Initial Film Research Articles

Synthesis and investigation of polymers containing aniline and indole fragments

By chemical modification of copolymers of ClPA with Ani of different composition polymers containing fragments of aniline and indole have been synthesized. Their structures and compositions were determined by IR-, NMR- and UV-spectroscopy and elemental analysis methods. Morphology, electrochemical characteristics, photoluminescence, thermal stability, photoconductive properties were evaluated. The results of the thermogravimetric analysis showed that there was a significant increase in the thermal stability of these polymers. The structural changes of the modified polymers have been studied by the method of electron microscopy. It has been established that a lamellar and agglomerated surface is formed: its parameters depend on the content of aniline and indole fragments. The photoconductivity of initial copolymer films as well as of polymer films after modification was investigated. It was found that the photoconductivity of polymer films increases with the transition to polymers with a large number of indole-containing units. The obtained results indicate that modified polymers can be considered as promising materials for application in modern electronics.

Close-contact melting of shear-thinning fluids

This study aims at establishing a model for close-contact melting (CCM) of shear-thinning fluids. We presented a theoretical framework for predicting the variation of liquid melt film thickness and motion of unmelted solid for both Carreau and power-law fluids. We identified the appropriate energy equation considering the convective effect and derived an analytical temperature profile across the liquid film. Using the lubrication approximation, force equilibrium relationships and the corresponding numerical approaches were built. By using laser interferometry and photographic recording methods, we found excellent agreement between numerical solutions and experimental results for Carreau liquids, revealing that the convective effect weakens heat transfer and melting rate. We identified the critical liquid film thickness that determines three situations of CCM in the theoretical model for Carreau fluids. Numerical prediction demonstrated that the CCM of Carreau fluids can be almost equivalent to that of power-law fluids if the initial film thickness is greater than the critical value. Finally, approximate analytical models were developed for both Carreau and power-law models. For the applicability of the approximate analytical solutions, we derived two- and three-dimensional dimensionless phase diagrams of validity range and identified a key dimensionless group $(\varLambda Re)^{4/3}{Re}\left [3\ln (Ste+1)\right ]^{1/3}{Pe}^{-1/3}$ , where $\varLambda$ is dimensionless characteristic time, Re is Reynolds number, Ste is Stefan number and Pe is Peclect number. The reliability of the approximate solutions was verified by comparing with the numerical results. These approximate solutions enable convenient and low-cost computational prediction of the dynamic CCM process of shear-thinning fluids.

Passivation behavior of Cr-modified rebar in simulated concrete pore solutions with different pH

In this study, the enhanced passivation effect of Cr-modified rebar compared with carbon rebar has been explored with regard to the formation process of the passive film, which could provide a theoretical basis for the development and application of concrete materials in harsh environments. X-ray photoelectron spectroscopy and capacitance-potential method were used to investigate the composition, structural depth distribution, and semiconductive properties of passive films formed by Cr-modified rebar and carbon rebar in simulated concrete pore solutions with different pH. The kinetics of passive film growth and formation were analyzed by tracking tests of potentiostatic current transients and open circuit potential under natural aeration. The results show that the activation energy of Cr-modified rebar is lower at 14.59 kJ/mol, compared to carbon rebar's 25.36 kJ/mol. In the early stage, Cr-modified rebar can achieve a thinner, more stable initial film in a shorter time than carbon rebar. The rate of reduction of the initial thickening rate of the passive film on Cr-modified rebar is five times than that of carbon rebar per unit pH. The film growth rate after early stage of Cr-modified rebar decreases, whereas that of carbon steel increases, with decreasing pH. The passive film containing Cr oxide or hydroxide enhances the barrier effect of the oxide film to ion migration, and the re-dissociation of Fe oxide hinders the passivation process. This grants the thickness of the stable passive film of the two rebars changing oppositely and the Cr-modified rebar compared to carbon rebar enhance passivation with pH falling.

