Solution Thin Films Research Articles

(Invited) Modification of Dielectric Properties of Film Dielectric Materials by Solid Solution System

Compound semiconductor based power devices such as SiC and GaN require high temperature operating passive devices such as a capacitor. SiC-based active devices can operate above 250 °C. The development of high-temperature operational passives is urgently needed to advance to the module and system level. In the case of capacitors, currently available capacitors can only operate efficiently up to 175 °C. Therefore, a thin film capacitor that can operate at high temperatures and be monolithically integrated near the active device should be developed. In this talk, I will present our achievements in the development of high-temperature operating dielectric film materials using the solid solution system. One topic is A2B2O7 pyrochlore ferroelectrics. The ferroelectric materials with the pyrochlore structure such as Sr2Nb2O7 exhibited the high dielectric constant above 100 at high and low temperature ranges. However, due to the crystallographic direction dependence of the Curie-Weiss temperature, the temperature stability of the dielectric constant from room temperature to 300 °C was not available. In order to obtain the high temperature stability of dielectric constant from room temperature to 300 °C with high dielectric constant over 100, the pyrochlore ferroelectric solid solution thin films were investigated by employing the combinatorial synthesis. Composition spread thin films of solid solution of two or three kinds of materials were deposited on substrates by physical vapor deposition technique, which provided the systematic physical properties. High-throughput combinatorial synthesis method is effective in the rapid optimization of the correlation between the crystallization and the dielectric property change behavior. For the composition spread solid solution film, the Sr- or La-containing A2B2O7 pyrochlore ferroelectrics were selected from the viewpoints of ion radios and crystallographic direction dependence of the Curie-Weiss temperature. The composition spread films were formed on a Pt/Ti/SiO2/Si substrate by combinatorial RF sputtering with stoichiometric composition targets. The X-ray fluorescence spectrum of the composition-spread film showed a linear variation of the metal composition. After deposition, the samples were annealed at different temperatures under oxygen atmosphere to reduce oxygen vacancies and improve crystallinity. The crystallization of the composition-spread solid solution thin film was confirmed by X-ray diffraction patterns, indicating the composition dependence of the crystallographic orientation. Some compositions showed high dielectric constant over 100 and high temperature stability from room temperature to 300 °C. In the presentation, the correlation between film composition, orientation and dielectric constant will be discussed in detail. In the presentation, we also introduce our achievement of the BaTiO3 based relaxor ferroelectrics and other dielectric materials development using the solid solution system. For the relaxor ferroelectrics, among the BaTiO3 based relaxor ferroelectrics, we have selected x[BaTiO3]-(1-x)[Bi(Mg2/3Nb1/3)O3] . The permittivity of 400 and the stability <8% from room temperature to 400 °C were obtained, which are promising as high-temperature dielectric medium.

Polypropylene membranes prepared via non-solvent/thermally induced phase separation: Effect of non-solvent nature

The goal of this work was to investigate the effect of non-solvent nature on the formation of porous membranes via non-solvent/thermally induced phase separation (N-TIPS). The hot solution of polypropylene (PP) in a mixture of dioctyl phthalate (DOP) and dibutyl phthalate (DBP) at 210 °C was placed as a thin film on a polyethylene terephthalate (PET) substrate, and then precipitated by immersion in the non-solvent (water, iso-propanol, 1-hexanol, or 1-decanol) at room temperature. It was found that the non-solvent nature greatly affected the morphology of the thin skin layer of the membrane facing the precipitation bath, which can be attributed to non-solvent induced phase separation (NIPS). The affinity between the polymeric solution and corresponding non-solvent was evaluated by using Hansen solubility parameters of components taken at room temperature and extrapolated to the temperature of 210 °C. An increase in the affinity between the non-solvent and the polymer transformed the surface layer structure from almost monolithic to cellular (with different pore sizes and porosity) and to spherulitic types. The non-solvent nature played a less pronounced role in the formation of the porous structure of the membrane bulk and the back side of the membrane (facing the PET substrate). Since the morphology of the rest of the membrane was correlated with thermophysical properties of non-solvents, it was concluded that the membrane formation took place due to temperature induced phase separation (TIPS). In the case of water, which has the highest cooling rate, the polypropylene crystallized by forming a “smectic” structure, while the standard α-lamellar structure was observed for other non-solvents. To gain insight into the TIPS process, a model of unsteady one-dimensional heat transfer was applied to simulate the change in the temperature profile of the hot, thin film of polymeric solution placed in the corresponding non-solvent. The resulting membranes were mainly in the microfiltration range with a mean through pore size of 0.05–0.61 μm, and iso-propanol permeance of 2.1–8.4 m3 m−2∙h−1∙bar−1. The rejection of 500 nm polystyrene microspheres was in the range of 45–98 %. The tensile strength was in the range of 2.9–3.2 MPa, and elongation at break was 30–190 % with respect to the non-solvent used.

