Stratified Microstructure Research Articles

Study on Method of Doping Au Nanoparticles on ZnO Stratified Microstructure to Enhance Photocatalytic Ability and Antibacterial Activity

In this study, stratified microstructure gold/zinc oxide (Au/ZnO) composites were successfully prepared by the method of dispersing Au nanoparticles (Au NPs) on the surface of the hierarchical flower ZnO via HAuCl4 reduction in the presence of different reducing agents such as sodium citrate (SC), sodium borohydride (SB), sodium hydroxide and ethanol (SE), and Hg lamp 250W. Au-doped samples were named Au/ZnO-SC, Au/ZnO-SB, Au/ZnO-SE, and Au/ZnO-Hg lamp, respectively. Au/ZnO-SC and Au/ZnO-SB revealed the uniform distribution of Au nanoparticles on the ZnO substrate, meanwhile, Au nanoparticles were very densely distributed in Au/ZnO-SE and Au/ZnO-Hg lamp samples. The pure ZnO only showed an absorption peak in the ultraviolet (UV) region, Au/ZnO samples indicated additional absorption peaks in the visible light region (500-600 nm), which were characteristic of the surface plasmon resonance (SPR) effect of Au NPs in composites. Therefore, their bandgap energy was reduced compared to ZnO (3.202 eV), leading to increased photocatalytic efficiency under visible light irradiation. Among the doped samples, Au/ZnO-SC (with Au content as 5 wt%) had the largest surface area (26.23 m2/g) and the highest pore volume (0.263 cm3/g) and average pore width (33.2 nm). As a result, it showed the highest catalytic efficiency through complete degradation of tartrazine (TA) within 30 min with a reaction rate of 0.124 min−1 under Hg lamp 250 irradiation. In addition, both pure ZnO and Au/ZnO nanocomposites exhibited high antimicrobial activity in killing Escherichia coli (E. coli), and their enhancing effect of them was reliant on the weight ratio of Au on ZnO and the concentration of tested samples. These results indicated that Au/ZnO material has prominent potential for applications in water environment treatment. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Shearing induced ordered structures in two-dimensional nanomaterials-based electrodes for boosted pseudocapacitive kinetics

Two-dimensional (2D) nanomaterials have been extensively pursued as functional electrodes in electrochemical energy storage devices. Numerous efforts have been devoted to improving the electrochemical performance by engineering the chemical composition and structure of 2D nanomaterials, while little attention was paid to optimizing their electrode manufacturing by wet processing techniques. Herein, we study how the shear processing impacts the electrochemical performance of 2D nanomaterial-based electrodes using graphene oxide/polyaniline (GO/PANI) colloidal hydrogels as a model electrode slurry. The GO/PANI hydrogels are processed into reduced GO/PANI (RGO/PANI) membranes by blade casting followed by chemical reduction. The formation process and microstructure of the RGO/PANI membranes were revealed by rheology and synchrotron small-angle X-ray scattering. We find that a high shear rate in blade casting is favourable for inducing ordered alignment of the 2D nanosheet-like network structure of GO/PANI hydrogels, leading to the formation of stratified microstructure in the RGO/PANI membranes. The high shear-induced ordered structures greatly boost the pseudocapacitive kinetics of RGO/PANI membranes as flexible supercapacitor electrodes. Our findings highlight the significance of electrode processing of 2D nanomaterials for large-scale manufacturing for future industrial applications.

