Oxide Composite Films Research Articles

A novel niobium based oxidation protective coating with three lines of defense at ultra-high temperature

To improve the ultra-high temperature oxidation and thermal shock resistance of Nb alloys, we prepared a novel niobium-based oxide protective coating that forms three lines of defense through multi-gradient design. In particular, Nb3B2-NbB2 prevents Si diffusion. WSi2 stores rich Si to generate SiO2. The composite oxide film can heal oxidation defects. The finite element and first-principles calculations results show that multi-gradient coating can radiate heat, relieve interlayer stress and CTE mismatch. The coating forcefully protects the substrate from O2 erosion, so that its oxidation life exceeds 13 h at 1850 ℃, and the thermal shock reaches 600 cycles.

Porous polyvinyl alcohol/graphene oxide composite film for strain sensing and energy-storage applications

In this study, a flexible porous polyvinyl alcohol (PVA)/graphene oxide (GO) composite film was developed and tested for flexible strain sensing and energy-storage applications. Morphology and mechanical properties were studied; tensile strength and Young’s modulus increased by 225% and 86.88%, respectively, at 0.5 wt% GO. The PVA/GO film possesses exceptional sensing ability to various mechanical strains, such as tension, compression, bending, and torsion. For example, the gauge factor of the PVA/GO film as a tensile-strain sensor was measured as 2.46 (246%). Under compression loads, the PVA/GO composite film showed piezoresistive and capacitive strain-sensing characteristics. Under 5 kPa of compression load, the relative resistance increased by 81% with a 100 msec response time; the relative capacitance increased by 160% with a 120 msec response time. The PVA/GO strain sensor exhibited high durability and reliability over 20 × 103 cycles of tensile strain and bending at 3.33 Hz. Moreover, the PVA/GO composite film showed good electrochemical properties due to its porous structure; the maximum capacitance was 124.7 F g−1 at 0.5 wt% GO. After 20 × 103 charging–discharging cycles, the capacitance retention rate was 94.45%, representing high stable capacitance performance. The results show that electrically conductive porous PVA nanocomposite films are promising candidates for strain sensing and energy-storage devices.

Oxidation kinetics and microstructure evolution of air oxidation behavior of TC18 alloy

The high-temperature air oxidation behaviors at 600 °C, 700 °C and 800 °C of the TC18 alloy were systematically studied. The oxidation kinetics of TC18 alloy, the phase composition, microscopic morphology and chemical composition of the surface oxide films were analyzed to elucidate possible oxidation mechanisms. The results revealed that the oxidation behavior of TC18 alloy followed a linear-parabolic law at 600 °C and 700 °C while being governed by a simple linear law at 800 °C. The long-term oxidation for 24 h at 600 °C and 700 °C resulted in the oxide films composed of both Ti3O and TiO2, with dominant Ti3O and TiO2 respectively for the oxide films formed at 600 °C and 700 °C specifically. Especially for the oxidation at 800 °C, the oxide film was revealed to consist of three layers of the outer layer Al2O3, the secondary outer layer TiO2 and the dominant inner layer TiO2.

Niobium Oxide Coated Mesoporous Platinum Nanoparticles for the Oxygen Reduction Reaction

