Films Of Different Compositions Research Articles

Second harmonic generation in structures with inhomogeneous magnetization distribution

The study of the interaction of laser radiation with ferromagnetic materials is not only an inexhaustible source of new effects, but also provides an opportunity to study magnetic media at the micro- and macroscale. This is especially important for the development of modern technologies to produce structures with fundamentally new magnetic and optical properties that can’t be observed in natural materials. The review presents the results of studies of nonlinear optical effects in ferromagnetic nano- and microstructures, as well as films of different compositions. The unique capabilities of nonlinear-optical diagnostics of anisotropic, vortex, exchange-biased magnetic structures, visualization of the micromagnetic structure of the surface layers of ferrite garnets, based both on the high sensitivity of the optical second harmonic generation method to the magnetic state of nanostructures and interfaces, and on the symmetry properties of high-order magnetizationinduced susceptibility tensor have been demonstrated.

Optimizing magneto-ionic performance in structure/composition-engineered ternary nitrides

Magneto-ionics, an emerging approach to manipulate magnetism that relies on voltage-driven ion motion, holds the promise to boost energy efficiency in information technologies such as spintronic devices or future non-von Neumann computing architectures. For this purpose, stability, reversibility, endurance, and ion motion rates need to be synergistically optimized. Among various ions, nitrogen has demonstrated superior magneto-ionic performance compared to classical species such as oxygen or lithium. Here, we show that ternary Co1−xFexN compound exhibits an unprecedented nitrogen magneto-ionic response. Partial substitution of Co by Fe in binary CoN is shown to be favorable in terms of generated magnetization, cyclability and ion motion rates. Specifically, the Co0.35Fe0.65N films exhibit an induced saturation magnetization of 1,500 emu/cm3, a magneto-ionic rate of 35.5 emu/(cm3·s) and endurance exceeding 103 cycles. These values significantly surpass those of other existing nitride and oxide systems. This improvement can be attributed to the larger saturation magnetization of Co0.35Fe0.65 compared to individual Co and Fe, the nature and size of structural defects in as-grown films of different composition, and the dissimilar formation energies of Fe and Co with N in the various developed crystallographic structures.

Memristive effect in niobium oxide thin films obtained by the pulsed laser deposition

NbOx thin films demonstrating the analog resistive switching characteristics in planar geometry were fabricated by the droplet-free pulsed laser deposition from Nb metal targets. The memristive properties of the films were controlled by tuning the oxygen pressure from 0.7 to 8 Pa and the wavelength of the ablative laser (λ = 248 nm or λ = 532 nm). The stoichiometry of the NbOx films was controlled by the X-ray photoelectron spectroscopy, optical and electrical investigations. Variation of the film thickness from 20 to 50 nm affects the resistive switching characteristics. The 20 nm NbO2 films obtained at the oxygen pressure of 1.3 Pa show a volatile memristive switching with a memory window of ON/OFF resistances ∼ 101 after 500 direct current cycles at an operating voltage of 4.5 V. The 30 nm Nb2O5 films fabricated at the oxygen pressure of 4 Pa, showed a gradual increase in device conductivity with successive positive voltage sweeps with an amplitude of +5 V, which is characteristic of non-volatile memristive switching. Thus, the use of NbOx memristive films of different compositions and crystallinity degree will allow creating neuromorphic systems based on the same material by controlling the memristive behavior by the laser synthesis conditions.

Synthesis of active packaging films from Lepidium sativum gum/polyvinyl alcohol composites and their application in preserving cheddar cheese

The interest in active packaging for extending food shelf life has increased lately. Moreover, the negative impact of synthetic plastic wastes on the environmental motivated the researchers to seek for bio-based alternatives. In this context, active packaging film made of a composite composed of Lepidium sativum extract (LSE), polyvinyl alcohol (PVA), and a fixed amount of hyperbranched polyamide amine (PAMAM) were prepared. The chemical, thermal, and mechanical properties of the film were investigated. Moreover, we examined the extract’s constituents and antioxidant properties. Cheddar cheese samples were coated with films of different compositions. The samples coated with active packaging films showed a longer preservation time of up to 4 weeks compared to other samples, which noticeably deteriorated. The films showed potent antimicrobial activity against five food-borne bacteria: three gram-negative bacteria including Escherichia coli O157.H7, Pseudomonas aeruginosa, and Salmonella Typhimurium, and two gram-positive bacteria, Listeria monocytogenes, and Staphylococcus aureus. Applying PVA films containing LSE improved the microbiological quality and delayed the visible decay of cheddar cheese. The oxidizability of the fat extracted from different cheese samples was 0.40–0.98, confirming oxidation resistance. Finally, cheese samples coated with treated films were protected from forming trans fats compared to other samples, demonstrating the effectiveness of modified films as antioxidant, antimicrobial, and food-preserving packaging.

