This article explores recent advances in the design and engineering of materials wholly or principally constructed from peptides. We focus on materials that are able to respond to changes in their environment (pH, ionic strength, temperature, light, oxidation/reduction state, presence of small molecules or the catalytic activity of enzymes) by altering their macromolecular structure. Such peptide-based responsive biomaterials have exciting prospects for a variety of biomedical and bionanotechnology applications in drug delivery, bio-sensing and regenerative medicine.

Peptide-based stimuli-responsive biomaterials

Capacitors are one type of reliability-critical components in power electronic systems. In the last two decades, many efforts in academic research have been devoted to the condition monitoring of capacitors to estimate their health status. Industry applications are demanding more reliable power electronics products with preventive maintenance. Nevertheless, most of the developed capacitor condition monitoring technologies are rarely adopted by industry due to the complexity, increased cost, and other relevant issues. An overview of the prior-art research in this area is therefore needed to justify the required resources and the corresponding performance of each key method. It serves to provide a guideline for industry to evaluate the available solutions by technology benchmarking, as well as to advance the academic research by discussing the history development and the future opportunities. Therefore, this paper first classifies the capacitor condition monitoring methods into three categories, then the respective technology evolution in the last two decades is summarized. Finally, the state-of-the-art research and the future opportunities targeting for industry applications are given.

A Review of the Condition Monitoring of Capacitors in Power Electronic Converters

Power cycling test is one of the important tasks to investigate the reliability performance of power device modules in respect to temperature stress. From this, it is able to predict the lifetime of a component in power converters. In this paper, representative power cycling test circuits, measurement circuits of wear-out failure indicators as well as measurement strategies for different power cycling test circuits are discussed in order to provide the current state of knowledge of this topic by organizing and evaluating current literature. In the first section of this paper, the structure of a conventional power device module and its related wear-out failure mechanisms with degradation indicators are discussed. Then, representative power cycling test circuits are introduced. Furthermore, on-state collector–emitter voltage $(V_{{\rm{CE\_ON}}})$ and forward voltage $(V_{F})$ measurement circuits for wear-out condition monitoring of power device modules during power cycling test are presented. Finally, different junction temperature measurement strategies for monitoring of solder joint degradation are explained.

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Power Cycling Test Methods for Reliability Assessment of Power Device Modules in Respect to Temperature Stress

Oxygen vacancies, especially their distribution, are directly coupled to the electromagnetic properties of oxides and related emergent functionalities that have implications for device applications. Here using a homoepitaxial strontium titanate thin film, we demonstrate a controlled manipulation of the oxygen vacancy distribution using the mechanical force from a scanning probe microscope tip. By combining Kelvin probe force microscopy imaging and phase-field simulations, we show that oxygen vacancies can move under a stress-gradient-induced depolarisation field. When tailored, this nanoscale flexoelectric effect enables a controlled spatial modulation. In motion, the scanning probe tip thereby deterministically reconfigures the spatial distribution of vacancies. The ability to locally manipulate oxygen vacancies on-demand provides a tool for the exploration of mesoscale quantum phenomena and engineering multifunctional oxide devices. The properties of complex oxides such as strontium titanate are strongly affected by the presence and distribution of oxygen vacancies. Here, the authors demonstrate that a scanning probe microscope tip can be used to manipulate vacancies by the flexoelectric effect.

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Controlled manipulation of oxygen vacancies using nanoscale flexoelectricity

Reactive Photo-Fenton ceramic membranes: Synthesis, characterization and antifouling performance.

Degradation testing and failure analysis of DC film capacitors under high humidity conditions

Wire bond degradation under thermo- and pure mechanical loading

Kelvin probe force microscopy is a widely used technique for measuring surface potential distributions on the micro- and nanometer scale. The data are, however, often analyzed qualitatively, especially for dielectrics. In many cases, the phenomenon of polarization and its influence on the measured signals is disregarded leading to misinterpretation of the results. In this work, we present a model that allows prediction of the surface potential on a metal/polymer heterostructure as measured by Kelvin probe force microscopy by including the tip-induced polarization of the dielectric that arises during measurement. The model is successfully verified using test samples.

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Modelling and experimental verification of tip-induced polarization in Kelvin probe force microscopy measurements on dielectric surfaces

The self-assembly of fibers from peptides have attracted a tremendous amount of attention due to the many applications such as drug-delivery systems, tissue engineering and electronic devices. Recently, the self-assembly potential of the designer peptide RFFFR has been reported. In the current study it is experimentally verified that the peptides form fibers that are entangled and form solid spheres without water inside. Upon dilution below the critical fiber concentration, the fibers untangle and become totally separated prior to dissolution. These structures readily bind Thioflavin T, resulting in achange in fluorescent properties, coherent with beta-sheet rich amyloid structures. Circular dichroism spectroscopy data is dominated by a pi-pi transition indicating that the fibers are stabilized by pi-stacking.Contrary to what was expected, the dissolution of the spheres/fibers results in increasing fluorescence anisotropy over time. This is explained by HomoFRET between phenylalanine residues with a T-shapedpi-stacking mode, which was determined as the dominant mode by atomistic simulations and semi-empirical calculations in another study. Kelvin probe force microscopy measurements indicate that the spheres and fibers have a conductivity comparable to that of gold. Hence these self-assembled structures may be applicable in organic solid-state electronic devices. The dissolution properties of the spheres also suggest that they may be used as drug-delivery systems.

The Physical Properties and Self-Assembly Potential of the RFFFR Peptide.

Failure mode and effect analysis (FMEA) is an important step in the reliability assessment process of electric components. It provides knowledge of the physics of failure of a component that has been subjected to a given stress profile. This knowledge enables improvement of the component robustness and durability and serves as verification that failure- and degradation mechanisms remain the same at different stress levels during accelerated testing. In this work we have used Kelvin probe force microscopy (KPFM) to analyze metallized film capacitors with the purpose of determining the degradation mechanism(s) they suffered from accelerated testing. We have prepared film capacitors for analysis by micro-sectioning and verified the quality of the preparation procedure using optical and atomic force microscopy. The potential distribution in the layer structure (alternating 7 μm thick dielectric and 50–100 nm thick metal) of a new capacitor was used as reference. KPFM measurements on the degraded capacitors showed a change in contact potential difference from −0.61V on the reference cap acitor to 3.2V on the degraded ones, indicating that corrosion of the metallization had happened. Studies also sho wed that some of the metallization stripes had lost contact to the end-spray. In conclusion we have shown that the surface electric potential distributions on micro-sectioned film capacitors can be obtained through KPFM analysis. We have, from KPFM measurements, shown that the degraded capacitors under investigation had suffered from metallization corrosion and some degree of end-spray detachment. The results obtained in this work, along with results from the literature, demonstrate the usefulness of KPFM as a tool for FMEA.

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Dennis Achton Nielsen

Papers

Degradation testing and failure analysis of DC film capacitors under high humidity conditions

Wire bond degradation under thermo- and pure mechanical loading

Modelling and experimental verification of tip-induced polarization in Kelvin probe force microscopy measurements on dielectric surfaces

The Physical Properties and Self-Assembly Potential of the RFFFR Peptide.

Electric field mapping inside metallized film capacitors