Microns In Thickness Research Articles

Observation and Control of Single-Component Adhesion Interphase of Polyamide 66 through Confocal Raman Microspectroscopy.

Manufacturing using adhesion technology has attracted much attention. Examples of adhesion include the lay-up of carbon fiber reinforced thermoplastic prepregs and the lamination of food packaging. In single-component adhesion systems, the analysis of the boundary region poses challenges because of the absence of chemical and physical discrimination at the adhesion interphase. Polyamide 66, one of the typical engineering plastics, is widely accepted as a structural material in automobiles and packaging films. Therefore, finer control of adhesion with polyamide 66 is crucial for advancing adhesion manufacturing. In this work, we focused and investigated the interphase of a single-component adhesion system with polyamide 66. For the analyses of single-component polyamide 66 laminates, an adhesion system with nondeuterated and deuterated polyamides was utilized, and their interphase structures were evaluated by confocal Raman microspectroscopy. The interphase region of the adhesion specimens was able to be characterized and evaluated, revealing an expansion to a thickness of several micrometers. The interphase thickness was increased with thermal annealing postlamination, whereas no thickness increase was observed in adhered specimens using the polyamide 66 substrates through thermal crystallization before lamination. The formation of the interphase region can be attributed to the crystal growing and lamella interlocking in the boundary region. Moreover, the larger interphase thickness was strongly associated with an increase in adhesion fracture toughness. These results suggested that the adhesion properties of crystalline substrates were decided by crystallization behavior and the thermal annealing process, even when using the same component adhesion systems.

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 provides information about the electronic and local geometric structural properties of newly developed electrocatalysts, especially when it is 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 (CL), as well as to the (partial) shielding of the CL with electrochemically evolved bubbles trapped within its pores. These limitations can be tackled by performing such spectrochemical measurements with low-loaded (and thus thin) electrodes, which call for the acquisition of XAS spectra in fluorescence mode and using an X-ray beam incidence angle of ≤0.1° with regards to the working electrode's substrate plane in a grazing-incidence (GI) configuration. Thus, in this work, we introduce a new spectroelectrochemical flow cell that allows one to perform such measurements in this GI mode and verify its functionality by tracking the potential-induced formation of palladium hydride (PdHx) in a Pd nanoparticle-based electrocatalyst. A time resolution of 10 s per spectrum was achieved with a very low Pd-loading of only 30 μgPd/cm2. Moreover, the implementation of an ion-conductive membrane to separate the working- and counter-electrode compartments enables the quantification of reaction products, which, in the case of gaseous species, can be detected in a time-resolved manner by means of mass spectrometry. Chiefly, this allows us to determine the electrocatalytic activity and selectivity of a given material in the same cell configuration used for the spectroscopic measurements and assures a reliable comparison among the results derived from both techniques.

Electromagnetic Coils for a 3000 Psi Hydraulic MEMS Valve Assembly

Electromagnetic coils serve many roles in MEMS technologies such as actuators, microfluidics, sensors, energy harvesting, wireless communication, inductive heating, and biomedical applications. Coils can be made using traditional semiconductor manufacturing techniques requiring near UV lithography to define photoresist molds, electroforming metal into the molds, chemical mechanical planarization, assembly, and packaging. Non-traditional techniques such as LIGA using x-rays and soft LIGA using near UV exposures can create higher aspect ratio structures therefor maximizing coil performance and minimizing coil size.Our work explores micro-fabrication techniques using soft LIGA lithography to create single sided and double-sided copper electroformed MEMS coils. The target coil feature sizes are 100+ micron in thickness of copper, 50 micron feature size, 50 micron gaps, and millimeters in total form factor. The microfabrication process including lithography, copper electrodeposition, and through wafer vias will be discussed along with lessons learned to meet the design criteria. Our goal is the demonstration of a single sided coil and double-sided coil device that could be assembled and arrayed across a 6 inch silicon wafer microfabrication process to create a hydraulic valve assembly. This would enable a digital flow control high-pressure hydraulic valve system capable of reaching 3000 psi. Ultimately this goal minimizes size and weight while increasing efficiency and maximizing power. The figure below depicts a cross sectional view of a single sided coil design assembled with a device layer having a through-wafer etch flow path.Figure 1: Cross sectional view showing a single hydraulic MEMs valve assembly. A single sided MEMs coil on top, a suspended spring able to open and close the valve, and a thru-wafer fluid flow path. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Figure 1

