Search

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., The authors acknowledge funding of this project by the German Research Foundation (Deutsche Forschungsgemeinschaft) under contract Ge 841/26. This work is supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy – 2082/1–390761711 and by the Carl Zeiss Foundation. S.H. acknowledges funding from the German Research Foundation (HE 7675/1-1) and from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 889546., Open access funding enabled and organized by Projekt DEAL.

An asymmetric bis-phenol-β-diketone (H4L) has been designed as a ligand programmed to promote the assembly of a molecular arrangement composed of three magnetically exchanged [NiCu] pairs, each exhibiting an S = 1/2 spin. The latter are shown by EPR and magnetometry to be good qubit realizations and non-equivalent within the molecule in the solid state, as required for conditional quantum gates., This research was supported by Spanish MINECO (PGC2018-098630-B-I00, PID2020-118329B-I00), the Aragón government (E31_20R PLATON) and the EU (FET-OPEN grant 862893 FATMOLS). G. A. thanks the Generalitat de Catalunya for the prize ICREA Academia 2018. B. L. G. thanks French GENCI/IDRIS-CINES centers for high-performance computing resources. The authors thank the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DEAC02-05CH11231, and the Zeiss Foundation for funding.

The relaxation of photoexcited nanosystems is a fundamental process of light–matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy is trapped in a metastable state that decouples from its environment. Here, we study helium nanodroplets excited resonantly by femtosecond extreme-ultraviolet (XUV) pulses from a seeded free-electron laser. Despite their superfluid nature, we find that helium nanodroplets in the lowest electronically excited states undergo ultrafast relaxation. By comparing experimental photoelectron spectra with time-dependent density functional theory simulations, we unravel the full relaxation pathway: Following an ultrafast interband transition, a void nanometer-sized bubble forms around the localized excitation (He∗) within 1 ps. Subsequently, the bubble collapses and releases metastable He∗ at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses., Funding from the Deutsche Forschungsgemeinschaft (MU 2347/8-1, STI 125/19-1, and the priority program 1840 QUTIF, the Carlsberg Foundation, National Science Foundation (DMR-1828019), Carl-Zeiss-Stiftung, Grant No. FIS2017-87801-P (AEI/FEDER, UE), and Swiss National Science Foundation (200020_162434) is gratefully acknowledged. O.G., D.M.N., and M.P.Z. were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division, through Contract No. DE-AC02-05CH11231.

21 p.-9 fig.-2 tab., Focal adhesion kinase (FAK) is a key component of the membrane proximal signaling layer in focal adhesion complexes, regulating important cellular processes, including cell migration, proliferation, and survival. In the cytosol, FAK adopts an autoinhibited state but is activated upon recruitment into focal adhesions, yet how this occurs or what induces structural changes is unknown. Here, we employ cryo-electron microscopy to reveal how FAK associates with lipid membranes and how membrane interactions unlock FAK autoinhibition to promote activation. Intriguingly, initial binding of FAK to the membrane causes steric clashes that release the kinase domain from autoinhibition, allowing it to undergo a large conformational change and interact itself with the membrane in an orientation that places the active site toward the membrane. In this conformation, the autophosphorylation site is exposed and multiple interfaces align to promote FAK oligomerization on the membrane. We show that interfaces responsible for initial dimerization and membrane attachment are essential for FAK autophosphorylation and resulting cellular activity including cancer cell invasion, while stable FAK oligomerization appears to be needed for optimal cancer cell proliferation in an anchorage-independent manner. Together, our data provide structural details of a key membrane bound state of FAK that is primed for efficient autophosphorylation and activation, hence revealing the critical event in integrin mediated FAK activation and signaling at focal adhesions., I.A. acknowledges support from the José Castillejo Mobility Grant issued by the Spanish Ministry of Education, Culture and Sports. R.D.R. acknowledges funding from the Fellowships for Excellence program sponsored by the Werner-Siemens Foundation and the University of Basel.H.S. acknowledges support by the Swiss National Science Foundation(grants 205320_166164 and 185544 (NCCR TransCure)). M.C.F., A.B., J.C., and C.S. were supported by a Cancer Research UK Programme Grant (C157/ A24837) to M.C.F. F.G. acknowledges funding by the Klaus Tschira Foundation, by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – 2082/1 –390761711, and the state of Baden-Württemberg through bwHPC and the DFG through grant INST 35/11341 FUGG.S.d.B. thanks the Carl Zeiss Foundation for financial support. D.L. acknowledges support from the Spanish Ministry of Economy, Industry and Competitiveness for the Retos Grant BFU2016-77665-R and the Ministry of Science, Innovation and Universities for the Spanish State Research Agency Retos Grant RTI2018-099318-B-I00,both co-funded by the European Regional Development Fund (FEDER) and from an intramural grant from the Spanish National Research Council(CSIC, Ref: 201820I124). O.L. is funded by SAF2017-82632-P grant from the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI), cofunded by the European Regional Development Fund (ERDF), by the National Institute of Health Carlos III and by projects Y2018/BIO4747 and P2018/NMT4443 from the Autonomous Region of Madrid and co-funded by the European Social Fund and the European Regional Development Fund. C.F.R. is funded by a BES-2015-071348 PhD fellowship by the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI).

