Oxide Multilayer Films Research Articles

High temperature oxidation behavior of Ni-based superalloy Nimonic95 and the effect of pre-oxidation treatment

The high-temperature oxidation behaviors of Nimonic95 alloy at 800 °C, 900 °C and 1000 °C were studied. The diffusion process of alloying elements in different stages of oxidation was studied and analyzed, and the pre-oxidation process was established. The results showed that multilayer oxide films formed in the air at 800 °C, 900 °C and 1000 °C, the outer layer was mainly Cr2O3 with a small amount of Al2O3, TiO2 and composite oxides such as CrTi spinel. The inner layer was mainly Al2O3. Nimonic95 alloy has excellent oxidation resistance at 800 °C and 900 °C, but poor oxidation resistance at 1000 °C and the oxide film peeled off in a short time. The oxidation resistance of Nimonic95 alloy at 1000 °C can be improved significantly by pre-oxidation at 800 °C for 140 h.

Density‐modulated multilayered homo‐junction tungsten oxide anode materials for high‐capacity Li‐ion batteries with long‐term stability

We report an effective strategy generally applicable towards improving Li-ion battery performance with insulating metal oxide-based anode materials. We fabricated density-modulated multilayered homo-junction tungsten oxide (WOx) films as anode materials for Li-ion batteries, in which high- and low-density thin layers were alternately deposited on Cu current collectors using radio frequency magnetron sputtering. The performance of the battery with multilayered WOx was systematically optimized by changing the number of layers and deposition order. A 4-layer density-modulated WOx anode with a low density on top WOx layer showed superior performance with a high reversible capacity of 508 mAh g−1 after 200 cycles at a current density of 0.2 A g−1. Moreover, it provided a reversible capacity of 150 mAh g−1 and good coulombic efficiency of 93.7% after 1000 cycles at a high current density of 2 A g−1 and showed excellent rate capability and cycling stability. The observed outstanding battery performance of the density-modulated multilayer WOx anode can be attributed to its controlled mass loading, optimized charge-transfer kinetics, and favourable morphology.

Intercalation of Dyes in Graphene Oxide Thin Films and Membranes.

Intercalation of dyes into thin multilayered graphene oxide (GO) films was studied by neutron reflectivity and X-ray diffraction. Methylene blue (MB) penetrates the interlayer space of GO in ethanol solution and remains intercalated after the solvent evaporation, as revealed by the expansion of the interlayer lattice and change in chemical composition. The sorption of MB by thin GO films is found to be significantly stronger compared to the sorption of Crystal violet (CV) and Rose bengal (RB). This effect is attributed to the difference in the geometrical shape of planar MB and essentially nonflat CV and RB molecules. Graphite oxides and restacked GO films are found to exhibit different methylene blue (MB) sorptions. MB sorption by precursor graphite oxide and thin spin-coated films of GO is significantly stronger compared to freestanding micrometer-thick membranes prepared by vacuum filtration. Nevertheless, the sorption capacity of GO membranes is sufficient to remove a significant part of the MB from diluted solutions tested for permeation in several earlier studies. High sorption capacity results in strong modification of the GO structure, which is likely to affect permeation properties of GO membranes. Therefore, MB is not suitable for testing size exclusion effects in the permeation of GO membranes. It is not only hydration or solvation diameter but also the exact geometrical shape of molecules that needs to be taken into account considering size effects for penetration of molecules between GO layers in membrane applications.

Controlling pore structure and conductivity in graphene nanosheet films through partial thermal exfoliation

Thermal exfoliation is an efficient and scalable method for the production of graphene nanosheets or nanoplatelets, which are typically re-assembled or blended to form new macroscopic “graphene-based materials”. Thermal exfoliation can be applied to these macroscopic graphene-based materials after casting to create internal porosity, but this process variant has not been widely studied, and can easily lead to destruction of the physical form of the original cast body. Here we explore how the partial thermal exfoliation of graphene oxide (GO) multilayer nanosheet films can be used to control pore structure and electrical conductivity of planar, textured, and confined GO films. The GO films are shown to exfoliate explosively when the instrument-set heating rates are 100 K/min and above leading to complete destruction of the film geometry. Textured films with engineered micro-wrinkling and crumpling show similar thermal behavior to planar films. Here, we also demonstrate a novel method to produce fairly large size intact rGO films of high electrical conductivity and microporosity based on confinement. Sandwiching GO precursor films between inert plates during partial exfoliation at 250 °C produces high conductivity and porosity material in the form of a flexible film that preserves the macroscopic structure of the original cast body.

