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- Ellipsometrie (2)
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- Spectroscopic Ellipsometry (2)
- White light interference microscopy (2)
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Die Oberflächentechnik ist eine Schlüsseltechnologie in nahezu zu allen industriellen Branchen. Mit Ausnahme der mechanischen Stabilität, die das Substrat bereitstellt, werden verschiedenartigste Funktionen materialsparend, zum Teil hochintegriert mit maßgeschneiderten Schichtdesigns unter Ausnutzung von Nano- und Quanteneffekten auf Oberflächen appliziert. Ein Großteil der Fertigungskosten in der Mikro- und Nanotechnik wird durch Reinräume und die Umsetzung ausgeklügelter Reinigungsstrategien zur Vermeidung von Restverschmutzungen und partikulären Belegungen
verursacht, da diese unweigerlich zum Bauteilversagen führen. Die Validierung des Reinigungszustandes ist somit von zentraler Bedeutung für die Schichtqualität und Produktfunktionalität. Dies gilt in Abhängigkeit von der Applikation und den vertikalen Schicht- bzw. lateralen Strukturdimensionen sowohl für Fertigungsprozesse im Reinraum als auch für solche in robuster Umgebung. In der Praxis kommt es häufig vor, dass man mikroskopisch scheinbar saubere Substrate erst durch die Beschichtung „enttarnt" und dann Defekte oft mit bloßem Auge sichtbar werden. Noch problematischer ist der Einbau von Verunreinigungen während der Schichtabscheidung, die zunächst nicht sichtbar sind, dann aber zum Bauteilversagen führen.
Fluid-assisted mass transport reactions by dissolution-precipitation, where a precursor mineral reacts with a fluid, play an important role in metamorphism and metasomatism. We investigated titanite growth on rutile in time series experiments between one and 107 days at constant P-T conditions of 600 °C and 400 MPa in the system TiO2-CaO-SiO2-Na2O-HCl-H2O. A two-capsule assemblage allows for transport of Ca and Si from dissolving wollastonite to dissolving rutile, the Ti-source, in a NaCl-bearing aqueous fluid, according to the general reaction CaSiO3 + TiO2 = CaTiSiO5. Complete overgrowth of rutile by titanite occurred after just one day of experiment. Fine-grained lozenge-shaped titanite crystals of short-time runs (up to 14 days) reorganize to larger predominantly prismatic crystals after >14 days.
After investigation by scanning electron microscopy, the titanite overgrowth was removed from the rutile by hydrofluoric acid, to provide a three-dimensional view of the dissolution-reaction front on the rutile surface. The morphology of the rutile surface is dominated by humps or ridges beneath the central region of a titanite crystal and valleys at the grain boundaries between adjacent titanite crystals. The dissolution pattern on the rutile surface mimics the titanite overgrowth and changes with changing grain size and shape of the titanite with longer run times. The preferred dissolution of rutile in the valleys is clearly linked to the position of the titanite grain boundaries, which served as pathways for fluid-assisted element transport. Rutile-titanite and titanite-titanite boundaries show a significant porosity in transmission electron microscopy images of foils prepared by focused ion beam milling. The large-scale dissolution pattern on the rutile surface is independent of the crystallographic orientation of the rutile and entirely dominated by the arrangement of titanite crystals in the overgrowth. Dissolution features on a scale smaller than ~1 µm are dominated by stepwise dissolution and etch-pits following the crystallographic orientation of the rutile. Similar observations were made in experiments with an additional Al-source, although these experiments result in a different overgrowth pattern; i.e., an exposed rutile surface is always present and solitary titanite crystals are accompanied by partial overgrowths. Quantitative characterization of the surface morphology by white-light interference microscopy demonstrates that, with increasing grain size of titanite, dissolution of rutile is strongly enhanced at the titanite grain boundaries.
Natural examples of titanite overgrowths on rutile show the same relations between element pathways, arrangement of titanite crystals and 3D dissolution pattern on rutile as in the experimental systems. We conclude that the transport of Ti away from the rutile and of Ca + Si into the reaction rim occurred in a grain boundary fluid, the composition of which must have been strongly different from the composition of the bulk fluid in the experiment, as well as in the natural system. The reaction progress depends on the availability of a fluid, and relicts of rutile in titanite indicate restricted availability of fluid in the natural system (e.g., a fluid pulse that was consumed by the reactions). The reaction examined here can serve as a proxy for other reactions of the conversion of oxide minerals (e.g., spinel or corundum) into silicates.
Most of the polymeric materials used are easy to ignite and show extensive flame spread along their surfaces. Apart from extensive heat release rates, their short time to ignition (tig), in particular, is a key fire hazard. Preventing ignition eliminates fire hazards completely. Protection layers that shift tig by more than an order of magnitude are powerful flame retardancy approaches presenting an alternative to the usual flame retardancy concepts.
