Thin Film Diffusion Research Articles

Real‐Time Observation of Oxygen Diffusion in CGO Thin Films Using Spatially Resolved Isotope Exchange Raman Spectroscopy

The exploitation of advanced materials for novel energy, health, and computing applications requires deep insight and fundamental understanding of physicochemical mechanisms, such as ionic and electronic conductivity, defect formation processes, and reaction kinetics. Therefore, access to the underlying constants of the functional materials via advanced but accessible and straightforward experimental techniques is key. Herein, a novel, cheap, fast, and widely applicable approach is presented to analyze oxygen tracer diffusion in thin films with unprecedented time resolution based on the novel in situ isotope exchange Raman spectroscopy (IERS) methodology. IERS utilizes the sensitivity of micro‐Raman spectroscopy to changes in the local isotopic composition. In‐plane tracer diffusion gradients are established by partially blocking the exchange at the surface followed by an isotope exchange. The isotope exchange and diffusion processes are followed via consecutive spatial and time‐resolved in situ Raman line scans. These isotopic gradients are analyzed to obtain mass transport coefficients, with an additional time component, not accessible by conventional destructive techniques. Diffusion coefficients of gadolinium‐doped ceria (CGO) thin films are reported within the range of interest for intermediate‐temperature emerging applications and confirm the validity of the measurement procedure and extracted parameters by comparison with the finite‐element method simulations and literature results.

Oxygen diffusion coefficients in ferroelectric hafnium zirconium oxide thin films

Oxygen diffusion coefficients in the metastable ferroelectric phase of polycrystalline hafnium zirconium oxide (HZO) thin films have been quantified using 18O tracers and time-of-flight secondary ion mass spectrometry. 11.5 nm thick HZO films containing 16O were deposited by plasma-enhanced atomic layer deposition followed by post-metallization annealing to crystallize into the ferroelectric phase. A 1.2 nm thick HZO layer containing 18O was then deposited using thermal atomic layer deposition with H218O as a reactant. Thermal anneals were conducted at 300, 350, and 400 °C and the ferroelectric phase confirmed after the anneals by x-ray diffraction, infrared spectroscopy, and electrical property measurements. 18O depth profiles were measured and fit with a thin film diffusion equation to determine the oxygen diffusion coefficients. Oxygen diffusion coefficients ranged from approximately 2 × 10−18 cm2/s at 300 °C to 5 × 10−17 cm2/s at 400 °C with an activation energy of 1.02 ± 0.24 eV.

Excitation-Dependent Exciton Diffusion in Semiconductor Quantum Dot Thin Films with Spatially Patterned Lifetimes

Excitation-Dependent Exciton Diffusion in Semiconductor Quantum Dot Thin Films with Spatially Patterned Lifetimes

Oxygen diffusion in freestanding body centered cubic tantalum structural thin films in air and in high vacuum

Sensors and actuators constructed from freestanding tantalum thin films show promise for micromachining applications and for the study of thin film mechanical behavior. To assess this promise, it is necessary to gain further understanding of the performance of Ta as a structural material. We first evaluate the coefficient of thermal expansion, αTa, using micromachined bent beams, which amplify displacement compared to linear expansion. The value for αTa is 6.8 × 10−6 m/m °C, in good agreement with the bulk value. This validation enables the study of interstitial oxygen diffusion in Ta, for which literature values of activation energy vary widely, from 0.60 to 1.98 eV. Displacement in air due to oxygen diffusion becomes measurable after 30 min exposure at 180 °C. We extract an activation energy for interstitial oxygen in Ta of 0.53 eV/atom. Analysis indicates that lattice rather than grain boundary diffusion is the associated mechanism. To inhibit the oxidation, we construct a thermal stage that controls specimen temperature in 10−5 Pa vacuum. Then, after a 24 h hold, oxidation is suppressed up to 400 °C. This result is discussed in terms of O dissolution from its native oxide, coupled with further absorption from background gases.

