Atomic Layer Deposition Research Articles

Scalable Atomic‐Layer Tailoring of Abundant Oxide Supports Unlocks Superior Interfaces for Low‐Metal‐Loading Dehydrogenation

Liquid organic hydrogen carriers (LOHCs) offer a promising solution for global hydrogen infrastructure, but their practical application faces two key challenges: sluggish dehydrogenation processes and the reliance on catalysts with high noble metal loadings. This study presents a scalable approach to reduce noble metal usage while maintaining high catalytic activity. We synthesized an ultralow Pt content (0.1 wt%) catalyst using γ‐Al2O3‐based pellet support with atomic layer deposition (ALD) of TiO2. Advanced characterization techniques reveal that the thin ALD‐TiO2 shell provides a heterogeneous interface, confining electronically rich Pt‐nanoparticle ensembles. The catalyst outperforms both equivalent Pt‐content catalysts and a commercial 0.5 wt% Pt/γ‐Al2O3 catalyst in homocyclic LOHC dehydrogenation. This study provides insights into the beneficial role of ALD‐engineered interfaces for catalytic supports and offers an efficient approach for scalable production of low‐noble‐metal‐content catalysts, with implications for various catalytic processes.

A New Back-End-Of-Line Ferroelectric Field-Effect Transistor Platform via Laser Processing.

The discovery of ferroelectricity in hafnia-based materials has revitalized interest in realizing ferroelectric field-effect transistors (FeFETs) due to its compatibility with modern microelectronics. Furthermore, low-temperature processing by atomic layer deposition offers promise for realizing monolithic three-dimensional (M3D) integration toward energy- and area-efficient computing paradigms. However, integrating ferroelectrics with channel materials in FeFETs for M3D integration remains challenging due to the dual requirement of a high-quality ferroelectric-channel interface and low-power operation, all while maintaining back-end-of-line (BEOL)-compatible fabrication temperatures. Recent studies on 2D semiconductors and metal oxide channels highlight these challenges. Polycrystalline silicon (poly-Si), a channel material long integrated into the semiconductor industry, presents a promising alternative; however, its high fabrication temperature has hindered its applications to M3D integration. To overcome this challenge, wedemonstrates a BEOL-compatible FeFET platform using poly-Si channels fabricated via locally-confined laser thermal processing and hafnia-based ferroelectrics by low-temperature atomic layer deposition with wafer-scale uniformity. The local nature of the laser processing mitigates the trade-off between the high-temperature crystallization for the quality of the interface and BEOL thermal budget constraints. The laser-processed FeFETs boast the largest effective memory widow for all BEOL-compatible FeFETs. Moreover, the fabricated FeFETs are integrated into wafer-scale synaptic arrays for neuromorphic computing, achieving record-high energy efficiency. Therefore, this work establishes a promising BEOL-compatible FeFET materials platform toward M3D integration.

Impact of Tetrakis(dimethylamido)tin(IV) Degradation on Atomic Layer Deposition of Tin Oxide Films and Perovskite Solar Cells.

Tin oxide (SnOx) films synthesized by atomic layer deposition (ALD) are widely explored in a range of optoelectronic devices including electrochemical sensors, transistors, and photovoltaics. However, the integrity of the key ALD-SnOx precursor, namely tetrakis(dimethylamido)tin (IV) (TDMASn), and its influence on the properties of ultimate films remain unexplored. Here a significant degradation of TDMASn into bis(dimethylamido)tin(II) via the Sn-imine complex is reported, and its impact on the corresponding films and devices is examined. It is found, surprisingly, that this degradation does not affect the growth kinetics and morphology of ALD-SnOx films. But it notably deteriorates their electronic properties, resulting in films with twice the electrical resistance due to different oxidation mechanisms of the degradation products. Perovskite solar cells employing such films exhibit a significant loss in power conversion efficiency, primarily due to charge transport and transfer losses. These findings urge strategies to stabilize TDMASn, a critical precursor for ALD-SnOx films, or to identify alternative materials to achieve efficient and reliable devices.

Scalable Atomic-Layer Tailoring of Abundant Oxide Supports Unlocks Superior Interfaces for Low-Metal-Loading Dehydrogenation.

