Cross-sectional Scanning Electron Microscopy Research Articles

Optimising Sodium Borohydride Reduction of Platinum onto Nafion-117 in the Electroless Plating of Ionic Polymer–Metal Composites

The effects of process parameters on the electroless plating of ionic polymer–metal composites (IPMCs) were studied in this work. Specifically, the NaBH4 reduction of platinum onto Nafion-117 was characterised. The effects of the concurrent variation of NaBH4 concentration, stir time and temperature on surface resistance were studied through a full factorial design. The three-factor three-level factorial design resulted in 27 runs. Surface resistance was measured using a four-point probe. A regression model with an R2 value of 97.45% was obtained. Surface resistance was found to decrease with increasing stir time (20 to 60 min) and temperature (20 to 60 °C). These responses were attributed to increased platinisation rates, resulting in more uniform electrode deposition, confirmed by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDAX) analysis. Surface resistance decreased, going from 1% to 5% NaBH4 concentration, but increased from 5% to 10% concentration. This behaviour was attributed to surface morphology: increased grain size inducing porous electrodes, in line with findings in the literature. The maximum tip displacement, measured through a computer vision system, as well as the maximum blocking force, measured through an analytical balance setup, were obtained for all 27 samples. The varying results were discussed with regards to surface and cross-sectional SEMs, alongside EDAX analysis.

Optimization of photocurrent and surface wettability of new As10Bi30Se30Te30 thin films through annealing at different temperatures for optoelectronic applications

Group V-VI-based metal-doped double chalcogenides are essential in thermoelectric and suitable optoelectronic devices. The present investigation is based on optimising various optical, structural, and electrical behaviours of quaternary As10Bi30Se30Te30 films through thermal annealing at different temperature scales. The structural study by X-ray diffraction (XRD) exhibited the presence of various Bi2Se3, Bi2SeTe2, and Bi2Te3 phases in the annealed films. The crystallinity gradually enhanced after the annealing process. The microstructural modifications in the material have been confirmed through the Raman spectra. The elemental confirmation was verified from the energy dispersive X-ray (EDX) spectra, whereas the cross-sectional scanning electron microscopy (SEM) view showed the annealing-induced modifications in the films. The granular structure in the films is seen from the surface morphology study. The reduction of the energy gap from 1.36±0.002 eV to 1.26±0.001 eV upon annealing induced the increment in refractive index from 3.08 to 3.15. With annealing, the non-linear refractive index varied from 4.341x10-10 esu to 5.218 x10-10 esu. This indicates the narrowing of the bandgap and enhancement in the non-linear optical response of the material after the annealing process. The 3rd-order nonlinear susceptibility is also increased by annealing, thus making it suitable for nonlinear device applications. Annealing-induced surface change in the material enhances its surface wettability and makes it more hydrophilic. The linear enhancement in photocurrent with the voltage is ohmic and makes it suitable for various optoelectronic applications.

The impact of pulsed Nd:YAG laser on the surface of n-Si and photo-electrical performance of silicon solar cells

Texturizing the surface of a silicon solar cell enhances performance by reducing reflection losses. Pyramidal texturization via wet chemical etching is standard in manufacturing, while plasma etching is often used for vertical hole texturization. Laser texturization offers a chemical-free, user-friendly alternative to plasma etching. Infrared (IR) transmission studies indicate that laser-textured samples transmit more IR light through n-Si than normally textured samples, suggesting that vertical grooves from laser texturization allow deeper light penetration. Analyses using cross-sectional Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersion x-ray (EDX), and Energy Dispersive Spectroscopy (EDS) demonstrate the effects of laser texturization on the front surface of textured n-Si wafers. However, silicon solar cells with laser-textured surfaces demonstrated lower conversion efficiencies (1.20% to 4.30%) compared to conventionally textured cells (14.30%). The short-circuit current density (JSC) was also lower in laser-textured cells, below 17 mA cm−2, compared to 34.44 mA cm−2 in normally textured cells. At the same time, higher laser power (114 W) during texturization also led to the lowest JSC and open-circuit voltage (VOC), indicating that laser texturization may introduce defects and dislocations that degrade Si properties.

