Using photo-activated localization microscopy (PALM) for imaging fluorophore-doped photoresists

Photoresists play a key role in the photolithographic process being necessary to print the structure layout of dies of microchips. Following Moore’s law leads to ever smaller assemblies reaching the single-digit nanometer range. Typical methods for quality assurance are scatterometry and atomic force microscopy facing challenges and disadvantages. Since overcoming the Abbe limit via superresolution techniques fluorescence microscopy can be another approach. This article describes the measurement analyses done with PALM/STORM on lithographical produced samples of positive resist doped with Atto 565. Lines with 200 nm thickness and equal spacing were studied. Thereby, ThunderSTORM provided better results than QuickPALM for data analysis. For the first experiment, using a permanently switched on 405 nm laser beam with low intensity shows the best resolution results. A rotating lambda half-wave plate in the second experiment leads to a slight increase of data quality. Further studies combining these two approaches will be carried out

Non-Classical Self-Assembly of Anisotropic Magneto-Organosilica Janus Particles Possessing Surfactant Properties and the Field-Triggered Breakdown of Surface Activity and Amphiphilic Properties

Using colloidal particles as models to understand processes on a smaller scale is a precious approach. Compared to molecules, particles are less defined, but their architecture can be more complex and so is their long-range interaction. One can observe phenomena that are unknown or much more difficult to realize on the molecular level. The current paper focuses on particle-based surfactants and reports on numerous unexpected properties. The main goal is creating an amphiphilic system with responsiveness in surface activity and associated self-organization phenomena depending on applying an external trigger, preferably a physical field. A key step is the creation of a Janus-type particle characterized by two types of dipoles (electric and magnetic) which geometrically stand orthogonal to each other. In a field, one can control which contribution and direction dominate the interparticle interactions. As a result, one can drastically change the system's properties. The features of ferrite-core organosilica-shell particles with grain-like morphology modified by click chemistry are studied in response to spatially isotropic and anisotropic triggers. A highly unusual aggregation–dissolution–reaggregation sequence w as discovered. Using a magnetic field, one can even switch off the amphiphilic properties and use this for the field-triggered breaking of multiphase systems such as emulsions

A Refined Prediction Parameter for Molecular Alignability in Stretched Polymers and a New Light-Harvesting Material for AlGaAs Photovoltaics

Light-harvesting concentrators have a high potential to make highly efficient but precious energy converters, such as multijunction photovoltaics, more affordable for everyday applications. They collect sunlight, including diffusively scattered light, on large areas and redirect it to much smaller areas of the highly efficiency solar cells. Among the best current concepts are pools of randomly oriented light-collecting donor molecules that transfer all excitons to few aligned acceptors reemitting the light in the direction of the photovoltaics. So far, this system has only been realized for the 350-550 nm wavelength range, suitable for AlGaInP photovoltaics. This was achieved by using acceptor molecules that aligned during mechanical stretching of polymers together with donors, that stay random in that very same material and procedure. However, until recently, very little was known about the factors that are responsible for the alignability of molecules in stretched polymers and therefore it was difficult to find suitable donors and acceptors, as well as for other spectral ranges. Recently, a structural parameter was introduced with a high predictivity for the alignability of molecules that contain rigid band-like structures or linear aromatic π-systems. However, for light concentrators in more red spectral ranges, molecular systems often contain larger and extended, planar-like π-systems for which the previously reported parameter is not directly applicable. Here, we present a refined prediction parameter also suitable for larger plane-like structures. The new parameter depends on the number of in-plane atoms divided by out-of-plane atoms as determined by computational geometry optimization and additionally the planar aspect ratio for molecules that contain only in-plane atoms. With the help of this parameter, we found a new system that can efficiently collect and redirect light for the second 500-700 nm AlGaAs layer of current world-record multijunction photovoltaics. Similarly, as the previously reported system for the blue-green layer, it has also overall absorption and re-directioning quantum efficiencies close to 80-100%. Both layers, together, already cover about 75% of the energy in the solar spectrum

Discovery of Non-Classical Self-Assembly in Janus Particle-Based Surfactants and the Field-Triggered Breakdown of Surface Activity and Amphiphilic Properties

The use of colloidal particles as models to understand processes on a smaller size-scale is a highly valuable approach. Compared to molecules, particles are less defined but their architecture can be more complex, so is their long-range interaction. Sometimes one can observe phenomena which are unknown or much more difficult to realize on the molecular level. The current paper focuses on particle-based surfactants and reports about numerous unexpected properties. The main goal is the creation of an amphiphilic system with responsiveness in surface activity and associated self-organization phenomena depending on the application of an external trigger, preferably a physical field. A key step is the creation of a Janus-type particle characterized by two types of dipoles (electric and magnetic) which geometrically stand orthogonal to each other. In a field, one can control which contribution and which direction dominates the inter-particle interactions and as a result one can change the properties of the system drastically. The features of ferrite-core organosilica-shell particles with grain-like morphology modified by click chemistry is studied in response to spatially isotropic and anisotropic triggers. A highly unusual aggregation-dissolution-reaggregation sequence was discovered. Using a magnetic field, one can even switch off the amphiphilic properties and use this for the field-triggered breaking of multiphase systems such as emulsions

