Structure Formation In Films Research Articles

Assembly Structure Formation in Bulk and Ultrathin Films of Poly(substituted methylene) Having an Azobenzene Side Chain.

The density of the side chain introduced to a polymer main chain greatly influences the properties and functions of the polymer. This work first reports on the packing structure and properties at an interface of a poly(substituted methylene) where an azobenzene side chain is introduced at every carbon atom in the main chain (C1PAz). The structure and properties are compared with those of a conventional vinyl polymer [poly(methacrylate)] possessing an identical side-chain structure (C2PAz). The packing structure in the bulk state analyzed by X-ray measurements revealed that C1PAz adopts a highly ordered rectangular unit cell structure, whereas C2PAz shows a less ordered lamellar one. Langmuir film balance experiments indicated that both polymers with the trans-azobenzene give essentially the identical 2D side-chain occupying area on water, which agrees well with the smectic B (hexatic packing) model based on the X-ray data. Upon transfer onto a solid substrate, only C1PAz shows a conformational transformation to a spread bilayer-type layer, most probably due to conformational frustration stemming from the crowding of the side chains. This study proposes new insights into the effects of side-chain density on the self-assembly and photoreaction of azobenzene-containing polymers, which are expected to expand the possibilities of polymer design for various applications.

Formation of submicron conical morphology of the surface of nanometer-thick films of the Al–Fe alloy under various conditions of ion-assisted deposition on glass

The morphology, topography and wetting with distilled water of Al–1.5 at. % Fe alloy films with a thickness 25–90 nm, formed on glass by ion-assisted deposition using a resonance ion source of vacuum electric arc plasma, have been studied. Using scanning probe microscopy, it is shown that, depending on the mode and the time of deposition, the modification of films is accompanied by changes in longitudinal and transverse roughness parameters, as well as parameters – dimensionless complexes, the measurement of which makes it possible to quantitatively describe the processes of coning in the Al–Fe alloy/glass system. Thus, the arithmetic mean roughness of the films increases with deposition time in the range 20–40 nm. Under self-irradiation conditions, a transition from island-like film growth to layer-by-layer film growth was detected. The influence of the substrate topography on the longitudinal step parameters of the film topography has been established. The size and surface density of the microdroplet fraction particles are studied by scanning electron microscopy. The frequency distributions of the microdroplet fraction by size are satisfactorily approximated by the lognormal distribution. It is found that in the mode of irradiation with intrinsic ions, 60–70% of the microparticles have a size of up to 0.8 μm. For the first time, a double Gaussian function was used to approximate the distribution histograms of local maxima and minima of the film relief, which made it possible to increase the accuracy of the description compared to the normal law. The effectiveness of this approach in analyzing the structure formation of nanometer films at various stages of growth has been demonstrated. Using the bi-Gaussian surface model, the role of topographic characteristics in controlling the wetting of modified coatings is revealed. The mechanism of heterogeneous wetting of hydrophilic films in the Cassie mode with contact angles ranging 50°–80° is discussed. It is found that in the potential mode, with an increase in the deposition duration to 10 h, the distribution of the film relief is close to the normal law, and the formation of a developed submicron conical morphology on the surface leads to blended wetting.

Features of forming a low-temperature cubic Li7La3Zr2O12 film by tape casting

Currently, interest to lithium and lithium-ion all-solid-state power sources is rapidly growing all over the world. However, several issues should be addressed before all-solid-state batteries production: high resistance values of the solid electrolyte membrane and poor contact between electrolyte and electrode materials. The transition to thin-film technologies is one of the promising ways to solve these problems. Tape casting can be proposed to obtain thin-film solid electrolytes. In this research, the features of the structure formation, morphology and lithium-ion conductivity of Li7La3Zr2O12 films were investigated. Li7La3Zr2O12 films with the thickness of 35 µm were obtained by tape casting on Ni substrate. The influence of organic components’ content on homogeneous coatings formation was established. Heat treatment conditions for dried films were chosen based on differential scanning calorimetry and optical dilatometry. Phase change from tetragonal to low-temperature cubic modification occurs after annealing the Li7La3Zr2O12 films at 700 °C and higher. The annealed Li7La3Zr2O12 films have developed surface, which can lead to improved contact between the solid electrolyte and an electrode in an electrochemical cell. Li7La3Zr2O12 films annealed at 800 °C have the highest lithium-ion conductivity values (2.5·10–7 and 1.5·10–5 S·cm–1 at 90 and 215 °С, respectively). The technology of Li7La3Zr2O12 films formation with the thickness of ~23 µm by tape casting was developed.

