Homogeneous Thin Films Research Articles

Complete Protection of O2-Sensitive Catalysts in Thin Films.

Energy conversion schemes involving dihydrogen hold great potential for meeting sustainable energy needs, but widespread implementation cannot proceed without solutions that mitigate the cost of rare metal catalysts and the O2 instability of biological and bioinspired replacements. Recently, thick films (>100 μm) of redox polymers were shown to prevent O2 catalyst damage but also resulted in unnecessary catalyst load and mass transport limitations. Here we apply novel homogeneous thin films (down to 3 μm) that provide protection from O2 while achieving highly efficient catalyst utilization. Our empirical data are explained by modeling, demonstrating that resistance to O2 inactivation can be obtained for nonlimiting periods of time when the optimal thickness for catalyst utilization and current generation is achieved, even when using highly fragile catalysts such as the enzyme hydrogenase. We show that different protection mechanisms operate depending on the matrix dimensions and the intrinsic catalyst properties and can be integrated together synergistically to achieve stable H2 oxidation currents in the presence of O2, potentially enabling a plethora of practical applications for bioinspired catalysts under harsh oxidative conditions.

Fine tuning of inkjet printability parameters for NiO nanofilms fabrication

Nickel oxide (NiO) is a fascinating compound due to its potential use as electrocatalytic material and in many other applications. In several technological applications, the NiO is require as continue and homogeneous thin film. In the present work three water‒based inks were formulated in order to analyze the effect of the presence of additives on their physicochemical properties and printability performance for the fabrication of NiO thin films by using inkjet printing technique. By means of integrated physicochemical analysis, the printability of the formulated inks was defined by a map in terms of Reynolds and Weber numbers. According to the obtained results, all the formulated inks are readily printable. The presence of additives in the respective inks reduced the contact angle value formed onto substrate surface favoring their wettability considerably. This characteristic influenced importantly on the interactions between the deposited droplets, requiring a smaller number of droplets for obtaining a homogeneous, continuous, and well–defined film. After optimization of parameters, NiO films with 1, 3 and 5 layers were inkjet–printed and sintering at 550 °C to obtain crystalline NiO phase characterized by the presence of nanoparticles with sizes of ∼15 nm, film thickness from 90 to 190 nm and Ni2+/Ni3+ surface chemical states.

Optimizing Homogeneous Thin Solid Films (HTSFs) from μL-Blood Droplets via Hyper-Hydrophilic Coatings (HemaDrop™) for Accurate Compositional Analysis via IBA, XRF, and XPS

ABSTRACTLiquid phase analysis dominates the field of blood diagnostics and requires drawing blood volumes of several ml for each test. To achieve acceptable accuracy, each single liquid blood test requires ∼7 mL per blood sample, and repeated blood tests are often needed. Frequent testing ca result in Hospital Acquired Anemia for infants, chronically ill, and critically ill patients. Blood testing methods that can be utilized with small amounts of blood are a critical need to save lives. Theranos claimed to have developed novel methods requiring only a few nL of blood. However, Theranos’ techniques led to errors that exceeded beyond the medically acceptable threshold of 10%. This work investigates solid state blood analysis using low volumes of several µL. The most common blood tests used as first line for diagnostics and monitoring patients’ status, always include blood electrolytes, iron, and in some cases, heavy metals.The present work investigates the formation of rapidly solidified Homogeneous Thin Solid Films (HTSFs) formed from blood drops, in order to make them suitable for solid state analysis in vacuo and in air. The solidification of ∼5 micro-liter (µL)-sized blood droplets into HTSFs is studied with two goals: achieve reproducible HTSFs optimized for producing accurate analysis, and successfully measure the potential accuracy of measurements made on HTSFs for blood electrolytes Na, K, Mg, Ca, and Cl and heavy metals such as Fe.The blood volumes selected for this work are in the µL range, one thousandth volumes drawn for current liquid phase analysis. Balanced Saline Solution (BSS) is used as an initial liquid for testing solidification uniformity and a potential calibration material. Next, canine and human blood are studied on two types of HemaDropTM coatings for solidification: super-hydrophilic and hyper-hydrophilic. HTSF formation from BSS and blood drops are compared on both coated and uncoated surfaces.Three solid state analytical methods are investigated in parallel to probe composition at different depths and test each for reproducibility and accuracy: Ion Beam Analysis (IBA), X-ray Fluorescence (XRF), and X-ray Photoelectron Spectroscopy (XPS). The results show that using solid films of blood yields composition, which can be reproducibly measured by IBA, XPS and XRF to varying degrees. XPS’s depth of analysis, limited to ∼5 nm, probes a small fraction of the HTSF, but provides insights into the range of thickness for homogeneous compositions in HTSFs. Statistical and error analysis help establish whether measurements taken in sets of three typically used in lab fall below the medically accepted error threshold (<10%) for each technique and element detected. Measurements are repeated and taken at various locations and on different HTSFs to establish reproducibility. XRF is of particular interest, because it is fast, accurate, portable and can be conducted in air, making it ideal for areas with limited resources.

