Atomic Layer Deposition Technique Research Articles

Multilayer stack structural designing of titania and zinc white using atomic layer deposition (ALD) technique and study of thermally governed dielectric dispersion and conduction under alternating electric fields

Multilayer stack structural designing of titania and zinc white using atomic layer deposition (ALD) technique and study of thermally governed dielectric dispersion and conduction under alternating electric fields

Enhancement in Photoelectrochemical Efficiency and Modulation of Surface States in BiVO4 through the TiO2 Outer Layer Using the Atomic Layer Deposition Technique

Owing to several important properties, BiVO4 is the promising photoanode material for the photoelectrochemical (PEC) water oxidation reaction; however, the poor charge transfer and transport and slow surface catalytic activity limit to achieve the expected high theoretical efficiency. In the present investigation, thin films of TiO2 have been formed over the BiVO4 photoanode surface using the atomic layer deposition technique (ALD). Films are formed at 5, 50, and 150 nm thicknesses, and the PEC performances have been evaluated. Enhancement in the performance has been observed upon inclusion of the ALD/TiO2 films over BiVO4. The performance has been observed to be higher in the case of 50 nm ALD/TiO2 films. The ALD/TiO2 films have several important roles in the enhancement in the PEC efficiency other than only the enhancement of stability through retardation of the photocorrosion process. The intensity modulated photocurrent spectroscopy measurements have been carried out for the selective evaluation of the different modes of charge transfer processes upon excitation of the photoanode materials on photoexcitation. The enhancement in the charge transfer rate constant (kt) over the relative retardation of the charge recombination rate constant (kr) indicated the specific roles of modulation of the surface states. The investigation revealed the significant scopes of the modifications of surfaces using ALD techniques to selectively modulate the surface electronic states of materials in enhancing catalytic efficiency.

Review of SOFC Cathode Performance Enhancement by Surface Modifications: Recent Advances and Future Directions

Cathode materials with high electrochemical catalytic activity, stability, and durability at medium/low temperatures are still critical challenges for the commercialization of solid oxide fuel cells (SOFCs). Therefore, various surface modification techniques have been employed to improve the performance of SOFC cathodes. Significant achievements have been made in enhancing the cathode catalytic activity and durability by surface modification, including solution infiltration, the atomic layer deposition technique (ALD), and the one-pot method. Surface modification is considered to be one of the most effective approaches to enhance the catalytic activity and durability of the cathodes with the advantages of low cost and time savings. This review illustrates the fundamental principles, recent progress, advantages, disadvantages, challenges, and prospects of these advanced surface modification technologies. Furthermore, this article provides valuable guidance and potential directions for these surface modification methods toward the commercialization of SOFC technology.

Process Controlled Ruthenium on 2D Engineered V-MXene via Atomic Layer Deposition for Human Healthcare Monitoring.

In searching for unique and unexplored 2D materials, the authors try to investigate for the very first time the use of delaminated V-MXene coupled with precious metal ruthenium (Ru) through atomic layer deposition (ALD) for various contact and noncontact mode of real-time temperature sensing applications at the human-machine interface. The novel delaminated V-MXene (DM-V2 CTx ) engineered ruthenium-ALD (Ru-ALD) temperature sensor demonstrates a competitive sensing performance of 1.11%°C-1 as of only V-MXene of 0.42%°C-1 . A nearly threefold increase in sensing and reversibility performance linked to the highly ordered few-layered V-MXene and selective, well-controlled Ru atomic doping by ALD for the successful formation of Ru@DM-V2 CTX heterostructure. The advanced heterostructure formation, the mechanism, and the role of Ru have been comprehensively investigated by ultra-high-resolution transmission/scanning transmission electron microscopies coupled with next-generation spherical aberration correction technology and fast, accurate elemental mapping quantifications, also by ultraviolet photoelectron spectroscopy. To the knowledge, this work is the first to use the novel, optimally processed V-MXene over conventionally used Ti-MXene and its surface-internal structure engineering by Ru-ALD process-based temperature-sensing devices function and operational demonstrations. The current work could potentially motivate the development of multifunctional, future, next-generation, safe, personal healthcare electronic devices by the industrially scalable ALD technique.