Rupture of Thin Film of Surfactant Solution due to Penetration of Spherical Particle

Rupture of Thin Film of Surfactant Solution due to Penetration of Spherical Particle

Electroformation of giant unilamellar vesicles from large liposomes

AbstractGiant unilamellar vesicles (GUVs) are widely used as model systems for biological membranes to study membrane-related processes in a precisely controlled in vitro environment, owing to their biophysical properties. The classical technique for the formation of giant liposomes starts with the dissolution of lipids or lipid mixtures in an organic solvent, which is then deposited as a thin lipid solution film on a support substrate. In this study, we present a comprehensive analysis investigating the effect of different lipid compositions on the generation of GUVs from preformed liposomes under non-ionic and ionic conditions. For all liposome types tested, the electroformation process, whether performed on indium tin oxide-coated glass slides or platinum wires, consistently produced GUVs that typically ranged in size from 5 to 20 μm. However, the yield of GUVs varied depending on the specific non-ionic or ionic conditions and the lipid composition of the preformed liposomes used. In general, the resulting population of giant vesicles was predominantly characterised by the presence of unilamellar and multivesicular vesicles. These findings have the potential to improve the refinement of protocol parameters for the formation of GUVs containing membrane proteins and for the study of the effects of lipid composition on membrane protein activity.

Ambient aerosols increase stomatal transpiration and conductance of hydroponic sunflowers by extending the hydraulic system to the leaf surface

IntroductionMany atmospheric aerosols are hygroscopic and play an important role in cloud formation. Similarly, aerosols become sites of micro-condensation when they deposit to the upper and lower surfaces of leaves. Deposited salts, in particular can trigger condensation at humidities considerably below atmospheric saturation, according to their hygroscopicity and the relative humidity within the leaf boundary layer. Salt induced water potential gradients and the resulting dynamics of concentrated salt solutions can be expected to affect plant water relations.MethodsHydroponic sunflowers were grown in filtered (FA) and unfiltered, ambient air (AA). Sap flow was measured for 18 days and several indicators of incipient drought stress were studied.ResultsAt 2% difference in mean vapor pressure deficit (D), AA sunflowers had 49% higher mean transpiration rates, lower osmotic potential, higher proline concentrations, and different tracer transport patterns in the leaf compared to FA sunflowers. Aerosols increased plant conductance particularly at low D.DiscussionThe proposed mechanism is that thin aqueous films of salt solutions from deliquescent deposited aerosols enter into stomata and cause an extension of the hydraulic system. This hydraulic connection leads – parallel to stomatal water vapor transpiration – to wick-like stomatal loss of liquid water and to a higher impact of D on plant water loss. Due to ample water supply by hydroponic cultivation, AA plants thrived as well as FA plants, but under more challenging conditions, aerosol deposits may make plants more susceptible to drought stress.

Growth of nanotextured thin films of GaInAsP and GaInAsSbBi solid solutions on GaP substrates by pulsed laser deposition

Growth of nanotextured thin films of GaInAsP and GaInAsSbBi solid solutions on GaP substrates by pulsed laser deposition

Laplace Transform Methods for Transient Diffusion; or, Some Good Questions from Ralph White

Motivated by years of correspondence with Prof. Ralph White, I discuss two unconventional ways to solve diffusion problems with Laplace transforms. A method to derive error-function series, alternatives to Fourier series that converge rapidly and avoid the Gibbs phenomenon at short times, is illustrated by example. It is shown how Mittag-Leffler partial-fractions expansions can facilitate derivations of Fourier-series solutions from the same starting point. Several basic problems pertinent to electrochemical transport are analyzed, culminating in the development of a modified Cottrell equation applicable to thin films of unsupported electrolytic solutions sandwiched between planar electrodes.