Graphene Multi-layer on Plastic Substrate

Vacuum filtration method was used in order to fabricate a homogeneous and uniform thin film of multi-layer graphene on plastic substrate. This self-regulating technique allows the number of graphene layer to be controlled thus controlling the film thickness by simply varying either the concentration of the graphene in the suspension or the filtration volume. Measurement of the sheet resistance as a function of graphene concentration in solution shows the percolation behavior of multi-layer graphene films.

Growth of lithium hydride thin films from solutions: Towards solution atomic layer deposition of lithiated films.

Lithiated thin films are necessary for the fabrication of novel solid-state batteries, including the electrodes and solid electrolytes. Physical vapour deposition and chemical vapour deposition can be used to deposit lithiated films. However, the issue of conformality on non-planar substrates with large surface area makes them impractical for nanobatteries the capacity of which scales with surface area. Atomic layer deposition (ALD) avoids these issues and is able to deposit conformal films on 3D substrates. However, ALD is limited in the range of chemical reactions, due to the required volatility of the precursors. Moreover, relatively high temperatures are necessary (above 100 °C), which can be detrimental to electrode layers and substrates, for example to silicon into which the lithium can easily diffuse. In addition, several highly reactive precursors, such as Grignard reagents or n-butyllithium (BuLi) are only usable in solution. In theory, it is possible to use BuLi and water in solution to produce thin films of LiH. This theoretical reaction is self-saturating and, therefore, follows the principles of solution atomic layer deposition (sALD). Therefore, in this work the sALD technique and principles have been employed to experimentally prove the possibility of LiH deposition. The formation of homogeneous air-sensitive thin films, characterized by using ellipsometry, grazing incidence X-ray diffraction (GIXRD), in situ quartz crystal microbalance, and scanning electron microscopy, was observed. Lithium hydride diffraction peaks have been observed in as-deposited films by GIXRD. X-ray photoelectron spectroscopy and Auger spectroscopy analysis show the chemical identity of the decomposing air-sensitive films. Despite the air sensitivity of BuLi and LiH, making many standard measurements difficult, this work establishes the use of sALD to deposit LiH, a material inaccessible to conventional ALD, from precursors and at temperatures not suitable for conventional ALD.

Hybrid Gibbsite Nanoplatelet/Cellulose Nanocrystal Multilayered Coatings for Oxygen Barrier Improvement.

We have investigated the ability of multilayered hybrid thin films of cellulose nanocrystals (CNCs) and gibbsite nanoplatelets (GNPs) to be built by the layer-by-layer (LbL) technique onto substrates selected for packaging applications, and to improve the oxygen barrier properties. Using complementary structural characterization techniques, namely atomic force microscopy, ellipsometry, and spectral reflectance, we show that when deposited onto model silicon substrates these hybrid films were homogenous and of reduced porosity, and were comprised of alternately deposited monolayers of GNPs and CNCs. The successful deposition of such homogeneous and dense hybrid thin films onto various types of flexible substrates showing different chemical compositions, hydrophilicity, and surface morphology, ranging from cardboard to smart paper, polyethylene (PE) films, and PE-coated cardboard was also confirmed by scanning electron microscopy observations. In view of the diversity of these substrates we could confirm the remarkable robustness of such a deposition process, likely due to (i) the adaptability of the LbL assembling technique and (ii) the strong electrostatic and hydrogen bonding interactions between GNPs and CNCs. The measurement of the oxygen transmission rate (OTR) at 23°C and 50% RH showed that the oxygen barrier properties of the bare substrates could be significantly improved (e.g., 75% decrease of the OTR) after the deposition of such thin (<100 nm) multilayered hybrid films. This lowered permeability was tentatively attributed to the highly tortuous morphology of the coating, acting to impede the gas diffusion. These partially biosourced very thin films stand as good candidates for using as coatings showing high oxygen barrier performance.