(Invited) On the Improvement of Ge Lasers

Electrically pumped Ge lasers were first demonstrated in 2012, which are considered a promising solution to Si-compatible on-chip lasers. Theoretical studies showed that laser structure design, stress engineering, and Ge material quality improvement are the three main methods for improving Ge laser performance. Epitaxial Ge thin films (epi-Ge) on Si have been the choice for Ge in photonic and microelectronic devices due to the suitable thickness in the micron or sub-micron scale. For Ge on-chip lasers, this thickness range is required to overcome the self-absorption, high lasing threshold, and coupling difficulty associated with larger thicknesses. However, the major problem of epi-Ge on Si is the high threading dislocation density (TDD) ranging from 106 to 1010 cm-2 despite the extensive research efforts to reduce the TDD. In contrast, bulk Ge, typically a few hundred microns thick, maintains superior crystal quality (TDD ≤ 104 cm-2).To take advantage of this ultra-high crystal quality, we successfully developed wet etching recipes to thin bulk Ge wafer pieces down to micron-scale free-standing Ge thin films with good sample integrity and surface roughness while maintaining the ultra-high crystal quality of the starting bulk-Ge samples. Two bulk Ge wafers were chosen and thinned from 535 or 405 µm to 1-2 µm. As a result, the photoluminescence (PL) peak intensity of the thinned Ge samples increased significantly. The key material parameters are shown in the table below. The specification values beneficial for more PL intensity are shaded in green, and those not desired are in red. The benchmarking epi-Ge control sample has been compared to the epi-Ge from the best Ge lasers, which have similar specifications and PL intensity. Compared with the bulk Ge or bulk-Ge-based thin films, the epi-Ge has a higher tensile strain, higher n-type doping, and lower surface roughness, which all support much higher PL intensity except for the much higher TDD. However, the samples with much increased PL peak intensities are from bulk-Ge-based thin films with non-optimized strain, doping, and surface roughness, demonstrating the TDD reduction's high effectiveness in improving Ge PL. Measurements showed much longer minority carrier lifetimes in these high PL samples due to the very low TDDs. TDD reduction in Ge relaxes the common requirements of high n-doping and stress in enhancing Ge laser performance. It thus reduces the side effects of high optical absorption, high non-radiative recombination, bandgap narrowing, and large footprints associated with these two techniques.After proving the bulk-Ge-based thin film concept, we also developed bonding, thinning, and polishing techniques to make thin Ge bonded on handle substrates and to introduce tensile strain from the bonding step. Ultra-high-quality Ge/poly-Si/SiO2 thin films on glass with sufficient bonding strength and surface smoothness were achieved. The minority lifetimes for these bonded Ge thin films range between 200 and 1000 ns, surpassing those achieved with epi-Ge on Si by at least 20 to 100 times. This is an important indication of the ultra-high quality of the bonded Ge thin films. Later, Ge microbridges were fabricated, which amplified the tensile strain introduced in the bonding step, reaching a maximum uniaxial tensile strain of 3.7%. This is crucial for reducing the difference between Ge's direct and indirect energy bands for much more efficient light emission.In summary, this work established an economical and convenient fabrication technology for producing high-crystal-quality and high-tensile-strained Ge thin films bonded on substrates — a pivotal step in exploring Ge's potential in light emission applications, especially for Ge lasers for on-chip optical interconnects. Figure 1

Electrochemically Induced Templated Sol-Gel Deposition of Mesoporous Silica and Nanocomposite Thin Films

