Cross-sectional Electron Microscopy Research Articles

In-plane charged antiphase boundary and 180° domain wall in a ferroelectric film

The deterministic creation and modification of domain walls in ferroelectric films have attracted broad interest due to their unprecedented potential as the active element in non-volatile memory, logic computation and energy-harvesting technologies. However, the correlation between charged and antiphase states, and their hybridization into a single domain wall still remain elusive. Here we demonstrate the facile fabrication of antiphase boundaries in BiFeO3 thin films using a He-ion implantation process. Cross-sectional electron microscopy, spectroscopy and piezoresponse force measurement reveal the creation of a continuous in-plane charged antiphase boundaries around the implanted depth and a variety of atomic bonding configurations at the antiphase interface, showing the atomically sharp 180° polarization reversal across the boundary. Therefore, this work not only inspires a domain-wall fabrication strategy using He-ion implantation, which is compatible with the wafer-scale patterning, but also provides atomic-scale structural insights for its future utilization in domain-wall nanoelectronics.

A Process Optimization Method of the Mini-LOCOS Field Plate Profile for Improving Electrical Characteristics of LDMOS Device

In this work, the effects of the mini-local oxidation of silicon (LOCOS) field plate’s bottom physical profile on the devices’ breakdown performance are analyzed through technology computer-aided design simulations. It is indicated that the “abrupt” bottom profile could certainly do with an optimization. This paper introduces an effective process improvement method by etching bias power adjustment and time reduction. The upgradation of the field plate physical profile has been proved by transmission electron microscope cross-section analysis. The angle for the bottom surface of mini-LOCOS field plate θ2 is improved from 11.9° to 12.6°, and the thickness ratio of Hup/Hbottom (field plate oxide thickness for the upper and bottom, respectively) is increased from 71.8% to 76.6%. Finally, the optimized laterally diffused metal oxide semiconductor devices have been fabricated, and both figure of merit curves and safe operation area curves are measured. The specific on-resistance Ron,sp could achieve as low as 11.3 mΩ mm2, while breakdown voltage BVds,max arrives at 37.4 V, which is nearly 19.3% improved.

Coaxial bioprinting of cellulose nanocrystal-reinforced core-sheath strands for alginate hydrogel construct fabrication

Alginate is among the most popular bioinks for 3D bioprinting because it is biocompatible, biodegradable, and is easily crosslinked using divalent cations. Here, we investigate the addition of cellulose nanocrystals (CNCs) to an alginate-based bioink to strengthen bioprinted structures. Using coaxial 3D bioprinting, alginate strands were constructed with a core-sheath structure reinforced by CNCs within the core. The addition of CNCs resulted in an increase in the storage modulus. Formulations containing CNCs resulted in more stable strands with uniformity factors and printability numbers close to 1. Based on the uniformity factor, the formulations containing 1.5 wt% CNCs deviated the least from a theoretically flawless strand. The alginate strands displayed microporous internal structures that were evident by scanning electron microscopy of the strand cross-sections. The addition of CNCs to the core compartment doubled both the modulus and the tensile strength, and the material was able to resist a strain above 50% before failure, thus demonstrating that the addition of the CNCs to the core of the strand leads to resilient printed structures.

A Simplified Microscopy Technique to Rapidly Characterize Individual Fiber Traits in Cotton.

Recent advances in phenotyping techniques have substantially improved the ability to mitigate type-II errors typically associated with high variance in phenotyping data sets. In particular, the implementation of automated techniques such as the High-Volume Instrument (HVI) and the Advanced Fiber Information System (AFIS) have significantly enhanced the reproducibility and standardization of various fiber quality measurements in cotton. However, micronaire is not a direct measure of either maturity or fineness, lending to limitations. AFIS only provides a calculated form of fiber diameter, not a direct measure, justifying the need for a visual-based reference method. Obtaining direct measurements of individual fibers through cross-sectional analysis and electron microscopy is a widely accepted standard but is time-consuming and requires the use of hazardous chemicals and specialized equipment. In this study, we present a simplified fiber histology and image acquisition technique that is both rapid and reproducible. We also introduce an automated image analysis program that utilizes machine learning to differentiate good fibers from bad and to subsequently collect critical phenotypic measurements. These methods have the potential to improve the efficiency of cotton fiber phenotyping, allowing for greater precision in unravelling the genetic architecture of critical traits such as fiber diameter, shape, areas of the secondary cell wall/lumen, and others, ultimately leading to larger genetic gains in fiber quality and improvements in cotton.

