Spatial Atomic Layer Deposition Research Articles

Spatial atomic layer deposition of nitrogen-doped alumina thin films for high-performance perovskite solar cell encapsulation

An atmospheric-pressure spatial atomic layer deposition (AP-SALD) system is used to deposit nitrogen-doped alumina (N-AlOx) thin-film-encapsulation layers. The rapid nature of the AP-SALD process facilitates deposition of 60-nm layers directly on perovskite solar cells at 130 °C with no damage to the temperature-sensitive perovskite and organic materials. Varying the bubbling of a NH4OH precursor varied the nitrogen concentration from 0.08 to 0.68 at%. These small concentrations were found to have a significant impact on the structural properties of the films and their moisture barrier performance. The N-AlOx thin films had slightly higher growth rates than undoped AlOx, less unwanted hydroxyl and carbon content, and were smoother and more compact, which was attributed to a higher flux of reactive species from the volatile NH4OH. Optical calcium tests showed that the N-AlOx films had lower water-vapor-transmission rates (∼10-5 g/m2/day) than undoped AlOx films and the transmission was minimized for 0.28% nitrogen. The increased compactness of the N-AlOx films is expected to minimize nanoscale percolation pathways, whereas higher nitrogen-defect concentrations may facilitate water permeation through these pathways. The stability of n-i-p and p-i-n perovskite solar cells under standard ISOS-D-1 and ISOS-D-3 testing conditions was significantly enhanced by the encapsulation layers. An N-AlOx encapsulation layer with 0.28% nitrogen improved the T80 value of a p-i-n formamidinium methylammonium lead iodide solar cell from 144 hrs to 855 hrs (ISOS-D-1) and 52 hrs to 300 hrs (ISOS-D-3).

Compositionally engineered amorphous InZnO thin-film transistor with high mobility and stability via atmospheric pressure spatial atomic layer deposition

Amorphous indium-zinc oxide (IZO) thin films, featuring indium atomic concentrations between 35.2 and 64.2 at.%, were fabricated using atmospheric pressure spatial atomic layer deposition (AP S-ALD) at 250 °C, employing trimethylindium (TMI) and diethylzinc (DEZ) as precursors and ozone as the reactant, based on the atomic layer processing. The crystallinity and chemical bonding states of the IZO films were found to vary with the metal cation composition, as confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We fabricated thin-film transistors (TFTs) employing the IZO films as the active layer on polyimide (PI) substrates, achieving high mobility (45.7 cm2/V·s), excellent bias-temperature stress (BTS) stability (ΔVTH = 0.63 V), and maintaining stable electrical properties even after mechanical bending tests along two different axes. This study highlights the successful development of high-performance flexible devices by precisely controlling the metal cation composition using AP S-ALD based on high deposition rate.

Low temperature (002)-oriented zinc oxide films prepared using ozone-based spatial atomic layer deposition

In this study, ZnO films are prepared at a low temperature of 150 °C by using spatial atomic layer deposition (sALD) with diethylzinc and ozone as precursor and oxidant. The ozone flow rate is varied to systematically investigate its effect on optical, structural and electrical properties. The experimental results show that the self-limiting surface reactions can occur at the low ozone flow rate of 200 sccm, confirming ALD growth mode. All the ozone flow rates lead to ZnO (002) crystalline orientation, which is difficult to be obtained for conventional water-based ALD ZnO films at the low temperature. The increased ozone flow rate results in an increased amount of oxygen vacancies, enhanced carrier concentration and a reduced stress. The resistivity and carrier concentration can be tuned in the range of 4.75–0.08 Ω-cm and (1.1–5.5) × 1018 cm−3. Finally, the sALD ZnO film on polyethylene terephthalate reveals a high stability in the film property against bending. This study is beneficial for the utilization of ZnO films in optoelectronic devices that demand the (002) preferred orientation, especially under low-temperature conditions.