Coatings are proposed that consist of a three-layer system to ensure adhesion to the substrate, acting as an infrared (IR) mirror and protecting against oxidation. The IR-mirror layer stack is realised by physical vapour deposition in the sub-micrometre (<1 µm) range, reducing heat absorption by up to an order of magnitude. Not only is the ease of ignition diminished (tig is increased by several minutes), the flame spread and fire growth indices are also remarkably reduced to as little as 1/10 of the values of the uncoated polymers open for further optimization. Sub-micrometre thin IR-mirror coatings yielding surface absorptivity <0.1 are proposed as a novel and innovative flame retardancy approach.
Embedding of information on surfaces is state of the art for identification testing in which public, hidden and forensic features are used. In many instances, the legal authentication of a product, a material or a document is required. Among the surface-based encoded labels, bar codes and data matrices are most frequently applied. They are publicly visible. The material itself is irrelevant, only a sufficient optical contrast is required.
However, a strong material dependence of the label can be achieved by means of Fabry-Perot layer stacks. Stack designs are described with regard to all three security levels: public features (e.g. color and tilt effect) perceptible by the human eye, hidden features (e.g. optical response in a given spectral range) detectable by commonly available instruments and forensic features (ellipsometric quantities Ψ and Δ as a function of wavelength λ and angle of incidence AOI) only detectable by sophisticated instruments.
Regarding material-correlated authentication, ellipsometric quantities Ψ and Δ are used as encoded forensic features for the first time. Hence, Fabry-Perot layer stacks as information carriers in combination with imaging ellipsometry as optical read-out system provide all-in-one anti-counterfeiting capabilities.
Optical constants of In2O3-SnO2 (Indium tin oxide, ITO)
Minenkov et al. 2024: on glass; n,k 0.191–1.69 µm
Optical constants of In2O3-SnO2 (Indium tin oxide, ITO)
Minenkov et al. 2024: on Si wafer, top; n,k 0.191–1.69 µm
Optical constants of In2O3-SnO2 (Indium tin oxide, ITO)
Minenkov et al. 2024: on Si wafer, bottom; n,k 0.191–1.69 µm
Abstract. In power electronics, compound semiconductors with large bandgaps, like silicon carbide (SiC), are increasingly being used as material instead of silicon. They have a lot of advantages over silicon but are also intolerant of nanoscale material defects, so that a defect inspection with high accuracy is needed. The different defect types on SiC samples are measured with various measurement methods, including optical and tactile methods. The defect types investigated include carrots, particles, polytype inclusions and threading dislocations, and they are analysed with imaging ellipsometry, coherent Fourier scatterometry (CFS), white light interference microscopy (WLIM) and atomic force microscopy (AFM). These different measurement methods are used to investigate which method is most sensitive for which type of defect to be able to use the measurement methods more effectively. It is important to be able to identify the defects to classify them as critical or non-critical for the functionality of the end product. Once these investigations have been completed, the measurement systems can be optimally distributed to the relevant defects in further work to realize a hybrid analysis of the defects. In addition to the identification and classification of defects, such a future hybrid analysis could also include characterizations, e.g. further evaluation of ellipsometric data by using numerical simulations.
The synthesis of polymerlike amorphous carbon (a-C:H) thin-films by microwave excited collisional hydrocarbon plasma process is reported. Stable and highly aromatic a-C:H were obtained containing significant inclusions of poly(p-phenylene vinylene) (PPV). PPV confers universal optoelectronic properties to the synthesized material. That is a-C:H with tailor-made refractive index are capable of becoming absorption-free in visible (red)-near infrared wavelength range. Production of large aromatic hydrocarbon including phenyl clusters and/or particles is attributed to enhanced coagulation of elemental plasma species under collisional plasma conditions. Detailed structural and morphological changes that occur in a-C:H during the plasma synthesis are also described.
Transparent conductive oxides such as indium tin oxide (ITO) are standards for thin film electrodes, providing a synergy of high optical transparency and electrical conductivity. In an electrolytic environment, the determination of an inert electrochemical potential window is crucial to maintain a stable material performance during device operation. We introduce operando ellipsometry, combining cyclic voltammetry (CV) with spectroscopic ellipsometry, as a versatile tool to monitor the evolution of both complete optical (i.e., complex refractive index) and electrical properties under wet electrochemical operational conditions. In particular, we trace the degradation of ITO electrodes caused by electrochemical reduction in a pH-neutral, water-based electrolyte environment during electrochemical cycling. With the onset of hydrogen evolution at negative bias voltages, indium and tin are irreversibly reduced to the metallic state, causing an advancing darkening, i.e., a gradual loss of transparency, with every CV cycle, while the conductivity is mostly conserved over multiple CV cycles. Post-operando analysis reveals the reductive (loss of oxygen) formation of metallic nanodroplets on the surface. The reductive disruption of the ITO electrode happens at the solid–liquid interface and proceeds gradually from the surface to the bottom of the layer, which is evidenced by cross-sectional transmission electron microscopy imaging and complemented by energy-dispersive X-ray spectroscopy mapping. As long as a continuous part of the ITO layer remains at the bottom, the conductivity is largely retained, allowing repeated CV cycling. We consider operando ellipsometry a sensitive and nondestructive tool to monitor early stage material and property changes, either by tracing failure points, controlling intentional processes, or for sensing purposes, making it suitable for various research fields involving solid–liquid interfaces and electrochemical activity.