Oxide-based Films Research Articles

Ionic liquid reinforced NaSICON-type oxide electrolyte films enabling solid state conversion metal fluoride-lithium batteries

Solid-state batteries (SSBs) with metal fluoride cathodes are an exciting combination due to their high theoretical energy density and good safety. However, owing to the high chemical compatibility requirements between metal fluoride cathode and the solid-state electrolyte (SSE), developing an adaptable SSE film with comprehensive properties is particularly challenging. Herein, a class of ionic liquid (IL) reinforced oxide SSE films was proposed. Among them, the combination of Li1.5Al0.5Ge1.5(PO4)3 (LAGP) oxide SSE and EMIM-based IL (LAGP-EMIM) exhibits good flame-retardant properties, exceptional air stability, high ionic conductivity and excellent chemical stability. The introduction of ILs can increase the ion transport channels in SSEs and render the usage of dry-process, well addressing the contradiction between the flexibility and ionic conductivity of oxide films. The thickness of LAGP-EMIM films is 59 μm and they show the highest ionic conductivity of 1.05 mS cm−1 among the NaSICON-type oxide-based SSE films till now. In addition, it can be stably matched with the conversion metal fluoride cathodes such as FeF3 and CuF2 to construct semi-solid-state batteries, delivering high initial discharge capacity of 820.2 and 539.6 mAh g−1, respectively. The present work shed new insight into designing the composite electrolytes toward the next-generation solid state conversion batteries.

Sustainable whey proteins-nanostructured zinc oxide-based films for the treatment of chronic wounds: New insights from biopharmaceutical studies

Chronic wounds represent silent epidemic affecting a large portion of the world population, especially the elders; in this context, the development of advanced bioactive dressings is imperative to accelerate wound healing process, while contrasting or preventing infections. The aim of the present work was to provide a deep characterization of the functional and biopharmaceutical properties of a sustainable thin and flexible films, composed of whey proteins alone (WPI) and added with nanostructured zinc oxide (WPZ) and intended for the management of chronic wounds. The potential of whey proteins-based films as wound dressings has been confirmed by their wettability, hydration properties, elastic behavior upon hydration, biodegradation propensity and, when added with nanostructured zinc oxide, antibacterial efficacy against both Gram-positive and Gram-negative pathogens, i.e. Staphylococcus aureus and Escherichia coli. In-vitro experiments, performed on normal human dermal fibroblasts, confirmed film cytocompatibility, also revealing the possible role of Zn2+ ions in promoting fibroblast proliferation. Finally, in-vivo studies on rat model confirmed film suitability to act as wound dressing, since able to ensure a regular healing process while providing effective protection from infections. In particular, both films WPI and WPZ are responsible for the formation in the wound bed of a continuous collagen layer similar to that of healthy skin.

Tuning the energy storage performance of graphene oxide-based nanocomposite films by encapsulating silver nanoparticles

In the current designed study, we explore the dielectric and energy storage performance of silver nanoparticle decorated graphene oxide nanocomposites incorporated into chitosan blended with poly (1-vinylpyrrolidone-co-vinyl acetate) in comparison with only graphene oxide nanocomposite doped into the same blend matrix. A sustainable and eco-friendly green route approach was used to form the silver nanoparticle decorated graphene oxide nanocomposites. The nanocomposite films so fabricated using the solvent evaporation method, were subjected to various characterisation techniques such as X-ray diffraction analysis, Fourier transform infrared spectroscopy, thermal analysis, surface morphology and impedance spectroscopy. Slight decrease in crystallinity (44.3 %), difference in the positioning of infrared bands, thermal stability (up to ∼77 °C) and evenly distributed morphology depict the advantage of silver coating over graphene oxide nanoparticles in the blended nanocomposite films. A boost in the dielectric properties and energy storage ability was displayed by the silver encapsulated graphene oxide reinforced nanocomposite blend films. The dielectric properties were examined by using a Nyquist plot (Bulk resistance - 1.01 × 104 Ω). An ionic conductivity of 1.044 × 10−4 S/cm and a DC conductivity of 1.196 × 10‐−4 S/cm was observed. Of note, it can be inferred that silver nanoparticle decorated graphene oxide nanocomposites impart tremendous electrical properties to the chitosan/poly (1-vinylpyrrolidone-co-vinylacetate) films, enabling them to be used in energy storage applications.

Improvement on Potential Drifting for Sol–Gel and Electroplated Iridium Oxide-Based pH-Sensing Films

Improvement on Potential Drifting for Sol–Gel and Electroplated Iridium Oxide-Based pH-Sensing Films

Atomic Layer Deposition of Titanium Oxide-Based Films for Semiconductor Applications-Effects of Precursor and Operating Conditions.