Time-dependent 532 nm laser irradiation for tuning in optical, structural, and surface wettability changes of Te/In2Se3 thin films for optoelectronic applications

Laser irradiation for tuning the optoelectronic parameters of semiconducting thin films is widely applicable and has many benefits. The aim of the study is 532 nm laser irradiation of Te/In2Se3 film at different laser exposure time scales. The bilayer structure and its conversion to a single layer with laser annealing were confirmed from cross-sectional scanning electron microscopy. At the same time, the element's appearance was found in the EDX analysis. FESEM probed the corresponding surface structure change. XRD and Raman's spectroscopy analyzed the increase in crystallinity with laser irradiation by mixing Te into the In2Se3 layer and related microstructural changes. The shift in Raman peak with lasing time signifies the effect of time of exposure. There is a systematic decrement in the transmittance of the films. Also, the absorption edge shift resulted in the decrement in bandgap with laser irradiation. The static refractive index and optical density increased as well. The skin depth was decreased with a minimal change in the optical electronegativity. The nonlinear refractive index increased from 1.638 × 10–9 esu to 1.773 × 10–9 esu by 60 min laser irradiation. Similarly, there was an increment in 3rd-order nonlinear susceptibility from 1.58 × 10–10 esu to 1.73 × 10–10 esu. The surface wettability test confirmed the hydrophilic nature of the samples with decreasing hydrophilicity by laser irradiation. The tuning in different properties of the Te/In2Se3 film by laser irradiation is suitable for various optoelectronic applications.

Double layer packaging based on active black chickpea protein isolate electrospun nanofibers and intelligent salep film containing black chickpea peel anthocyanins for seafood products

In this study, a double-layer active and intelligent packaging system was developed based on two main natural macromolecules i.e. protein and carbohydrate with green perspective. Firstly, the salep-based films containing different concentrations (0–8 % w/w) of the inclusion complex of β-cyclodextrin/black chickpea anthocyanins (βCD/BCPA) were produced. The salep film containing 8 % of βCD/BCPA complex was specified as the optimized film sample based on its performance as a color indicator. The electrospinning of black chickpea protein isolate nanofibers (BCPI NFs) containing citral nanoliposomes (NLPs) was done on the optimized salep film. The cross-sectional field emission scanning electron microscopy approved the creation of double-layer structure of the developed film. The study of chemical and crystalline structure, as well as the thermal properties of the film exhibited the physical attachment of BCPI electrospun NFs on salep film. The effectiveness of the developed system was studied in detection of spoilage and increasing the shelf life of seafood products, including shrimp and fish fillet. The performance of the intelligent layer in detection of freshness/spoilage was acceptable for both seafood products. In addition, the active layer of the film controlled the changes of pH, total volatile basic nitrogen, oxidation, and microbial load in samples during storage time.

Thermal cycling characterization of an integrated low-inductance GaN eHEMT power module

To exploit the potential of wide-bandgap semiconductors in high-frequency applications, innovative packaging designs are developed to minimize the parasitic inductance of power modules. This study presents an integrated power module with a hybrid PCB/DBC structure, which uses top-side cooling prepackaged GaN enhancement-mode high-electron-mobility transistors. The module achieves a remarkably low parasitic inductance of 2.65 nH. However, there is relatively scarce research on the reliability of this heterostructure, particularly its sensitivity to thermomechanical stress due to the coefficients of thermal expansion mismatch among material interfaces. In this work, the thermal cycling characteristics of the integrated power module are comprehensively investigated. Electrical and thermal parameters were periodically and separately measured offline on a simplified package to monitor the health conditions and decouple possible synergy and competition effects among the failure modes from all packaging components. A thorough failure analysis was conducted using nondestructive visual inspections and scanning acoustic microscopy, complemented by destructive cross-sectional examination and scanning electron microscopy. The findings identified the delamination of the DBC upper copper layer, which exhibited a conchoidal fracture interface, as the primary factor that contributed to the failure of the power module with increased thermal resistance. Furthermore, the study dissected its initiation and propagation mechanisms. This investigation provides valuable insights for the development of more reliable low-inductance power module designs.