Transport of convected soluble surfactants on and within the foam film in the context of a foam fractionation process

This study models convective transport of soluble surfactant in a foam fractionation system with reflux. Owing to reflux, initial surfactant concentration in films is lower than in Plateau borders. Marangoni flows and film drainage flows arise convecting surfactant both on the film surface and in the bulk. An interface is set up within the film bulk called a separatrix: this divides two regions of uniform surfactant concentration, one with concentration equal to that of the initial film and one with concentration equal to that in the Plateau border. The evolution of the separatrix is tracked to determine surfactant recovery and enrichment for the film. Surfactant lean films benefit most from reflux. However for films that are initially comparatively surfactant rich, recovery might actually decrease at long times owing to film drainage. Nonetheless surfactant lean films and those containing surfactant with only moderate solubility benefit from reflux even despite film drainage.

Femtosecond Laser Ablation-Induced Magnetic Phase Transformations in FeRh Thin Films

In this study, we present a novel investigation into the magnetic and morphological properties of equiatomic B2-ordered FeRh thin films irradiated with single high-intensity ultrashort laser pulses. The goal is to elucidate the effect of femtosecond laser ablation on the magnetic properties of FeRh. We employed Scanning Magneto-Optical Kerr Effect (S-MOKE) microscopy to examine the magnetic phase after laser processing, providing high spatial resolution and sensitivity. Our results for the first time demonstrated the appearance of a magneto-optical signal from the bottom of ablation craters, suggesting a transition from antiferromagnetic to ferromagnetic behavior. Fluence-resolved measurements clearly demonstrate that the ablation threshold coincides with the threshold of the antiferromagnet-to-ferromagnet phase transition. The existence of such a magnetic phase transition was independently confirmed by temperature-dependent S-MOKE measurements using a CW laser as a localized heat source. Whereas the initial FeRh film displayed a reversible antiferromagnet-ferromagnet phase transition, the laser-ablated structures exhibited irreversible changes in their magnetic properties. This comprehensive analysis revealed the strong correlation between the femtosecond laser ablation process and the magnetic phase transformation in FeRh thin films.

Porous-Spherical Cr2O3-Cr(OH)3-Polypyrrole/Polypyrrole Nanocomposite Thin-Film Photodetector and Solar Cell Applications

This study utilized the exceptional optical and electrical properties of polypyrrole (Ppy) to fabricate high-performance optoelectronic devices. The synthesis of the porous-spherical Cr2O3-Cr(OH)3-Ppy/Ppy nanocomposite thin film was achieved by preparing a second thin film of Cr2O3-Cr(OH)3-Ppy on the initial Ppy film using K2Cr2O7 as an oxidant. The nanocomposite’s properties were thoroughly characterized, including XRD and optical absorbance analyses. The XRD analysis showed that the crystalline size of the nanocomposite was 20 nm, while optical absorbance analysis demonstrated that the nanocomposite had a higher absorbance in a wide optical range compared to Ppy nanomaterials, as evidenced by the enhancement in bandgap (Eg) value from 3.33 eV for Ppy to 1.89 eV for Cr2O3-Cr(OH)3-Ppy. The fabricated nanocomposite thin film exhibited excellent light-sensing behavior, as evidenced by the evaluation of Jph values under different light conditions and various monochromatic lights with a detectivity (D) of 3.6 × 106 Jones (at 340 nm). The device demonstrated its potential as a solar cell, with a short circuit current (JSC) of 13 µA and an open circuit voltage (VOC) of 1.91 V. Given the nanocomposite’s low cost, high technical production, and superior optoelectronic properties, it has significant potential for use in commercially available high-tech devices.

Thermal atomic layer etching of CoO using acetylacetone and ozone: Evidence for changes in oxidation state and crystal structure during sequential exposures

Thermal atomic layer etching (ALE) of CoO was demonstrated using sequential exposures of acetylacetone (Hacac) and ozone (O3). During the surface reactions, Hacac can remove CoO according to: CoO + 2Hacac → Co(acac)2 + H2O. Ozone was employed to eliminate carbon residue resulting from Hacac adsorption. In situ spectroscopic ellipsometry observed a linear decrease in CoO film thickness versus Hacac and O3 exposures with an etch rate of 0.43 Å/cycle at 250 °C. The surface of the CoO film was also observed to undergo changes in oxidation state and crystal structure with each reactant exposure. Ex situ grazing incidence X-ray diffraction (GIXRD) studies revealed that the initial h-CoO thin films were oxidized to c-Co3O4 by O3. Subsequently, the GIXRD analysis showed that the c-Co3O4 thin films were reduced to c-CoO by Hacac. X-ray photoelectron spectroscopy investigations confirmed the oxidation state of the various cobalt oxides. Quadrupole mass spectrometry measurements observed Co(acac)2 etch products during Hacac exposures on Co3O4 and CoO powder. Atomic force microscopy measurements also monitored a reduction in surface roughness during CoO ALE. These studies reveal that alternating changes in oxidation state and crystal structure occur during the sequential Hacac and O3 exposures that define CoO thermal ALE.

