Including Film Thickness Research Articles

Construction and analysis of a detailed new database for gas separation membranes

The countless possibilities associated with the design of new materials for the Membrane Gas Separation Process highlight the need for the creation of databases, that are great tools to guide design choices. The scientific literature is poor in providing detailed information on gas separation membranes. This work aimed to present a heterogeneous and detailed database, which encompasses various types of membranes and permeating gases. In addition, its construction was presented in a transparent manner (ensuring its suitability and safe use) and an analysis of the mined attributes was performed. A database with 1672 records was built with more than 280 different membranes. In total, 29 attributes were collected from 42 different bibliographic references. A wide range of values was mined for most of the attributes. Permeation data for 11 gases were collected and five major types of membranes are present: polymer, zeolite, MMM, CMS, MOF, and ceramic. Most of the attributes had an insignificant linear correlation with gas permeability (including film thickness, pore size, temperature, and pressure), indicating a complex and contextually specific relationship. Total Pore Volume, Micropore Volume, and BET Area attributes were the morphological attributes that are most linearly correlated with gas permeability and can be good performance indicators for membranes, regardless of the material type. It is expected that the results presented will be useful to guide decision-making in the steps of designing new membranes for gas separation in a big picture context.

Electrochemical Activation of Atomic-Layer-Deposited Nickel Oxide for Water Oxidation.

NiO-based electrocatalysts, known for their high activity, stability, and low cost in alkaline media, are recognized as promising candidates for the oxygen evolution reaction (OER). In parallel, atomic layer deposition (ALD) is actively researched for its ability to provide precise control over the synthesis of ultrathin electrocatalytic films, including film thickness, conformality, and chemical composition. This study examines how NiO bulk and surface properties affect the electrocatalytic performance for the OER while focusing on the prolonged electrochemical activation process. Two ALD methods, namely, plasma-assisted and thermal ALD, are employed as tools to deposit NiO films. Cyclic voltammetry analysis of ∼10 nm films in 1.0 M KOH solution reveals a multistep electrochemical activation process accompanied by phase transformation and delamination of activated nanostructures. The plasma-assisted ALD NiO film exhibits three times higher current density at 1.8 V vs RHE than its thermal ALD counterpart due to enhanced β-NiOOH formation during activation, thereby improving the OER activity. Additionally, the rougher surface formed during activation enhanced the overall catalytic activity of the films. The goal is to unravel the relationship between material properties and the performance of the resulting OER, specifically focusing on how the design of the material by ALD can lead to the enhancement of its electrocatalytic performance.

Fabrication of Hydroxyl‐Group‐Rich Reduced Graphene Oxide Film and its Application for Electrochemical Detection of Hydrogen Peroxide

AbstractGraphene oxide (GO) can be obtained economically from graphite, and it has, therefore, been used for energy storage, conversion, and biosensor fabrication. To overcome the limitations associated with the poor electrical conductivity of GO, mild thermal reduction is widely used. However, owing to considerable variations in GO in terms of size and shape, uniform reduction of GO films is highly challenging. Herein, it reports a mildly reduced uniform graphene oxide thin film (mrUG) that is enriched with functional hydroxyl groups. This film is effective for electrochemical H2O2 decomposition and detection. A uniform graphene oxide thin film (UGTF) is first fabricated on an indium tin oxide (ITO) substrate and subjected to mild thermal annealing at 300 °C. Remarkably, the variations in all important parameters, including film thickness, surface roughness, reduction level, are significantly low in the case of mrUG. Moreover, It is found that unlike GO, UGTF undergoes structural rearrangement easily and possesses many hydroxyl groups (─OH) when reduced for a specific duration (t = 10 s, mrUG(10)). mrUG(10) is highly stable and effectively decomposed H2O2, which is advantageous for the electrochemical detection of H2O2 with extremely low signal variations. Therefore, mrUG(10) can be used as a carbon‐based metal‐free electrocatalyst in biosensors, energy, and electronic applications.