Two widely used atomic layer deposition precursors, Tetrakis (dimethylamido) titanium (TDMA-Ti) and titanium tetrachloride (TiCl4), were investigated for use in the deposition of TiOx-based thin films as a passivating contact material for solar cells. This study revealed that both precursors are suited to similar deposition temperatures (150 °C). Post-deposition annealing plays a major role in optimising the titanium oxide (TiOx) film passivation properties, improving minority carrier lifetime (τeff) by more than 200 µs. Aluminium oxide deposited together with titanium oxide (AlOy/TiOx) reduced the sheet resistance by 40% compared with pure TiOx. It was also revealed that the passivation quality of the (AlOy/TiOx) stack depends on the precursor and ratio of AlOy to TiOx deposition cycles.

Synergistic effect of strain and oxygen vacancy on the ferroelectric properties of hafnium oxide-based ferroelectric films

In this paper, a multiphase coexistence phase field model considering mobile oxygen vacancy is established to investigate the synergistic effect of strain and oxygen vacancy on the ferroelectric properties of hafnium oxide-based ferroelectric films. Uniform strain introduced by flat substrate and heterogeneous strain caused by miscut substrate are considered. Our study demonstrates that whether the HfO2 film is under flat substrate-induced strain or miscut substrate-induced strain, the regulation of oxygen vacancy concentration on the ferroelectric phase transition and domain switching of the film is double-sided. When the oxygen vacancy concentration is 1 × 1020 cm−3, the film under 1.2 % uniform strain reaches a maximum remanent polarization of 0.36 C/m2. The optimal concentration interval of oxygen vacancy can be widened by −1.2 % flat substrate-induced uniform strain or 6° and 8° miscut substrate-induced heterogeneous strain. These results embodied the synergistic relationship between oxygen vacancy and strain in regulating the ferroelectric properties of hafnium-oxide based films, which offers guidance for us to understand the phase transition behavior of hafnium-based ferroelectric films and to optimize the electric properties of thin films in device applications.

An X-ray Photoelectron Spectroscopy Study of Ultraviolet Photoannealing-Induced Surface Transformations of Sol–Gel Derived Zinc Oxide-Based Films

An X-ray Photoelectron Spectroscopy Study of Ultraviolet Photoannealing-Induced Surface Transformations of Sol–Gel Derived Zinc Oxide-Based Films

Synergistic effect of Si concentration and distribution on ferroelectric properties optimization of Si:HfO2 ferroelectric thin films

In this paper, a phase-field model of Si-doped hafnium oxide-based ferroelectric thin films is established. And then, the synergistic effect of Si concentration and distribution on ferroelectric properties optimization of Si:HfO2 ferroelectric thin films is studied with the proposed model. It is found that no matter how Si dopant is distributed in the film, the volume fraction of the ferroelectric phase in the film increases first and then decreases with the increase of Si concentration. However, compared with the uniform distribution, the layered distribution is more likely to great improve ferrelectric properties. When Si dopant is uniformly distributed in the film, the highest remanent polarization value that the film can obtain via Si concentration modulation is 38.7 μC cm−2, and the corresponding Si concentration is 3.8 cat%, which is consistent with the experimental results. When Si dopant is layered in the film, and the concentration difference between the Si-rich and Si-poor layers is 7.6%, in the Si concentration range of 3.6 cat%–3.8 cat%, the residual polarization of the film reaches 46.4–46.8 μC cm−2, which is 20% higher than that when Si dopant are evenly distributed in the film. The above results show that selecting the Si layered distribution mode and controlling the concentration difference between Si-rich and Si-poor layers in an appropriate range can greatly improve the films’ ferroelectric properties and broaden the Si concentration optimization range of the ferroelectric properties of the films. The result provides further theoretical guidance on using Si doping to adjust the ferroelectric properties of hafnium oxide-based films.