Mechatronic Spatial Atomic Layer Deposition for Closed‐Loop and Customizable Process Control

AbstractA customized atmospheric‐pressure spatial atomic layer deposition (AP‐SALD) system is designed and implemented, which enables mechatronic control of key process parameters, including gap size and parallel alignment. A showerhead depositor delivers precursors to the substrate while linear actuators and capacitance probe sensors actively maintain gap size and parallel alignment through multiple‐axis tilt and closed‐loop feedback control. Digital control of geometric process variables with active monitoring is facilitated with a custom software control package and user interface. AP‐SALD of TiO2 is performed to validate self‐limiting deposition with the system. A novel multi‐axis printing methodology is introduced using x‐y position control to define a customized motion path, which enables an improvement in the thickness uniformity by reducing variations from 8% to 2%. In the future, this mechatronic system will enable experimental tuning of parameters that can inform multi‐physics modeling to gain a deeper understanding of AP‐SALD process tolerances, enabling new pathways for non‐traditional SALD processing that can push the technology towards large‐scale manufacturing.

Enhancing control in spatial atomic layer deposition: insights into precursor diffusion, geometric parameters, and CVD mitigation strategies

In recent years, spatial atomic layer deposition (SALD) has gained significant attention for its remarkable capability to accelerate ALD growth by several orders of magnitude compared to conventional ALD, all while operating at atmospheric pressure. Nevertheless, the persistent challenge of inadvertent contributions from chemical vapor deposition (CVD) in SALD processes continues to impede control over film homogeneity, and properties. This research underscores the often-overlooked influence of diffusion coefficients and important geometric parameters on the close-proximity SALD growth patterns. We introduce comprehensive physical models complemented by finite element method simulations for fluid dynamics to elucidate SALD growth kinetics across diverse scenarios. Our experimental findings, in alignment with theoretical models, reveal distinctive growth rate trends in ZnO and SnO2 films as a function of the deposition gap. These trends are ascribed to precursor diffusion effects within the SALD system. Notably, a reduced deposition gap proves advantageous for both diffusive and low-volatility bulky precursors, minimizing CVD contributions while enhancing precursor chemisorption kinetics. However, in cases involving highly diffusive precursors, a deposition gap of less than 100 μm becomes imperative, posing technical challenges for large-scale applications. This can be ameliorated by strategically adjusting the separation distance between reactive gas outlets to mitigate CVD contributions, which in turn leads to a longer deposition time. Furthermore, we discuss the consequential impact on material properties and propose a strategy to optimize the injection head to control the ALD/CVD growth mode.

Silver Nanowire-Based Transparent Electrodes for V2O5 Thin Films with Electrochromic Properties.

The development of electrochromic systems, known for the modulation of their optical properties under an applied voltage, depends on the replacement of the state-of-the-art ITO (In2O3:Sn) transparent electrode (TE) as well as the improvement of electrochromic films. This study presents an innovative ITO-free electrochromic film architecture utilizing oxide-coated silver nanowire (AgNW) networks as a TE and V2O5 as an electrochromic oxide layer. The TE was prepared by simple spray deposition of AgNWs that allowed for tuning different densities of the network and hence the resistance and transparency of the film. The conformal oxide coating (SnO2 or ZnO) on AgNWs was deposited by atmospheric-pressure spatial atomic layer deposition, an open-air fast and scalable process yielding a highly stable electrode. V2O5 thin films were then deposited by radio frequency magnetron sputtering on the AgNW-based TE. Independent of the oxide's nature, a 20 nm protective layer thickness was insufficient to prevent the deterioration of the AgNW network during V2O5 deposition. On the contrary, crystalline V2O5 films were grown on 30 nm thick ZnO or SnO2-coated AgNWs, exhibiting a typical orange color. Electrochromic characterization demonstrated that only V2O5 films deposited on 30 nm thick SnO2-coated AgNW showed characteristic oxidation-reduction peaks in the Li+-based liquid electrolyte associated with a reversible orange-to-blue color switch for at least 500 cycles. The electrochromic key properties of AgNW/SnO2 (30 nm)/V2O5 films are discussed in terms of structural and morphological changes due to the AgNW network and the nature and thickness of the two protective oxide coatings.

Growth of p-doped 2D-MoS2 on Al2O3 from spatial atomic layer deposition

In this letter, we report on the synthesis of monolayers of MoS2 via chemical vapor deposition directly on thin films of Al2O3 grown by spatial atomic layer deposition. The synthesized monolayers are characterized by atomic force microscopy as well as confocal Raman and photoluminescence spectroscopies. Our data reveal that the morphology and properties of the 2D material differ strongly depending on its position on the substrate. Close to the material source, we find individual flakes with an edge length of several hundred microns exhibiting a tensile strain of 0.3 %, n-doping on the order of ne = 0.2 × 1013 cm−2, and a dominant trion contribution to the photoluminescence signal. In contrast to this, we identify a mm-sized region downstream, that is made up from densely packed, small MoS2 crystallites with an edge length of several microns down to the nanometer regime and a coverage of more than 70 %. This nano-crystalline layer shows a significantly reduced strain of only <0.02 %, photoluminescence emission at an energy of 1.86 eV with a reduced trion contribution, and appears to be p-doped with a carrier density of nh = 0.1 × 1013 cm−2. The unusual p-type doping achieved here in a standard chemical vapor deposition process without substitutional doping, post-processing, or the use of additional chemicals may prove useful for applications.