Effective and economic methods of converting chemical energy into electricity or vice versa (i.e., through the use of fuel cells) must be developed to aid in the transition to renewable energy sources. One of the major barriers in the commercialization of fuel cells is the disparity in speed and efficiency between the two fuel cell reactions: the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) of which the latter is orders of magnitude slower.1 Mesoporous Pt prepared by electrodeposition has been shown to have increased activity towards the ORR than the industry standard Pt nanoparticles (NPs) supported on carbon.2 Platinum based catalysts, however, lack long term stability under acidic fuel cell conditions. One method that has been found to mitigate the long-term loss of Pt catalyst stability and activity is coating platinum with nanoscale thin films of niobium oxide.3 In this work, niobium oxide was investigated as a stabilizing coating for mesoporous Pt NP catalysts.Mesoporous Pt NPs were synthesized via electrodeposition to form ~50 nm diameter NPs. The Pt NPs were then coated with niobium oxide films with a varying nanoscale thickness that ranged from 3 to 50 nm. The niobium oxide films were fabricated using atomic layer deposition (ALD) or electrodeposition.3,4 Scanning electron microscopy and transmission electron tomography were used to evaluate the porosity and surface morphology of the Pt NPs before and after coating with niobium oxide. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy were used to confirm the presence and composition of the niobium oxide films. Electrochemical characterization by cyclic voltammetry and electrochemical impedance spectroscopy under acidic conditions was used to determine an optimal thickness of the niobium oxide film that stabilizes the size and morphology of the Pt NPs while maintaining catalyst activity. The Pt NPs coated with <10-nm thick niobium oxide films were observed to have an increased long-term performance in comparison to their uncoated counterparts. Stabilizing NP catalysts for improving their long-term activity is a vital step towards creating affordable alternatives to fossil fuels by maximizing renewable energy resources. Debe, M. K. Electrocatalyst Approaches and Challenges for Automotive Fuel Cells. Nature 2012, 486, 43–51.Paul, M. T. Y.; Gates, B. D. Mesoporous Platinum Prepared by Electrodeposition for Ultralow Loading Proton Exchange Membrane Fuel Cells. Sci. Rep. 2019, 9, 4161.Eastcott, J.; Gates, B. D. Nanoscale Thin Films of Niobium Oxide on Platinum Surfaces: Creating a Platform for Optimizing Material Composition and Electrochemical Stability. Can. J. Chem. 2017, 96, 260–266.Zhitomirsky, I. Electrolytic Deposition of Niobium Oxide Films. Mater. Lett. 1998, 35, 188–193.

Multilevel effective material approximation for modeling ellipsometric measurements on complex porous thin films

Abstract Catalysts are important components in chemical processes because they lower the activation energy and thus determine the rate, efficiency and selectivity of a chemical reaction. This property plays an important role in many of today’s processes, including the electrochemical splitting of water. Due to the continuous development of catalyst materials, they are becoming more complex, which makes a reliable evaluation of physicochemical properties challenging even for modern analytical measurement techniques and industrial manufacturing. We present a fast, vacuum-free and non-destructive analytical approach using multi-sample spectroscopic ellipsometry to determine relevant material parameters such as film thickness, porosity and composition of mesoporous IrOx–TiOy films. Mesoporous IrOx–TiOy films were deposited on Si wafers by sol–gel synthesis, varying the composition of the mixed oxide films between 0 and 100 wt%Ir. The ellipsometric modeling is based on an anisotropic Bruggeman effective medium approximation (a-BEMA) to determine the film thickness and volume fraction of the material and pores. The volume fraction of the material was again modeled using a Bruggeman EMA to determine the chemical composition of the materials. The ellipsometric fitting results were compared with complementary methods, such as scanning electron microscopy (SEM), electron probe microanalysis (EPMA) as well as environmental ellipsometric porosimetry (EEP).

Comprehensive Characterization of Solution-Cast Pristine and Reduced Graphene Oxide Composite Polyvinylidene Fluoride Films for Sensory Applications.

