Two-phase Films Research Articles

Expanded Stability of Layered SnSe-PbSe Alloys and Evidence of Displacive Phase Transformation from Rocksalt in Heteroepitaxial Thin Films.

Bulk PbSnSe has a two-phase region, or miscibility gap, as the crystal changes from a van der Waals-bonded orthorhombic 2D layered structure in SnSe-rich compositions to the related 3D-bonded rocksalt structure in PbSe-rich compositions. This structural transition drives a large contrast in the electrical, optical, and thermal properties. We realize low temperature direct growth of epitaxial PbSnSe thin films on GaAs via molecular beam epitaxy using an in situ PbSe surface treatment and show a significantly reduced two-phase region by stabilizing the Pnma layered structure out to Pb0.45Sn0.55Se, beyond the bulk limit around Pb0.25Sn0.75Se at low temperatures. Pushing further, we directly access metastable two-phase films of layered and rocksalt grains that are nearly identical in composition around Pb0.50Sn0.50Se and entirely circumvent the miscibility gap. We present microstructural and compositional evidence for an incomplete displacive transformation from a rocksalt to layered structure in these films, which we speculate occurs during the sample cooling to room temperature after synthesis. In situ temperature-cycling experiments on a Pb0.58Sn0.42Se rocksalt film reproduce characteristic attributes of a displacive transition and show a modulation in electronic properties. We find well-defined orientation relationships between the phases formed and reveal unconventional strain relief mechanisms involved in the crystal structure transformation using transmission electron microscopy. Overall, our work adds a scalable thin film integration route to harness the dramatic contrast in material properties in PbSnSe across a potentially ultrafast crystalline-crystalline structural transition.

Ion- and temperature-induced 3-dimensional nanoscale patterning in Ti1-xAlxN deposited by High Power Impulse Magnetron Sputtering

We report on surface-driven self-organization in the TiN-AlN binary system during ion-assisted deposition at elevated temperatures. With an Al:Ti ratio slightly above the boundary of stable cubic growth, various morphologies from single-phase films to highly ordered two-phase films with v-shaped and oblique, striped structures were obtained. The high metal ion fractions and high ion energies obtained by High Power Impulse Magnetron Sputtering result in unique morphologies that are not accessible by conventional magnetron sputtering. A comprehensive structural and chemical analysis of the two-phase films is presented to enlighten the mechanism of phase separation and crystallographic orientation evolution.

Controlled Electronic and Magnetic Landscape in Self-Assembled Complex Oxide Heterostructures.

Complex oxide heterointerfaces contain a rich playground of novel physical properties and functionalities, which give rise to emerging technologies. Among designing and controlling the functional properties of complex oxide film heterostructures, vertically aligned nanostructure (VAN) films using a self-assembling bottom-up deposition method presents great promise in terms of structural flexibility and property tunability. Here, the bottom-up self-assembly is extended to a new approach using a mixture containing a 2Dlayer-by-layer film growth, followed by a 3D VAN film growth. In this work, the two-phase nanocomposite thin films are based on LaAlO3 :LaBO3 , grown on a lattice-mismatched SrTiO3001 (001) single crystal.The 2D-to-3D transient structural assembly is primarily controlled by the composition ratio, leading to the coexistence of multiple interfacial properties, 2D electron gas, and magnetic anisotropy. This approach provides multidimensional film heterostructures which enrich the emergent phenomena for multifunctional applications.

Synergistically enhanced flexibility, mechanical strength and microwave absorption performances of TPE-based hybrid films via thermally assisted homogeneous separation technology

