Smooth Films Research Articles

Electrical and thermal conductivity in graphene-enhanced carbon-fibre/PEEK: The effect of interlayer loading

Combining graphene at different loadings with composites offers the possibility of tailored electrical and thermal properties for the aerospace sector, including electrostatic dissipation, thermal management and lightning strike protection applications. The effects of interlaminar graphene loadings to impart property enhancement in fibre reinforced thermoplastic composites remains unknown. Spray deposition offers a highly scalable, and rapid method to embed graphene. This study investigates the application of spray-deposited graphene suspension synthesised via liquid phase exfoliation (LPE) to functionalise carbon fibre/polyether ether ketone (CF/PEEK) composites. LPE graphene suspensions were spray deposited onto CF/PEEK prepreg ply substrates to create smooth thin films. With increased deposition time the graphene thin film root mean squared roughness decreased from 3.51 μm to 2.52 μm. The addition of 0.25 wt%, 0.7 wt% and 1.1 wt% graphene to the interlaminar regions in consolidated CF/PEEK imparted enhanced electrical and thermal conductivity. Electrical conductivity enhancement of up to ∼252% transverse to the fibre direction and up to ∼204% through thickness was measured after the addition of 0.25 wt% graphene. Thermal diffusivity increased up to ∼183% through-thickness, while 61% in the transverse to the fibre direction with 0.7 wt% additions. However, increased graphene loading also increased the void content in the composite resulting in reduced shear strength. Excess surfactant vapourisation during high temperature processing likely created voids up to 2.8 vol% often located within the interply and interlaminar region hindering anisotropic conductivity enhancement. Nevertheless, graphene loadings within the interlaminar region show promise in imparting bulk property enhancement.

Highly conductive RuO2 thin films from novel facile aqueous chemical solution deposition

Ruthenium dioxide (RuO2) thin films were synthesized by Chemical Solution Deposition (CSD) on silicon substrates using only water and acetic acid as solvents. The microstructure, phase purity, electrical and optical properties as well as the thermal stability of the thin films have been characterized. The microstructure of the thin films strongly depends on the annealing temperature: A smooth thin film was achieved at an annealing temperature of 600 °C. Higher annealing temperatures (800 °C) led to radial grain growth and an inhomogeneous thin film. A very low resistivity of 0.89 µΩm was measured for a 220 nm-thick thin film prepared at 600 °C. The resistivity of the thin films increases with temperature, which indicates metallic behavior. Phase purity of the thin films was confirmed with X-ray Diffraction (XRD) measurements, X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. Transmission and reflectivity measurements indicate that RuO2 efficiently blocks the UV-VIS and IR wavelengths. The optical constants determined via spectroscopic ellipsometry show high absorption in the near-IR region as well as a lower one in the UV-VIS region. The thermal stability was investigated by post-annealing, confirming that the thin films are stable up to 750 °C in synthetic air.Graphical

Mechanical properties and meso-structure of concrete under the interaction between basalt fiber and polymer

Insufficient adhesion of the fibers to the concrete matrix causes the fibers to be pulled out under load, making the fiber concrete unable to meet the support requirements of deep roadways. Basalt fiber (BF) and polymers were selected for the design of mechanical experiments and studied using CT scanning, scanning electron microscopy (SEM) and discrete element simulation. The results show that the fiber mainly affects the compressive and flexural strength of concrete, and the polymer has an effect on the splitting tensile strength of the fibers. From the fine viewpoint, the increase in BF admixture resulted in the conversion of medium pores to small pores within the concrete. Incorporation of polymers results in a smooth polymer film inside the concrete matrix and more hydration products on the surface of the BF to enhance the adhesion of the BF to the concrete matrix. In the discrete element simulation, the fracture evolution can be divided into three stages and the angle of the microscopic fracture is mainly distributed in the range of 60°∼130°. Under loading, BF shares the stress of the matrix and presents itself as a tensile force at its tip, and the increase in BF doping improves the integrity of the specimen at damage.

