6 Materialchemie
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Paper des Monats
- ja (19)
Multi-functional coatings are a key requirement for surface engineering. General demands are adhesion and long-term stability under service conditions. The modification of surfaces by means of PVD-, ECD- or hybrid processes allows an add-on functionalization of surfaces by a huge diversity of materials with both lateral and vertical micro-/nano-designs. This fact is a prerequisite for micro- and sensor-systems in lab-on-chip and sensor-on-chip technology. Two layer-based sensor principles are presented, i.e. surface plasmon resonance enhanced spectroscopic ellipsometry (SPREE) for detection of hazardous gases and magneto-optical sensors on smart-coated fiber Bragg gratings (FBG) for structural health monitoring (SHM).
The interdependence of substrate features, coating properties, and layer design is discussed firstly for gas sensitivity and selectivity of SPREE-sensors and secondly for sensitivity and selectivity of magneto-strictive coatings to mechanical strain or external magnetic fields resulting in an optical displacement of the Bragg wavelength of FBG-sensors. Moreover, generic features such long-term stability, crucial process-related fabrication conditions, and effects of operational and environmental parameters are discussed with respect to the sensor performance. It has been shown that appropriate layer design and adapted selection of layer materials (SnOx/Au, Fe/Ni:SnOx/Au; Ni/NiFe-Cu-Cr) result in improved sensor parameters and may enable new sensor applications.
Der Vortrag widmet sich der „ELLIPSOMETRISCHE KLASSIFIZIERUNG VON KOHLENSTOFFSCHICHTEN“ und beschreibt die Punkte: 1. Anwendungen Kohlenstoffschichten–Carbon–based films (DLC) aus dem Vortrag N. Ohtakeet. al. (ISO TC 107, Tokyo 2017),2. Präparation der Kohlenstoffschichten für ISO TC 107 Ringversuch aus Vortrag M. Hiratsuka et. al. (ISO TC 107, Tokyo 2017), 3. Ellipsometrische Charakterisierung von Kohlenstoffschichten, Ergebnisse des Ringversuchs (ISO TC 107, Tokyo 2017) Vortrag Beck et. al. und 4.Deutsche Normungsaktivitäten national/international zur Ellipsometrie DIN NA 062-01-061 (DIN 50989-1)/TC 107 (PWI DE)“ im Einzelnen.
Imaging of surfaces regarding topographical, morphological, micro-structural, and chemical features is a key requirement for quality control for the identification of contaminated, degraded, damaged or deliberately modified surface areas vs. clean, virgin, undamaged or unmodified regions. As optical functions may represent any of these changes on the micro- and nano-scale, imaging ellipsometry (IE) is the technique of choice using either intensity, phase, or/and amplitude contrast for visualization of low-contrast surface modifications [1, 2]. Defects or surface and film features whether native or artificial, intended or unintended, avoidable or unavoidable as well as surface pattern are of interest for quality control. In contrast to microscopic techniques operated at normal incidence, ellipsometry as oblique-incidence technique provides improved contrast for vertically nano-scaled add-on or sub-off features such as ultra-thin transparent films, metallic island films, carbon-based thin films, laser modification or laser induced damage, dried stain, cleaning agent or polymeric residue. Two-sample reference techniques, i.e. referenced spectroscopic ellipsometry (RSE) may further increase sensitivity and decrease measurement time. In case of particulate accumulations depolarization contrast imaging (DCI) may improve the lateral resolution beyond the Abbe limit. This has been proven for silica spheres as reference in terms of single particles, particulate accumulations or particulate monolayers and layer stacks. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used for reference measurements of particle diameter, particle height, or particulate layer/accumulation thickness. It has been shown that single silica particles of 250 nm in diameter, i.e. at least a factor of 4 better than the lateral resolution limit as of now, can be visualized on even substrates. However, the ellipsometric measurement of particle diameters of this size needs further efforts interpretation.
Auf dem Weg zu Industrie 4.0: Bestimmung von Messunsicherheitsbudgets in der Oberflächentechnik
(2019)
Vorgestellt wurde die Bestimmung von Messunsicherheitsbudgets für sehr unterschiedliche physikalische Größen, die in der Oberflächentechnik von hoher Relevanz sind: Stufenhöhe h, Schichtdicke d, Eindringhärte HIT und Haftfestigkeit. Die Unterschiede betreffen die Art der Prüfmethodik (optisch zerstörungsfrei vs. mechanisch invasiv/zer-störend), die laterale Größe des Integrationsgebietes der Messung (lokal:nano bis sub-mikro vs. global: mikro bis makro) und die Art der Bestimmung von Messunsicherheitsbudgets (physikalische Größen: direkt rückführbar; Werkstoffkenngröße: genormt; Systemkenngröße: genormt).