Element redistributions during early stages of oxidation in a Ni38Cr22Fe20Mn10Co10 multi-principal element alloy

Element redistributions after initial oxidation of a Ni38Cr22Fe20Mn10Co10 (at.%) multi-principle element alloy at 120 °C and 300 °C is captured via in situ atom probe tomography. All cations contribute to the oxide in both conditions, consisting of a Cr-rich inner oxide and a Fe, Mn, Co and Ni-rich outer oxide. At lower temperature, Ni tends to be trapped at the outer/inner oxide interface, while Ni enriches at the oxide/metal interface at higher temperature in tandem with Cr metal depletion. These observations confirm oxidation of complex alloys involves the formation of metastable, multi-layered oxide films, with a distinct tendency for solute trapping.

Rapid assessment of structural and compositional changes during early stages of zirconium alloy oxidation

A multimodal chemical imaging approach has been developed and applied to detail the dynamic, atomic-scale changes associated with oxidation of a zirconium alloy (Zircaloy-4). Scanning transmission electron microscopy, a gas-phase reactor chamber attached to an atom probe tomography instrument, and synchrotron-based X-ray absorption near-edge spectroscopy were employed to reveal morphology, composition, crystal, and electronic structure changes that occur during initial stages of oxidation at 300 °C. Oxidation was carried out in 10 mbar O2 gas for short exposure times of 1 and 5 min. A multilayered oxide film with a cubic ZrO adjacent to the oxide/metal interface, a nanoscopic transition region with a graded composition of ZrO2−x (where 0 < x < 1), and tetragonal ZrO2 in the outermost oxide were formed. Partitioning of the major alloying element (tin) to the oxide/metal interface and heterogeneously within the oxide accompanied the development of the layered oxide. Our work provides a rapid, high-throughput approach for detailed characterisation of initial stages of zirconium alloy oxidation at an accelerated time scale, with implications for several other alloy systems.

Effect of solution aging on properties of spin coated zinc oxide thin films

A series of multilayer zinc oxide (ZnO) films were deposited on glass substrate by solution processed spin coating method. The effect of aging time of ZnO sol on the structural and optical properties of the films was studied. The structural characteristics of the samples were analyzed by an X-ray diffractometer (XRD) and Scanning electron microscopy (SEM). The optical properties were studied by a UV–Vis spectrophotometer and a fluorescence spectrometer. The obtained ZnO thin films show very good transmittance with average transmittance of 85% with no fluctuations in the 300–600 nm range of visible spectrum. The band gap increases with the increase in the sol aging time. The enhanced crystalline quality of films and decrease of defects concentration contributed to improve the ultraviolet emission and weaken the visible emissions with prolonging sol aging time.

Deposition of Multilayer Films of ZnO by Sol-gel Process on Stainless Steel Substrates for Energy Harvesting Devices

The mechanical vibrations surrounding the environment can be converted in electrical energy by piezoelectric energy harvesters (PEH). The increase on the availability of Wireless Sensor Networks (WSN) increases the need for power supply that replaces ordinary batteries. In this paper, an electromechanical modelling and a deposition of multilayer zinc oxide (ZnO) films for an PEH are presented. The aim of the study is to obtain the thickness of the multilayer ZnO films in different conditions, in order to improve the energy harvesting capacity for a PEH device. The ZnO synthesis was performed by the sol-gel method with dehydrated zinc acetate as a precursor, making deposits of 5, 10 and 15 layers. The depositions were made at room temperature by spin coating at 1440 revolutions per minute for 16 s. An UV-Vis test showed that ZnO were present, with a percentage of peak reflectance at 370 nm and a XRD test showed a preferential crystalline orientation at (002). Also, a Finite Element Modelling (FEM) simulation of the substrate behaviour was performed, functioning as a cantilever beam. When adding a seismic mass and oscillating in the resonance frequency of 103.31 Hz and with 15 layers of ZnO deposited, 2.67 volts were obtained.