Transfer-free synthesis of large-area 2D boron films on non-wetting liquid gallium substrate

Two-dimensional (2D) boron films have been studied for their attractive physical and chemical properties in diverse technologies. However, the synthesis of large scale and high-quality boron films is still challenging, which limit its applications in high-performance devices. In this work, thin 2D boron films have been synthesized by chemical vapor deposition (CVD) on non-wetting liquid gallium (Ga) spheres by using boron and boron oxide powders as solid sources. The thin films were directly exfoliated onto SiO2/Si substrates to prepare smooth and uniform boron films by means of mechanical exfoliation method. The peak of boron at 618 cm−1 wave number is obtained by Raman characterization and the boron peak at 188.8 eV is obtained by XPS, which indicates that the film is elemental boron film. By controlling the intercalation chemistry, we obtained large-area 2D polycrystalline boron films with a thickness of 0.8 nm by using transfer-free Synthesis, which avoids the introduction of impurities. The research promotes the application of 2D boron thin film materials in electrical and optical devices.

Investigation of temperature dependant current transport mechanism in Ag/In2O3/p-Si/Al heterojunction

Employing the pulsed laser ablation technique nano-crystalline thin films of Indium oxide (In2O3) are deposited successfully on boron doped silicon substrate. The structural and morphological parameters of the films are investigated by using X-ray diffraction and atomic force microscopic (AFM) spectroscopy, respectively. The deposited films are the crystalline nanostructures with (400) as preferred diffraction peak and grain size of 56.56 nm approximately. The computed roughness (Rq) of In2O3 film is 1.02 nm. The AFM analysis validated the deposition of homogeneous smooth In2O3 films with surface roughness of the order of nanometer. UV–vis spectroscopy was used to study the optical properties of the films. Greater than 80% transparency in visible region was exhibited by the films. The value of the optical band gap was found to be 3.89 eV. The electrical parameters dominating the mechanism of current transport in n-In2O3/p-Si heterojunction were explored by observing the temperature-dependent current–voltage (I–V) properties. In the temperature range of 80–300 K, the ideality factor and barrier height were found to be strongly temperature dependent. It was noticed that with the decrease in temperature there is increase in ideality factor whereas decrease in barrier height which confirm the interfacial imperfections and inhomogeniety in potential barrier height distributions. The temperature dependence of I–V data has revealed the existence of double Gaussian distribution of barrier heights with mean values of 0.85eV and 0.78eV with standard deviation of 0.014 V and 0.012 V respectively. The modified Richardson's plot gives the average barrier height and Richardson's coefficient as 0.86eV and 4.7 × 105 Am−2K−2 in the temperature range 300 K–180 K and 0.77eV and 5.2 × 105 Am−2K−2, respectively in the temperature range 160 K–80 K. The values of Richardson's constants are of the order of known theoretical value of 3.2 × 105 Am−2 K−2.

Hydrodynamic and thermal model for gravity-driven smooth laminar film flow undergoing flash evaporation cooling: Case study and correlation development

Hydrodynamic and thermal analyses have been carried out for gravity-driven smooth laminar film flow, undergoing flash evaporation at the free surface. A classical one-dimensional semi-analytical approach has been adopted to address a unique problem where hydrodynamic and thermal boundary layers (TBLs) approach from opposite directions and eventually intersect each other. This occurs due to the rapid evaporation cooling at the film-free surface exposed to the low-pressure ambiance, leading to the growth of a TBL from the free surface. In contrast, the hydrodynamic boundary layer (HBL) grows from the solid wall over which the film flow occurs. The intersections between the TBL and HBL edges, HBL edge and the free surface, and TBL edge and the wall, in conjunction with the attainment of a fully developed hydrodynamic condition, result in the division of the overall film domain into three distinct hydrodynamic and five distinct thermal sub-zones requiring zone-specific formulations. The model is successfully validated for hydrodynamic formulations with the existing experimental data. However, the lack of available experimental studies limits the validation of the proposed thermal model. Correlations for relevant thermal and hydrodynamic parameters, such as local Nusselt number, local free surface temperature, local bulk mean temperature, and local film thickness, are developed based on the model predictions. The proposed model and the correlations derived from its predictions are anticipated to serve as crucial benchmarks for optimizing the design of thermal management and desalination systems that are fundamentally driven by the film evaporation process.