Numerical Simulation of Spatial Atomic Layer Deposition on Moving Substrates with Microgrooves and Porous Structures

The need of ultrathin and highly conformal coatings on large-area microstructure substrates such as photovoltaic cells, flexible displays, and Li-ion battery (LIB) electrodes has driven the development of high-efficient ALD. Spatial ALD is a promising high-throughput technique capable of producing ultrathin films on large substrates, which can reach up to two orders of magnitude faster than temporal ALD. However, spatial ALD is a complex and strong-coupled process of fluid flow, heat and mass transfer, as well as chemical reactions. Compared to the flat substrate, the diffusion process in the microstructures takes longer, limiting the substrate velocity and the deposition rate. In this work, spatial ALD on moving microgroove substrates and porous LIB electrodes are quantitatively studied through the multiscale modelling method by coupling computational fluid dynamics (CFD) with chemical kinetics. Dynamic mesh method is implemented to simulate the ALD reaction with the in-line movement of the substrate. Results show that the vortices always exist in the micro-gap with microgroove substrates. Besides, the top of the microstructure on the first contact with the precursor is the highest, and the surface coverage at the corner on the other side of the microstructure is the lowest. For porous LIB electrodes with large specific surface area, the film coating depth is limited by both the low precursor diffusion rate and the amount of precursor supply. Increasing the carrier gas flow rate increases the film coating depth by increasing the precursor supply over the same time period. Besides, the gas byproduct of ALD remaining at the electrode bottom can be more effectively removed. Quantitative process optimizations of substrate velocity and precursor concentration for different electrode structures are also carried out. It is found that the electrode gradient design with higher porosity on the top is beneficial for obtaining deeper coating depth and higher precursor utilization compared to the inverse gradient design. The present multiscale modeling work provides a comprehensive understanding and important guidance for the industrial application of the spatial ALD process on microstructure substrates.

Spatial Atomic Layer Deposition of Iridium Oxide Electrocatalyst Layers for PEM Electrolysis

Proton Exchange Membrane Water Electrolysis (PEMWE) is a commonly used technique to produce green hydrogen from water. A massive upscaling of PEMWE installations is required in the coming decade to keep up with the foreseen demand for green hydrogen. State-of-the-art PEM electrolyzers make use of iridium-based electrocatalyst layers with iridium loadings of 1-2 mg/cm2. The high cost and limited availability of iridium will limit the scalability of PEMWE if the iridium loading cannot be reduced.Atomic Layer Deposition can be used to apply thin and highly conformal IrO2 films on porous substrates with atomic-scale control of the amount of material that is deposited. When applied to PEM electrolyzers, this can be used to significantly reduce the loading of IrO2. Recently, IrO2 catalyst layers for PEM electrolyzers applied by Spatial ALD with iridium loadings well below 0.1 mg/cm2 have been reported [1]We will present plasma enhanced Spatial ALD of iridium oxide and metallic iridium films using a new iridium precursor developed by Air Liquide Advanced Materials. The electrocatalytic efficiency and stability has been characterized using RDE, showing that IrO2 films of just a few nanometer demonstrate an excellent catalytic activity and stability. IrO2 films have been conformally deposited on high surface area titanium porous transport layers (PTL’s) as well as Nafion membranes. First demonstrations on full PEM stack scale show that Spatial ALD can enable iridium loads 10-100x lower than the state of the art while demonstrating an excellent stability in accelerated stress tests.We will also discuss how Spatial ALD of IrO2 films can be up-scaled to mass production, with emphasis on efficiency or precursor utilization and precursor recovery for recycling.[1]: https://www.tno.nl/en/newsroom/2022/10/breakthrough-electrolyser-development/

Inherently Selective Atomic Layer Deposition for Optical and Sensor Applications: Microreactor Direct Atomic Layer Processing (μDALP™)