Achieving Ohmic conduction behavior at high electric field via interface manipulation

Interface in complex oxide heterostructures provides a new platform for uncovering emergent physical phenomena and engineering novel functionalities. Compared to the control of lateral interface in bilayer or multilayer complex oxide films, the investigation on manipulating the vertical interface in vertically aligned nanocomposite films is rarely studied so far. Here, the vertical interface effect on the leakage behavior of vertically aligned nanocomposite BaTiO3:Sm2O3 films grown on (1 1 1) Nb-SrTiO3 (Nb-STO) substrates is reported. We found that the vertical interface without visible misfit dislocations is formed between BaTiO3 and Sm2O3. Consequently, the leakage mechanism is determined to be Ohmic conduction up to an electric field of 1000 kV/cm. Also, the leakage current is reduced to be around 3 × 10−7 A/cm2, which is almost two and three orders of magnitude lower than that of BaTiO3:Sm2O3/(0 0 1) Nb-STO and pure BaTiO3/(1 1 1) Nb-STO films, respectively. This work demonstrates the ability to realize Ohmic conductive mechanism at high electric field and further provides a new pathway to reduce leakage current and improve ferroelectric polarization of ferroelectric oxide films by manipulating the vertical interface, which opens the door to the design of advanced nanostructures with the emergent functionalities.

Fabrication of a plasma electrolytic oxidation/anodic aluminum oxide multi-layer film via one-step anodizing aluminum in ammonium carbonate

A plasma electrolytic oxidation (PEO)/anodic aluminum oxide (AAO) multi-layer film was fabricated via one-step galvanostatic anodizing of high-purity aluminum in 0.3–2.0 M ammonium carbonate ((NH4)2CO3) solutions at 283–333 K and 25–400 Am−2. Anodizing at higher concentrations and higher temperatures caused the formation of relatively uniform anodic oxide film on the aluminum substrate. Characteristic voltage-time curves with two high-plateau voltages at approximately 250 V and 375 V were obtained during galvanostatic anodizing. A multi-layer structure of an outer PEO layer with a crystalline γ-Al2O3 structure and an inner amorphous AAO layer with nano-cylinerical pores was formed by continuous visible sparking occurring after passing the first voltage plateau region. The whole aluminum surface was covered with the multi-layer structure after reaching the second voltage region. The thickness of the multi-layer increased with time via the further anodizing process at the second plateau voltage. Pore sealing of the inner nanoporous film was achieved by immersion post-treatment in boiling water.

Element Redistribution During Early Stages of Oxidation in a Ni &lt;sub&gt;38&lt;/sub&gt;Cr &lt;sub&gt;22&lt;/sub&gt;Fe &lt;sub&gt;20&lt;/sub&gt;Mn &lt;sub&gt;10&lt;/sub&gt;Co &lt;sub&gt;10&lt;/sub&gt; Multi-Principal Element Alloy

Element redistributions after initial oxidation of a Ni38Cr22Fe20Mn10Co10 (at. %) multi-principle element alloy at 120 °C and 300 °C is captured via in situ atom probe tomography. All cations contribute to the oxide in both conditions, consisting of Cr-rich inner oxide and Fe, Mn, Co and Ni-rich outer oxide. At lower temperature, Ni tends to be trapped at the outer/inner oxide interface, while Ni enriches at the oxide/metal interface at higher temperature in tandem with Cr metal depletion. These observations confirm oxidation of complex alloys involves the formation of metastable, multi-layered oxide films, with a distinct tendency for solute trapping.

Electromagnetic loss mechanisms in antimony doped tin oxide and reduced graphene oxide multilayer films

In this paper, the antimony doped tin oxide (ATO) and reduced graphene oxide (rGO) were prepared by coprecipitation method and modified Hummers’ method, respectively. Both were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vector network analyzer (VNA). The as-prepared rGO showed typical sheets-like structure and the as-prepared ATO showed typical nano-particle shape. Then, the ATO and rGO multilayer films were designed and the microwave absorption performances were numerically evaluated using finite element methods. The results showed that synergetic effects of interfacial polarization resonance and 1/4λ elimination were stimulated in 10-layerd 1.8 mm multilayer films to give a minimal reflection loss of −45.2 dB @ 16.1 GHz, and −10 dB bandwidth of 5.4 GHz, which was enhanced more than −30 dB in ATO or rGO monophase absorbers with the same thickness. This work provides a novel technical route to realize high-performance microwave absorbers in terms of simultaneously stronger absorption, broader absorption bandwidth and smaller thickness to facilitate higher flexibility and stability for practical applications.

