Substrate Plane Research Articles

Morphological control for hollow rod crystals of a photochromic diarylethene on spherulites by surface properties of substrates

Sublimation methods utilizing the surface properties of substrates can address the challenge of controlling hollow morphologies in rod crystals. Spherulites were formed on the hydrophilic surface of the (0001) planes of α-quartz and sapphire substrates by sublimation of 1,2-bis(3,5-dimethyl-2-thienyl)perfluorocyclopentene (1a). Various types of hollow morphologies, distinguished by the size and shape of their cross sections and by the presence or absence of branching structures, were formed separately on α-quartz and sapphire substrates. Such precise control of the hollow morphologies was attributed to the wettability of each substrate, leading to the formation of spherulites of 1a. In addition, it was indicated that the formation process of the surface morphologies of spherulites was associated with the hollow morphologies of rod crystals of 1a.

Super Low Profile 5G mmWave Highly Isolated MIMO Antenna with 360∘ Pattern Diversity for Smart City IoT and Vehicular Communication

This study introduces a planar folded super low profile 5G mmWave monopole antenna for small IoT devices with superior efficiency and gain. Low-loss Rogers RT-5880 substrate material has been utilized to achieve higher efficiency, gain, and diversity performance in a relatively compact size. The unit element planar monopole antenna has been designed within 6.15×5.13×0.8mm3 with a partial ground. Four unit element antenna was orthogonally arranged on alternating sides of the substrate plane with narrow inter-component spacing in the multiple input multiple output (MIMO) system. The integration of the double negative (DNG) metamaterial array on the antenna led to a cumulative improvement in the overall performance of the antenna, which includes gain, efficiency, and isolation. The minimum isolation of the antenna increased by 11 dB with substrate-loaded metamaterial. The proposed MIMO antenna model with substrate-loaded metamaterial demonstrates 8 GHz instantaneous bandwidth (33.1 GHz - 41.1 GHz), 0.001 envelope correlation coefficient (ECC), diversity gain (DG) greater than 9.99 dB, channel capacity loss (CCL) less than 0.2bits/s/Hz, and a total active reflection coefficient (TARC) of 25 dB, which suggests that the diversity characteristics of the MIMO antenna system is impressive. Moreover, a densely packed 12-element antenna model has been introduced in this study with 360∘ pattern diversity, capable of receiving signals from any direction. Three 4-element MIMO systems have been arranged in an architecture to develop the 12-element MIMO system, and the size of the 12-element MIMO architecture is 15×15×15mm3. Despite having this compact size and dense packing, the 12-element MIMO antenna model shows similar diversity performance as the 4-element antenna model. Analog equivalent circuit models or resistor-inductor-capacitor (RLC) equivalent systems for the antenna models were created. A concept of a 128-element massive MIMO antenna has been presented to support the end devices, creating an application scenario of an IoT-interconnected smart city.

The Standardized Spectroscopic Mixture Model

The standardized spectral mixture model combines the specificity of a physically based representation of a spectrally mixed pixel with the generality and portability of a spectral index. Earlier studies have used spectrally and geographically diverse collections of broadband and spectroscopic imagery to show that the reflectance of the majority of ice-free landscapes on Earth can be represented as linear mixtures of rock and soil substrates (S), photosynthetic vegetation (V) and dark targets (D) composed of shadow and spectrally absorptive/transmissive materials. However, both broadband and spectroscopic studies of the topology of spectral mixing spaces raise questions about the completeness and generality of the Substrate, Vegetation, Dark (SVD) model for imaging spectrometer data. This study uses a spectrally diverse collection of 40 granules from the EMIT imaging spectrometer to verify the generality and stability of the spectroscopic SVD model and characterize the SVD topology and plane of substrates to assess linearity of spectral mixing. New endmembers for soil and non-photosynthetic vegetation (NPV; N) allow the planar SVD model to be extended to a tetrahedral SVDN model to better accommodate the 3D topology of the mixing space. The SVDN model achieves smaller misfit than the SVD, but does so at the expense of implausible fractions beyond [0, 1]. However, a refined spectroscopic SVD model still achieves small (<0.03) RMS misfit, negligible sensitivity to endmember variability and strongly linear scaling over more than an order of magnitude range of spatial resolution.