Insight into heterogeneous dynamics of growing islands using coherent x-ray scattering

Understanding the non-equilibrium structure formation of thin films is a fundamental challenge with important implications also for technical applications. The interplay between adsorption, desorption, and surface diffusion may result in the formation of nontrivial surface morphologies. X-ray photon correlation spectroscopy opens up new possibilities for understanding these processes. In this work, we perform in situ x-ray experiments in grazing incidence geometry to follow the growth of diindenoperylene thin films in real time, revealing details of the dynamics during molecular island formation. Comparison with simulations allows to extract dynamic and kinetic time scales. We observe time scales in the range of a few hundred seconds which occur mainly due to kinetics, i.e. island growth. Importantly, we can relate the observed heterogeneous behavior in dynamics to the number of open layers, revealing information about the change in the roughness, and the growth speed of each layer.

Thick film MEMS process using reverse lift-off

The lift-off process is a microfabrication technique that has the capability of forming thin film structures. However, several issues, such as structural shape and burr formation, arise when applying this method to the formation of thick film structures. Thick film structures formed through the lift-off process exhibit a mountainous cross-sectional shape and non-uniform film thickness due to variations in the width of the structure. These challenges make it difficult to apply the method to MEMS. While the reverse lift-off process addresses some of the structural shape problems, its initial development using metal molds makes it challenging to directly apply to MEMS without modification. Therefore, this paper proposes an adaptation to the Si process and presents a method to reduce burrs. The microfabrication characteristics are evaluated by comparing the cross-sectional shapes of thick metallic glass structures formed through both the lift-off and reverse lift-off processes. The structures formed through the reverse lift-off process exhibit a rectangular cross-sectional shape, and the film thickness remains consistent regardless of the structure's width. However, burrs persist on the backside edge of the structure, which hinders its application to MEMS. This paper confirms that pre-etching the underlying Si substrate into an inverse tapered shape effectively reduces burrs. As an illustration of the improved reverse lift-off process applied to MEMS, MEMS mirror structures are fabricated, and their resonance frequency closely aligns with the design value.

Application of Laser Thermocycling to Improve the Quality of Plasma Wear-Resistant Coatings

The problem of the article is designed to reveal the proposed, developed and researched new method of improving the adhesion strength of plasma wear-resistant coatings on the outer surfaces of weapons made of high-alloy, heat-resistant steels, using additional cyclic (3-4) times their heating by laser radiation to temperatures of 0.6 – 0.8Tpl for a few milliseconds. The purpose of increasing the resource of use and the quality of the appearance of the weapon by applying wear-resistant coatings with increased adhesion strength to the base using plasma gas-thermal spraying followed by laser thermal cycling. Determination of the main factors and parameters of the process of laser thermocycling of plasma coatings, their interrelationships, development of an algorithm for determining the conditions of laser thermocycling, establishment of the rational range of their values by mathematical modeling and experimental research. The results of mathematical modeling of laser cyclic heating of plasma coatings of HTN of different thicknesses are presented, which allows determining the irradiation parameters that ensure their heating to temperatures at the "coating-substrate" boundary ≤1000ºС, on the surface - to Т< Тpl, at maximum cooling rates. It has been proven that laser thermocycling provides an increase in the adhesion strength of coatings to the base from 14–18 to 90–110 MPa, a decrease in porosity from 10–12% to 7–8%, which is due to the redistribution of alloying components at the “coating–base” interface, with the formation of elements of the metallurgical connection, contributes to a significant increase in wear resistance and a decrease in the coefficient of friction due to the formation of secondary ultradispersed film structures. We consider laser thermocycling of plasma coatings is an effective method of improving their quality and strength of adhesion to the base.

Untangling effects of proteins as stabilizers for foam films

Foam film’s properties have a high impact on the properties of the macroscopic foams. This work focusses on protein stabilized foam films. The direct comparison of three different proteins with a concentration normalized to the protein surface enables to distinguish between electrostatic, steric and network stabilization effects. In order to untangle those effects, we study and compare two globular proteins (β − lactoglobulin, BLG, and bovine serum albumin, BSA) and a disordered, flexible protein (whole casein, CN) at low ionic strengths with varying solution pH. Image intensity measurement as a recently developed image analysis method in this field allows to record spatially resolved disjoining pressure isotherms in a Thin Film Pressure Balance (TFPB). This reveals insights into the structure formation in inhomogeneous protein films. As a novel method we introduce tracking inhomogeneities (features) which enables the measurement of interfacial mobility and stiffness of foam films. Around the isoelectric point (IEP), Newton Black Films (NBF) form which are stable for the globular proteins while they are unstable for the disordered flexible one. This difference in film stability is explained by different characteristics of the network structures which is supported by findings in the bulk and at the surface of the respective protein solutions.

