Ultrathin Al2O3 Layer Research Articles

Effect of Al doping on structural and electrical properties of HfO2/ZrO2 layered structures for high-k applications

ZrO2 films with ultrathin Al2O3 layers have effectively contributed to the miniaturization of dynamic random access memory (DRAM) capacitors for many years. However, as memory devices continue to shrink, higher dielectric constants are required to maintain cell capacitance. To address this challenge, research has explored the use of tetragonal HfO2 layers, which theoretically possess a higher dielectric constant than ZrO2, as dielectrics. However, the thermodynamically stable phase of HfO2 is monoclinic with a lower dielectric constant, necessitating a phase transition to the tetragonal form for DRAM capacitor applications. Although attempts have been made to induce this phase transition to achieve high dielectric constants by applying an HfO2/ZrO2 layered structure or doping HfO2 with elements such as Zr, Al, and Si, significant challenges remain in completely eliminating the monoclinic phase or implementing a pure tetragonal phase of HfO2. In this study, we systematically investigated the crystallinity changes and improved the electrical properties of HfO2/ZrO2 layered structures with Al doping in the HfO2 layers. Our findings demonstrate that optimizing the partitioning of the ZrO2 and HfO2 layers, combined with Al doping, effectively achieves equivalent oxide thickness scaling.

Durability improvement of electrochromic WO3 thin films by deposition of an ultra-thin Al2O3 layer via atomic layer deposition

Introduction of an ultra-thin Al2O3 protective layer via atomic layer deposition (ALD) significantly enhances the durability and performance of amorphous tungsten trioxide (a-WO3) thin films for electrochromic devices. The Al2O3 layer, despite being less than 4 nm thick, effectively suppresses the dissolution of WO3 that typically occurs through hydration reactions forming WO3·H2O and tungstic acid (H2WO4). XRD and XPS analyses confirmed the presence of Al2O3 and its minimal impact on the amorphous structure of WO3 thin films. Optical transmittance measurements showed that the Al2O3-protected a-WO3 thin films maintained a higher transmittance modulation (ΔT) compared to bare a-WO3 thin films, with the ALD30 sample retaining 87.9 % of its initial transmittance modulation after 1000 cycles, in contrast to the rapid degradation observed in unprotected films. Microstructural analysis revealed significantly fewer surface cracks and reduced thickness loss in Al2O3-coated films after 100 cycles. Additionally, ICP-MS analysis indicated a much lower W concentration in the electrolyte for Al2O3-protected samples, confirming reduced dissolution.

Fabrication and electrical properties of flexible polymer-based MIM capacitors of high-k nanolaminate dielectrics of HfO2–SnO2–TiO2 with ultrathin Al2O3 insertion layer by plasma-enhanced atomic layer deposition

Abstract Flexible metal–insulator–metal (MIM) capacitors of high-k nanolaminate HfO2–SnO2–TiO2 thin films were fabricated on several polymer substrates of polyethylene terephthalate, polyimide and epoxy resin at 80 °C by plasma-enhanced atomic layer deposition. The electrical properties were optimized by adjusting the sub-cycle ratio of Hf: Sn: Ti to 6: 5: 4. In order to reduce the leakage current density of flexible capacitors, the ultrathin Al2O3 layer varying from 0.5 to 1.5 nm was inserted to form Al2O3/HfO2–SnO2–TiO2/Al2O3 stacking capacitors. The effect of the Al2O3 insertion layer thickness and the super-cycle number of HfO2–SnO2–TiO2 on the capacitance density, leakage, and quadratic voltage linearity was investigated. Under optimal processing, flexible MIM capacitors could stand 40 000 bending cycles at curvature radius of 8.2 mm, indicative of better electrical stability. Moreover, compared with the polymer-based HfO2–SnO2–TiO2 capacitors, the introduction of 1 nm Al2O3 ultrathin layer greatly decreases the leakage current density by 4 orders of magnitude (10−8 A cm−2) with relative lower voltage linearity (350–540 ppm V−2), but the capacitance density also declines (∼3 fF μm−2) simultaneously. Despite this, the method of inserting Al2O3 ultra-thin layer is still an effective method to improve the electrical performances of polymer-based HfO2–SnO2–TiO2 nanolaminate capacitors for flexible electronics.