Electrochemically induced sol-gel depositions have recently been gaining scientific interest for their ability to synthesize highly ordered mesoporous silica thin films on electrode substrates.1 The process works by using cathodic reactions to electrogenerate OH- ions through the reduction of a pro-base (e.g., water) and form an alkaline diffusion layer near the electrode surface. Within this alkaline zone, the gelation reactions of a pre-hydrolyzed, kinetically-inhibited silica sol-gel precursor solution are catalyzed, thus triggering the growth of a gel film onto the electrode. The addition of surfactant templates allows for the formation of mesoporous thin films with highly organized pore structures that have a wide range of applications in a wide range of fields. The advantages of this electrochemically induced process include the ability to control the deposition using electrochemical parameters, the faster gelation compared to conventional sol-gel, the option to omit high-temperature treatment/solidification steps and the ability to coat 3D structured electrodes. Furthermore, the rapid gelation is limited to the zone within the alkaline diffusion layer during film growth. Recently, we demonstrated improved process control by tuning the diffusion layer thickness using rotating disk electrodes2, thereby inhibiting the formation of aggregated particle byproducts, and provided an in-depth overview of the mechanism and relevant aspects of the film growth3.In the present work, the same electrochemically induced sol-gel process is performed using an ionic liquid as the template, leading to the controlled deposition of a functional ionic-liquid-templated silica gel layer that can be dried to an ionically conductive nanocomposite with applications for sensors, supercapacitors and solid-state Li-ion batteries. The nanocomposite under study is based on recent works wherein a Li-ion ionic liquid electrolyte (ILE) was nanoconfined in an inert silica matrix, synthesized via sol-gel reactions.4–6 The nanoconfinement of the ILE in the mesoporous silica matrix results in a monolithic solid structure, while the Li+-ions retain liquid-like high ionic conductivities exceeding that of a pure ILE when the ion diffusion along silica wall/ILE interface dominates.4,6 The conventional sol-gel process used to synthesize the ionic liquid-templated silica requires several days to solidify into the product. By using the electrochemically induced sol-gel process, we demonstrated the ability to controllably grow coatings of 1 to 35 micrometers thickness on electrode surfaces in mere seconds to minutes. The obtained films show comparable properties as films prepared through conventional gelation.This presentation starts from an overview of the electrochemically induced sol-gel process for mesoporous silica thin films and outlines the methodology used to electrodeposit ionic-liquid-templated silica nanocomposite coatings. The functionality of the coatings as thin-film electrolyte was demonstrated in all-solid-state thin-film test-cells using TiO2, LiMnO2 (LMO) and LiNi0.5Mn1.5O4 (LNMO) as cathodes with Li metal as the anode. Since these thin-film model systems allowed the formation of single, well-defined interfaces between the different components, the underlying electrochemical processes during charge-discharge cycles could be carefully monitored. In this way, this work demonstrates the flexibility of the electrochemically induced sol-gel process by extending the methodology to grow composite coatings, in this case useful for thin-film solid-state batteries. References (1) Walcarius, A.; Sibottier, E.; Etienne, M.; Ghanbaja, J. Electrochemically Assisted Self-Assembly of Mesoporous Silica Thin Films. Nat. Mater. 2007, 6 (8), 602–608. https://doi.org/10.1038/nmat1951.(2) Vanheusden, G.; Philipsen, H.; Herregods, S. J. F.; Vereecken, P. M. Aggregate-Free Micrometer-Thick Mesoporous Silica Thin Films on Planar and Three-Dimensional Structured Electrodes by Hydrodynamic Diffusion Layer Control during Electrochemically Assisted Self-Assembly. Chem. Mater. 2021, 33 (17), 7075–7088. https://doi.org/10.1021/acs.chemmater.1c02197.(3) Vanheusden, G.; De Taeye, L.; Blom, M. J. W.; Jobbagy, M.; Vereecken, P. M. Unravelling the Mechanism of Electrochemically Induced Sol-Gel Depositions: PH Profiles Near Electrode and Influence on Film Growth. J. Electrochem. Soc. 2024, 171 (3), 032508. https://doi.org/10.1149/1945-7111/ad3500.(4) Chen, X.; Put, B.; Sagara, A.; Gandrud, K.; Murata, M.; Steele, J. A.; Yabe, H.; Hantschel, T.; Roeffaers, M.; Tomiyama, M.; Arase, H.; Kaneko, Y.; Shimada, M.; Mees, M.; Vereecken, P. M. Silica Gel Solid Nanocomposite Electrolytes with Interfacial Conductivity Promotion Exceeding the Bulk Li-Ion Conductivity of the Ionic Liquid Electrolyte Filler. Sci. Adv. 2020, 6 (2), eaav3400. https://doi.org/10.1126/sciadv.aav3400.(5) Sagara, A.; Chen, X.; Gandrud, K. B.; Murata, M.; Mees, M.; Kaneko, Y.; Arase, H.; Vereecken, P. M. High-Rate Performance Solid-State Lithium Batteries with Silica-Gel Solid Nanocomposite Electrolytes Using Bis(Fluorosulfonyl)Imide-Based Ionic Liquid. J. Electrochem. Soc. 2020, 167 (7), 070549. https://doi.org/10.1149/1945-7111/ab80d0.(6) Sagara, A.; Yabe, H.; Chen, X.; Put, B.; Hantschel, T.; Mees, M.; Arase, H.; Kaneko, Y.; Uedono, A.; Vereecken, P. M. Interfacial Conductivity Enhancement and Pore Confinement Conductivity-Lowering Behavior inside the Nanopores of Solid Silica-Gel Nanocomposite Electrolytes. ACS Appl. Mater. Interfaces 2021, 13 (34), 40543–40551. https://doi.org/10.1021/acsami.1c09246.