Chiral Opto‐Fluidics and Plasmonic Nanostructures as a Functional Nanosystem for Manipulating Surface Deformations

AbstractPhotothermal conversion of energy in plasmonic nanostructures brought a new fascinating field of plasmon‐induced optofluidics to life. Notably, the heat generation by plasmonic nanostructures and consequent fluid convection recently attracted wide attention; however, the possibility of controlling and manipulating liquid surfaces has been sparsely investigated. The plasmon heating and convective fluid flow lead to the emergence of the surface tension gradient on a free liquid surface interface with air, resulting in the Marangoni effect‐driven fluid flow observed as water deformation. Here, nanoscale asymmetric fluid deformation anchored on the chiral plasmon‐induced optofluidic effect is reported on. To understand the fluid dynamics of surface deformation, a theoretical model is developed. The results demonstrate that deformation at different depths can be obtained by adjusting structural parameters or incident light intensity. The fundamental understanding of light‐induced asymmetric deformation will contribute to expanding chirality‐related discipline and open new avenues for controlling fluid flow at the micro‐ or nano‐scale. The proposed method can encourage the research and applications of optofluidics, including integrated fluidic devices, biochemistry, and clinical biology. Moreover, the use of the asymmetric fluid deformation on thermal dewetting of thin films of polymer solutions can be employed for the fabrication of functional and nanopatterned metal/polymer metasurfaces.

Evaporation-driven gravitational instability in the liquid layer of a polymer solution: Theoretical and numerical studies

The drying of the thin liquid film of polymer solution is a complex process accompanying instabilities induced by concentration gradients that develop during the evaporation. This study investigates evaporation-driven gravitational instabilities (Rayleigh–Taylor instability) in the thin liquid film of a polymer solution based on theoretical and numerical analyses, specifically focusing on the onset of instability at the early stage of the drying process. Evaporation-driven convection is taken into account by employing a dynamic moving boundary condition and concentration-dependent material functions (dynamic viscosity and diffusivity). A theoretical analysis predicts the onset of gravitational instability (τc), showing good agreement with the results of a numerical simulation analysis (τd), suggesting scaling relationships between the onset of instability and the initial concentration (Ci), τc∼Ci−1/2, for a slow evaporation rate and dilute concentration range, which rapidly increases with an increase in the concentration due to an instability-retardation effect. A nonlinear two-dimensional numerical simulation visualizes the development of a polymer-dense layer, pluming, and a convection–diffusion flow throughout the liquid film under transient evaporation. The concentration-gradient-driven convection–diffusion flow enhances the gravitational instability and pluming further at higher frequencies. Meanwhile, for a polymer solution with high viscosity, viscosity thickening delays the onset of instability, retarding the development of instability. This study provides a fundamental understanding of the mechanism behind how convective instability develops in a drying polymer solution during evaporation and information on how to develop pluming of a polymer-dense skin layer at early stages of drying of a polymer solution film. The findings suggest that the proper control of hydrodynamic instability induced by a concentration gradient in a thin polymer solution film is important to prevent or enhance the formation of a convection pattern in the thin polymer film.

Explosive crystallization of amorphous germanium-tin films by irradiation with a 3-keV electron beam

Much effort has been expended to obtain thin films of metastable solid solutions of germanium (Ge) that contain as high tin (Sn) content as possible because of their excellent electronic and optoelectronic properties. On the basis of our previous study on amorphous Ge, we demonstrated in this study that irradiation of substrate-free films of amorphous Ge100−xSnx (x = 8, 11, and 19 at. %) with a low-energy electron beam of 3 keV at ambient temperature can induce instantaneous wide-area crystallization (explosive crystallization). Characteristic spiral crystal growth associated with explosive crystallization occurred with areas exceeding 50 μm in diameter around a scanned area of the electron beam of 8 × 8 μm2. As a result, solid solutions of GeSn with Sn concentration up to 19 at. % were obtained with the suppression of precipitation of β-Sn. The region of explosive crystallization reduced in size with increasing Sn content. In addition, thermal analyses revealed that the heat released during crystallization of amorphous GeSn films decreased with increasing Sn content. This relationship indicates that the heat release at the growth front plays a key role in the propagation of explosive crystallization of a-GeSn.