Dual-Wave ZnO Film Ultrasonic Transducers for Temperature and Stress Measurements.

ZnO film ultrasonic transducers for temperature and stress measurements with dual-mode wave excitation (longitudinal and shear) were deposited using the reactive RF magnetron sputtering technique on Si and stainless steel substrates and construction steel bolts. It was found that the position in the substrate plane had a significant effect on the structure and ultrasonic performance of the transducers. The transducers deposited at the center of the deposition zone demonstrated a straight columnar structure with a c-axis parallel to the substrate normal and the generation of longitudinal waves. The transducers deposited at the edge of the deposition zone demonstrated inclined columnar structures and the generation of dominant shear or longitudinal shear waves. Transducers deposited on the bolts with dual-wave excitation were used to study the effects of high temperatures in the range from 25 to 525 °C and tensile stress in the range from 0 to 268 MPa on ultrasonic response. Dependencies between changes in the relative time of flight and temperature or axial stress were obtained. The dependencies can be described by second-order functions of temperature and stress. An analysis of the contributions of thermal expansion, strain, and the speed of sound to changes in the time of flight was performed. At high temperatures, a decrease in the signal amplitude was observed due to the decreasing resistivity of the transducer. The ZnO ultrasonic transducers can be used up to temperatures of ~500 °C.

In-situ optimization of lateral film uniformity in PVD system by using Fiber Bragg grating temperature sensors

Fiber Bragg grating (FBG) based temperature sensing method has been employed in this work for measuring the lateral temperature distribution on substrate plane during pulse DC magnetron sputtering deposition for optimization of lateral film uniformity. The evolution of temperature distribution with the variation of important process parameters like pulse width (496–1616 ns), deposition pressure (3.1 × 10−3–1.9 × 10–2 mbar) and sputtering power (25–250 W) have been measured over 40 mm radial distance on glass substrate horizon. To investigate the effect of substrate height on the temperature distribution, the later has been measured at two different substrate heights (60 mm and 90 mm) for varying sputtering power. Finally, the effect of variation in temperature distribution on uniformity of thickness and optical, morphological and structural properties have been investigated by separately depositing two HfO2 thin films at two representative extreme deposition powers (75 W and 200 W). The correlation of film non-uniformity of the above properties with the temperature distribution suggests that FBG based multipoint temperature sensing can be possibly used as an indicative tool for in situ optimization of the lateral film uniformity. In addition, the fast response and workability in plasma environment of FBG sensors enables precise in situ mapping of temperature distribution in sputtering process.

Molecular semiconductors with Carbazole versus Triazatruxene endcaps: A matter of self-assembly

In this work, we describe the design and synthesis of a novel soluble conjugated molecule, CAR-TzDPP, consisting of a central diketopyrrolopyrrole core (DPP) connected to carbazole endcaps through thiazole rings. To evaluate its properties, a triazatruxene-based molecule (TAT-TzDPP) was used as a model for comparison. The electrochemical and the in-solution optical properties are in good agreement with those obtained from DFT calculations. However, the thin-film self-assemblies of CAR-TzDPP exhibited distinct differences, forming a more standard crystalline structure including insulating side-chains layers that disallowed side interactions between aromatic rings. This resulted in a reduced charge transport ability to a two-dimensional (2D) ambipolar charge transport in CAR-TzDPP, compared to the nearly isotropic unipolar charge transport in TAT-TzDPP. Despite this, CAR-TzDPP can be considered a viable alternative for device configurations requiring semiconducting pathways aligned in the substrate plane due to its simplified and high yield synthesis route, ease of processing, and reliable charge mobility in OFETs. This research highlights the significance of molecular units in small semiconducting organic molecules, not only in terms of their individual optoelectronic properties but also in terms of their self-assembly capabilities, which ultimately influence their charge transport properties.