The Role of Volume Change in Lithium Oxygen Battery Electrodes

Lithium oxygen batteries have an exceptionally high theoretical specific capacity, but a variety of obstacles stand in the way of reaching that high capacity over many cycles. Recent research into catalysts and redox shuttles has improved the reversibility of the reaction between lithium ions and oxygen to form lithium peroxide, creating renewed interest in lithium oxygen technologies.A significant obstacle is that achieving high capacity necessarily implies that a large volume fraction of lithium peroxide must be stored in the cathode during discharge, to be released upon charge. Likewise, a large volume fraction of lithium metal must be stored as part of the anode during charge, to be released upon discharge. Such large volume changes create severe materials and reversibility issues. For instance, lithium peroxide particles displace electrolyte and cause the cathode to expand many times its original volume. The cathode material must be carefully selected to provide a good conductive lattice with high porosity and the ability to handle massive volume changes while also allowing the movement of electrolyte in and out of the cathode. To address this issue our research group has adopted the use of a binderless carbon nanotube (CNT) paper as our cathode. The CNT paper consists of layers of interconnected CNTs and displays high tensile strength, conductivity, porosity, and reaction sites. In typical slurry-coated electrodes a large volume expansion can cause fractures and cracks, electrically isolating sections of the carbon matrix and decreasing capacity with increased cycling. The durability and layer structure of the CNT paper permits high volumetric expansion with reduced damage to the carbon matrix. The CNT paper cathodes showed a discharge capacity of 10.000 mAh/g C, which is equivalent to 12 mAh/cm2. Figure 1 shows the substantial volume changes during the charge process. During lithiation of the cathode from (a) to (b) we can observe the cathode increased from approximately 28 microns to 160 microns thickness, or about six times the starting volume. Discharged cathodes were then rinsed in DI water to dissolve the lithium peroxide and observe the response of the carbon matrix (panel c). It can be seen that the removal of lithium peroxide left large gaps in the carbon matrix, which must be subsequently remedied in a charge cycle. We will present these and other results from our experiments on this system. Figure 1

Theoretical Design of Smart Bionic Skins with Self-Adaptive Temperature Regulation.

Thermal management presents a significant challenge in electric design, particularly in densely packed electronic systems. This study proposes a theoretical model for radiative bionic skin that emulates human skin, enabling the self-adaptive modulation of the thermal exhaustion rate to maintain homeostasis for objects covered by the skin in fluctuating thermal environments. The proposed artificial skin consists of phase change material (VO2) nanoparticles embedded in a low-loss matrix situated on a metallic substrate with a minimal thickness of several micrometers. The findings from our theoretical analyses indicate that substantial alterations in thermal radiation power around the phase transition temperature of 340 K enable a silicone substrate to sustain a relatively stable temperature, with variations confined to ±6 K, despite external heat fluxes ranging from 150 to 450 W/m2. Furthermore, to improve the spectral resemblance to natural skin, a plasmonic surface composed of self-assembled silver nanocubes is incorporated, allowing for modifications to the visible light properties of the bionic skin while maintaining its infrared characteristics. This theoretical investigation offers a cost-effective and conformal approach to the design of ultra-compact, fully passive, and versatile thermal management solutions for robotic systems and related technologies.

