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Microscopic electric fields govern the majority of elementary excitations in condensed matter and drive electronics at frequencies approaching the Terahertz (THz) regime. However, only few imaging schemes are able to resolve sub-wavelength fields in the THz range, such as scanning-probe techniques, electro-optic sampling, and ultrafast electron microscopy. Still, intrinsic constraints on sample geometry, acquisition speed and field strength limit their applicability. Here, we harness the quantum-confined Stark-effect to encode ultrafast electric near-fields into colloidal quantum dot luminescence. Our approach, termed Quantum-probe Field Microscopy (QFIM), combines far-field imaging of visible photons with phase-resolved sampling of electric waveforms. By capturing ultrafast movies, we spatio-temporally resolve a Terahertz resonance inside a bowtie antenna and unveil the propagation of a Terahertz waveguide excitation deeply in the sub-wavelength regime. The demonstrated QFIM approach is compatible with strong-field excitation and sub-micrometer resolution—introducing a direct route towards ultrafast field imaging of complex nanodevices in-operando.Novel Quantum-probe Field Microscopy (QFIM) captures ultrafast movies of Terahertz electric waveforms inside microstructures using fluorescent quantum dots.

Bullet-proof materials made of nanostructured composites outperform conventional materials, yet little is known of their nanoscale response to high-speed impact. Using laser-propelled microscopic projectiles, Lee et al. directly visualize this process in layered nanocomposites. Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.

A thorough knowledge and understanding of the structure–property relationship between thermal conductivity and C-fiber morphology is important to estimate the behavior of carbon fiber components, especially under thermal loading. In this paper, the thermal conductivities of different carbon fibers with varying tensile modulus were analyzed perpendicular and parallel to the fiber direction. Besides the measurement of carbon fiber reinforced polymers, we also measured the thermal conductivity of single carbon fibers directly. The measurements clearly proved that the thermal conductivity increased with the tensile modulus both in fiber and perpendicular direction. The increase is most pronounced in fiber direction. We ascribed the increase in tensile modules and thermal conductivity to increasing anisotropy resulting from the orientation of graphitic domains and microvoids. Graphical abstract

Passive radiative daytime cooling is an emerging technology contributing to carbon‐neutral heat management. Optically engineered materials with distinct absorption and emission properties in the solar and mid‐infrared range are at the heart of this technology. Owing to their low emissive power of about 100 W m−2 during daytime, substantial areas need to be covered with passive cooling materials or coatings to achieve a sizeable effect on global warming. Consequently, biocompatible materials are urgently needed to develop suitable coatings with no adverse environmental impact. It is shown how chitosan films with different thicknesses can be produced from slightly acidic aqueous solutions. The conversion to their insoluble form chitin in the solid state is demonstrated and the conversion is monitored with infrared (IR) and NMR spectroscopy. In combination with a reflective backing material, the films show below‐ambient temperature cooling capabilities with a suitable emissivity in the mid‐IR region and low solar absorption of 3.1–6.9%, depending on the film thickness. This work highlights the potential of chitosan and chitin as widely available biocompatible polymers for passive radiative cooling applications. The potential of chitosan and chitin for the application as passive radiative cooling materials is investigated. A solid‐state reaction is used to convert chitosan to its insoluble form chitin. Based on extensive optical characterization, both biopolymers are capable of below ambient temperature passive cooling.

Scanning electrochemical microscopy (SECM) is a versatile scanning probe technique that allows monitoring of a plethora of electrochemical reactions on a highly resolved local scale. SECM in combination with atomic force microscopy (AFM) is particularly well suited to acquire electrochemical data correlated to sample topography, elasticity, and adhesion, respectively. The resolution achievable in SECM depends critically on the properties of the probe acting as an electrochemical sensor, i.e., the working electrode, which is scanned over the sample. Hence, the development of SECM probes received much attention in recent years. However, for the operation and performance of SECM, the fluid cell and the three-electrode setup are also of paramount importance. These two aspects received much less attention so far. Here, we present a novel approach to the universal implementation of a three-electrode setup for SECM in practically any fluid cell. The integration of all three electrodes (working, counter, and reference) near the cantilever provides many advantages, such as the usage of conventional AFM fluid cells also for SECM or enables the measurement in liquid drops. Moreover, the other electrodes become easily exchangeable as they are combined with the cantilever substrate. Thereby, the handling is improved significantly. We demonstrated that high-resolution SECM, i.e., resolving features smaller than 250 nm in the electrochemical signal, could be achieved with the new setup and that the electrochemical performance was equivalent to the one obtained with macroscopic electrodes.