Advanced film/substrate interface engineering for adhesion improvement employing time- and energy-controlled metal ion irradiation

Pre-deposition substrate etching by metal ion bombardment is an efficient and fast cleaning method that ensures improved chemical and topological substrate surface modification. Here, we study the effects of metal ion mass and kinetic energy on etching of industrially-relevant cemented carbide (WC) substrate as well as on adhesion at the Ti0.50Al0.50N/WC interface. Cr+ or W+ ion fluxes are generated by high-power impulse magnetron sputtering (HiPIMS), while their kinetic energy Ekin is tuned by applying negative substrate bias voltage synchronously with the metal ion-rich portion of the flux. The time evolution of ion fluxes at the substrate plane is studied with energy- and time-resolved ion mass spectrometry. The threshold substrate bias voltage required to initiate substrate etching is in the 900–1000 V range for both Cr+ and W+ fluxes. Moreover, we show that the adhesion strength of Ti0.50Al0.50N coatings correlates with Ekin. For Ekin < 900 eV, Cr or W interlayers are grown and no significant improvement in the adhesion strength is observed. Contrary, for Ekin > 900 eV, effective substrate etching with energetic metal ions significantly improves the adhesion strength: we demonstrate an increase of 76–79 % after etching with metal ions as compared to the untreated substrate.

Integrated Circuit Bonding Distance Inspection via Hierarchical Measurement Structure.

Bonding distance is defined by the projected distance on a substrate plane between two solder points of a bonding wire, which can directly affect the morphology of the bonding wire and the performance between internal components of the chip. For the inspection of the bonding distance, it is necessary to accurately recognize gold wires and solder points within the complex imagery of the chip. However, bonding wires at arbitrary angles and small-sized solder points are densely distributed across the complex background of bonding images. These characteristics pose challenges for conventional image detection and deep learning methods to effectively recognize and measure the bonding distances. In this paper, we present a novel method to measure bonding distance using a hierarchical measurement structure. First, we employ an image acquisition device to capture surface images of integrated circuits and use multi-layer convolution to coarsely locate the bonding region and remove redundant background. Second, we apply a multi-branch wire bonding inspection network for detecting bonding spots and segmenting gold wire. This network includes a fine location branch that utilizes low-level features to enhance detection accuracy for small bonding spots and a gold wire segmentation branch that incorporates an edge branch to effectively extract edge information. Finally, we use the bonding distance measurement module to develop four types of gold wire distribution models for bonding spot matching. Together, these modules create a fully automated method for measuring bonding distances in integrated circuits. The effectiveness of the proposed modules and overall framework has been validated through comprehensive experiments.

An equivalent surface model bridging intermolecular interactions and the normalization of substrate wettability

A liquid deposited on a solid surface exhibits various wetting properties, primarily influenced by solid–liquid intermolecular interactions. Achieving a well-estimation of wetting behaviors on textured surfaces remains challenging because the influence of surface textures on intermolecular interactions is unclear. Here, an equivalent surface model is proposed to unify the wettability of both plane and textured substrates through intermolecular interactions. We show that by incorporating intermolecular interactions, lattice structures, and surface topographies, the substrate wettability can be tailored in an equivalent plane with the same average Lennard–Jones potential energy field E. The wettability of one substrate (plane or patterned) is transferred from non-wetting, partial wetting to complete wetting by adjusting the potential well depth of E, εa. With enhancing εa, complete wetting is achieved under the critical potential well depth of E, εac. Before εac, the spreading radius grows as R ∼ t1/1.47 until reaches equilibrium. In this scenario, the equilibrium contact angle θ and spreading factor β are strongly dependent on εa, and cos θ is linear to εa. When exceeding εac, complete wetting is achieved, and droplets spread with a precursor film as R ∼ t1/2.3 latterly. This model builds a bridge to link intermolecular interactions and substrate wettability normalization. This strategy offers a framework for substrate surface design and wettability manipulation, catering to applications such as photoresist-drop dispensing in nanoimprint lithography, surface design for grating antifouling, and anti-icing on aircraft surfaces.