Experimental study on thermal characteristics of pure water flashing evaporation from thin-liquid film

An experimental investigation on thermodynamic phenomena of liquid film flash evaporation is presented. During experiments the pure waterfilm is flashed at an initial temperature range of 60–85 °C, an initial liquid film height range of 3–20 mm, and a superheat range of 2–22 K. The results show that the enthalpy difference is the dominant parameter for flashing phenomena and process. The static pressure distribution in the liquid film has an obvious impact on flashing evaporation process since the water static pressure can cause the change of saturation temperature. The liquid film height during the flash can be reached many times of the initial heightand it represents the intensity of the flashing. The flashing evaporation can be stepped more rapidly to the mild evaporation due to the lower water film. The NEF(non-equilibrium fraction) and the intensity of the flashing increased with the height of water film.

Transformation of bimetallic Ag–Cu thin films into plasmonically active composite nanostructures

Formation of plasmonically active silver, copper and composite silver-copper nanostructures were studied in this paper. Metallic nanostructures were fabricated by thermal disintegration, so called dewetting, of the thin films in an argon atmosphere. The formation process of the nanostructures was in-situ observed by a novel method, based on resistance measurements. The influence of the material and thickness of the initial thin film on temperature of their disintegration was investigated. Electrical measurements were validated by scanning electron microscopy observations, while metallic the behavior of nanostructures was studied by XPS method. The formation of silver-copper nanocomposite structures was confirmed by UV–vis spectroscopy. Plasmon resonance with two characteristic peaks for nanocomposite structures was observed.

Extensional flow of a free film of nematic liquid crystal with moderate elasticity

The human tear film is a multilayer structure in which the dynamics are often strongly affected by a floating lipid layer. That layer has liquid crystalline characteristics and plays important roles in the health of the tear film. Previous models have treated the lipid layer as a Newtonian fluid in extensional flow. Motivated to develop a more realistic treatment, we present a model for the extensional flow of thin sheets of nematic liquid crystal. The rod-like molecules of these substances impart an elastic contribution to the rheology. We rescale a weakly elastic model due to Cummings et al. [“Extensional flow of nematic liquid crystal with an applied electric field,” Eur. J. Appl. Math. 25, 397–423 (2014).] to describe a lipid layer of moderate elasticity. The resulting system of two nonlinear partial differential equations for sheet thickness and axial velocity is fourth order in space, but still represents a significant reduction of the full system. We analyze solutions arising from several different boundary conditions, motivated by the underlying application, with particular focus on dynamics and underlying mechanisms under stretching. We solve the system numerically, via collocation with either finite difference or Chebyshev spectral discretization in space, together with implicit time stepping. At early times, depending on the initial film shape, pressure either aids or opposes extensional flow, which changes the free surface dynamics of the sheet and can lead to patterns reminiscent of those observed in tear films. We contrast this finding with the cases of weak elasticity and Newtonian flow, where the sheet retains the same qualitative shape throughout time.

Formation of Antifouling Brushes on Various Substrates Using a Melanin-Inspired Initiator Film.

In this study, we developed a substrate-independent initiator film that can undergo surface-initiated polymerization to form an antifouling brush. Inspired by the melanogenesis found in nature, we synthesized a tyrosine-conjugated bromide initiator (Tyr-Br) that contains phenolic amine groups as the dormant coating precursor and α-bromoisobutyryl groups as the initiator. The resultant Tyr-Br was stable under ambient air conditions and underwent melanin-like oxidation only in the presence of tyrosinase to form an initiator film on various substrates. Subsequently, an antifouling polymer brush was formed using air-tolerant activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) of zwitterionic carboxybetaine. The entire surface coating procedure, including the initiator layer formation and ARGET ATRP, occurred under aqueous conditions and did not require organic solvents or chemical oxidants. Therefore, antifouling polymer brushes can be feasibly formed not only on experimentally preferred substrates (e.g., Au, SiO2, and TiO2) but also on polymeric substrates such as poly(ethylene terephthalate) (PET), cyclic olefin copolymer (COC), and nylon.