With the ever-growing electromagnetic (EM) wave pollution and the rising demand of flexible absorbing materials pasted onto the surfaces of different geometric surfaces, it is urgent to develop high-efficiency EM wave absorption films with good flexibility and mechanical strength. Traditional processing methods endow the film superior features that can be adapted to targeted geometric surfaces and complex conditions, however, the durability is not satisfactory. Confronted with the tough problem, in this work, optimized thermally assisted homogeneous separation technology was proposed to fabricate the thermoplastic elastomer-based magnetic/dielectric two-phase mixed EM wave absorption films, which can achieve good flexibility, machinability, mechanical strength, as well as excellent EM wave absorption performances due to the uniform filling of elastoplastic skeletons and chain-bridge effect between chains and particles. Benefitting from these merits, the as-prepared films exhibit good flexibility and fine mechanical properties, like good deformability (300% of the deformation compared to its original length) and low elastic coefficient (323.8 Pa). Moreover, good EM wave absorption performances can also be balanced, for example, broad effective bandwidth (>14 GHz) and tunable frequency response from high frequency to low frequency. In all, this work opens up a new pathway to realize the integration of strong EM response, good flexibility, and fine mechanical properties, and the obtained films exhibit great potentials as flexible EM wave absorption materials that can be pasted on or peeled off the targeted surfaces at any time.

Ordered hybrid metamaterial of La0.7Sr0.3MnO3–Au vertically aligned nanocomposites achieved on templated SrTiO3 substrate

Coupled multifunctionalities in nanocomposite thin films offer a pathway toward future integration of device applications. The oxide–metal two-phase nanocomposite thin films in a vertically aligned nanocomposite (VAN) morphology allow for unique structural control and functionality tuning toward future nanoscale devices. However, achieving in-plane ordering of the two phases remains challenging. In this work, we demonstrate an initial success of in-plane long-range ordering achieved in a new oxide–metal VAN system, La0.7Sr0.3MnO3 (LSMO)–Au, through annealed SrTiO3 (STO) substrates. The combination of plasmonic Au and ferromagnetic LSMO enables multifunctionalities, including magneto-optic coupling, hyperbolic dispersion, and tunable ferromagnetic anisotropy. Beyond this LSMO–Au VAN system demonstrated in this work, the long-range ordered two-phase structures induced by perovskite substrate surface terraces can be applied to other oxide–metal VAN systems.

Effect of Ultraviolet Radiation and Electric Field on the Conductivity of Structures Based on α- and ε-Ga2O3

The effect of ultraviolet radiation and a strong electric field on the conductivity of structures based on two types of polymorphic gallium-oxide films is studied. Both types of Ga2O3 films are obtained by hydride vapor phase epitaxy on smooth and patterned sapphire substrates with the orientation (0001). In one and the same process, on smooth substrates, α-Ga2O3 films are obtained and, on patterned substrates, gallium-oxide films with regular structures perpendicular to the substrate containing alternating regions of α- and e-phases are deposited. Resistive structures based on two-phase films exhibit a transition from a state with low resistance to a state with high resistance under the action of radiation with λ = 254 nm and a strong electric field. The time of response to UV radiation is 5 s, and the recovery time is shorter than 1 s.

Properties of Resistive Structures Based on Gallium Oxide Polymorphic Phases

The effect of UV radiation and a strong electric field on the current–voltage characteristics of resistive structures based on polymorphic gallium oxide (Ga2O3) films is discussed. Ga2O3 films were deposited by the method of halide vapor phase epitaxy (HVPE) on smooth and patterned sapphire substrates with a baseline orientation (0001). α-Ga2O3 films grow on smooth substrates, and gallium oxide films containing α and e phases grow on patterned ones. A switching effect was detected in the metal/Ga2O3/metal structures based on two-phase films. When exposed to radiation with λ = 254 nm and a strong electric field, the structures pass from a low resistive state to a high resistive state.

Transport and magnetic phenomena in ZnO-С thin-film heterostructures

Abstract ZnO- and C-based heterostructures were fabricated by the layer-by-layer deposition technique using the ion-beam sputtering process. Structure, electrical and magnetic properties of fabricated heterostructures are discussed. The two-phase (ZnO and C) films are evolved into a multilayer structure, consisting of amorphous carbon and crystalline ZnO layers when the bilayer thickness increases. When carbon is added to ZnO, its electrical resistivity reduces. The conduction mechanism changes from the variable-range hopping in a narrow energy band to the nearest neighbors hopping in ZnO–C films with a thickness of h