Graphene capping layer for improving the photovoltaic stability of ZnO nanorods solar cells under temperature variations

The present study evaluates the role of the graphene capping layer on the optoelectronic performance of ZnO/Si solar cells at different ambient temperatures. The n-ZnO buffer thin film was sputter-deposited on the p-Si substrates to form a p-n heterojunction. Next, ZnO nanostructures were chemically synthesized on top of the ZnO/Si substrates, and few-layer graphene was deposited on ZnO nanostructures using an electrophoretic deposition technique. The planar and cross-sectional electron microscopy analyses exhibited that the graphene capping layer entirely covered the surface of ZnO nanostructures, and their morphology remained intact after graphene transfer. Their photoluminescence (PL) properties before and after graphene deposition were analyzed at various temperatures to evaluate the graphene role in the optical behavior of ZnO nanostructures. The PL intensity was reduced for the graphene-containing sample because of the slight light absorption in each graphene layer. However, the stability of PL spectra at elevated temperatures was improved after graphene transfer. Next, a heterojunction solar cell was developed by depositing top and back contacts to study the photovoltaic performance of nanostructures at various temperatures. The current-voltage results, recorded under a solar light simulator, illustrated that the efficiency of the bare ZnO device was reduced at high temperatures because of the available interstitials and oxygen vacancies. After graphene transferring, this decay was moderated, which enhanced the photovoltaic stability of ZnO-based solar cells. Therefore, the graphene capping layer can act as a stabilizing thin film to enhance the photovoltaic durability of ZnO nanostructures under harsh conditions.

Low Interfacial Resistance and Superior Suppression to Li-Dendrite Penetration Facilitated by Air-Stable and Mechanically Robust Al/Mg-Co-Doped Li-La-Zirconate as Electrolyte for Li-Based Solid-State Cells.

In the context of usage as a solid electrolyte (SE) for Li-based solid-state cells, the interfacial characteristics of Li-La-zirconate (LLZO) with the electrodes and the mechanical properties of LLZO influence the overall impedance and stability. In this regard, the newly developed air-stable Al/Mg-co-doped LLZO has been found to possess greater resistance to crack propagation (by ∼31%) and fracture stress (by ∼52%), along with elevated hardness and stiffness, as compared to simply Al-doped LLZO. Furthermore, as directly visualized via cross-section electron microscopy at the Li/LLZO interfaces, the air-stability, along with mechanical robustness of Al/Mg-co-doped LLZO, facilitates the complete absence of impurity phase and cracks at the Li/LLZO interface, unlike for the simply Al-doped LLZO. These result in a very low area specific resistance for the Li/"Al/Mg-co-doped LLZO" interface of ∼9 Ω cm2, which is ∼3 times lower than that at the Li/"Al-doped LLZO" interface and is also among the lowest reported to date for Li/LLZO interfaces, that too sans any surface/interfacial coating/engineering. Galvanostatic Li-plating/stripping cycles indicate that the critical current density toward initiating Li-dendrite nucleation/propagation is higher in the case of Al/Mg-co-doped LLZO SE, viz., ∼0.45 mA/cm2, than for the Al-doped counterpart (viz., ∼0.25 mA/cm2). Furthermore, Li-stripping/plating cycles @ 0.1 mA/cm2 have revealed outstanding stability of polarization voltage up to at least 100 cycles upon using Al/Mg-codoped LLZO as the SE, in contrast to the instability right from the 36th cycle onward with the Al-doped LLZO. This indicates superior suppression toward Li-dendrite nucleation/propagation by the Al/Mg-codoped LLZO, unlike by Al-doped LLZO, as also directly visualized via cross-section electron microscopy post-cycling. The air-stability induced a clean Li/LLZO interface (viz., good contact), which, together with the mechanical robustness of Al/Mg-codoped LLZO, resulted in the very low interfacial resistance and excellent suppression toward Li-dendrite nucleation/propagation, leading to high CCD and very stable long-term Li-stripping/plating. Overall, in addition to highlighting the notable advantages offered by the Al/Mg-co-doped LLZO solid electrolyte, the insights obtained as part of this work are expected to lead to the successful and facile development of high-performance solid-state Li-based cells.