Theoretical connection from the dielectric constant of films to the capacitance of capacitors under high temperature

AbstractIn the process of coping with energy and environmental protection issues, technologies such as energy materials, energy devices, and energy systems have made great progress. With excellent performance, film capacitors play an increasingly important role in energy‐related fields. With the increase of application scenarios and the continuous development of film material technology, it is urgent to establish a better theoretical connection from films to capacitors. First, the main components of the capacitor including the film and the positional relationships among them are given. Then, from the two perspectives of indirect calculation according to the volume and the direct calculation according to the winding process, the equation between the dielectric constant of films and the corresponding capacitance of capacitors is established. Further, the measurement data and error analysis results of the built test platform prove the accuracy and great potential of the proposed calculation methods. In addition, error sources, including film thickness uniformity, are listed. Finally, the challenges faced by the proposed calculation methods and the paths that can be referenced for future research are summarised and discussed.

Chemical-Physical Characteristics of Edible Film Incorporated Bali Cattle Hide Gelatin and Encapsulated Gaharu Leaf Extract

The objectives of this study were to analyze the potential of incorporating bali cattle hide gelatin and gaharu leaf extract encapsulated as an edible film with antioxidant potential. The research method was using Completely Randomized Design, ie concentration of gaharu leaf extract encapsulated (G0 = 0%, G1 = 5%, G2 = 10%, G3 = 15% and G4 = 20%). The results showed that the characteristics of edible films were significantly different (P <0.05), such as moisture content (7.37%) in G4; protein (86.25%) in G0, phenol (10.84 mg / 100 g GAE) in G4 and antioxidant (150.36 mg / L. GAEAC) in G4, and the effect was not significant on ash content of the film. It film thickness, tensile strength, elongation, and water vapor transmission rate of edible film were significant (P <0.05) influence with results for 0.04 mm (G0); 1.64 Mpa (G0); 54.86% (G1) and 11.20 g.mm/m2.day in G4, respectively. The conclusion of the research is edible film of incorporation of balicattle skin bali gelatin and gaharu leaf extract encapsulated with 20% concentration yielding functional characteristics (potency antioxidant) with the highest value. Indicators of chemical characteristics include moisture content (7.37%); ash content (0.49%); protein content (71,98%); phenol (10.84 mg / 100 g GAE) and antioxidant (150.36 mg / L GAEAC). While physical indicators include film thickness (0.02 mm); tensile strength (1.54 MPa); elongation (71.48%) and water vapor transmission rate (11.20 g.mm/m2.day).

Rizatriptan-Loaded Oral Fast Dissolving Films: Design and Characterizations.

Rizatriptan (RZT) is an efficient anti-migraine drug which belongs to the class of selective 5 HT (1B/1D) serotonin receptor agonists. Nevertheless, RZT elicits several adverse effects and RZT nasal sprays have a limited half-life, requiring repeated doses that could cause patient noncompliance or harm to the nasopharynx and cilia. The current research aimed to develop orally disintegrating films (ODFs) of RZT employing maltodextrin (MTX) and pullulan (PUL) as film-forming polymers, as well as propylene glycol (PG) as a plasticizer. The ODFs were prepared by solvent casting method (SCM). The technique was optimized using Box-Behnken design (BBD), contemplating the ratios of PUL: MTX and different levels of PG (%) as factor variables. The influence of these factors was systematically analyzed on the selected dependent variables, including film thickness, disintegration time (D-time), folding endurance (FE), tensile strength (TS), percent elongation (%E), moisture content (%), and water uptake (%). In addition, the surface morphology, solid state analysis, drug content uniformity (%), drug release (%), and pH of the RZT-ODFs were also studied. The results demonstrated a satisfactory stable RZT-ODFs formulation that exhibited surface homogeneity and amorphous RZT in films with no discernible interactions between the model drug and polymeric materials. The optimized film showed a rapid D-time of 16 s and remarkable mechanical features. The in vitro dissolution kinetics showed that 100% RZT was released from optimized film compared to 61% RZT released from conventional RZT formulation in the initial 5 min. An animal pharmacokinetic (PK) investigation revealed that RZT-ODFs had a shorter time to achieve peak plasma concentration (Tmax), a higher maximum plasma concentration (Cmax), and area under the curve (AUC0-t) than traditional oral mini capsules. These findings proposed a progressive approach for developing anti-migraine drugs that could be useful in reducing the complications of dysphagia in geriatric and pediatric sufferers.