Evidence for metabolic diversity in Meso-Neoproterozoic stromatolites (Vazante Group, Brazil)

Deciphering the evolution of ecological interactions among the metabolic types during the early diversification of life on Earth is crucial for our understanding of the ancient biosphere. The stromatolites from the genus Conophyton cylindricus represent a datum for the Proterozoic (Meso to Neoproterozoic) on Earth. Their typical conical shape has been considered a result of a competition between microorganisms for space, light and nutrients. Well-preserved records of this genus from the “Paleontological Site of Cabeludo”, Vazante Group, São Francisco Craton (Southern Brazil) present in situ fossilized biofilms, containing preserved carbonaceous matter. Petrographic and geochemical analyses revealed an alternation between mineral laminae (light grey laminae) and fossilized biofilms (dark grey laminae). The dark grey laminae comprise three different biofilms recording a stratified microstructure of microbial communities. These three biofilms composing the dark grey laminae tend to be organized in a specific pattern that repeats through the stromatolite vertical section. Iron and manganese are distributed differently along the dark and light grey laminae; X-ray absorption and luminescence data showed possible different areas with authigenic iron and iron provided from diagenetic infiltration. Cryptocrystalline apatite in the lowermost biofilms in each dark grey laminae may suggest past metabolic activity of sulfide-oxidizing bacteria. These findings suggest that the microorganisms reached a complex metabolic diversification in order to maintain an equilibrium situation between the three different biofilms along the vertical section of the structures, thus benefiting the whole microbial community. This means that the stromatolites from the Conophyton genus may have formed as a result of a greater complexity of interactions between microorganisms, and not only from competition between photosynthesizers.

The Study of Graphene Oxide on the Regulations and Controls of the Sol-Gel Film Structure and Its Performance

A facile strategy to boost anticorrosion potency of graphene oxide/silica hybrid sol-gel coating is developed through fully exploiting the capabilities of graphene oxide (GO). Together with a barrier to corrosives and crack inhibitor, GO was further explored herein as a regulator to regulate the gelation process and provide robust coating films with stratified microstructures and ultimately extended diffusion paths. The sol-gel coating with stratified microstructure achieved on AA5052 aluminum alloy surface afforded greatly enhanced corrosion protection capability as assessed by electrochemical measurements and immersion tests. The corrosion current density of the sample of a hybrid GO sol-gel film was about 30 times less than that of sample of pure sol-gel film sample. The regulation mechanism of GO during the film formation process and the anticorrosive protection properties of the film were discussed.

Effects of Substitution of Y with Yb and Ce on the Microstructures and Mechanical Properties of Mg88.5Zn5Y6.5

The microstructures and mechanical properties of the Mg88.5Zn5Y6.5-XREX (RE = Yb and Ce, X = 0, 1.5, 3.0, and 4.5) (wt.%) alloys were investigated in the present study. Mg88.5Zn5Y6.5 is composed of three phases, namely, α-Mg, long-period stacking ordered (LPSO) phases, and intermetallic compounds. The content of the LPSO phases decreased with the addition of Ce and Yb, and no LPSO phases were detected in Mg88.5Zn5Y2.0Yb4.5. The alloys containing the LPSO phases possessed a stratified microstructure and exhibited excellent mechanical properties. Mg88.5Zn5Y5.0Ce1.5 exhibited the highest creep resistance and mechanical strength at both room temperature and 200 °C, owing to its suitable microstructure and high thermal stability. The yield strength of Mg88.5Zn5Y5.0Ce1.5 at room temperature was 358 MPa. The ultimate tensile strength of Mg88.5Zn5Y5.0Ce1.5 at room temperature and 200 °C was 453 MPa and 360 MPa, respectively.

Mechanical Stimulation and Diameter of Fiber Scaffolds Affect the Differentiation of Rabbit Annulus Fibrous Stem Cells.

Degeneration of the annulus fibrosus (AF), an important structure of the intervertebral disc, is one of the main causes of degenerative disc disease. Fabrication of scaffolds replicating the stratified microstructure of the AF is critical for the successful regeneration of AF. In this study, we cultured rabbit AF-derived stem cells (AFSCs) using fabricated electrospun fibrous poly-L-lactic acid scaffolds with different diameters. We applied cyclic tensile strain (CTS) on the scaffolds to regulate the differentiation of AFSCs into specific cell types that resided at the inner, middle, and outer zones of the AF. We found that the morphologies of AFSCs on the smaller-fiber-diameter scaffolds were nearly round, whereas spindle-like cells morphologies were observed on large-diameter scaffolds. CTS enhanced these phenomena and made the cells slender. The expression levels of collagen-I in cells increased as a function of the fiber diameter, whereas collagen-II and aggrecan exhibited opposite trends. Moreover, the application of CTS upregulated the gene expressions of collagen-I, collagen-II, and aggrecan. Overlaying the scaffolds with different CTS-stimulated cells could eventually lead to engineered AF tissues with hierarchical structures that approximated the native AF tissue. Thus, the proposed methodologies could be potentially applied for AF regeneration.

