Atomic Layer Deposition Research Articles

Boosting the Mechanical Strength and Photocatalytic Activity of 3D-Printed Titania Aerogels by Atomic Layer Deposition and Heat Treatment

Perovskite solar cells (PSCs) have achieved rapid progress in recent years owing to their high-power conversion efficiency (PCE), low cost, and processability. However, poor device stability and carrier recombination remain significant obstacles to further development. Atomic layer deposition (ALD), with its atomic-level control over film thickness, excellent uniformity, and interfacial engineering capability, has attracted considerable attention in PSC research. This review summarizes the applications of ALD in PSCs, including low-temperature synthesis (typically below 350 °C), thickness and composition control (approximately 1 nm per 10 ALD cycles), defect passivation, encapsulation (water vapor transmission rates as low as 10−6 g·m−2·day−1 under optimized conditions), and tandem devices. In addition, the mechanisms by which ALD enhances device efficiency and stability are discussed in depth, and the challenges and future prospects of this technique are analyzed.

Abstract The crystal orientation uniformity of MoS 2 monolayers grown by atomic layer deposition (ALD) on sapphire substrates is investigated, and their integration with spin‐coated WS 2 in a MoS 2 /WS 2 heterostructure. Polarization‐resolved second harmonic generation (SHG) microscopy reveals that the heterostructure exhibits an exceptionally consistent orientation across 180 × 180 µm 2 areas, with deviations of less than two degrees, despite the polycrystallinity of the WS 2 layer. The SHG response of the heterostructure seems to be dominated by the orientation of the underlying MoS 2 layer; only locally aligned WS 2 domains (if present) contribute marginally. These findings demonstrate the robustness of the MoS 2 crystal orientation and provide insights into interfacial alignment mechanisms and the orientation coherence achievable by ALD, providing a foundation for layer‐selective studies of interfacial ordering in wafer‐scale transition metal dichalcogenide heterostructures.

Abstract With unique properties such as enhanced photoluminescence (PL) efficiency, improved thermal stability, and favourable optical properties, polyfluorenes (PFs) are well-suited for organic light-emitting diode (OLED) applications. However, the conventional PF layers are found to have drawbacks, including variation in charge transport, which minimizes the overall PL efficiency due to uneven coating and photo-oxidation. Current research aims to overcome the above difficulties and to synthesize PF reinforced with alumina (Al 2 O 3 ) nanoparticles (3 wt%) along with encapsulation coating via Atomic Layer Deposition (ALD) and investigates the influence of varying encapsulation coating thicknesses (0, 10, 30, and 50 nm) in the enhancement of optoelectronic performances and operational stability. The fabricated devices were characterized using electroluminescence (EL) spectra, external quantum efficiency (EQE), current–voltage (I–V) plots, and encapsulation effectiveness tests. The investigational results indicate that an encapsulation thickness of 30 nm yields the maximum EL intensity, with a peak wavelength of 470 nm and an external quantum efficiency (EQE) of 8.1 %. This configuration exhibited a low turn-on voltage of 3 V. The I–V plot demonstrated a maximum current density of 8.2 mA/cm 2 . The Hall mobility was increased to 1.0 × 10 −4 cm 2 /V.s with the observed carrier concentration of 2.6 × 10 16 cm −3 . The alumina encapsulation significantly improved the durability and stability, with a device lifetime of 312 hours, and reduced the oxygen permeation rate to 5 cm 3 /m 2 /day/atm. The findings highlight the crucial role of optimizing alumina encapsulation thickness in enhancing the functional performance of PF-based OLED devices.

Abstract In this study, we established a microwave remote plasma source (MW-RPS) to perform plasma-enhanced atomic layer deposition to grow In 2 O 3 channel for FET applications. We compared MW-RPS and a conventional capacitively coupled plasma (CCP) source to investigate the effects of oxidation time in O 2 plasma on the physical and electrical properties of In 2 O 3 . Our results demonstrate that MW-RPS enables both smooth surface morphology and sufficient oxidation even with prolonged plasma exposure. The extracted intrinsic field-effect mobility of the fabricated FETs with MW-RPS-derived In 2 O 3 channels increased significantly with oxidation time compared to that of CCP, reaching a value of 106.2 cm 2 /Vs.

