “imprint” of their non-classical nucleation process, something that has been overlooked until now. Furthermore, the nano-scale misalignment of the structural sub-units within these crystals can propagate through the length-scales, and be expressed macroscopically as misaligned zones/domains in large single crystals (Fig. 1). Indeed, by considering large anhydrite crystals from the famous Naica Mine (“Cueva de los cristales”) we observed a suite of correlated self-similar void defects spanning multiple length-scales7 (Fig 2). These flaws, in the macroscopic crystal, stem from “seeds of imperfection” originating from a particle-mediated nucleation pathway. Hence, building a crystal could be viewed as Nature stacking blocks in a game of Tetris, whilst slowly forgetting the games core concept and failing to fill rows completely.
In the present talk the basics of the Raman spectroscopy and particularly of Raman microscopy are explained. Advantages and disadvantages of the method are highlighted through selected case studies. In the second part of the lecture examples of correlative imaging with electron, X-ray, ion and optical microscopies from micro- to the nanoscale are highlighted.
MALDI-ToF mass spectrometry for the characterization of biobased polymers suitable for depollution
(2022)
In this work, bio-based polymers were synthesized and designed as polymers phases for adsorption of a variety of pollutants from aqueous solutions. The obtained adsorption results showed that the integration of bio-sourced synthons generate attractive hydrophilicity, and wettability of the resulting adsorbent phase. Such polymers phases enable stronger interactions with the organic and inorganic pollutants in water.
A wide variety of different bio-based polymers structures (e. g. poly(ethersulfones, poly(etherphosphines or poly(etherpyridines) with different functional groups were successfully designed in order to adapt chemical structure to different pollutants type and matrice nature.
In order to characterize and to determine the correlation between polymer structures and nature of interaction with pollutants, different analytical technics (NMR, GPC, ATG, DSC, Mass spectrometry) were successfully used. Amongst them, MALDI TOF mass spectrometry plays a superior role since this technique enables the simultaneous determination of the polymer structure, polymer end groups and molecular weight.
This work focusses on the characterization of synthesized polymers. The chemical structure of the repeating unit, the nature of the end groups, as well as the molecular weight, which are all important for the specific interactions of the polymer with the pollutants were clearly determined and suggestions to improve these interactions by changing the synthetic pathway could be given.
Calcium sulfate minerals are abundant in natural and engineered environments and they exist in the form of three hydrates: gypsum (CaSO4·2H2O), bassanite (CaSO4·0.5H2O), and anhydrite (CaSO4). Due to their relevance in natural and industrial processes, the formation pathways of these calcium sulfate phases from aqueous solution have been the subject of intensive research1.
The state-of-the-art of the calcium sulfate formation mechanisms builds upon and goes beyond what we have come to appreciate in the astounding intricacy of other mineral formation processes from ions in aqueous solutions. The original, and rather naive, 'textbook' image of these phenomena, stemming from the adaptation of classical nucleation and growth theories, has increased in complexity due to the discovery of a variety of precursor and intermediate species2. These include solute clusters (e.g. prenucleation clusters, PNCs), liquid(-like) phases, as well as amorphous and nanocrystalline solids etc.. In this context, a number of studies have already revealed that nucleation in the CaSO4-H2O system is non-classical, where the formation of the different crystalline phases involves several steps including a common amorphous precursor1, 3, 4.
In this contribution we show that the formation of the amorphous phase involves the aggregation of small primary particles into larger disordered aggregates exhibiting a "brick-in-the-wall" structure5, 6. The actual crystallization occurs by the restructuring and coalescence of the particles ("bricks") into a given calcium sulfate phase depending on the physicochemical conditions of the solution. Importantly, the rearrangement process does not continue until a (nearly-)perfect homogeneous single crystal is obtained. Instead it comes to a stop, or at least significantly slows down. Such a process thus yields a final imperfect mesocrystal, composed of smaller domains rather than a continuous crystal structure, within which the domains are separated by an amorphous (i.e. less ordered) calcium sulfate phase.