Ultrathin nanocapacitor assembled via atomic layer deposition

We fabricated ultrathin metal - oxide - semiconductor (MOS) nanocapacitors using atomic layer deposition. The capacitors consist of a bilayer of Al2O3 and Y2O3 with a total thickness of ~10 nm, deposited on silicon substrate. The presence of the two materials, each slab being ~5 nm thick and uniform over a large area, was confirmed with Transmission Electron Microscopy and X-ray photoelectron spectroscopy (XPS). The capacitance in accumulation varied from 1.6 nF (at 1MHz) to ~2.8 nF (at 10 kHz), which is one to two orders of magnitude higher than other nanocapacitors. This high capacitance is attributed to the synergy between the dielectric properties of ultrathin Al2O3 and Y2O3 layers. The electrical properties of the nanocapacitor are stable within a wide range of temperatures, from 25 °C to 150 °C, as indicated by capacitance-voltage (C - V). Since the thickness-to-area ratio is negligible, the nanocapacitor could be simulated as a single parallel plate capacitor in COMSOL Multiphysics, with good agreement between experimental and simulation data. As a proof-of-concept we simulated a MOSFET device with the nanocapacitor gate dielectric, whose drain current is sufficiently high for micro and nanoelectronics integrated circuits, including for applications in sensing.

Enhancing photo-response performance through ultrathin Al2O3 modification at the p-SnO2:Al/n-GaN heterojunction interface

We report on photoconductive and p-n heterojunction ultraviolet (UV) photodetectors based on p-type Al-doped SnO2 (p-SnO2:Al) thin films. We investigated the structural, optical, and electrical properties of Al-doped SnO2 thin films prepared using sol-gel methods, with our results being strongly supported by first-principles calculations. To achieve a self-powered photodetector device at zero bias, we fabricated p-SnO2:Al thin film on an n-GaN layer to form a p-n heterojunction. The responsivity of the p-n heterojunction UV detector, measured at zero bias, is 0.05 A/W, indicating good rectification properties. In order to improve device performance, a p-n heterojunction with a passivation layer was formed by inserting an ultrathin Al2O3 layer between the n-GaN layer and the p-SnO2:Al layer. With this change, the device's responsivity was 0.44 A/W at 350 nm at zero bias, roughly 10 times better than the detector without the Al2O3 passivation layer. The insertion of an ultrathin Al2O3 layer, which increases the efficiency of carrier separation on the SnO2 side while lowering the rate of carrier recombination at the interface, is responsible for the increased light responsivity performance.

Facile Fabrication of Large-Area CuO Flakes for Sodium-Ion Energy Storage Applications.

CuO is recognized as a promising anode material for sodium-ion batteries because of its impressive theoretical capacity of 674 mAh g-1, derived from its multiple electron transfer capabilities. However, its practical application is hindered by slow reaction kinetics and rapid capacity loss caused by side reactions during discharge/charge cycles. In this work, we introduce an innovative approach to fabricating large-area CuO and CuO@Al2O3 flakes through a combination of magnetron sputtering, thermal oxidation, and atomic layer deposition techniques. The resultant 2D CuO flakes demonstrate excellent electrochemical properties with a high initial reversible specific capacity of 487 mAh g-1 and good cycling stability, which are attributable to their unique architectures and superior structural durability. Furthermore, when these CuO flakes are coated with an ultrathin Al2O3 layer, the integration of the 2D structures with outer nanocoating leads to significantly enhanced electrochemical properties. Notably, even after 70 rate testing cycles, the CuO@Al2O3 materials maintain a high capacity of 525 mAh g-1 at a current density of 50 mA g-1. Remarkably, at a higher current density of 2000 mA g-1, these materials still achieve a capacity of 220 mAh g-1. Moreover, after 200 cycles at a current density of 200 mA g-1, a high charge capacity of 319 mAh g-1 is sustained. In addition, a full cell consisting of a CuO@Al2O3 anode and a NaNi1/3Fe1/3Mn1/3O2 cathode is investigated, showcasing remarkable cycling performance. Our findings underscore the potential of these innovative flake-like architectures as electrode materials in high-performance sodium-ion batteries, paving the way for advancements in energy storage technologies.