Liquid organic hydrogen carriers (LOHCs) offer a promising solution for global hydrogen infrastructure, but their practical application faces two key challenges: sluggish dehydrogenation processes and the reliance on catalysts with high noble metal loadings. This study presents a scalable approach to reduce noble metal usage while maintaining high catalytic activity. We synthesized an ultralow Pt content (0.1 wt%) catalyst using γ-Al2O3-based pellet support with atomic layer deposition (ALD) of TiO2. Advanced characterization techniques reveal that the thin ALD-TiO2 shell provides a heterogeneous interface, confining electronically rich Pt-nanoparticle ensembles. The catalyst outperforms both equivalent Pt-content catalysts and a commercial 0.5 wt% Pt/γ-Al2O3 catalyst in homocyclic LOHC dehydrogenation. This study provides insights into the beneficial role of ALD-engineered interfaces for catalytic supports and offers an efficient approach for scalable production of low-noble-metal-content catalysts, with implications for various catalytic processes.

Modification of High-Surface-Area Carbons Using Self-Limited Atomic Layer Deposition

This study explores the application of Atomic Layer Deposition (ALD) to functionalize high-surface-area carbon supports with metal and metal oxide films and particles for applications in catalysis and electrocatalysis. The work reported here demonstrates that, through careful choice of precursors and absorption and reaction conditions, self-limited ALD growth on a high-surface-area carbon support can be achieved. Specific examples presented include the growth of conformal films of ZrO2 and SnO2 and the deposition of Ga2O3 and Pt particles on a carbon black support with a surface area of 250 m2·g−1. A novel strategy for controlling the Pt weight loading and producing sub-nanometer Pt particles on a carbon support using a single ALD cycle is also presented.

Quantitative Defect Analysis in CVD‐Grown Monolayer MoS2 via In‐Plane Raman Vibration

ABSTRACTThe synthesis of two‐dimensional transition metal dichalcogenide (2D‐TMD) materials gives rise to inherent defects, specifically chalcogen vacancies, due to thermodynamic equilibrium. Techniques such as chemical vapor deposition (CVD), metal‐organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), flux growth method, and mechanical exfoliation produce large‐scale, uniform 2D TMD films, either in bulk or monolayers. However, defects on the film surface impact its quality, and it is necessary to measure defect density. The phonon confinement model indicates that the first‐order Raman band frequency shift depends on defect density. Monolayer Molybdenum disulfide (MoS2) exhibits three phonon dispersions at the Brillouin zone edge (M point): out‐of‐plane optical phonon vibration (ZO), in‐plane longitudinal optical phonon vibration (LO), and in‐plane transverse optical phonon vibration (TO). The LO and ZO modes overlap with Raman in‐plane vibration (𝐸12g) and Raman out‐of‐plane vibration (𝐴1g), respectively, causing peak broadening. In the presence of defects, the Raman 𝐸12g vibration energy decreases due to a reduced restoring force constant. The Raman 𝐴1g vibration trend is random, influenced by both restoring force constant and mass. The study introduces a quantitative defect measurement technique for CVD‐grown monolayer MoS2 using Raman 𝐸12g mode, employing sequential data processing algorithms to reveal defect density on the film surface.

Atomic layer deposition of tin monosulfide thin film using Sn(acac)2 and H2S

In this study, we deposited tin monosulfide (SnS) thin film using Tin(II) 2,4-pentanedionate [Sn(acac)2] precursor and hydrogen sulfide (H2S) reactant. And we performed post annealing to improve the crystallinity of SnS thin films. The process window was 130 °C–150 °C, and the growth rate was 0.34 Å/cycle. To investigate crystallinity and the phase of SnS thin films, grazing incidence x-ray diffraction (GI-XRD) and Raman spectroscopy were performed. SnS thin films showed a single orthorhombic phase after annealing. In addition, transmission electron microscopy (TEM) was utilized to confirm the two-dimensional (2D) layered structure of SnS thin films. Post-annealed SnS thin film clearly showed a 2D layered structure. X-ray photoelectron spectroscopy (XPS) was performed to confirm the bonding state of the thin film. The results indicated that the SnS thin film only shows binding energies corresponding to the oxidation states of Sn2+ in the Sn 3d spectra and S2- in the S 2p spectra. Ultraviolet–visible (UV–vis) spectroscopy and ultraviolet photoelectron spectroscopy (UPS) were performed to confirm the optical properties and to calculate the band structure of the thin film. All of SnS thin film showed a p-type characteristic. The post-annealed SnS thin films exhibited better electric properties, confirmed by Hall measurement.