A Universal Surface Treatment for p-i-n Perovskite Solar Cells.

Perovskite interfaces critically influence the final performance of the photovoltaic devices. Optimizing them by reducing the defect densities or improving the contact with the charge transporting material is key to further enhance the efficiency and stability of perovskite solar cells. Inverted (p-i-n) devices can particularly benefit here, as evident from various successful attempts. However, every reported strategy is adapted to specific cell structures and compositions, affecting their robustness and applicability by other researchers. In this work, we present the universality of perovskite top surface post-treatment with ethylenediammonium diiodide (EDAI2) for p-i-n devices. To prove it, we compare devices bearing perovskite films of different composition, i.e., Sn-, Pb-, and mixed Sn-Pb-based devices, achieving efficiencies of up to 11.4, 22.0, and 22.9%, respectively. A careful optimization of the EDAI2 thickness indicates a different tolerance for Pb- and Sn-based devices. The main benefit of this treatment is evident in the open-circuit voltage, with enhancements of up to 200 mV for some compositions. In addition, we prove that this treatment can be successfully applied by both wet (spin-coating) and dry (thermal evaporation) methods, regardless of the composition. The versatility of this treatment makes it highly appealing for industrial application, as it can be easily adapted to specific processing requirements. We present a detailed experimental protocol, aiming to provide the community with an easy, universal perovskite post-treatment method for reliably improving the device efficiency, highlighting the potential of interfaces for the field.

Design of Shape Memory Micro-Actuator Modules with Sequential Actuation

Shape memory alloy film-based micro-actuators have their behaviour controlled by a change in the thermomechanical stress that occurs in the bimorph - shape memory alloy film plus substrate assembly. The modification of the composition of the shape memory alloy leads to a change of the transformation temperature and implicitly of the temperature at which the stress change takes place in the bimorph. The design of micro-actuator blocks in which the composition and/or the temperature control mode of each micro-actuator in the block allows to obtain successive or sequential transformation sequences. The paper analyses the case of cantilever actuator modules with films of different compositions, deposited on the same substrate. It is highlighted how the composition of the alloy film with shape memory influences the modification of the curvature of bimorph cantilever type actuators in the studied block.

Relationship between the Formation of Magnetic Clusters and Hexagonal Phase of Gold Matrix in AuxFe1-x Nanophase Thin Films.

AuxFe1−x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, Superconducting Quantum Interference Device magnetometry and Conversion Electron Mössbauer Spectroscopy. It was proven that depending on the preparation conditions, different configurations of defect α-Fe magnetic clusters, i.e., randomly distributed or auto-assembled in lamellar or filiform configurations, can be formed in the Au matrix. A close relationship between the Fe clustering process and the type of the crystalline structure of the Au matrix was underlined, with the stabilization of a hexagonal phase at a composition close to 70 at. % of Au and at optimal thickness. Due to different types of inter-cluster magnetic interactions and spin anisotropies, different types of magnetic order from 2D Ising type to 3D Heisenberg type, as well as superparamagnetic behavior of non-interacting Fe clusters of similar average size, were evidenced.

Simple Methods for Evaluating Acid Permeation and Biofilm Formation Behaviors on Polysiloxane Films.

The sulfuric acid permeation and biofilm formation behaviors of polysiloxane films have been investigated, and simple methods for evaluating the sulfuric acid permeation and biofilm formation behaviors have been proposed in this paper. The polysiloxane films used in these experiments were practically impermeable to the aqueous sulfuric acid solution, and the amount of biofilm formation varied depending on the composition of the films. Further, the amount of sulfuric acid permeation can be estimated by measuring the polarization curves of polysiloxane films with different thicknesses formed on iron electrodes. By measuring the adhesion work of pure water and simulated biofilm droplets on polysiloxane films of different compositions, we can estimate the resistance of biofilm formation on the polysiloxane films.