Crystallization of D-A Conjugated Polymers: A Review of Recent Research.

D-A conjugated polymers are key materials for organic solar cells and organic thin-film transistors, and their film structure is one of the most important factors in determining device performance. The formation of film structure largely depends on the crystallization process, but the crystallization of D-A conjugated polymers is not well understood. In this review, we attempted to achieve a clearer understanding of the crystallization of D-A conjugated polymers. We first summarized the features of D-A conjugated polymers, which can affect their crystallization process. Then, the crystallization process of D-A conjugated polymers was discussed, including the possible chain conformations in the solution as well as the nucleation and growth processes. After that, the crystal structure of D-A conjugated polymers, including the molecular orientation and polymorphism, was reviewed. We proposed that the nucleation process and the orientation of the nuclei on the substrate are critical for the crystal structure. Finally, we summarized the possible crystal morphologies of D-A conjugated polymers and explained their formation process in terms of nucleation and growth processes. This review provides fundamental knowledge on how to manipulate the crystallization process of D-A conjugated polymers to regulate their film structure.

Structure formation and depolarization relaxation processes in porous piezoactive polyvinylidene fluoride films

Piezoactive porous polyvinylidene fluoride films prepared in the process based on melt extrusion with subsequent isometric annealing, uniaxial extension and thermal fixation have been studied. It was shown that two competing orientation processes -polymorphous transition of non-polar α-phase into polar piezoactive β-phase and formation of porous structure - occur during the uniaxial extension of annealed films. It has been established that orientation degree of extruded films is the key factor determining the efficiency of both processes. Thermally stimulated depolarization method was used to investigate the dipole relaxation in oriented films, and activation energy of these processes was found. The films were polarized using corona discharge and high-voltage contact methods, both, and the dependence of piezoelectric modulus on the polarization conditions has been obtained. The maximum value of piezoelectric modulus d31=30.1 pC/N was achieved by polarization of films in corona discharge method. Keywords: polyvinylidene fluoride, porous films, supramolecular structure, piezoelectric properties, polarization, relaxation processes.

Investigation of the features of the porous morphology of anodic alumina films at the initial stage of anodization

The work is devoted to the study of the porous structure formation of anodic alumina films at the initial stage of aluminium anodizing. SEM images of the surface morphology of the oxalic acid anodic films were analyzed. It was shown that at the initial stage, both major and minor pores are formed, the diameter ratio of which is about 1.16 and does not depend on the anodizing voltage. The results obtained indicate that the minor pores in the anodic films are located inside hexagonal cells composed of the major pores.

Features of the structure formation of PZT thin films by reactive plasma sputtering

The electrophysical characteristics of the PZT film formed on a silicon by the method of high-frequency reactive plasma sputtering were studied, and their relationship with the structure of the film was established. In particular, the hysteresis in the capacitance-voltage characteristics of the metal - ferroelectric - semiconductor indicates the polarization of the film, which, in turn, indicates the presence of the perovskite phase in the PZT film. However, the crystallite size of this phase is so small that it cannot be detected by X-ray diffraction analysis.

Optical anisotropy of laser-induced graphene films

Films of laser-induced graphene (LIG) were obtained by line-by-line scanning of a cw CO2 laser beam over the surface of a polyimide (PI) film. It was found that the formation of a LIG layer with a thickness of about 60 μm occurs due to the pyrolysis of a thin surface layer of a PI film with a thickness of about 15 μm. The morphology of the synthesized film structure is shown to be significantly affected by the ratio between the laser beam diameter and the distance between the lines along which the laser beam moves. In the synthesized film structures, oriented light-reflecting carbon flakes have been found, which lead to the anisotropy of diffusely scattered light in the plane perpendicular to the plane of light incidence on the film. The observed phenomenon is characteristic of LIG synthesized with a cw laser, which provides a more homogeneous structure of graphene along the scanning line of the laser beam, compared to the graphene obtained with a repetitively pulsed laser. Our findings may help in the analysis of line-by-line cw laser scanning synthesized LIG and in the formation of film structures based on LIG for cold field electron emission technology.