Circulating Flow-Electric-Field-Configuration-Enhanced Cadmium Cementation from Sulfate Systems and Its Optimization Mechanism.

In this work, a novel flow-electric field coupling configuration was designed and implemented for enhancing Zn-Cd cementation. A series of tests was conducted to explore the optimization of the Zn-Cd cementation process and its mechanism. Firstly, the various characteristics of the sponge cadmium at various locations in the device were compared, and it was concluded that the optimum purity of the sponge cadmium obtained from the anode was up to 94.1%. The generation and stripping of the cadmium sponge was revealed for the first time by cross-sectional electron microscopy. The four stages of the apparent reaction in the system were analyzed in relation to the pH, cadmium concentration and cadmium sponge flaking at each flow rate. It was proved that the separation of cadmium sponge mainly occurred in the third phase. Secondly, by comparing the morphology and specific surface area of the cadmium sponge at different flow rates, the optimum flow field velocity was identified as 30 mL/s. At this point, the specific surface area reached a maximum of 1.151 m2/g. Six flow field configurations were compared and preferred. The results demonstrated that the LCAH (Low-Cathode-Anode-High) modulation resulted in a sparser structure of the cadmium sponge, which was more easily exfoliated from the zinc anode surface by fluid impact. This was considered to be the most beneficial flow field configuration for improving the cadmium cementation rate and reducing the cost of the reaction. Moreover, the reaction steps of the system were analyzed. Its rate-limiting step was initially empirically identified as the diffusion step and proven by calculating the activation energy of 12.6 kJ/mol. It was confirmed that the diffusion process under different flow field configurations followed the first-order kinetic principle. In addition, the system's reaction phases were compared. Calculations confirmed that the diffusion process under various flow field configurations followed first-order kinetics. The diffusion coefficient of LACH proved to be the highest in the comparative tests, and the evident experimental results supported this conclusion.

Bottom-up self-assembly of macroporous ZnO nanostructures for photovoltaic applications

The present study utilized a template-assisted electrodeposition route for the bottom-up epitaxial growth of macroporous zinc oxide nanostructures. To this end, the ZnO seed layer was coated on the p-type silicon substrates using a radio frequency magnetron sputtering technique to form a p-n heterojunction. Then, polymer microspheres were implanted on ZnO/Si substrates to act as a template. Subsequently, ZnO nanostructures were electrodeposited through the interstitial spaces between the microspheres. After the deposition, the microspheres were removed by dissolving in chloroform solvent, forming a porous structure. The planar and cross-sectional electron microscopy analyses exhibited a uniform macroporous morphology with an average pore diameter of ∼1 μm. The pores were homogeneously distributed on the surface of the electrodeposited ZnO layer. The advantage of this technique over the top-down approaches, such as electrochemical etching, is that the porosity and size of pores can be easily adjusted by varying the concentration and diameter of microsphere templates. The optical investigations revealed enhancement in photon absorption and photoluminescence (PL) intensity due to multiple light scattering in the pore walls of the deposited ZnO nanostructures. For the templated sample, a PL blue shift was observed due to the reduction in crystallite size of ZnO nanostructures. A heterojunction thin film solar cell was designed by the metallization of ZnO/p-Si samples to study the power conversion capability of macroporous ZnO nanostructures. The photovoltaic performance of the developed devices was evaluated under a solar light simulator. The device based on the templated sample showed increased shunt resistance and reduced series resistance compared to the flat sample. The optoelectrical results indicated an efficiency improvement for the fabricated solar cells based on the macroporous ZnO sample due to its higher exposed area and increased rate of electron-hole generation.