Recent Developments of Light-Harvesting Excitation, Macroscope Transfer and Multi-Stage Utilization of Photogenerated Electrons in Rotating Disk Photocatalytic Reactor

The rotating disk photocatalytic reactor is a kind of photocatalytic wastewater treatment technique with a high application potential, but the light energy utilization rate and photo quantum efficiency still need to be improved. Taking photogenerated electrons as the starting point, the following contents are reviewed in this work: (1) Light-harvesting excitation of photogenerated electrons. Based on the rotating disk thin solution film photocatalytic reactor, the photoanodes with light capture structures are reviewed from the macro perspective, and the research progress of light capture structure catalysts based on BiOCl is also reviewed from the micro perspective. (2) Macroscope transfer of photogenerated electrons. The research progress of photo fuel cell based on rotating disk reactors is reviewed. The system can effectively convert the chemical energy in organic pollutants into electrical energy through the macroscopic transfer of photogenerated electrons. (3) Multi-level utilization of photogenerated electrons. The photogenerated electrons transferred to the cathode can also generate H2O2 with oxygen or H2 with H+, and the reduction products can also be further utilized to deeply mineralize organic pollutants or reduce the nitrate in water. This short review will provide theoretical guidance for the further application of photocatalytic techniques in wastewater treatment.

Drying Liquid Coatings with an Evaporation Mask: Theory and Experiments.

We report a study of the spatially varying thickness of dried films of polymer solutions resulting from a nonuniform evaporation flux. The controlled heterogeneity of the evaporation flux is imposed by placing a solid mask above the evaporating film spread on a solid substrate. At the end of drying, a depression has formed under the mask, together with overthicknesses extending from the edge of the mask and over distances that may be larger than its size. By considering the flows induced in a vertically homogeneous film, we obtain analytical solutions for the thickness profiles during drying using a linear approximation in the limits of either gravity or capillarity-driven flows. We demonstrate that gravity can play a role in the deformations of the films, even if their initial thicknesses are 1 order of magnitude smaller than the capillary length. In addition, we examine two possible reference states for the linear approximation, i.e., far from the mask in the film of decreasing thickness and increasing viscosity, or under the mask where no evaporation occurs. We further compare these results with experimental ones obtained by drying thin films of polymer solutions under a mask. Both the extent and amplitude of the thickness heterogeneities of the dry film are quantitatively predicted by the linear analysis for a reference state under the mask. Our results therefore provide new insight on the patterns resulting from evaporation masks and can be generalized to minimize thickness heterogeneities in any situation in which the evaporation flux is nonuniform.

Assessing rheometry for measuring the viscosity-average degree of polymerisation of cellulose in paper degradation studies

In paper degradation studies, the viscosity-average degree of polymerisation (DPv) is often used as a key indicator of the extent of degradation of cellulosic paper. DPv can be deduced from the viscosity of dilute paper solutions, as typically measured through glass capillary viscometry. The current study proposes an efficient, alternative method to evaluate DPv of cellulosic paper, which is based on rotational rheometry. The proposed methodology relies on the application of a shear flow in a thin film of cellulose solution to measure its dynamic viscosity, from which DPv can be subsequently derived in a straightforward fashion. Rheometry allows to measure the viscosity for a range of shear rates, which results in multiple DPv evaluations per sample, and thus in statistically representative data from an individual test. Further, rheometry typically requires considerably less paper mass per test than glass capillary viscometry, which makes the method attractive for paper degradation studies with limited sample availability. Also, rheometry measurements are less work-intensive than glass capillary viscometry measurements. The rheometry method has been applied to 4 hygrothermally aged cellulose paper samples and the unaged counterpart. The measurement results regarding the age-dependency of DPv and the number of cellulose chain scissions are compared to those obtained by glass capillary viscometry, showing a very good agreement. At a longer ageing time, both experimental methods reveal a non-linear decrease in time of DPv, and a non-linear increase in time of the number of cellulose chain scissions, which indicate that the cellulose ageing process is realistically captured. The agreement in measurement results further demonstrates that rheometry is an easy-to-use, accurate and efficient alternative for DPv measurements by glass capillary viscometry.