Optical, Optoelectronic, and Third‐Order Nonlinear Photonics of Ultrathin Molybdenum Oxide Film Deposited by Atomic Layer Deposition

The atomic layer deposition (ALD) technique has attracted significant attention because it enables the control of film synthesis at the subnanometre scale. Herein, molybdenum oxide (MoO3) ultrathin films using the ALD system through Bis(t‐butylimido)bis(dimethylamino)molybdenum (VI) as a molybdenum (Mo) source are prepared. To understand the effect of deposition temperature, thin films are prepared at three different temperatures 100, 150, and 250 °C. The morphological and elemental properties are assessed using a field emission scanning electron microscope, scanning transmission electron microscopy, and energy‐dispersive X‐ray spectroscopy techniques. It is observed that the film thicknesses increase with the increase in the deposition temperature. It is found that the film growth at 150 °C is the most potential one for UV optoelectronic applications with high stability even under low applied bias voltages. Moreover, these films show interesting nonlinear optical behaviors as investigated with the z‐scan technique applying open and closed aperture methods. The calculated nonlinear optical parameters including nonlinear absorption coefficient (β), nonlinear refractive index (n 2), nonlinear refractive coefficient (γ), and third‐order nonlinear susceptibility (χ (3)) are 10−11 m W−1, 10−16 cm2 W−1, 10−11 cm2 W−1, and 10−11 esu, respectively.

Atomic layer deposition of ZnO on Li1.3Al0.3Ti1.7(PO4)3 enables its application in all solid-state lithium batteries

BackgroundAll-solid-state Li batteries (ASSLBs) are emerging as potential electrochemical energy storage devices for next-generation large-scale electrical power systems. In particular, Li1.3Al0.3Ti1.7(PO4)3 (LATP) is an efficient cost-effective solid-state electrolyte with high ionic conductivity for high energy density and safety ASSLBs. Since LATP is unstable verus metallic Li. Therefore, the application of Li-based all-solid-state batteries is practically limited. MethodsAs a possible solution to overcome the LATP instability, the interface was modified by adding a 5 nm thin ZnO layer on LATP using the atomic layer deposition (ALD) technique. Significant FindingsThe ZnO layer reduces the observed overpotential in a Li|ZnO@LATP|Li symmetric cell compared to an unmodified LATP-based cell. In contrast to the unmodified LATP-based Li cells, the ZnO-modified symmetric LATP-based Li cells show stable cycling for more than 500 h without a short circuit. The full-cell configuration of the LiFePO4|ZnO@LATP|Li system showed a reversible capacity of 156 mAh/g over 50 cycles and exposed good capacity retention (98.79% after 50 cycles) during the cycling test. The results indicate that ZnO coating by ALD on LATP could overcome the stability issues of pristine LATP versus metallic Li. Therefore, this work will lead to prove the simple manner of interfacial modification and improvement of electrochemical performance of inorganic oxide based solid electrolytes for all-solid-state lithium battery applications.

Secondary electron emission characteristics of alumina coating on metallic substrate prepared by atomic layer deposition

The main objective of this study is to research the secondary electron emission characteristic of different thickness alumina coatings which are prepared by atomic layer deposition (ALD) technique on several metallic secondary-emitting materials. The experimental results reveal that secondary electron yield (SEY) property concerned with the metal work function and the surface topography of alumina coatings when coating thickness is in the nanometer level. In addition, after utilizing SEY measurement setup and pulsed electron gun, the SEY curves of metallic substrates with different thickness alumina coatings and primary energy (PE) of incident electron could be measured. From an analysis of the SEY curves, some key parameters related to secondary electron emission characteristics such as the maximum SEY value and its corresponding PE of incident electron, and the penetration depth of incident electron can be obtained. Furthermore, basing on the ALD technique and on the SEY results of stainless steel substrate coated with 80-cycle alumina thin film, a novel 18-stage discrete dynode electron multiplier (DDEM) was fabricated and tested. The gain of DDEM 1.6× 106 was obtained.