Pristine and doped polyvinylidene fluoride (PVDF) are actively investigated for a broad range of applications in pressure sensing, energy harvesting, transducers, porous membranes, etc. There have been numerous reports on the improved piezoelectric and electric performance of PVDF-doped reduced graphene oxide (rGO) structures. However, the common in situ doping methods have proven to be expensive and less desirable. Furthermore, there is a lack of explicit extraction of the compression mode piezoelectric coefficient () in ex situ rGO doped PVDF composite films prepared using low-cost, solution-cast processes. In this work, we describe an optimal procedure for preparing high-quality pristine and nano-composite PVDF films using solution-casting and thermal poling. We then verify their electromechanical properties by rigorously characterizing -phase concentration, crystallinity, piezoelectric coefficient, dielectric permittivity, and loss tangent. We also demonstrate a novel stationary atomic force microscope (AFM) technique designed to reduce non-piezoelectric influences on the extraction of in PVDF films. We then discuss the benefits of our measurements technique over commercially sourced piezometers and conventional piezoforce microscopy (PFM). Characterization outcomes from our in-house synthesized films demonstrate that the introduction of 0.3%w.t. rGO nanoparticles in a solution-cast only marginally changes the -phase concentration from 83.7% to 81.7% and decreases the crystallinity from 42.4% to 37.3%, whereas doping increases the piezoelectric coefficient by 28% from = 45 pm/V to = 58 pm/V, while also improving the dielectric by 28%. The piezoelectric coefficients of our films were generally higher but comparable to other in situ prepared PVDF/rGO composite films, while the dielectric permittivity and -phase concentrations were found to be lower.

Ultrathin flexible electrospun carbon nanofibers reinforced graphene microgasbags films with three-dimensional conductive network toward synergetic enhanced electromagnetic interference shielding

In recent years, graphene-based composite films have been greatly developed in the field of electromagnetic shielding interference (EMI). However, it is still a huge challenge to prepare graphene-based composite films with excellent mechanical properties, conductivity and electromagnetic shielding properties. In this work, we adopted a facile and effective method by annealing the alkali-treated polyacrylonitrile (aPAN) nanofibers reinforced graphene oxide (GO) composite films at 2000 °C to obtain graphene-carbon nanofibers composite films (GCFs). Microscopically, carbon nanofibers (CNFs) were intercalated into the graphene sheets, and microgasbags structure was formed during the heat treatment process. The special structure makes GCFs have superior tensile strength (10.4 MPa) at 5% strain. After repeated folding over 1000 times, the films still demonstrate excellent structural integrity and flexibility performance. Interestingly, the graphene-based composite films with 10 wt% aPAN nanofibers exhibit an extremely low density of about 0.678 g/cm3 and excellent electrical conductivity of 1.72 × 105 S/m. Further, an outstanding electromagnetic shielding effectiveness (SE) of 55–57 dB was achieved, and the corresponding value of the specific SE/thickness can reach 67,601–70,059 dB·cm2/g, which is the highest among reported graphene-based shielding materials. The significant electromagnetic shielding performance is due to the synergistic enhancement effect brought by the excellent conductivity of carbon nanofibers and graphene, the formed effective conductive network and the microgasbags structure. Electromagnetism simulation further clarified that the underlying mechanism should be mainly attributed to the conduction loss and multiple reflections caused by the special structure of GCFs. This work will provide new solutions for low density, high flexibility and excellent electromagnetic shielding properties materials in the next generation of foldable and wearable electronics.

Oxidation behaviors of the rotary friction welded joints of HT700 superalloy in saturated water steam at 700 ℃

The oxidation behavior of welded joints with or without heat-treatment of HT700 alloy was studied in 700 ℃ saturated water vapor with regards to oxidation kinetics, oxide film composition, and microstructure. The results show that the oxide film compositions of the as-welded joints and heat-treated welded joints were basically the same. The oxide film is composed of a small amount of iron oxide, NiCr2O4, and a large amount of Cr2O3 from the outer layer to the inner layer, with a small amount of internal oxidation products Al2O3. At the beginning of the oxidation process, the double layer oxide film grew at the same time, so that the as-welded joint had better performance in the later stage of oxidation. The formation of a continuous internal oxidation layer was later in heat-treated welded joints as compared to the as-welded joint, resulting in a larger thickness of the oxide film. The oxidation behavior of the welded seams in different regions of as-welded state and heat treatment state after welding displayed the following characteristics: small grain size, thin oxide film, and the weld fusion line with thin oxide film.

Accurate determination of anisotropic thermal conductivity for ultrathin composite film

Highly anisotropic thermal conductive materials are of significance in thermal management applications. However, accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance, severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide (MMT/rGO) composite film with a thickness range from 0.2 μm to 2 μm. The in-plane thermal conductivity measurement is realized by one-dimensional (1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.