Biocompatible Chemically Fueled Transient Polymer Nanoparticles for Temporally Programmable in Vivo Imaging

Biocompatible Chemically Fueled Transient Polymer Nanoparticles for Temporally Programmable in Vivo Imaging

Capturing the onset of thermocapillary convection in the Cattaneo–Christov flow of electrically conducting thin film of Welan gum solution

An investigation of heat transfer characteristics of electrically conducting Welan gum solution over a sheet, influenced by thermocapillary convection (thermal Marangoni convection) and magnetic field is carried out. In order to correctly predict the heat transfer characteristics, the more realistic heat flux model i.e. Cattaneo–Christov model has been utilized whereas the Maxwell-power-law model is used to capture the rheological attribute of Welan gum liquid. The Joule dissipation effect produced by the interaction between magnetic field and fluid is also considered in the energy equation. Simplified Navier–Stokes equation under above-mentioned assumptions/considerations have been obtained and are metamorphosed to a set of ODEs using appropriate Lie-group transforms. Set of ODEs are solved by Runge–Kutta fourth-order method facilitated by the shooting technique. Numerical results are displayed via graphs and tables. One of the key findings of this research work is the evidence of Marangoni convection altering the two boundary layers near the interfacial region and having almost no effect on the flow near the sheet. It has been found that the temperature and velocity of Welan gum solution can be decreased by increasing the thermal relaxation time. It has also been observed that the skin friction coefficient, a representative of shear stress is higher for a more solid-like material.

Block and single-crystal films of bismuth-antimony alloy 3-12 at.% with an underlayer of antimony

The influence of an antimony sublayer (10 nm) on the structure and galvanomagnetic properties of thin films of a bismuth-antimony solid solution (3-12 at.% Sb) up to 1 μm thick has been studied. The films were produced on mica substrates by discrete vacuum evaporation and zone recrystallization. We found that the misorientation of the crystallite plane (111) increases relative to the film plane as well as the crystallite sizes decrease. The antimony underlayer does not change the crystallographic orientation during recrystallization and increases the film adhesion. The change in the galvanomagnetic coefficients when using a sublayer is due to the classical dimensional effect and increasing plane deformation. Keywords: bismuth, antimony, thin film, antimony underlayer, single-crystal film, atomic force microscopy

The impact of outgassing of CO2 and prior calcium precipitation to the isotope composition of calcite precipitated on stalagmites. Implications for reconstructing climate information from proxies

Degassing of CO2 and precipitation of calcite to the surface of stalagmites can strongly impact isotope signals imprinted into the calcite of these speleothems. Here, we show that in all the variety of conditions occurring in nature only two distinct types of degassing exist. First, when a thin film of calcareous solution comes in contact to cave air, which has a lower pCO2 value than that of the aqueous CO2 in the water, molecular CO2 escapes by physical diffusion in several seconds. In a next step lasting several ten seconds, pH and DIC in the solution achieve chemical equilibrium with respect to the CO2 in the cave atmosphere. This solution becomes supersaturated with respect to calcite. During precipitation for each unit CaCO3 deposited one molecule of CO2 is generated and escapes from the solution. This precipitation driven degassing is active during precipitation only. We show that all variations of out gassing proposed in the literature are either diffusive outgassing or precipitation driven degassing and that diffusive outgassing has no influence on the isotope composition of the HCO3− pool and consequently on that of calcite. Its isotope imprint is determined solely by precipitation driven degassing in contrast to most explanations in the literature. We present a theoretical model of δ13C and δ18O that explains the contributions of various parameters such as changes in temperature, changes of pCO2 in the cave atmosphere, and changes in the drip intervals to the isotope composition of calcite precipitated to the apex of the stalagmite. We use this model to calculate quantitatively changes of δ13C and δ18O observed in field experiments (Carlson et al., 2020) in agreement to their experimental data. We also apply our model to prior calcite precipitation (PCP) in the field as reported by Mickler et al. (2019). We discuss how PCP influences isotope composition signals. In summary, we present a transparent method based on few commonly accepted equations that allows calculation of the isotope composition δ13C and δ18O of CaCO3 under various temperatures, pCO2 in the cave air, degrees of PCP, and concentrations cCao of the water entering the cave.