In this work, we investigate the deposition of VOx thin films by plasma-enhanced atomic layer deposition. Specifically, we focus on the effects of the plasma operating conditions, including applied power, O2/Ar gas flow ratio, pressure, and coupling mode on the resulting thin film crystallinity and stoichiometry. In addition, we characterize the plasma and correlate the findings to the changes observed in the produced VOx thin films. The majority of conditions investigated yield crystalline V2O5. However, by increasing the pressure during the plasma half cycle, the V2O5 film can be deposited with a reduction in the crystalline character without any significant changes in stoichiometry. Langmuir probe measurements reveal that both the ion flux and plasma potential decrease with increasing pressure during the plasma step, which results in a corresponding drop in the energy flux density and ion energy delivered to the surface of the thin film. Analysis of the various plasma conditions investigated shows that increasing the pressure uniquely resulted in a decrease in the energy flux density and ion energy below a critical barrier necessary for complete crystallization of the deposited VOx films.

Ultraviolet (UV) radiation is the major cause of polymer degradation in outdoor environments, accelerating mechanical failure and color change, leading to plastic waste accumulation. Effective UV-protective strategies that preserve polymer functionality are therefore critical for extending material longevity in UV-intense environments. Here, we present a synergistic approach combining vapor phase infiltration (VPI) and atomic layer deposition (ALD) to engineer nanoscale zinc oxide (ZnO) coatings on poly(lactic acid) (PLA), a UV-sensitive polymer. Individually, ALD and VPI offer minimal enhancement in UV stability; however, their sequential application enables the formation of conformal, polycrystalline ZnO films that dramatically improve UV resistance in both 3D-printed structures and thin-film PLA models. In situ microgravimetry and cross-sectional electron microscopy reveal that VPI introduces ZnO nucleation sites within and atop the polymer matrix, promoting a >10-fold increase in ZnO growth per ALD cycle. The resulting ZnO-PLA hybrids absorb over 90% of incident UV-C radiation while maintaining high optical transparency in the visible range. This low-temperature, scalable process provides a promising platform for the development of transparent, durable UV-barrier coatings on polymers for use in environmentally demanding applications.

MXene represents a promising class of two-dimensional carbides and nitrides of transition metals. Due to their unique combination of high electrical conductivity, large specific surface area, hydrophilicity, and tunable surface chemistry, they have attracted significant scientific interest. These properties enable the application of MXenes in energy storage systems, sensors, electrocatalysis, filtration, and environmental remediation. However, their susceptibility to oxidation and insufficient long-term stability remain major challenges for practical use.To address these limitations, silicon-based modifications – specifically involving Si, SiO₂, and SiOx – are proposed as effective strategies for enhancing the structural stability of MXenes. This review analyzes functionalization methods employing silicon-containing components, including sol–gel synthesis, the Stöber method, chemical vapor deposition (CVD), atomic layer deposition (ALD), and sputtering techniques. Silicon modification improves oxidation resistance, thermal stability, surface area, and compatibility with composites. These enhanced properties contribute to improved performance of silicon-modified MXenes in lithium- and aluminum-ion batteries, supercapacitors, sensors, and catalysts. Additionally, their photocatalytic activity and pollutant adsorption capabilities support applications in environmental protection technologies. The review also explores sustainable and scalable strategies for integrating MXenes into future multifunctional systems.

A nanometer-thick indium oxide (In2O3) layer is studied in terms of gap states, by means of subgap photocurrent spectroscopy. The In2O3 layer is prepared by atomic layer deposition, where its nanostructure is changed from an amorphous to poly-crystalline phase, via changing the layer thickness. Two groups of gap states are distinguished: shallow and deep levels, reflecting the valence band (VB) tail and a specific type of defects, respectively. The VB tail is clearly broadened for the amorphous phase, where the broadening is characterized by the Urbach energy, e.g., 326 ±30 meV. The deep-level defect states are recognized at ≈ 2.3 eV from the conduction band edge, with a distribution of ≲110 meV. Interestingly, the energy level and distribution are not strongly changed, regardless of an amorphous or poly-crystalline structure.