A high throughput study of both compositionally graded and homogeneous Fe–Pt thin films

Compositionally graded Fe–Pt thin films were prepared on stationary 100 mm Si substrates by magnetron sputtering a base target of Fe on which a piece of Pt is asymmetrically positioned. Energy dispersive X-ray analysis was used to map the variation in film composition across the substrate, as a function of the size of the Pt piece. A scanning polar Magneto-Optical-Kerr-Effect system was used to probe the influence of composition and post-deposition annealing conditions (temperature and time) on coercivity. In this way, the maximum coercivity achievable for the sputtering system used could be established in a high throughput fashion. The evolution in coercivity with composition was correlated with the formation of L10 FePt and changes in its lattice parameters, as determined by scanning X-ray diffraction. High throughput coercivity mapping was then carried out on homogeneous Fe–Pt thin films of different compositions treated to different annealing conditions. This study serves as a step towards the integration of coercive FePt films into collectively fabricated devices.

Mechanism analysis of laser coloring of Ti alloy by optical simulation

The effects of laser energy density on the coloring effect were examined using a nanosecond fiber laser to color the surface of a TC4 Ti alloy. The surface of samples turns yellow, orange, purple, and blue as the single pulse energy density increases. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) results demonstrated that a mixed film containing TiN and TiO was formed on the surface of samples after laser coloring. The TiN content in the mixed film reduced with increase in single pulse energy density, whereas the TiO content increased. Based on the equivalent medium and optics theory, the SCOUT optical simulation software was used to create a three-layer structure model of ambient/mixed film/Ti alloy substrate. The superposition of reflection and interference in the mixed film was simulated to examine the effect of the mixed film’s composition and thickness on the reflective spectrum of sample. The reflective spectrum of different colors obtained by simulations and tests was extremely consistent, and the simulation composition and thickness of the mixed film were consistent with the tested results, indicating that the laser coloring mechanism is influenced by light interference between mixed films of different composition and thickness formed on the sample surface.

Thermoplastic sago starch nanocomposites wound dressing fortified with antibiotic-modified HNT

Starches were reported to promote wound healing. However, the hydrophilicity of starch help absorbs the exudates from the wounds during the healing process, but it also enables a bacterial infection that slows the healing process. Halloysite nanotubes (HNT) are attracting many biological technologies because of their high loading capacity and biocompatibility. This paper investigates the modified HNT as a carrier for antimicrobials agent in wound healing materials. Halloysite was modified by dispersing it with chloramphenicol solution using a magnetic stirring method. Thermoplastic sago Starch (TPSS)/modified HNT (MHNTs) biocomposite films of different compositions (0.25, 0.5, 0.75 and 1 wt. % HNT) were then developed using the solution casting method. SEM revealed that modified HNT shows good dispersion on the TPSS matrix. With the introduction of modified HNT, the FTIR peaks of TPSS have altered at the peak of 3693.21 cm-1 and 1040.05 cm-1. In addition, modified HNT reduced the water absorption rate of the TPSS films. Furthermore, modified HNT showed good resistance to bacterial culture and significantly reduced the biodegradability rate of TPSS compared to pristine HNT. From the findings, HNT can be a potential carrier for antibacterial agents to withstand bacterial attacks.

Fabrication and Characterisation of PP/TS Biocomposites

Biocomposites are eco-friendly composite materials formed by the combination of any polymer matrix and the reinforcement of any natural fiber. This particular composite is gaining more attention in research field in order to reduce the utilization of inorganic fillers in the reinforcement of thermoplastics and biodegradable plastics. In this study, we used various amounts of turmeric spent (TS) viz, 5%, 7%, 10%, 15%, 20% and 25% (w/w) for the fabrication of Polypropylene/TS composites. These various composition mixtures are blended and melt on a Haake mixer, then it is placed over a compression mould of 2mm thickness and forms composite films of different composition. The developed composites were characterized using different techniques such as scanning electron microscopy, contact angle measurement and water absorption. SEM images clearly shows the presence of TS content in biocomposites. From contact angle measurement, it is clear that the 7% PP/TS composite shows better hydrophobic nature. From absorption measurement technique, the higher composition samples show better absorption capacity due to the presence of OH-group within the turmeric spent.

Characterization and Performance Analysis of BST-Based Ferroelectric Varactors in the Millimeter-Wave Domain

We present the realization and analysis of the microwave performances of interdigited varactors integrating thin ferroelectric layers of barium and strontium titanate (BaxSr1−xTiO3). Devices based on ferroelectric films of different compositions (x = 0.8 and x = 0.5) have been characterized in the millimeter-wave domain, from 200 MHz to 110 GHz. By applying different bias voltages, the tunability of the capacitance can reach up to 40% for the Ba0.8Sr0.2TiO3 composition, under relatively low applied electric fields of about 167 kV/cm. These promising characteristics allow the integration of the varactor devices in tunable antennas for a large frequency domain, from the microwaves to the millimeter waves range.