Characterizing asphalt emissions under in-service conditions

Recent studies have suggested that asphalt related emissions at environmentally pertinent conditions are a major contributor of volatile organic compounds ubiquitous to the environment. Many variables such as temperature/viscosity of asphalt binder, solar irradiance of the asphalt binder, and geometric constraints including film thickness, the act of coating aggregate to produce Hot Mix Asphalt, and compaction into pavements influence the magnitude and composition of measured emissions. Continuous films of asphalt binder were used to determine how temperature/viscosity and film thicknesses can influence measured emissions. The magnitude of emissions scaled with the inverse of viscosity, whereas the composition of emissions varied with film thickness and age of the asphalt binder sample. Asphalt binder exposed to solar irradiance showed short term impacts on emissions in the first hours of exposure. Compacted asphalt pavements were used to simulate real world new in-service conditions. The emissions from a freshly compacted asphalt pavement were compared to a 17-year-old pavement sample collected from the field to determine how the act of compacting asphalt binder coated in aggregate influenced emissions over a 17-year period. An increase in the complexity of the system caused slowing in the total emissions profile. While lower than what was observed in the freshly compacted samples, emissions were still observed in the 17-year-old pavement. The composition of emissions indicated that smaller and more volatile compounds are capable of being released from deeper within the compacted pavement, whereas the larger and less volatile compounds tend to remain trapped. • Asphalt emission generator used to measure emissions under in-service conditions. • The effects of solar irradiation on asphalt pavement emission. • Solar irradiation of asphalt binders generates short term increases in emissions. • Effects of asphalt pavement compaction on released emissions.

Biodegradable composite films based on Trigonella foenum‐graceum galactomannan—xanthan gum: Effect of grape seed oil on various aspects of emulsified films

AbstractNowadays, preparing biodegradable films based on hydrocolloids has become thoroughly crucial in food packaging. Also, to enhance some of the aspects of these films, adding oil to the formulation of the films has been considered as a valid method. In this study, a variety of films based on two biopolymers (fenugreek galactomannan and xanthan gum) in the presence or absence of grape seed oil were produced and the various aspects of the obtained films were comprehensively investigated. The obtained data demonstrated that preparing composite films based on two hydrocolloids improved the aspects including film thickness, water vapor permeability (WVP), oxygen permeability (OP), mechanical and thermal properties more than films based on only one hydrocolloid. This improvement was mostly related to the good and acceptable interaction between two biopolymers. The X‐ray diffraction (XRD) patterns indicated that all films had an amorphous or non‐crystalline structure. Also, the scanning electron microscope images demonstrated that films based on fenugreek galactomannan and composite films based on two hydrocolloids. The value of film thickness and strain at break (SAB) increased by adding oil to the formulation. Contrarily, the moisture content and absorption, WVP, OP, opacity, and ultimate tensile strength (UTS) values of the films decreased by adding oil.

3D Printing of Largescale Functional Nanofilm using Electrically assisted Direct Ink Deposition

Functional nanofilms show significant importance for various applications in different fields, such as sustainable energy, biomedicine, electronics, and optics. However, there are still many challenges in the fabrication of nanostructured films with tailored properties using traditional manufacturing technologies. A novel 3D printing approach called electrical field-assisted direct ink deposition (EF-DID) was developed to produce large-scale nanofilms with controllable nanostructures and patternable features. In the proposed method, the formation of nanodroplets in the direct ink deposition was investigated under an electrostatic field with high voltage. Critical printing parameters, including solution concentration, deposition height, applied voltage, and ink flow rate, were studied systematically to understand fundamental mechanisms of the nanostructures generation during the printing. In addition, the scientific relationship between deposition parameters and nanofilm properties, including film thickness, electrical conductivity, and contact angle, were explored. Finally, patterned nanofilms with well-organized nanostructures were fabricated to demonstrate potential application prospects in the field of nanotechnology.