Mucoadhesive buccal films for treatment of xerostomia prepared by coupling HME and 3D printing technologies

Polyethylene oxide-based muco-adhesive buccal films containing adipic acid active pharmaceutical ingredient (API) and xylitol were developed using hot-melt extrusion (HME) coupled with Fused Deposition Modeling (FDM) three-dimensional (3D) printing. The immediate release mucoadhesive buccal films are intended for treatment or amelioration of xerostomia (dry mouth condition). Different formulae containing adipic acid and xylitol as the main saliva stimulating ingredients, and polyethylene oxide N80 (Polyox-N80) as the polymeric carrier were extruded using Thermo Scientific™ Process 11 Parallel Twin-Screw Extruder by Thermo Fisher Scientific (Waltham, MA, USA) equipped with 1.5 mm die. The extrudates were evaluated for printability using 3-point bend test and the ones which exhibited appropriate mechanical strength were 3D printed using Prusa i3 MK3 S 3D printer at 50 °C bed temperature, and 200 °C extruder temperature. The printed films demonstrated uniform content of adipic acid and desirable drug release upon quantification by high performance liquid chromatography. More than 80% of the adipic acid was released in 15 min and 100% of the adipic acid was released within 30 min. The DSC thermographs of the printed formulations revealed the adipic acid was dispersed in the polymer. The results of this study present an alternative formulation approach for the treatment of xerostomia by combining HME with FDM-3D printing for the development of muco-adhesive films containing adipic acid and xylitol.

Spontaneous-polarization-induced photovoltaic effect in rhombohedrally stacked MoS2

Stacking order in van der Waals materials determines the coupling between atomic layers and is therefore key to the materials' properties. By exploring different stacking orders, many novel physical phenomena have been realized in artificial vdW stacks. Recently, 2D ferroelectricity has been observed in zero-degree aligned hBN and graphene-hBN heterostructures, holding promise in a range of electronic applications. In those artificial stacks, however, the single domain size is limited by the stacking-angle misalignment to about 0.1 to 1 $\mu$m, which is incompatible with most optical or optoelectronic applications. Here we show MoS$_2$ in the rhombohedral phase can host a homogeneous spontaneous polarization throughout few-$\mu$m-sized exfoliated flakes, as it is a natural crystal requiring no stacking and is, therefore free of misalignment. Utilizing this homogeneous polarization and its induced depolarization field (DEP), we build a graphene-MoS$_2$ based photovoltaic device with high efficiency. The few-layer MoS$_2$ is thinner than most oxide-based ferroelectric films, which allows us to maximize the DEP and study its impact at the atomically thin limit, while the highly uniform polarization achievable in the commensurate crystal enables a tangible path for up-scaling. The external quantum efficiency of our device is up to 16% at room temperature, over one order larger than the highest efficiency observed in bulk photovoltaic devices, owing to the reduced screening in graphene, the exciton-enhanced light-matter interaction, and the ultrafast interlayer relaxation in MoS$_2$. In view of the wide range of bandgap energy in other TMDs, our findings make rhombohedral TMDs a promising and versatile candidate for applications such as energy-efficient photo-detection with high speed and programmable polarity.

ZnO Films from Thermal Oxidation of Zn Films: Effect of the Thickness of the Precursor Films on the Structural, Morphological, and Optical Properties of the Products

Zinc oxide (ZnO) films with different structural, morphological, and optical properties were obtained by (fixed) thermal oxidation of deposited metallic zinc (Zn) films. The main characteristics of the oxidized films are discussed in terms of the Zn film thickness. On-axis preferential crystallographic oriented growth of ZnO can be tuned based on the control of the thickness of the deposited Zn: c-axis (a-axis) for the thinnest (thicker) Zn film. The thicker ZnO film is rather a-textured, whereas the grains hosted by the ZnO films corresponding to the Zn films of intermediate thicknesses are more randomly oriented. For Zn films of ever-increasing thickness, a tendency towards the crystallization of larger ZnO nanocrystals holds, combined with a continuous increment on the surface roughness. In contrast, the fundamental bandgap of the resultant oxide-based films decreases with thickness. The roughness of the ZnO films is not directly measured. It is qualitatively described by the analysis of Zn-film micrographs obtained by Scanning Electron Microscopy and by the demonstration of strong optical scattering interactions present in the thicker ZnO films by their random lasing activity.

Spontaneous Polarization induced Photovoltaic Effect In rhombohedrally stacked MoS2

Stacking order in van der Waals materials determines the coupling between atomic layers and is therefore key to the materials' properties. By exploring different stacking orders, many novel physical phenomena have been realized in artificial vdW stacks. Recently, 2D ferroelectricity has been observed in zero-degree aligned hBN and graphene-hBN heterostructures, holding promise in a range of electronic applications. In those artificial stacks, however, the single domain size is limited by the stacking-angle misalignment to about 0.1 to 1 $\mu$m, which is incompatible with most optical or optoelectronic applications. Here we show MoS$_2$ in the rhombohedral phase can host a homogeneous spontaneous polarization throughout few-$\mu$m-sized exfoliated flakes, as it is a natural crystal requiring no stacking and is, therefore free of misalignment. Utilizing this homogeneous polarization and its induced depolarization field (DEP), we build a graphene-MoS$_2$ based photovoltaic device with high efficiency. The few-layer MoS$_2$ is thinner than most oxide-based ferroelectric films, which allows us to maximize the DEP and study its impact at the atomically thin limit, while the highly uniform polarization achievable in the commensurate crystal enables a tangible path for up-scaling. The external quantum efficiency of our device is up to 16% at room temperature, over one order larger than the highest efficiency observed in bulk photovoltaic devices, owing to the reduced screening in graphene, the exciton-enhanced light-matter interaction, and the ultrafast interlayer relaxation in MoS$_2$. In view of the wide range of bandgap energy in other TMDs, our findings make rhombohedral TMDs a promising and versatile candidate for applications such as energy-efficient photo-detection with high speed and programmable polarity.