Self-repair by stress-induced diffusion of noble elements during oxidation of Zr48Cu36Al8Ag8 bulk metallic glass

Long-term oxidation behavior of Zr48Cu36Al8Ag8 BMG under atmospheric conditions at 600 K was investigated using in-situ X-ray diffraction analysis. Two oxide zones develop: an outer oxide zone (OOZ), consisting of a stratified distribution of CuOx, Ag, and ZrO2, and an inner oxide zone (IOZ) consisting of tetragonal ZrO2 showing Cu-enriched lines inclined to the surface. The stratified microstructure in the OOZ and the Cu enrichments in the IOZ are ascribed to micro-cracks resulting from the compressive stresses induced by ZrO2 formation. Segregation of noble elements towards these oxidation-generated free surfaces “repairs” the micro-cracks and can consistently explain the microstructural features.

Preparation of Superhydrophobic Film on Ti Substrate and Its Anticorrosion Property.

Superhydrophobic films were fabricated on a titanium substrate with or without anodizing by using a self-assembling method. Firstly, the pretreatments of mechanical polishing/anodizing or mechanical polishing only were conducted, respectively. Subsequently, the preparation of polydopamine film layer, deposition of nano-silver particles, and post modification of 1H,1H,2H,2H-perfluorodecanethiol were performed on the surface of the pretreated substrate. The surface morphologies, compositions, wettability, and corrosion resistance of the films were investigated with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), water contact angle measurements, and electrochemical tests, respectively. Meanwhile, the effect of the deposition time in the silver nitrate solution on the hydrophobicity of the specimen surface was investigated. The result showed that with the increase of deposition time, the hydrophobic property enhanced gradually. The surface deposited for 7 h exhibited an optimum hydrophobic effect, which was characterized with a large water contact angle (WCA) of 154°, and the surface was rather rough and covered by a relatively uniform layer of micro-nano silver particles. The excellent hydrophobicity was attributed to a rough stratified microstructure along with the low surface energy. The electrochemical measurements showed that the existence of the superhydrophobic film can effectively enhance the corrosion resistance of Ti samples.

Diting: A polarized time-of-flight neutron reflectometer at CMRR reactor in China

A new time-of-flight neutron reflectometer with a polarization option is developed and tested at the Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, China. Its scattering geometry is horizontal. The constructed neutron reflectometer is a multipurpose instrument that can be used for the characterization of a stratified microstructure and hidden interfaces of solid thin films. Diting is designed for both magnetic and nonmagnetic multi-layer thin films. Spin polarization and analysis are achieved by transmission magnetized supermirrors. The sample unit is equipped with an electromagnet, which can provide a vertical magnetic field range of 0-1.2 tesla. The available neutron beam is a white beam with wavelength range of 0.15-1.25 nm, which can be cut into different wavelength resolution neutron pulses by a four-disk chopper. A two-dimensional position-sensitive detector is employed to count the specular and off-specular reflected neutron beam. A minimum reflectivity of 10-6 is measured on this instrument.