Numerical Analysis of Flow Characteristics of Upper Swirling Liquid Film Based on the Eulerian Wall Film Model

The Upper Swirling Liquid Film (USLF) phenomenon that occurs in the upper cylinder of the Gas–Liquid Cylindrical Cyclone (GLCC) separator is the direct cause of the low separation efficiency of the liquid phase. In this study, first, the USLF formation and development were simulated by an improved Eulerian-EWF coupled simulated method. By introducing a profile-defined inlet boundary and considering entrainment droplet size distributions, the Eulerian-EWF method got reasonable results which agreed well with the experimental. Then, the flow characteristics and changing laws of the USLF including film thickness, film axial velocity, and film tangential velocity were analyzed by this method under different gas–liquid flow rates. It suggested that the liquid film thickness often reaches a maximum at the aspect ratio (z-z0)/D=(1.2–3.9) above the tangential inlet, and the film thickness appears to be more sensitive to the gas flow than to the liquid flow. For the film axial velocity, the direction of film velocity on the front and back sides seems to be generally opposite. Finally, typical distributions of the aforementioned USLF variables were presented and corresponded accordingly, and two obvious rules were found. One is that the position where the thickest liquid film is located always corresponds to the position where the axial film velocity turns from positive to negative for the first time. The other is that the tangential film velocity has a strong synchronous relationship with the film thickness. This research might provide somewhat valid information for the future LCO-prevented measurement in GLCC separators.

Electrochemical Impedance Spectroscopic Investigations of Nanocomposite Thin-Film Formation at an Electrified Micro Liquid-Liquid Interface

Herein, the interface between two immiscible electrolyte solutions (ITIES) has been exploited as a pristine platform for electropolymerization of the 2D and 3D nanocomposite materials, i.e., metal nanoparticles (NPs) embedded within a conductive polymer matrix that are electrogenerated/electropolymerized simultaneously The free-standing conductive thin film can be prepared with an adjustable loading of metallic NPs, to be tailored for a variety of applications, including as catalytic electrodes in fuel cells, or act as a bioreceptor in a biosensor. Electrochemical impedance spectroscopy (EIS) has been used to investigate mechanistic aspects of film growth through two types of charge transfer processes, ion and electron transfer, that occur during electropolymerization. The thermodynamics of a heterogeneous electron transfer (HET) between redox centers, KAuCl4(aq) and terthiophene (TT, org), across the interface governs the electropolymerization reaction, including the rate, which is itself affected by the rate of diffusion of reactants toward the interface, ohmic resistance of the two electrolyte solutions, distance between reactants due to arrangement of ions at the interface, and reorganization energy of the involved species in the reaction. Electropolymerization is controlled through application of an applied external potential difference and monitored voltammetrically as well as by EIS. Curve fitting of EIS data was performed using an equivalent circuit incorporating a phase constant element (CPE) parallel to a resistor for non-ideal interfacial capacitance, and HET resistance across the film as it forms at the ITIES. Next, those elements are parallel to a resistor (R), and a Warburg element (W) to approximate ion transfer across the ITIES/porous thin-film as it grows (Fig. 1). Data suggest that the films electronic conductivity improves with increasing the [TT]:[KAuCl4] ratio. Increased capacitance was hypothesized to be linked to an increase in the effective surface area of the polymer film during its growth phase versus the molecularly smooth ITIES. Higher [TT]:[KAuCl4] ratios elicited higher capacitance as well as diffusion resistance which can be attributed to formation of a more compact film structure. Cyclic voltammetric and potential step methods are compared and discussed, highlighting the formed films final properties, including film thickness and conductivity. Figure 1

