Surface Coverage Of Films Research Articles

Enhanced performance of ambient-air processed CsPbBr3 perovskite light-emitting electrochemical cells via synergistic incorporation of dual additives

Metal halide perovskite light-emitting electrochemical cells (MHP-LECs) are promising due to their facile solution processability and exceptional optoelectrical properties. However, commercialization is hindered by poor thin-film coverage and the need for glovebox processing. This study addresses these issues by incorporating poly(ethylene oxide) (PEO) and potassium hexafluorophosphate (KPF6) into cesium lead bromide perovskite (CsPbBr3) emitting layers (EML), processed under ambient-air conditions. These perovskite composite thin films were spin-coated on a preheated substrate, and the device structure was ITO/PEDOT:PSS/EML/Al. Notably, the MHP-LEC based on CsPbBr3:PEO:KPF6 (100:65:0.2, weight ratio) exhibited pure-green emission with a peak at 524 nm and a narrow full width at half-maximum of 27 nm. Compared to a reference device (CsPbBr3:PEO (100:65, weight ratio)), the new device showed 1.5-, 4-, and 5-fold improvements in current density, electroluminescence (EL) intensity, and lifetime, respectively. These enhancements are attributed to reduced non-radiative current leakage, improved film surface coverage and passivation, and balanced charge carrier injection and transportation. This study offers a straightforward approach for processing CsPbBr3 thin films under ambient-air conditions, enhancing the EL performance of MHP-LECs.

Tweaking the Non-Volatile Write-Once-Read-Many-Times (WORM) Memory using Donor-Acceptor Architecture with Isatin as Core Acceptor.

Organic memory devices have attracted attention because they promise flexible electronics, low manufacturing costs, and compatibility with large-scale integration. A series of new D-A architectures were synthesized employing different donor groups and the isatin moiety as the acceptor through Suzuki-Miyaura coupling reactions. Strong intramolecular interactions were observed in the synthesized compounds, further corroborated by an optimal bandgap. The SEM investigation confirmed good molecular ordering and superior thin film surface coverage. All the compounds demonstrated notable binary Write-Once-Read-Many-Times (WORM) memory behaviour. The threshold switching voltage for these D-A systems ranged from -0.79 to -2.37 V, with the compound having isobutyl substituent showing the lowest threshold voltage and maximum ON/OFF ratio of 102, thus outperforming others. The combined effects of charge transfer and charge trapping are responsible for the resistive switching mechanism prevailing in these systems. The alterations in D-A molecules that affect molecular packing, thin film morphology, and, finally, the memory performance of the active layer are highlighted in this work.

High–Quality and Stable Quasi‐2D Perovskite Film Prepared by Introducing Alkali Metal Ion Additive

AbstractDue to the excellent stability, researchers have shown great interest in quasi two–dimensional (2D) perovskite in recent years. However, the poor film quality and low photoelectric conversion efficiency (PCE) of 2D perovskite solar cells are still a major issue that restricts them from catching up with three–dimensional (3D) perovskite. Herein, we introduce sodium iodide as an additive to improve the surface coverage of 2D perovskite ((BA)2(MA)3Pb4I13) films and reduce the number of grain boundaries. Steady–state photoluminescence (PL) and ultraviolet photoelectron spectroscopy (UPS) indicate that non–radiative defects are suppressed and the band alignment is regulated. After modified by NaI, the film surface coverage enhances and the number of holes decreases. As a result, the PCE of device with NaI increases from 13.63 % to 16.40 % at optimal concentration, and the hysteresis effect is also suppressed. Besides, the humidity and thermal stability of perovskite are enhanced. The device with NaI modification can keep 80 % of initial efficiency, compared to 30 % for reference device after stored 30 days under ambient air condition. This work provides a simple method to improve the quality of quasi 2D perovskite films.