(Invited) Spatially–Resolved Luminescence Properties of Etched Quantum Well Microstructures

Fabrication processes for photonic devices, especially micro- or nano-photonic devices, call for some kind of control of the materials’ optical properties at the stage of the final device. Our study focusses on measuring the optical quality of quantum well (QW) containing materials after device processing, using steps such as etching which allows fabrication of optical waveguides for example. We first designed and realized specific material structures based on an InP substrate, with a series of InAsxP1-x quantum wells such as illustrated on the figure. The samples were grown by gas-phase molecular beam epitaxy. The samples were characterized by spatially-resolved photoluminescence (PL) at low temperature (10 K). The top right part shows a typical spectrum measured from the sample we have grown: sharp lines associated with each QW can be clearly identified thanks to a careful grading of the As/P composition in each QW, while keeping its thickness to a constant value (typically 7 to 8 nm). Then we etched the samples (in the form of rectangular ridges as shown) using different etching processes, based either on wet etching or reactive ion etching (RIE), and recorded the PL spectra with high spatial resolution across the obtained structures. In parallel, the samples after etching were also characterized by cross-sectional scanning electron microscopy. Data processing from the series of PL spectra was then performed in order the characterize the effects of etching on the QW materials.We show PL intensity profiles across a series of etched stripes of different widths resulting from a RIE process. These intensity profiles were obtained from the lines associated with the different QWs in the structure. One can observe, first of all, that the PL intensity gradually increases from the edges to the center of the stripes, over a range of up to 10 µm. One can also observe that for “wide” stripes, i.e. 30 or 50 µm, the PL intensity for each line saturates at the same level in the central part. However, for the narrower stripes (10 or 20 µm), the PL signal does not reach the same level. This is the signature of some PL-limitation phenomenon, which extends its effects far from the etched sidewalls. A “standard” phenomenon resulting solely from non-radiative recombination at the etched sidewalls is excluded. Non-radiative recombination can only affect regions which are less than one charge carrier diffusion length from the sidewalls. Diffusion length in our materials is less than 1 µm. Therefore, some kind of “long range” interaction seems to affect our samples. We propose that this long range interaction is due to some stray static electric field resulting from the presence of residual ions left by the etching process at the sidewalls. The electric field affects the PL intensity through dissociation of excitons. Moreover, we observed that different conditions for the etching process (wet etching versus RIE, crystallographic orientation of the stripes) impact the magnitude of this PL intensity quenching.[1] Pearton S 1997 Materials Science and Engineering: B 44 1–7[2] Landesman J P, Isik-Goktas N, LaPierre R R, Levallois C, Ghanad-Tavakoli S, Pargon E, Petit-Etienne C and Jiménez J 2021 Journal of Physics D: Applied Physics 54 445106[3] Fiore A, Rossetti M, Alloing B, Paranthoen C, Chen J X, Geelhaar L and Riechert H 2004 Physical Review B 70 205311[4] Bludau W and Wagner E 1976 Physical Review B 13 5410–5414 Figure 1

The role of thickness on the structural and luminescence properties of Y2O3:Ho3+, Yb3+ upconversion films

The structural, surface, and upconversion (UC) luminescence properties of Y2O3:Ho3+,Yb3+ films grown by pulsed laser deposition, for different numbers of laser pulses, were studied. The crystallinity, surface, and UC luminescence properties of the thin films were found to be highly dependent on the number of laser pulses. The X-ray powder diffraction analysis revealed that Y2O3:Ho3+,Yb3+ films were formed in a cubic structure phase with an Ia 3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{3 }$$\\end{document} space group. The thicknesses of the films were estimated by using cross-sectional scanning electron microscopy, depth profiles using X-ray photoelectron spectroscopy (XPS), and the Swanepoel method. The high-resolution XPS was used to determine the chemical composition and oxidation states of the prepared films. The UC emissions were observed at 538, 550, 666, and 756 nm, assigned to the 5F4 → 5I8, 5S2 → 5I8, 5F5 → 5I8, and 5S2 → 5I7 transitions of the Ho3+ ions. The power dependence measurements confirmed the involvement of a two-photon process in the UC process. The color purity estimated from the Commission International de I’Eclairage coordinates confirmed strong green UC emission. The results suggested that the Y2O3:Ho3+,Yb3+ UC transparent films are good candidates for various applications, including solar cell applications.

Polymer-Supported Graphene Sheet as a Vertically Conductive Anode of Lithium-Ion Battery.