Computational Modelling of Doubly‐Photopolymerized Holographic Biosensors

AbstractHolographic sensors are optical devices capable of tuning reflection wavelength, dependent upon nanostructured variations in refractive index. Computational modelling is utilized to simulate the recording and swelling characteristics of developed doubly photopolymerized (DP) holographic sensors. The holographic devices simplify fabrication processes, reduce financial costs, and improve biocompatibility. A holographic grating is achieved through in situ photopolymerization of a highly crosslinked polymer to produce nanostructured refractive index modulation. The unique swelling characteristics DP holographic sensors possess necessitate the development of system‐specific computational modelling. Hydrogel parameters, including film thickness, refractive index change, layer number, and external medium refractive index are examined for their effect on reflection spectra. Optimized computational models are utilized to study the effect of differential swelling rates of individual layer spacings on sensor response, indicating an idealized reduction in a swelling of 50% for the highly crosslinked region. A 2D photonic crystal geometry with additional periodicity is developed, to inform further sensor design opportunities. Optimized parameters for both 1D and 2D photonic structures will assist the further development of DP holographic sensors.

Etching and annealing treatment to improve the plasma-deposited SiOx film adhesion force

In this paper, an atmospheric pressure plasma jet driven by an AC power supply was applied for SiOx film deposition on a metal surface. To improve the adhesion strength between the film and substrate, the processes of plasma etching and annealing were applied. The deposited SiOx film properties, including film thickness, surface morphology, chemical composition and electrical properties, were studied systematically. In addition, the deposited film was used for the metal particle lift-off voltage in a gas-insulated line (GIL) system. Our results showed that the adhesion strength between the film and substrate was 5 times higher in the films subjected to plasma etching and annealing treatment than that in the untreated group. The high oxygen content attained in the SiOx film after the etching and annealing processes was responsible for the adhesion force improvement. The composition changes in the film also increased the relative constant value, which was in good agreement with the metal particle lift-off voltage results. After thermal annealing, the sample showed a 119% improvement in the lift-off voltage compared to that of the bare electrode.

Water-induced polymer swelling and its application in soft electronics

Polymer blend system has been commonly applied in a wide variety of applications. Herein, we propose to introduce sugar particles to polymer matrix, which results in a controllable polymer swelling under the action of osmotic pressure upon soaking in water. Taking advantage of this economic and environment-friendly, water-induced polymer swelling process, we have fabricated wrinkled conductive films and 3D structures by depositing conductive materials on the swollen polymer substrates for stretchable strain sensing devices. Several commercial silicone elastomers were utilized in the study. Key processing factors affecting the polymer swelling were investigated, including film thickness, sugar concentration, and temperature of soaking medium. The swelling ratio can be regulated by changing these parameters and the soaking duration. By sputtering gold (Au) on the swollen films (through vapor deposition) or depositing graphene on 3D complex structures companied by polymer swelling (in aqueous dispersion), wrinkled conductive elastomer films and 3D structures have been fabricated. These conductors not only demonstrated high sensitivity in electrical response when subjected to external deformations from 5% up to 100%, but also possessed good stability after long-term stretching/releasing cycles. The excellent electrical properties of these elastomer conductors implied a great potential in applications of flexible and stretchable sensors.

Predicted Impacts of Catalyst Layer Ionomer Microstructure and Distribution on PEMFC Performance