A slotted frustum-shaped 4 × 4 MIMO dielectric resonator antenna with enhanced isolation for 5G Wi-Fi applications

In this paper, a slotted frustum-shaped 4 × 4 multiple-input multiple-output (MIMO) dielectric resonator antenna (DRA) is designed and developed for portable 5G Wi-Fi ( 5.15 − 5.85 GHz ) applications. The DRA is excited by HE M 11 δ and HE M 21 δ modes. A slotted right-angle frustum-shaped (SRFS) structure of alumina material as a dielectric resonator (DR) is positioned on the ground plane of the FR4 substrate to design a DRA. Based on the designed DRA, a compact ( 2.57 λ g × 2.57 λ g , where λ g is guided wavelength and calculated at a lower cut-off frequency, 5.0 GHz , for ϵ f of 4.4 ) 4 × 4 MIMO antenna with high isolation of greater than 27.13 dB (from 5.0 to 6.1 GHz ) and 24.3 dB (from 6.1 to 6.25 GHz ) is proposed. The developed MIMO antenna's measured working frequency ranges from 5.0 to 6.25 GHz , with an impedance bandwidth, B W i of 22.22 % , peak gain, G P of 5.85 dBi and an average peak gain, G av of 5.25 dBi . The calculated MIMO antenna's diversity performance parameters, channel capacity loss ( C CL ij ) , diversity gain ( D G ij ) , envelop correlation coefficient ( E CC ij ) , mean effective gain ( M EG i ) , total active reflection coefficient ( T ARC ) , and channel capacity ( C C ) are obtained as < 0.17 bits / sec / Hz , > 9.99 dB , < 0.0301 , < − 6.06 dB , < − 12.5 dB , and < 21.6 bits / sec / Hz , respectively. The agreement between the simulation and measurement results is found to be remarkably consistent.

Best Practices to Directly Assess Heterogeneous Singlet Oxygen Photosensitization by Phosphorescence

AbstractLiterature proves that the direct detection of 1O2(1Δg) at the solid gas interface is systematically performed from its phosphorescence using high intensity excitation sources (i.e., lasers), which lead to quasi‐ubiquitous chemical problems, such as sensitizer degradation, and photophysical counter‐active issues such as ultrafast exciton migration, singlet‐singlet and triplet‐triplet annihilation, and thermally activated delayed fluorescence mediated by 1O2(1Δg). To avoid these inconveniences, low excitation intensity is required but leads to serious analytical challenges. The best practices to reliably detect 1O2(1Δg) phosphorescence at various interfaces using a standard excitation source and near‐IR detector. The two main practices consist in a gas purging test for reliable identification of 1O2(1Δg), and in a particularly fine optimization of the angle made by excitation beam versus substrate plane. These practices are applied to porphyrin sensitizers H2TPP and ZnTPP, either neat or physiosorbed on glass, quartz, paper and hospital bandages, graphene oxide (GO), and embedded inside electrospun polystyrene fibers and spin coated poly(methyl methacrylate) films. Porphyrin‐based metal‐organic framework PCN‐224, freshly activated, is also examined.

Selective growth and unveiling semiconductor nanostructured based La,Mo and O elements: Structural, morphological, and optical investigations

La2Mo2O9 ternary compound thin film has been prepared by the chemical spray pyrolysis technique on glass substrates at 460°C. Characterization via X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray, X-ray photoelectron spectrometry (XPS) and spectrophotometry through reflectance and transmittance measurements were performed. X-ray analysis shows that La2Mo2O9 material crystallizes in cubic structure belonging to the P 213 space group with a preferred orientation of the crystallites along (210) direction parallel to the substrate plane. Raman spectroscopy witnesses the presence of bonds like La-O and Mo-O. SEM observation shows that the prepared film exhibits a uniform grain of regular sizes in the range of 70–120 nm and some chains. EDX spectroscopy highlights the presence of La, Mo and O elements with a slight non-stoichiometry reflecting the oxygen deficiency. XPS measurements reveal the well defined states O 1s, Mo 3d5/2, Mo 3d3/2, La 3d5/2 and La 3d3/2 of oxygen, molybdenum and lanthanum elements. Optical measurements show a high transparency in the visible range. These measurements were used to deduce the optical band gap and Urbach energy.