Hence, the non-classical crystallization process of CaSO4 yields a final imperfect mesocrystal with an overall morphology resembling that of a single crystal, yet composed of smaller nano-domains. Importantly, these observations reveal that organic-free calcium sulfate mesocrystals grown by a particle mediated-pathway preserve in the final crystal structure a “memory” or “imprint” of their non-classical nucleation process, something that has been overlooked until now. Furthermore, the nano-scale misalignment of the structural sub-units within these crystals can propagate through the length-scales, and be expressed macroscopically as misaligned zones/domains in large single crystals. Indeed, by considering large anhydrite crystals from the famous Naica Mine (“Cueva de los cristales”) we observed a suite of correlated self-similar void defects spanning multiple length-scales7. These flaws, in the macroscopic crystal, stem from “seeds of imperfection” originating from a particle-mediated nucleation pathway. Hence, building a crystal could be viewed as Nature stacking blocks in a game of Tetris, whilst slowly forgetting the games core concept and failing to fill rows completely.
Calcium sulfate minerals are abundant in natural and engineered environments in the form of three phases: gypsum (CaSO4·2H2O), bassanite (CaSO4·0.5H2O), and anhydrite (CaSO4). Due to their relevance in natural and industrial processes, the formation pathways of these phases from aqueous solution have been the subject of intensive research, a number of studies have already revealed that nucleation in the CaSO4-H2O system is non-classical, The formation of the different crystalline phases involves several steps including a common amorphous precursor.
In this contribution we show that the formation of the amorphous phase involves the aggregation of small primary particles into larger disordered aggregates exhibiting a "brick-in-the-wall" structure. The actual crystallization occurs by the restructuring and coalescence of the "bricks" into a given calcium sulfate phase depending on the physicochemical conditions of the solution. Such a process yields a final imperfect mesocrystal, composed of smaller domains rather than a continuous single crystal structure.
These observations reveal that organic-free calcium sulfate mesocrystals grown by a particle mediated-pathway might preserve in the final crystal structure an “imprint” of their growth pathways. Indeed, by considering large anhydrite crystals from the famous Naica Mine we observed a suite of correlated self-similar void defects spanning multiple length-scales. These flaws, in the macroscopic crystal, stem from “seeds of imperfection” originating from an original particle-mediated growth. Hence, building a crystal could be viewed as Nature stacking blocks in a game of Tetris, whilst slowly forgetting the games core concept and failing to fill rows completely.
Over the years, industrial and human activities and agricultural practices have caused a serious threat to human health and the environment. Indeed, it has been demonstrated that these activities are responsible for the presence of pollutants in the soil, air and water.
Water is one of the most strategic issues today, as it is associated with the living world. Therefore, water pollution is becoming a universal scourge that leads to environmental degradation, decrease of water quality and threatens public health.
Water pollution is mainly due to the discharge of certain harmful chemical compounds that are not very or not at all biodegradable (phenolic compounds, heavy metals, hydrocarbons, dyes, pesticides, etc.) by various industries: chemical, pharmaceutical, textile, food processing, etc. The impact of these industrial effluents on fauna and flora is very harmful. A sensitization of the socio-economic actors and the public, accompanied by a severe regulation in relation to the discharges, would contribute to fight against this drift, but also, by the development of effective methods allowing to remove these pollutants, not only in an analytical purpose but also of depollution.
Thus and within the framework of the preservation of an environment with regard to any anthropogenic activity, our research topic relates to the use of original biosourced polymeric phases for the extraction of the organic compounds and the heavy metals in aqueous mediums.
Therefore, we have proceeded to the synthesis and characterization of a large variety of monomers, polymers and cross-linked materials. These products, partially derived from biomass, contain various functional groups with the ability to interact with chemical components without discriminating effect.
The developed polymer phases have been successfully used for the adsorption of some organic pollutants and heavy metals in synthetic aqueous solutions.