Intrinsic 90° charged domain wall and its effects on ferroelectric properties

The domain is an important characteristic of ferroelectric materials, and the type of domain can have significant effects on the performance of ferroelectric materials. In particular, the unique wake-up and fatigue effects of Hf0.5Zr0.5O2 (HZO) films severely restrict improvements in terms of film performance. Recently, using integrated differential phase contrast (iDPC) scanning transmission electron microscopy (STEM) imaging, we observed the existence of intrinsic tail-to-tail 90° domain structures, charged domain walls (CDWs), and polarization relaxation on the TiN/HZO/TiN interfaces of HZO films. Based on this experimental investigation, we establish a phase-field model of the tail-to-tail 90°CDWs based on the time-dependent Ginzburg–Landau equation. In our model, the tail-to-tail 90°CDW affects the mesoscopic domain switching through a built-in electric field, which, in turn, affects the macroscopic ferroelectric properties of the thin film. The following conclusions are drawn: (a) the CDWs that are distributed horizontally or vertically along the thickness of the film cause a A-wake-up effect (antiferroelectric-like wake-up) with double hysteresis loops or a S-wake-up effect (spindle-like wake-up), with thick portions in the middle and both ends points of the hysteresis loop; (b) the S-wake-up caused by the CDWs distributed along the thickness of the film performs badly in fatigue tests and is easier to break down. The model proposed herein reveals the mechanism of the wake-up effect in hafnium oxide-based ferroelectric films. It provides a theoretical basis for the development of a new type of hafnium oxide-based ferroelectric memory system.

Synergistic Effect of Strain and Oxygen Vacancy on the Ferroelectric Properties of Hafnium Oxide-Based Ferroelectric Films

Synergistic Effect of Strain and Oxygen Vacancy on the Ferroelectric Properties of Hafnium Oxide-Based Ferroelectric Films

Surface free energy and wettability properties of transparent conducting oxide-based films with Ag interlayer

ITO, ZTO, AZO and Ag are commonly used in transparent conducting oxide (TCO)/metal/TCO electrodes to form multilayered thin films on a suitable substrate. A detailed surface free energy (SFE) knowledge of these films is critical to design desirable TCO-based sandwich structures. In this study, TCO/Ag/TCO multilayer thin films were coated onto glass substrates using ITO, ZTO, AZO and Ag targets by magnetron sputtering. The wettability properties of TCO, Ag interlayer and TCO/Ag/TCO were evaluated by contact angle measurements of seven different liquids having various surface tension values. The dispersive and polar components of SFE were calculated using geometric and harmonic mean approaches. The acidic and basic components of SFE were calculated using van Oss-Chaudhury-Good method. Following this, the work of adhesion values between TCO films and Ag interlayer were estimated using SFE values of the films. The results show that the SFE components of the surfaces differ depending on the TCO type, the total SFE values of TCO/Ag/TCO films were lower than that of TCO films, and AZO/Ag adhesion is stronger than the other TCO/Ag structures. The reasons behind these differences were discussed by evaluating the SFE, XRD, AFM and SEM analysis simultaneously.

Controlling the optical properties of nanostructured oxide-based polymer films

A bulk scale process is implemented for the production of nanostructured film composites comprising unary or multi-component metal oxide nanoparticles dispersed in a suitable polymer matrix. The as-received nanoparticles, namely Al_2O_3, SiO_2 and TiO_2 and binary combinations, are treated following specific chemical and mechanical processes in order to be suspended at the optimal size and composition. Subsequently, a polymer extrusion technique is employed for the fabrication of each film, while the molten polymer is mixed with the treated metal oxide nanoparticles. Transmission and reflection measurements are performed in order to map the optical properties of the fabricated, nanostructured films in the UV, VIS and IR. The results substantiate the capability of the overall methodology to regulate the optical properties of the films depending on the type of nanoparticle formation which can be adjusted both in size and composition.