Model development methodology for localized corrosion of copper

A 2-D axisymmetric time-dependent model for the corrosion of copper under an Evans droplet was developed using the finite-element method. Some unique features of the model are inclusion of 6 heterogeneous and 15 homogeneous reactions, implicit calculation of nm-scale films, and treatment of the influence of films on surface concentrations and potentials. Cathodic and anodic regions are not pre-defined on the electrode surface but are determined by values of local concentrations and potentials. The model shows time-dependent radial distributions for current density and surface coverage of films. The present work describes the methodology for the development of this mechanistic model.

PH Tunable Thin Film Gradients of Magnetic Polymer Colloids for MRI Diagnostics.

Magnetic polymer colloids comprising of magnetite (Fe3O4) nanoparticles and Eudragit E100 were employed to fabricate thin film gradients and were investigated for in-vitro magnetic resonance imaging. Magnetic polymer colloids (MPC) and polyacrylic acid (PAA) with stimuli-responsive cationic and anionic functional groups respectively facilitate the formation of thin film gradients via layer by layer technique. The characteristics of films were controlled by changing the pH and level of the adsorbing solutions that lead to the development of gradient films having 5.5, 10.5 and 15.5 bilayers. Optical microscopy, scanning electron microscopy and magnetic force microscopy was carried out to determine the surface coverage of films. Surface wettability demonstrated the hydrophilicity of adsorbed colloids. The developed thin-film gradients were explored for in vitro magnetic resonance imaging that offers a point of care lab-on-chip as a dip-stick approach for ultrasensitive in-vitro molecular diagnosis of biological fluids.

Atomic layer deposition of Al2O3 and TiO2 on MoS2 surfaces

In this work, the authors compare the surface coverage obtained in the initial and intermediate steps of Al2O3 and TiO2 atomic layer deposition on MoS2 surfaces prepared by either mechanical exfoliation or chemical vapor deposition (CVD). They find that the film surface coverage is highly dependent on the origin and preparation of the MoS2 starting surface. While mechanical exfoliation can be used to quickly obtain few-layer MoS2 surfaces, these surfaces exhibit significant variability in quality and cleanliness, leading to unpredictable film growth. Conversely, MoS2 grown by CVD provides a more reliable starting surface resulting in significantly improved scattering in the surface coverage. They find that, on CVD MoS2, neither Al2O3 nor TiO2 film growth strongly exhibits temperature dependence described by the Langmuir adsorption model. For both processes, films up to 6 nm thick deposited on CVD MoS2 are not fully coalesced and exhibit a large concentration of pinhole type features.

Monitoring the Formation of a CH3NH3PbI3–xClx Perovskite during Thermal Annealing Using X‐Ray Scattering

Grazing incidence wide and small angle X‐ray scattering (GIWAXS and GISAXS) measurements have been used to study the crystallization kinetics of the organolead halide perovskite CH3NH3PbI3–xClx during thermal annealing. In situ GIWAXS measurements recorded during annealing are used to characterize and quantify the transition from a crystalline precursor to the perovskite structure. In situ GISAXS measurements indicate an evolution of crystallite sizes during annealing, with the number of crystallites having sizes between 30 and 400 nm increasing through the annealing process. Using ex situ scanning electron microscopy, this evolution in length scales is confirmed and a concurrent increase in film surface coverage is observed, a parameter crucial for efficient solar cell performance. A series of photovoltaic devices are then fabricated in which perovskite films have been annealed for different times, and variations in device performance are explained on the basis of X‐ray scattering measurements.

Preparation of films of nanodiamonds by step-by-step deposition approach through hydrogen bonding

The films of nanodiamond (ND) have been prepared at room temperature by Step-by-Step (SbS) assembly of ND particles on glass substrates mainly through hydrogen bonding. The ND SbS films have regularly organized nanostructures, which could be tuned by the number of steps deposited. The ND SbS film growth shows a two-step mode with the first step having higher growth rate than that of the second one, which is probably attributed to the difference in the film surface coverage as well as the size of ND aggregates. This SbS assembly process for the preparation of films of ND is simple and economic with controllable film morphology. Since high surface curvature of nanostructure is able to help retain the structural features of biomolecules, the ND SbS film could be a desirable platform for biological applications such as biomolecule immobilization.