Phenolic compounds constitute a widespread and important class of water pollutants that should be efficiently removed from wastewater because of their toxicity even at low concentrations. They are indeed discharged in the liquid effluents from various factories: chemical, petrochemical, paper, wood, metallurgy and cocking plants 1. Phenols are also found in the waste waters of agroindustrial processes like the olive oil mills, tomato processing and wine distilleries 2,3. These contaminants cause several health problems for humans and aquatic organisms 4. Therefore, numerous studies on the removal of polyphenols from wastewaters have been conducted and many techniques have been used. Among them, adsorption is considered to be the best effective and low cost method. In this context, we have focused our efforts on optimizing adsorption process by development of novel, low-cost adsorbents derived from biobased byproducts with high adsorptive capacity.
The main aim of this study is to synthesize triazole-based poly(ether-pyridine)s as new synthetic adsorbent phases for the extraction of phenolic compounds from aqueous solutions. For this purpose, new fluoromonomers containing 1,2,3-triazole units were prepared by the Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction and then used for the elaboration of novel poly(ether-pyridine-triazole)s (PEPTs) by direct polycondensation with isosorbide and bisphenol A. Chemical structure of fluorinated pyridinic monomers as well as resulting polymers was confirmed by 1H and 19F NMR spectroscopic methods. The thermal behaviour of the obtained PEPTs was characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Their uptake performance to eliminate organic compounds was determined using High Performance Liquid Chromatography (HPLC).
Mechanochemical reactions promise a new direction for environmentally benign preparation of materials, and has been dubbed by IUPAC as one of the 10 chemical innovations that will change our world. Despite this significant promise, very little is known about the mechanisms that drive mechanochemical transformations, posing significant barriers to realizing their full potential. To this end, there is growing need to follow mechanochemical reactions in situ and in real time. We here describe advances in the development and application of XAS methods to monitor material synthesis in real time under mechanochemical conditions. We demonstrate the generality of our approaches by describing mechanochemical syntheses of materials by both vibratory ball milling and by Resonant Acoustic Mixing (RAM), where a time resolution of 1 second is for a whole XAS spectrum was achieved. Moreover, we describe how spectroscopic methods can be coupled to diffraction-based approaches, thereby providing new dimensions in understanding mechanochemical synthesis.
Mechanochemical reactions promise a new direction for environmentally benign preparation of materials, and has been dubbed by IUPAC as one of the 10 chemical innovations that will change our world. Despite this significant promise, very little is known about the mechanisms that drive mechanochemical transformations, posing significant barriers to realizing their full potential. To this end, there is growing need to follow mechanochemical reactions in situ and in real time. We here describe advances in the development and application of XAS methods to monitor material synthesis in real time under mechanochemical conditions. We demonstrate the generality of our approaches by describing mechanochemical syntheses of materials by both vibratory ball milling and by Resonant Acoustic Mixing (RAM), where a time resolution of 1 second is for a whole XAS spectrum was achieved. Moreover, we describe how spectroscopic methods can be coupled to diffraction-based approaches, thereby providing new dimensions in understanding mechanochemical synthesis.
Nanoparticle Populations
(2022)
Two new projects P15 Measurement of particle size and shape distribution of bipyramidal titania including deposition from liquid suspension and P16 Measurement of (relative) number concentration of bimodal silica nanoparticles including deposition from liquid suspension have been started at VAMAS/TWA 34 under the lead of BAM. First results are presented and discussed.
The modern economy is dependent on catalysis, which is main efforts to create environmentally and energy-friendly technologies. The storage of excess electrical energy into chemical energy by splitting water into hydrogen and oxygen is a feasible solution to this energy demand. Due to their abundance on Earth and inherent stability in alkaline solution, transition-metal oxides have become one of several viable alternatives to noble-metal catalysts. Since NiFe oxide is one of the most active oxygen evolution reaction (OER) electrocatalysts for alkaline water electrolysis, it has been the subject of extensive research.
In this work, NiFe2O4 nanoparticles (NPs) of various sizes, specific stoichiometric and non-stoichiometric Fe:Ni surface ratios are synthesized. we will use a combination of ultra-high vacuum surface analysis techniques, such as time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS), to obtain the detailed characterization of the OER electrocatalysts top-surface layer, which is required to identify the rate-limiting step intermediates, and surface morphological changes at the electrolyte/catalyst.