Straightening properties of heterostructures based on fullerene and hybrid zinc complex

This work presents the results of using a new coordination compound C24H24N6O3Zn as a component for constructing heterostructures based on C60 fullerene. A procedure for the synthesis and preparation of a hybrid material is described. The formation of film structures from initial powder materials was carried out by pouring from a solution onto substrates using various types of solvents. The results of microscopy of the surfaces of the obtained films, as well as optical and luminescent properties are presented. Additionally, the optical band gap of the obtained films from hybrid materials was calculated. The addition of a zinc complex to a bond with fullerene suggests the appearance of a potential barrier at the interface between active layers. The resulting thin-film structures have rectifying light current-voltage characteristics. Additionally, the possibility of using the theoretical Poole--Frenkel model to explain the hopping conduction mechanism of the heterostructure under study is considered.

Structure formation, optical properties and energy loss functions of meso-tetraphenylporphyrin manganese(III) chloride complex thin films for energy conversion applications

Abstract Thin films of meso-tetraphenylporphyrin manganese chloride complex (MnClTPP) have been prepared by evacuated thermal evaporation technique. The structure formation of MnClTPP films has been identified using atomic force microscopy and X-ray diffraction techniques. The pristine MnClTPP films revealed amorphous structure, whereas after annealing temperature up to 490 K, the films turned to nanocrystalline structure formation. The spectrophotometric measurements of transmittance, absorbance and reflectance of pristine and annealed films have been carried out in spectral range 200–2000 nm. The absorbance revealed many electronic transition bands including high intense Soret band (B), Q-band, and two other weaker (M and N) bands extended in UV–visible spectrum. Optical constants (refractive index and absorption index) of pristine and annealed films were determined. The absorption edge analysis was performed to estimate the type of electronic transitions and the value of optical band gap. Additionally, the surface and volume energy loss functions of pristine and annealed MnClTPP films have been estimated. The annealing process improved the performance of those films and reduced the values of energy loss functions that would be utilized a potential material in energy conversion applications.

Factors Affecting the Nonsolvent-Induced Phase Separation of Cellulose from Ionic Liquid-Based Solutions.

In the present work, we report for the first time an in-depth study of the factors influencing porous cellulose film structure formation during the nonsolvent-induced phase separation (NIPS) process from biopolymer solutions in ionic liquid-based solvents. The length of the alkyl chain of the ionic liquid’s cation, the solvent/co-solvent ratio, and the type of the cellulose precursor used were found to have great influence both on cellulose solution formation and properties and to the NIPS process with water acting as nonsolvent. In the undiluted form, both studied ionic liquids proved to dissolve almost equally well the cellulose; however, due to differences in viscosities of the formed biopolymer solutions and due to differences in miscibility with water of the two ionic liquids, the used ionic liquid had a strong influence on the film’s porous structure formation. The use of increasing amounts of an aprotic co-solvent, here dimethylsulfoxide, improved biopolymer solubilization and also led to the formation of a more pronounced macroporous structure during the NIPS process. The cellulose type also affected the porous structure generation during the NIPS process: with the increase of the molecular weight of the precursor, the viscosity of the formed biopolymer solution increased and the tendency to generate macroporous structures decreased.

Predictive modelling of structure formation in semiconductor films produced by meniscus-guided coating.

Meniscus-guided coating methods, such as zone casting, dip coating and solution shearing, are scalable laboratory models for large-area solution coating of functional materials for thin-film electronics. Unfortunately, the general lack of understanding of how the coating parameters affect the dry-film morphology upholds trial-and-error experimentation and delays lab-to-fab translation. We present herein a model that predicts dry-film morphologies produced by meniscus-guided coating of a crystallizing solute. Our model reveals how the interplay between coating velocity and evaporation rate determines the crystalline domain size, shape anisotropy and regularity. If coating is fast, evaporation drives the system quickly past supersaturation, giving isotropic domain structures. If coating is slow, depletion due to crystallization stretches domains in the coating direction. The predicted morphologies have been experimentally confirmed by zone-casting experiments of the organic semiconductor 4-tolyl-bithiophenyl-diketopyrrolopyrrole. Although here we considered a small molecular solute, our model can be applied broadly to polymers and organic-inorganic hybrids such as perovskites.

