Atomic Layer Deposition Technique Research Articles

Scalable and highly tunable conductive oxide interfaces

Conducting oxide interfaces have attracted considerable attention, motivated by both fundamental science and potential for oxide electronic devices. An important gap for maturing such device technology is scalability and routes to control the electronic properties, which can narrow the device engineering space. Here, we demonstrate and explain the mechanisms of highly tunable conductive oxide interfaces. We synthesized amorphous–crystalline Al2O3/SrTiO3 interfaces using the scalable and industry-compatible atomic layer deposition (ALD) technique. An NH3 plasma pretreatment is employed in the ALD chamber, and its duration is used as a tuning parameter for the electrical properties, where a span of three orders of magnitude in the sheet resistance is observed at room temperature. For the most conductive sample, our results are comparable to the highest carrier density values reported for all-crystalline oxide interfaces prepared with state-of-the-art epitaxial growth techniques, such as pulsed laser deposition. We pinpoint the origin of conductivity to oxygen vacancies caused by the SrTiO3 reduction by the NH3 plasma pretreatment. These results present a simple, scalable, and industry-compatible route for realizing conductive oxide interfaces, with a broad parameter space, offering a versatile and flexible toolkit for oxide device engineering.

Atomic Layer Deposition of Perpendicularly Magnetized Co Layers Showing Current-Induced Domain Wall Motion

Successful preparation of perpendicularly magnetized Co thin layers on Pt seed-layers using atomic layer deposition (ALD) technique with Co(PF3)4H as a precursor is reported. The residual phosphorus content in the samples, due to low deposition temperatures to realize ALD, was reduced effectively by tuning ALD parameters. Spin-orbit-torque driven current-induced domain wall motion was observed in the strip containing ALD Co layer prepared with the low phosphorus condition.

Optimization of photoelectric properties of transparent conductive B and Ga co-doped ZnO films for electrochromic applications

To improve the performance of electrochromic devices, it is urgently necessary to develop transparent indium-free conductive electrodes with high conductivity and transparency. In this study, thin films of Ga-doped ZnO (GZO) and B–Ga co-doped ZnO (BGZO) were prepared on glass substrates using the plasma-assisted atomic layer deposition (PEALD) technique, and their structural and optoelectronic properties were characterized. It is found that all thin films were consistent with hexagonal fibrous ZnO structure, and the surface morphology of the membrane was homogenous at nanoscale. UV spectroscopy analysis showed that the doping of B and Ga elements could increase the transparency of ZnO films. The electrical properties can be remarkably enhanced by doping with B and Ga elements. Further more, tungsten oxide (WO3) was deposited on the as-prepared BGZO films using magnetron sputtering method. We activated the sample by applying voltage and observed a color transition from transparent to dark blue. It has a modulation range of 65 % in the 633 nm spectrum and a coloring efficiency of 37.8 cm2C-1. This work opens up remarkable new opportunities for developing high-performance transparent conductive electrode in electrochromic devices.

Enhancing electron interaction between Pt and support for superior electrochemical performance through atomic layer deposition of tungsten oxide

The stabilization of platinum (Pt) catalysts through strong metal-support interactions is crucial for their successful implementation in fuel cell applications. Tungsten oxide (WO3) has demonstrated excellent CO tolerance and has been recognized as a promising substrate for anchoring and stabilizing Pt nanoparticles (NPs). However, the limited specific surface area of conventional tungsten oxide restricts its effectiveness in dispersing noble metal NPs. In this study, we present a pioneering approach by employing atomic layer deposition (ALD) to create a WO3 interlayer between Pt NPs and a carbon substrate. Using nitrogen-doped carbon nanotubes (NCNT) as the foundation, WO3 nanoparticles (2–5 nm) were selectively synthesized, followed by the subsequent deposition of Pt NPs using a bottom-up approach. The Pt-WO3-NCNT catalyst, with a WO3 bridge layer effectively inserted between the active site and carbon support, has displayed a notable augmentation in electrocatalytic activity and notable stability when compared to commercial Pt catalysts in oxygen reduction reaction (ORR). The detailed microstructure and the enhanced electrochemical reaction mechanism of Pt-WO3-NCNT catalyst has been investigated by X-ray adsorption spectrum and density functional theory (DFT) calculations. This work presents an innovative approach for enhancing the stability of Pt catalysts through the utilization of the ALD technique.