Im Rahmen von Industrie 4.0 werden ausgehend der geforderten Spezifikation des beschichteten Produkts (Mittelwert mit Vertrauensbereich oder Mindestwert) durchgehende Toleranzbänder zur Oberflächenmodifizierung/Beschichtung des Substrats, einhergehend mit Prozessfenstern, die diese Toleranzbänder garantieren, erforderlich, die zuverlässig erfasst werden müssen. Die Frage der anzuwendenden Mess- und Prüftechnik und die damit notwendige Betrachtung von Messunsicherheitsbudgets ist für die Digitalisierung von Konditionierungs-, Zustands-, Regel- und Steuergrößen unverzichtbar. Mit Blick auf die Einhaltung von Prozessfenstern und die dafür notwendige Prozessführung wird technologisches Kern-Know-how digitalisiert, das es unbedingt zu schützen gilt. Nur lokale Netze können diese Sicherheit garantieren, in globalen Netzen ist die Datensicherheit bestenfalls maximierbar.
Sufficient adhesion/tensile strength are basic requirements for any coating/composite material. For coatings, adhesive strength in N/mm2 is of Major interest for various applications such as decorative and water-repellent coatings on wood (paints and varnishes), optical coatings on glass and polymers (reflectors and filters), electrical coatings on semiconductors, glass and polymers (conducting and bondable layers), mechanical coatings on metals and polymers (wear-reduction, scratch-resistance) and adhesion-promoting layers. For composite materials, tensile strength in N/mm2 is also a key quantity for carbon fiber reinforced composites (CFC), laminates and adhesive-bonded joints. Centrifugal adhesion testing (CAT) transfers the single-sample tensile test from a tensile or universal testing machine into an analytical centrifuge as multiple-sample test of up to eight test pieces. The one-sided sample support instead of a two-sided sample clamping and the absence of mounting- and testing-correlated shear forces provides fast and reliable results both for adhesive strength and bonding strength by means of bonded test stamps. For bonding strength, the evaluation of failure pattern from microscopic inspection is required in order to determine the failure pattern according to ISO 10365 such as adhesive failure (AF), delamination failure (DF) and cohesive failure (CF). Hence, one test run by CAT-technology provides either statistics or ranking of up to eight samples at once. For adhesive strength of coatings, a variety of examples is discussed such as ALD-Al203 layers as adhesion promoters, evaporated Ag-layers on N-BK7 glass, sputtered Cr- and Al-layers on Borofloat 33 glass, evaporated Au-films on N-BK7 glass and sputtered SiO2 -layers on CR39 Polymer. Provided adhesive or bonding strength are high enough, the substrate or the joining part may also fail.
Proposal for revision of en 15870 „Adhesives determination of tensile strength of butt joints”
(2021)
The paper addresses the PROPOSAL FOR REVISION OF EN 15870
„ADHESIVES -DETERMINATION OF TENSILE STRENGTH OF BUTT JOINTS” “ and the follow points are discussed in more detail: Adhesives-Determination of tensile strength of butt joints, Introduction of Centrifugal Adhesion Testing, Comparison of Testing Methods.
The lack of on-line validation procedures for structure-embedded fiber-optical strain sensors, in particular fiber-Bragg-gratings (FBG), resulted in limited applications in structural health monitoring (SHM). Degradation under service conditions and ageing as a result of climatic influences or delamination under load were unsolved Validation issues. This could be overcome by means of an auto-diagnosis procedure based on FBG-sensors coated by electrochemical deposition (ECD) with a magnetostrictive NiFe-coating on top of an adhesive Cu/Cr adhesive layer deposited by physical vapour deposition (PVD) around the FBG strain sensor. This allows at any time under Service a validation of sensor functionality, stability, and reliability. For this purpose, a magnetic strain-proportional reference field is introduced. The optical read-out is realized by the measurement of the Bragg-wavelength shift.
The ratio of resulting strain and exciting magnetic reference field should be constant given that the sensor is in proper function.
In principle, the magnetostrictive coating around the FBG should also work as on-line magnetic field sensor and other applications in material science. One of these applications is the in-situ monitoring of ECD processes as the deposition of the ECD NiFe-layer on the FBG revealed. Challenges are the monitoring of temperature, deposition
stages/thickness, and resulting mechanical stress under given plating conditions. Monitoring problems can be solved by applying a pre-coated FBG to the electrolytic process as the shift of the Bragg wavelength is affected by both the temperature of the electrolyte near the substrate and the stress formation in the growing layer. The experimental FBG set-up and the quantitative determination of temperature- and stress-related strain are described for a nickeliron
electrolyte. The in-situ measurement of Bragg wavelength shifts of a pre-coated FBG during electrochemical deposition allows a detailed analysis of stress states due to changes in the growth morphology of the layer. The separation of mechanical and thermal contributions to this shift provides information on the individual Deposition processes in terms of a process fingerprint.