Observation of MOSFET-like behavior of a TFT based on amorphous oxide semiconductor channel layer with suitable integration of atomic layered deposited high-k gate dielectrics

A series of different high κ dielectrics such as HfO2, ZrO2, and Al2O3 thin films were studied as an alternative material for the possible replacement of traditional SiO2. These large areas, as well as conformal dielectrics thin films, were grown by the atomic layer deposition technique on a p-type silicon substrate at two different deposition temperatures (150 and 250 °C). Atomic force microscopic study reveals that the surface of the films is very smooth with a measured rms surface roughness value of less than 0.4 nm in some films. After the deposition of the high κ layer, a top metal electrode was deposited onto it to fabricate metal oxide semiconductor capacitor (MOSCAP) structures. The I–V curve reveals that the sample growth at high temperatures exhibits a high resistance value and lower leakage current densities. Frequency-dependent (100 kHz to 1 MHz) C–V characteristics of the MOSCAPs were studied steadily. Furthermore, we have prepared a metal oxide semiconductor field-effect transistor device with Al-doped ZnO as a channel material, and the electrical characteristic of the device was studied. The effect of growth temperature on the structure, surface morphology, crystallinity, capacitance, and dielectric properties of the high κ dielectrics was thoroughly analyzed through several measurement techniques, such as XRD, atomic force microscopy, semiconductor parameter analysis, and ultraviolet-visible spectroscopy.

Heterostructure Films of SiO2 and HfO2 for High-Power Laser Optics Prepared by Plasma-Enhanced Atomic Layer Deposition

Absorption losses and laser-induced damage threshold (LIDT) are considered to be the major constraints for development of optical coatings for high-power laser optics. Such coatings require paramount properties, such as low losses due to optical absorption, high mechanical stability, and enhanced damage resistance, to withstand high-intensity laser pulses. In this work, heterostructures were developed by sub-nanometer thin films of SiO2 and HfO2 using the plasma-enhanced atomic layer deposition (PEALD) technique. Thin-film characterization techniques, such as spectroscopic ellipsometry, spectrophotometry, substrate curvature measurements, X-ray reflectivity, and Fourier transform infrared spectroscopy, were employed for extracting optical constants, residual stress, layer formation, and functional groups present in the heterostructures, respectively. These heterostructures demonstrate tunable refractive index, bandgap, and improved optical losses and LIDT properties. The films were incorporated into antireflection coatings (multilayer stacks and graded-index coatings) and the LIDT was determined at 355 nm wavelength by the R-on-1 method. Optical absorptions at the reported wavelengths were characterized using photothermal common-path interferometry and laser-induced deflection techniques.

An Environmental and Technical Evaluation of Vacuum-Based Thin Film Technologies: Lithium Niobate Coated Cathode Active Material for Use in All-Solid-State Battery Cells

Research on All-Solid-State Batteries (ASSBs) currently focuses on the development of innovative materials, cell concepts, and production processes, aiming to achieve higher energy densities compared to other battery technologies. For example, it is been demonstrated that coating the Cathode Active Material (CAM) can enhance the rate capability and cycle life and reduce the interfacial resistance of an ASSB cell. For this reason, various techniques for coating the CAM have been explored, along with a variety of coating materials, including lithium niobate. Since ASSBs are still an emerging technology, more research is needed to determine how their production processes will perform from a technical, economic, and environmental perspective. In this paper, two innovative techniques for producing lithium niobate-coated CAMs are presented and evaluated. Particularly, Atomic Layer Deposition (ALD) and Physical Vapor Deposition (PVD) techniques for coating NCM811 particles are investigated. The methodology for environmental and technical feasibility assessments at an early stage of development is further presented and discussed. Based on process-specific data and expert knowledge, an environmental assessment is conducted and further supported with a qualitative technical feasibility assessment. The results help guide early-stage decision-making regarding the identification of promising process routes with relatively low impacts.