Dynamic mode optimization for the deposition of homogeneous TiO2 thin film by atmospheric pressure PECVD using a microwave plasma torch

An atmospheric pressure plasma-enhanced chemical vapor deposition process using a microwave plasma torch has been used for titania thin film synthesis. A dynamic deposition mode was set up to cover a square centimeter surface with a nanostructured TiO2 film. The process parameters were studied and optimized to control the coating crystallinity and morphology and limit the formation of powder in the plasma phase. Contrary to static deposition, the substrate movement promotes a film growth by particles agglomeration in the reference conditions, leading to a cauliflower-like morphology. Then, the precursor proportion in the plasma appears to be determinant in the TiO2 film microstructure. For a precursor flow rate beyond 0.2 slpm, the titania nanoparticles formation in the gas phase is promoted and the thin film is growing by particles agglomeration, leading to a columnar cauliflower-like morphology. At a flow rate of 0.2 slpm, the growth by surface reaction is promoted and the TiO2 film is columnar, where each column is an anatase crystal. After the optimization of the substrate holder movement, it was possible to deposit this last microstructure homogeneously on a square centimeter surface.

Cellulose carbamate derived cellulose thin films: preparation, characterization and blending with cellulose xanthate

Cellulose carbamate (CC) was employed as a water-soluble precursor in the manufacturing of cellulose based thin films using the spin coating technique. An intriguing observation was that during spin coating of CC from alkaline aqueous solutions, regeneration to cellulose was accomplished without the addition of any further chemicals. After rinsing, homogeneous thin films with tunable layer thickness in a range between 20 and 80 nm were obtained. Further, CC was blended with cellulose xanthate in different ratios (3:1, 1:1, 1:3) and after regeneration the properties of the resulting all-cellulose blend thin films were investigated. We could observe some slight indications of phase separation by means of atomic force microscopy. The layer thickness of the blend thin films was nearly independent of the ratio of the components, with values between 50 and 60 nm for the chosen conditions. The water uptake capability (80–90% relative to the film mass) determined by H2O/D2O exchange in a quartz crystal microbalance was independent of the blend ratio.

Solution-Processable Superatomic Thin-Films.

Atomically precise nanoscale clusters could assemble into crystalline ionic crystals akin to the atomic ionic solids through the strong electrostatic interactions between the constituent clusters. Here we show that, unlike atomic ionic solids, the electrostatic interactions between nanoscale clusters could be frustrated by using large clusters with long and flexible side-chains so that the ionic cluster pairs do not crystallize. As such, we report ionic superatomic materials that can be easily solution-processed into completely amorphous and homogeneous thin-films. These new amorphous superatomic materials show tunable compositions and new properties that are not achievable in crystals, including very high electrical conductivities of up to 300 S per meter, ultra low thermal conductivities of 0.05 W per meter per degree kelvin, and high optical transparency of up to 92%. We also demonstrate thin-film thermoelectrics with unoptimized ZT values of 0.02 based on the superatomic thin-films. Such properties are competitive to state-of-the-art materials and make superatomic materials promising as a new class of electronic and thermoelectric materials for devices.