Optimizing Li Ion Transport in a Garnet-Type Solid Electrolyte via a Grain Boundary Design

Garnet-type solid electrolytes have gained considerable attention owing to their exceptional ionic conductivity and broad electrochemical stability window, making them highly promising for solid-state batteries (SSBs). However, this polycrystalline ceramic electrolyte contains an abundance of grain boundaries (GBs). During the repetitive electroplating and stripping of Li ions, uncontrolled growth and spreading of lithium dendrites often occur at GBs, posing safety concerns and resulting in a shortened cycle life. Reducing the formation and growth of lithium dendrites can be achieved by rational grain boundary design. Herein, the garnet-type solid electrolyte LLZTO was firstly coated with Al2O3 using the atomic layer deposition (ALD) technique. Subsequently, an annealing treatment was employed to introduce Al2O3 into grain boundaries, effectively modifying them. Compared with the Li/LLZTO/Li cells, the Li/LLZTO@Al2O3-annealed/Li symmetric batteries exhibit a more stable cycling performance with an extended period of 200 h at 1 mA cm−2. After matching with the NMC811 cathode, the capacity retention rate of batteries can reach 96.8% after 50 cycles. The infusion of Al2O3 demonstrates its capability to react with LLZTO particles, creating an ion-conducting interfacial layer of Li-Al-O at the GBs. This interfacial layer effectively inhibits Li nucleation and filament growth within LLZTO, contributing to the suppression of lithium dendrites. Our work provides new suggestions for optimizing the synthesis of solid-state electrolytes, which can help facilitate the commercial application of solid-state batteries.

Passivation of MXene via atomic layer deposition of SnO2 to achieve improved NO2 sensing

MXene is a promising candidate for low power electronic devices, such as gas sensor at room temperature. However, achieving rapid response and complete recovery and simultaneously addressing the issue of baseline drift due to the oxidation of MXene are challenging for MXene sensors. Herein, we demonstrate a general strategy by using atomic layer deposition (ALD) to passivate Ti3C2Tx MXene. The abundant hydroxyl groups on MXene, which could lead to the oxidation of MXene, facilitate efficient deposition of SnO2. Gas sensor tests reveal that the passivated MXene@SnO2 exhibits a response of 35.2% to 20 ppm NO2, which is approximately three times higher than that of pure MXene. Importantly, the response time to NO2 was as fast as 18 s, with full and complete recovery to baseline within 27 s. Our strategy highlights the prospects of utilizing ALD technique for the development of MXene-based gas sensors.

Atomic layer deposition of alumina on hollow nickel phyllosilicate nanosheets for enhanced CO2 thermal hydrogenation performance

Herein, NiSiO3@Al2O3 catalysts were prepared by encapsulating Al2O3 films on nickel phyllosilicate nanosheets via atomic layer deposition (ALD) technique, and used for CO2 hydrogenation reaction. The NiSiO3-R600 catalyst without Al2O3 films underwent serious agglomeration of Ni particles after H2 reduction at 600 °C, leading to poor CO2 conversion of 22.6%. In comparison, CO2 conversion over NiSiO3@5Al2O3-R600 catalyst reached 66.9% due to that the ALD-Al2O3 film can effectively alleviate the agglomeration of Ni particles (6.3 vs. 22.1 nm). Furthermore, the electronic interaction between Al2O3 and the metallic nickel site was confirmed by both XPS spectroscopy and DFT calculations. The chemisorption behaviors of probe molecules on the catalyst surface also prove the better dispersion of metallic Ni sites in the presence of the ALD-Al2O3 layer. Moreover, in-situ DRIFTS characterization indicates that the presence of ALD-Al2O3 film promoted the hydrogenation of HCOO* to CH3O*, which then increased the CO2 conversion and CH4 selectivity.

De-Pinning Fermi Level and Accelerating Surface Kinetics with an ALD Finish Boost the Fill Factor of BiVO4 Photoanodes to 44.

