Carbon‐film‐based Zernike phase plates with smooth thickness gradient for phase‐contrast transmission electron microscopy with reduced fringing artefacts

Phase plates (PPs) in transmission electron microscopy (TEM) improve the contrast of weakly scattering objects under in-focus imaging conditions. A well-established PP type is the Zernike (Z)PP, which consists of a thin amorphous carbon (aC) film with a microscaled hole in the centre. The mean inner potential of the aC film is exploited to shift the phase of the scattered electrons while the unscattered electrons in the zero-order beam propagate through the hole and remain unaffected. However, the abrupt thickness increase at the hole edge induces an abrupt change of the phase-shift distribution and leads to fringing, that is, intensity oscillations around imaged objects, in TEM images. In this work, we have used focused-ion-beam milling to fabricate ZPPs with abrupt and graded thickness profiles around the centre hole. Depending on the thickness gradient and inner hole radius, graded-ZPP-TEM images of an aC/vacuum interface and bundles of carbon nanotubes (CNTs) show strongly reduced fringing. Image simulations were performed with ZPP-phase-shift distributions derived from measured thickness profiles of graded ZPPs, which show good agreement with the experimental images. - Fringing artefacts, that is, intensity oscillations around imaged objects, are strongly reduced for Zernike phase plates with a graded thickness profile around the centre hole. - Focused-ion-beam milling is used to fabricate graded Zernike phase plates with specific inner hole radius and thickness gradients. - The phase-shift distribution is obtained from measured thickness profiles around the centre hole. - Image simulations based on experimentally measured thickness/phase-shift distributions show good agreement with experimental Zernike phase-plate TEM images

Solomon equations for qubit and two-level systems

We model and measure the combined relaxation of a qubit, a.k.a. central spin, coupled to a discrete two-level system (TLS) environment. We present a derivation of the Solomon equations starting from a general Lindblad equation for the qubit and an arbitrary number of TLSs. If the TLSs are much longer lived than the qubit, the relaxation becomes non-exponential. In the limit of large numbers of TLSs the populations are likely to follow a power law, which we illustrate by measuring the relaxation of a superconducting fluxonium qubit. Moreover, we show that the Solomon equations predict non-Poissonian quantum jump statistics, which we confirm experimentally

Intrinsic nano-diffusion-couple for studying high temperature diffusion in multi-component superalloys

We present a new approach for the quantitative study of high-temperature diffusion in compositionally complex superalloys on the nano-scale. As key element, the approach utilizes the γ/γ\u27-microstructure itself as intrinsic nano-diffusion-couple (NDC). By establishing equilibrium at one temperature followed by annealing at a different temperature, well-defined transient states are generated which are studied using STEM-EDXS. We demonstrate this approach for a multi-component superalloy of CMSX-4 type. The temporal evolution of element concentrations is consistently revealed for γ- and γ\u27-forming elements and is compared to diffusion simulations based on DICTRA. Excellent agreement is obtained for Ni, Co, and Cr whereas diffusion of Al and, in particular, Re lacks behind in experiment. Finally, it is demonstrated that transient states can also be captured by in situ TEM using chip-based heating devices. The NDC approach offers great opportunities for diffusion studies in compositionally complex superalloys and might be extended to other two-phase multi-component systems

Fano Interference in Microwave Resonator Measurements

Resonator measurements are a simple but powerful tool to characterize a material's microwave response. The losses of a resonant mode are quantified by its internal quality factor $Q_\mathrm{i}$, which can be extracted from the scattering coefficient in a microwave reflection or transmission measurement. Here we show that a systematic error on $Q_\mathrm{i}$ arises from Fano interference of the signal with a background path. Limited knowledge of the interfering paths in a given setup translates into a range of uncertainty for $Q_\mathrm{i}$, which increases with the coupling coefficient. We experimentally illustrate the relevance of Fano interference in typical microwave resonator measurements and the associated pitfalls encountered in extracting $Q_\mathrm{i}$. On the other hand, we also show how to characterize and utilize the Fano interference to eliminate the systematic error

Selective Detection of NADPH Oxidase in Polymorphonuclear Cells by Means of NAD(P)H-Based Fluorescence Lifetime Imaging

NADPH oxidase (NOX2) is a multisubunit membrane-bound enzyme complex that, upon assembly in activated cells, catalyses the reduction of free oxygen to its superoxide anion, which further leads to reactive oxygen species (ROS) that are toxic to invading pathogens, for example, the fungus Aspergillus fumigatus. Polymorphonuclear cells (PMNs) employ both nonoxidative and oxidative mechanisms to clear this fungus from the lung. The oxidative mechanisms mainly depend on the proper assembly and function of NOX2. We identified for the first time the NAD(P)H-dependent enzymes involved in such oxidative mechanisms by means of biexponential NAD(P)H-fluorescence lifetime imaging (FLIM). A specific fluorescence lifetime of 3670±140 picoseconds as compared to 1870 picoseconds for NAD(P)H bound to mitochondrial enzymes could be associated with NADPH bound to oxidative enzymes in activated PMNs. Due to its predominance in PMNs and due to the use of selective activators and inhibitors, we strongly believe that this specific lifetime mainly originates from NOX2. Our experiments also revealed the high site specificity of the NOX2 assembly and, thus, of the ROS production as well as the dynamic nature of these phenomena. On the example of NADPH oxidase, we demonstrate the potential of NAD(P)H-based FLIM in selectively investigating enzymes during their cellular function

Combined 3D characterization of porous zeolites by STEM and FIB tomography

German Research Foundation Priority Program 1570German Research Foundation Cluster of Excellence EXC 315 “Engineering of Advanced Materials

Surface functionalisation of sol-gel-based bioactive glass scaffolds for drug delivery

ITN FP-7 project “GlaCERCo

Amorphous NiCu Thin Films Sputtered on TiO2 Nanotube Arrays: A Noble-Metal Free Photocatalyst for Hydrogen Evolution

In this work, NiCu co-catalysts on TiO2 are studied for photocatalytic hydrogen evolution. NiCu co-catalyst films are deposited at room temperature by argon plasma sputtering on high aspect-ratio anodic TiO2 nanotubes. To tune the Ni : Cu atomic ratio, alloys of various compositions were used as sputtering targets. Such co-catalyst films are found to be amorphous with small nanocrystalline domains. A series of parameters is investigated, i. e., i) Ni : Cu relative ratio in the sputtered films, ii) NiCu film thickness, and iii) thickness of the TiO2 nanotube layers. The highest photocatalytic activity is obtained with 8 μm long TiO2 nanotubes, sputter-coated with a 10 nm-thick NiCu films with a 1 : 1 Ni : Cu atomic ratio. This photocatalyst reaches a stable hydrogen evolution rate of 186 μL h−1 cm−2, 4.6 and 3 times higher than that of Ni- and Cu-TiO2, respectively, demonstrating a synergistic co-catalytic effect of Ni and Cu in the alloy co-catalyst film