Quantitative Microstructural Analysis - VAMAS TWA 37 & Liaison with ISO/TC 202 Microbeam Analysis
(2022)
The progress in activities on Microbeam Analysis under VAMAS/TWA 37 is reviewed. Particularly the liaison with the new projects within the ISO technical committee TC 202 is presented and discussed with respect to the possibility of identifying and launching related VAMAS projects. The recently started project FIB sample processing for TEM is highlighted. Need of more promotion for the engagement of more participants from industry and academia at national, European and international level is highlighted. Also, the competition with the other technical working areas (on 'nano' or materials-related) is critically discussed. Further, a short overview of the VAMAS areas of activities is given where Germany is involved. Planed regional VAMAS Workshops in Germany in 2023 are announced.
A comparative analysis is performed by XPS, HAXPES and SEM of industrial functionalised graphene powder of different morphology. The chemical analysis carried out by XPS, which probing depth is around 10nm, and HAXPES, which can reach up to 30nm probing depth. By combining these two techniques is possible to get a rough, non-destructive depth profiling of the sample's surface. The results show a higher concentration of the functionlisation elements on the surface of the sample and the influence of the morphology on the functionalisation process and the C/O ratio.
Chemical bonding and coordination environments are crucial descriptors of material properties. They have previously been applied to creating chemical design guidelines and chemical heuristics. They are currently being used as features in machine learning more and more frequently. I will discuss implementations and algorithms (ChemEnv and LobsterEnv) for identifying these coordination environments based on geometrical characteristics and chemical bond quantum chemical analysis. I'll demonstrate how these techniques helped in testing chemical heuristics like the Pauling rule and thereby improved our understanding of chemistry. I'll also show how these tools can be used to create new design guidelines and a new understanding of chemistry. To use quantum-chemical bonding analysis on a large-scale and for machine-learning approaches, fully automatic workflows and analysis tools have been developed. After presenting the capabilities of these tools, I will also point out how these developments relate to the general trend towards automation in the field of density functional based materials science.
XPS of GR2M
(2022)
Die Reduktion von Reibung und Verschleiß in technischen Systemen bietet ein großes Potenzial zur Reduktion von CO2-Emissionen. Dieser Beitrag diskutiert die Erzeugung und tribologische Charakterisierung von Ultrakurzpuls-generierten Nano- und Mikrostrukturen auf Metallen (Stahl, Titan). Besonderes Augenmerk wird dabei auf die Rolle der laserinduzierten Oxidschicht im Zusammenspiel mit verschleißreduzierenden Additiven in ölbasierten Schmiermitteln gerichtet.
The microstructure of most Seljuk and Ilkhanid stucco decorations consists of micrometer-sized crystals of gypsum. The stucco-masters of these periods (neither nowadays stucco-masters) were not able to directly control the properties of these tiny crystals with their hands or centimeter-sized tools. There are, however, traces of chaîne opératoire accumulated in the materialistic body of these pieces, some of which could be explored through an interdisciplinary approach. Such an investigation requires very careful in situ observation of the macrostructure, and scientific analyses of the material to discover part of the production process for each body of stucco. Furthermore, there are deterioration factors, some of which are not yet fully understood, and should be identified using modern analytical instruments. These damaging factors could easily affect the micro and macro structure of a stucco decoration, influencing our interpretation. The concept of chaîne opératoire reframes our questions about the production process and probable dating technique of Seljuk and Ilkhanid stuccoes, while analyses of labmade replicas and historic materials enhance our understanding and interpretation of these materials. Here we present the results of such a study for a large body of Seljuk and Ilkhanid stucco decorations at various sites in Iran, and present the potential of this approach as a new perspective in this field of research.