Substantial improvement of InGaN/GaN visible-light polarization-induced self-depletion phototransistor by thermally oxidized Al2O3

Atomic layer deposited (ALD) Al2O3 acting as gate dielectric and surface passivation is widely adopted in power electronics but seldom used in optoelectronic fields for its sophisticated and expensive technology. Herein, a simple but efficient Al2O3 passivation is used in the fabrication of InGaN/GaN visible-light (VL) polarization-induced self-depletion field effect phototransistors (FEPTs), for suppressing the surface leakage and recombination. The Al2O3 layer obtained by thermal oxidation (TO) of 2-nm-thick thermally evaporated metal Al shows high electrical insulation and even better passivation effect than the ALD-Al2O3. As a result, the dark current of TO-Al2O3 passivated device decreases by about 2 orders of magnitudes; meanwhile, the photoresponse increases by about 65%. Under a weak VL illumination of 6.8 μW/cm2, the InGaN/GaN FEPT exhibits a large photo-to-dark current ratio of 3.1 × 108 and an ultrahigh shot-noise-limited detectivity of 1.9 × 1018 jones. In addition, the FEPTs exhibit a strong wavelength selectivity with a 600 nm/400 nm spectral response rejection ratio exceeding 5 × 105. All these performances show huge potential in emerging VL applications that are limited by the insufficiencies of current Si photodetectors.

Numerical simulation of the temperature excursions of porous substrates during atomic layer deposition

Atomic layer deposition (ALD) processes are usually highly exothermic. For ALD on substrates with high specific surface area, the reaction heat per ALD cycle may lead to a substantial temperature rise of the substrates. The novelty of this study lies in quantifying the temperature excursions of porous substrates during ALD via numerical simulation and further addresses the issue of tuning this type of thermal effect. A comprehensive model has been developed and validated to investigate the ALD thermal effect with accounting for the roles of the precursor transport phenomena within the ALD reactor system, and the coupling among the precursor diffusion, heat transfer, film deposition, reaction heat generation within the porous substrates. The results show that the thermal effect of the sub-saturated ALD can change with different substrate thickness, precursor partial pressure profile, heat transfer coefficient, and kinetic parameters. In contrast, for saturated ALD with adiabatic condition, the maximum temperature rise of the substrate is a deterministic value, independent of the substrate thickness and precursor partial pressure profile. The thermal effect with the porous substrates can influence the ultimate deposit amount and its distribution for sub-saturated ALD and change the time required for attaining saturation for saturated ALD. The temperature rises of certain common substrates during typical half-ALD cycles have been simulated to demonstrate the capability of the present model in predicting the thermal effect of ALD.

Design of an atomic layer deposition system with in situ reflection high energy electron diffraction.

We report the design, fabrication, and testing of an atomic layer deposition (ALD) system that is capable of reflection high energy electron diffraction (RHEED) in a single chamber. The details and specifications of the system are described and include capabilities of RHEED at varied accelerating voltages, sample rotation (azimuthal) control, sample height control, sample heating up to set temperatures of 1050 °C, and either single- or dual-differential pumping designs. Thermal and flow simulations were used to justify selected system dimensions as well as carrier gas/precursor mass flow rates. Temperature calibration was conducted to determine actual sample temperatures that are necessary for meaningful analysis of thermally induced transitions in ALD thin films. Several demonstrations of RHEED in the system are described. Calibration of the camera length was conducted using a gold thin film by analyzing RHEED images. Finally, RHEED conducted at a series of increasing temperatures was used to monitor the crystallization of an ALD HfO2 thin film. The crystallization temperature and the ring pattern were consistent with the monoclinic structure as determined by separate x-ray diffraction-based measurements.

Reliability analysis under bias stress and elevated temperature of dual-gate IGZO TFT

Indium–gallium–zinc oxide (IGZO) as a star material has been broadly applied in multiple functional devices, including planar displays, flexible electronic devices, and photoelectronics. In recent years, the development of artificial intelligence and great data also extends the application of IGZO-based thin film transistors (TFTs) to memory, memristors, and neuromorphic computing. Thus, the research of high performance and reliable IGZO TFTs attracts tremendous attention worldwide. Herein, a high-quality IGZO thin film was deposited via atomic layer deposition, and a dual-gate (DG) IGZO TFT was fabricated. Comprehensive electrical characterization was conducted on the fabricated DG IGZO TFTs, revealing that DG IGZO TFTs exhibited good performance for reliability analysis. The reliability and degradation mechanism of the DG IGZO TFT was systematically investigated under bias stress at room temperature and elevated temperatures of 350, 400, and 450 K by the comprehensive electrical characterization. Results indicate that the defects of the dual gate insulators and the interfaces majorly influence the degradation under bias stresses, while the carrier scattering of the IGZO channel is the major degradation mechanism under elevated temperatures. These findings highlight the degradation mechanism of the DG IGZO TFT under bias stress and elevated temperatures from a novel viewpoint, which provides a utilizable reference to its application in circuits.