Fabrication of Multiphase Liquid Metal Composites Containing Gas and Solid Fillers: From Pastes to Foams

Gallium-based liquid metals (LMs) are suitable for many potential applications due to their unique combination of metallic and liquid properties. However, due to their high surface tension and low viscosity, LMs are challenging to apply to substrates in useful shapes, such as dots, wires, and films. These issues are mitigated by mixing the LMs in air with other materials, such as mixing with solid particles to form LM solid pastes or mixing with gases to form LM foams. Underlying these deceivingly simple mixing processes are complex and highly intertwined microscale mechanisms. Air microbubbles are inevitably incorporated while making LM pastes, making them partly foams. On the other hand, for foaming of the LM to occur, a critical volume content of solid particles must be internalized first. Consequently, both LM pastes and foams are multiphase composites containing solid and fluid microcomponents. Here, we systematically study the impact of the mixing procedure, solid particle size, and volume fraction (SiO2) on the air content of the multiphase LM composites. We demonstrate that decreasing the particle size and increasing their volume fraction substantially decrease the composite density (i.e., increases air entrapment). The foaming process can also be enhanced with the use of high-speed mechanical mixing, although leading to the formation of a more disordered internal structure. In contrast, manual mixing with larger microparticles can promote the formation of more paste-like composites with minimal air content. We explain the microscopic mechanisms underlying these trends by correlating macroscopic measurements with cross-sectional electron microscopy of the internal structure.

Comparative Study on Leaf Anatomy in Selected Garcinia Species in Peninsular Malaysia

A comparative study of leaf anatomy was attempted on Garcinia species in Peninsular Malaysia to identify anatomical features useful in species identification and classification. The species are Garcinia mangostana var. mangostana , Garcinia mangostana var. malaccensis , and Garcinia celebica. Leaves were collected from two different regions: Kuantan, Pahang and Kepong, Kuala Lumpur. The leaf anatomical study was done using the methods of leaf peeling, leaf venation, leaf cross-section, and scanning electron microscopy. The assessment of the leaf anatomy found that these three Garcinia species showed similarities in anatomical features, including the presence of paracytic stomata on the abaxial surface, a straight to wavy anticlinal wall of both adaxial and abaxial surfaces, a thick cuticle wax layer, the presence of druses, mucilage canal, petiole vascular bundle, the presence of collenchyma cells in the midrib, and also the presence of sclerenchyma cells in midrib and petiole. Meanwhile, the notable anatomical variation observed in this study included three types of midrib vascular bundles: the outline of the leaf margin, the presence of tanniferous idioblast, leaf marginal, and laminal venation as six types of epicuticular waxes present on epidermal surface. Overall, this study highlighted the anatomical features that are taxonomically valuable, which could be used to identify selected Garcinia species in Malaysia.

Two-Dimensional Siloxene Nanosheets: Impact of Morphology and Purity on Electrochemistry.

Two-dimensional (2D) siloxene (Si6O3H6) has shown promise as a negative electrode material for Li-ion batteries due to its high gravimetric capacity and superior mechanical properties under (de)lithiation compared to bulk Si. In this work, we prepare purified siloxene nanosheets through the removal of bulk Si contaminants, use ultrasonication to control the lateral size and thickness of the nanosheets, and probe the effects of the resulting morphology and purity on the electrochemistry. The thin siloxene nanosheets formed after 4 h of ultrasonication deliver an average capacity of 810 mA h/g under a 1000 mA/g rate over 200 cycles with a capacity retention of 76%. Interestingly, the purified siloxene shows lower initial capacity but superior capacity retention over extended cycling. The 2D morphology benefit is illustrated where the parent siloxene nanosheet morphology and structure were largely maintained based on operando optoelectrochemistry, in situ Raman, ex situ scanning electron microscopy, and ex situ transmission electron microscopy. Furthermore, the purified siloxene-based electrode free from crystalline Si impurity experiences the least expansion upon (de)lithiation as visualized by cross-section electron microscopy of samples recovered post-cycling.

An Alternative Method of Measuring Area Specific Resistance of Chromia Scales Using Electrochemical Impedance Spectroscopy

A novel method that employs electrochemical impedance spectroscopy (EIS) is developed to characterize the oxide scale resistance and thickness of Crofer 22 APU after exposure at 800 °C in humidified air. Crofer 22 APU, is one of the most commonly used materials for solid oxide fuel cell (SOFC) interconnects, an application for which oxide scale resistance is of paramount importance. The kinetics of oxide growth were studied for up to 6,000 h using three different techniques: electron microscopy of cross-sections, gravimetry, and EIS capacitance measurements of the oxide scale. EIS was used to evaluate the scale thickness starting from the material capacitance, and the material resistance at high temperature was estimated using extrapolation of the impedance values at room temperature. The result obtained with this novel EIS method are comparable to those obtained using conventional techniques, and in addition, the new method is cheaper, faster, and more reliable. Moreover, it enables repetitive exposures of the same sample without altering the specimen properties.