Optical Thin Films of Metal Oxides Produced by the Sol-Gel Method for Photovoltaic Applications

The use of thin films in optoelectronic and photovoltaic devices is aimed at improving the physical properties of the substrate material. The modification of the surface of the silicon substrate is thus one of the greatest challenges in research on photovoltaic materials, in order to achieve even greater efficiency or better adapt their properties depending on the application. The technologies of applying layers vary depending on the effect to be obtained and the material from which the layer is formed. In practice, the most common method is chemical vapor deposition and physical vapor deposition, and the most commonly applied optical materials are SiO2, TiO2 and Si3N4.This paper presents the results of investigations on morphology and optical properties of the prepared aluminium oxide thin films. Thin films were prepared with use of sol-gel spin coating method. Surface morphology studies were carried out using an atomic force microscope. To characterize the surface of the thin films, 3D images and histograms of the frequency of individual inequalities were made. In order to characterize the optical properties of Al2O3 thin films, the reflectance and light transmission tests were performed using a spectrophotometer. Optical constants were determined using a spectroscopic ellipsometer. Results and their analysis show that the sol-gel method allows the deposition of homogenous thin films of Al2O3 with the desired geometric characteristics and good optical properties. Uniform, continuous thin layers with a roughness not exceeding a few nanometres were deposited. Their deposition enabled to reduce the reflection of light from the polished substrate below 15% in a wide range (425-800nm) while maintaining high transparencies (over 90%). The obtained results causes that mentioned thin films are good potential material for optics, optoelectronics and photovoltaics.

Spray coating of poly(acrylic acid)/ZnO tetrapod adhesion promoting nanocomposite films for polymer laminates

Zinc oxide tetrapods (ZnO TP) have reached a high level of interest in the last years due to their broad fields of applications. Here, the combination of the adhesion promoting properties of both ZnO TP and poly(acrylic acid) (PAA) is demonstrated. A very rapid spray coating of water-based dispersions has been used to deposit homogenous thin nanocomposite films on poly(propylene) (PP) foils considered as model system. The characterization of ZnO TPs has been carried out by field-emission scanning electron microscopy (FE-SEM), high-resolution X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The increased shear strength values exhibited by PP/PP laminates with interfacial ZnO TP/PAA films could be attributed to mechanical interlocking of ZnO TP and the macromolecular adhesion promotion by PAA. FE-SEM imaging after shear tests indicated a failure in the core of the ZnO TP. The fast application method via plasma activation of the PP foils and spray coating of the composite films with low concentrations of 0.085 mM PAA and 8 mg/ml ZnO TP makes this technique rather interesting for industrial applications.

Molybdenum-based two-dimensional materials: Synthesis, dispersion, exfoliation and thin film deposition

We report a simple and effective route to synthesize, disperse, exfoliate and process different molybdenum-based 2-dimensional (2D) materials. Starting from a reaction between ammonium molybdate and ammonium sulfide solutions, a powder consisting of a mixture between amorphous molybdenum oxide and sulfide is obtained. By tuning the atmosphere and the temperature, different compositions can be prepared by thermal treatment of this sample: heat treatments in ambient atmosphere produce MoO3 with different morphologies, controllable according to the chosen temperature. On the other hand, heat treatments in inert atmosphere produce mixtures between crystalline 2D MoS2 and MoO3. Further handling of these mixtures with acetonitrile separates the components due to the different solvent/solid affinities, with the layered MoS2 becoming homogeneously dispersed, and the MoO3 agglomerating as a solid easily removed by centrifugation. The resulting sulfide dispersions in acetonitrile present high stability, and they are constituted by exfoliated MoS2, which means that acetonitrile is a tri-functional agent, separating the sulfide/oxide mixture, exfoliating the sulfide and stabilizing the dispersion. The MoS2 dispersions were used to produce homogeneous, freestanding and transparent thin films through the liquid-liquid interfacial route, which were easily deposited over different substrates and characterized by different techniques.

Fine growth control of electrografted homogeneous thin films on patterned gold electrodes

Electrochemical grafting of two different diazonium salts was performed on patterned gold electrodes of micrometric size. One of the molecules, a tris-bipyridine iron (II) derivative (TBPFe) enables a fine control over the final thickness of the electrografted layer thanks to its redox centers that acts as intermediate for charge transfers between the solution and the working electrode. The other one, an aromatic cycle with a fluorinated carbon chain (DzF8), forms an insulating layer that stops the charge transfer from the working electrode to the solution and thus limits the thickness of the resulting organic layer. Grafting parameters (concentration, time, tip passivation, etc.) were investigated in details. Their precise control leads to compact and homogeneous thin films. Smooth TBPFe layers with an adjustable thickness in the 5–100 nm range are obtained, while the thickness is limited to 2–6 nm in the DzF8 case. With the achieved film quality, direct metal evaporation on top of these electrodes is possible and yields 85% of working devices. Electrical measurements for the two molecules are compared for different thicknesses.