One-Step Fabrication Bioinspired Flexible Hierarchical Micro-Nano Structures with Different Morphologies.

In this study, different flexible structures that are morphologically like the micro-nano pillars, setae, and cilia on many natural organism surfaces are created with a novel fabricating strategy to explore the phenomenon and mechanism of static and dynamic droplets forming on them. Just by adjusting the mold pattern during fabrication, different micro/nanomorphologies including micro-nano pillar, filament, or flake arrays could be conveniently obtained on a pristine smooth film surface. Due to the existence of uniformly distributed hierarchical micro-nano structure arrays that are composed of top-down nanoscale filamentous tips, micro block bases, and grooves on the film, air trapped in arrays connects the atmosphere continuously and forms a successive air-pocket layer, which greatly reduces the solid-liquid interfacial fraction and endows the micro-nanotextured film with the capability of superhydrophobicity, low-adhesion, self-cleaning, anti-icing, and deicing characteristics. Through various mechanical and chemical tests, the film has demonstrated its robustness, making it highly suitable for a wide range of practical engineering applications.

Characterization of Nano-SiO2/Zein Film Prepared Using Ultrasonic Treatment and the Ability of the Prepared Film to Resist Different Storage Environments.

This study has developed, ultrasound-assisted, a novel food packaging film (U-zein/SiO2) for food packaging applications. Incorporating an optimal concentration of 18 mg/mL of nano-SiO2 and subjecting the film to 10 min of ultrasonic treatment resulted in a remarkable increase of 32.89% in elongation at break and 55.86% in tensile strength. In addition, the incorporation of nano-SiO2 effectively reduces the water content and solubility of the composite film, resulting in improved water/oxygen barrier properties. These physiochemical properties were further improved with the application of ultrasound. The analysis of attenuated total reflectance-Fourier transform infrared, X-ray diffraction, differential scanning calorimetry, and scanning electronic microscope demonstrated that the ultrasound treatment improved the hydrogen bonds, improved thermal stability, molecular arrangement, structure stability, and intermolecular compatibility of the composite film, resulting in enhanced physio-mechanical properties of the film. In addition, the ultrasound treatment led to a smoother film surface and reduced the pores on the film's cross-section. Moreover, the U-zein/SiO2 film exhibited excellent mechanical and water/oxygen barrier properties in different storage environments over a period of 30 days. These results offer sound theoretical support for the practical application of the prepared preservative film.

New Straw Coating Material for Improving the Slow-Release Performance of Fertilizers.

In this work, we extracted cellulose from agricultural waste and produced a new straw coating material (ethyl cellulose, EC) through a series of modification operations. The slow-release properties of ethyl cellulose-coated urea (EU) and its absorption and utilization by plants were evaluated. The surface of EU can form a smooth and fine film, and the initial nutrient release rate is only 37.91% that of the uncoated fertilizer. Compared with common urea, the nitrogen of plants cultivated with EU increased by 17.69%, and the leached nitrogen decreased by 61.29%, indicating that EU can reduce nitrogen waste to the greatest extent and continuously supply nutrients to crops. Therefore, the application of EU could be a more practical, environmentally friendly, and sustainable alternative to nitrogen fertilizers.