In parallel to additive manufacturing leading the revolution in traditional manufacturing, the same principles can revolutionize traditional thin film deposition techniques. Where lithography and vapor phase deposition techniques struggle, for example, with rapid iterations for prototyping or incompatibility with the used chemistry, additive manufacturing can shine. Indeed, several approaches are in development for 3D nanopriting1,2,3.Atomic Layer Deposition, and in more general Atomic Layer Processing, offers a unique opportunity for localized 3D processing/printing due to its two-step process. While simple in theory, due to well-developed examples of Spatial Atomic Layer Deposition (SALD), in practice miniturization of SALD requires substantial effort into the creation of suitable micro-nozzles. Uniquely, ATLANT 3D has developed proprietary Spatial ALD micronozzles, naming the process microreactor Direct Atomic Layer Processing - µDALPTM.The µDALPTM process undergoes the same cyclic ALD process but, thanks to the in-house microreactor development, is only done in a localized area. The microreactor or micronozzle confines the flows of gases used for ALD within a µm-scale area on the substrate, wherein the reactive species adsorb on the surface to deposit one monolayer of the desired material. Similarly, to spatial ALD, the creation of this monolayer then hinges on the movement of the substrate.4 Since the µDALPTM process is based on physical separation, it is theoretically compatible with any ALD process. As such, the material capabilities can match traditional ALD and exceed other special or patterning thin film techniques, such as lithography, which can be costly and time-consuming, especially for rapid prototyping required for innovation.Films deposited with ATLANT 3D technology have been shown to produce high-quality, crystalline, atomically precise thin films.1 It has been used to fabricate temperature (Fig.1) and capacitive sensors with sensitivities that meet or exceed those of devices made using conventional vapor phase deposition techniques.5 Low-cost rapid prototyping facilitated by ATLANT 3D technology of such devices enables design innovation and optimization not possible with other thin film deposition techniques.ATLANT 3D platform provides flexibility in deposition geometry (Fig.2) that enables a range of optical applications that require high-precision fabrication techniques. Optically transparent films can be used as localized thin protective layers for device encapsulation, as well as for atomic corrections of defects. Alternating deposition materials enable multilayer mirror fabrication of custom dimensions. Smooth thickness gradients can be used to manufacture ultrathin optical lenses. Overlapping depositions with discrete steps enable the manufacturing of binary lenses and phase masks. Growth rate enhancement in rastered direct processing mode using ATLANT 3D technology can produce periodic grating structures.1 Conformal coatings on complex surfaces can act as functionalization layers or seed layers for further material deposition through e.g. electrochemical processes.[1] Kundrata I. et al., ALD/ALE 2022 [Int. Conf.], 2022 [2] de la Huerta C. A. M. et al., arXiv, 2020, 0523. [3] Winkler, R. et al., J. Appl. Phys., 2019, 125, 210901[4] Paul Poodt., JVSTA., 2012, 30, 010802[5] Kundrata, I. et al., Small Methods., 2022, 6 (5), 2101546 Figure 1

Atomic Layer Deposition of Multi-Component Films Using Precursor Co-Dosing

A growing number of ALD applications require the deposition of ternary or quarternary compounds. Examples include doped films (e.g. ZnO:Al), mixed oxides to tune dielectric properties (e.g. HfZrO), tunable bandgap materials for solar cells (e.g. ZnOS) or opto-electronic materials (e.g. InGaN), and high mobility oxide semiconductors (e.g. InGaZnO). A common method to deposit multicomponent films in ALD is the supercycle approach [1], where sub-cycles of different binary compounds are combined to deposit films where the resulting net composition is determined by the cycle ratio of the individual sub-cycles. A drawback of the supercycle method is that essentially multilayer stacks are deposited instead of true alloys and the film composition varies out-of-plane, potentially impacting film properties.An alternative method is to use precursor co-dosing, where two or more precursors are simultaneously dosed and co-adsorb during a half-reaction. The resulting film composition is then determined by the ratio of the partial pressures of the individual precursors during the precursor dose. As each ALD cycle deposits a true alloy, it results in excellent out-of-plane compositional uniformity. The co-dosing method has first been reported in the late 1980’s to deposit ternary and quarternary III-V compounds [2] and has been used since for a wide range of materials. In the last decade it has become the method of choice for depositing multicomponent materials with Spatial ALD.A proper understanding of the relation between film composition and precursor partial pressure during co-dosing is essential for accurate control of the film composition. This is not straightforward, as the surface chemistry of co-dosing can be quite complex, involving competitive adsorption, heterogeneity of reactive sites, exchange reactions and more. We will discuss how the surface chemistry of precursor co-dosing determines the film composition. In analogy to the IUPAC classification of adsorption isotherms for single adsorbents [3], we will introduce a similar classification of adsorption isotherms for multiple absorbing precursors which we will use to review and explain results reported in literature. Finally, we will discuss some interesting new opportunities for co-dosing, such as the deposition of gradient composition films and the use of co-dosing for area-selective deposition.[1]: A. Mackus et al, Chem. Mater. 31 (2019) 1142[2]: M. Tischler, S. Bedair, J. Cryst. Growth 77 (1986) 89[3]: M. Thommes et al, Pure & Appl. Chem. 87 (2015) 87