International audience; Biodiversity monitoring is the standard for environmental impact assessment of anthropogenic activities. Several recent studies showed that high-throughput amplicon sequencing of environmental DNA (eDNA metabarcoding) could overcome many limitations of the traditional morphotaxonomy-based bioassessment. Recently, we demonstrated that supervised machine learning (SML) can be used to predict accurate biotic indices values from eDNA metabarcoding data, regardless of the taxonomic affiliation of the sequences. However, it is unknown to which extent the accuracy of such models depends on taxonomic resolution of molecular markers or how SML compares with metabarcoding approaches targeting well-established bioindicator species. In this study, we address these issues by training predictive models upon five different ribosomal bacterial and eukaryotic markers and measuring their performance to assess the environmental impact of marine aquaculture on independent data sets. Our results show that all tested markers are yielding accurate predictive models and that they all outperform the assessment relying solely on taxonomically assigned sequences. Remarkably, we did not find any significant difference in the performance of the models built using universal eukaryotic or prokaryotic markers. Using any molecular marker with a taxonomic range broad enough to comprise different potential bioindicator taxa, SML approach can overcome the limits of taxonomy-based eDNA bioassessment.

Solar cells based on organic–inorganic halide perovskites are now leading the photovoltaic technologies because of their high power conversion efficiency. Recently, there have been debates on the microstructure-related defects in metal halide perovskites (grain size, grain boundaries, etc.) and a widespread view is that large grains are a prerequisite to suppress nonradiative recombination and improve photovoltaic performance, although opinions against it also exist. Herein, we employ blends of methylammonium lead iodide perovskites with an insulating polymer (polyvinylpyrrolidone) that offer the possibility to tune the grain size in order to obtain a fundamental understanding of the photoresponse at the microscopic level. We provide, for the first time, spatially resolved details of the microstructures in such blend systems via Raman mapping, light beam-induced current imaging, and conductive atomic force microscopy. Although the polymer blend systems systematically alter the morphology by creating small grains (more grain boundaries), they reduce nonradiative recombination within the film and enhance its spatial homogeneity of radiative recombination. We attribute this to a reduction in the density of bulk trap states, as evidenced by an order of magnitude higher photoluminescence intensity and a significantly higher open-circuit voltage when the polymer is incorporated into the perovskite films. The solar cells employing blend systems also show nearly hysteresis-free power conversion efficiency ∼17.5%, as well as a remarkable shelf-life stability over 100 days.

The optical and magneto-optical behavior in periodically nanostructured surfaces at the threshold of surface continuity is revealed. We address Co films that evolve from an island-like array to a connecting network of islands that form a membrane pattern. The analysis of magneto-optical spectra as well as numerical simulations show significant differences between continuous and broken membranes that depend dramatically on the energy of the incoming radiation. Light localization increases the magneto-optical signal in the membranes. However, the generation of hot spots is not accompanied with magneto-optic enhancement. The electromagnetic field profile within the membrane system can explain the differences in the transmission and in the magneto-optic Kerr signal., E.Th.P acknowledges the collaborative research center SFB/TRR 173: SPIN+X: Spin in its collective environment-Project B07 of the Deutsche Forschungsgemeinschaft (DFG), and the Carl Zeiss Foundation. H.F. acknowledges the financial support by the China Scholarship Council (CSC). A.G.-M. and B.C. gratefully acknowledge support by the Spanish Ministry of Economy and Competitiveness through grant MAT2014-58860-P and by the Comunidad de Madrid through Contract No. S2013/MIT-2740. E. M. A. acknowledges the Guangdong Innovative and Entrepreneurial Team Program: Plasmonic Nanomaterials and Quantum Dots for Light Management in Optoelectronic Devices.

The phonon dispersion of graphene on Ir(111) has been determined by means of angle-resolved inelastic electron scattering and density functional calculations. Kohn anomalies of the highest optical-phonon branches are observed at the $\overline{\ensuremath{\Gamma}}$ and $\overline{\text{K}}$ point of the surface Brillouin zone. At $\overline{\text{K}}$ the Kohn anomaly is weaker than observed for pristine graphene and graphite. This observation is rationalized in terms of a decrease of the electron-phonon coupling due to screening of graphene electron correlations by the metal substrate.

We present here a generalization of the scattering-matrix approach for the description of the propagation of electromagnetic waves in nanostructured magneto-optical systems. Our formalism allows us to describe all the key magneto-optical effects in any configuration in periodically patterned multilayer structures. The method can also be applied to describe periodic multilayer systems comprising materials with any type of optical anisotropy. We illustrate the method with the analysis of a recent experiment in which the transverse magneto-optical Kerr effect was measured in an Fe film with a periodic array of subwavelength circular holes. We show, in agreement with the experiments, that the excitation of surface plasmon polaritons in this system leads to a resonant enhancement of the transverse magneto-optical Kerr effect. © 2012 American Physical Society., B.C. and A.G.-M. acknowledge funding from the EU (NMP3-SL-2008-214107-Nanomagma), the Spanish MICINN (“MAPS” MAT2011-29194-C02-01, “MAGPLAS” MAT2008-06765-C02-01/NAN, and “FUNCOAT” CONSOLIDER INGENIO 2010 CSD2008-00023), and the Comunidad de Madrid (“MICROSERES-CM” S2009/TIC-1476). J.C.C. acknowledges financial support from the Spanish MICINN (Contract No. FIS2011-28851-C02-01) and from the German foundations Carl Zeiss Stiftung and Stifterverband für die Deutsche Wissenschaft via the award of an “InnoLecture-Gastdozentur.”