In-situ formation of Ag nanoparticles in the MAO coating during the processing of cp-Ti

Silver nanoparticle (Ag-NP) containing antibacterial micro-arc oxidation (MAO) coatings have already been synthesized over titanium-based materials via the MAO process employed in silver acetate (AgC2H3O2) containing electrolyte. However, the way of incorporation and in-situ formation of Ag-NPs within the MAO coating have not been documented yet. Present work was initiated to reveal the mechanism of Ag-NP formation within the MAO coatings. Thus, the structure of the MAO coating fabricated on commercial purity titanium in the AgC2H3O2-containing electrolyte was investigated by electron microscopy techniques. To this end, the cross-sectional high-resolution electron microscopy studies were carried out on lamella cut out with the focused ion beam technique, and these investigations were backed by X-ray photoelectron spectroscopy measurements of chemical composition on the surface of the MAO coating. These studies revealed that Ag is dispersed in the form of nanoparticles throughout the coating and that a higher density was confirmed closer to the micro-pores.

Durability of TiAl based surface acoustic wave devices for sensing at intermediate high temperatures

TiAl based surface acoustic wave (SAW) devices, which offer a promising cheap and easy to handle wireless sensor solution for intermediate high temperatures up to 600 °C, were prepared and investigated with respect to their durability. To obtain the devices, Ti/Al multilayers were deposited on high-temperature stable piezoelectric catangasite (CTGS) substrates and structured as electrodes via the lift-off technique. AlNO cover layers and barrier layers at the substrate site served as an oxidation protection. The devices were characterized regarding their electrical behavior by ex-situ measurements of their frequency characteristics after heat treatments up to 600 °C in air. In addition, long-term in situ measurements up to 570 °C were performed to analyze a possible drift of the resonant frequency in dependence on the temperature and time. Scanning electron microscopy of the surfaces of the devices and scanning transmission electron microscopy of cross sections of TiAl interdigital transducer electrode fingers and the contact pads were conducted to check the morphology of the electrode metallization and to reveal if degradation or oxidation processes occurred during the heat treatments.The results demonstrated a sufficient high-temperature stability of the TiAl based devices after a first conditioning of system. A linear dependence of the resonant frequency on the temperature of about −37 ppm/K was observed. In summary, the suitability of TiAl based SAW sensors for long-term application at intermediate temperatures was proven.

Biased quartz crystal microbalance method for studies of chemical vapor deposition surface chemistry induced by plasma electrons.

A recently presented chemical vapor deposition (CVD) method involves using plasma electrons as reducing agents for deposition of metals. The plasma electrons are attracted to the substrate surface by a positive substrate bias. Here, we present how a standard quartz crystal microbalance (QCM) system can be modified to allow applying a DC bias to the QCM sensor to attract plasma electrons to it and thereby also enable in situ growth monitoring during the electron-assisted CVD method. We show initial results from mass gain evolution over time during deposition of iron films using the biased QCM and how the biased QCM can be used for process development and provide insight into the surface chemistry by time-resolving the CVD method. Post-deposition analyses of the QCM crystals by cross-section electron microscopy and high-resolution x-ray photoelectron spectroscopy show that the QCM crystals are coated by an iron-containing film and thus function as substrates in the CVD process. A comparison of the areal mass density given by the QCM crystal and the areal mass density from elastic recoil detection analysis and Rutherford backscattering spectrometry was done to verify the function of the QCM setup. Time-resolved CVD experiments show that this biased QCM method holds great promise as one of the tools for understanding the surface chemistry of the newly developed CVD method.

