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Unveiling Nanoscale Heterogeneities at the Bias-Dependent Gold-Electrolyte Interface
Full text linkElectrified solid-liquid interfaces (SLIs) are extremely complex and dynamic, affecting both the dynamics and selectivity of reaction pathways at electrochemical interfaces. Enabling access to the structure and arrangement of interfacial water in situ with nanoscale resolution is essential to develop efficient electrocatalysts. Here, we probe the SLI energy of a polycrystalline Au(111) electrode in a neutral aqueous electrolyte through in situ electrochemical atomic force microscopy. We acquire potential-dependent maps of the local interfacial adhesion forces, which we associate with the formation energy of the electric double layer. We observe nanoscale inhomogeneities of interfacial adhesion force across the entire map area, indicating local differences in the ordering of the solvent/ions at the interface. Anion adsorption has a clear influence on the observed interfacial adhesion forces. Strikingly, the adhesion forces exhibit potential-dependent hysteresis, which depends on the local gold grain curvature. Our findings on a model electrode extend the use of scanning probe microscopy to gain insights into the local molecular arrangement of the SLI in situ, which can be extended to other electrocatalysts
On the coexistence of pressure regulation and oscillation modes in soft hysteretic valves
Full text linkFluidic circuits are a promising recent development in embodied control of soft robots. These circuits typically make use of highly non-linear soft components to enable complex behaviors given simple inputs, such as constant flow or pressure. This approach greatly simplifies control, as it removes the need for external hardware or software. However, detailed fundamental understanding of the non-linear, coupled fluidic and mechanical behavior of these components is lacking. Such understanding is needed to guide new designs and increase the reliability of increasingly autonomous soft robots. Here, we develop an analytical model that captures the coexistence of a pressure regulation mode and an oscillatory mode in a specific soft hysteretic valve design, that we previously used to achieve reprogrammable activation patterns in soft robots. We develop a model that describes the mechanics, fluidics and dynamics of the system by two coupled non-linear ordinary differential equations. The model shows good agreement with the experimental evidence, as well as correctly predicts the effect of design changes. Specifically, we experimentally show that we can remove the regulation mode at low input flow rates by changing the fluidic response of the valve. Taken together, the present study contributes to better understanding of system-level behavior of fluidic circuits for controlling soft robots. This may contribute to the reliability of soft robots with embodied control in future applications such as autonomous exploration and medical prosthetic devices
Pre-ablation regime light-induced optical changes in nanometer thick metal films
Full text linkWe report on small optical reflection increases after illumination of nanometer thick gold and aluminum thin films on different substrates with single, femtosecond 400 nm wavelength pump laser pulses, in a pre-ablation fluence regime. In this fluence regime, small, irreversible and subtle morphological changes of the sample are observed. Dark-field, scanning electron, and atomic force microscopy images reveal subwavelength spallation features in the aluminum, and delamination in the gold layers in this pre-ablation regime. All of these morphological changes coincide with minute optical increases in the reflectivity, at the 0.1 − 2% level, as observed in-situ with a weak probe beam. From Liu-analysis, transfer-matrix, and two-temperature model calculations, we infer that in this pre-ablation regime, the aluminum layers already reach the melting temperature. Electron Backscatter Diffraction measurements show that the Al grains melt and resolidify into bigger grains. This suggests that for Al, resolidification into bigger grains is responsible for both the increased reflection, and the spallation in the pre-ablation regime. For gold, the optical change is most likely due to the etalon effect caused by delamination
Predicting concentration changes via discrete receptor sampling
Full text linkTo successfully navigate chemical gradients, microorganisms need to predict how the ligand concentration changes in space. Due to their limited size, they do not take a spatial derivative over their body length but rather a temporal derivative, comparing the current signal with that in the recent past over the so-called adaptation time. This strategy is pervasive in biology, but it remains unclear what determines the accuracy of such measurements. Using a generalized version of the previously established sampling framework, we investigate how resource limitations and the statistics of the input signal set the optimal design of a well-characterized network that measures temporal concentration changes: the Escherichia coli chemotaxis network. Our results show how an optimal adaptation time arises from the trade-off between the sampling error, caused by the stochastic nature of the network, and the dynamical error, caused by uninformative fluctuations in the input. A larger resource availability reduces the sampling error, which allows for a smaller adaptation time, thereby simultaneously decreasing the dynamical error. Similarly, we find that the optimal adaptation time scales inversely with the gradient steepness, because steeper gradients lift the signal above the noise and reduce the sampling error. These findings shed light on the principles that govern the optimal design of the E. coli chemotaxis network specifically, and any system measuring temporal changes more broadly
Pneumatic coding blocks enable programmability of electronics-free fluidic soft robots
Full text linkDecision-making based on environmental cues is a crucial feature of autonomous systems. Embodying this feature in soft robots poses nontrivial challenges on both hardware and software that can undermine the simplicity and autonomy of such devices. Existing pneumatic electronics-free soft robots have so far mostly been approached by using system fluidic circuit architectures analogous to digital electronics. Instead, here we design dedicated pneumatic coding blocks equivalent to If, If...break, and For software control statements, which are based on the analog nature of nonlinear mechanical components. We demonstrate that we can combine these coding blocks into programs to implement sequences and to control an electronics-free autonomous soft gripper that switches between behaviors based on interactions with the environment. As such, our strategy provides an alternative approach to designing complex behavior in soft robotics that is more reminiscent of how functionalities are also encoded in the body of living systems