The increasing demand for electric vehicles necessitates the development of cost-effective, mass-producible, long-lasting, and highly conductive batteries. Making this kind of battery is exceedingly tricky. This study introduces an innovative fabrication technique utilizing a laser-induced graphene (LIG) approach on commercial Kapton film to create hexagonal pores. These pores form vertical conduction paths for electron and ion transportation during lithiation and delithiation, significantly enhancing conductivity. The nongraphitized portion of the Kapton film makes it a binder-less, free-standing electrode, providing mechanical stability. Various analytical techniques, including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, and atomic force microscopy (AFM) are utilized to confirm the transformation of a 3D porous graphene sheet from a commercial Kapton film. Cross-sectional SEM images verify the vertical connections. The specific capacity of 581 mAh g-1 is maintained until the end, with 99% coulombic efficiency at 0.1C. This simple manufacturing method paves the pathway for future LIG-based, cost-effective, lightweight, mass-producible, long-lasting, vertically conductive electrodes for lithium-ion batteries.

Nanomechanical and microstructural properties of experimental bilayered zirconia ceramics after hydrothermal aging

Two experimental ceramic systems, 3Y-TZP/5Y-PSZ (3Y/5Y) and 4Y-PSZ/5Y-PSZ (4Y/5Y), underwent analysis before (3Y/5Yi or 4Y/5Yi) and after hydrothermal aging (3Y/5Ya or 4Y/5Ya) to simulate low-temperature degradation (LTD). The samples were sintered and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy, alongside nanoindentation tests to measure elastic modulus (Em) and hardness (H). Assessments were conducted on the external surfaces and at individual layers on cross-sectioned samples at predetermined regions of interest (ROIs). Degraded superficial regions were observed in the cross-sectional SEM images of the 3Y and 4Y zirconia layers after aging. XRD indicated a tetragonal→monoclinic phase transformation in the aged groups for both 3Y (66 % m-ZrO2) and 4Y (29 % m-ZrO2). Raman spectroscopy revealed monoclinic phase amounts of 86 % for 3Y and 62 % for 4Y in the degradation regions observed in the SEM micrographs. Monoclinic phase peaks were virtually no longer detected in either material beyond a depth of 15 μm. Hydrothermal aging significantly diminished the H and Em values for the 3Y and 4Y zirconia surfaces. For the analysis of different zirconia surfaces within the same subgroup, all pairwise comparisons showed statistically significant differences, except for the values of H of 3Y/5Yi and Em for 4Y/5Yi. Regarding the nanoindentation results of cross-sectioned samples, the aging protocol did not affect the H and Em values of the equivalent ROIs (layers), regardless of the bilayered system. However, significant differences in H values were observed among the ROIs (layers) within the same bilayered system. Despite surface changes, nanomechanical properties remained preserved below the surface and at the interfaces of bilayered materials after aging. Nanoscale H values varied among some layers and interfaces, whereas the Em values exhibited differences across certain surfaces.

Multiscale phonon thermal transport in nano-porous silicon

We performed a comprehensive multi-scale phonon-mediated thermal transport study of nano-porous silicon (np-Si) films with average porosities in the range of φ = 30%–70%. This depth-resolved thermal characterization involves a combination of optical methods, including femtosecond laser-based time-domain thermo-reflectance (TDTR) with MHz modulation rates, opto-thermal micro-Raman spectroscopy, and continuum laser wave-based frequency domain thermo-reflectance (FDTR) with kHz modulation rates probing depths of studied samples over 0.5–1.2, 2–3.2, and 23–34 μm, respectively. We revealed a systematic decrease in thermal conductivity (k) with the rise of φ, i.e., with the lowering of the Si crystalline phase volumetric fraction. These data were used to validate our semi-classical phonon Monte Carlo and finite element mesh simulations of heat conduction, taking into account disordered geometry configurations with various φ and pore size, as well as laser-induced temperature distributions, respectively. At high φ, the decrease in k is additionally influenced by the disordering of the crystal structure, as evidenced by the near-surface sensitive TDTR and Rutherford backscattering spectroscopy measurements. Importantly, the k values measured by FDTR over larger depths inside np-Si were found to be anisotropic and lower than those detected by the near-surface sensitive TDTR and Raman thermal probes. This finding is supported by the cross-sectional scanning electron microscopy image indicating enhanced φ distribution over these micrometer-scale probed depths. Our study opens an avenue for nano-to-micrometer scale thermal depth profiling of porous semiconducting media with inhomogeneous porosity distributions applicable for efficient thermoelectric and thermal management.