Polarization switching in nanoscale ferroelectrics

The polarization switching kinetics of ferroelectric crystals and the transition between homogeneous and domain switching in the nanoscale ferroelectric films are considered. Homogeneous switching according to the Ginzburg-Landau-Devonshire (LGD) theory is possible only in two-dimensional ferroelectrics. A review of the experimental results for two-dimensional films of a ferroelectric polymer, barium titanate nanofilms, and hafnium oxide-based films is given. For ultrathin polymer films, the results are confirmed by first-principle calculations. Fitting of the transition region from homogeneous to domain switching by sigmoidal Boltzmann functions is carried out.

XANES Study of Tribofilm Formation With Low Phosphorus Additive Mixtures of Phosphonium Ionic Liquid and Borate Ester

The development of low phosphorus engine oils is important to minimize phosphorus-induced exhaust catalyst poisoning and resulting in harmful emissions. In this study, low phosphorus oil formulations were prepared by using an ashless additive mixture of borate ester (SB) with ionic liquid composed of a phosphonium cation and phosphate anion (P_DEHP) at 350 and 700 ppm phosphorus. Tribological properties of this binary additive system were evaluated using a reciprocating cylinder on a flat test configuration. Favorable interaction between P_DEHP and SB resulted in a significant reduction in friction coefficient and wear volume, in particular for P_DEHP(700P) + SB oil blend. Time-scale analysis of tribofilm formation was determined by running the tribological experiments for 5, 15, and 60 min duration. Electrical contact resistance (ECR) results revealed that the addition of P_DEHP at 350 ppm of phosphorus to SB at 500 ppm of boron can reduce the incubation time from 300 to 100 s for stable tribofilm formation. X-ray absorption near-edge spectroscopy (XANES) analysis of tribofilms indicates that the tribofilm mechanism for additive mixtures of P_DEHP and SB initially involves the formation of boron oxide-based films, which later interact with phosphorus to form boron phosphates in addition to iron phosphates. Incorporation of the high amount of boron phosphates in addition to boron oxide/acid and iron phosphates in the tribofilms contributed to the improved tribological performance of P_DEHP(700P) + SB oil. XANES results reveal that tribofilms formed due to the interaction of SB and P_DEHP evolve to a cross-linked structure, wherein the chain length of polyphosphates is increased with the increase in rubbing time.

Towards high performance flexible planar supercapacitors: In-situ laser scribing doping and reduction of graphene oxide films

A novel, scalable, single-step and low-synthesis temperature fabrication approach is proposed for real-time doping, reduction, and patterning of graphene oxide-based films supported on flexible polyethylene terephthalate (PET) substrate using a CO2 Laser system. Laser reduced graphene oxide (LrGO), nitrogen-doped laser reduced graphene oxide (N-LrGO), and sulfur-nitrogen co-doped laser reduced graphene oxide (SN-LrGO) planar supercapacitors (PSCs) are readily fabricated with the proposed approach. Structural and elemental characterizations prove the successful integration of nitrogen and sulfur atoms into the graphene framework with high contents up to 3.71 at% N and 1.82 at% S, and at a low density of structural defects. An areal capacitance as high as 13.8 mF cm−2 at 10 mV s−1 and a maximum power density of 151.7 mW cm−3 at an energy density of 0.152 mWh cm−3 is achieved by SN-LrGO PSC composed of 10 interdigitated fingers with an excellent retention rate after 2000 charging/discharging cycles at 0.125 mA cm−2. Furthermore, higher operating voltage window and current ratings are easily achieved via series and parallel combinations of SN-LrGO PSCs directly on the same substrate. This manifests the versatility of the proposed approach for producing flexible and high-performance graphene-based electrochemical storage devices.

Reduced graphene oxide-based Transparent Conductive Films: The preliminary review of reductant materials agent

This review aims to present reductant materials that can be used to reduce the oxygen content of graphene oxide which supports the manufacturing of TCF so the development of TCF increases in the future. Reducing agents are separated into two types i.e. toxic materials and green materials. The method that was used to make TCF based on graphene oxide reduction in this paper review was drop-casting, spray coating, vacuum filtration, and spin coating. From the results of the study, it was found that the resistance sheet for each reductant material ranged from 3.4×109 to 52.2 Ω/sq. Besides, the use of toxic reductant materials still dominates as a reducing agent because it has a lower sheet resistance than the green reductant materials. Although there are still many challenges in the study of the transparent conductive film based on reduced graphene oxide, the information in this review is expected to contribute to the development of various optoelectronic devices, especially for the development of flexible, portable, and smart device.