Aqueous degradation and atomic layer deposition (ALD) stabilization of BaAl2O4: Eu2+, Dy3+ long afterglow phosphors

This paper presents the aqueous degradation mechanisms of BaAl2O4:Eu2+, Dy3+ phosphors and demonstrates an ability to prevent degradation via Al2O3 nano encapsulation of powders by atomic layer deposition (ALD) technique. Phosphor powder is synthesized from the solid-state reaction method. The aqueous degradation of this phosphor is systematically studied. This phosphor is found to hydrolyze and degrade within just 30 min of exposure in water. The degradation of BaAl2O4 host lattice directly affects the blue-green light emission at 497 nm, producing blue- and red-emissions that are peaked at 429 nm and 687 nm, respectively. Hydrated and structural decomposed BaAl2O4 reveals a continuous change in the phase assemblage over 30 days of immersion. To prevent this rapid degradation, use of a protective nanocoating was investigated. 10 nm Al2O3 coatings were applied to the surface of the phosphor powder via ALD. ALD coated BaAl2O4:Eu2+,Dy3+ phosphor retains its phosphorescence for at least 7 days of water exposure. Successful encapsulation of such phosphor particles will make them possible to use in aqueous applications or store in long-term humid environments.

Fabrication of Aluminum Oxide Thin-Film Devices Based on Atomic Layer Deposition and Pulsed Discrete Feed Method

This study demonstrates the low-temperature (<100 °C) process for growing a thin silica buffer layer and aluminum oxide by atomic layer deposition (ALD) in the same reaction chamber. Heterogeneous multilayer thin films are prepared by a dual-mode equipment based on atomic layer deposition and plasma-enhanced chemical vapor deposition (PECVD) techniques. The pulse discrete feeding method (DFM) was used to divide the precursor purging steps into smaller intervals and generate discrete feeds, which improved the saturated distribution of gas precursors, film density and deposition selectivity. The experimental results show that the process method produces a uniform microstructure and that the best film uniformity is ±2.3% and growth rate is 0.69 Å/cycle. The thickness of aluminum oxide film has a linear relationship with the cyclic growth number from 360 to 1800 cycles. Meanwhile, the structural and mechanical stress properties of aluminum oxide thin films were also verified to meet the requirements of advanced thin-film devices.

Laser crystallization of amorphous TiO2 on polymer

The deposition of crystalline TiO2 on polymers can boost its use in a large plethora of applications. In this work, we deposited, through the low-temperature atomic layer deposition (LT-ALD) technique, a thin layer of amorphous TiO2 on polymethyl-methacrylate (PMMA), and afterwards, we induced a phase transition from amorphous to crystalline anatase by pulsed UV-laser irradiation. A pulsed UV laser with a low penetration length was used to avoid the heating and damaging of the polymeric substrate. The diffusion of the heat and the temperature behaviour were simulated and discussed. We studied experimentally the effect of the laser fluence and pulse number on the amorphous-crystal transition. We observed the presence of two thresholds for the formation of the crystalline phase: on the fluence and the number of laser shots. Moreover, widening of pre-existing cracks is observed, as soon as fluence and the number of pulses increase. To improve further the quality of the deposited layer, we introduced a ZnO interlayer between TiO2 and the PMMA substrate. The effect of this interlayer was also discussed. Lastly, wettability, as a measure of the overall quality of the layer, was measured and interpreted by using the Cassie model.

Excitation of Epsilon‐Near‐Zero Mode in Optical Fiber

AbstractExperimental excitation of a highly confined epsilon‐near‐zero (ENZ) mode in a side‐polished optical fiber coated with a deep subwavelength thick layer of aluminum‐doped zinc oxide (AZO) is reported. The uniform AZO layer on the fiber is fabricated by atomic layer deposition technique and optimized to exhibit close‐to‐zero permittivity at the near‐infrared wavelength. Highly polarization‐ and wavelength‐dependent transmission with strong resonance strength up to 25 dB is observed in a 30‐nm ENZ‐coated fiber that is 17 mm long. Different from the excitation of the ENZ mode in a planar conducting oxide thin film, the hybrid ENZ mode can be excited via direct phase matching between the fundamental mode of the fiber and the ENZ mode supported by the AZO thin film. The hybrid ENZ mode in the fiber exhibits a relatively long propagation/light–matter interaction length which is a few orders of magnitude longer than those on the planar ENZ substrates. It is further shown that the hybrid resonance in the ENZ fiber can be actively tuned through the refractive index of surrounding medium and the large ENZ's nonlinearity. These ENZ‐optical fibers serve as emerging in‐fiber optical devices, such as advanced in‐fiber ultrafast optical switches/modulators, mode‐locked fiber lasers, and in‐fiber optical gas/biomolecule sensors.