Thickness Variation of Conductive Polymer Coatings on Si Anodes for the Improved Cycling Stability in Full Pouch Cells.

Si-dominant anodes for Li-ion batteries provide very high gravimetric and volumetric capacity but suffer from low cycling stability due to an unstable solid electrolyte interphase (SEI). In this work, we improved the cycling performance of Si/NCM pouch cells by coating the Si anodes with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) prior to cell assembly via an electropolymerization process. The thicknesses of the PEDOT coatings could be adjusted by a facile process parameter variation. Glow-discharge optical emission spectroscopy was used to determine the coating thicknesses on the electrodes prior to the cell assembly. During electrochemical testing, improvements were observed closely linked to the PEDOT coating thickness. Specifically, thinner PEDOT coatings exhibited a higher capacity retention and lower internal resistance in the corresponding pouch cells. For the thinnest coatings, the cell lifetime was 18% higher compared to that of uncoated Si anodes. Postmortem analyses via X-ray photoelectron spectroscopy and cross-sectional scanning electron microscopy revealed a better-maintained microstructure and a chemically different SEI for the PEDOT-coated anodes.

Exploring microstructural evolution, nitrogen depth profile, and dry wear performance in 31CrMoV9 steel through combined severe shot peening and plasma nitriding

The present study investigates the influence of severe shot peening (SSP) on the plasma nitriding behavior and sliding wear performance of 31CrMoV9 steel. Initially, the steel was austenitized at 880 °C, followed by oil quenching, and tempering at 520 °C for one hour. These samples were shot peened using high-carbon steel shots, resulting in an enhancement in surface hardness up to 447 HV, gradually converging to the initial martensitic hardness after 140 µm depth. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) scrutinized the initial and surface treated martensitic samples. Afterward, the plasma nitriding treatments were carried out at temperatures of 400 °C, 450 °C, and 500 °C for 8 hours in a 30% N2 + 70% H2 atmosphere and 300 Pa pressure. Microhardness testing, SEM, XRD, and glow-discharge optical emission spectroscopy (GDOES) evaluated both plasma nitrided (PN) and severe shot peened/plasma nitrided (SSP-PN) samples. Cross-sectional SEM observations revealed compound layer thicknesses of approximately 2.8 µm, 5.0 µm, and 6.3 µm for PN samples at 400 °C, 450 °C, and 500 °C, respectively. SSP-PN samples exhibited a substantial increase — roughly 71%, 44%, and 33% increase, respectively, compared to PN samples. GDOES analysis supported this trend and indicated enhanced nitrogen diffusion depth, particularly evident in SSP-PN samples at consistent temperatures. The XRD results showed the stability of Fe4N, Fe2–3N, and CrN phases at all three nitriding temperatures. Furthermore, the intensity of these phases increases with temperature and is augmented by the application of the SSP. Microhardness measurements indicated hardness escalation: from 775 HV to 980 HV at 400 °C, 932 HV to 1096 HV at 450 °C, and 1011 HV to 1205 HV at 500 °C due to SSP. Finally, the wear performance was investigated between the non-nitrided, SSP, PN, SSP-PN, samples. Initially, SSP led to decreased wear performance up to 500 m, followed by improved behavior up to 1500 m. At 400 °C, the SSP-PN sample exhibited a 12% lower wear rate than PN. At 450 °C and 1500 m, the SSP-PN sample displayed a 24% reduction, while at 500 °C, it showed a 27% reduction compared to PN. SEM observations indicated abrasion as the primary wear mechanism across all samples. The overall results indicated a significant similarity in the nitrogen depth profile, hardness depth, and wear performance between the SSP-PN sample at 450 °C and the PN sample at 500 °C. The fact suggested a potential reduction of approximately 50 °C in the typical plasma nitriding temperature for 31CrMoV9 steel as a result of the SSP process.