A New Solution to the Grain Boundary Grooving Problem in Polycrystalline Thin Films When Evaporation and Diffusion Meet in Power Electronic Devices.

This paper constituted an extension of two previous studies concerning the mathematical development of the grain boundary grooving in polycrystalline thin films in the cases of evaporation/condensation and diffusion taken separately. The thermal grooving processes are deeply controlled by the various mass transfer mechanisms of evaporation-condensation, surface diffusion, lattice diffusion, and grain boundary diffusion. This study proposed a new original analytical solution to the mathematical problem governing the grain groove profile in the case of simultaneous effects of evaporation-condensation and diffusion in polycrystalline thin films by resolving the corresponding fourth-order partial differential equation ∂y∂t=C∂2y∂x2-B∂4y∂x4 obtained from the approximation ∂y∂x2≪1. The comparison of the new solution to that of diffusion alone proved an important effect of the coupling of evaporation and diffusion on the geometric characteristics of the groove profile. A second analytical solution based on the series development was also proposed. It was proved that changes in the boundary conditions of the grain grooving profile largely affected the different geometric characteristics of the groove profile.

Visualizing Carrier Diffusion in Cs‐Doping FAPbI3 Perovskite Thin Films Using Transient Absorption Microscopy

AbstractThe determination of the semiconducting materials performance heavily relies on the diffusion coefficient and length of the carrier. Recently, significant progress is made in enhancing solar cell efficiency through improved carrier diffusion in perovskite thin films. However, the spatial‐temporal mechanisms underlying carrier transport remain unclear. Recent advancements in utilizing transient absorption microscopy (TAM) offer promising opportunities to directly visualize the carrier transport dynamics within perovskite films. Here, the wide‐field imaging TAM combined with X‐ray diffraction and scanning electron microscopy is employed to investigate the spatial‐temporal carrier transport dynamics in FA1−xCsxPbI3 perovskites with varying Cs doping ratios. The experimental results indicate that the diffusion constant remains consistent regardless of the excitation power. Moreover, a decrease in the Cs doping ratio leads to an increase in the diffusion length within FA1−xCsxPbI3 perovskites. The measurements reveal a highest diffusion coefficient of up to 0.085 cm2 s−1 and a maximum diffusion length of ≈1.4 µm in FA0.97Cs0.03PbI3. Comparative analysis of short‐circuit current density, open‐circuit voltage, fill factor, and power conversion efficiency demonstrates that FA0.97Cs0.03PbI3 exhibits superior device efficiency. The TAM visualizes spatial/ temporal carrier diffusion dynamics, showing a significant correlation with device efficiency and thus providing valuable insights for further enhancing device performance.

Significance of chemical reaction and viscous dissipation on magnetized-Marangoni convective flow of dusty Casson hybrid (AA7072+AA7075/sodium alginate) nanofluid with Soret and Dufour effects

ABSTRACT In the current study, mass and heat transfer flow of radiated Casson hybrid nanofluid with nanoparticles and dust deferment over sheet are explored. The Soret and Dufour effects, activation energy and microorganisms in the hybrid nanofluid model are described. Marangoni convection, a prominent occurrence in microgravity caused by surface tension gradients. It can be used for many different things, such as the creation of molten crystals, thin-film diffusion, the generation of vapour bubbles during nucleation, and semiconductor manufacturing. In sodium alginate, we wondered about the aluminium alloys AA7072 and AA7075. The aluminium alloys included in this study are specially made materials with improved heat transmission characteristics. aluminium and zinc are combined in AA7072 alloy in the ratios of 98 & 1, respectively, with the addition of silicon, ferrous metals, and copper. Similarly, AA7075 is a blend of aluminium, magnesium, zinc, and copper in the proportions of ~ 90, ~3, ~6, and ~ 1, respectively, with silicon ferrous and magnesium as additional metals. The controlling PDEs are transformed into nonlinear ODEs with the aid of a new set of similarity variables. These ODEs are then numerically solved using the RKF-45th method. The findings show that when the Marangoni convection parameter increases, the concentration, temperature, and microbiological characteristics drop while the velocity profile increases for both the dust and fluid phases.