Orientation‐Driven Large Magnetic Hysteresis of Er(III) Cyclooctatetraenide‐Based Single‐Ion Magnets Adsorbed on Ag(100)

The molecular self‐assembly and the magnetic properties of two cyclooctatetraenide (COT)‐based single‐ion magnets (SIM) adsorbed on Ag(100) in the sub‐monolayer (ML) range are reported. Our study combines scanning‐tunneling microscopy, X‐ray photoemission spectroscopy and polarized X‐ray absorption spectroscopy to show that Cp*ErCOT (Cp* = 1,2,3,4,5‐pentamethylcyclopentadienide anion) SIMs self‐assemble as alternating compact parallel rows including standing‐up and lying‐down conformations, following the main crystallographic directions of the substrate. Conversely, K[Er(COT)2], obtained from subliming the [K(18‐c‐6)][Er(COT)2]·2THF salt, forms uniaxially ordered domains with the (COT)2− rings perpendicular to the substrate plane. The polarization‐dependent X‐ray absorption spectra reproduced by the multiX simulations suggest that the strong in‐plane magnetic anisotropy of K[Er(COT)2]/Ag(100) and the weak out‐of‐plane anisotropy of Cp*ErCOT/Ag(100) can be attributed to the strikingly different surface ordering of these two complexes. Compared to the bulk phase, surface‐supported K[Er(COT)2] exhibits a similarly large hysteresis opening, while the Cp*ErCOT shows a rather small opening. This result reveals that despite structural similarities, the two organometallic SMMs have strongly different magnetic properties when adsorbed on the metal substrate, attributed to the different orientations and the resulting interactions of the ligand rings with the surface.

A compact linearly polarized RLSA antenna integrated with circular ring resonator (CRR) for 5G mm-wave applications

This article introduces a compact linearly polarized (LP) radial line slot array antenna (RSLA) that incorporates a metamaterial of circular ring resonator (CRR) reflector for improving the bandwidth. Hence, this enables the antenna to operate at n257 (26.5–29.5), n258(24.25–27.5), and n261(27.5–28.35) frequency bands which are standardized by Federal Communications Commission (FCC) with a minor reduction of the directivity. Due to the short wavelength of the millimeter wave bands, the technique of the RLSA design has been advantageous for achieving high gain. The prototype of the RLSA antenna and the metamaterial CRR reflector are designed and fabricated at 28 GHz resonance frequency utilizing Rogers 5880 substrate and fed using an SSMA coaxial connector with an air gap cavity equivalent to half guide wavelength (λg/2) between substrate and ground plane. The method of integrating the CRR reflector with the LP-RLSA antenna delivered a passband transmission operating at (22–29.5) GHz. The proposed antenna has a similar agreement between simulated and measured for directivity and bandwidth. it achieved a peak directivity of 20 dB with a squinted main lobe at 12° and a fractional bandwidth of 29.13%. The fabricated RLSA antenna dimensions are 130 mm × 130 mm × 10.65 mm which is compact compared to conventional RLSA antennas.

Clutch model for focal adhesions predicts reduced self-stabilization under oblique pulling

Cell-matrix adhesions connect the cytoskeleton to the extracellular environment and are essential for maintaining the integrity of tissue and whole organisms. Remarkably, cell adhesions can adapt their size and composition to an applied force such that their size and strength increases proportionally to the load. Mathematical models for the clutch-like force transmission at adhesions are frequently based on the assumption that mechanical load is applied tangentially to the adhesion plane. Recently, we suggested a molecular mechanism that can explain adhesion growth under load for planar cell adhesions. The mechanism is based on conformation changes of adhesion molecules that are dynamically exchanged with a reservoir. Tangential loading drives the occupation of some states out of equilibrium, which for thermodynamic reasons, leads to the association of further molecules with the cluster, which we refer to as self-stabilization. Here, we generalize this model to forces that pull at an oblique angle to the plane supporting the cell, and examine if this idealized model also predicts self-stabilization. We also allow for a variable distance between the parallel planes representing cytoskeletal F-actin and transmembrane integrins. Simulation results demonstrate that the binding mechanism and the geometry of the cluster have a strong influence on the response of adhesion clusters to force. For oblique angles smaller than about 40∘, we observe a growth of the adhesion site under force. However this self-stabilization is reduced as the angle between the force and substrate plane increases, with vanishing self-stabilization for normal pulling. Overall, these results highlight the fundamental difference between the assumption of pulling and shearing forces in commonly used models of cell adhesion.