Ultra-thin silver nanowires’ synthesis in pore-confined space of mesoporous silica thin film

In the present work, we report a synthesis procedure for the preparation of vertically aligned mesoporous silica thin films containing long, nanometer-scale thin silver nanowires inside pores. The inter-channel nanowires had a fine crystalline structure and a diameter of no more than 2 nm. Despite the diameter being the edge of the theoretical possibility of synthesis, the nanowires were stable enough to be observed by transmission electron microscope and could be clearly observed. For the synthesis, we applied the idea of silica nanoreactors, and the procedure consists of two steps: fabrication of an initial organically-functionalized silica thin film containing silver ions distributed regularly inside vertically aligned pores and following thermal decomposition resulting in the decomposition of the organic anchoring groups and the formation of metallic crystalline nanowires from released silver atoms. Both the final nanocomposite and the initial material were studied by means of transition electron microscopy and electrochemical techniques: linear scan and differential pulse anodic stripping voltammetry. The crystallinity of silver nanowires inside silica mesopores was proved by electron diffraction. The spatial confinement realized by silica nanochannels facilitated the stabilization of relatively small and ultra-thin nanowires and the formation of a hexagonal P63/mmc silver crystalline structure instead of the more common Fm3m cubic.

Strain and Optoelectronic Tuning in Mixed‐Halide Perovskites with Ion Irradiation

AbstractDefects usually behave as imperfections in materials that significantly degrade their performance. However, the unusual optoelectronic performance in metal halide perovskites in the presence of defects opens the way for strain and optoelectronic properties tailoring with ion irradiation. Defects and strain engineering is performed in triple‐cation mixed halide perovskites using proton irradiation at 1 MeV and different fluences. At intermediate fluence, the initial polycrystalline film compressive strain (−0.15%) can be released, improving exciton lifetimes from about 500 ns to ≈1 µs. In contrast, high irradiation fluence is shown to restore compressive strain leading to sample degradation, with lower lifetime values (≈200 ns). Also, the phase segregation occurring under light illumination between bromine‐rich and iodine‐rich regions is shown to be defects‐mediated as the segregation rate increases by a factor of four for high proton irradiation fluence. The irradiation defects are revealed with low‐temperature photoluminescence (PL) through bound exciton radiative recombination mechanisms. The PL temperature dependence gives some insight into electron–phonon coupling mechanism and their modification with ion irradiation.

VIRTUAL FRACTURE CLINIC TRIAGE AND SELECTIVE USE OF MRI: A HYBRID MODEL FOR MANAGING SUSPECTED SCAPHOID FRACTURES

In current practice in the UK there are three main approaches to investigating suspected scaphoid fractures not seen on initial plain film x-rays.Early MRI of all casesReview all cases in clinic at two weeks with repeat x-raysHybrid model. Virtual Fracture Clinic (VFC) triage to reduce those who are seen in clinic at two weeks by:Organising early MRI for those with high-risk presentation.Discharging those with an alternative more likely diagnosis.Our unit uses the VFC model. We aimed to evaluate its efficiency, safety, clinical outcomes and economic viability.All patients attending the emergency department with either a confirmed or suspected scaphoid fracture between March and December 2020 were included (n=305). Of these 297 were referred to the VFC: 33 had a confirmed fracture on x-ray and 264 had a suspected fracture.Of the suspected fractures reviewed in VFC 14% had an MRI organised directly owing to a high-risk presentation, 79% were brought for fracture clinic review and 17% discharged with an alternative diagnosis such as osteoarthritis.Of those subsequently reviewed in fracture clinic at two weeks: 9% were treated as scaphoid fractures (based on clinical suspicion and repeat x-rays), 17% had MRI or CT imaging organised, 5% did not attend and 69% were discharged.Overall, 17% of cases initially triaged, had further imaging – 41 MRIs and 5 CTs. MRI detected: 5% scaphoid fracture, 17% other fracture, 24% bone contusion, complete ligament tear 10%, partial ligament tear 39% and normal study 10%. The results of MRI minimally affected management. 3 patients were taken out of plaster early, 1 patient was immobilized who was not previously and no patients underwent operative management.In the following 12-month period one patient re-presented with a hand or wrist issue.This approach avoided 218 MRIs, equating to £24000 and 109 hours of scanner time.VFC triage and selective use of MRI scanning is a safe, efficient and cost-effective method for the management suspected scaphoid fractures. This can be implemented in units without the resource to MRI all suspected scaphoid fractures from the emergency department.