Performance and Degradation of Electrolyte Supported SOECs with Advanced Thin-Film Gadolinium Doped Ceria Barrier Layers in Long-Term Stack Test

Electrolyte supported Solid Oxide Cells (ESCs) with advanced thin-film Gd-doped ceria diffusion barrier layers between electrolyte and electrodes were assembled and electrochemically investigated in steam electrolysis mode in a so-called “rainbow” stack with 30 repeat units (RUs). The barrier layers were deposited onto the electrolyte supports via electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. In this paper, the investigation mainly focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers. At the initial stage of the SOEC operation, the stack reached a high performance with an electrical efficiency of 99.65% at 75% steam conversion and a total power input of 1.98 kW. A long-term stack test was performed in SOEC mode for over 5000 h and demonstrated a low voltage degradation of approx. +11.3 mV·kh–1 per RU (+0.9% kh–1). The RUs with EB-PVD GDC thin-films revealed similar initial performance and degradation rate to the state-of-the-art cells with screen printed GDC layers.

Evolution of interfacial phases between Al alloy and high entropy alloy during annealing

While the interfacial phases between Al and high-entropy alloy (HEA) share the same types as that between Al and steel, it has been found previously that the thermal stability of the Al-HEA interfacial phases is significantly higher than that of the Al-steel interfacial phases. To further elucidate the reason for the exceptional thermal stability of Al-HEA interfacial phases, this study investigated the evolution of the interfacial phases formed between Al alloy and FeCoCrNiMn HEA during annealing. An Al-FeCoCrNiMn thin film diffusion couple was extracted from a friction stir lap welding (FSLW) joint by focused ion beam and then annealed at 400 °C. An amorphous layer is formed initially at the interface due to the high strain rate deformation during FSLW. The amorphous layer remained even after prolonged annealing at 400 °C (∼0.72 Tm of Al alloy) for 60 min with very limited thickening (from 50 nm to 55 nm), showing remarkable thermal stability at the relatively high temperature. Al13Fe4-type intermetallic compound (IMC) with the Fe site occupied by Fe, Co, Cr, Ni and Mn first nucleates at the interface between Al alloy and amorphous layer. With the annealing time extended to 180 min, the amorphous layer is partially transformed into Al5Fe2-type IMC. The rate constant for the thickening of the reaction layer at the Al/FeCoCrNiMn interface is 0.03 μm∙min1/2, which is much smaller than (only 0.02 times) that at the Al/steel interface under similar annealing condition. The high thermal stability of Al-HEA interfacial layer is thus attributed to the slow kinetics in crystallization of the initially formed amorphous layer, the barrier effect of amorphous layer for interdiffusion, and the reduced diffusivity inside of IMCs caused by significant fluctuations in lattice potential energy due to high-density doping with HEA elements. This finding provides new insights into the fabrication of thermally stable Al-HEA hybrid structures suitable for service conditions involving high-temperature exposure.

Fabrication and characterization of highly enriched thin 176Yb targets for the reaction dynamic studies on fission mass distribution

The fabrication, transfer, and storage of a highly enriched isotopic target is very much crucial because of air gases and moistures being chemically active at room temperature. One must limit the amount of time that the target surface is exposed to the atmosphere during the transfer of air sensitive targets. The highly interactive targets are not easy to store for longer time and demand an in-vacuum transfer facility. Getting an alternative technique to remove all such imperative is a need of the hour specially for the nuclear physics community, more particularly for reaction dynamic studies of fission fragment mass distribution induced by stable and radioactive ion beams. Highly enriched materials are rare and very expensive, so an effective and highly efficient technique is needed to deal with such materials. Here, an attempt has been made to fabricate 96.63% enriched thin targets of 176Yb by evaporation techniques enabling ≈129.1 μg/cm2 thickness with a ≈25.93 μg/cm2 carbon backing to increase its stability and durability. Numerous trials have been performed using natural Yb to optimize the evaporation setup and associated growth parameters for efficient Yb isotope deposition with thin film deposition unit and diffusion pump based coating unit at Inter University Accelerator Centre (IUAC), New Delhi. Thickness and elemental composition of the targets have been analysed using characterization techniques such as X-ray diffraction, α-energy loss technique, Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy. Essentially no significant impurities are found by these measurements, describing high purity and robustness of the fabricated targets. During the nuclear experiments, 30Si and 16O beams of intensity of the order of ≈1010 particles per second were bombarded on the targets for 5–6 days and no ill effects on the target were observed. Isotopic abundance of the target has been obtained experimentally, which ensured the isotopic purity of the target required for the reaction studies. This article will admire our readers about the qualitative nature of the fabrication technique, measurement and characterization citing valuable insights, aiding in a comprehensive understanding of their quality.