Structural colors arise from selective light interaction with (nano)structures, which give them advantages over pigmented colors such as resistance to fading and possibility to be fabricated out of traditional low-cost and non-toxic materials. Since the color arises from the photonic (nano)structures, different structural features can impact their photonic response and thus, their color. Therefore, the detailed characterization of their structural features is crucial for further improvement of structural colors. In this work, we present a detailed multi-scale structural characterization of ceramic-based photonic glasses by using a combination of high-resolution ptychographic X-ray computed tomography and small angle X-ray scattering. Our results uncover the structure-processing-properties’ relationships of such nanoparticles-based photonic glasses and point out to the need of a review of the structural features used in simulation models concomitantly with the need for further investigations by experimentalists, where we point out exactly which structural features need to be improved.

Smart, responsive materials are required in various advanced applications ranging from anti‐counterfeiting to autonomous sensing. Colloidal crystals are a versatile material class for optically based sensing applications owing to their photonic stopband. A careful combination of materials synthesis and colloidal mesostructure rendered such systems helpful in responding to stimuli such as gases, humidity, or temperature. Here, an approach is demonstrated to simultaneously and independently measure the time and temperature solely based on the inherent material properties of complex colloidal crystal mixtures. An array of colloidal crystals, each featuring unique film formation kinetics, is fabricated. Combined with machine learning‐enabled image analysis, the colloidal crystal arrays can autonomously record isothermal heating events — readout proceeds by acquiring photographs of the applied sensor using a standard smartphone camera. The concept shows how the progressing use of machine learning in materials science has the potential to allow non‐classical forms of data acquisition and evaluation. This can provide novel insights into multiparameter systems and simplify applications of novel materials. The optical response of multicomponent photonic crystals contains intricate information regarding a sample's thermal history. In this work, a reproducible sensor fabrication method coupled with fast data acquisition via digital photography is presented. Machine learning assisted evaluation allows smartphone‐based sensing of thermal events. Time and temperature can thereby be obtained independently and without specialized equipment.

Electromagnetically induced absorption (EIA) is an optical phenomenon that enhances light absorption of plasmonic systems. Depending on the plasmonic system under investigation, the decisive role of intrinsic versus radiative damping and phase retardation has been pointed out to control the EIA. Herein, a unified interpretation is provided and the mechanism of EIA for plasmonic–dielectric composites and all‐plasmonic dipolar–quadrupolar antennas is unraveled. In this theoretical work, the finite element method is used to elucidate how EIA is attributed to an absorption enhancement of a resonance mode excited by near‐field coupling. For a fundamental understanding, a quantitative analysis is developed by designing an extended coupled‐oscillator model. A critical parameter to maximize EIA is found, which is different from previous interpretations of such coupled plasmonic systems. Namely, the ratio of coupling strength to the total damping of the entire system controls EIA. The generalized interpretation of EIA given by this work can be applied to many plasmonic systems and is essential for designing future optical components and devices. The mechanism of electromagnetically induced absorption (EIA) is elucidated for coupled plasmonic systems comprising a bright and dark oscillator. Numerical simulations reveal that EIA originates from the excitation of the dark oscillator by near‐field coupling. Using a quantitative coupled‐oscillator model, one can derive specific conditions to maximize EIA of such coupled plasmonic systems.

Passive radiative cooling materials that spontaneously cool below ambient temperature can save tremendous amounts of energy used for cooling applications. A multitude of materials, structures, and fabrication strategies have been reported in recent years. Important material parameters like a tailored or broadband emissivity, angle selectivity, or the influence of nonradiative heat losses were discussed in detail. The material thickness has been far less researched and is typically chosen sufficiently thick to ensure high emission in the atmospheric transparency window between wavelengths of 8–13 μm. However, not only the material emittance but also atmospheric and solar energy uptake depend on the material thickness. This broadband interplay has been less addressed so far. Herein, it is shown how an optimum thickness of a passive cooling material can be predicted when the optical properties of the material are known. Using complex refractive index data, the thickness‐dependent cooling performance of polydimethylsiloxane (PDMS) in back‐reflector geometry as exemplary material is calculated. For both day‐ and nighttime operation, an optimum emitter thickness is reported. The findings are verified experimentally by measuring the equilibrium temperatures of PDMS films with different thicknesses in a rooftop experiment. The presented analytical approach is directly transferable to other materials. Materials that spontaneously cool below ambient temperature are of great interest to fight global warming. Increased film thicknesses typically improve thermal radiation, but simultaneously increase uptake of solar radiance. A general approach is presented to balance these two contributions and to determine the optimum thickness for passive daytime cooling films.