A hole-selective hybrid TiO2 layer for stable and low-cost photoanodes in solar water oxidation

The use of conductive and corrosion-resistant protective layers represents a key strategy for improving the durability of light absorber materials in photoelectrochemical water splitting. For high performance photoanodes such as Si, GaAs, and GaP, amorphous TiO2 protective overlayers, deposited by atomic layer deposition, are conductive for holes via a defect band in the TiO2. However, when coated on simply prepared, low-cost photoanodes such as metal oxides, no charge transfer is observed through amorphous TiO2. Here, we report a hybrid polyethyleneimine/TiO2 layer that facilitates hole transfer from model oxides BiVO4 and Fe2O3, enabling access to a broader scope of available materials for practical water oxidation. A thin polyethyleneimine layer between the light absorber and the hybrid polyethyleneimine/TiO2 acts as a hole-selective interface, improving the optoelectronic properties of the photoanode devices. These polyethyleneimine/TiO2 modified photoanodes exhibit high photostability for solar water oxidation over 400 h.

Nanocolumnar platinum-coated ITO electrodes prepared by atomic layer deposition and glancing angle deposition for electrocatalytic hydrogen peroxide determination

Nanocolumnar platinum-coated ITO electrodes prepared by atomic layer deposition and glancing angle deposition for electrocatalytic hydrogen peroxide determination

A Novel Strategy to Achieve High-Performance Titanium-Doped InZnO Thin-Film Transistors Using Atomic Layer Deposition

A Novel Strategy to Achieve High-Performance Titanium-Doped InZnO Thin-Film Transistors Using Atomic Layer Deposition

Impact of atomic layer deposition supercycle design on the reliability of heterogenous IGZO channel TFTs

Oxide semiconductor thin-film transistors (TFTs) are promising candidates for application in display backplanes and memory devices. To ensure both high performance and stable electrical properties of oxide TFTs over long-term use, superior mobility and device stability need to be obtained. In this regard, atomic layer deposition (ALD) has gained attention as a facile method for obtaining conformal oxide films under defect-free conditions and adjusting the composition or distribution for targeted TFT performance. Here, we propose that, even with the same bulk composition, variations in the local composition using an ALD supercycle design can significantly affect the TFT performance, particularly the bias-temperature stability. To ascertain the influence of the local cation distribution on the performance, we compared two supercycle designs by reversing the sub-cycles of indium, gallium, and zinc with identical bulk In–Ga–Zn ratios. Despite minimal changes in the electrical characteristics, such as the mobility and threshold voltage, of the two TFTs designed with ALD supercycles, there was a significant difference in their reliability. Devices with an indium-rich IGZO active layer on the back channel exhibited a hump phenomenon and approximately five times greater Vth degradation (ΔVth: −0.67 V to −3.36 V). By conducting an additional case study of IGZO TFTs and film analysis, we confirmed that mobility is largely governed by the bulk composition, whereas the local surface composition, serving as the back channel, is the key to reliability. The device performance results could be confirmed through the surface and bulk analyses of heterogeneous films engineered through the ALD supercycle design. Furthermore, it has been proposed that optimizing the ALD supercycle design is the key to obtaining high-performance oxide semiconductor TFTs.

Effect of ultra-thin ZnS passivation using ALD technique on the performance of heterojunction solar cells

Hybrid solar cells (HSCs) using poly (3,4-ethylenedioxy-thiophene) polystyrene sulfonate (PEDOT:PSS) and n-silicon provide heterojunctions with the potential of light trapping, cost effectiveness, and high efficiency. However, charge recombination at rear interface hampers built-in potential and power conversion efficiency (PCE). Here, a superior, conformal, and uniform ultra-thin layer of Zinc sulfide (ZnS) is deposited on rear interface using atomic layer deposition (ALD) technique. The ALD-deposited ZnS thin layer serves as a passivation, electron conductive, and hole-blocking layer. The optimized HSCs exhibit a remarkable PCE of 12.37 % alongside a high open-circuit voltage of 0.625 V and a substantial fill factor of 71.5 %. These advancements stem from enhanced back junction quality between n-Si and electrode. The outcomes demonstrate an effective suppression of charge recombination and enhanced charge transfer facilitated by ALD-deposited ZnS thin layer, resulting an improved photovoltaic performance.