Regioselective super-assembly of Prussian blue analogue

The construction of high-asymmetrical structures demonstrates significant potential in improving the functionality and distinctness of nanomaterials, but remains a considerable challenge. Herein, we develop a one-pot method to fabricate regioselective super-assembly of Prussian blue analogue (PBA) —— a PBA anisotropic structure (PBA-AS) decorated with epitaxial modules——using a step-by-step epitaxial growth on a rapidly self-assembled cubic substrate guided by thiocyanuric acid (TCA) molecules. The epitaxial growth units manifest as diverse geometric shapes, which are predominantly concentrated on the {100}, {111}, or {100}+{111} crystal plane of the cubic substrate. The crystal plane and morphology of epitaxial module can be regulated by changing the TCA concentration and reaction temperature, enabling a high level of controllability over specific assembly sites and structures. To illustrate the advantage of the asymmetrical structure, phosphated PBA-AS demonstrates improved performance in the oxygen evolution reaction compared to simple phosphated PBA nanocube. This method offers valuable insights for designing asymmetrical nanomaterials with intricate architectures and versatile functionalities.

Aqueous inks for ecofriendly processing of organic solar cells: Investigation of morphological changes

Aqueous dispersions of organic semiconducting nanoparticles (NPs) are particularly attractive as inks for the environmentally friendly preparation of organic solar cells. The internal morphology of the NPs, which depends on their elaboration process, is a key parameter, which has a significant influence on the final morphology of the active layer and therefore its effectiveness. In the present study, core-shell (PF2:PC71BM) NPs were prepared by miniemulsion. Their internal morphology including the composition of the two phases was characterized by scanning transmission X-ray microscopy (STXM) showing a core composed of 77% PC71BM and a shell composed of 75% PF2. It was found that thermal annealing promotes PC71BM diffusion from the core to the shell, increasing its proportion in the shell from 25% to 42%. This annealing, when applied after NPs deposition by spincoating, allows partial coalescence of the NPs, reducing the roughness of the active layer, and increases electron mobility, thus demonstrating the formation of PC71BM percolation paths for electron transport. A PCE of 1.6% could thus be obtained after 10 min of thermal annealing at 100°C. At higher temperature, Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS) analyses demonstrate the modification of the PF2 structuration from randomly oriented lamella after deposition to edge-on orientation after annealing, leading to an unfavorable decrease of the hole mobility in the direction perpendicular to the substrate, while increasing the hole mobility in the substrate plane. This study demonstrates the need to systematically characterize the internal morphology of NPs in order to rationalize the morphology of the active layer and optimize its properties.

Generation of highly anisotropic physical properties in ferromagnetic thin films controlled by their differently oriented nano-sheets