Calix[4]arene crown-4 ether modified glassy carbon electrode for electrochemical determination of norepinephrine

A sensitive and selective electrochemical method for the determination of norepinephrine (NE) was developed by using a calix[4]arene crown-4 ether (CACE) film modified glassy carbon electrode (GCE). The fabrication of the CACE film and its electrocatalytic effect for electrochemical oxidation of NE were investigated by electrochemical impedance spectroscopy (EIS) and voltammetric methods. It was found that the electrochemical behavior of NE on the CACE film modified electrode depended on the film thickness of CACE. Based on the electrochemical data, the CACE film surface coverage (theta), the charge transfer number (z) and the amount of the surface-bound NE (Gamma) were calculated. The effects of the experimental variables such as the solution pH and the applied potential were investigated for optimum analytical performance. Excellent linear relationships were obtained in two concentration ranges of NE: one was from 0.55 to 9.7 microM and the other was 9.7 to 230 microM. The detection limit (S/N = 3) of NE obtained by steady-state amperometry was 0.28 microM. The relative standard deviation (RSD) for 10 successive measurements of 0.05 mM NE was 2.2%. This method could be applied for the direct determination of NE in injection samples. In addition, effects of possible interferences (e.g. ascorbic acid, AA) were investigated. The present work provides an effective method for amperometric determination of NE by using a CACE modified electrode.

Integrated model for chemically enhanced physical vapor deposition of tantalum nitride-based films

A zero-order semiempirical model has been developed for chemically enhanced physical vapor deposition (CEPVD), a recently developed hybrid approach to film deposition offering the step coverage of chemical vapor deposition while maintaining film quality similar to films produced by ionized physical vapor deposition (IPVD). CEPVD is done by introducing a chemical precursor to the substrate during IPVD. A synergistic effect between the two processes results in which the high energy ions from IPVD aid in the decomposition of the precursor. The precursor then provides film deposition on surfaces that are not easily impacted by IPVD’s directional ions. The model stems from knowledge of reactive sputtering and plasma-enhanced chemical-vapor deposition processes as well as results acquired from CEPVD experiment. It focuses on the Ta–N material system since Ta∕TaN is widely used as a diffusion barrier in Cu damascene processing. Processing parameters are correlated with the target and film surface coverage by Ta,...

Sequential deposition of Cu–Ni by electron beam evaporation and its characterisation

Sequential deposition of Cu–Ni was carried out on glass and mild steel substrates by electron beam evaporation technique. The films were vacuum annealed at 200°C for 1 h. A smooth deposit with 7·8 μm thickness was observed using a profilometer. The polycrystalline nature with FCC structure of the films was determined with X-ray diffraction analysis. The uniform coverage of film surface was observed with atomic force microscopy (AFM). X-ray fluorescence (XRF) showed a change in composition for the vacuum annealed Cu–Ni film. A high transmittance in the visible region and a very low transmittance in the infrared region were observed for these films. Corrosion behaviour of the evaporated Cu–Ni films in 3·5% w/v NaCl solution was examined.

Macroscopically ordered thin films of an organic salt grown by low-pressure organic vapor-phase deposition

We demonstrate the process of low-pressure organic vapor-phase deposition (LP-OVPD) for the growth of crystalline thin films of the organic charge-transfer salt 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) on amorphous TiO 2 substrates. LP-OVPD grown films exhibit polycrystallinity with long-range structural ordering limited only by substrate size. Film surface coverage and macroscopic ordering are strongly determined by the preparation of the TiO 2 surface prior to growth. The morphology and ordering of the films are also found to depend on the deposition temperature and the composition of the precursor molecules. These results suggest that LP-OVPD films are of sufficient quality for use in optical waveguide and related photonic devices.

Surface Morphological Study of J-Aggregate Thin Films by Atomic Force Microscopy

Surface Morphological Study of J-Aggregate Thin Films by Atomic Force Microscopy