Study of the response of Zircaloy- 4 cladding to thermal shock during water quenching after double sided steam oxidation at elevated temperatures

This study investigates the failure of embrittled Zircaloy-4 cladding in a simulated loss of coolant accident condition and correlates it with the evolved stratified microstructure. Isothermal steam oxidation of Zircaloy-4 cladding at high temperatures (900–1200 °C) with soaking periods in the range 60–900 s followed by water quenching was carried out. The combined oxide + oxygen stabilized α-Zr layer thickness and the fraction of the load bearing phase (recrystallised α-Zr grains + prior β-Zr or only prior β-Zr) of clad tube specimens were correlated with the %ECR calculated using Baker-Just equation. Average oxygen concentration of the load bearing phase corresponding to different oxidation conditions was calculated from the average microhardness using an empirical correlation. The results of these experiments are presented in this paper. Thermal shock sustainability of the clad was correlated with the %ECR, combined oxide+α-Zr(O) layer thickness, fraction of the load bearing phase and its average oxygen concentration.

Microstructural effects in non linear stratified composites

In this paper, we analyze the microstructural effects on non linear elastic and periodic composites within the framework of asymptotic homogenization. We assume that the constitutive laws of the individual constituents derive from strain potentials. The microstructural effects are incorporated by considering the higher order terms, which come from the asymptotic series expansion. The complete solution at any order requires the resolution of a chain of cell problems in which the source terms depend on the solution at the lower order. The influence of these terms on the macroscopic response of the non linear composite is evaluated in the particular case of a stratified microstructure. The analytic solutions of the cell problems at the first and second order are provided for arbitrary local strain–stress laws which derive from potentials. As classically, the non-linear dependence on the applied macroscopic strain is retrieved for the solution at the first order. It is proved that the second order term in the expansion series also exhibits a non linear dependence with the macroscopic strain but linearly depends on the gradient of macroscopic strain. As a consequence, the macroscopic potential obtained by homogenization is a quadratic function of the macroscopic strain gradient when the expansion series is truncated at the second order. This model generalizes the well known first strain gradient elasticity theory to the case of non linear elastic material. The influence of the non local correctors on the macroscopic potential is investigated in the case of power law elasticity under macroscopic plane strain or antiplane conditions.

Abnormal effect of substrate temperature on perpendicular magnetic anisotropy in sputter-deposited NdFeCo films on silicon substrates

The effect of substrate temperature on the perpendicular magnetic anisotropy (PMA) in sputtered NdFeCo films on Si(111) has been studied. A strong PMA is observed in the NdFeCo films deposited at 310°C, while the room temperature (RT) deposited films show an in-plane dominated anisotropy. The microstructure reveals a stratified microstructure along film thickness due to diffusion occurring at Si(111)/NdFeCo interface of the films deposited at 310°C. Nd2(FeCo)17 nano-crystals and Nd2(FeCo)14Si3 and/or Nd6(FeCo)13Si intermetallic compounds in nano-size appear in the films deposited at 310°C, while the RT deposited NdFeCo films are in amorphous state. Annealing at 300°C results in atomic relaxation and thus ordering of the stripe domains. The distinguishing dependence of the micro/magnetic structure and magnetic characteristics of the NdFeCo films on substrate temperature and annealing temperature is presented. It is concluded that the strong PMA is mainly from the magnetoelastic anisotropy caused by the induced interfacial stress due to the opposite thermal expansion behavior between the NdFeCo layer and Si-doped interfacial layer.

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Mg97Zn1Y1RE1 Alloys

Mg97Zn1Y1RE1 (RE=La, Ce, Nd and Sm, at. %) alloys were prepared by high-frequency induction melting in an Ar atmosphere. Rods were extruded at 623K and a ram speed of 2.5mm·s−1 using a circular die with an extrusion ratio of 10. The microstructure and mechanical properties of the extruded alloys were investigated. The Mg97Zn1Y1Nd1 and Mg97Zn1Y1Sm1 alloys consisted of only two phases: α-Mg and a Mg-RE intermetallic compound. The Mg97Zn1Y1La1 and Mg97Zn1Y1Ce1 alloys consisted of three phases: α-Mg, a Mg-RE intermetallic compound, and a Mg12ZnY phase with a long-period stacking ordered (LPSO) phase. Additionally, after extrusion, the three-phase Mg97Zn1Y1RE1 alloys, i.e., those with an LPSO phase, had a stratified microstructure and exhibited better mechanical properties than those without an LPSO. At room temperature, the yield strength and ultimate tensile strength of the three-phase Mg97Zn1Y1La1 and Mg97Zn1Y1Ce1 alloys were 381–384MPa and 427–429MPa, respectively, and yield strengths greater than 280MPa were observed at the elevated temperature of 523K.