Zero-gap electrolyzers based on submicron thick proton-conducting oxide membranes (POMs) represent a promising approach to increasing the efficiency of H2 production from water electrolysis while moving away from conventional perfluorosulfonic acid (PFSA) membranes. A critical barrier to the commercialization of such electrolyzers is that the ultrathin nature of POMs, which is necessary to achieve low cell resistance, makes them more susceptible to defects that can lead to unacceptably high rates of H2 crossover. Herein, we demonstrate an approach to mitigate this problem through selective deposition of carbon-containing silicon oxide (SiOxCy) "nanoplugs" into the defects of submicron thick SiO2 membranes using a facile electrochemically mediated deposition process. Selective deposition of nanoplugs within the defects was verified by multiple characterization techniques, while scanning electrochemical microscopy (SECM) was used to confirm selective plugging of H2-crossover hotspots associated with defects at identical locations. Thanks to the use of nanoplugs, the H2 permeance of 250 nm thick SiO2 membranes was reduced by 5 to 6 orders of magnitude compared to the unmodified atomic layer deposition (ALD) SiO2 membranes while having negligible impact on the ionic resistance of the membrane. These plug-modified membranes also enabled safe and stable operation of a zero-gap full cell electrolysis cell, in contrast to cells lacking nanoplugs that produced anode effluent streams having H2 concentrations near or exceeding the lower flammability limit (LFL) of H2. Beyond water electrolysis, this defect-sealing strategy has the potential to be broadly implemented in other applications, such as fuel cells and flow batteries, offering a versatile solution to mitigate crossover-related performance losses.

It has been demonstrated that mixing atomic-layer deposition subcycles of aluminum oxide (Al2O3) and aluminum fluoride (AlF3) at an optimal ratio yields an aluminum oxyfluoride (AlOxFy) compound with virtually no internal defects. By systematically analyzing the defect structures formed in AlOxFy thin films as a function of the Al2O3 to AlF3 subcycle ratio, the optimal composition was identified. Because hydrogen migrates either through intrinsic defects in the film or via repeated bonding and dissociation with oxygen, a defect-free AlOxFy film in which AlF3 sublayers providing no hydrogen-diffusion pathways are periodically repeated represents an exceptionally effective hydrogen barrier. The barrier performance of AlOxFy was experimentally validated for indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). During thermal annealing, the fluorine (F) from the AlOxFy film diffuses into the IGZO layer, further enhancing its resistance to hydrogen-related degradation. Even in IGZO TFTs incorporating a silicon nitride dielectric with a high hydrogen content, the introduction of an AlOxFy barrier effectively suppresses hydrogen-induced threshold voltage (Vth) shifts. In addition, the F doping induced by the AlOxFy layer conferred extra stability, maintaining minimal Vth variation even under prolonged positive-bias stress and negative-bias stress. This work identified a defect-free AlOxFy thin film as a highly effective hydrogen diffusion barrier and demonstrated its capability to significantly improve the hydrogen stability of IGZO TFTs. The enhancement in hydrogen tolerance is attributed not only to the superior barrier properties of AlOxFy but also to the beneficial F-doping effect imparted to the IGZO channel layer.

MXenes have emerged as a promising class of two-dimensional (2D) materials for gas sensing applications, owing to their exceptional electrical conductivity, abundant surface functional groups, and tunable surface chemistry. However, the practical implementation of MXene-sensors is significantly hindered by the rapid oxidative degradation of their surface metallic atoms under ambient conditions. To address this challenge, anatomic-level surface engineering strategy is developed using atomic layer deposition (ALD) to integrate ZnO and Pd onto Ti3C2Tx MXene. The ZnO coating, selectively grown at hydroxyl-rich edges/surfaces, acts as adual-functional layer: an ultra-effective oxidation barrier preserving MXene's conductivity while enabling charge transport. Concurrently, Pd nanoparticles serve ashighly active catalytic sitesfor efficient H2 dissociation and spillover. This synergistic design yields exceptional room-temperature hydrogen sensing performance. The optimized Pd-ZnO/MXene sensor achieves a rapid response/recovery (23 s/64 s to 50ppm H2), outperforming most reported MXene-based sensors. Density functional theory (DFT) confirms Pd'sbifunctional catalytic role, drastically lowering energy barriers for both H2 dissociationandO2 adsorption/dissociation on ZnO-key to the low-temperature activity. This ALD-based approach establishes auniversal platformfor fabricating robust, high-stability MXene sensors, advancing their real-world deployment in hydrogen safety and clean energy applications.