Electric vehicles powered by proton exchange membrane fuel cells (PEMFCs) are a promising means to reduce environmentally harmful emissions. PEMFCs offer low weight, high range (miles traveled before refueling), and quick refueling times; however, persistent technical challenges limit commercialization of fuel cell electric vehicles (FCEVs). In addition to system-level challenges such as an immature refueling infrastructure and H2 production, it remains challenging to manufacture low-cost PEMFCs that meet durability and performance requirements. Addressing the performance issues of low-cost PEMFCs has proven difficult due to a gap in understanding physiochemical resistances within the heterogeneous catalyst layer (CL).Electrochemical reactions occurring in the CL—and therefore PEMFC performance—depend in complex ways upon the CL microstructure. Reactants and products are transported to and from Pt catalysts through nano-thin films of Nafion ionomer, which coat carbon-dispersed Pt catalysts. Through the use of neutron reflectometry (NR) [1,2] and conductivity measurements [3], previous studies show that the structure and material transport properties of Nafion are linked and depend on multiple factors including film thickness, substrate interactions, temperature, and relative humidity. Previously [4], we developed pseudo-2D Newman-type computational models that incorporate novel structure-property relationships derived from these studies. The results concluded that increasing the ionomer film thickness surrounding Pt-covered carbon particles in the CL may lead to a higher PEMFC performance due to an increased conductivity caused by increased ionomer volume fraction and increased Nafion water absorption.In this presentation, we extend our previous model to further advance understanding of how ionomer structure and distribution influence PEMFC performance. The current modeling efforts include two-phase water transport to understand the role of flooding in performance limits under low-Pt loading. Additionally, structure-property relationships from our previous work are updated to include more relevant structures taken from NR experiments performed with Nafion on technologically relevant substrates (Pt and carbon). Presented results will demonstrate the predicted impacts of non-uniform ionomer distribution within the cathode CL, including novel design concepts such as ionomer-rich regions to enhance ion transport for increased catalyst utilization further from the membrane. These predicted impacts provide insight for future PEMFC design modifications to accelerate FCEV commercialization.[1] J. A. Dura, V. S. Murthi, M. Hartman, S. K. Satija, and C. F. Majkrzak, “Multilamellar Interface Structures in Nafion,” Macromolecules, vol. 42, no. 13, pp. 4769–4774, 2009.[2] S. C. DeCaluwe, A. M. Baker, P. Bhargava, J. E. Fischer, and J. A. Dura, “Structure-property relationships at Nafion thin-film interfaces: Thickness effects on hydration and anisotropic ion transport,” Nano Energy, vol. 46, pp. 91–100, 2018.[3] D. K. Paul, R. McCreery, and K. Karan, “Proton Transport Property in Supported Nafion Nanothin Films by Electrochemical Impedance Spectroscopy,” Journal of The Electrochemical Society, vol. 161, no. 14, 2014.[4] C. R. Randall and S. C. DeCaluwe, “Physically Based Modeling of PEMFC Cathode Catalyst Layers: Effective Microstructure and Ionomer Structure-Property Relationship Impacts,” Journal of Electrochemical Energy Conversion and Storage, vol. 17, no. 4, 2020.

The role of surface stoichiometry in NO2 gas sensing using single and multiple nanobelts of tin oxide.

Typically used semiconducting metal oxides (SMOs) consist of several varying factors that affect gas sensor response, including film thickness, grain size, and notably the grain-grain junctions within the active device volume, which complicates the analysis and optimisation of sensor response. In comparison, devices containing a single nanostructured element do not present grain-grain junctions, and therefore present an excellent platform to comprehend the correlation between nanostructure surface stoichiometry and sensor response to the depletion layer (Debye length, LD) variation after the analyte gas adsorption/chemisorption. In this work, nanofabricated devices containing SnO2 and Sn3O4 individual nanobelts of different thicknesses were used to estimate their LD after NO2 exposure. In the presence of 40 ppm of NO2 at 150 °C, LD of 12 nm and 8 nm were obtained for SnO2 and Sn3O4, respectively. These values were associated to the sensor signals measured using multiple nanobelts onto interdigitated electrodes, outlining that the higher sensor signal of the Sn4+ surface (up to 708 for 100 ppm NO2 at 150°) in comparison with the Sn2+ (up to 185) can be explained based on a less depleted initial state and a lower surface electron affinity caused by the Lewis acid/base interactions with oxygen species from the baseline gas. To support the proposed mechanisms, we investigated the gas sensor response of SnO2 nanobelts with a higher quantity of oxygen vacancies and correlated the results to the SnO system.

Investigation on Phase-Induced Surface Energy Change of HfO2 Thin Films Prepared By Plasma Enhanced Atomic Layer Deposition