Bandgap enhancement of layered nanocrystalline silicon from excimer laser crystallization

Excimer laser irradiation is used to crystallize hydrogenated amorphous silicon thin films.The resulting films show a stratified microstructure with a crystalline volume fraction ofup to 90%. There is a range of excimer laser energy that can produce stratifiednanocrystalline silicon with a Tauc gap as high as 2.2 eV. This value is greater than thatof amorphous or crystalline silicon and is contrary to that predicted from thetheoretical analysis of mixed-phase silicon thin films. The phenomenon is explainedby employing transmission electron microscopy and spectroscopic ellipsometry,and the observed bandgap enhancement is associated with quantum confinementeffects within the nanocrystalline silicon layers, rather than an impurity variation.

Multiparameter inversion in anisotropic elastic media

Summary In this paper, we formalize the linearized inverse scattering problem for a general anisotropic, elastic medium and describe two approaches to the construction of a stable inversion procedure. The first uses generalized Radon inversion and requires extra information limiting the independent variation of material parameters. The second uses a stationary phase approximation and requires extra information to the effect that the medium is everywhere locally stratified with known dip. The point of common departure is the single-scattering or Born approximation to the scattered field in perfectly elastic media. The formalism is simple to outline: the medium being modelled (or reconstructed) is thought of as a perturbation of a simpler, known, background medium. We are to find the unknown medium perturbation, given the scattered field, which is defined as the difference between the actual (total) field and the background field that would have been present if the actual medium were replaced by the background medium. If the background medium is sufficiently smooth, the background field can be well approximated within the framework of ray theory for elastic waves. If the background medium is sufficiently close to the actual medium, the scattered field can be well approximated by an integral involving the background field and linear in the medium perturbation (the Born approximation). Within this regime we show how to find which combinations of parameters can be determined for a given arrangement of sources and receivers (acquisition geometry). Many expressions simplify when sources and receivers coincide (zero-offset), but then only one parameter may be reconstructed. At several points we use ‘generalized’ linear inversion, implemented through a singular-value decomposition, which enables us to find and rank the best-determined linear combinations of the unknown parameters. Our first method of inversion depends upon the inversion formula for the generalized Radon transform (GRT) to leading order asymptotically for high spatial frequencies. Our second method benefits from the use of further information to the effect that the medium has a locally stratified microstructure within which the medium properties vary rapidly ∈ the direction normal to the local layering, and, assuming that the orientation of the layering can be estimated separately, the scattering problem becomes locally 1-D and the inversion procedure reduces to an amplitude versus (scattering) angle (AVA) analysis.

Waves in elastic and anelastic stratified microstructure: A numerical comparison

Burridge et al. [J. Acoust. Soc. Am. 94, 2884–2894 (1993)] presented a fast algorithm to compute wave propagation through a stack of finely layered elastic or anelastic microstructure. The method goes beyond previous work in two aspects: (a) the sample autocorrelation is used so that the coda of the computed response is preserved; and (b) the anelastic effect due to intrinsic attenuation is incorporated and by order-of-magnitude argument, the terms governing the scattering and anelastic effects enter separately but in a similar way. The present work is a numerical justification of the perturbation theory. Using a standard linear solid model with a single Debye relaxation mechanism, a finely layered microstructure was made anelastic. Using the SH case as an example, impulse responses were computed using two methods: the approximate method and an exact method for both elastic and anelastic media at normal and oblique angles of incidence. The impulse responses obtained by the two methods agree well for both elastic and anelastic cases. The results of the investigation can be summarized in several points: (a) accuracy is best for the head of the pulse; (b) the presence of anelasticity increases the time delay and dispersion of the broad pulse; and (c) the perturbation code is 30–54 times faster than the exact code.