A Role of Coagulant in Structure Formation of Fibers and Films Spun from Cellulose Solutions.

Replacing the aqueous coagulation bath with an alcoholic one during spinning cellulose fibers (films) from solutions in N-methylmorpholine-N-oxide leads to a radical restructuring of the hydrogen bonds net of cellulose and, as a result, to a change in the structure and properties of the resulting material. By the method of optical interferometry, it was possible to identify the intrinsic features of the interaction of the solvent and isomeric alcohols and to construct phase diagrams of binary systems describing the crystalline equilibrium. Knowledge of the phase states of the system at different temperatures renders it possible to exclude the process of solvent crystallization and conduct the spinning in pseudo-homogeneous conditions. The structure and morphology of samples were studied using X-ray diffraction and scanning electron microscopy methods for a specific coagulant. When the solution under certain conditions is coagulated at contact with alcohol, the solvent may be in a glassy state, whereas, when at coagulation in water, an amorphous-crystalline structure is formed. The structural features of cellulose films obtained by coagulation of solutions with water and alcohols help to select potential engineering or functional materials (textile, packaging, membranes, etc.), in which their qualities will manifest to the best extent.

Thermal aging of bitumen mixtures with crushed sand

Public roads with advanced types of coatings are mainly constructed of asphalt concrete. Along with good performance, they have some disadvantages. One of them is temperature aging. The aging process is inevitable. However, to increase the stability of bituminous mixtures, it is important to study the structure formation and aging processes of bitumen films on the surface of all components separately, including the areas of contact with crushed sand. In order to study the aging processes, the methods of studying the aging of bituminous mixtures have been critically analyzed. Considering the shortcomings of the methods available, a new method has been developed. Based on the experiments performed using this method, we studied the aging processes of bituminous mixtures at the temperature of +150° C for various periods of time. The resulting mathematical models describe the aging process based on the considered factors. The experimental results were analyzed in accordance with the theoretical concepts of the interaction of bitumen films on the surfaces of crushed sand particles of amorphous rocks. The conducted research has practical conclusions.

Structural, optical and electrical properties of Cu:MnO2 nanostructured thin films for glucose sensitivity measurements

In the present investigation, pure MnO2 and Cu doped MnO2 (Cu:MnO2) thin films were successfully prepared by the spray pyrolysis deposition technique. Different Cu concentrations were used to analyze the morphological, structural, optical, electrical properties and as well glucose sensitivity measurement has been performed. MnO2 doped with Cu induces microstructure and is set in the lattice by keeping Mn+2 leading to the micro spherical shape of the samples highlighted from a scanning electron microscope. X-ray diffraction analysis has confirmed the tetragonal MnO2 crystal structure with α-phase. The crystallite size, crystal structure, texture, and nanoparticle formation in MnO2 films have been influenced by Cu dopant. The maximum optical transmittance is found to be about 83%. The energy band gap associated with the allowed direct transition is found to increase from 3.82 to 3.96 eV with increasing Cu doping concentration up to 4 at%. Glucose sensitivity was measured by the four-probe technique. Notably, 4 at% Cu:MnO2 films have demonstrated the superior sensing ability of glucose of 29%.

Systematics of the allotrope formation in elemental gallium films

Elemental gallium forms unusual allotropes, whose structures all differ distinctly from the close-packing of spheres typical for nearly all elemental metals. At standard pressure, four different crystalline allotropes are known where the α-Ga allotrope is the thermodynamically stable one. Since the other allotropes can only be obtained under special conditions such as spatial confinement or undercooling, the structural relations among the gallium allotropes are not well-explored. We present here a systematic investigation of the dependence of the crystal structure formation in elemental gallium films on the deposition temperature and the subsequent annealing procedures using in situ x-ray powder diffraction and Raman measurements, complemented by ab initio calculations. The films were prepared with the femtosecond pulsed-laser-deposition technique on a substrate kept at constant temperature in the range of –190 °C to 25 °C, followed by cooling + heating cycles in the same temperature range. Besides preparing α-, β-, γ- and amorphous Ga films as a single phase, a new gallium allotrope, β′-Ga, was synthesized, which is a distorted derivative of the β-Ga crystal structure. Furthermore, no direct transition between the α-Ga phase on one side and the β-, β′-, and γ-Ga phases on the other side was observed in the solid state. Surprisingly, at room temperature amorphous gallium and below –60 °C the α-Ga allotrope, respectively, is formed in the deposited films.