A nanoscale inorganic coating strategy for stabilizing hydrogel neural probes in vivo.

Hydrogels with adaptable optical and mechanical characteristics show considerable promise for light delivery in vivo with neuroengineering applications. However, the unlinked amorphous polymer chains within hydrogels can cause volumetric swelling after water absorption under physiological conditions over time. Chemically cross-linked poly(vinyl alcohol) (PVA) hydrogels showcase fatigue-resistant attributes and promising biocompatibility for the manufacture of soft neural probes. However, possible swelling of the PVA hydrogel matrix could impact the structural stability of hydrogel-based bioelectronics and their long-term in vivo functionality. In this study, we utilized an atomic layer deposition (ALD) technique to generate an inorganic, silicon dioxide (SiO2) coating layer on chemically cross-linked PVA hydrogel fibers. To evaluate the stability of SiO2-coated PVA hydrogel fibers mimicking the in vivo environment, we conducted accelerated stability tests. SiO2-coated PVA hydrogel fibers showed improved stability over a one-week incubation period under a harsh environment, preventing swelling and preserving their mechanical and optical properties compared to uncoated fibers. These SiO2-coated PVA hydrogel fibers demonstrated nanoscale polymeric crystalline domains (6.5 ± 0.1 nm), an elastic modulus of 73.7 ± 31.7 MPa, a maximum elongation of 113.6 ± 24.2%, and minimal light transmission loss (1.9 ± 0.2 dB cm-1). Lastly, we applied these SiO2-coated PVA hydrogel fibers in vivo to optically activate the motor cortex of transgenic Thy1::ChR2 mice during locomotor behavioral tests. This mouse cohort was genetically modified to express the light-sensitive ion channel, channelrhodopsin-2 (ChR2), and implanted with hydrogel fibers to deliver light to the motor cortex area (M2). Light stimulation via hydrogel fibers resulted in optogenetically modulated mouse locomotor behaviors, including increased contralateral rotation, mobility speeds, and travel distances.

Linear and nonlinear optical properties of Al2O3/Y2O3 nanolaminates fabricated by atomic layer deposition

The structure and composition of nanocomposites constitute design parameters that can be manipulated to get control over their linear and nonlinear optical response. In this work, we report the linear and nonlinear optical properties of samples consisting of multiple Al2O3/Y2O3 bilayers with a total thickness of ∼ 500 nm, fabricated through the atomic layer deposition technique onto Si and SiO2 substrates. Fabrication of the multiple layer configurations was made for four Y2O3 layer thicknesses, while maintaining a constant Al2O3 layer thickness for all the samples fabricated. Physical and chemical characterization of the samples produced was conducted by optical ellipsometry, transmission electron microscopy and XRD. Moreover, their third-order nonlinear optical properties were studied through the z-scan technique with 100 fs pulses at 800 nm from a Ti:Sapphire laser, allowing the resolution of the refractive and absorptive contributions to the response. The nonlinear parameters extracted from the experiments are discussed in terms of the fabrication thickness of the selected materials. Additionally, figures of merit relevant for the possible application of these materials in optical processing system are calculated and discussed.

Improvement of Mechanical Characteristics on Ultra-High Molecular Weight Polyethylene Surface through Zinc Oxide Atomic Layer Deposition Film

Wear failures in ultra-high molecular weight polyethylene (UHMWPE) compartments are known to limit the life of a joint implant. In this study, we applied atomic layer deposition (ALD) technique to produce wear-resistant zinc oxide (ZnO) films to improve mechanical and wear characteristics on the surface of UHMWPE. Organic material layers in molecular units were mixed with ALD ZnO films to minimize surface cracks through a molecular layer deposition (MLD) technique. We aimed to examine (1) the effect of organic layers on minimizing surface cracks and (2) the mechanical properties of ZnO and inorganic/organic hybrid films. We prepared UHMWPE samples with pure ZnO and five different hybrid films with ZnO to organic layer ratios of 1 : 1, 2 : 1, 3 : 1, 4 : 1, and 5 : 1. Surface cracks were observed by using a field-emission scanning electron microscope. Hardness and elastic modulus of an ALD-coated UHMWPE were measured by nano-indentation examinations. Severe cracks were found in the samples with pure ZnO films. However, no cracks were found in the samples with all hybrid films except the samples with a ZnO to organic layer ratio of 5 : 1. The hardness and elastic modulus of the samples with pure ZnO and hybrid films significantly increased compared to those of the native UHMWPE. The hardness to elastic modulus ratios, indicating the wear resistance, increased over 50% for all films compared to the values of native UHMWPE. These results suggested that ALD ceramic coatings with organic layers may become a potential solution for realizing a wear-resistant protection coating for the polymer compartment of joint prostheses.