Plasmonic Nanostructuring by Means of Industrial-Friendly Laser Techniques

The continuously growing demand for functional plasmonic devices or systems urges the implementation of economical and accelerated nanostructuring techniques. Laser annealing represents a promising approach to address this challenge, given its widespread usage in industry and research, as well as its unique advantages. This study proposes a scalable, rapid, versatile, and cost-efficient method to grow self-assembled nanostructures on metallic ultrathin films and multilayers, with high precision and patterning freedom. By employing industrial-grade equipment, specifically a 1070 nm nanosecond fiber laser and magnetron sputtering system, we directly grew self-assembled nanoparticles on Ag ultrathin films and AgPd multilayers deposited on Corning glass, via laser annealing at ambient conditions. The self-assembled nanoparticles were formed in designated areas by varying several laser parameters and exhibited intense localized surface plasmon resonances. Optical and structural characterization were realized via UV–Vis spectroscopy and atomic force microscopy, respectively. The plasmonic characteristics were found to depend on the initial film thickness and laser annealing parameters. Laser-treated films exhibited remarkable plasmonic behavior, demonstrating that this method does not lack nanostructuring quality while offering scalability and practicality. Further optimization of the laser settings can refine the process and result in an even faster, cheaper, and more qualitative nanostructuring method.

Molecular dynamics data-driven study of leidenfrost phenomena in context to liquid thin film phase transformation

In many micro and nanoscale applications of thin film phase transition, identifying the circumstances that allows stable liquid contact with a heated surface is critical. Using molecular dynamics (MD) simulations, our current data driven machine learning-based study attempts to examine the properties of liquid interaction with a solid surface at nanoscale. A few nanometer-thick liquid argon layer over a platinum surface has been used to simulate a liquid-solid contact system. The wall temperature is raised linearly after necessary initial equilibration of the entire system, with different boundary heating rates for various surface wetting conditions, namely hydrophobic, hydrophilic, and superhydrophilic. Our current investigation shows that the heating condition, liquid film thickness, and surface wetting condition all have a significant impact on the type of liquid wall contact that persists during the phase transition phenomena of thin liquid argon film (i.e., normal evaporation or explosive boiling). In the event of normal evaporation, a stable liquid contact with the solid surface continues, however in the case of explosive boiling, the liquid film is splashed away from the solid surface resembling the macroscopic Leidenfrost effect. For various system configurations in regard to liquid initial film thickness, liquid heating rate as well as solid-liquid interaction, a wide variation of the onset time as well as the wall temperature of boiling explosion have been found in the present study. An accurate mapping of the Leidenfrost conditions in context to nanoscale thin film liquid-vapor phase process has been generated using a predictive model based on deep neural networks that has been designed, trained and cross validated against molecular dynamics data of the present study.

Comparison of the performances of different drying enhancers for waterborne polyvinyl alcohol films

AbstractWaterborne polyvinyl alcohol (PVA) films show lower environmental impact but render high residual solvent on account of hydrophilicity of PVA and low volatility of water. Plasticizers have shown high potential to act as drying enhancers in some recent studies. Plasticizers triphenyl phosphate (TPP) and polyethylene glycol (PEG400) with their favorable chemical structures and relatively low molar masses are promising options. Their performances in drying waterborne PVA films are compared with the plasticizers used in earlier works, at different initial wet film thicknesses, polymer contents, enhancer contents, and enhancer molar masses. Films were solvent casted by drying PVA‐water solutions in a substrate. TPP causes maximum lowering of the residual solvent and does this at high drying rate corresponding to low initial wet film thickness and PVA content. The least value of residual solvent is 0.20% at optimum TPP loading. The next best residual solvent results of 0.21% and 0.59% are, respectively, exhibited by PEG400 and PEG6000, but at low drying rate for high wet film thickness, for both the enhancers; however, at high drying rate for low wet film thickness anomalous skinning increased the residual solvent. At 0.51%, Capstone FS‐63 also gives good results and at high drying rate. Their relative performances are correlated to the viscosity of cast solutions, glass transition temperature of films (DSC), and chemical structures of the polymer and enhancers. TPP thus proved to be most effective. SEM showed dense films and disappearance of defects with optimum loading of TPP, and TGA/DTG showed thermally stable coatings. In spite of the higher cost of TPP it can have useful specialized applications that exploit its excellent flame retardance features.