Laser-Induced Periodic Surface Structures (LIPSS, ripples) are a universal phenomenon and can be generated in a contactless, single-step process on almost any material upon irradiation of solids with intense laser radiation. Nowadays, processing rates of up to m^2/min are enabling new industrial applications in medicine, optics, tribology, biology, etc. Depending on the specific type of LIPSS, their structural sizes typically range from several micrometers down to less than 100 nanometers – far beyond the optical diffraction limit – while their orientations exhibit a clear correlation with the local polarization direction of the laser radiation. From a theoretical point of view, however, a controversial and vivid debate has emerged during the last two decades, whether LIPSS originate from electromagnetic effects (seeded already during the laser irradiation) – or whether they emerge from matter reorganization processes, i.e. distinctly after the laser irradiation. This presentation reviews the currently existent theories of LIPSS. A focus is laid on the historic development of the fundamental ideas, their corresponding mathematical descriptions and numerical implementations, along with a comparison and critical assessment of the different approaches.
We investigate the molecular dynamics and electrical conductivity for a homologous series of linear shaped guanidinium based cyclic ILCs that vary in alkyl chain length, CLCRs (R = 8, 10, 12, 14, 16) by employing broadband dielectric spectroscopy (BDS), and calorimetry comprised of Fast Scanning Calorimetry (FSC) and temperature modulated FSC (TMFSC). Besides conductivity at high temperatures, the dielectric dispersion reveals two relaxation modes: the fast γ and the slow α1 relaxation. The former is assigned to the localized fluctuations while the latter is due to segmental dynamics of the alkyl chains. The γ mode slows down for long chain length CLCs (12,14,16) compared to their shorter analogues. Calorimetric investigation reveals one process, the α2 process, for all ILCs. The α2 process for CLC10, 12, and 14 has a similar temperature dependence as the dielectric α1 relaxation, while for the CLC8 and 10, it's shifted to a higher temperature. For all CLCRs, the absolute values of DC conductivity increase by 4 orders of magnitude at the transition from the plastic crystalline to hexagonal columnar phase. This increase is due to the change in the underlying conduction mechanism from delocalized electron hopping in the crystalline phase to one-dimensional ion mobility in the columnar phase. The glassy dynamics shifts to higher temperatures with increasing alkyl chain length. Conversely, the DC conductivity drops by 3 orders of magnitude from CLC8 to CLC16.
VAMAS-Enabling international standardisation for increasing the take up of Emerging Materials
(2022)
VAMAS (Versailles Project on Advanced Materials and Standards) supports world trade in products dependent on advanced materials technologies by providing technical basis for harmonized measurements, testing, specification, reference materials and standards. The major tools for fulfilling this task are interlaboratory comparisons (ILC). The organisation structure of VAMAS is presented. It is discussed, how a new technical activity can initiate.
Ultrashort pulse laser micromachining at repetition rates of several hundreds of kHz allows a cost-effective high precision manufacturing, which makes this method attractive for many industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per laser pulse is low, for currently available high-repetition-rate laser systems the accumulated X-ray dose becomes significant and radiation safety must be considered. Influences of the processing parameters are discussed and radiation protection aspects will be outlined
The main outcomes of the EMPIR project nPSize are presented and the suitability of the new capabilities, e.g. reference materials, sample preparation protocols, measurement procedures, and data analysis, to be standardized and implemented in accredited analytical laboratories is discussed. Complementation and/or filling gaps of published and ongoing standardisation projects on size, shape and number concentration measurements under ISO/TC 229/JWG 2 are offered.
The two VAMAS inter-laboratory comparisons resulted from the nSPize project and just started under TWA 34 Nanoparticle Populations (Projects #15 and #16) of bipyramidal TiO2 anatase and bimodal SiO2 nanoparticles are presented in detail.
Both essential aspects of the surface of solid matter, its morphology and chemistry, are studied traditionally at BAM starting in the 60’s with different cyclical research focus areas, mostly related either to applicative research or method development. In the recent years, the focus has shifted almost exclusively to the nano-analytics of advanced materials such as complex nanoparticles, (ultra)thin films/coatings, nanocomposites, 2D materials, energy materials, etc. This is also the reason why BAM has established recently the new Competence Center nano@BAM (www.bam.de/Navigation/DE/Themen/Material/Nanotechnologie/sichere-nanomaterialien.html) with the five sub-fields nanoCharacterisation, nanoMaterial, nanoSafety, nanoData and nanoTechnology. The link to the BAM central guidelines to the safety in technology and chemistry is given by the development of reference products such as reference measurement procedures, reference (nano)materials, and newly reference data sets. Thus, an internationally well-networked group in surface analysis has been established @BAM, with regular contributions to integral analytical characterization with metrological and standardization background.