Fourier Transform Thermoreflectance Method Under Front-Heat Front-Detect Configuration

The thermoreflectance method, which can measure thermal diffusivity in the cross-plane direction of thin films, mainly has two possible configurations; rear-heat front-detect (RF) and front-heat front-detect (FF) configuration. FF configuration is applicable to a wide variety of thin films including thin films deposited on opaque substrates, but this configuration has some problems in determination of the thermal diffusivity. One of the main problems is the effect of the penetration of pump beam and probe beam in thin film, which affects the initial temperature distribution near the sample’s surface after pulse heating. Several studies have tried to analyze the effect but there have been no practical analytical solutions which can solve this problem in FF configuration. In this paper, we propose a new analytical solution which considers the penetration of pump beam and probe beam into thin film, and by applying Fourier expansion analysis which we developed in a previous study to thermoreflectance signals, we have determined the thermal diffusivity of thin film in the thermoreflectance method under FF configuration. We measured platinum thin films with different thickness under both FF and RF configuration and obtained consistent thermal diffusivity values from both configurations.

Elucidating the role of water films on solute diffusion in unsaturated porous media by improved pore‐scale modeling

AbstractSolute diffusion in partially saturated porous media is an important fundamental process in many natural and environmental systems. At low water saturation, the solute transport is governed by the diffusion in thin water films on the surfaces of solids. In this study, we established an improved pore‐scale simulation framework successfully describing the solute diffusion in variably saturated porous media (e.g., soils), which considers the contribution of the diffusion within the thin water film on the surface of the solid matrix. The model takes into account the liquid–gas distribution in the underlying porous media by the Shan‐Chen lattice Boltzmann Method (LBM) and simulates the solute diffusion in the bulk liquid phase and the water film. Based on the numerical results, an easy‐to‐use theoretical formula was also developed to predict the effective diffusivity in microporous materials at low saturation levels. The average relative error of its prediction with respect to the experimental data from the literature is about 30%, while that of the classical power law exceeds 70%. A simple phase diagram was defined, which allows us to identify the situations under which it is necessary to take the influence of surface water films on the effective diffusivity in unsaturated microporous media into account. The present study improves the pore‐scale model to address solute diffusion in the water films at low water saturation and elucidates the contribution of thin water films on solute transport.

Inhibited Surface Diffusion in Nanoporous Multi-Principal Element Alloy Thin Films Prepared by Vacuum Thermal Dealloying

Nanoporous structures with 3D interconnected networks are traditionally made by dealloying a binary precursor. Certain approaches for fabricating these materials have been applied to refractory multi-principal element alloys (RMPEAs), which can be suitable candidates for high-temperature applications. In this study, nanoporous refractory multi-principal element alloys (np-RMPEAs) were fabricated from magnesium-based thin films (VMoNbTaMg) that had been prepared by magnetron sputtering. Vacuum thermal dealloying (VTD), which involves sublimation of a higher vapor pressure element, is a novel technique for synthesizing nanoporous refractory elements that are prone to oxidation. When VMoNbTaMg was heated under vacuum, a nanoporous structure was created by the sublimation of the highest vapor pressure element (Mg). X-ray photoelectron spectroscopy depth profiling indicated significantly less ligament oxidation during VTD as compared to traditional dealloying methods. Furthermore, np-RMPEAs exhibited outstanding stability against coarsening, retaining smaller ligaments (~25 nm) at elevated temperature (700 °C) for a prolonged period (48 h).