With the rapid development of performance and long-term stability, bismuth vanadate (BiVO4 ) has emerged as the preferred photoanode in photoelectrochemical tandem devices. Although state-of-the-art BiVO4 photoanodes realize a saturated photocurrent density approaching the theoretical maximum, the fill factor (FF) is still inferior, pulling down the half-cell applied bias photon-to-current efficiency (HC-ABPE). Among the major fundamental limitations are the Fermi level pinning and sluggish surface kinetics at the low applied potentials. This work demonstrates that the plasma-assisted atomic layer deposition technique is capable of addressing these issues by seamlessly installing an angstrom-scale FeNi-layer between BiVO4 and electrolyte. Not only this ultrathin FeNi layer serves as an efficient OER cocatalyst, more importantly, it also effectively passivates the surface states of BiVO4 , de-pins the surface Fermi level, and enlarges the built-in voltage, allowing the photoanode to make optimal use of the photogenerated holes for achieving high FF up to 44% and HC-ABPE to 2.2%. This study offers a new approach for enhancing the FF of photoanodes and provides guidelines for designing efficient unassisted solar fuel devices.

Impact of thickness on optoelectronic properties of α-MoO3 film photodetectors: Integrating first-principles calculations with experimental analysis

This study focused on investigating the optoelectronic properties of molybdenum trioxide (α-MoO3) thin films using the atomic layer deposition (ALD) technique through different cycle numbers and theoretical investigation. Initial band gap calculations using standard DFT with GGA-PBE resulted in a value of 1.19 eV, which deviated significantly from experimental measurements. The GGA + U method with Hubbard U corrections was applied for the first time to improve the accuracy. This refinement led to a more precise band gap value of 3.09 eV, closely matching previously reported experimental data. The electronic parameters of the α-MoO3 photodetector, such as ideality factor (n), barrier height (Φ0), and series resistance (Rs), were analyzed using the thermionic emission theory and confirmed by Cheung and Nord's methods. The results demonstrated that the sample deposited with 100 pulses exhibited higher photodetector performance under UV illumination, despite having a lower Rs.

Alumina layers deposited by atomic layer deposition with different precursors: Surface photovoltage measurements

The electrical and passivation properties of alumina layers deposited by the atomic layer deposition (ALD) technique with trimethylaluminium (TMA) and two different oxidants (ozone and water) and their mixture under different deposition conditions were investigated by using surface photovoltage. In all alumina layers negatively charged defects were observed after the ALD deposition. The density of interface states (Dit) and the density of negative charge (CFix) in as-deposited alumina layers prepared with water was found to be lower in comparison to wafers prepared with O3 or with a mixture of H2O and O3. The minority carrier diffusion length was also larger in wafers prepared with H2O and TMA. By comparing the deposition conditions of different alumina layers we concluded that interstitial oxygen could be responsible for the appearance of the negatively charged defects. After the broadband illumination we also observed a significant increase of CFix in all alumina layers independent of the precursors used for the deposition and only small changes of Dit were detected. O-related defects could also lead to such changes of CFix after the illumination.

Catalyzing Generation and Stabilization of Oxygen Vacancies on CeO2-x Nanorods by Pt Nanoclusters as Nanozymes for Catalytic Therapy.

Although CeO2 nanomaterials have been widely explored as nanozymes for catalytic therapy, they still suffer from relatively low activities. Herein, the catalyzing generation and stabilization of oxygen vacancies on CeO2 nanorods by Pt nanoclusters via H2 gas reduction under mild temperature (350°C) to obtain Pt/CeO2- x , which can serve as a highly efficient nanozyme for catalytic cancer therapy, is reported. The deposited Pt on CeO2 by the atomic layer deposition technique not only can serve as the catalyst to generate oxygen vacancies under mild temperature reduction through the hydrogen spillover effect, but also can stabilize the generated oxygen vacancies. Meanwhile, the oxygen vacancies also provide anchoring sites for Pt forming strong metal-support interactions and thus preventing their agglomerations. Importantly, the Pt/CeO2- x reduced at 350°C (Pt/CeO2- x -350R) exhibits excellent enzyme-mimicking catalytic activity for generation of reactive oxygen species (e.g., ·OH) as compared to other control samples, including CeO2 , Pt/CeO2 , and Pt/CeO2- x reduced at other temperatures, thus achieving excellent performance for tumor-specific catalytic therapy to efficiently eliminate cancer cells in vitro and ablate tumors in vivo. The excellent enzyme-mimicking catalytic activity of Pt/CeO2- x -350R originates from the good catalytic activities of oxygen vacancy-rich CeO2- x and Pt nanoclusters.