The geometry, purity, and grain orientation database of the Cu stabilizer layer and the effect on the electrical and thermal properties of commercial REBCO tapes

Abstract Building upon our previous database of the thermal, electrical, and mechanical properties of commercial REBCO tape, we have constructed a subsequent database focusing on the Cu layer of such tapes from eight distinct manufacturers. This database encompasses information pertaining to the geometry, purity, and grain orientation of the Cu layer. The primary objective of this database is to not only elucidate the material science of the Cu layer across various commercial tapes but also to establish correlations between the thermal, electrical, and mechanical properties and the aforementioned geometry, purity, and grain orientation parameters. After analysis, three significant findings have been validated. Firstly, the non-uniformity of geometry plays a critical role in the electrical resistivity in the radial direction, primarily through altering the actual contact surface area. Secondly, it has been observed that the total grain boundary length per micrometer thickness exhibits a nearly linear correlation with the thermal conductivity in the circumferential direction. Thirdly, the purity of the Cu layer in all the commercial REBCO tapes is lower than anticipated. It is our aspiration that this database will facilitate enhanced comprehension of the Cu layer in REBCO tapes among a broader spectrum of researchers.

A novel coalesced quantum dot buffer approach to mitigate large lattice mismatch in III–V epitaxy

III–V compound semiconductors, such as indium arsenide (InAs), are crucial in the fields of electronics and optoelectronics due to their unique properties, including a narrow bandgap, high electron mobility, low effective electron mass, and outstanding optoelectronic performance. However, the lattice constant mismatch of 7.2% between InAs and gallium arsenide (GaAs) leads to a high dislocation density in the InAs epilayer, typically around 109 cm−2 or higher when InAs is directly grown on GaAs (001). A common traditional approach to reduce material defect density involves using a compositionally graded buffer structure, which requires a thickness of several micrometers. This paper presents an innovative method for growing device-quality InAs epilayers on GaAs (001) substrates through an InAs coalesced quantum dot buffer (CQDB) layer. Remarkably, the InAs CQDB method requires a thickness of only several tens of nanometers, leading to significant improvements in film quality. Utilizing the InAs CQDB layer allows for a substantial reduction in dislocation density from 1.8 × 109 to 3.6 × 107 cm−2. The findings of this study provide a crucial research foundation for addressing lattice mismatch challenges in epitaxial growth, particularly for those investigating methods to integrate different materials in advanced device applications.

Polymer composite cladding for selective frequency filtration: An experimental and modeling study

Laser selective frequency filtering is currently performed using expensive, heavy, and bulky (millimeters in thickness) ceramic composite claddings around the laser rod, which limits the miniaturization and transportability of the laser. The cladding absorbs undesired spontaneous emissions and reflects the desired wavelength of the "pump" diode. As an improved alternative for the cladding on, say, a diode-pumped solid-state Nd:YAG laser rod, we investigate a spray-coated polymer composite cladding (micrometers in thickness). The polymer composite cladding is easier to process and lighter and has a much smaller volume vs. traditional ceramic composite claddings. The approach is demonstrated on spray-coated glass slides, where cubic samaria (Sm2O3) particles are used as the filler in the polymer composite cladding. The rationale for using samaria as the filler in the composite is its absorption near the laser spontaneous emission wavelength (i.e., 1064 nm) and high reflectivity at the incident pump wavelength (i.e., 808 nm). The addition of a second polymer composite layer loaded with alumina particles enables reduction of the samaria composite layer thickness. The Kubelka-Munk model is shown to successfully predict the experimentally measured optical performance of single and bilayer claddings, making it a reliable design tool for multilayer claddings.

Impact of Shelf life on the Quality of Cocoa Butter Extracted by Screw Press

Aims: To evaluate the changes in the quality of cocoa butter during storage extracted using the developed screw press-type cocoa butter extractor. Study Design: Statistical analysis was done using t-test. Place and Duration of Study: The study was conducted at Processing and Food Engineering lab, Kelappaji College of Agricultural Engineering and Food Technology, Tavanur under ICAR-AICRP on Post-Harvest Engineering and Technology Scheme for 3 months. Methodology: Shelf life study of the cocoa butter extracted at optimized condition (100ºC barrel temperature, 50 rpm screw speed, 2 kg/hr feed rate) was done in polyethylene pouch of 80 micron thickness and stored under ambient temperature (25±5°C) for a period of 3 months. Various quality parameters viz., free fatty acid, iodine number, peroxide number, moisture content and water activity of stored butter were determined at regular intervals of 30 days for 3 months. Results: Statistical analysis (t-test) showed that, there was no significant changes in the quality of cocoa butter during storage. The quality parameters of cocoa butter viz.,free fatty acid (1.28%), iodine number (34.74), peroxide value (1.685), moisture content (0.15%) and water activity (0.645) were within the allowable limits recommended by CODEX standards even after 3 months of storage. Conclusion: During the course of storage, all quality parameters viz., free fatty acid, peroxide value, iodine number, moisture content and water activity were found to be increased. However, all the quality parameters of cocoa butter stored under ambient temperature were within the acceptable limit prescribed by CODEX standards till 90 days with constant quality attributes.