A facile solution-based aluminum oxide interface layer for enhancing the efficiency and stability of perovskite solar cells

An ultrathin Al2O3 layer is modified on a perovskite surface via in situ hydrolysis and condensation of aluminum triisopropoxide. The Al2O3 layer can prevent moisture ingress, reduce the defect concentration, and suppress iodine migration in the devices.

Influence of passivating interlayers on the carrier selectivity of MoOx contacts for c-Si solar cells

The application of molybdenum oxide (MoOx) as a hole-selective contact for silicon-based solar cells has been explored due to superior optical transmittance and potentially leaner manufacturing compared to fully amorphous silicon-based heterojunction (SHJ) devices. However, the development of MoOx contacts has been hampered by their poor thermal stability, resulting in a carrier selectivity loss and an S-shaped IV curve. The aim of this study is to understand the influence of different passivating interlayers on the carrier selectivity of hole-selective MoOx contacts for crystalline silicon (c-Si) solar cells. We highlight the effect of different interlayers on the surface passivation quality, contact selectivity, and the thermal stability of our MoOx-contacted devices. The interlayers studied are intrinsic hydrogenated amorphous silicon (a-Si:H(i)), thermally grown ultrathin SiO2, and a stack consisting of an ultrathin SiOy and Al2O3 layer. Additionally, we simulate the interacting interlayer properties on the carrier selectivity of our MoOx contacts using a simplified model. Among these interlayers, the Al2O3/SiOy stack shows to be a promising alternative to SiO2 by enabling efficient transport of holes while being able to sustain an annealing temperature of at least 250 °C underlining its potential in module manufacturing and outdoor operation.

Proton Permeable, Oxygen Blocking, Ultrathin Al2O3 Layers for Electrocatalytic Applications

Operating zero-gap electrolyzers at current densities above 1 Acm-2 is very challenging because ohmic losses associated with ion transport across the ion exchange membrane become predominant.[1] Technically, we can reach current densities up to 10 Acm-2. However, even a 100 micrometer thin nafion membrane would lead to cell voltages over 3 V [2] due to ohmic losses. Therefore, research and experimental development efforts are still needed to enable and increase the cell efficiency at elevated current densities.Implementing an ultrathin membrane of only a few nanometers in electrolyzers will minimize ion transport (i.e. protons) losses and will enable high-throughput electrolysis at low temperatures. However, to date, there is no concept available to perform electrochemical conversions using membranes of only of a few nanometers thickness that can block molecules but permeate protons.Multiple reports have demonstrated that dense ultrathin oxide layers, i.e. SiO2, can be used as electrocatalyst coatings to increase selectivities by blocking undesired ions/molecules from reaching the electrode.[3,4] The properties of such dense ultrathin oxide layers in principle fulfil the requirements of a proton exchange membrane, being only a couple of nanometer thin.To implement a nanometer thin proton exchange membrane into an electrolysis setup and enable mechanical integrity we envision a 3D-nanotube array design as shown in Figure 1a. In the ‘inside’ of the tube we perform the Hydrogen evolution reaction, and on the ‘outside’ the water oxidation reaction. Cathode and anode are separated only by a dense ultrathin oxide layer that permeates protons but blocks oxygen.Herein, we discuss the performance of ultrathin dense and amorphous Al2O3 layers made via pulsed laser deposition (2.5 nm, 3 nm, and 5 nm) with regard to proton and oxygen permeability. Electrochemical impedance spectroscopy allows us to determine diffusion coefficients and charge transfer resistances (Figure 1b). We use state-of-the-art operando FT-IR reflection-absorption spectroelectrochemistry that enables us to probe the dynamic structural and morphological changes of the dense alumina layer over time vs. applied potential (Figure 1c). In fact, we observe that proton permeation improves over time while we can exclude dissolution of the Al2O3 layer.