Development of Fourier Transform Ultrafast Laser Flash Method for Simultaneous Measurement of Thermal Diffusivity and Interfacial Thermal Resistance

The thermoreflectance technique is one of the few methods which can measure thermal diffusivity of thin films as thin as 100 nm or thinner in the cross-plane direction. The thermoreflectance method under rear-heat front-detect configuration is sometimes called ultrafast laser flash method because of its similarity to laser flash method. Up to now it has typically only been possible to attempt to evaluate the interfacial thermal resistance between the thin films by preparing and measuring several samples with different thicknesses. In this study, a method to directly determine interfacial thermal resistance by a single measurement of a thin film on substrate is represented, by analyzing the shape of thermoreflectance signals with analytical solutions in frequency domain and time domain. Thermoreflectance signals observed from metallic thin films on sapphire substrate with different thickness steps were analyzed by Fourier analysis and fitted by analytical equations with four parameters: heat diffusion time across the first layer, ratio of virtual heat sources, characteristic time of cooling determined by interfacial thermal resistance and relative amplitude of the signal. Interface thermal resistance between the thin film and substrate was able to be determined reliably with smaller uncertainty.

Regulating thermal diffusion of gold thin films at solid-state interfaces for site-selective decoration of gold nanoparticles on titania nanotubes as an efficient SERS sensing platform

Regulating thermal diffusion and dewetting of Au thin films at the confined ZnO/TiO2 interface favors an optimal distribution of the produced Au nanoparticles for forming localized electromagnetic field hot spots.

Increase of electrode life in resistance spot welding of aluminum alloys by the combination of surface patterning and thin-film diffusion barriers

When resistance spot welding aluminum alloys, high electrode forces are required to reduce the electrical contact resistances between the electrodes and the sheet metals. The high contact resistances and the resulting thermal load cause extensive degradation of the electrode working faces. Weld spatter occurs after only a few weld cycles, significantly reducing the quality of the weld. Conventional resistance welding machines are limited in terms of maximum electrode force and weld current. As a result, weld quality and electrode life are inadequate. The aim is to increase the achievable electrode life by surface patterning the electrode working faces and creating thin-film diffusion barriers by physical vapor deposition (PVD). Patterning is intended to penetrate the oxide layers of the aluminum sheets and increase the proportion of electrically conductive contact areas. The different influences of patterning by particle blasting and contour turning will be investigated. As a further approach, thin-film diffusion barriers of up to 3 μm are deposited on the electrodes to prevent direct Al-Cu contact. Therefore, metallic coating materials (Ni and W) and an electrically highly conductive ceramic coating material (TiB2) are investigated. The combination of electrode patterning and thin-film diffusion barriers is tested in electrode life studies. It is shown that these modified electrode working faces can limit degradation effects and contribute to an increase in electrode life. In addition, the weld quality can be improved compared to the reference condition.

Thermal Fatigue Effect on the Grain Groove Profile in the Case of Diffusion in Thin Polycrystalline Films of Power Electronic Devices.

In a previous paper, we solved the partial differential equation of Mullins' problem in the case of the evaporation-condensation in electronic devices and gave an exact solution relative to the geometric profile of the grain boundary grooving when materials are submitted to thermal and mechanical solicitation and fatigue effect. In this new research, new modelling of the grain groove profile was proposed and new analytical expressions of the groove profile, the derivative and the groove depth were obtained in the case of diffusion in thin polycrystalline films by the resolution of the fourth differential equation formulated by Mullins that supposed y'2≪1. The obtained analytical solution gave more accurate information on the geometric characteristics of the groove that were necessary to study the depth and the width of the groove. These new findings will open a new way to study with more accuracy the problem of the evaporation-condensation combined to the diffusion phenomenon on the material surfaces with the help of the analytical solutions.