Optimization of the deposited Al2O3 thin film process by RS-ALD and edge passivation applications for half-solar cells

Al2O3 film process experiments were conducted utilizing atomic layer deposition (ALD) technology to optimize the process conditions for rotating-space type ALD Al2O3 thin films, which were then applied to edge passivation of tunneling oxide (TOPCon) solar cells. The composition of the films was characterised using XPS, the thickness and refractive index were measured using ellipsometry, the surface morphology was examined using AFM, and the passivation impact of the alumina films was assessed using a minority carrier lifetime meter. High-quality Al2O3 films were formed on silicon wafers at a temperature of 200 °C and a rotational speed of 60 rpm utilizing trimethylaluminum (TMA) and water as precursors. In this setting, the Al2O3 film deposition rate was 0.12 nm/s, surface roughness was 0.883 nm, and minority carrier lifetime was 189.6μs. And, under these conditions, edge passivation of solar cells resulted in the greatest enhancement, with a 0.123 % increase in cell efficiency and a 3.78W increase in module power.

An automatic multi-precursor flow-type atomic layer deposition system

Designs for two automated atomic layer deposition (ALD) flow reactors are presented, and their capabilities for coating additively manufactured (AM) metal prints are described. One instrument allows the coating of several AM parts in batches, while the other is useful for single part experiments. To demonstrate reactor capabilities, alumina (Al2O3) was deposited onto AM 316L stainless steel by dosing with water (H2O) vapor and trimethylaluminum (TMA) and purging with nitrogen gas (N2). Both instruments are controlled by custom-programmed LabVIEW software that enables in situ logging of temperature, total pressure, and film thickness using a quartz crystal microbalance. An initial result shows that 150 ALD cycles led to a film thickness of ∼55 nm, which was verified with Rutherford backscattering spectroscopy. This indicates that the reactors were indeed depositing single atomic layers of Al2O3 per ALD cycle, as intended.

Enhanced photocatalysis via inverse opal structures: Synthesis and characterization of TiO2/ZnO and ZnO/TiO2 composites using plasma-enhanced ALD

Inverse opals (IO) based functional materials show potential in photocatalysis due to their unique light interaction properties. This study presents a low-temperature plasma-enhanced atomic layer deposition (PEALD) method for synthesizing TiO2, ZnO, and composite IOs using a polystyrene nanoparticle-based opal template. We comprehensively characterized the obtained materials using SEM-EDX, TSEM, TG, FTIR, XRD, Raman, ellipsometry, photoluminescence (PL), and UV–Visible spectroscopy. SEM analysis confirmed the successful formation of PEALD IOs with a periodically ordered structure, enabling conformal coating while preserving their original architecture. XRD and Raman analysis also confirmed that the IOs consisted of anatase for TiO2 and hexagonal wurtzite for ZnO. UV–Vis reflectance spectroscopy revealed strong UV absorption and modified photonic bandgaps (PBGs) for all materials. The bare and composite IOs exhibited PBGs in the visible region, suggesting that the arising “slow photon” effect might enhance photocatalysis. This study explored the photocatalytic degradation of 4-Nitrophenol (4-NP) and Rhodamine 6G (Rh6G) using pristine and composite IO photocatalysts under UV and visible light irradiation. Pristine TiO2 and ZnO IOs demonstrated superior performance for 4-NP degradation under UV light. This can be attributed to two key factors: their highly ordered macroporous structure (with a large surface area for efficient dye adsorption, and their band gaps (3.0 eV for TiO2 and 3.2 eV for ZnO) that enable strong absorption of UV light photons for effective pollutant degradation. Conversely, composite IOs (TiO2/ZnO and ZnO/TiO2) displayed higher activity for both test molecules under visible light due to a synergistic effect between bandgap harmonization and the PBG effect.

Vapor Infiltration Synthesis of Indium Sulfide Magic Size Cluster.

The energetically favorable formation of atomically precise clusters, known as magic size clusters, in the solution phase enables a precision nanoscale synthesis with exquisite uniformity. We report the synthesis of magic size clusters via vapor infiltration of atomic layer deposition precursors directly in a polymer thin film. Sequential infiltration of trimethylindium vapor and hydrogen sulfide gas into poly(methyl methacrylate) leads to the formation of clusters with uniform properties consistent with a magic size cluster─In6S6(CH3)6. While an increase in cluster size might be expected with additional sequential infiltration cycles of the reactive In and S precursors, uniform properties consistent with magic size clusters form in multiple polymers under a range of processing conditions. Ultraviolet-visible absorption spectra of In6S6(CH3)6 are largely independent of the number of sequential infiltration cycles and exhibit air stability, both of which are attributed to an energetically favorable synthetic pathway that is evaluated with density functional theory.