Formation of n-type polycrystalline silicon with controlled doping concentration by flash lamp annealing of catalytic CVD amorphous silicon films

We investigated the properties of polycrystalline silicon (poly-Si) films formed by the flash lamp annealing (FLA) of hydrogenated amorphous Si (a-Si:H) films. Phosphorus- (P-) doped a-Si:H films with a thickness of several micrometers deposited by catalytic chemical vapor deposition (Cat-CVD) on a silicon nitride- (SiN x -) coated textured glass substrate are crystallized by FLA. P doping was achieved by flowing phosphine (PH3) during Cat-CVD, and the P concentration was controlled within a range of 1016–1021 cm−3, which was measured by secondary ion mass spectrometry. We also fabricated simple back-contact Si heterojunction solar cells to estimate a potential of flash-lamp-crystallized poly-Si as an absorption layer. The current-density–voltage (J–V) characteristics of the cells measured under 1 Sun light irradiation show an open-circuit voltage (V OC) of >0.4 V.

Centimeter-scale single-crystal hexagonal boron nitride freestanding thick films as high-performance VUV photodetectors

Large-scale hexagonal boron nitride (h-BN) single crystals are highly desirable not only as the substrate or dielectric for van der Waals heterostructures, but also the promising candidates in optoelectronics, electronics, detectors, as well as recently boomed room-temperature single-photon sources. Here, we report the synthesis of centimeter-scale single-crystal h-BN films with hundreds of micrometer thickness via the metal flux method. The growth control along the out-of-plane and in-plane directions of h-BN crystals is realized by the adjustment of NiCr alloy composition, from which the limited solubility of N atoms can be promoted by high diffusion in molten reactants. This also benefits to forming a distinct interface between the synthesized h-BN crystals and the metal ingot, giving rise to an easy exfoliation of the large area high-quality thick films. Such h-BN crystals have been demonstrated as both self-powered flexible and rigid vacuum-ultraviolet photodetectors, allowing for efficient photodetection in terms of high responsivity, rapid response speed, and high operational temperature. A maximum photoresponsivity of 3.35 mA/W is achieved at a wavelength of 185 nm with an operational temperature spanning to 500 °C (and possibly beyond). The large-area freestanding h-BN single crystal described herein reveals great potential as a high-performance photodetector, and versatile platform for other superb electronic and optoelectronic devices.

Electrically tunable infrared optics enabled by flexible ion-permeable conducting polymer-cellulose paper

Materials that provide dynamically tunable infrared (IR) response are important for many applications, including active camouflage and thermal management. However, current IR-tunable systems often exhibit limitations in mechanical properties or practicality of their tuning modalities, or require complex and costly fabrication methods. An additional challenge relates to providing compatibility between different spectral channels, such as allowing an object to be reversibly concealed in the IR without making it appear in the visible range. Here, we demonstrate that conducting polymer-cellulose papers, fabricated through a simple and cheap approach, can overcome such challenges. The papers exhibit IR properties that can be electrochemically tuned with large modulation (absolute emissivity modulation of 0.4) while maintaining largely constant response in the visible range. Owing to high ionic and electrical conductivity, the tuning of the top surface can be performed electrochemically from the other side of the paper even at tens of micrometer thicknesses, removing the need for overlaying electrode and electrolyte in the optical beam path. These features enabled a series of electrically tunable IR devices, where we focus on demonstrating dynamic radiative coolers, thermal camouflage, anti-counterfeiting tags, and grayscale IR displays. The conducting polymer-cellulose papers are sustainable, cheap, flexible and mechanically robust, providing a versatile materials platform for active and adaptive IR optoelectronic devices.