Ultra-high temperature oxidation resistance of a novel (Mo, Hf, W, Ti)Si2 ceramic coating with Nb interlayer on Ta substrate

In order to solve the challenge of recyclability of tantalum substrates in high temperature oxidation environments, a novel MoSi2-WSi2-HfSi2-TiSi2 composite ceramic coating containing an Nb interlayer was prepared on the surface of tantalum substrate by a three-step method. The mix ceramic silicide coating exhibited superior performance and effective protection for 10.2 h at 1800 °C, possibly due to the formation of an outer SiO2-HfO2-HfSiO4 composite oxide film with low oxygen permeability, moderate viscosity and thermal expansion coefficient, as well as good self-healing ability. Furthermore, the coating successfully passed 537 thermal cycles from room temperature to 1800 °C. The presence of Nb interlayer significantly mitigated the thermal mismatch between the ceramic coating and the tantalum substrate, and the bidirectional diffusion of Nb element during the high temperature oxidation and thermal shock process further reduced the tendency of the coating to crack.

Enhanced charge transport of conjugated polymer/reduced graphene oxide composite films by solvent vapor pre-treatment

In this study, a facile approach that could provide a significant enhancement of the charge transport properties of the conjugated polymer/reduced graphene oxide (rGO) composite films using a non-solvent vapor treatment is reported. As the methanol vapors were exposed to the poly(3-hexylthiophene) (P3HT)/rGO composite solution, P3HT chains self-assembled to create nanofibrillar structures via favorable π–π interactions. The π–π staking in P3HT occurred by the non-solvent vapor exposure to minimize unfavorable interactions of P3HT chains with the non-solvent vapor molecules. The self-assembly of P3HT chains was chiefly facilitated by the presence of rGO. This is because the surface of rGO can serve as nucleation sites for the growth of P3HT nanowires. Consequently, P3HT/rGO composite films obtained from the methanol vapor treated corresponding solutions exhibited a high charge carrier mobility (1.3 × 10−1 cm2 V−1 s−1), which is approximately 11-times and 6.5-times higher than those of pristine P3HT (1.2 × 10−2 cm2 V−1 s−1) and P3HT/rGO (2.0 × 10−2 cm2 V−1 s−1) composite films, respectively.

Design of thin-film configuration of SnO2–Ag2O composites for NO2 gas-sensing applications

Abstract In this study, a two-layered thin-film structure consisting of a dispersed nanoscaled Ag2O phase and SnO2 layer (SA) and a mono-composite film layer (CSA) consisting of a nanoscale Ag2O phase in the SnO2 matrix are designed and fabricated for NO2 gas sensor applications. Two-layered and mono-layered SnO2–Ag2O composite thin films were synthesized using two-step SnO2 and Ag2O sputtering processes and Ag2O/SnO2 co-sputtering approach, respectively. In NO2 gas-sensing measurement results, both SA and CSA thin films that functionalized with an appropriate Ag2O content exhibit enhanced gas-sensing responses toward low-concentration NO2 gas in comparison with that of pristine SnO2 thin film. In particular, a gas sensor made from the mono-composite SnO2–Ag2O layer demonstrates apparently higher NO2 gas-sensing performance than that of double-layered SnO2–Ag2O thin-film sensor. This is attributed to substantially numerous p–n junctions of Ag2O/SnO2 formed in the top region of the SnO2 matrix. The gas-sensing response of the optimal sample (CSA270) toward 10 ppm NO2 gas is 5.91, and the response/recovery speeds in a single cycle dynamic response plot are 28 s/168 s toward 10 ppm NO2, respectively. Such a p–n thin-film configuration is beneficial to induce large electric resistance variation before and after the introduction of NO2 target gas during gas-sensing tests. The experimental results herein demonstrate that the gas-sensing performance of p–n oxide composite thin films can be tuned via the appropriate design of composite thin-film configuration.