Super-capacitive capabilities of wafer-scaled two-dimensional SnO2-Ga2O3n-p heterostructures fabricated by atomic layer deposition

Two-dimensional (2D) conformal SnO2-Ga2O3n-p heterostructures were fabricated on a wafer scale for the first time by atomic layer deposition (ALD) technique and their physicochemical properties as well as electrochemical behaviors as supercapacitor electrodes were subsequently investigated. High specific capacitance of 167 F g−1 was achieved at the current density of 7.69 A g−1 after annealing SnO2-Ga2O3n-p heterostructures at 250 °C for 1 h in air. Moreover, sub-10 nm thick n-p heterostructures demonstrated high capacitance retention (~92.55 %) even after 10,000 continuous cycles. These findings are primarily attributed to the development of ultra-thin 2D SnO2-Ga2O3 heterostructures with high crystallinity, enabling fast charge transport through n-p heterojunctions. The results obtained could pay the way for the development of high-performance energy storage devices.

Effect of Nano Ceramic Coating on Color Perceptibility and Acceptability of Polymethylmethacrylate: In Vitro and Clinical Study.

The effect of a novel nano-ceramic coating (TiO2) using an atomic layer deposition (ALD) technique on the surface of polymethyl methacrylate (PMMA) material was investigated. The patients' and clinicians' perception and acceptance of the PMMA color with TiO2 coating were also examined. In vitro color measurement was performed on thirty specimens (light, original, and dark pink) before and after TiO2 coating. Patients' and clinicians' perception and acceptance of color changes on PMMA were measured and compared. Descriptive and analytic statistics were analyzed (a = 0.05). TiO2 films were successfully deposited on the PMMA specimen by the ALD technique. Color changes after TiO2 coating were observed on all three PMMA shades, significantly higher than the established 50:50% perceptibility threshold, but below the established 50:50% acceptability threshold. The percentage of patients that perceived a color difference after TiO2 coating were 83.3%, 63.9%, and 77.8% for light, original, and dark pink, respectively. The percentages of clinicians that were satisfied with the color difference were 96.4%, 80%, and 69.2% for light, original, and dark pink, respectively. Color changes after TiO2 coating were observed, but below the acceptable threshold. The clinical survey demonstrated that a color difference was perceived but was clinically acceptable. In general, laypeople have lower perception and higher acceptance of changes in PMMA color than clinicians.

Progress of Atomic Layer Deposition and Molecular Layer Deposition in the Development of All‐Solid‐State Lithium Batteries

AbstractAs one of the most promising candidates for next‐generation high‐energy storage systems, all‐solid‐state lithium batteries (ASSLBs) including the bulk‐type and thin‐film‐type configurations have attracted great attention currently. The rational construction of the electrodes and electrolytes, as well as well‐controlled interface modification, are indispensable for realizing the practical application of ASSLBs. In recent decades, atomic layer deposition (ALD) and molecular layer deposition techniques (MLD) have been widely applied as powerful tools to achieve the accurate control of atomic/molecular thickness and composition adjustment of the thin protective layers or electrodes. Owing to the unique features, ALD/MLD techniques show great potential in manipulation of interfacial properties and constructing novel electrode structures in the research of ASSLBs. In this review, we highlight the recent progress in the developments and applications of ALD/MLD techniques in ASSLBs, including the interface modification for both cathodes and lithium metal anodes in bulk‐type ASSLBs, and the preparation of electrodes and solid electrolytes in thin‐film type batteries. In addition, an overview of the existing challenges and the application prospects of ALD/MLD in ASSLBs are also presented.