Forming Artificial Solid-Electrolyte-Interfaces between Lithium Metal Anodes and Halide and Sulfide Solid Electrolytes in All-Solid-State-Batteries Via Spatial-Atomic-Layer-Deposition

Increasing need in energy density and safety of current lithium-ion batteries has resulted in a search for next generation battery technologies1,2. All-solid-state-batteries (ASSBs) could answer these needs owing to the use electrode materials with higher capacities and potential difference, and by replacing flammable liquid electrolytes with solid electrolytes3,4. ASSBs using inorganic sulfide and halide solid electrolytes in particular have drawn a lot of attention as the electrolytes have very high RT ionic conductivities (>10-3 S.cm-1)5–7. Nevertheless, they suffer from issues related to electro-chemical and chemo-mechanical stabilities at electrode – electrolyte interfaces7,8. One promising approach to mitigate this issue is depositing an artificial solid-electrolyte-interface (SEI) layer via atomic-layer-deposition (ALD)9–11. In this work, we deposited a variety of artificial layers with different thicknesses and chemistries on the lithium metal anode using spatial ALD. We characterized the bonding within the thin film layer using X-ray photoelectron spectroscopy, and evaluated the stabilizing effect of the artificial SEI layer using electrochemical impedance spectroscopy and galvanostatic lithium plating and stripping methods. We compared the growth of lithium dendrites within the solid electrolyte pellets post-mortem analysis via scanning electron microscopy. J. Janek and W. G. Zeier, Nat. Energy (2023) https://www.nature.com/articles/s41560-023-01208-9.Q. Wang, L. Jiang, Y. Yu, and J. Sun, Nano Energy, 55, 93–114 (2019) https://doi.org/10.1016/j.nanoen.2018.10.035.J. B. Goodenough and M. H. Braga, Dalt. Trans. (2017) http://xlink.rsc.org/?DOI=C7DT03026F.J. Janek and W. G. Zeier, Nat. Energy, 1, 16141 (2016) http://www.nature.com/articles/nenergy2016141.R. Schlem et al., Adv. Energy Mater., 11, 2101022 (2021) https://onlinelibrary.wiley.com/doi/10.1002/aenm.202101022.S. Ohno et al., Prog. Energy, 2, 022001 (2020) https://iopscience.iop.org/article/10.1088/2516-1083/ab73dd.T. Koç, F. Marchini, G. Rousse, R. Dugas, and J. M. Tarascon, ACS Appl. Energy Mater., 4, 13575–13585 (2021).Y. He, C. Lu, S. Liu, W. Zheng, and J. Luo, Adv. Energy Mater., 9, 1–40 (2019).L. Han, C. Te Hsieh, B. Chandra Mallick, J. Li, and Y. Ashraf Gandomi, Nanoscale Adv., 3, 2728–2740 (2021).J. Liu and X. Sun, Nanotechnology, 26, 24001 (2015) http://dx.doi.org/10.1088/0957-4484/26/2/024001.Y. Jiang et al., Energy Storage Mater., 28, 17–26 (2020) https://doi.org/10.1016/j.ensm.2020.01.019.