Improving the minority carrier lifetime of PERC solar cells via bi-layer rear interface passivation strategy

Passivated emitter and rear contact (PERC) based solar cells are dominating the current photovoltaic (PV) market due to their high power conversion efficiency (PCE) and low cost. However, issues like the lower minority carrier lifetime (MCLT) and high density of surface dangling bonds are limiting their further improvement in PCE. To overcome this issue, a bi-layer rear interface passivation strategy is developed with the ultra-thin Al2O3 and SiO2 layers in PERC solar cells. Applying single (Al2O3) and double (SiO2/Al2O3) passivation layers revealed that each process parameter such as plasma conditions, deposition temperature, post-annealing temperature, and the film thickness in the ALD process affect the MCLT values as well as overall device performance. Especially, post-annealing treatment which improves crystallinity, and reduces interfacial defects was found to be most influential for the MCLT value. The single Al2O3 layer applied in PERC solar cells revealed an increase and decrease in MCLT values at a relatively lower (<10 nm) and higher thickness (>15 nm), respectively. Further, integration of SiO2 with the Al2O3 layer showed its more prominent effect than just single Al2O3 and SiO2 passivation layers. An optimal SiO2 thickness combination (4 nm) with an Al2O3 layer (12 nm), demonstrated reduced density of surface dangling bonds and diffusion of Al atoms from Al2O3 layers. As a result, it improved the carrier extraction yield by increasing the negative fixed charge. Finally, SiO2/Al2O3 (4/12 nm) double passivation layer post-annealed at 450 °C for 15 min delivers improved PCE from 19.4% to 19.9% in PERC solar cells.

Multilayering FeGa with NiFe and Al2O3 to enhance the soft magnetic properties

In this study, the impact of insulating Al2O3 interlayers on the static and dynamic magnetic properties of FeGa/NiFe multilayers was investigated. A multilayer structure consisting of ten (10 nm FeGa)/(2.5 nm NiFe) bilayers was first established to show a reduction in coercivity and high frequency losses compared to a single (100 nm FeGa)/(2.5 nm NiFe) bilayer, which itself shows better performance than a single 100 nm FeGa film. By strategically placing 2.5 nm Al2O3 interlayers in the FeGa/NiFe multilayers (after the FeGa layer but before the next NiFe layer), the composite displayed a reduced coercivity down to 3 Oe while retaining a strong uniaxial anisotropy. Due to the effectiveness of these ultra-thin Al2O3 layers in reducing the eddy current losses across the FeGa/NiFe multilayer stack, this multilayer structure exhibited excellent performance at high frequency, including a gilbert damping coefficient of 0.0081 and an inhomogeneous linewidth of 38 Oe. These results demonstrate that Al2O3 interlayers can improve the soft magnetic properties of (FeGa/NiFe)-based multilayers to enable integration in magnetoelastic and high frequency applications.

Controlled orientation and microstructure of p-type SnO thin film transistors with high-k dielectric for improved performance

Despite its relatively high hole mobility, the electrical performance of p-type SnO thin-film transistors (TFTs) lags behind that of n-type oxide TFTs. In this study, we present an approach to enhance the performance of p-type SnO TFTs by utilizing an atomic-layer-deposited SnO/high-k structure, with crystalline HfO2 (c-HfO2) serving as a high-k dielectric. However, the grain boundaries on the c-HfO2 surface influenced the microstructure and orientation of the SnO layer, resulting in a random orientation and surface roughening. To address this issue, we modified the c-HfO2 surface with an amorphous ultrathin Al2O3 layer to eliminate the grain boundaries on the deposition surface. This enabled the alignment of the (00l) SnO planes parallel to the substrate surface and provided a smooth surface. Moreover, the introduction of ultrathin Al2O3 into SnO/high-k stacks substantially improved the electrical performance of p-type SnO TFTs. Our findings highlight the potential of integrating van der Waals semiconductors with high-k dielectrics, facilitating opportunities for advanced device applications.