Fiber Bragg Grating (FBG) sensors facilitate compact, multiplexed, and electromagnetic interference-immune monitoring in embedded and harsh environments. The removal of the polymer jacket, a measure taken to withstand elevated temperatures or facilitate integration, exposes the fragile glass. This underscores the necessity of functional coatings, which are critical for enhancing durability, calibrating sensitivity, and improving compatibility with host materials. This review methodically compares coating materials and deposition routes for FBGs, encompassing a range of techniques including top-down physical-vapor deposition (sputtering, thermal/e-beam evaporation, cathodic arc), bottom-up chemical vapor deposition (CVD)/atomic layer deposition (ALD), wet-chemical methods (sensitization/activation, electroless plating (EL), electrodeposition (ED)), fusion-based processes (casting and melt coating), and hybrid stacks (e.g., physical vapor deposition (PVD) seed → electrodeposition; gradient interlayers). The consolidation of surface-preparation best practices and quantitative trends reveals a comprehensive understanding of the interrelationships between coating material/stack, thickness/microstructure, adhesion, and sensitivity across a range of temperatures, extending from approximately 300 K to cryogenic regimes. Practical process windows and design rules are distilled to guide method selection and reliable operation across cryogenic and high-temperature regimes.

Nanostructured α‐hematite (Fe 2 O 3 ) is a widely studied material for photoanode applications, particularly for driving the oxygen evolution reaction (OER) under visible light irradiation in photoelectrochemical (PEC) cells. Our recent work has shown that Fe 2 O 3 suffers from photocorrosion in alkaline and neutral electrolytes, with a noticeable decline in performance after 5 h of operation. This highlights the need for strategies that enhance the stability of Fe 2 O 3 ‐based photoanodes. To enhance the stability of Fe 2 O 3 nanorods (NR), we employed atomic layer deposition (ALD) to coat the NR with a well‐defined, controlled TiO 2 overlayer designed to protect the photoanode from photocorrosion during PEC operation. The influence of overlayer thickness is evaluated regarding the PEC activity, stability, and photocurrent retention in alkaline electrolyte using a PEC scanning flow cell coupled to an inductively coupled plasma mass spectrometer (PEC‐ICP‐MS). This setup can quantify metal dissolution during PEC OER, allowing the characterization of the photo‐degradation under realistic illumination conditions. An accelerated stress test (AST) protocol was designed to drive degradation faster and obtain insightful information about the stability of the TiO 2 @Fe 2 O 3 heterostructures using in situ PEC‐ICP‐MS. PEC‐ICP‐MS measurements demonstrate that the TiO 2 coating significantly enhances the photocorrosion resistance of Fe 2 O 3 NR in alkaline electrolytes during operation. A TiO 2 thickness of 2.8 nm (50 ALD cycles) offered the most favorable compromise between activity, photocurrent retention, and decrease of Fe dissolution. The proposed methodology combines in situ stability quantification and ASTs as a powerful tool to advance material development and can be extended to other protected photoanodes.

Atomic-level control of solution-processed hybrid halide perovskites is achieved experimentally by solution atomic layer deposition (sALD). This method transfers the surface chemical principles of gas-phase ALD (gALD) to precursors dissolved in the liquid phase. Circumventing limitations associated with precursor volatility, sALD broadens the portfolio of reaction chemistries usable and material classes accessible. We establish its applicability to depositing ultrathin films of ionic semiconductors by developing an sALD procedure for the most prominent halide perovskite, methylammonium triiodoplumbate (CH3NH3PbI3, 'MAPI'). The process saturates upon precursor dosage variation to self-limiting growth typical for ALD, as analyzed by ex-situ and in-situ techniques. sALD-deposited MAPI is highly pure, stoichiometric, and polycrystalline. When MAPI films are prepared in congruent pairs by sALD and by a state-of-the-art spin-coating method, sALD-grown films clearly outperform their spin-coated counterparts in terms of charge carrier lifetimes and stability. They exhibit high carrier mobility and yield functional light absorbing layers in solar cells.