Ultra-Low Loading IrO2 on Porous Transport Layer for Catalysis of Proton Exchange Membrane Water Electrolysis

Proton Exchange Membrane Water Electrolysis (PEMWE) is a commercial technology with specific advantages such as high-power density and rapid start-up times, which makes it a perfect match to produce hydrogen from intermittent renewable energy sources (green H2). [1] However, very scarce materials, such as iridium and platinum, are currently used as catalysts and protection coatings to withstand the harsh operating conditions in PEMWE. Iridium is the anode catalyst in the state-of-the-art PEMWE, with loadings in the range 1-2 mg/cm2. This metric translates into using 200-500 kg of iridium per GW, which accounts for roughly 10% of the global iridium production per year. Reducing iridium usage in PEMWE is critical to realize the 10-100 GW/year growth in green H2 power. [2,3]To significantly reduce the Ir loading, while maintaining the lateral conductivity, we coated the iridium catalyst by atmospheric spatial Atomic Layer Deposition (sALD) on titanium porous transport layer (PTL), which acts as the electrically conductive substrate. The coating renders ultra-low iridium loadings, which is 100-200 times less iridium than the state-of-the-art catalyst coated membrane technology, while retaining ca. 60-80% of the performance (in terms of current density), with durability demonstrated up to 100 h (see Figure 1). We will also show here that protection coatings on the titanium PTL are beneficial to yield good durability with these ultra-low loadings of iridium and demonstrated that sALD has the potential to produce non-PGM based protection coatings.[1] Barbir, F. Solar Energy 78 (2005) 661-669.[2] Gavrilova, A., Wieclawska, S.M. “Towards a green future. Part 2” (2021). TNO report 21-12158.[3] Minke, C., Suermann, M., Bensmann, B., & Hanke-Rauschenbach, R. J. Hydrogen Energy 46 (2021) 23581-23590. Figure 1

(Invited) Atomistic Insights into Continuous and Area-Selective ALD Processes: First-Principles Simulations of the Underpinning Surface Chemistry

Atomic layer deposition (ALD) is a highly advanced thin film deposition technology that has found widespread use in nanoelectronics, photovoltaics, fuel cell and recently all-solid-state battery applications. It is widely regarded as the state-of-the-art technique for producing thin films due to its exceptional conformality on high-aspect ratio structures, atomic level thickness control, and tuneable film composition. In recent years, area-selective atomic layer deposition (AS-ALD) has emerged as a promising technology for high-fidelity nano-patterning, and significant progress has been made in understanding and developing highly selective processes for various material systems. Along these lines, we have recently shown that high-throughput, low defectivity, highly selective SiO2 deposition can be achieved on various substrates by combining atmospheric-pressure spatial ALD with integrated area-deactivation using small molecule inhibitors and plasma-enhanced spatial etching [1].ALD is a surface-controlled technique that relies on the self-limiting reactions of the precursors and co-reactants with the deposition surface in alternating cycles. The initial step in ALD nucleation on the target substrate is a key factor in the deposited film quality, and efficient precursor binding on the surface is critical. Molecular dynamics (MD) simulations and minimum-energy reaction pathway analysis based on ab initio Density Functional Theory (DFT) calculations provide invaluable insights into the surface chemistry, enabling customisation of ALD processes to boost uniformity, conformality, and area-selectivity of the resulting films.In this talk, I will discuss how first-principles simulations can be used synergistically with experimental findings to achieve high-efficiency plasma-enhanced atomic-layer cleaning (ALC) of impurities from various ALD films and substrates, design proper chemical surface modifications that enable continuous and conformal ALD nucleation even on chemically-inert surfaces (like graphene), and unveil the particular surface chemistry governing high-fidelity area-selectivity with an atomic-level precision in ultrathin coatings [1-9]. By combining the insights gained from first-principles simulations with experimental techniques, we can push the frontiers of device manufacturing to new heights, opening up exciting possibilities for further technological advances in nanoelectronics, photovoltaics, fuel cell and energy storage applications.[1] Advanced Materials, Just Accepted, (DOI: 10.1002/adma.202301204); [2]Nanoscale, 2021, 13, 10092-10099; [3] Chem. Mater. 2019, 31 (4), 1250-1257.; [4] Adv. Mater. Interfaces 2018, 5 (13), 1800268.; [5] Chem. Mater. 2017, 29 (3), 921–925.; [6] ACS Nano 2017, 11 (9), 9303–9311.; [7] Sol. Energy Mater. Sol. Cells 2017, 163, 43–50.; [8] Chem. Mater. 2017, 29 (5), 2090–2100.; [9] Nanoscale 2016, 8 (47), 19829–19845. Figure 1