Свойства резистивных структур на основе полиморфных фаз оксида галлия

The influence of UV radiation and a strong electric field on the I–V characteristics of resistive structures based on polymorphic films of gallium oxide (Ga2O3) is considered. Ga2O3 films were deposited by the method of chloride vapor-phase epitaxy (HVPE) on smooth and structured sapphire substrates with a baseline (0001) orientation. α-Ga2O3 films were produced on smooth substrates, and deposition on patterned sapphire substrates templates produced a mixed structure containing both α-Ga2O3 and ε-Ga2O3. The switching effect was observed in metal / Ga2O3 / metal structures based on two-phase films. Structures pass from a low-resistance (LR) state to a high-resistance (HR) state when exposed to a strong electric field and radiation with λ = 254 nm.

Design of Friction, Morphology, Wetting, and Protein Affinity by Cellulose Blend Thin Film Composition.

Cellulose derivate phase separation in thin films was applied to generate patterned films with distinct surface morphology. Patterned polymer thin films are utilized in electronics, optics, and biotechnology but films based on bio-polymers are scarce. Film formation, roughness, wetting, and patterning are often investigated when it comes to characterization of the films. Frictional properties, on the other hand, have not been studied extensively. We extend the fundamental understanding of spin coated complex cellulose blend films via revealing their surface friction using Friction Force Microscopy (FFM). Two cellulose derivatives were transformed into two-phase blend films with one phase comprising trimethyl silyl cellulose (TMSC) regenerated to cellulose with hydroxyl groups exposed to the film surface. Adjusting the volume fraction of the spin coating solution resulted in variation of the surface fraction with the other, hydroxypropylcellulose stearate (HPCE) phase. The film morphology confirmed lateral and vertical separation and was translated into effective surface fraction. Phase separation as well as regeneration contributed to the surface morphology resulting in roughness variation of the blend films from 1.1 to 19.8 nm depending on the film composition. Friction analysis was successfully established, and then revealed that the friction coefficient of the films could be tuned and the blend films exhibited lowered friction force coefficient compared to the single-component films. Protein affinity of the films was investigated with bovine serum albumin (BSA) and depended mainly on the surface free energy (SFE) while no direct correlation with roughness or friction was found. BSA adsorption on film formed with 1:1 spinning solution volume ratio was an outlier and exhibited unexpected minimum in adsorption.

Studying the Composition and Phase State of Thin PZT Films Obtained by High-Frequency Magnetron Sputtering under Variation of Working Gas Pressure

Variation of the working gas pressure (from 8 to 2 Pa) during RF magnetron sputtering deposition of thin perovskite lead zirconate titanate (PZT) films revealed strong changes in their lead content, which decreased below the stoichiometric level and led to the formation of a two-phase (perovskite–pyrochlore) structure upon subsequent high-temperature annealing. Measurements of the composition of perovskite islands in the two-phase films showed that the lead content in these islands was equal to or greater than stoichiometric. These results lead to the conclusion that the obtained PZT films are free of lead vacancies.

AlN-based hybrid thin films with self-assembled plasmonic Au and Ag nanoinclusions

Aluminum nitride (AlN)-based two-phase nanocomposite thin films with plasmonic Au and Ag nanoinclusions have been demonstrated using a one-step thin film growth method. Such AlN-based nanocomposites, while maintaining their wide bandgap semiconductor behavior, present tunable optical properties such as bandgap, plasmonic resonance, and complex dielectric function. Depending on the growth atmosphere, the metallic nanoinclusions self-organized into different geometries, such as nano-dendrites, nano-disks, and nanoparticles, providing enhanced optical anisotropy in-plane and out-of-plane. The infrared transmission measurements demonstrate the signature peaks of AlN as well as a broad transmission window attributed to the plasmonic nanoinclusions. This unique AlN-metal hybrid thin film platform provides a route to modulate the optical response of wide bandgap III-V nitride semiconductors towards infrared sensing or all optical based integrated circuits.