Property Variations in Modern REBCO Coated Conductors from Multiple Manufacturers

The complex, multilayer structure of REBCO Coated Conductor (CC) poses significant challenges in the fabrication of high magnetic field devices where large stresses may initiate various forms of damage. Our goal is to peer below the cartoon representations of CC so that, amongst other things, we might better understand whether a CC from one manufacturer is interchangeable with that from another. This involves knowledge of a broad range of electromagnetic, geometric, microstructural, and Jc (θ,B,T) properties, and their variations that collectively pose challenges for the fault tolerance of REBCO CC devices. Accordingly, comparative measurements of Jc , visualization of flux penetration with Magneto-Optical Imaging (MOI), tape geometry from Scanning Electron Microscopy (SEM) of polished cross-sections, and extensive optical microscopy was performed on recently purchased samples from multiple manufacturers. Our analyses reveal many deviations from or characteristics absent from manufacturers’ specifications, while a comparison of different manufacturers’ mechanically and laser slit tapes shows a diverse array of slitting characteristics amongst the manufacturers and variation in properties those made to the same specification. Laser slit tapes from several manufacturers reveal ablated edges with damaged regions extending up to 50 μm, comparable to the damaged region found in the mechanically slit CC of this study. Overall, the aim of this study is to flesh out appropriate ways to understand the real conductor below the manufacturers’ cartoons to avoid surprises in our REBCO CC coil development program. The goal of this work was to perform a broad array of characterizations of the type needed for validation of purpose for making high field magnets: to our surprise we found a wide range of properties which greatly impact the mechanical strength and electromagnetic performance of solenoids composed of these conductors and reinforced the need for a broad characterization program for each conductor prior to its implementation.

Optical response and temperature shielding coatings using tri-layer structure composed of titania/silica/titania

The fabrication of metamaterials with inspiration from nature paved the door for the creation of revolutionary passive and active devices. Butterfly wings are one of them, and their multilayered structure motivated nanotechnologists, physicists, and other optoelectronic and photonic engineers to develop photonic crystals, dielectric reflectors, and Bragg reflectors for use in visible light communication, solar cells, and other photonic and optoelectronic applications. We report the sol–gel spin coating of a dielectric reflector on the glass substrate, an optical passive component consisting of titania and silica thin films for infrared radiation reflection. Individual thin films of titania and silica on glass substrates were studied using an x-ray diffractometer, which indicated anatase of titania and the amorphous nature of silica at a Bragg angle of 25° with a sharp and wide peak, respectively. The multilayer structure of titania/silica/titania was further investigated using Fourier transform infrared spectroscopy, which revealed the presence of Ti–O–Ti and Si–O–Si vibrational bonds at wavenumbers 546 and 973 cm−1, respectively, as well as the presence of Ti–O–Si vibrational bond at 1100 cm−1. The thickness of the multilayer titania/silica/titania was measured using a cross-sectional field emission scanning electron microscope (FESEM) and found to be 160/240/160 nm, respectively. Finally, reflection investigation on the multilayer structure using ultraviolet–visible–near-infrared spectroscopy validated the reflection of the infrared spectrum area by around 70% and showed to be beneficial for temperature shielding applications on glass furnishings.

Improved uniformity of atomic-layer-deposited HfO2 film along the length of glass monocapillary with high length-diameter ratio

It has been a difficult to deposit a uniform film on the inner surface of monocapillary due to the high length-diameter ratio. Atomic layer deposition (ALD) shows great potential to coat conformal film on complex substrates. However, it is still a challenge to coat uniform film along the length of the capillary for regular deposition parameters. In this work, HfO2 film was deposited inside monocapillary via ALD. The film uniformity along the monocapillary was investigated by cross-section scanning electron microscope (SEM) images and the bond states of one of the HfO2 films were studied via X-ray photoelectron spectroscopy (XPS). Using the routine deposition parameters, the gas flowing through the monocapillary is controlled to be small, large and medium qualitatively by covering some of the inlets or outlets, changing the connection between monocapillary and outlets simply. SEM results demonstrate that smooth HfO2 film with uniform thickness can be acquired on the inner surface of monocapillary with length-diameter ratio 200 (length 10 cm and inner diameter 0.5 mm). XPS results show that Hf hydroxide is generated when the gas flowing through the monocapillary is large.

Bipolar pulse anodizing of aluminum: Understanding the fundamental electrochemical mechanisms

Anodic aluminum oxides (AAO) with attractive morphological properties might be obtained by pulse anodizing via controlled hydrogen release during the cathodic step. In order to enhance such processes currently relying on empirical studies, the present paper aims to investigate basically the AAO formation on pure aluminum in sulfuric acid during a bipolar pulse anodizing process, by combining in situ electrochemical measurements and cross-section scanning electron microscopy. Results show that the hydrogen evolution at the metal/oxide interface during the cathodic step can be easily managed by current control. Actually, under cathodic galvanostatic conditions, successive mechanisms occur, depending on both the duration and the current density: a first stage corresponds to the reorganization of the electric charges and the migration of H+ through the AAO barrier layer and is followed by hydrogen evolution at the metal/oxide interface, which induces the formation of local or more extended defects at the metal/oxide interface until the detachment of the AAO layer.