Optimizing energy storage performance of ALD YSZ thin film devices via yttrium concentration variations

In the last decade, research has focused on fabricating new materials to accelerate the development of energy storage devices. In this work, metal-electrolyte-metal (Au-YSZ-Ru) structures were fabricated on silicon substrates using atomic layer deposition, sputtering, and thermal evaporation techniques. The effect of the yttrium concentration in YSZ films on their chemical, structural, optical, and electrical properties were studied. XPS analysis showed yttrium concentrations of 14.6, 10.3, 6.8, and 5.3 at.% for films with ALD cycle ratios Zr:Y of 2:1, 4:1, 6:1, and 8:1. Deconvolution of the oxygen XPS signal demonstrate the yttrium to oxygen vacancies ratio. The band gap was calculated through UV–vis indicating an increase in values with yttrium concentration. In addition, the trend was confirmed by reflection electron energy loss spectroscopy (REELS). The structure was investigated by performing X-ray diffraction (XRD) and infrared attenuated total reflectance spectroscopy (IR-ATR) measurements. Both results indicate a better crystallization of the cubic phase for the samples with lower concentrations, as the intensity of (111) diffraction peaks and IR band increased for lower yttrium concentrations. Impedance spectroscopy revealed an activation energy of 1.69, 1.32, and 1.28 eV for the 10.3, 6.8, and 5.3 at.% film concentration, respectively. According to cyclic voltammetry and charge-discharge tests, a lower yttrium concentration, 5.3 at.%, promotes electrode REDOX reactions improving the energy-storage properties.

Study of Atomic Layer Deposition Nano-Oxide Films on Corrosion Protection of Al-SiC Composites.

In recent years, aluminum matrix composites (AMCs) have attracted attention due to their promising properties. However, the presence of ceramic particles in the aluminum matrix renders AMCs a high corrosion rate and makes it challenging to use traditional corrosion protection methods. In this study, atomic layer deposition (ALD) techniques were used to deposit HfO2, ZrO2, TiO2, and Al2O3 thin films on AMC reinforced with 20 vol.% SiC particles. Our results indicate that the presence of micro-cracks between the Al matrix and SiC particles leads to severe micro-crack-induced corrosion in Al-SiC composites. The ALD-deposited films effectively enhance the corrosion resistance of these composites by mitigating this micro-crack-induced corrosion. Among these four atomic-layer deposited films, the HfO2 film exhibits the most effective reduction in the corrosion current density of Al-SiC composites in a 1.5 wt% NaCl solution from 1.27 × 10-6 A/cm2 to 5.89 × 10-11 A/cm2. The electrochemical impedance spectroscopy (EIS) investigation shows that HfO2 deposited on Al-SiC composites has the largest Rp value of 2.0 × 1016. The HfO2 film on Al-SiC composites also exhibits effective inhibition of pitting corrosion, remaining at grade 10 even after 96 h of a salt spray test.

Nanomechanical resonators fabricated by atomic layer deposition on suspended 2D materials

Atomic layer deposition (ALD), a layer-by-layer controlled method to synthesize ultrathin materials, provides various merits over other techniques such as precise thickness control, large area scalability and excellent conformality. Here we demonstrate the possibility of using ALD growth on top of suspended 2D materials to fabricate nanomechanical resonators. We fabricate ALD nanomechanical resonators consisting of a graphene/MoS2 heterostructure. Using atomic force microscope indentation and optothermal drive, we measure their mechanical properties including Young’s modulus, resonance frequency and quality factor, showing a lower energy dissipation compared to their exfoliated counterparts. We also demonstrate the fabrication of nanomechanical resonators by exfoliating an ALD grown NbS2 layer. This study exemplifies the potential of ALD techniques to produce high-quality suspended nanomechanical membranes, providing a promising route towards high-volume fabrication of future multilayer nanodevices and nanoelectromechanical systems.