Dendrite growth inhibition in a V6O13 nanorods based non-aqueous Zn-ion battery by a scalable polycarbazole@Carbon nanotubes overlayer

Inhibiting the growth of dendrites, one of the most serious issues faced by zinc-ion batteries (ZIBs) is addressed by coating the Zn anode with a layer of poly(carbazole)-carbon nanotubes (PCz@CNTs) composite. The electrically conducting robust composite overlayer ensures that the Zn-deposition during charging cycles is homogeneous and completely free of any fiber-like growth. This is confirmed from the cross-sectional electron microscopy analysis of post-cycled PCz@CNTs@Zn electrode. A vanadium oxide nanorods-porous graphitic flakes (V6O13 NRs@PGFs) composite is used as a cathode. It has a large specific surface area, affording short ion-diffusion distances and many vacant sites thus permitting facile Zn2+ ion ingress and egress, is used. A remarkable performance results for the non-aqueous ZIB: V6O13 NRs@PGFs//PCz@CNTs@Zn with a capacity of 286 mAh g−1 after 300 cycles at 30 mA g−1 (with 98% capacity retention), energy density of ∼172 Wh kg−1 and a nominal voltage of 1.8 V. It is significantly enhanced compared to its analogous ZIB of V6O13 NRs@PGFs//Zn (193 mAh g−1, and 80% capacity retention). The PCzCNTs overlayer imparts long lifespan with nominal capacity fade, guarantees ultra-safe operation, is cost-effective and also easy to scale-up thus providing a solution that can be adapted to other metal-ion batteries free of dendrites and long term cycling stability.

High-throughput dry transfer and excitonic properties of twisted bilayers based on CVD-grown transition metal dichalcogenides.

van der Waals (vdW) layered materials have attracted much attention because their physical properties can be controlled by varying the twist angle and layer composition. However, such twisted vdW assemblies are often prepared using mechanically exfoliated monolayer flakes with unintended shapes through a time-consuming search for such materials. Here, we report the rapid and dry fabrication of twisted multilayers using chemical vapor deposition (CVD) grown transition metal chalcogenide (TMDC) monolayers. By improving the adhesion of an acrylic resin stamp to the monolayers, the single crystals of various TMDC monolayers with desired grain size and density on a SiO2/Si substrate can be efficiently picked up. The present dry transfer process demonstrates the one-step fabrication of more than 100 twisted bilayers and the sequential stacking of a twisted 10-layer MoS2 single crystal. Furthermore, we also fabricated hBN-encapsulated TMDC monolayers and various twisted bilayers including MoSe2/MoS2, MoSe2/WSe2, and MoSe2/WS2. The interlayer interaction and quality of dry-transferred, CVD-grown TMDCs were characterized by using photoluminescence (PL), cathodoluminescence (CL) spectroscopy, and cross-sectional electron microscopy. The prominent PL peaks of interlayer excitons can be observed for MoSe2/MoS2 and MoSe2/WSe2 with small twist angles at room temperature. We also found that the optical spectra were locally modulated due to nanosized bubbles, which are formed by the presence of interface carbon impurities. The present findings indicate the widely applicable potential of the present method and enable an efficient search of the emergent optical and electrical properties of TMDC-based vdW heterostructures.