Enhanced Oxygen Reduction Activity on Silver-Palladium Alloyed Thin Film Electrocatalysts in Alkaline Media

The oxygen reduction reaction (ORR) requires a large overpotential, which is a factor limiting the large-scale deployment of clean energy technologies such as hydrogen fuel cells (H2 FCs), direct methanol FCs, and metal-air batteries. Designing strategies to enhance catalyst activity, stability, and selectivity for the ORR is one method towards enhancing H2 FCs technology. Many predicted active catalysts are not stable in acidic media, resulting in limited catalyst options for standard proton exchange membrane H2 FCs. Some theoretically active, yet acid-unstable, catalysts, such as Ag, can be stabilized in alkaline media making anion exchange membrane (AEM) fuel cells an attractive alternative. Ag-rich catalysts are specifically ideal because of their low cost and Ag’s high abundance relative to other catalysts materials such as Pt. We have previously shown that Cu atoms in Ag-Cu alloys can be modified by Ag to produce an enhanced activity for the ORR at high Cu atomic loadings. Better understanding the nature of intrinsic enhancements for the ORR on alloys will help in the development of new ORR alloy electrocatalysts.Besides, Ag-Cu alloys, several other Ag-bimetallics (including Ag-Pd, Ag-Mn, Ag-Fe, and Ag-Co) have been predicted to be good catalysts for the ORR. Alloying could lead to activity enhancements via changes in electronic structure, strain, and/or localized geometry. The activity of Ag-based catalysts for the ORR needs to be enhanced. One strategy to do this is to alloy Ag, which binds oxygen adsorbates too weakly, to a metal such as Pd, which binds oxygen adsorbates too strongly and is also very active. In this work, we use a thin film model system to show intrinsic activity enhancements for the ORR on Ag-Pd catalysts, resulting in activities higher than those of both parent materials even after reducing the Pd content by half.Ag-Pd thin films of different compositions are prepared using electron beam physical vapor co-deposition. X-ray diffraction indicate alloying across the full compositional range tested and atomic force microscopy shows that the films are highly flat (roughness factor < 1.02). Electrochemical testing in 0.1 M KOH shows significant activity improvements for the Ag-Pd films. The films with +40 at% Pd have activities, at 0.9 V vs RHE, greater than the linear combination of pure Ag and Pd activities. On a Pd content basis, the thin films with +50 at% Pd exhibit higher kinetic current densities, at 0.9 V vs RHE, than both pure Ag and Pd. Ag10Pd90 is the most enhanced thin film, both on a surface area and Pd loading bases, demonstrating a 5-fold activity enhancement relative pure Pd. By correlating density functional theory with experimental activity and physical characterization measurements, we hypothesize that Ag is modifying Pd’s surface electronic structure to adsorb OH more weakly via ligand and strain effects. These enhanced Ag-Pd ORR catalysts could facilitate the large-scale implementation of efficient clean energy electrochemical systems such as fuel cells and metal-air batteries.

Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition

Chromogenic thin films are crucial building blocks in smart windows to modulate the flux of visible light and heat radiation into buildings. Electrochromic materials such as tungsten oxide are well established in those devices. Sputter deposition offers a well-suited method for the production of such layers, which can also be used on an industrial scale. Tungsten oxide films were prepared by means of reactive ion-beam sputter deposition. The choice of distinct gas mixtures as well as the growth temperature during the sputtering process allows to tune the properties of the resulting layers. Especially, the variation in the growth temperatures was found to have an impact on the structure of the resulting samples and, as a consequence, on their optical and electrochemical properties. By specific choice of the reactive gas, the deposition of colorless transparent as well as blue films of different composition is possible. The optical transmittance in the visible spectral range was up to 75% for as-deposited oxygen-rich layers. Additionally, hydrogen-doped tungsten oxide samples were grown. Superior electrochromic switching was observed for H^{+}-doped layers, probably by some kind of preconditioning. This resulted in a value for the standardized optical coloration efficiency of 26.5 cm^{2}/C.