Исследование состава и фазового состояния тонких пленок цирконата-титаната свинца, полученных высокочастотным магнетронным осаждением, при изменении давления рабочего газа

AbstractVariation of the working gas pressure (from 8 to 2 Pa) during RF magnetron sputtering deposition of thin perovskite lead zirconate titanate (PZT) films revealed strong changes in their lead content, which decreased below the stoichiometric level and led to the formation of a two-phase (perovskite–pyrochlore) structure upon subsequent high-temperature annealing. Measurements of the composition of perovskite islands in the two-phase films showed that the lead content in these islands was equal to or greater than stoichiometric. These results lead to the conclusion that the obtained PZT films are free of lead vacancies.

A study on the effects of temperature and substrate structure on the templated two-phase film growth via a hybrid model

Templated growth of two-phase thin films can achieve desirably ordered microstructures. In such cases, the microstructure of the growing films follows the topography of the template. By combining the Potts model Monte Carlo simulation and the “level set” method, an attempt was previously made to understand the physical mechanism behind the templated growth process. In the current work, this model is further used to study the effect of two parameters within the templated growth scenario, namely, the temperature and the geometric features of the template. The microstructure of the thin film grown with different lattice temperatures and domes is analyzed. It is found that within a moderate temperature range, the effect of geometric features took control of the ordering of the microstructure by its influence on the surface energy gradient. Interestingly, within this temperature range, as the temperature is increased, an ordered microstructure forms on a template without the optimal geometric features, which seems to be a result of competition between the kinetics and the thermodynamics during deposition. However, when the temperature was either above or below this temperature range, the template provided no guide to the whole deposition so that no ordered microstructure formed.

Phase map, composition and resistivity of reactively magnetron sputtered and annealed Ta–N films

Thin films of tantalum nitride (Ta–N) have been prepared by reactive magnetron deposition under various nitrogen partial pressures and subsequently annealed (Ta = 450–950 °C). The structure, density, composition and electrical resistivity of the prepared films were systematically investigated. A phase map was constructed from the results of structural analysis. With increasing of from 0 to 0.2, a single-phase or two-phase mixture films of tetragonal Ta, Ta2N ( °C), ϵ-TaN ( °C), θ-TaN ( °C) and fcc δ-TaN are sequentially observed. For –0.45, the as grown and annealed films exhibit δ-TaN structure. Amorphous films grown in the –0.75 range crystallize as cubic Ta2N3 upon annealing at °C or as δ-TaN at °C. A cubic Ta2N3 is grown at highest (0.85), which decomposes to δ-TaN at °C. The N / Ta atomic ratio in the film linearly increases for –0.5, ranging from 0 to 2.1, while the mass density monotonically decreases with . Upon annealing, a part of N atoms out-diffuses from the films deposited at . The electrical resistivity strongly depends on both and Ta. However, in the as grown and annealed δ-TaN films the resistivity was of the order of 100–1000 cm. In these films, a correlation between the resistivity and the average number of defects (Ta vacancies and N atom excess) is observed. Finally, the influence of thermally introduced oxygen on the films resistivity has been revealed.

The influence of an air atmosphere on the electrical properties of two-phase films of hydrogenated silicon

Amorphous and microcrystalline hydrogenated silicon is an important material in modern thinfilm electronics. In some cases, the electrical parameters of silicon film samples depend on the ambient environment, in particular, the air. In this work we studied the effect of air exposure on the electrical properties of two-phase silicon films with a volume fraction of the crystalline phase of 0 to 80%. It was shown that the change in the conductivity of the two-phase films that were exposed to the air atmosphere depends on the proportion between the amorphous and microcrystalline phases that form the film microstructure. The use of two differing methods for film manufacturing allowed us to qualitatively evaluate how the conductivity of the films with a nonuniform structure across the thickness is affected by gas adsorption from air onto the film surface. Air exposure of the samples with a small amount of the crystalline phase located near the film surface leads to the specific features of temperature dependence of their conductivity.