Conductive TiN thin films grown by plasma-enhanced atomic layer deposition: Effects of N-sources and thermal treatments

This work consists of optimizing TiN plasma-enhanced atomic layer deposition using two different N-sources: NH 3 and N 2. In addition to maximizing the growth per cycle (GPC) and to shorten the deposition duration, comprehensive in situ and ex situ physicochemical characterizations give valuable information about the influence of the N-source nature, their dilution in Ar, and the plasma power on layer’s final properties. N 2 and NH 3 dilutions within Ar are extensively investigated since they are critical to decreasing the mean free path ( ℓ) of plasma-activated species. A 1:1 gas ratio for the N-sources:Ar mixture associated with low flows (20 sccm) is optimal values for achieving highest GPCs (0.8 Å/cycle). Due to lower reactivity and shorter ℓ of the excited species, N 2 plasma is more sensitive to power and generator-to-sample distance, and this contributes to lower conformality than with NH 3 plasma. The resistivity of the initial amorphous films was high ( ≥ 1000 μ Ω cm) and was significantly reduced after thermal treatment ( ≤ 400 μ Ω cm). This demonstrates clearly the beneficial effect of the crystallinity of the film conductivity. Though N 2 process appears slightly slower than the NH 3 one, it leads to an acceptable film quality. It should be considered since it is nonharmful, and the process could be further improved by using a reactor exhibiting optimized geometry.

Vapor Phase Ammonia Curing to Improve the Mechanical Properties of Antireflection Optical Coatings Designed for Power Laser Optics

Projects of inertial confinement fusion using lasers need numerous optical components whose coatings allow the increase in their transmission and their resistance to high laser fluence. A coating process based on the self-assembly of sol-gel silica nanoparticles and a post-treatment with ammonia vapor over the surfaces of the optical components ("ammonia curing process") was developed and successfully optimized for industrial production. Manufacturing such antireflective coatings has clear advantages: (i) it is much cheaper than conventional top-down processes; (ii) it is well adapted to large-sized optical components and large-scale production; and (iii) it gives low optical losses in transmission and high resistances to laser fluence. The post-treatment was achieved by a simple exposition of optical components to room-temperature ammonia vapors. The resulting curing process induced strong optical and mechanical changes at the interface and was revealed to be of paramount importance since it reinforced the adhesion and abrasion resistance of the components so that the optical components could be handled easily. Here, we discuss how such coatings were characterized and how the initial thin nanoparticle film was transformed from a brittle film to a resistant coating from the ammonia curing process.

Formation and growth kinetics of the initial amorphous oxide film on the aluminum melt: A ReaxFF molecular dynamics simulation

Understanding on oxidation is critical for the improvement of aluminum melt quality which determines the properties of the aluminum alloy processed by casting. However, the oxidation mechanism of aluminum melt is still unclear in atomistic scale. In this work, we performed reactive molecular dynamics simulation to investigate the oxidation mechanism of aluminum melt on an atomic scale. Our results focus on the island-like nucleation on the melt surface and the following growth of the oxide film. The oxide grows via ion diffusion and the diffusion of O anions plays a greater effect. The evolution of the diffusion coefficient indicates an island-by-layer growth on the aluminum melt. Kinetically, the oxide growth obeys a linear law during the nucleation stage and switches to a logarithmic law after a closed oxide film forms. Besides, we emphasize the effect of oxygen content and ambient temperature on the formation of oxides. Our research can provide insights into the atomic-scale oxidation mechanism of aluminum melt which contributes to the better design for anti-oxidation methods during casting and the oxide-based functional materials.