Enhanced corrosion resistance of 2024 aluminum alloys with Cr2O3 thin layers by Atomic Layer Deposition

Owing to the low refractive index of conventional passivation materials and sidewall defects, AlGaInP-based red miniaturized light-emitting diodes (mini-LEDs) suffer from low light extraction efficiency (LEE) and external quantum efficiency (EQE). Here, we propose a HfO2-based hybrid passivation layer comprising a 5-nm-thick atomic-layer-deposited (ALD) HfO2 passivation layer, a 15-nm-thick ALD-Al2O3 passivation layer, and an 800-nm-thick plasma-enhanced-chemical-vapor-deposited SiO2 passivation layer. Owing to a more compatible refractive index with that of AlGaInP, the HfO2 could increase the light emission angle at the HfO2/AlGaInP interface and thus improve the LEE of AlGaInP-based mini-LEDs. Simulation results indicate that mini-LEDs with an HfO2-based hybrid passivation layer exhibit enhanced light output performance with a 15.1% increment in LEE. Furthermore, experimental results demonstrate that mini-LEDs with an HfO2-based hybrid passivation layer achieve a peak EQE of 20.19% at 5 mA, representing an improvement of 6.7% in EQE compared to mini-LEDs without an HfO2-based hybrid passivation layer. This work provides an HfO2-based hybrid passivation layer as a scalable strategy for advancing high-performance mini-LEDs in next-generation display technologies.

Plasma-enhanced atomic layer deposition of Al2O3 on graphene via an in situ-deposited interlayer

Atomic-scale processing and precise control of superconducting thin films are essential for the advancement and large-scale implementation of superconducting quantum technologies. Consequently, detailed analysis of the structural features and elemental composition of such superconducting films is a key element in developing highly sensitive and efficient superconducting nanowire single photon detectors. In this work, we use advanced techniques in scanning transmission electron microscopy (STEM), specifically 4-dimensional STEM (4DSTEM) and electron energy loss spectroscopy (EELS), to analyze the structure and chemistry of two few-nanometer-thick films of NbN and NbTiN deposited by plasma-enhanced atomic layer deposition. Digital dark field imaging is used to image the crystalline core of the films, separate from the silicon substrate and protective platinum overlayer, and the data are used for quantitative measurement of lattice parameters. EELS mapping correlates the structural data with local chemistry and indicates the coexistence of superconducting NbC within the films. Crystalline rock-salt structured carbonitrides are found in both cases, and their lattice parameters can be accurately and reliably measured from hundreds of datapoints from different pixels in the scan area. These correlate well with the expected chemical composition. Both films feature a Si–N rich reaction layer, with Ti also present in NbTiN films. Interestingly, significant diffusion seems to occur in both films, differing from the atomic-layer sharpness sometimes presumed. Nevertheless, the presence of a continuous film with an appropriate structure and composition confirms that the process is suitable for superconducting applications, although further optimization could improve interface control and composition.

The detection and monitoring of ions are essential for a broad range of applications, including industrial process control and biomedical diagnostics. Traditional ion-sensitive field-effect transistors require bulky and expensive reference electrodes, which face several limitations, including device miniaturization, high fabrication costs, and incompatibility with semiconductor manufacturing processes. Here, we introduce a reference-less semiconductor ion sensor (RELESIS) that utilizes anodic aluminum oxide film as both the sensitive and dielectric layer. The RELESIS is composed of a metal-oxide-semiconductor field-effect transistor and an interdigital electrode, which fundamentally eliminates the need for a reference electrode, thereby enabling device miniaturization. During fabrication, the anodic oxidation process is employed in place of the expensive atomic layer deposition method, significantly reducing manufacturing costs while maintaining high surface quality. In practical measurements, the RELESIS device demonstrated an excellent pH sensitivity of 57.8 mV/pH with a low hysteresis of 7 mV. As a proof-of-concept application, the RELESIS device was employed for real-time, non-destructive monitoring of milk freshness, accurately detecting pH changes from fresh to spoiled in milk samples. The combination of reference-less structure, low-cost fabrication, and superior sensing performance positions this technology as a promising platform for next-generation portable ion sensing systems in food safety, environmental monitoring, and point-of-care diagnostics.