Atomic Layer Deposition of Ultrathin Al2O3 Layer on Carbon Nanotube Anodes for Potassium Ion Batteries with High Initial Coulombic Efficiency and Electrochemical Performance

AbstractPotassium ion batteries (PIBs) have emerged as one of the most attractive alternatives to lithium‐ion batteries (LIBs) to satisfy the burgeoning energy demand. The continuous growth of solid electrolyte interphase (SEI) and consumption of potassium resources cause poor initial Coulombic efficiency (ICE), unstable cycling performance, and even safety issues. Herein, the fabrication of an artificial SEI of an ultrathin Al2O3 layer by atomic layer deposition (ALD) on a multi‐walled carbon nanotubes (MWCNTs) anode for high‐performance PIBs is reported. The SEI resistance and the charge transfer resistance in the MWCNTs electrode are significantly reduced according to electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration (GITT) measurements. The MWCNT electrode with a 2‐nm Al2O3 layer exhibits a much higher ICE of up to 85.9% than that of the uncoated one (20.8 %). It also maintains a remarkably high reversible capacity of 284 mA h g−1 at 100 mA g−1 after 100 cycles. In particular, the anode delivers superior rate capability of 558, 303, 251, 203, and 154 mAh g−1 at a current density of 50, 100, 200, 400, and 800 mA g−1, respectively. This work offers an effective approach for fabricating PIBs with high ICE and electrochemical performance.

Improved Efficiency and Stability of Organic Solar Cells by Interface Modification Using Atomic Layer Deposition of Ultrathin Aluminum Oxide

The interfacial contacts between the electron transporting layers (ETLs) and the photoactive layers are crucial to device performance and stability for OSCs with inverted architecture. Herein, atomic layer deposition (ALD) fabricated ultrathin Al2O3 layers are applied to modify the ETLs/active blends (PM6:BTP‐BO‐4F) interfaces of OSCs, thus improving device performance. The ALD‐Al2O3 thin layers on ZnO significantly improved its surface morphology, which led to the decreased work function of ZnO and reduced recombination losses in devices. The simultaneous increase in open‐circuit voltage (), short‐circuit current density () and fill factor (FF) were achieved for the OSCs incorporated with ALD‐Al2O3 interlayers of a certain thickness, which produced a maximum PCE of 16.61%. Moreover, the ALD‐Al2O3 interlayers had significantly enhanced device stability by suppressing degradation of the photoactive layers induced by the photocatalytic activity of ZnO and passivating surface defects of ZnO that may play the role of active sites for the adsorption of oxygen and moisture.

Synthesis of TiO2/Al2O3 Double-Layer Inverse Opal by Thermal and Plasma-Assisted Atomic Layer Deposition for Photocatalytic Applications.

In comparison to conventional nano-infiltration approaches, the atomic layer deposition (ALD) technology exhibits greater potential in the fabrication of inverse opals (IOs) for photocatalysts. In this study, TiO2 IO and ultra-thin films of Al2O3 on IO were successfully deposited using thermal or plasma-assisted ALD and vertical layer deposition from a polystyrene (PS) opal template. SEM/EDX, XRD, Raman, TG/DTG/DTA-MS, PL spectroscopy, and UV Vis spectroscopy were used for the characterization of the nanocomposites. The results showed that the highly ordered opal crystal microstructure had a face-centered cubic (FCC) orientation. The proposed annealing temperature efficiently removed the template, leaving the anatase phase IO, which provided a small contraction in the spheres. In comparison to TiO2/Al2O3 plasma ALD, TiO2/Al2O3 thermal ALD has a better interfacial charge interaction of photoexcited electron-hole pairs in the valence band hole to restrain recombination, resulting in a broad spectrum with a peak in the green region. This was demonstrated by PL. Strong absorption bands were also found in the UV regions, including increased absorption due to slow photons and a narrow optical band gap in the visible region. The results from the photocatalytic activity of the samples show decolorization rates of 35.4%, 24.7%, and 14.8%, for TiO2, TiO2/Al2O3 thermal, and TiO2/Al2O3 plasma IO ALD samples, respectively. Our results showed that ultra-thin amorphous ALD-grown Al2O3 layers have considerable photocatalytic activity. The Al2O3 thin film grown by thermal ALD has a more ordered structure compared to the one prepared by plasma ALD, which explains its higher photocatalytic activity. The declined photocatalytic activity of the combined layers was observed due to the reduced electron tunneling effect resulting from the thinness of Al2O3.