Multi-layer shearing induced high orientation of graphene oxide sheets towards high-performance macrostructures

The orientation of graphene nanosheets in microstructures is directly related to the mechanical properties and thermal conductivity of graphene-based macrostructures. However, efficient and scalable modulation of the orientation of 2D graphene nanosheets remains challenging. Herein, a simple and effective approach was proposed by introducing a multi-layer shearing field in thick graphene oxide (GO) gel coatings to improve the total orientation of GO films. Hydrodynamic simulations were performed via the lattice-Boltzmann method to reveal the microscale mechanism of the flow profile in improving the orientation of GO nanosheets. The result was experimentally verified by fast Fourier transform (FFT) of the cross-section scanning electron microscope (SEM) images of freeze-dried GO films and wide-angle X-ray scattering (WAXS) patterns of 16 various samples under different shearing line distances, velocities, and GO concentrations. The obtained GO films exhibit high orientation (Herman's orientation factor ƒ = 0.922), high strength (419.2 MPa), and high modulus (26.2 GPa), respectively, which are 1.06, 5.57, and 3.49 times higher compared to GO films prepared through the frequently used doctor blade method. The good orientation of GO is remained and further improved to the ultra-high orientation (ƒ = 0.968) after being graphitized at 3150 °C and roll pressing, and the oriented thick graphene films achieved the highest thermal conductivity (1629 W m−1 K−1 for 86 μm and 1593 W m−1 K−1 for 110 μm) compared to other graphene films mentioned in the literature as having a similar thickness. The multi-layered shearing strategy represents a facile technology for assembling two-dimensional (2D) nanoscale building blocks into a macroscopic structure with good orientation and high performance.

Pressure Indicator Composite Films via Compressive Deformation of a Translucent Matrix Containing a Contrasting Filler.

A neglected mechanism for pressure-responsive color change is demonstrated using cellulose acetate composites prepared by direct (solvent) immersion annealing (DIA), with different loadings of activated charcoal filler. Namely, compressive plastic deformation of the translucent cellulose acetate leads to a decrease in the optical path length and a concomitant increase in the visibility of the opaque contrasting filler. Composites bearing 1-7 wt% activated charcoal exhibited a linear relationship between applied pressure and resulting pressure mark brightness in the range of 12-56 MPa. Comparison of pressure mark patterns with cross-sectional scanning electron microscopy (SEM) supports the importance of the porous morphology arising from DIA for the tuning of the pressure indicator sensitivity. A simple ball drop test is used to illustrate the robustness and utility of these indicators in optical impact assessment.

One-step sputtering of MoSSe metastable phase as thin film and predicted thermodynamic stability by computational methods

We present the fabrication of a MoS2−xSex thin film from a co-sputtering process using MoS2 and MoSe2 commercial targets with 99.9% purity. The sputtering of the MoS2 and MoSe2 was carried out using a straight and low-cost magnetron radio frequency sputtering recipe to achieve a MoS2−xSex phase with x = 1 and sharp interface formation as confirmed by Raman spectroscopy, time-of-flight secondary ion mass spectroscopy, and cross-sectional scanning electron microscopy. The sulfur and selenium atoms prefer to distribute randomly at the octahedral geometry of molybdenum inside the MoS2−xSex thin film, indicated by a blue shift in the A1g and E1g vibrational modes at 355 cm−1 and 255 cm−1, respectively. This work is complemented by computing the thermodynamic stability of a MoS2−xSex phase whereby density functional theory up to a maximum selenium concentration of 33.33 at.% in both a Janus-like and random distribution. Although the Janus-like and the random structures are in the same metastable state, the Janus-like structure is hindered by an energy barrier below selenium concentrations of 8 at.%. This research highlights the potential of transition metal dichalcogenides in mixed phases and the need for further exploration employing low-energy, large-scale methods to improve the materials’ fabrication and target latent applications of such structures.