Surface characterization, biocompatibility and osteogenic differentiation of drop-casted multilayer graphene oxide film towards human wharton’s jelly derived mesenchymal stem cells

ABSTRACTGraphene oxide (GO) materials have been extensively employed in mesenchymal stem cell (MSCs) research due to its unique nanotopography. Herein, various concentrations of GO flakes were used to fabricate different thickness of multilayer graphene oxide (m-GO) films using a simple drop-casting method and characterized by FTIR and AFM. The biocompatibility of m-GO films in culturing WJ-MSCs was investigated based on cell morphology, cell viability and osteogenic differentiation ability. Importantly, WJ-MSCs adhered and proliferated successfully on the m-GO films (6.25 µg, 12.5 µg and 25 µg) and showed no difference in cell morphology and viability after 5 days culture. Moreover, the WJ-MSCs growth on GO films (6.25 µg, 12.5 µg and 25 µg) enhanced the osteogenic differentiation as compared to the control (glass coverslip). Hence, the simple and inexpensive drop-casted fabrication strategy could provide biocompatible m-GO films to unlock the wider potential of WJ-MCSs in tissue engineering application.

A bilayer Al nanowire-grid polarizer integrated with an IR-cut filter

A bilayer Al nanowire-grid polarizer integrated with an IR-cut filter has been developed to exhibit high polarization sensitivity in a visible region. The IR-cut filter consisting of Ti3O5/SiO2 multilayer oxide film completely blocks the incoming light over 680 nm wavelength and shows high transmittance over 95% in the visible range. By incorporating the reversible nanostructures molding lithography and the two-step oblique angle deposition of the e-beam evaporator, we are able to secure the nanowire-grid patterning with 50-nm resolution in a form of bilayer Al grating. Then, it is found that the plasmonic coupling between the nearby Al layers leads to the high transmittance of TM-mode light passing through the IR-cut filter, while there is no plasmonic coupling between them for TE-mode case. Both the Finite-Difference Time-Domain simulation and experimental results show that the transmittance of the TM polarization for the grid height of 110 nm reaches up to 90% and the extinction ratio is around 300∶1 in the visible range. Therefore, the observed results can provide an insight in designing the bilayer Al based plasmonic polarizer combined with the IR-cut filter in order to achieve better performance utilizing the plasmonic coupling effect.

High temperature oxidation behavior of low temperature aluminized Mirrax® ESR steel

The aim of this study was to investigate the effect of aluminizing process on the oxidation resistance of mirrax steel. The oxidation behavior of pack cemented aluminizing coatings on Mirrax ESR Steel was investigated at 1000 °C for 5, 25 and 70 h. Low temperature aluminizing process was carried out at 700 °C for 2, 4 and 6 h by pack cementation method. The microstructures, surface morphologies and phase distribution of both coatings before and after oxidation were investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffractometry (XRD). Analysis of the coating layer showed that the coating was homogeneous, non-porous and had a good bond at the interface of the coating-matrix. Coating layer was mainly composed of aluminum-rich Fe2Al5 phase. Depending on the increased process time, the coating thickness varied approximately from 17 to 58 microns. The aluminizing process could greatly improve the oxidation resistance of the substrate. Al diffused outward to form multi-layer oxide films, which prevented the diffusion of oxygen. A sticky, protective, non porous alumina film layer was obtained successfully. The results show that oxidation resistance increased with the increased aluminizing time.

ZnO-Ge MULTILAYER THIN FILM STRUCTURES DEPOSITED BY THERMAL EVAPORATION TECHNIQUE

Zinc oxide and germanium multilayer films have been deposited on glass substrate using electron beam evaporation and resistive heating system, respectively, for alternate layers. The structural optical and electrical parameters have been investigated for the deposited films. The layer formation was confirmed by employing Rutherford back-scattering technique. Optical properties exhibit quantum confinement effect by showing the separate band gaps for ZnO and Ge. Electrical conductivity increases due to combined effect of all six layers (six alternate layers of Ge and ZnO).