Water-suspended MoO3 nanoparticles prepared by LASIS and fast processing as thin film by ultrasonic spray deposition

Crystalline molybdenum oxide nanoparticles (MoO3 NPs) were prepared by laser ablation synthesis in solution (LASiS). The resulting MoO3 NPs are water suspended with average size of 23 nm. Subsequently, in order to produce hole injection layers for solar cells, these nanoparticles were processed as thin films onto indium tin oxide (ITO)/glass substrate using ultrasonic spray deposition, which allows fast and uniform deposition in large areas with controllable thickness and low roughness; the water is removed by heating the substrate during the processing. Moreover, scanning electronic microscopy images pointed out that the bottom of the films is mainly composed of small nanoparticles. Thereafter, the optimized glass/ITO/MoO3NPs/PTB7:PC71BM/Ca/Al solar cells displayed open circuit voltage (Voc) of 0.75 V, short circuit current density (Jsc) of 13 mA/cm2, fill factor (FF) of 58% and power conversion efficiency of 5.7% under AM1.5 illumination, presenting increased stability when compared with devices having polymeric hole transporting layer. Since LASiS method does not require the use of organic precursors/solvents, it is a green route to produce MoO3 NPs. In addition, the ultrasonic spray deposition is a versatile method to achieve homogeneous and transparent thin films from water suspended nanoparticles. The organic solar cell response pointed out the potential use of these procedures to produce hole injection layers for photovoltaic devices.

Molecular magnetic thin films made from Ni-Co Prussian blue analogue anchored on silicon wafers

Formation of a polycrystalline thin film from a Prussian blue analogue (PBA) on insulating substrates through a chemical method is reported here. One of the typical PBAs, Ni-Co PBA, K0.4Ni2.8[Co(CN)6]2·nH2O, was selected to demonstrate the growth process. Silicon substrate surface is functionalized through a typical self-assembled monolayer process using aminopropyltrimethoxysilane (APTMS) to form relatively robust interface with PBAs through the coordination bonds with the terminal amino-groups of APTMS. Then, these amino-functionalized silicon wafers are used as anchors for the controlled assembly of homogeneous Ni-Co PBA thin films which shows several kinds of pyramidal structures on the surface. The obtained thin films exhibit paramagnetic properties at room temperature without a negative magnetization.

Long‐range dipole–dipole energy transfer enhancement via addition of SiO2/TiO2 nanocomposite in PFO/MEH‐PPV hybrid thin films

ABSTRACTDifferent weight ratios of poly(9,9‐dioctylfluorene‐2,7‐diyl) (PFO)/poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) hybrid thin films, with and without a SiO2/TiO2 nanocomposite (NC), were successfully prepared using a solution blending method. All samples were deposited onto glass substrates by a spin coating technique to produce homogeneous thin films. The effect of the SiO2/TiO2 NC on the enhancement of the energy transfer mechanism in the PFO/MEH‐PPV hybrids was investigated. The energy transfer parameters were calculated on the basis of the absorption and emission measurements. The long‐range dipole–dipole energy transfer (Förster type) between the acceptor and donor molecules was enhanced in the presence of the SiO2/TiO2 NC in the hybrid thin films. The addition of the SiO2/TiO2 NC in the PFO/MEH‐PPV hybrids reduced the distance between the donor and acceptor molecules more than the individual addition of SiO2 or TiO2 nanoparticles. Moreover, the direct relationships between the acceptor contents and energy transfer parameters, such as the energy transfer radius (RDA), energy transfer efficiency (η), and energy transfer probability (PDA), were estimated using theoretical fittings. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47845.