Effect of different oxygen precursors on alumina deposited using a spatial atomic layer deposition system for thin-film encapsulation of perovskite solar cells

An atmospheric-pressure spatial atomic layer deposition system operated in atmospheric-pressure spatial chemical vapor deposition conditions is employed to deposit alumina (AlO x ) thin films using trimethylaluminum and different oxidants, including water (H2O), hydrogen peroxide (H2O2), and ozone (O3). The impact of the oxygen precursor on the structural properties of the films and their moisture-barrier performance is investigated. The O3-AlO x films, followed by H2O2-AlO x , exhibit higher refractive indexes, lower concentrations of OH− groups, and lower water-vapor-transmission rates compared to the films deposited using water (H2O-AlO x ). The AlO x films are then rapidly deposited as thin-film-encapsulation layers on perovskite solar cells at 130 °C without damaging the temperature-sensitive perovskite and organic materials. The stability of the p–i–n formamidinium methylammonium lead iodide solar cells under standard ISOS-D-3 testing conditions (65 °C and 85% relative humidity) is significantly enhanced by the encapsulation layers. Specifically, the O3-AlO x and H2O2-AlO x layers result in a six-fold increase in the time required for the cells to degrade to 80% of their original efficiency compared to un-encapsulated cells.

High mobility and productivity of flexible In2O3 thin-film transistors on polyimide substrates via atmospheric pressure spatial atomic layer deposition

We fabricate In2O3 films using atmospheric pressure spatial atomic layer deposition (AP S-ALD) and investigate their properties at various temperatures (150 °C–225 °C). As the temperature increased, the growth per cycle (GPC) increases, with the GPC and refractive index reaching values of 1.33 and 2.02, respectively, at 225 °C. The In2O3 thin film indicates a reduction in carrier concentration from 1.53 ± 1.37 × 1021 to 3.09 ± 0.53 × 1020 cm−3 as the temperature increased, and a decrease in the resistance from 3.55 ± 0.07 × 10−3 to 3.70 ± 0.01 × 10−4 Ω∙cm, which is attributed to a decrease in the impurity concentration (150 °C: 1.5 at.%; 175 °C: 1.0 at.%; 200 °C: N/A; 225 °C: N/A) and an increase in crystallinity. We use the In2O3 film as a channel layer in a top-gate bottom-contact thin-film transistor (TG-BC TFT). The device shows excellent performance characteristics, including a field-effect mobility of 69.8 cm2/V·s, a threshold voltage of −0.06 ± 0.22 V, and a subthreshold swing of 0.16 ± 0.01 V/decade. We successfully fabricated high-mobility TFTs and demonstrated their reliability via bias and 50,000 bending tests. The high-performance channel layer of the TFTs fabricated using AP S-ALD are promising for flexible applications.

Multiscale computational fluid dynamics modelling of spatial ALD on porous li-ion battery electrodes

The self-limiting surface reaction characteristic of atomic layer deposition (ALD) makes it ideal for the surface modification of electrode materials for lithium-ion batteries (LIBs). Spatial ALD shows promise as a scalable method for the coating on pre-fabricated electrode sheets. As a strong-coupled multiscale process, various process conditions and microstructure parameters have great influences on the macroscale fluid dynamics and the pore-scale diffusion–reaction process, thus affecting the coating efficiency. This study presents a multiscale numerical model that combines computational fluid dynamics (CFD) with multilevel pore-scale diffusion–reaction kinetics to explore the spatial ALD process on porous LIB electrodes. The dynamic mesh method is utilized to simulate electrode movement. The considerable active surface-to-volume ratio of the porous structure limits the precursor infiltration depth due to the low diffusion rate and inadequate precursor supply. As the electrode velocity increases, an asymmetric distribution of precursor concentration under the injector is observed with a rapid decrease. Elevating both the precursor concentration and inlet gas velocity augments the coating depth by enhancing the supply of the precursor. The experimental data aligns well with our numerical results, verifying the accuracy of the multiscale CFD model. Our observations reveal that a relatively lower operating pressure, around 0.1 atm, compared to 0.01 atm and 1 atm, optimizes the deposition rate along the electrode depth during the half-ALD cycle, especially when the pore size is larger. Electrode porosity of about 0.4 notably improves coating uniformity by elevating the precursor diffusion rate. Predictions show that with a substrate velocity of 0.2 m/s, the coating depth on an electrode having higher porosity at the top compared to the bottom via atmospheric spatial ALD could reach a depth of 38 μm with a precursor utilization of 78 %.