We fabricated ferromagnetic nano-crystalline thin films of Co, Fe, Co–Fe and Co-rich and Fe-rich, Co–MT and Fe–MT (MT = transition metal), constituted by nano-sheets with a controlled slant. Visualization of these nano-sheets by Scanning Tunneling Microscopy and High-Resolution Transmission Electron Microscopy (HRTEM) showed typically tilt angles ≈56° with respect to the substrate plane, and nano-sheets ≈3.0–4.0 nm thick, ≈30–100 nm wide, and ≈200–300 nm long, with an inter-sheet distance of ≈0.9–1.2 nm, depending on their constitutive elements. Induced by this nano-morphology, these films exhibited large uniaxial magnetic anisotropy in the plane, the easy direction of magnetization being parallel to the longitudinal direction of the nano-sheets. In the as-grown films, typical values of the anisotropy field were between Hk ≈ 48 and 110 kA/m depending on composition. The changes in the nano-morphology caused by thermal treatments, and hence in the anisotropic properties, were also visualized by HRTEM, including chemical analysis at the nano-scale. Some films retained their nano-sheet morphology and increased their anisotropies by up to three times after being heated to at least 500 °C: for example, the thermal treatments produced crystallization processes and the growth of CoV and CoFe magnetic phases, maintaining the nano-sheet morphology. In contrast, other annealed films, Co, Fe, CoZn, CoCu… lost their nano-sheet morphology and hence their anisotropies. This work opens a path of study for these new magnetically anisotropic materials, particularly with respect to the nano-morphological and structural changes related to the increase in magnetic anisotropy.

An Electrochemical Cell for Operando Grazing-Incidence X-Ray Absorption Spectroscopic Studies of Low-Loaded Electrodes

X-ray absorption spectroscopy (XAS) is a powerful technique that can provide element specific information on the local electronic and structural properties of newly developed electrocatalysts, especially when performed under operating conditions (i.e., operando). However, the large amounts of catalyst typically needed to achieve sufficiently high spectral quality and temporal resolution can result in working electrodes of several micrometers in thickness. This can in turn lead to an inhomogeneous potential distribution across the electrode, delamination and/or incomplete utilization of the catalyst layer, severe bubble formation and accumulation due to poor mass transport properties.[1, 2] In addition, the activity and selectivity of a catalyst are often measured in a different cell geometry (e.g., using rotating disk electrodes (RDEs)), leading to uncertainties in comparison with the results inferred from spectroscopic data.[3]To tackle these problems we have developed a new spectroelectrochemical XAS flow cell that enables spectral acquisition in fluorescence mode using an X-ray beam incidence angle of ≤ 0.1° with regards to the working electrode’s substrate plane, i.e., in a so called grazing incidence (GI) configuration (see Figure 1). In this acquisition configuration we successfully tracked the formation of palladium hydride with a time resolution of 10 seconds per spectrum while using a Pd-loading as low as 50 µgPd∙cm-2. Moreover, the careful design of the working electrode flow field allows the study of faradaic processes (e.g., O2-reduction) under mass-transport controlled conditions entailing currents comparable to those attained in RDE measurements (≤ 10 mA∙cm−2). The combination of these features with an ion-conductive membrane to separate the working- and counter-electrode compartments additionally enables the detection of gaseous products (e.g., from CO2-electroreduction) by degassing them out of the electrolyte and analyzing them in time-resolved fashion by means of mass spectrometry.[4] References Diklić, N., et al., Potential Pitfalls in the Operando XAS Study of Oxygen Evolution Electrocatalysts. ACS Energy Letters, 2022. 7(5): p. 1735-1740. Diercks, J.S., et al., Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements. Angew Chem Int Ed Engl, 2023: p. e202216633. Diercks, J.S., et al., Interplay between Surface-Adsorbed CO and Bulk Pd Hydride under CO2-Electroreduction Conditions. ACS Catalysis, 2022: p. 10727-10741. Khanipour, P., et al., Electrochemical Real-Time Mass Spectrometry (EC-RTMS): Monitoring Electrochemical Reaction Products in Real Time. Angew Chem Int Ed Engl, 2019. 58(22): p. 7273-7277 Figure 1

Surface-Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications.

Numerous bio-organisms employ template-assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, a facile procedure is presented to deposit bio-inspired birefringent crystals of xanthine derivatives on a template of single-crystal quartz. Crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300-600nm thick, are obtained. The crystal sheets are characterized with a well-defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn ≈ 0.25 and a refractive index along the slow axis of n ≈ 1.7. It is further shown that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization-dependent diffractive meta-surface, opening the door to the fabrication of various optical devices from a platform of small-molecule based organic dielectric crystals.