Surface structures and adhesion enhancement of poly(tetrafluoroethylene) films after modification by graft copolymerization with glycidyl methacrylate

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film were carried out via near-UV light-induced graft copolymerization with glycidyl methacrylate (GMA). The structure and chemical composition of the copolymer surface and interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For PTFE substrate with a substantial amount of grafting, the grafted GMA polymer penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains to form a stratified surface microstructure. The concentration of the surface-grafted GMA polymer increases with the plasma pretreatment time, the near-UV light illumination time, and the monomer concentration. The GMA graft copolymerized PTFE surfaces adhere strongly to one another when brought into direct contact and cured (i) in the presence of a diamine alone or (ii) in the presence of an epoxy adhesive (epoxy resin plus diamine curing agent). In the presence of diamine alone, failure occurs in the interfacial region. For epoxy adhesive-promoted adhesion, the failure mode is cohesive, i.e. it takes place in the bulk of one of the delaminated PTFE films. The lap shear strengths in both cases increase with the amount of surface-grafted epoxide polymer. The development of the adhesion strength depends on the concentration of the surface graft, the microstructure of the graft copolymerized PTFE surface, the interfacial reactions, and the nature of the bonding agent.

Surface structures and adhesion characteristics of poly(tetrafluoroethylene) films after modification by graft copolymerization

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film were carried out via near-UV light-induced graft copolymerization with acrylic acid (AAc), Na salt of styrenesulfonic acid (NaSS) and N,N-dimethylacrylamide (DMAA). The structure and chemical composition of each copolymer surface and interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For each PTFE substrate with a substantial amount of grafting, the hydrophilic graft penetrated or became partially submerged beneath a thin surface layer of dense substrate chains to form a stratified microstructure. This surface microstructure was further confirmed by the water contact angle results. In all cases, the concentration of surface grafted polymer increased with the plasma pretreatment time and monomer concentration. Adhesive-free adhesion studies revealed that the AAc graft copolymerized PTFE surface adhered strongly to another similarly modified surface (homo-interface) or to a DMAA graft copolymeri...

Surface structures of fluoropolymer, polyolefin and polyester films after modification by graft polymerization

AbstractPristine and argon plasma pretreated polytetrafluoroethylene (PTFE), polystyrene (PS), high‐density polyethylene (HDPE) and poly(ethylene terrephthalate) (PET) films have been subjected to near‐UV light‐induced graft polymerization with water‐soluble acrylamide (AAm), the sodium salt of styrene sulfonic acid (NaSS), acrylic acid (AAc) and N,N‐dimethylaminoethylmethylacrylate (DMAEMA) monomers. The structure and composition at the substrate surface with grafted polymer were studied by angle‐resolved X‐ray photoelectron spectroscopy (XPS). In most cases, the density of surface grafting is enhanced by plasma pretreatment. For each polymer substrate with a substantial amount of grafting, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This stratified microstructure is consistent with the static secondary ion mass spectroscopy (SIMS) and Ar+beam depth profiling results. The two latter techniques also suggest that when the grafted polymer has a bulky substituent, there is less efficient penetration of the grafted polymer below the surface.

Laser crystallised poly-Si TFTs

Layers of α-Si:H have been crystallised into poly-Si using a pulsed KrF excimer laser. Examination of the these layers by cross-sectional TEM has revealed a vertically stratified microstructure, with a large grain surface region crystallising from the molten phase. TFT behaviour correlated with both the thickness of this large grain region and the duration of the molten phase. With appropriate irradiation conditions, high quality TFTs have been fabricated on glass substrates with on:off current ratios of 10 8 and electron field effect mobilities up to 160cm 2/Vs.