CMOS back-end-of-line compatible ferroelectric tunnel junction devices

Ferroelectric tunnel junction devices based on ferroelectric thin films of solid solutions of hafnium dioxide can enable CMOS integration of ultra-low power ferroelectric devices with potential for memory and emerging computing schemes such as in-memory computing and neuromorphic applications. In this work, we present ferroelectric tunnel junctions based on Hf0.5Zr0.5O2 with materials and processes compatible with CMOS back-end-of-line integration. We show a device architecture based on W-Hf0.5Zr0.5O2-Al2O3-TiN stacks featuring low temperature annealing at 400° with performance comparable to those obtained with higher temperature annealing conditions.

FEM Simulation of Frequency-Selective Surface Based on Thermoelectric Bi-Sb Thin Films for THz Detection

Terahertz (THz) filters and detectors can find a wide application in such fields as: sensing, imaging, security systems, medicine, wireless connection, and detection of substances. Thermoelectric materials are promising basis for THz detectors’ development due to their sensitivity to the THz radiation, possibility to be heated under the THz radiation and produce voltage due to Seebeck effect. Thermoelectric thin films of Bi-Sb solid solutions are semimetals/semiconductors with the band gap comparable with THz energy and with high thermoelectric conversion efficiency at room temperature. Detecting film surface can be transformed into a periodic frequency selective surface (FSS) that can operate as a frequency filter and increases the absorption of THz radiation. We report for the first time about the simulation of THz detector based on thermoelectric Bi-Sb thin-filmed frequency-selective surface. We show that such structure can be both detector and frequency filter. Moreover, it was shown that FSS design increases not only a heating due to absorption but a temperature gradient in Bi-Sb film by two orders of magnitude in comparison with continuous films. Local temperature gradients can reach the values of the order of 100 K·mm−1. That opens new perspectives for thin-filmed thermoelectric detectors’ efficiency increase. Temperature difference formed due to THz radiation absorption can reach values on the order of 1 degree. Frequency-transient calculations show the power dependence of film temperature on time with characteristic saturation at times around several ms. That points to the perspective of reaching fast response times on such structures.

Lithium isotopes and partition coefficients in inorganic carbonates: Proxy calibration for weathering reconstruction

We report Li measurements from cave-analogue carbonate-precipitation experiments in order to: i) assess the expected isotope fractionation factors applicable to speleothem growth, and ii) contribute to the wider understanding of lithium incorporation in carbonates. The experimental setup closely mimics natural processes (e.g. precipitation driven by CO2 degassing, low ionic strength solution, thin solution film) but within a laboratory setting that allows for controlled growth conditions (temperature, pCO2, drip rate, carbonate saturation index and the composition of the initial solution). For the main batch of calcite growth experiments our average 1000lnαcalcite-solution is -8.5±2(2σ). This low sensitivity of 1000lnα to in-cave growth conditions is encouraging for weathering intensity reconstruction using speleothem samples. At each temperature, growth rate was varied independently with calcite saturation indices ranging between 0.1 and 0.6, with no significant impact on either D(Li) or 1000lnα. For the full range of growth conditions (considering all temperatures and calcite saturation indices) we observe a small but significant decrease in 1000lnα, which we do not attribute to temperature. Based on an inter-study comparison we define LogDLi = 0.09(±0.04)×GR-3.2(±0.2), where GR is growth rate in units of 10-8mmolcm-2s-1. This is similar to the previously defined relationship over a reduced range of growth rates. Over this study’s full range of growth rates, 1000lnα = -0.13(±0.04)×GR-7.1(±0.3) is significant at the ρ=0.018 level, consistent with a surface entrapment control. Future experiments should test factors such as growth rate and pH, independently of other variables, to further assess their role in defining 1000lnα. A subset of 20 °C experiments, with increasing [Mg]solution, provides 1000lnα for calcite, high-magnesian calcite (HMC) and aragonite. Our values of 1000lnα for these three mineralogies range between -7.3 and -10.7. For HMC and aragonite in particular there is close agreement with other published values of 1000lnα for CaCO3 grown in laboratory and in natural settings. In agreement with measurements in bulk carbonates, benthic foraminifera and brachiopods, this suggests that differences in 1000lnα between carbonate mineralogies may not always be as large as suggested by some earlier studies.