Hydrogen diffusion in cerium oxide thin films fabricated by pulsed laser deposition

Cerium oxide (CeO2) is well known to be reducible by hydrogen (H2), yet the diffusion and solution properties of hydrogen in ceria at elevated temperatures have remained challenging to evaluate. We therefore fabricated nanometer-thin (∼100 nm) cerium oxide films on Si(111) substrates by pulsed laser deposition (PLD) and quantitatively investigated the H depth distributions therein by means of resonant 1H(15N,αγ)12C nuclear reaction analysis (NRA) before and after annealing in H2 gas at 773–973 K. X-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) reveal that the as-deposited films exhibit single phase CeO2 structure and partially reduced stoichiometry (CeO1.69). H2 annealing does not largely change the H content of the as-deposited films; in all conditions several atomic percent of hydroxyl (OH) are found to exist in a thin (∼4 nm) surface layer, whereas stably bound hydrogen in the bulk of the films is almost uniformly distributed and of much smaller quantity (∼0.2 at.%) than the oxygen vacancy concentration in the partially reduced ceria. Its low concentration and high thermal stability identify this bulk H species as likely being strongly bound to defects in the polycrystalline films rather than as a hydride species that interacts weakly with O-vacancies. The H diffusion coefficient and activation energy in the ceria films are determined as > 10−18 m2 s−1 at 773–973 K and <1.69 eV, respectively. The observed diffusion activation energy is somewhat larger than theoretical predictions for thermal diffusion of H in stoichiometric bulk CeO2, suggesting that defects and oxygen vacancies in the PLD-fabricated ceria thin films possibly have an impact on the H mobility.

Simultaneous Determination of Thermal Conductivity and Heat Capacity in Thin Films with Picosecond Transient Thermoreflectance and Picosecond Laser Flash

ABSTRACT Combining the picosecond transient thermoreflectance (ps-TTR) and picosecond laser flash (ps-LF) techniques, we have developed a novel method to simultaneously measure the thermal effusivity and the thermal diffusivity of metal thin films and determine the thermal conductivity () and the heat capacity () altogether. In order to validate our approach and evaluate the uncertainties, we analyzed five different metal films (Al, Cr, Ni, Pt, and Ti) with thicknesses ranging from 297 nm to 1.2 µm. Our results on thermal transport properties and heat capacity are consistent with reference values, with the uncertainties for the thermal conductivity and the heat capacity measurements below 25% and 15%, respectively. Compared with the ps-TTR technique alone, the combined approach substantially lowers the uncertainty of the thermal conductivity measurement. Uncertainty analyses on various materials show that this combined approach is capable of measuring most of the materials with a wide range of thicknesses, including those with low thermal conductivity (e.g., mica) down to thicknesses as small as 60 nm and ultrahigh thermal conductivity materials (such as cubic BAs) down to 1400 nm. Simultaneous measurement of thermal conductivity and heat capacity enables exploration of the thermal physical behavior of materials under various thermodynamic and mechanical perturbations, with potential applications in thermal management materials, solid-state phase transitions, and beyond.

Effect of a silicon dioxide diffusion barrier layer and its sublimation on the migration of strontium implanted into SiC

Thin film diffusion barriers are inevitable in nuclear reactors for preventing the release of radioactive waste products. The combination of chemical stable silicon carbide (SiC) and silicon oxide (SiO2) layers has been considered being beneficial, thus, we studied the migration and stability of strontium implanted SiC upon annealing, owing an additional SiO2 surface layer. Our investigations show that annealing at 1100 and 1200 °C retained the Sr atoms in comparison to pure SiC and induced strong strontium segregation at the SiO2/SiC interface and SiO2 surface. However, this enhanced the sublimation of the SiO2 layer, while pure SiO2 layers (i.e., without impurities) showed no sublimation after annealing under the same conditions. On the other hand, higher temperatures at 1300 and 1400 °C, resulted also in significant sublimation of the pure SiO2 layer.