Biophysical elucidation of the mechanism of enhanced drug release and topical delivery from polymeric film-forming systems

The effect of incorporating the lipidic medium-chain triglyceride (MCT) into polymeric film-forming systems (FFS) for topical drug delivery has been evaluated. First, the in vitro release of betamethasone-17-valerate (BMV), a representative dermatological drug, was determined from FFS comprising either hydrophobic polyacrylate co-polymers, or hydrophilic hydroxypropyl cellulose, with and without MCT. Release was enhanced from both polymers in the presence of MCT. Atomic force microscopy imaging and nanoindentation of FFS with MCT revealed two-phase structured films with softer inclusions (0.5 to 4μm in diameter) surrounded by a more rigid structure. Chemical mapping with Raman micro-spectroscopy showed that MCT was primarily confined to the inclusions within the polymer, which predominated in the surrounding film. BMV was distributed throughout the film but was more concentrated outside the inclusions. Furthermore, while BMV dissolved better into the hydrophobic films, it was more soluble in the MCT inclusions in hydrophilic films, suggesting its increased availability for diffusion from these softer regions of the polymer and explaining the release enhancement observed. Second, ex vivo skin penetration studies clearly revealed that uptake of BMV was higher from hydrophobic FFS than that from the more hydrophilic polymer due, at least in part, to the superior anti-nucleation efficiency of the former. Drug was quickly taken up into the SC from which it then diffused continuously over a sustained period into the lower, viable skin layers. In the presence of MCT, the overall uptake of BMV was increased and provides the basis for further optimisation of FFS as simple, convenient and sustained formulations for topical therapy.

Influence of Hetero Grain Boundaries on Oxygen Exchange Activity: Investigation of Two-Phase (La,Sr)CoO3-δ / (La,Sr)2CoO4+δ Cathode Materials

Several recent publications have claimed that the oxygen exchange surface reaction is accelerated at hetero grain boundaries betwen La1-xSrxCoO3- d and (La1-ySry)2CoO4+ d. To investigate this effects in a greater detail, PLD films with a high density of such hetero grain boundaries are prepared from a two-phase target, and characteristic crystal morphologies are observed. The issue of preferential Sr accumulation in the (La1-ySry)2CoO4+ d Ruddlesden-Popper phase is exemplarily quantified for two-phase powder samples based on X-ray diffraction. The implications of this uneven Sr distribution (occurring similarly in the two-phase films) for the analysis of the oxygen exchange kinetics and quantification of the specific hetero grain boundary effect are discussed

Fabrication of c-axis Oriented Epitaxial EuBa2Cu3O7-δ and EuBa2Cu4O8 Films on SrTiO3 (100) Substrate by Molten Hydroxide Method at 450°C

EuBa2Cu3O7-δ (Eu123) and EuBa2Cu4O8 (Eu124) films oriented in c-axis were deposited on SrTiO3 (100) substrates with eutectic NaOH-KOH flux at 450°C. Synthesized phase has changed by using various types of barium source materials. Pure Eu124 films showed superconducting transition at ∼70K, zero-resistance was not observed for Eu123/124 two-phase films. One of the possible reasons of this is Eu/Ba substitution of Eu123 phase. According to Tc of the Eu124, the molten hydroxide method enables to deposit high-quality Eu124 films.

High open-circuit voltage (1.04 V) n–i–p type thin film silicon solar cell by two-phase silicon carbide intrinsic material

We prepared two-phase hydrogenated silicon carbide (SiC:H) intrinsic materials from silane–methane gas mixtures at a low temperature of 150°C using radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD). We then employed Raman, HRTEM and FT-IR measurements to investigate the structural evolution of the resulting two-phase heterostructure films, and confirmed the medium range order of SiC:H materials based on the intensity of the transverse acoustic mode and microstructure factor. High concentration of medium order materials associated with nanocrystalline Si was obtained in the amorphous silicon carbide/nanocrystalline silicon hybrid layers. Under optimized deposition conditions, the intrinsic film has an optical band gap of up to ~2.0eV and photosensitivity of up to ~4×106; these qualities make it an excellent intrinsic material to use when fabricating wide band gap top cells for multi-junction thin film silicon solar cells. Using both wide band gap window layers and intrinsic layers, a high open-circuit voltage of 1.04V and short-circuit current density of 9.66mA/cm2 were achieved for a single junction n–i–p solar cell on stainless steel.