Ga2O3 metal–insulator-semiconductor solar-blind photodiodes with plasmon-enhanced responsivity and suppressed internal photoemission

Metal-semiconductor-metal (MSM) architectures are popular for achieving high-responsivity Ga2O3 solar-blind photodetectors (SBPDs), however, the hot-electron-induced internal photoemission (IPE) effect restricts their detecting performance. Herein, we demonstrate the rational design of an Al/Al2O3/Ga2O3 metal–insulator-semiconductor (MIS) SBPD that has merits of enhanced responsivity, suppressed sub-gap response and ultralow dark current based on the simulation results obtained using Lumerical software. For the cylindrical patterned detectors with Al/Al2O3/Ga2O3 MIS structures, the optimized dimensions of Al electrodes with a conformed ultra-thin (2 nm) Al2O3 layer support the surface plasmon polariton resonances at 250 nm, thus improving the photoresponsivity to 74 mA W−1. Furthermore, the sandwiched Al2O3 layer lifts the barrier for hot electrons in electrodes, which significantly suppresses the IPE-induced sub-gap photoresponse by more than 105 in magnitude with respect to the Al/Ga2O3 MSM counterpart. Optical and electrical field distributions are overlapped in cylindrically patterned MIS detectors, simultaneously improving the excitation and collection efficiencies of excess carriers and resulting in the 103-boosted rejection ratio.

Core-shell structured, mixed cellulose ester-alumina composite membranes for air filters with improved environmental resistance

In this study, a composite membrane was developed by conformally coating an ultrathin Al2O3 layer through low-temperature (90 °C) atomic layer deposition (ALD) on a hydrophilic mixed cellulose ester (MCE) membrane with a 3D networked microporous structure. The thickness of the deposited Al2O3 layer, without clogging the pores of the membrane, was precisely controlled by varying the number of ALD cycles from 100 to 300. The ultrathin (∼33 nm) Al2O3 layer greatly enhanced the resistance to various environmental stimuli and contributed to the improved removal efficiency of airborne particulate matter (PM), owing to the reduced pore size. The resulting composite membrane installed on an insect screen exhibited excellent removal efficiency (>99%) for PM of various sizes (PM1.0, PM2.5, and PM10) at a controlled flow rate of 1 L/min. In particular, unlike polypropylene-based commercial PM filters that strongly rely on electrostatic adsorption for PM filtration, the reduction in the PM removal efficiency caused by water or ethanol was negligible in the developed composite membrane, enabling long-term use even in extreme environments.

Improved Properties of Li-Ion Battery Electrodes Protected By Al2O3 and ZnO Ultrathin Layers Prepared By Atomic Layer Deposition

Surface modification using thin layers grown by atomic layer deposition (ALD) is an effective strategy for performance improvement of Li-ion batteries. Ultrathin Al2O3 layers are the most studied coating material. In our contribution we compare properties of Al2O3 and ZnO ultrathin layers prepared by ALD on lithium-iron-phosphate (LFP) cathodes and Si-graphite anodes.Ultrathin Al2O3 and ZnO films were grown at 100 °C using trimethylaluminum (TMA) and diethylzinc (DEZ) precursors, respectively, with water vapors as reactant. The growth rates of the Al2O3 and ZnO films were about 0.1 nm/cycle on control flat Si substrates. ALD layers thickness in this study ranged from 5 to 20 cycles. A modified deposition recipe utilizing a prolonged precursor dwell time in the reactor chamber for coverage of the highly porous battery electrodes has been utilized. As TMA, DEZ and H2O all have rather high vapor pressures, we assume that significant part of the electrodes were coated.Porous LFP cathodes (NANOMYTE BE-60E, NEI Corp.) with the thickness of 70 μm were used as a substrate. The average particle size of the LFP substrate was ~ 2 μm with the specific surface area of 15 m2/g and active material loading of 7.3 mg/cm2. Experimental capacity C of the LFP electrode is 170 mAh/g in the voltage range 2.5 - 4.1 V using 0.1 charging/discharging c-rate.As an anode material porous silicon-graphite composite electrode sheets NANOMYTE BE-150E (NEI Corp) with the thickness of 65 μm and composition of active material 20% Si and 65 % graphite were used. The nominal capacity C of the silicon-graphite anode is 750mAh/g in the voltage range 0.05 - 1V using 0.05 charging/discharging c-rate.In our contribution we present specific discharge capacity of the electrodes as a function of charging/discharging cycles. For both pristine and Al2O3 protected LFP cathode sheets specific discharge capacity of 160 mAh/g was achieved at the c-rate of 0.2. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g at the c-rate 0.2 to about 90 mAh/g for the c-rate 1, while the electrode protected by 0.5 nm of Al2O3 saturated at 120 mAh/g. Properties of ZnO- protected LFP cathodes are compared to that covered by Al2O3.Electrochemical properties of the silicon-graphite anode were studied using low c-rate of 0.05. During the first cycles the specific capacity is relatively low due to the formation of the solid-electrolyte interface layer at the surface. After several cycles the capacity increased to the nominal value of 750 mAh/g. In our study we compare the charging/discharging capability of the pristine silicon-graphite anode and that of the electrodes covered by 5 -20 ALD cycles of Al2O3 and ZnO films during the first charging/discharging cycles. We discuss the effect of ALD protecting layers on the rate capability of the silicon-graphite anode. Finally, the results of the electrochemical measurements are compared to those obtained by X-ray photoelectron spectroscopy.