Acid-responsive behavior promoted by imine units in novel triphenylamine-based oligomers functionalized with chromophoric moieties

A series of oligomeric poly(ether-imine)s, named by us oligo(ether-imine)s were synthesized by polycondensation reaction of some di(ether-aldehyde)s with a CF3-substituted and ortho-catenated triphenylamine (TPA) diamine. The obtained TPA-based oligomers with ortho-link structural pattern, not encountered yet for this class of compounds, displayed excellent organosolubility in the majority convenient and accessible solvents. This enabled their easy processing in homogenous thin film with granular or vesicular morphology, another novel feature highlighted for this class of compounds. The photo-optical activity of oligo(ether-imine)s was investigated in detail by UV–vis and fluorescence spectroscopy, which evidenced the occurrence of a dual intramolecular charge transfer between TPA and both CF3 units and imine-phenyl framework. The acid sensing properties were surveyed both in solution and solid state, being found that upon protonation the planarity is lessen, the donor-acceptor strength decreases and the ICT bands are hipsochromically shifted. Instead, due to pH-induced conformational changes of the present molecules, the quenched fluorescence of the neutral states was turned-on. The redox behavior measured by cyclic voltammetry before and after protonation was contingent on the type of chromophoric unit incorporated into the dialdehyde segment. Owing to their ability to promote favorable, multifunctional properties, applications of these oligomers in optoelectronic devices or pH-sensors are foreseen.

Effective two-step chemical deposition for homogeneous lead sulfide thin films on a flexible polymer substrate

Chalcogenide PbS has been extensively studied as a p-type semiconductor material for various optoelectronic devices. Here, an effective two-step chemical bath deposition process is introduced to achieve dense microstructure of PbS thin films specifically for a flexible polyethylene terephthalate (PET) substrate. Three different types of substrates, such as Cu foils, glass substrate and PET, were initially examined to compare different crystal growth behaviors of PbS thin films depending on the choice of substrate. Only the PET substrate demonstrated an unacceptable coverage of films even with the extended deposition due to a retarded growth presumably with more scattered initial distribution of nuclei. Conclusively, two-step deposition processing at a low temperature of 40 °C for the PET substrate was successful in achieving homogeneous microstructures with proper bandgap and film thickness. As a promising result, the 60 min plus 60 min-double depositions at 40 °C produced an ideal bandgap of ~1.58 eV with a proper film thickness of ~200 nm.

Composition control and introduction of an Fe2O3 seed layer in metalorganic chemical vapor deposition of epitaxial BiFeO3 thin films

We investigated the compositional self-regulation and seeding effects of an Fe2O3 layer during the metalorganic chemical vapor deposition of epitaxial BiFeO3 thin films. The growth of the BiFeO3 films was explained in terms of the prior deposition of Fe2O3 and the subsequent incorporation of Bi2O3 into Fe2O3. The self-regulation of film composition was achieved by supplying excess Bi at high growth temperature. The introduction of an Fe2O3 seed layer as thin as 5 nm promoted homogeneous thin film growth and consequently reduced the leakage and its fluctuation as well as the compositional fluctuation. The seed layer also served to control the interfacial composition between BiFeO3 and SrRuO3.

Enhancing of the nonlinear absorption and optical limiting performances of the phthalocyanine thin films by adding of the single walled carbon nanotubes in poly(methyl methacrylate) host

Unlike the earlier nonlinear optical studies of single walled carbon nanotubes (SWCNTs) which were generally carried out as solvent, in this study, we established to deposit the unsoluble SWCNTs as homogeneous thin films by blending them with phthalocyanines in PMMA host. The structural and morphological features of the thin films were studied by SEM and TEM imaging techniques while the linear, nonlinear-absorptions and carrier dynamic properties of the thin films were investigated with the UV–Vis spectrophotometer, open aperture Z-scan experiments and pump-probe technique, respectively. In addition, the optical limiting performances of the samples were calculated from nonlinear absorption spectra. It was observed that the linear- and nonlinear-absorptions and optical limiting performance of the thin films increased with the mixing of the SWCNT sample with the Pcs complexes. We have clearly explained the mechanisms contributing to the nonlinear optical absorption and optical limiting performances.