Advance application of Raman spectroscopy for quantitative analysis of noncrystalline components in thin films of poly(ε‐caprolactone)/poly(butadiene) blends

AbstractA quantitative analysis method for the distribution of noncrystalline poly(butadiene) component in poly(ε‐caprolactone)/poly(butadiene) (PCL/PB) binary blends have been analyzed by advance application of Raman spectroscopy, optical microscopy, and differential scanning calorimetry (DSC) techniques. Thin films of different compositions of PCL/PB binary blends were prepared from solution and isothermally crystallized at a certain temperature. After calibration with real data, quantitative analyses by Raman spectroscopy revealed the amorphous PB are trapped inside the PCL crystals. Polarized optical microscopy and real time atomic force microscopy were used to collect data for the crystal morphology and crystal growth rate. For pure PCL crystals, a morphology of truncated lozenge shape was observed, independent of crystallization temperature and regardless of the blends compositions. For the pure PCL and their blends, almost unique crystal growth rate was found. The miscibility behaviors using DSC were drawn through melting point depression method. The Hoffman‐Weeks extrapolations of the blends were found to be linear and identical with those of the neat PCL. The interaction parameter for the blends indicating that the PCL and PB blends have no intermolecular interaction, confirming the blends are immiscible. Despite the immiscibility of the blend, the PCL crystals do not bend during the growth process and do not reduce the growth rate as they do for miscible blend systems.

The Influence of γ Radiation on the Dielectric Properties of Ferroelectric Langmuir–Blodgett Films

Dielectric relaxation of Debye type has been found for thin vinylidene fluoride‒trifluoroethylene copolymer films of different composition, fabricated by the Langmuir–Blodgett (LB) technique. The influence of γ radiation on the dielectric response of LB films is studied. It is established that the relaxation time increases after the γ irradiation, the phase transition is observed at a lower temperature, and the temperature hysteresis is reduced.

Nanozyme-Triggered DNA Release from Alginate Films

Alginate hydrogel thin films of different compositions were electrochemically produced at an electrode surface, and their interfacial reactions were studied for biomolecule release. Nanozyme catalytic species represented by Au nanoparticles were used to trigger biomolecule release from an Fe3+-cross-linked alginate hydrogel film upon receiving a glucose signal. The oxidase-mimicking reaction catalyzed by Au nanoparticles resulted in the production of H2O2, which yielded free radicals through a Fenton-type reaction in the presence of iron cations. The generated free radicals resulted in degradation/dissolution of the alginate matrix and stimulated the release of entrapped DNA molecules. The systematic study addressed the issues of the uncontrolled leakage of the DNA molecules from alginate hydrogel and demonstrated the signal-triggered DNA release in systems with various configurations, ranging from a simple addition of H2O2 to the bulk solution to the in situ production of H2O2 by the nanozyme coentrapped in the alginate film. The present study adds an additional feature to the multioperational functions of nanozymes, representing their use in signal-controlled biomolecule-releasing systems.

Epitaxial growth of full range of compositions of (1 1 1) PbZr1-xTixO3 on GaN

Integrating functional complex oxides with conventional (“non-oxide”) semiconductors emerges to be an important research field and has been attracting great interest. Because of their superior intrinsic material properties, such as a relatively high dielectric constant and polarization, the utilization of PbZr1-xTixO3 (PZT) materials as a dielectric layer is expected to greatly improve the performance of the GaN high electron mobility transistor. The functional PbZr1-xTixO3 exhibits quite different crystal structures and consequently physical properties depending on the composition. In this work we report the growth of full range of compositions of PZT films on MgO buffered GaN substrates. Besides revealing the temperature effect on phase formation and surface morphology, we demonstrated the strong effect of composition on the growth: pure (1 1 1) phase is formed in Ti-rich PZT (x > 0.48) while pyrochlore impurity phase is found in Zr-rich PZT (x < 0.48). By introducing an ultrathin Ti-rich PZT seed layer, we are able to achieve epitaxial growth of Zr-rich PZT. The epitaxial PZT films of different composition all exhibit good ferroelectric properties, showing great promise for future GaN device applications.

Magnetic properties of GdCo-Al2O3 composite films

The purpose of this work was to synthesize and study magnetic properties of composite films consisting of Gd-Co ferrimagnetic system and Al2O3 dielectric matrix. GdCo-Al2O3 films of different composition were synthesized by magnetron co-sputtering of Gd, Co, and Al2O3 targets in an Ar atmosphere. Investigation of magnetic properties was carried out using a vibrating sample magnetometer in the temperature range from 10 to 300 K. The obtained results showed that in the composite system with a volume of dielectric material exceeding 50% a superparamagnetic state is realized, indicating granular microstructure. In this case, the granules show signs of ferrimagnetic ordering.