Effect of Sb2S3 sacrificial layer thickness on structural, optical and electrical properties of CuSbS2 films and investigation of diode parameters of CuSbS2/CdS heterojunctions

The ternary copper chalcogenides CuSbS2 (CAS) is found to have appealing optical and photovoltaic properties to be used as absorber layer in thin film solar cells. However, the difficulty to grow good quality CuSbS2 layer of micrometer thickness by chemical bath deposition method holds a big challenge. In this work, we reported the effect of incorporating Sb2S3 sacrificial layer of different thickness on structural, optical and electrical properties of CAS films. The X-ray diffraction results and Raman spectroscopic analysis confirm the formation of single-phase orthorhombic crystal structure for CuSbS2. The increase of Sb content in CAS films with the increase in deposition time of Sb2S3 layer has been reflected in the change in relative intensity ratio of characteristic Raman peaks as well as in diffraction peak profiles. The magnitude of defect states in terms of Urbach energy is decreased drastically by increasing Sb percentage in the films. A clear improvement in electrical properties of CAS films is observed with the decrease in Cu/Sb ratio. The carrier density is increased by one order of magnitude from 1016 to 1017 cm−3 and hole mobility increases from 1.14 to 4.87 cm2/Vs. The impact of Sb concentration on Scottky diode parameters of CAS/CdS heterojunction was studied by using thermionic emission model. Both the ideality factor and series resistance are decreased with the increase in Sb content. The J-V measurements reveal that the integration of Sb2S3 sacrificial layer improves the PV parameters such as fill factor, open circuit voltage, photocurrent and efficiency. The overall improvement in diode parameters can be ascribed to decrease in defect states, better film quality, absorber layer thickness and improved stoichiometry of CAS films.

High energy density picoliter-scale zinc-air microbatteries for colloidal robotics.

The recent interest in microscopic autonomous systems, including microrobots, colloidal state machines, and smart dust, has created a need for microscale energy storage and harvesting. However, macroscopic materials for energy storage have noted incompatibilities with microfabrication techniques, creating substantial challenges to realizing microscale energy systems. Here, we photolithographically patterned a microscale zinc/platinum/SU-8 system to generate the highest energy density microbattery at the picoliter (10-12 liter) scale. The device scavenges ambient or solution-dissolved oxygen for a zinc oxidation reaction, achieving an energy density ranging from 760 to 1070 watt-hours per liter at scales below 100 micrometers lateral and 2 micrometers thickness in size. The parallel nature of photolithography processes allows 10,000 devices per wafer to be released into solution as colloids with energy stored on board. Within a volume of only 2 picoliters each, these primary microbatteries can deliver open circuit voltages of 1.05 ± 0.12 volts, with total energies ranging from 5.5 ± 0.3 to 7.7 ± 1.0 microjoules and a maximum power near 2.7 nanowatts. We demonstrated that such systems can reliably power a micrometer-sized memristor circuit, providing access to nonvolatile memory. We also cycled power to drive the reversible bending of microscale bimorph actuators at 0.05 hertz for mechanical functions of colloidal robots. Additional capabilities, such as powering two distinct nanosensor types and a clock circuit, were also demonstrated. The high energy density, low volume, and simple configuration promise the mass fabrication and adoption of such picoliter zinc-air batteries for micrometer-scale, colloidal robotics with autonomous functions.

Corrosion Initiation on Reinforcing Steel with Mill Scale in Mortar

Corrosion of reinforcing steel rebar is the main cause of loss of the long-term reliability of concrete structures. When the rebar is corroded, the rust induces cracks and detachment of the cover concrete. The mill scale, a thick oxide film, is formed on the rebars when the rebar is hot rolled. The role of mill scale on the corrosion resistance of rebars in concrete has not been clarified, yet. This study studied the corrosion behavior of rebars with mill scale in mortar.The samples are commercial rebars with 19 mm diameter, which have a mill scale of several tens of micrometers in thickness. The rebars without mill scale prepared by the electrolytic polishing were used as the comparison samples. A Hyperbaric-oxygen accelerated corrosion test (HOACT) [1] was carried out using the rebars embedded in the mortar with a 5.5 mm cover thickness. To prompt the breakdown of passive film on the rebars, 2.1 M NaCl solution was mixed with the mortar. In the HOACT, pressurized oxygen gas is supplied to the sample, and the oxygen reduction reaction on the steel surface is enhanced, leading to the steel's corrosion acceleration. The oxygen pressure was 0.6 MPa and the test period was 14 days. The corrosion of the rebar with a mill scale was more significant than that without a mill scale. This result shows that the mill scale reduces the corrosion resistance of the steel rebar in concrete [2].To investigate the effect of the mill scale on the corrosion resistance of the rebar, anodic polarization measurements of the rebars with and without the mill scale were carried out in a saturated Ca(OH)2 solution containing Cl-. The pitting potential of the rebar with mill scale was more noble than that of the sample without mill scale. However, when the mill scale was scratched, the pitting potential was significantly shifted to the less noble direction, and it was below that of the rebar without the mill scale. These results show that the mill scale improves the corrosion resistance of the rebar in concrete, in contrast, the corrosion resistance of the rebar with a defective mill scale becomes even worse than that of the rebar without the mill scale [2].[1] K. Doi, S. Hiromoto, H. Katayama, E. Akiyama, J. Electrochem. Soc., 165(9), C582-C589 (2018).[2] K. Doi, S. Hiromoto, T. Shinohara, K. Tsuchiya, H. Katayama, E. Akiyama, Corrosion Science, 177, 108995 (2020).