(Digital Presentation) Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Ammonia electrosynthesis is considered promising for the production of ammonia as an energy carrier, as the process could provide greater flexibility and compatibility to the fluctuations of renewable energy than the industrial Haber-Bosch process. One approach for enhancing the ammonia formation rate is the electrochemical promotion of catalysis (EPOC) [1], in which a non-faradaic acceleration of ammonia synthesis is observed; however, much of the mechanism remains unclear. Further mechanistic insight would aid in designing better electrode structures that are suited for efficient ammonia electrosynthesis. In this presentation, we explore the mechanism underlying the electrochemical promotion of ammonia synthesis, using electrochemical cells with iron-based cathodes on a proton-conducting BaCe0.9Y0.1O3 (BCY) electrolyte.Previously, our group reported that the ammonia formation rate of a cathodically polarized cell can be enhanced by adding H2 to the cathode gas feed (commonly pure N2) [2, 3]. Further kinetic and isotopic analysis using deuterium showed that the primary hydrogen source for the ammonia produced was the gaseous hydrogen feed, rather than the protons conducted via the electrolyte [4]. Cells with a porous pure Fe cathode resulted in higher ammonia formation rates than those with a porous 10 wt.% Fe-BCY cathode, suggesting that the pure Fe surfaces near the cathode-electrolyte interface, as opposed to the triple phase boundaries, are active for ammonia electrosynthesis [3]. However, the 10 wt.% Fe-BCY cathode, fabricated by the impregnation method, was thought to be limited by lack of Fe network formation needed for electron conduction.In this study, we fabricated a cermet cathode with the composition 56 wt.% Fe-BCY, aiming for Fe and BCY to form separate networks for electron and proton conduction, respectively. Electrochemical cells of the configurations Pt|BCY|Fe and Pt|BCY|Fe-BCY [Fig. 1a], with similar Fe mass (0.5 and 0.4 mg) were compared. Ammonia synthesis was conducted in a single-chamber reactor at 500-600˚C with a 50% H2/50% N2 feed. The gaseous ammonia produced was captured by bubbling into a dilute H2SO4 solution and quantified via high-performance liquid chromatography.Using the pure Fe electrode, an ammonia formation rate of 1.3 × 10-8 mol s-1 cm-2 (26 mmol gFe -1 h-1) was obtained at 600˚C and -1 V [Fig. 1b]. This corresponds to an almost 5-fold increase in ammonia formation compared to the catalytic reaction at 0 V. In contrast, a lower ammonia formation rate of 7.0 × 10-9 mol s-1 cm-2 (17 mmol gFe -1 h-1) was obtained using the Fe-BCY electrode at the same conditions. Despite the cermet electrode having a slightly higher current density, and despite the comparable iron loading on the two cells, the pure Fe cell still resulted in a faster ammonia formation rate per electrode area and per iron mass. As the cermet electrode is expected to have a significantly longer triple phase boundary length, from the comparison of these two electrochemical cells, the triple phase boundaries do not appear to be the primary active sites. We further analyze the roles of the bulk Fe surfaces and the Fe/BCY triple phase boundaries, by examining the effect of the electrode thickness and by post-experiment cross-sectional electron microscopy approaches.AcknowledgementsThis work was supported by JSPS KAKENHI Grant Number JP21H04938.

In situ spectroscopic ellipsometry and rigorous coupled wave analysis for real time profile evolution of atomic layer deposited films inside SiO2 nanotrenches

Rigorous coupled wave analysis (RCWA) is conducted on in situ spectroscopic ellipsometry data to understand profile evolution during film deposition inside nanotrenches. Lithographically patterned SiO2 nanotrenches are used as test structures. The nanotrenches are 170 nm wide at the top with a taper angle of 4.5° and are 300 nm in depth. Atomic layer deposition of ZnO is used as a model process where the thickness (cycles) of the film is varied from 0 (0 cycles) to 46 nm (300 cycles). The analysis predicts transient behavior in deposition affecting film conformality and changes to the trench taper angle. In the process, the aspect ratio varies from 2.05 at the start of the process to 6.67 at the end. The model predicts changes in the refractive index of the ZnO film as a function of thickness. The real and imaginary parts of the refractive index at a wavelength of 350 nm change from 1.81 to 2.37 and 0.25 to 0.87, respectively. Scanning electron microscopy cross sections confirm thickness at the top and bottom of the trench to within 13% of those predicted by RCWA. The experimentally measured conformality degrades as film deposition proceeds from 97.3% at 100 cycles to 91.1% at 300 cycles. These results demonstrate the potential of using RCWA for continuous and in situ monitoring of growth inside 3D nanostructures.

Au Wire Ball Welding and Its Reliability Test for High-Temperature Environment.

The long-term application of sensors in a high-temperature environment needs to address several challenges, such as stability at high temperatures for a long time, better wiring interconnection of sensors, and reliable and steady connection of the sensor and its external equipment. In order to systematically investigate the reliability of thin coatings at high temperatures for a long time, Au and Cr layers were deposited on silicon substrates by magnetron sputtering. Additionally, samples with different electrode thicknesses were annealed at different temperatures for a varied duration to study the effect of electrode thickness, temperature, and duration on the reliability of samples. The results of tensile and probe tests before and after heat treatment revealed that the mechanical strength and electrical properties have changed after annealing. In addition, the bonding interface was analyzed by a cross-sectional electron microscope. The analysis showed that long-term continuous high-temperature exposure would result in thinning of the electrode, formation of pores, recrystallization, and grain growth, all of which can affect the mechanical strength and electrical properties. In addition, it was observed that increasing the thickness of the gold layer will improve reliability, and the test results show that although the thin metal layer sample is in poor condition, it is still usable. The present study provides theoretical support for the application of thin coatings in high temperatures and harsh environments.