Memristive Characteristics of Composite Hafnium/Tantalum Anodic Oxides

A composite anodic oxide film is formed by electrochemical treatment of an ultra‐thin Hf film superimposed on Ta, due to the growth of Ta2O5 columns through HfO2. The oxidation dynamic is governed by an electrical version of the Rayleigh–Taylor effect, the current preferring the more conductive path via Ta during anodization of the superimposed Hf film. Memristive devices obtained by patterning Pt top electrodes are investigated and their electrical behavior is reported. The effect of electrolyte species incorporation on the memristive behavior is analyzed by anodization in different solutions. The influence of citrate‐buffered (CB) and phosphate‐buffered (PB) electrolytes is studied, and the presence of P in the composite anodic oxides is evidenced in the latter case leading to early device failure. Composite memristors grown in citrate electrolytes show both unipolar and bipolar switching, high stability, very good retention, and endurance. The coexistence of both switching mechanisms is related to the special composite oxide nanostructuring.

Near 90% Transparent ITO-Based Flexible Electrode with Double-Sided Antireflection Layers for Highly Efficient Flexible Optoelectronic Devices.

As a widely used substrate for flexible electronics, indium-tin oxide-based polymer electrodes (polymer-ITO electrodes) exhibit poorly visible light transmittance of less than 80%. The inferior transmittance for polymer-ITO electrodes severely limits the performance improvement of polymer-ITO based electronics. Here, a conceptually different approach of the double-sided antireflection coatings (DARCs) strategy is proposed to modulate both the air-polymer substrate interface and ITO-air interface refractive index gradient, to synergistically improve the transmittance of polymer-ITO electrodes. On the basis of SiO2 nanoparticles antireflection layer on polymer substrate, a polymer-metal oxide composite antireflection film is fabricated on the ITO side. Resultantly, the transmittance of ITO-based flexible electrodes is successfully improved from 76.8% to 89.8%, which is the highest transmittance among the reported ITO-based flexible electrodes. Furthermore, the photoluminescence emission intensity of luminescent materials enveloped with the DARCs electrodes increases by 74% over that with reference electrodes, demonstrating the DARCs antireflection strategy can efficiently improve the performance of flexible optoelectronic devices. With DARCs electrode, the flexible perovskite solar cells exhibit an enhanced efficiency from 18.80% to 20.85%.

Simultaneous voltammetric sensing of three DNA bases guanine, adenine and thymine at poly(L-arginine)-electrochemically reduced graphene oxide composite film modified glassy carbon electrode

Simultaneous voltammetric sensing of three DNA bases guanine, adenine and thymine at poly(L-arginine)-electrochemically reduced graphene oxide composite film modified glassy carbon electrode

High-temperature oxidation and wear properties of TiC-reinforced CrMnFeCoNi high entropy alloy composite coatings produced by laser cladding

Extensive studies have been conducted on high entropy alloy composite coatings reinforced with micro-sized ceramic particles at the room-temperature. However, studies on their high temperatures properties are rare. The oxidation and tribological properties of CrMnFeCoNi/xTiC composite coatings produced by laser cladding were studied at 600 °C. The addition of TiC to the coating promoted the oxidation process due to “short-circuit diffusion”. During the high temperature wear process, brittle cracking did not occur on the worn surface, and a good wear-resistant intermediate layer was formed. The coatings exhibited low hardness, low wear rate, and high coefficient of friction due to the formation of composite oxide film formed on the worn surface with good adhesion to the matrix.

Emergence of Insulating Ferrimagnetism and Perpendicular Magnetic Anisotropy in 3d-5d Perovskite Oxide Composite Films for Insulator Spintronics.