Carotenoid dark state to chlorophyll energy transfer in isolated light-harvesting complexes CP24 and CP29

We present a comparison of the energy transfer between carotenoid dark states and chlorophylls for the minor complexes CP24 and CP29. To elucidate the potential involvement of certain carotenoid–chlorophyll coupling sites in fluorescence quenching of distinct complexes, varying carotenoid compositions and mutants lacking chlorophylls at specific binding sites were examined. Energy transfers between carotenoid dark states and chlorophylls were compared using the coupling parameter, ΦCouplingCar S1-Chl, which is calculated from the chlorophyll fluorescence observed after preferential carotenoid two-photon excitation. In CP24, artificial reconstitution with zeaxanthin leads to a significant reduction in the chlorophyll fluorescence quantum yield, Φ F1, and a considerable increase in ΦCouplingCar S1-Chl. Similar effects of zeaxanthin were also observed in certain samples of CP29. In CP29, also the replacement of violaxanthin by the sole presence of lutein results in a significant quenching and increased ΦCouplingCar S1-Chl. In contrast, the replacement of violaxanthin by lutein in CP24 is not significantly increasing ΦCouplingCar S1-Chl. In general, these findings provide evidence that modification of the electronic coupling between carotenoid dark states and chlorophylls by changing carotenoids at distinct sites can significantly influence the quenching of these minor proteins, particularly when zeaxanthin or lutein is used. The absence of Chl612 in CP24 and of Chl612 or Chl603 in CP29 has a considerably smaller effect on Φ F 1 and ΦCouplingCar S1-Chl than the influence of some carotenoids reported above. However, in CP29 our results indicate slightly dequenching and decreased ΦCouplingCar S1-Chl when these chlorophylls are absent. This might indicate that both, Chl612 and Chl603 are involved in carotenoid-dependent quenching in isolated CP29

Two-Photon Correlation Spectroscopy in Single Dendritic Spines Reveals Fast Actin Filament Reorganization during Activity-Dependent Growth.

Two-photon fluorescence correlation spectroscopy (2P-FCS) within single dendritic spines of living hippocampal pyramidal neurons was used to resolve various subpopulations of mobile F-actin during activity-dependent structural changes such as potentiation induced spine head growth. Two major classes of mobile F-actin were discovered: very dynamic and about a hundred times less dynamic F-actin. Spine head enlargement upon application of Tetraethylammonium (TEA), a protocol previously used for the chemical induction of long-term potentiation (cLTP) strictly correlated to changes in the dynamics and filament numbers in the different actin filament fractions. Our observations suggest that spine enlargement is governed by a mechanism in which longer filaments are first cut into smaller filaments that cooperate with the second, increasingly dynamic shorter actin filament population to quickly reorganize and expand the actin cytoskeleton within the spine head. This process would allow a fast and efficient spine head enlargement using a major fraction of the actin filament population that was already present before spine head growth

Two-Photon Spectra of Chlorophylls and Carotenoid–Tetrapyrrole Dyads

We present a direct comparison of two-photon spectra of various carotenoid–tetrapyrrole dyads and phthalocyanines (Pc) as well as chlorophylls (Chl) in the spectral range between 950 and 1360 nm, corresponding to one-photon spectra between 475 and 680 nm. For carotenoids (Car) with 8, 9, or 10 conjugated double bonds, the two-photon absorption cross section of states below the optical allowed carotenoid S₂ is at least about 3–10 times higher than that of Pc or chlorophyll <i>a</i> and <i>b</i> at 550/1100 nm. A quantitative comparison of spectra from Pc with and without carotenoids of eight and nine conjugated double bonds confirms energy transfer from optically forbidden carotenoid states to Pc in these dyads. When considering that less than 100% efficient energy transfer reduces the two-photon contribution of the carotenoids in the spectra, the actual Car two-photon cross sections relative to Chl/Pc are even higher than a factor of 3–10. In addition, strong spectroscopic two-photon signatures at energies below the optical allowed carotenoid S₂ state support the presence of additional optical forbidden carotenoid states such as S*, S_<i>x</i>, or, alternatively, contributions from higher vibronic or hot S₁ states dominating two-photon spectra or energy transfer from the carotenoids. The onset of these states is shifted about 1500–3500 cm^–1 to lower energies in comparison to the S₂ states. Our data provides evidence that two-photon excitation of the carotenoid S*, S_<i>x</i>, or hot S₁ states results in energy transfer to tetrapyrroles or chlorophylls similar to that observed with the Car S₁ two-photon excitation