Simulation and measurement of beam-induced heating of ceramic vacuum chambers

In this article, we summarize recent theoretical and experimental studies of the impedance and beam-induced heating of titanium-coated ceramic vacuum chambers used in the NSLS-II injection kickers. The impedance was calculated using the field matching theory assuming planar approximation and compared with the mpedanceake2 code. For the coating thickness of a few microns, we demonstrated that the beam-induced power is dissipated in the titanium coating and that the longitudinally averaged two-dimensional power density is approximated by an analytical expression, thus allowing the use of a simplified model of the power density as input for the code to simulate the temperature distribution with realistic nonuniform thickness of the Ti coating. For a few values of the NSLS-II beam current, we measured the beam-induced heating of two ceramic chambers using thermal sensors installed along the chamber and compared the measurement results with the simulations. Published by the American Physical Society 2024

The use of nonlinear guided-wave features for detection and assessment of intermetallic compounds within dissimilar joints – an experimental investigation

Abstract Welding dissimilar materials is widely employed in industrial construction and manufacturing to enhance cost-effectiveness and performance, often utilizing non-fusion methods like solid-state and high-energy beam welding. However, a significant challenge is the formation of intermetallic compounds (IMCs) at the joint interface, which can weaken the bond and increase brittleness, leading to hidden internal cracks. Nonlinear ultrasound detection methods are employed as advanced, non-destructive testing techniques for early damage inspection in various materials. This research investigates the assessment of the thickness of the intermetallic layer within dissimilar joints using non-linear ultrasound-wave features. Numerical and experimental investigations were performed using four friction stir welding (FSW) lap joints, between AA5052-H32 aluminum and ASTM 516-70 steel, with various intermetallic thicknesses. The methodology involved examining the generation of second-order harmonic frequency by exciting Lamb waves (LW) at specific frequencies. To determine the necessary LWs' excitation frequency, synchronism, and non-zero power flux conditions were employed. The collected signals were measured and analyzed in the time and frequency domains to understand the behavior of the non-linear parameter β′ with the thickness of the intermetallic layer. The results show that β′ changes in a linear manner with the thickness of the intermetallic compound layer (several micrometers in thickness). This provides strong evidence that nonlinear LW features are sensitive to microstructural variations in the FSW joints, which enables them to effectively evaluate their strength.

Self-assembled skin-like metamaterials for dual-band camouflage.

Skin-like soft optical metamaterials with broadband modulation have been long pursued for practical applications, such as cloaking and camouflage. Here, we propose a skin-like metamaterial for dual-band camouflage based on unique Au nanoparticles assembled hollow pillars (NPAHP), which are implemented by the bottom-up template-assisted self-assembly processes. This dual-band camouflage realizes simultaneously high visible absorptivity (~0.947) and low infrared emissivity (~0.074/0.045 for mid-/long-wavelength infrared bands), ideal for visible and infrared dual-band camouflage at night or in outer space. In addition, this self-assembled metamaterial, with a micrometer thickness and periodic through-holes, demonstrates superior skin-like attachability and permeability, allowing close attachment to a wide range of surfaces including the human body. Last but not least, benefiting from the extremely low infrared emissivity, the skin-like metamaterial exhibits excellent high-temperature camouflage performance, with radiation temperature reduction from 678 to 353 kelvin. This work provides a new paradigm for skin-like metamaterials with flexible multiband modulation for multiple application scenarios.