Wettability of nanomaterials has been researched for the scientific physics based on solid/liquid interfaces. In particular, wettability of ceramic materials which is directly relevant to the surface free energy has been researched for its nature continuously in terms of thin film coatings.1 The development of such materials with finely tunable surface free energy and adequate stability under harsh conditions has been attracted enormous interests involving various applications.2,3 Among them, Hafnium oxide (HfO2), one of the representative transition metal oxides, has been recently studied for robust coating materials with investigation of its surface free energy. However, due to the complexity derived from environmental factors in a stack and differences between variety of deposition parameters, the surface free energy of HfO2 films has not been fully understood. Apart from the fact that the previously reported water contact angle (WCA) of HfO2 thin or bulk films highly vary between literatures, the interpretation of surface free energy of HfO2 and its intrinsic wettability still lacks of systematic approaches. In this study, we comprehensively investigated the surface free energy variation in HfO2 films prepared by plasma enhanced atomic layer deposition (PE-ALD). Upon precise control of film thickness with the aid of PE-ALD technique, we analyzed the surface free energy changes depending on the various properties of HfO2 films including film thickness, chemical composition, surface roughness, film crystallinity. We focused on a dependency of surface free energy of HfO2 films on film crystallinity as a determining factor for wettability changes. For in-depth studies, we performed thermal annealing treatment on PE-ALD HfO2 films and observed apparent correlation between wettability and film crystallinity. Based on the control of film crystallinity, PE-ALD HfO2 thin films show versatile wetting behaviors as to exposure of liquids with different surface energies. The experimental results from our work will contribute to the fundamental understanding of surface free energy of thin film HfO2 and its scientific backgrounds, and can also lead to feasible applications including liquid separation and purifications using HfO2 as robust coating film.

Bulk and Surface Chemistry of Photoactive Electrodeposited Cu2O Films Using X-Ray Absorption Spectroscopy

Cu2O is an attractive photocathode for important renewable energy reactions such as water splitting and CO2 reduction. A variety of synthesis methods for Cu2O films have been reported such as physical vapour deposition techniques1,2, chemical vapour deposition3,4, hydrothermal methods5 and electrodeposition6–8. Electrodeposition is a particularly popular method due its low cost and versatility, which appears to get consistent and even film deposition on conductive substrates. However, very little is known on the effects of the synthesis conditions on structure and properties. Majority of works in the literature often show vastly different photoelectrochemical activity, morphology and conductivity type with seemingly slight variation in the synthesis conditions. These variations can be in the electrolyte bath composition, deposition temperature, time, solution pH and electrochemical conditions.While commonly used characterisation methods like XRD, SEM, XPS and Raman spectroscopy are necessary to provide basic information of Cu2O formation, they are insufficient in providing a further understanding of the composition in terms of the Cu species present in each film. In this work, we take a systematic look into the bulk and surface chemistry of electrochemically deposited Cu2O using high resolution XANES and EXAFS spectroscopy. By using HERFD-XAS, we were able to see that changing the deposition parameters altered the Cu(II) amounts. A series of quantitative analyses revealed that none of films were purely composed of Cu(I) species, with amounts of Cu(II) varying from 0.7% to 9.35% across samples.Photoelectrochemical measurements appear to show a correlation in the amount of Cu(II) and the activity of the photocathodes. Highest photocurrent generation was observed in the film with the highest Cu(II) content, however, this was at the expense of stability due to reductive decomposition to Cu metal. We propose that the Cu(II) species initially reduce to Cu metal, forming Schottky barriers at the newly formed metal semiconductor contacts, hence the increase in photocurrent. Nevertheless, this is limited by other factors including film thickness and crystallite grain size. The most stable film was consistent with the quantitative analyses from XAS, which indicated that this film had the lowest amount of Cu(II) in its structure.We concluded that there must be a compromise between activity and stability when optimising deposition parameters for electrodeposition of Cu2O as a photocathode. This work shows the importance of advanced characterisation techniques for gaining a more thorough understanding of structure and composition, and how this may correlate to the performance or functionality of a material. It serves as a guide for future development of more active Cu2O based films for photoelectrochemical processes as well as for solar cell applications.Manuscript in preparation.References1 D. S. Darvish and H. A. Atwater, J. Cryst. Growth, 2011, 319, 39–43.2 S. Dolai, S. Das, S. Hussain, R. Bhar and A. K. Pal, Vacuum, 2017, 141, 296–306.3 M. Ottosson and J.-O. Carlsson, Surf. Coatings Technol., 1996, 78, 263–273.4 C. R. Crick and I. P. Parkin, J. Mater. Chem., 2011, 21, 14712–14716.5 A. D. Handoko, C. W. Ong, Y. Huang, Z. G. Lee, L. Lin, G. B. Panetti and B. S. Yeo, J. Phys. Chem. C, 2016, 120, 20058–20067.6 A. E. Rakhshani and J. Varghese, Sol. Energy Mater., 1987, 15, 237–248.7 A. E. Rakhshani and J. Varghese, J. Mater. Sci., 1988, 23, 3847–3853.8 W. Siripala, L. D. R. . Perera, K. T. L. De Silva, J. K. D. S. Jayanetti and I. M. Dharmadasa, Sol. Energy Mater. Sol. Cells, 1996, 44, 251–260.