Atomic layer deposited aluminium oxide membranes for selective hydrogen separation through molecular sieving

Ultra-thin membranes have significant potential for the gas separation. However, the fabrication of ultra-thin membrane with high selectivity and permeance remains a challenge. Herein, we develop a high-performance hydrogen separation membrane using atomic layer deposition (ALD) method to deposit ultra-thin Al2O3 layer (ALD-Al2O3) on a porous anodic aluminum oxide (AAO) support. The pore openings of the AAO substrate were fully covered, but not sealed, by the Al2O3 overlayer after 260 ALD cycles. Due to the low deposition temperature (50 °C), angstrom-scale pores were formed within the Al2O3 overlayer. Single gas permeance results revealed that the size of the pores to be smaller than 0.364 nm, but larger than the kinetic diameter of molecular H2 (0.289 nm). This membrane at room temperature, exhibits high H2 permeance of ∼3.03 × 10−7 mol m−2 s−1 Pa−1 and high H2 selectivity for H2/CO2 (5148.2), H2/O2 (120.7), H2/N2 (161.5) and H2/CH4 (219.5), showing great potential for industrial H2 purification and recovery.

Ultralong Lifespan for High-Voltage LiCoO2 Enabled by In Situ Reconstruction of an Atomic Layer Deposition Coating Layer

Although the rapid development of electrical energy storage devices has slowed down environmental pollution, their large-scale application has posed huge challenges to battery-related mineral resources; thus, extending the lifespan of high-voltage lithium cobalt oxide (LCO) is of great importance. Surface oxide coating is considered as the most common low-cost modification method for addressing unstable cycling performance. However, studies have shown that the oxide layer would further react with an electrolyte, while the investigation on the corresponding component evolution is lacking. Herein, a typical example utilizing the above reaction to realize surface reconstruction is presented. Applying atomic layer deposition (ALD), originally, an ultrathin Al2O3 layer is coated on the LCO surface; however, this coating layer has undergone reconstruction after reacting with electrolyte decomposition products during the cycling. Compared with simple coating, the in situ formed Li3AlF6 layer has a tighter binding to the LCO surface while possessing good Li+ conductivity and electrochemical stability. In addition, the unique properties of the ALD technology allow us to achieve ultrathin (1 nm) and conformal coating, which is beneficial for electronic conductivity and cycling stability. Furthermore, the surface phase transition layer stripping failure mechanism has first been revealed to explain the loss of Co and O, while the reconstructed Li3AlF6 effectively suppresses the surface stripping. Thus, excellent high-voltage performance has been realized (an 89% capacity retention after 1000 cycles at 4.5 V and an 88% capacity retention after 200 cycles at 4.6 V). This work casts a new understanding on the surface reconstruction of the oxide coating layer, which is also significant for other electrode materials' modification.