Synergetic Effects of Nanoscale ALD-HfO2 Coatings and Bionic Microstructures for Antiadhesive Surgical Electrodes: Improved Cutting Performance, Antibacterial Property, and Biocompatibility.

The high temperature induced by surgical electrodes is highly susceptible to severe surface adhesion and thermal damage to adjacent tissues, which is a major challenge in improving the quality of electrosurgery. Herein, we reported a coupled electrode with micro/nano hierarchical structures fabricated by depositing nanoscale hafnium oxide (HfO2) coatings on bionic microstructures (BMs) via laser texturing, acid washing, and atomic layer deposition (ALD) techniques. The synergistic effect of HfO2 coatings and BMs greatly enhanced the hemophobicity of the electrode with a blood contact angle of 162.15 ± 3.16°. Furthermore, the coupled surface was proven to have excellent antiadhesive properties to blood when heated above 100 °C, and the underlying mechanism was discussed. Further experiments showed that the coupled electrode had significant advantages in reducing cutting forces, thermal damage, and tissue adhesion mass. Moreover, the antibacterial rates against Escherichia coli and Staphylococcus aureus were 97.2% and 97.9%, respectively. In addition, the noncytotoxicity levels of HfO2 coatings were verified by cell apoptosis and cycle assays, indirectly endowing the coupled electrode with biocompatibility. Overall, the coupled electrode was shown to have broad potential for application in the field of electrosurgery, and this work could provide new insights into antiadhesion properties under high-temperature conditions.

Structural, Optical, and Electrical Properties of Hafnium-Aluminum-Zinc-Oxide Films Grown by Atomic Layer Deposition for TCO Applications.

ZnO is a widely studied material that exhibits versatile doping possibilities. Most research presents singly doped ZnO, leaving the potential of codoping unexplored. Within this study, hafnium-aluminum codoped zinc oxide (HAZO) thin films were grown on a glass substrate using the atomic layer deposition technique at 200 °C. A comprehensive analysis of the surface morphology and electrical and optical properties of the samples was conducted for varying the Al/Hf doping ratio. X-ray diffraction studies showed that the obtained films are polycrystalline, exhibiting a preferential growth direction along the (1 0 0) plane without any detectable precipitates. Moreover, the electrical measurements of HAZO films revealed that they exhibit lower resistivity (∼9.5 × 10-4 Ωcm) than the commonly used aluminum zinc oxide films (AZO). This improvement can be primarily attributed to the promotion of the n-type carrier concentration to 4.45 × 1020 cm-3 while maintaining a mobility value equal to 14.7 cm2/Vs. The doping also influences the optical properties of the material by widening the band gap and changing the refractive index, as observed by spectroscopy and ellipsometry studies. These findings highlight the potential of proposed HAZO thin films for future applications in electronic devices utilizing transparent conducting oxides.

Atomic-layer-deposited BOx/Al2O3 stack for crystalline silicon surface passivation

Surface passivation is a crucial factor in improving the efficiency of c-Si solar cells. In this work, we develop a boron oxide/aluminum oxide stack (BOx/Al2O3) using the atomic layer deposition technique, and investigate the passivation quality and mechanism on c-Si surfaces. The BOx/Al2O3 stacks display excellent surface passivation on c-Si surfaces after annealing, superior to that of Al2O3 single layers. With the optimal BOx/Al2O3 passivation stack, we obtained a very low dark current density (J0) of 7.8 fA/cm2 (iVoc 725 mV) and 4.7 fA/cm2 (iVoc 714.6 mV) on industrial n-type (5.3 Ω cm) and p-type (3.0 Ω cm) Cz wafers, respectively. The BOx/Al2O3 stack also shows excellent passivation performance on boron-doped p+ emitters (110 Ω/sq), achieving a low J0 of 15.1 fA/cm2. The enhanced passivation quality of the BOx/Al2O3 stack can be attributed to the increased fixed negative charge density after thermal annealing. BOx/Al2O3 passivation stacks also can potentially act as an effective p-type dopant source for laser processing, which would be very desirable for high-efficiency c-Si solar cells.