Highly Transparent and Stable Flexible Electrodes Based on MgO/AgNW Nanocomposites for Transparent Heating Applications

AbstractTransparent electrodes (TE) based on silver nanowire (AgNW) exhibit good physical properties and constitute a promising alternative to transparent conductive oxides due to their low cost, flexibility, and low toxicity. Nevertheless, they suffer from stability issues over harsh conditions, and encapsulation allows to overcome these limitations. Herein, the low‐cost, scalable fabrication and study of transparent electrodes based on sprayed AgNW networks coated with MgO thin films deposited by atmospheric pressure spatial atomic layer deposition (AP‐SALD) at mild deposition temperature (≤220 °C) is reported. Fabrication of MgO thin films by AP‐SALD is reported here for the first time, and their deposition on different substrates is optimized. MgO exhibits a pure phase and conformal growth with a preferential (220) crystalline orientation and a higher growth rate as compared to conventional atomic layer deposition (ALD). Furthermore, thanks to the conformal coating of MgO on AgNW, the obtained nanocomposites exhibit great optical transparency of ≈85% and flexibility while maintaining high stability under thermal and electrical stress. Indeed, this study shows a clear enhancement of the stability of AgNW networks for thin MgO coatings of only a few nanometers thick. Finally, a proof‐of‐concept transparent heater is fabricated to melt a piece of cheese.

Excellent conformality of atmospheric-pressure plasma-enhanced spatial atomic layer deposition with subsecond plasma exposure times

Atmospheric-pressure spatial atomic layer deposition (s-ALD) has emerged as a scalable deposition technique combining the advantages of ALD with high deposition rates, suitable for low-cost and high-volume applications. There is a growing interest in atmospheric-pressure plasma-enhanced spatial ALD (PE-s-ALD), e.g., to allow for deposition at reduced temperatures or for materials that are otherwise difficult to prepare by thermal ALD. For low-pressure PE-ALD, conformal films on high aspect ratio features have been achieved despite plasma radical recombination, and the aspects influencing conformality are fairly well understood. This work addresses surface recombination and conformality for atmospheric-pressure PE-s-ALD films. We demonstrate that conformality can be achieved for SiO2 and TiO2 films deposited by atmospheric-pressure PE-s-ALD inside high-aspect-ratio trenches with short plasma exposure times. Using plasma exposure of 0.73 s results in conformal SiO2 and TiO2 films in structures with aspect ratios of 74 and 219, respectively. Additionally, the recombination probabilities of oxygen radicals at atmospheric pressure are extracted to be 4×10−4 for SiO2 and 6×10−5 for TiO2. These results demonstrate that atmospheric-pressure PE-s-ALD can be used for conformal and high-speed depositions on 3D substrates.

Impact of air exposure on growth rate and electrical properties of SnO2 thin films by atmospheric pressure spatial atomic layer deposition

SnO2 thin film is one of the most studied transparent conductive materials that can be deposited using vacuum-free techniques such as atmospheric pressure spatial atomic layer deposition (AP-SALD). This work studies SnO2 thin films prepared from tin(II) acetylacetonate and water vapor, with a particular focus on the impact of air exposure during the AP-SALD process on the growth rate and electrical properties of the films. In-situ resistance measurements and ex-situ Hall effect characterization demonstrated that longer exposure time of the growing film surface to the open air (t air) at 240 °C led to conductivity degradation, while the film thickness decreases. The theoretical calculations show that −OH and (oxygen molecule adsorbed on the five-coordinated Sn atom, also called O2 dimer) are the two most stable surface structures. The formation of is shown as the most thermodynamically favorable oxygen-related species on SnO2(110) surface formed when the film is exposed to the open air, giving rise to both the decrease of film thickness (associated with the desorption of −OH surface groups) and the increase of film resistivity versus t air. The optimized polycrystalline SnO2 sample demonstrated relatively good electrical performance, including an electrical resistivity of 9.3 × 10−3 Ω.cm, carrier density of 9.2 × 1019 cm−3, and Hall mobility of 7.3 cm2 V−1 s−1 at a growth temperature as low as 240 °C. Our findings reveal the critical impact of processing in the open air on the electrical conductivity of the obtained SnO2 films by AP-SALD coating technology.