High-performance ultraviolet Cs3Cu2I5 photodetector derived from two-step annealing process

Perovskite based ultraviolet photodetectors have great potential in fire warning, disease treatment and missile guidance, etc. owing to its high mobility, large absorption coefficient and solution processability. However, poor stability and toxic lead element hinder it further applications in current stage. Recently, all-inorganic lead-free perovskite Cs3Cu2I5 demonstrates great potential in ultraviolet detection for its outstanding long-term stability and suitable bandgap. Nevertheless, pinholes and roughness of film lead to leakage current and lower carrier mobility, restricting detection performance. Herein, a two-step annealing method was introduced to optimize the nucleation and crystallization of Cs3Cu2I5 grains. Owing to the improvement of grain quality, fewer pinholes and precipitated phases occurred during crystallization process, thus, resulting in compact and smooth film surface. The hole and electron mobilities of the two-step annealed film were promoted up to 0.697 cm2/(V·s) and 1.579 cm2/(V·s) respectively. As a consequence, the constructed Cs3Cu2I5 photodetector exhibits high on/off ratio of 6.3 × 104, a shorter response time of 26.2 ms (τrise)/49.9 ms (τfall), external quantum efficiency of 3.04%, moderate responsivity of 8.46 mA/W and detectivity of 3 × 1013 Jones. Basing on these merits, an ultraviolet imaging was demonstrated. This work provides an effective but simple strategy to endow Cs3Cu2I5 photodetector with improved performance for further applications in the future.

Effect of protonic acid concentration on electrical properties of fly ash magnetic beads/polyaniline composites

AbstractMagnetic polyaniline nanofibers were synthesized by oxidative polymerization using protonic acid and fly ash magnetic beads as dopants and ammonium persulfate as oxidant. The synthesized magnetic polyaniline was characterized by FT‐IR, UV, XRD and SEM, and its morphology and structure were revealed. Polyaniline magnetic electrodes were prepared by pressing method, and their electrochemical properties were analyzed by cyclic voltammetry and constant current charge–discharge methods. The capacities of polyaniline powders doped with optimal concentration of hydrochloric acid and p‐toluene sulfonic acid at current density of 1 A/g were 250.75 and 410.5 F/g, respectively. The magnetic polyaniline doped with optimal acid concentration has good conductivity through impedance measurement analysis. A smooth and uniform film was prepared by pressing magnetic polyaniline powder and its photosensitivity was observed under different monochromatic illumination. The results show that the current and voltage have a linear relationship and that different monochromatic light energies can be distinguished significantly with the increase of voltage.

Nanodiamond Influence on the Nucleation and Growth of YBCO Superconducting Film Deposited by Metal-Organic Decomposition.

It was recently shown that the introduction of nanodiamond (ND) into a superconducting metal-organic deposited YBa2Cu3O7-δ (YBCO) film produces an increase in critical current density in self-field conditions (B = 0 T). Such improvement appears to be due to the formation of denser and smoother films than the samples deposited without ND. This paper presents the work done to understand the role of ND during YBCO nucleation and growth. A detailed study on YBCO+ND films quenched at different temperatures of the crystallization process was carried out. Results showed that the reaction responsible for YBCO production appeared effectively affected by ND. In particular, ND stabilizes one of the YBCO precursors, BaF2(1-x)Ox, whose conversion into YBCO requires a prolonged time. Therefore, the YBCO nucleation is slowed down by ND and begins when the experimental conditions favor both thermodynamically and kinetically the formation of YBCO along the c-axis. This effect has important implications because the growth of a highly epitaxial c-axis YBCO film enables excellent superconducting performance.

Silicone Polymer Thin Films Fabricated by Ion‐Assisted Deposition Methods

The ion‐assisted vapor deposition (IAD) method is utilized to prepare silicone polymer thin films with low surface energy. Methacryl‐modified silicone oligomer is deposited under irradiation of argon ions with various ion energies and currents. Fourier transform infrared analysis and solvent durability test reveal that the polymerization reaction is enhanced with increasing ion energy. Smooth and insoluble films are obtained under ion irradiation at the energy of 1 kV. The films have surface free energy of about 26 mJ m−2, and the peeling strength of an adhesive tape on their surface can be controlled by the ion current of IAD. X‐ray photoelectron spectroscopy analysis shows that the ion irradiation induces dissociation of methyl side groups and cross‐linking by Si–O network formation, leading to an increase in the peeling strength and improvement in film robustness. The silicone films deposited by IAD have potential applicability to the anti‐adhesive surfaces.

Bowl-Assisted Ball Assembly for Solvent-Processing the C60 Electron Transport Layer of High-Performance Inverted Perovskite Solar Cell.