Magnetic insulators with strong perpendicular magnetic anisotropy (PMA) play a key role in exploring pure spin current phenomena and developing ultralow-dissipation spintronic devices, rendering them highly desirable to develop new material platforms. Here, we report the epitaxial growth of La2/3Sr1/3MnO3 (LSMO)-SrIrO3 (SIO) composite oxide films (LSMIO) with different crystalline orientations fabricated by a sequential two-target ablation process by pulsed laser deposition. The LSMIO films exhibit high crystalline quality with a homogeneous mixture of LSMO and SIO at an atomic level. Ferrimagnetic and insulating transport characteristics are observed, with the temperature-dependent electric resistivity well fitted by the Mott variable-range-hopping model. Moreover, the LSMIO films show strong PMA. By further constructing all-perovskite-oxide heterostructures of the ferrimagnetic insulator LSMIO and a strong spin-orbital-coupled SIO layer, pronounced spin Hall magnetoresistance (SMR) and spin Hall-like anomalous Hall effect (SH-AHE) were observed. These results illustrate the potential application of the ferrimagnetic insulator LSMIO in developing all-oxide ultralow-dissipation spintronic devices.

The Reinforced Electromagnetic Interference Shielding Performance of Thermal Reduced Graphene Oxide Films via Polyimide Pyrolysis.

In this work, thin reduced graphene oxide (GO) composite films were fabricated for electromagnetic interference (EMI) shielding application. High solid content GO slurry (7 wt %) was obtained by dispersing GO clay in polymer solution under high-speed mechanical stirring. A composite film with varied thickness (10–150 μm) could be fabricated in pilot scale. After an optimized thermal annealing procedure, the final product showed good conductivity, which reached 500 S·cm–1. The thin sample (thickness < 0.1 mm) containing 10% polymer showed an enhanced EMI shielding performance of 55–65 dB. The outstanding EMI shielding efficiency as well as good suppleness and industrialized potential of thermal reduced graphene oxide polymer composite films could make a progress on their application in flexible devices as an EMI shielding material.

Photocatalytic efficiency under visible light of a novel Cu\u2013Fe oxide composite films prepared by one-step sparking process

Copper–iron (Cu–Fe) oxide composite films were successfully deposited on quartz substrate by a facile sparking process. The nanoparticles were deposited on the substrate after sparking off the Fe and Cu tips with different ratios and were then annealed at different temperatures. The network particles were observed after annealing the film at 700 °C. Meanwhile, XRD, XPS and SAED patterns of the annealed films at 700 °C consisted of a mixed phase of CuO, γ-Fe2O3, CuFe2O4 and CuFe2O. The film with the lowest energy band gap (Eg) of 2.56 eV was observed after annealing at 700 °C. Interestingly, the optimum ratio and annealing temperature show the photocatalytic activity under visible light higher than 20% and 30% compare with the annealed TiO2 at 500 and 700 °C, respectively. This is a novel photocatalyst which can be replaced TiO2 for photocatalytic applications in the future.

Study on 3D multi-performance composite films of Fe3O4 decorated CNTs/graphene oxide

In this work, three-dimensional (3D) Fe3O4 decorated CNTs/graphene oxide (Fe3O4-CNTs/GO) composite film was used to enhance glass fiber reinforced polymer (GFRP) resulting in three excellent performances of interlaminar toughening, resistance to temperature changes, and electromagnetic interference (EMI) shielding were all achieved. The end notch bending (ENF) test results showed that Fe3O4-CNTs/GO film enhanced GFRP was 60.51% and 79.64% higher than the baseline (GFRP without reinforcement film) after RT or temperature cycle treatment, while the GFRP of pure CNTs film was 21.79% and 26.34% higher than the baseline, respectively. The change in interlaminar toughness of Fe3O4-CNTs/GO samples by temperature cycle was also lower than that of the other two samples (Fe3O4-CNTs/GO film: 4.15%, pure CNTs film:11.15%, baseline: 14.35%). The average EMI shielding effectiveness of Fe3O4-CNTs/GO films with a thickness of only 0.052 mm was 25 dB, about 500% higher than the 5 dB of the control group (ordinary CNTs/Fe3O4/GO films, thickness 0.047 mm). Scanning electron microscopy (SEM) further confirmed the existence of the 3D frame structure and interlamellar strengthening interface of Fe3O4-CNTs/GO films.