Host–Guest Complexation in Wide Bandgap Perovskite Solar Cells
Full text linkWide-bandgap hybrid halide perovskites are increasingly relevant in the fabrication of tandem solar cells. However, their efficiency and stability during operation are still limited by several factors, among which ion migration at the interface with charge-selective extraction layers is one of the most detrimental ones. Herein, a host–guest complexation strategy is employed to control interfacial ion migration by using dibenzo-21-crown-7 in wide-bandgap hybrid halide perovskites based on methylammonium lead bromide. The capacity of the crown ether is demonstrated that affect the performances and stabilities of MAPbBr3 solar cells. As a result, power conversion efficiencies of up to 5.9% are achieved with an open circuit voltage as high as 1.5 V, which is accompanied by stability over 300 h at 85 °C under nitrogen atmosphere, as well as more than 300 h at ambient temperature, maintaining ∼80% of initial performance. This provides a versatile strategy for wide-bandgap photovoltaic devices
Free Electron–Plasmon Coupling Strength and Near-Field Retrieval through Electron Energy-Dependent Cathodoluminescence Spectroscopy
Full text linkTightly confined optical near fields in plasmonic nanostructures play a pivotal role in important applications ranging from optical sensing to light harvesting. Energetic electrons are ideally suited to probing optical near fields by collecting the resulting cathodoluminescence (CL) light emission. Intriguingly, the CL intensity is determined by the near-field profile along the electron propagation direction, but the retrieval of such field from measurements has remained elusive. Furthermore, the conditions for optimum electron near-field coupling in plasmonic systems are critically dependent on such field and remain experimentally unexplored. In this work, we use electron energy-dependent CL spectroscopy to study the tightly confined dipolar mode in plasmonic gold nanoparticles. By systematically studying gold nanoparticles with diameters in the range of 20–100 nm and electron energies from 4 to 30 keV, we determine how the coupling between swift electrons and the optical near fields depends on the energy of the incoming electron. The strongest coupling is achieved when the electron speed equals the mode phase velocity, meeting the so-called phase-matching condition. In aloof experiments, the measured data are well reproduced by electromagnetic simulations, which explain that larger particles and faster electrons favor a stronger electron near-field coupling. For penetrating electron trajectories, scattering at the particle produces severe corrections of the trajectory that defy existing theories based on the assumption of nonrecoil condition. Therefore, we develop a first-order recoil correction model that allows us to account for inelastic electron scattering, rendering better agreement with measured data. Finally, we consider the albedo of the particles and find that, to approach unity coupling, a highly confined electric field and very slow electrons are needed, both representing experimental challenges. Our findings explain how to reach unity-order coupling between free electrons and confined excitations, helping us understand fundamental aspects of light–matter interaction at the nanoscale
Zirconium doped indium oxide thin films as transparent electrodes for photovoltaic applications
Full text linkIn this work we report on ultra-thin Zirconium doped In2O3 transparent conductive films grown at room temperature via RF-Magnetron co-sputtering. Samples from 15 nm to 90 nm thick, and low Zr atomic concentration (0.6–0.9 at.%), were annealed at T = 200 °C after the deposition. The phase-transition from amorphous to crystalline, confirmed by XRD measurements, leads to an improvement of both electrical and optical properties. The thinnest film (15 nm) shows electrical resistivity as low as 5 × 10−4 Ωcm, with carrier mobility of 20 cm2V−1s−1, and optical transmittance up to 80 % in visible and near-infrared range. IZrO electrode performances were tested through external quantum efficiency (EQE) measurements on a semi-finite Silicon Heterojunction bi-facial solar cell. The EQE values for 90 nm thick film are comparable to that of standard ITO when IZrO films are implemented as front electrodes. These results suggest that ultra-thin IZrO films may be successfully used to reduce costs and the amount of Indium used in Indium-based transparent conductive oxide layers for solar cells
Designing Complex Tapestries with Photography‐Inspired Manipulation of Self‐Organized Thin‐Films
Full text linkThin-films patterned with complex motifs are of fundamental interest because of their advanced optical, mechanical and electronic properties, but fabrication of these materials remains challenging. Self-organization strategies, such as immersion controlled reaction-diffusion patterning, have shown great potential for production of patterned thin-films. However, the autonomous nature of such processes limits controllable pattern customizability and complexity. Here, it is demonstrated that photography inspired manipulation processes can overcome this limitation to create highly-complex tapestries of micropatterned films (MPF's). Inspired by classical photographic processes, MPF's are developed, bleached, exposed, fixed, and contoured into user-defined shapes and photographic toning reactions are used to convert the chemical composition MPF's, while preserving the original stripe patterns. By applying principles of composite photography, highly complex tapestries composed of multiple MPF layers are designed, where each layer can be individually manipulated into a specific shape and composition. By overcoming fundamental limitations, this synergistic approach broadens the design possibilities of reaction-diffusion processes, furthering the potential of self-organization strategies for the development of complex materials
Roadmap on photonic metasurfaces
Full text linkHere we present a roadmap on Photonic metasurfaces. This document consists of a number of perspective articles on different applications, challenge areas or technologies underlying photonic metasurfaces. Each perspective will introduce the topic, present a state of the art as well as give an insight into the future direction of the subfield