Pristine fullerene C60 is an excellent electron transport material for state-of-the-art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high-quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl-shaped additive, corannulene, to assist in C60 -assembly into a smooth and compact film through the favorable bowl-ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C60 , it also plays a critical role in forming C60 -corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution-processed-C60 (SP-C60 ) ETL. Moreover, the stability of the CC device is far superior to that of the C60 -only device because corannulene can retard and curb the spontaneous aggregation of C60 . This work establishes the bowl-assisted ball assembly strategy for developing low-cost and efficient SP-C60 ETLs with high promise for fully-SP PSCs.

Water vapor permeability of smooth cellulose nanofiber film prepared via spraying

Eco-friendly and greener barrier materials are required to replace the synthetic packaging materials as they produce a threat to environment. These can be fabricated by natural polymers such as cellulose nanofiber (CNF). The sustainability of CNF was so amazing due to its potential for circular economy and provides alternative platform for synthetic plastics. The challenging task to fabricate CNF films still existed and also current methods have various limitations. CNF films have good oxygen permeability and the value was lower than synthetic plastics. However, CNF films have poor water vapour permeability and higher than that of synthetic plastics. The fabrication method is one of strong parameters to impact on the water permeability of CNF films. The deposition of CNF suspension on the stainless-steel plate via spraying, is a potential process for fabrication for CNF films acting as barrier material against water vapour. In spraying process, the time required to form CNF films in diameter of 15.9 cm was less than 1 min and it is independent of CNF content in the suspension. The uniqueness of CNF films via the spraying process was their surfaces, such as rough surface exposed to air and smooth surface exposed to stainless steel. Their surfaces were investigated by SEM, AFM and optical profilometry micrographs, confirming that the smooth surface was evaluated notable lower surface roughness. The spray coated surface was smooth and glossy and its impact on the water vapor permeability remains obscure. The spraying process is a flexible process to tailor the basis weight and thickness of CNF films can be adjusted by the spraying of CNF suspension with varying fibre content. The water vapour permeability of CNF films can be tailored via varying density of CNF films. The plot between water vapour transfer rate (WVTR)/water vapour and density of CNF films has been investigated. The WVP of spray coated CNF films varied from 6.99 ± 1.17 × 10−11 to 4.19 ± 1.45 × 10−11 g/m.s.Pa. with the density from 664 Kg/m3 to 1,412.08 Kg/m3. The WVP of CNF films achieved with 2 wt% CNF films (1,120 Kg/m3) was 3.91 × 10−11 g/m.s.Pa. These values were comparable with the WVP of synthetic plastics. Given this correspondence, CNF films via spraying have a good barrier against water vapour. This process is a potential for scale up and commercialization of CNF films as barrier materials.

Realization of High-Efficiency Inverted Planar Perovskite Solar Cells Based on PEDOT: PSS Doped with Lithium Fluoride

The photovoltaic performance of perovskite solar cells with inverted structure depends on the conductivity of the hole transport layer and the charge transport rate to some extent. To further enhance the effect of the hole transport layer, lithium fluoride (LiF) was doped into poly (3,4-ethylene dioxythiophene)-polystyrene sulfonic acid (PEDOT: PSS) to improve its rate of conductivity and interfacial charge transport. The optimal photoelectric conversion efficiency of LiF-based perovskite solar cells that dope hole transport layer is 20.32% with negligible hysteresis, which is much higher than that of the control group (16.70%). Among all photovoltaic parameters, the improvement of open circuit voltage and fill factor is significant. LiF can not only promote the electrical characteristics of PEDOT: PSS and its hole mobility, but also optimize the quality of the upper perovskite film. Perovskite film shows a crystal orientation more conducive to hole transport on the modified hole transport layer, which obtains a dense and smooth absorption layer film. In this study, PEDOT: PSS-based perovskite solar cells with inverted structure doped with LiF are prepared, which provides a simple and effective method to commercialize perovskite solar cells.