Examples of newly developed methodical approaches will be given with an emphasis on correlative nano-analysis of morphology and chemistry of nanomaterials. Correlative imaging by STEM-in-SEM with high-resolution SEM and EDX, and further with AFM or the new technique TKD (Transmission Kikuchi Diffraction) will be explained on various examples of nanostructures, both as starting materials and embedded/functionalized nanoparticles in products. The unique analytical benefits of the Auger electron probe as a veritable nano-tool for surface chemistry will be highlighted. The panoply of advanced surface characterization methods @BAM is completed by discussing examples of hybrid analysis of the bulk of nanomaterials by X-ray Spectroscopy with the highest surface-sensitive methods X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Particularly for the analysis of the surface chemistry of nanostructures, such as the completeness of the shells of core-shell nanoparticles or in-depth and lateral gradients of chemistry within mesoporous thin layers, the latter methods are inherent.
Other special developments like approaches for the quantitative determination of the roughness of particle surface by electron microscopy or for the quantitative determination of the porosity of thin mesoporous layers by electron probe microanalysis (EPMA) with SEM will be presented.
Experience gained at BAM within the European project ISGScope on the accurate measureemnt of graphene oxide flakes by electron microscopy is presented. Particularly, factors such as the type of solvent, substrate temperature, but also proper, gentle measurement parameters and image analysis conditions towards automation are highlighted. The measurement procedures in develeopment are being prepared to launch an inter-laboratory comparison under VAMAS (TWA41) as preparatory guidance for future standardisation at ISO.
The progress in the activities on Microbeam Analysis under VAMAS/TWA 37 is reviewed. Particularly the liaison with the new projects within the ISO technical committee TC 202 is presented and discussed with respect to the possibility of identifying and launching related VAMAS projects/inter-laboratory comparisons. The recently started project FIB sample processing for TEM is presented. Next projects in the pipeline involving EBSD and TKD are shortly announced. The need of more promotion for the engagement of more experts from industry and academia at national, European and international level is highlighted. Also, the competition with the other technical working areas (on 'nano' or materials-related) is critically discussed.
Molecular crystalline materials are usually brittle and are prone to breaking when mechanically stressed. This fragility greatly limits they application in next the generation of adaptable, functional materials. The recent discovery of mechanical compliancy in molecular crystals has solved this problem.1 Based on the nature of the deformation, molecular crystals can be divided into being plastically (irreversibly) or elastically (reversibly) bendable. The plastic deformation is generally associated with anisotropic molecular arrangements and the existence of low energy slip planes which allow a permanent motion within the lattice. Here we report 4-bromo-6-[(6-chloropyridin-2-ylimino)methyl]phenol (CPMBP) as a promising candidate for future waveguide technologies.2 CPMBP has been found to have two different polymorphs with distinct optical and mechanical properties. The brittle crystals of Form I exhibits very weak emission at 605 nm (λex = 425 nm; photoluminescence quantum yield Φ = 0.4 %). In contrast, Form II has a large plastic regime together with a bright emission at 585 nm (λex = 425 nm; Φ = 8.7 %). Taking advantage of the favorable mechanical flexibility and optical properties, Form II was used as a shapeable optical waveguide. By changing the wavelength of the light source, active or passive waveguiding can be realized. CPMBP could thus be used as a flexible wavelength filter.
This talk was part of the inauguration event for the new x-ray photoelectron spectrometer with the possibility to measure HAXPES (hard energy x-ray photoelectron spectroscopy). With HAXPES detailed chemical information can now be gained not only from the first outermost nanometres of the sample surface, but also from deeper regions. In this talk first results and experiences handling the spectrometer are shown.