Incorporation of zwitterionic materials into light-curable fluoride varnish for biofilm inhibition and caries prevention

We incorporated zwitterionic materials into light-curable fluoride varnish (LCFV) in order to inhibit biofilm accumulation and prevent dental caries, and the properties of LCFV with three different zwitterionic materials, namely, 2-methacryloyloxyethyl phosphorylcholine (MPC), carboxybetaine methacrylate (CBMA), and sulfobetaine methacrylate (SBMA) polymers (each at a weight percentage of 3%), were compared; unmodified LCFV without any zwitterionic material was used as a control. Material properties including film thickness and degree of conversion (DC) of each type of LCFV were evaluated. In addition, protein-repellent effects and inhibitory effects on Streptococcus mutans adhesion and saliva-derived biofilm accumulation of LCFV were estimated. Finally, the preventive effect of LCFV on enamel demineralization was assessed in vitro on extracted human teeth specimens stored in S. mutans-containing medium. The film thickness of LCFV significantly decreased with the incorporation of zwitterionic materials compared to the control LCFV, whereas there were no significant differences in the DC among all of the LCFV groups. Furthermore, the amount of adsorbed protein, adherent S. mutans colony-forming unit (CFU) counts, and saliva-derived biofilm thickness and biomass were all significantly lower for LCFV with incorporated zwitterionic materials compared with the control. All LCFV groups including the control showed certain preventive effects against enamel demineralization during a 14-day immersion in the medium with S. mutans and sucrose, and the depth of demineralization was significantly lower in LCFV with zwitterionic materials than in the control. Thus, the incorporation of zwitterionic materials such as MPC, CBMA, and SBMA appears to confer superior antifouling effects to LCFV.

Fabrication of Ordered Arrays of Quantum Dot Molecules Based on the Design of Pyramidal Pit Patterns on Semiconductor Surfaces

We report computational results on the formation of complex nanostructures on surfaces of coherently strained thin films that are deposited epitaxially on semiconductor substrates with periodic pit patterns, where individual pits have the shape of an inverted truncated pyramid. The simulated nanostructures consist of quantum dot molecules (QDMs) containing quantum dots (QDs) arranged in one-dimensional (1D) and two-dimensional (2D) regular arrays, as well as elongated QDs. We use a continuum-scale three-dimensional (3D) kinetic model that has been validated experimentally and perform self-consistent simulations of film surface morphological evolution according to the model. The results of our computational analysis are supported by a nonlinear stability theory that provides a comprehensive explanation for the observed nanopattern formation on the film surface as the outcome of a recently introduced “tip-splitting” instability that accompanies the well-known Stranski–Krastanow instability during epitaxial growth. Emphasis is placed on the effects of systematically varying geometrical design parameters of individual pyramidal pits in periodic pit patterns, including film thickness, period of the pit pattern, pit depth, length and width of the pit opening, and inclination of the pit wall on the resulting film surface nanopattern formation. We show that complex nanostructures are formed on the film surface, including ridges and quantum dot molecules inside film surface pits, as well as elongated QDs at the rims of the pits, as a result of varying the pit opening dimensions and the pit wall slope. Through our simulation predictions, we demonstrate that the geometrical parameters of the substrate pit pattern can be tuned properly in order to achieve a precise control of the ordered nanostructure patterns that form on the film surface. Our findings have important implications for designing optimal semiconductor surface patterns toward enabling future nanofabrication technologies.