Surface modification of Poly(p-phenylene terephthalamide) fibers by polydopamine-polyethyleneimine/graphene oxide multilayer films to enhance interfacial adhesion with rubber matrix

In order to improve the interfacial adhesion between the poly(p-phenylene terephthalamide) fibers and rubber matrix while enhance the fiber strength simultaneously, a mild surface modification method was presented to graft polydopamine-polyethyleneimine/graphene oxide (PDA-PEI/GO) multilayer films onto the fiber surface. In this way, PDA could be first non-covalently deposited onto the fiber surface via dopamine biomimetic modification, and then the positively charged PEI was absorbed on the PDA through Michael addition reaction. After that, the negatively GO was grafted on the surface by the layer-by-layer (LbL) assembly to construct the PDA-PEI/GO multilayer films. The results of mechanical properties tests and pull-out force tests showed that the highest single-filament tensile strength and the highest pull-out force of the modified fibers increased by 15.1% and 78.1%, respectively. The optimal time of PEI/GO multilayer for the enhancement of adhesive properties was 7 and the excessive amount of PEI/GO would lead to high aggregation to decrease the adhesive strength.

Molecular orbital studies of the initial process of gallium oxide chemical vapor deposition: micro-hydrolysis of triethylgallium

Gallium-doped zinc oxide films prepared by atomic layer deposition have received much attention. When triethylgallium is hydrolyzed on the surface of zinc hydroxide, a multi-layered metal oxide film containing a specific amount of gallium at a controlled position is formed. In this study, to elucidate the micro-hydrolysis mechanism of triethylgallium, reaction mechanisms involving one or two water molecules were investigated by molecular orbital calculations. The complete hydrolysis of triethylgallium occurs in three steps with the first partial hydrolysis being the rate limiting step. The activation energy of hydrolysis by two molecules of water is ∼10 kcal mol−1 lower than that with one molecule of water for all steps. The addition of further water molecules significantly decreases the activation energy because the transition state is stabilized by hydrogen bonding between the water molecules. These results suggest the hydrolysis reaction proceeds spontaneously under mild conditions by controlling the concentration of water molecules.

Covalently grafting of self-assembled functionalized graphene oxide multilayer films on Si substrate for solid film lubrication

Graphene-based polymer brush containing multilayer film has been fabricated on silicon wafer (SW) via self-assembled multistep approach based on covalent insertion of 3-aminopropyltrimethoxysilane as a chemical linker on graphene oxide (GO) followed by covalently anchored with polyethyleneimine (PEI). A multilayer polymer brush film was then constructed by electrostatic layer-by-layer (LBL) self-assembly technique between positively charged outer layer PEI grafted GO and anionic polyelectrolyte, poly (sodium 4-styrenesulfonate) (PSS). The LBL formation and microstructure of as prepared films were characterized by Raman spectroscopy, atomic force microscopy, field emission scanning electron microscopy and elemental electron dispersive spectroscopy analysis. The changes in wettability of films during grafting of chemical components on silicon substrate were determined by water contact angle measurement. Microtribological performances of the films were investigated using ball-on-disc contact geometry in ambient condition. The influence of contact pressure and sliding velocity were also studied under reciprocating tribo contact to evaluate the load bearing ability of the films. The multilayer films exhibited low (~0.15–0.17) and steady coefficient of friction (COF) at 1 N load (contact pressure ~ 0.54 GPa) compared to bare SW (~0.6) with remarkable wear-resistivity. With increasing contact pressure (4 N, ~0.86 GPa), the multilayer films provided minimal COF and low wear depth with improved sliding durability among the films. The improved friction and wear resistivity of the multi-layer films are attributed to densely packed polymeric graphene lamella contributing low-resistance to shear during sliding and the presence of sulphur on PSS might assists in superior adhesion of delaminated film to steel counterface ball during shearing, which was investigated by microscopic and Raman spectral analysis.

Assembly of graphene oxide multilayer film for stable and sustained release of nitric oxide gas

Achieving slow release of gas molecules from a thin solid film is challenging because of the high release rates of gas molecules. Graphene oxide (GO) is a well-known material in the field of gas barriers and separation and is the best choice for long-term gas-release applications. To generate the release of nitric oxide (NO) gas from GO, N-diazeniumdiolate (NONOate)—an NO donor source—is conjugated to a GO sheet, and a multilayer film is fabricated via layer-by-layer (LbL) assembly. Two strategies are used in this study. First, the gas permeability is reduced owing to the two-dimensional structure of GO, which generates a physical barrier. This increases the length of the diffusion path. Second, the intra-H bonding of neighboring cation amines and intercalated water molecule between GO layers stabilizes the NO gas. When these two strategies are applied, the multilayer film exhibits release times 2 and 15 times longer than those for the solution and monolayer film, respectively. The sustained and highly controllable release of NO gas from the multilayer GO film is applied for cell-migration tests. The results indicate excellent cell migration—which is related to the surface modification—suitable for wound-healing applications.