In current Li-ion batteries electrode materials consist typically of inorganic materials, such as LiCoO2, LiNixCoyMn1-zO2, LiFePO4, Li4Ti5O12. These materials struggle with toxicity or limited mineral resources, making them expensive. Therefore, eco-friendly, sustainable, and low-cost alternatives are researched for in recent years. A series of organic compounds were investigated as electrode materials for alkali-ion batteries. Among them organic carbonyl-based materials show reversible storage of lithium- or sodium-ions. Metal terephthalates stand out with their easy synthesis, moderate operational voltage and enhanced dissolution stability compared to other organic compounds. One degradation pathway consists of the dissolution of the electrode material by HF, formed in a side reaction by water and the fluorous electrolyte. Fluorinated metal terephthalates could offer higher dissolution stability against HF and less contamination by water due to their increased hydrophobicity.
The goal of this project is the synthesis and the investigation of the formation mechanism of a series of calcium-based MOFs with increasing fluorine content. For this purpose, we aimed for the construction of calcium-based MOFs with terephthalic acid (H2-pBDC), 2-fluoro-terephthalic acid (H2-2F-pBDC), 2,3,4,5-tetrafluoroterephthalic acid (H2-pBDC-F4), isophthalic acid (H2-mBDC) and 5-fluoro-isophthalic acid (H2-5F-mBDC).
Influence of oxidation in the formation and performance of laser-induced periodic surface structures
(2022)
The fabrication of laser-induced periodic surface structures (LIPSS) has been reported for metallic, semiconductor and dielectric materials when irradiated with linearly polarized ultrashort laser pulses. Different sets of processing parameters have been identified and extensively studied, allowing the use of LIPSS for applications in medicine, tribology and surface wetting to name a few. One important parameter that is often not considered is the laser-induced oxidation that is produced especially when oxidation prone materials are irradiated in air environment. This surface oxidation can potentially influence the final structures
size, shape and orientation and modify their functionality in some specific applications.
In this work, we first study the influence of the laser-induced oxidation layer on the formation of LIPSS by characterizing the response of the oxidation prone
hard-coating material chromium nitride. Moreover, we employ complementary surface and depth-profiling analytic techniques to reveal morphological, chemical and structural features of different types of surface structures and LIPSS produced on titanium-based substrates. Finite-difference time-domain (FDTD) calculations finally explain how this superficial oxidation layer promotes the formation of a new type of low spatial frequency LIPSS. Also, we measure the depth-extent of the different oxides formed and demonstrate its beneficial influence for friction reduction and wear resistance applications.
The Competence Centre nano@BAM is presenting a new X-ray Photoelectron Spectrometer – the HAXPES (XPS at hard energy) – for researching advanced materials at the nanoscale. With HAXPES detailed chemical information can now be gained not only from the first outermost nanometres of the sample surface, but also from deeper regions.
Top international experts will share their knowledge and key findings on how to utilise HAXPES for exploring the surface of various advanced materials. Following the lectures, we will show you a short demo of the new instrument and answer your questions.
In the face of rising energy demand and the impending climate change the development of a sustainable, fossil-free fuel and chemical production is of global importance. One possible goal is the development of electrochemical conversion processes using catalysts. Porous materials play an important role in such energy applications. The activity and stability of each catalyst is highly dependent on the properties of the coating, i.e., phase composition, crystallinity, accessible surface area, and many other factors. The key to the development of improved catalysts is a better understanding of the relations between their performance, stability and physico-chemical properties. However, the complex morphology of such catalysts constitutes a challenge even for modern analytical techniques. Spectroscopic ellipsometry (SE) is a versatile method for studying material properties by using appropriate models (e.g., film thickness, optical and electronic properties). Ellipsometric models need to be validated in order to produce accurate results. In a first step, the model for the ellipsometric fit studies of a calcination series of mesoporous iridium oxide films (300 – 600 °C) was investigated and validated with respect to their material properties.[4] The information on electronic structure of the catalysts shows a direct correlation with electrochemical activities. The development of an environmental electrochemical cell offers the possibility of investigations under operando conditions. Thus, changes in optical and electronic properties can be induced and monitored during the electrocatalytic oxygen evolution reaction.