Bowl‐Assisted Ball Assembly for Solvent‐Processing the C60 Electron Transport Layer of High‐Performance Inverted Perovskite Solar Cell

AbstractPristine fullerene C60 is an excellent electron transport material for state‐of‐the‐art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high‐quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl‐shaped additive, corannulene, to assist in C60‐assembly into a smooth and compact film through the favorable bowl‐ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C60, it also plays a critical role in forming C60‐corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution‐processed‐C60 (SP‐C60) ETL. Moreover, the stability of the CC device is far superior to that of the C60‐only device because corannulene can retard and curb the spontaneous aggregation of C60. This work establishes the bowl‐assisted ball assembly strategy for developing low‐cost and efficient SP‐C60 ETLs with high promise for fully‐SP PSCs.

Nanoscale Quantized Oscillations in Thin‐Film Growth Greatly Enhance Transconductance in Organic Transistors

AbstractA growth mode of pentacene thin films deposited by high vacuum sublimation where the morphology versus thickness h “rings” back and forth between rough 3D films with pyramid islands and smooth 2D films with ziqqurat islands is discovered. The roughness σ versus h exhibits seamless coherent oscillations whose amplitude and wavelength increase as integer multiples of 1.5 ML thickness. The quantized oscillations are reconducted to dynamic wetting/dewetting transitions involving the upper layers of pentacene film. Importantly, the transconductance of organic field effect transistors, either in solid state or electrolyte‐gated, exhibits antiphase oscillations with one‐decade swing. Charge mobilities in the wetting regime reach 0.1 cm2 V−1 s−1, in line with high‐end values reported for thin‐film pentacene transistors. Controlling this growth mode enables the limitations of charge transport imposed by the roughening transition to be overcome, a universal feature of high vacuum growth to date.

Monodisperse Adducts-Induced Homogeneous Nucleation Towards High-Quality Tin-Based Perovskite Film.

The classic solvent system can't sufficiently separate one-dimensional edge-sharing SnI2 crystals in solution, which severely restricts the fabrication of high-quality tin-based perovskite film. Herein, a strong Lewis base (hexamethylphosphoramide, HMPA) has been introduced to coordinate Sn2+ to modulate solvation behaviors on perovskite precursor and regulate crystallization kinetics. The large molecular volume of HMPA and stronger bind energy of SnI2·2HMPA (-0.595 eV vs -0.118 eV for SnI2·2DMSO) change the solvation structure of SnI2 from edge-sharing cluster to monodisperse adduct, which contributes to uniform nucleation sites and prolongs crystal growth process. Delightfully, a fully-covered perovskite film is formed on the large-area substrate and tin-based perovskite solar cells processed with HMPA exhibit an excellent efficiency of 13.46%. This research provides novel insights and directions for the solution preparation of smooth and uniform large-area tin-based perovskite film.

High Q‐Factor and Low Threshold Continuous‐Wave Near‐Infrared Lasing with Quasi‐2D Perovskites

AbstractQuasi‐2D perovskites have shown great potential in achieving solution‐processed electrically pumped laser diodes due to their multiple‐quantum‐well structure, which induces a carrier cascade process that can significantly enhance population inversion. However, continuous‐wave (CW) optically pumped lasing has yet to be achieved with near‐infrared (NIR) quasi‐2D perovskites due to the challenges in obtaining high‐quality quasi‐2D films with suitable phase distribution and morphology. This study regulates the crystallization of a NIR quasi‐2D perovskite ((NMA)2FAn−1PbnI3n+1) using an 18‐crown‐6 additive, resulting in a compact and smooth film with a largely improved carrier cascade efficiency. The amplified spontaneous emission threshold of the film is reduced from 47.2 to 35.9 µJ cm−2. Furthermore, by combining the film with a high‐quality distributed feedback grating, this study successfully realizes a CW NIR laser of 809 nm at 110 K, with a high Q‐factor of 4794 and a low threshold of 911.6 W cm−2. These findings provide an important foundation for achieving electrically pumped laser diodes based on the unique quasi‐2D perovskites.