Ultra-Low Loading of Iron Oxide and Platinum on CVD-Graphene Composites as Effective Electrode Catalysts for Solid Acid Fuel Cells

We propose a new design for electrocatalysts consisting of two electrocatalysts (platinum and iron oxide) that are deposited on the surfaces of an oxidized graphene substrate. This design is based on a simple structure where the catalysts were deposited separately on both sides of oxidized graphene substrate; while the iron oxide precipitated out of the etching solution on the bottom-side, the surface of the oxidized graphene substrate was decorated with platinum using the atomic layer deposition technique. The Fe2O3-decorated CVD-graphene composite exhibited better hydrogen electrooxidation performance (area-normalized electrode resistance (ANR) of ~600 Ω·cm−2) and superior stability in comparison with bare-graphene samples (ANR of ~5800 Ω·cm−2). Electrochemical impedance measurements in humidified hydrogen at 240 °C for (Fe2O3|Graphene|Platinum) electrodes show ANR of ~0.06 Ω·cm−2 for a platinum loading of ~60 µgPt·cm−2 and Fe2O3 loading of ~2.4 µgFe·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. This ANR value is ~30% lower than the charge transfer resistance of the same electrode composition in the absence of Fe2O3 nanoparticles. Detailed study of the Fe2O3 electrocatalytic properties reveals a significant improvement in the electrode’s activity and performance stability with the addition of iron ions to the platinum-decorated oxidized graphene cathodes, indicating that these hybrid (Fe2O3|Graphene|Platinum) materials may serve as highly efficient catalysts for solid acid fuel cells and beyond.

Improved memory performance of ALD grown HfO2 films by nitrogen doping

Resistive switching devices have shown potential in storage class memory and artificial intelligence applications but however, it faces drastic limitations due to low endurance, bad retention, low ON/OFF ratio and variant operating voltages. Here we have reported the resistive switching characteristics of nitrogen (N)-doped HfOx films synthesized by atomic layer deposition (ALD) technique. The N-doping in hafnia films significantly enhances the stability of devices, its ON/OFF ratio and retention thus showing its potential in storage class memory applications. The increase in memristor performance has been classified due to the formation of oxygen vacancy and nitrogen (Vo + 2 N) clusters which influence the ionic conductivity and reduces the total energy of the system thus increasing its ON/OFF ratio and device electrical stability. The Vo + 2 N clusters also scrutinize the conductive filament formation in the HfOx matrix and punch them to grow in localized directions which results in uniform distribution of SET/RESET voltages and high endurance. Overall, this study provides a facile way to improve the device performance of resistive switching devices for enhanced memory applications and neuromorphic computing.

Electrochemical and photocatalytic properties of ZnO nanostructures deposited on nanoporous anodized aluminum oxide membrane and its application for degradation of reactive blue 19 in textile wastewater

The current study's objective was to develop a ZnO photocatalyst for the treatment of reactive blue 19 (RB19) from textile wastewater by depositing ZnO nanostructures over nanoporous anodized aluminum oxide (ZnO-AAO). The ZnO-AAO membrane was created using the atomic layer deposition (ALD) technique. SEM, XRD, and EDS morphological and structural characterizations demonstrated that ZnO nanostructures were successfully deposited on the AAO membrane. Studying the optical properties revealed that the band gap energies for ZnO, AAO, and ZnO-AAO membranes were found to be 3.19, 2.85, and 2.92 eV, respectively. This resulted in an improvement in the separation efficiency of photo-excited electrons and holes as well as an increase in the photocatalytic activity of the ZnO-AAO sample in the visible light region. Studying the electrochemical parameters revealed that ZnO-AAO had the lowest charge transfer resistance, which indicates that photoinduced electrons and holes in ZnO-AAO contacts effectively transfer charge and have slower recombination rates. According to research on photocatalytic performance, ZnO-AAO and ZnO photocatalysts required 70 and 90 min of visible light exposure to completely decolorize RB19, respectively. The photocatalytic decolorization of RB19 in an actual sample of textile wastewater showed that the dye could be effectively removed by photocatalytic means when ZnO-AAO membrane photocatalyst was present.