Layer Deposition Of Al2O3 Research Articles

Reaction Dynamics between Formamidinium Lead Iodide and Copper Oxide.

Copper oxide (CuOx) has been announced as a very promising hole-transporting layer for perovskite solar cells. However, in our previous work, we have shown that once a formamidinium lead triiodide (FAPI) perovskite is spin-coated on a spray-coated cuprous oxide (Cu2O) substrate, the Cu2O diffuses into and reacts with the FAPI film. In order to verify if the degradation products are related to the oxidation state of CuOx and/or its preparation method, in this work, we first prepared CuOx films by thermal oxidation at temperatures ranging from 120 to 300 °C. While increasing the process temperature, a transformation from copper I (Cu2O) to copper II (CuO) oxidation states was observed. For both oxidation states of copper, FAPI perovskite degradation was found; however, some alterations in the reaction products were noticed. In contrast to our expectations, the introduction of an ultrathin plasma-enhanced atomic layer deposited Al2O3 layer in between both films only partially blocked the CuOx migration into the FAPI film. It can be concluded that regardless of the chemical composition and/or preparation method of CuOx, the overlayered FAPI film gets decomposed. In order to use CuOx as a hole-transporting layer in solar cells, new strategies must be developed to limit these unwanted chemical reactions.

Efficacy of atomic layer deposition of Al2O3 on composite LiNi0.8Mn0.1Co0.1O2 electrode for Li-ion batteries

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a popular cathode material for Li-ion batteries, yet degradation and side reactions at the cathode-electrolyte interface pose significant challenges to their long-term cycling stability. Coating LiNixMnyCo1−x−yO2 (NMC) with refractory materials has been widely used to improve the stability of the cathode-electrolyte interface, but mixed results have been reported for Al2O3 coatings of the Ni-rich NMC811 materials. To elucidate the role and effect of the Al2O3 coating, we have coated commercial-grade NMC811 electrodes with Al2O3 by the atomic layer deposition (ALD) technique. Through a systematic investigation of the long-term cycling stability at different upper cutoff voltages, the stability against ambient storage, the rate capability, and the charger transfer kinetics, our results show no significant differences between the Al2O3-coated and the bare (uncoated) electrodes. This highlights the contentious role of Al2O3 coating on Ni-rich NMC cathodes and calls into question the benefits of coating on commercial-grade electrodes.

Impact of NaOH solution surface treatment on Al2O3/β-Ga2O3 MOS capacitors

A suitable semiconductor surface treatment could improve the gate dielectric quality and reduce the interface states and traps to enhance the performance of metal–oxide semiconductor capacitors (MOSCAPs). In this paper, β-Ga2O3 surface treatment using NaOH solution prior to atomic layer deposition of Al2O3 was investigated. In comparison with piranha pretreatment, MOSCAPs with NaOH solution surface pretreatment show a larger maximum accumulation capacitance with less frequency dispersion, reduced charges/traps and interface state density D it. The improvement in MOSCAPs performance could be attributed to the NaOH solution pretreatment induced slight surface etching effect and relatively effective hydroxylation surface. These results suggest that the process optimization of NaOH solution surface pretreatment could lead to further improvement of β-Ga2O3 MOSCAPs and have a potential in application of β-Ga2O3 metal–oxide semiconductor field-effect transistors in the future.

Enhanced cyclability of lithium-ion batteries resulting from atomic layer deposition of Al2O3 on LiFePO4 electrodes

Enhanced cyclability of lithium-ion batteries resulting from atomic layer deposition of Al2O3 on LiFePO4 electrodes

Coherent acoustic vibrations of Au nanoblocks and their modulation by Al2O3 layer deposition.

Coherent acoustic phonons induced in metallic nanostructures have attracted tremendous attention owing to their unique optomechanical characteristics. The frequency of the acoustic phonon vibration is highly sensitive to the material adsorption on metallic nanostructures and, therefore, the acoustic phonon offers a promising platform for ultrasensitive mass sensors. However, the physical origin of acoustic frequency modulation by material adsorption has been partially unexplored so far. In this study, we prepared Al2O3-deposited Au nanoblocks and measured their acoustic phonon frequencies using time-resolved pump-probe measurements. By precisely controlling the thickness of the Al2O3 layer, we systematically investigated the relation between the acoustic phonon frequency and the deposited Al2O3 amounts. The time-resolved measurements revealed that the acoustic breathing modes were predominantly excited in the Au nanoblocks, and their frequencies increased with the increment of the Al2O3 thickness. From the relationship between the acoustic phonon frequency and the Al2O3 thickness, we revealed that the acoustic phonon frequency modulation is attributed to the density change of the whole sample. Our results would provide fruitful information for developing quantitative mass sensing devices based on metallic nanostructures.

(Invited) Small Molecule Inhibitor-Based Approaches for Area-Selective Deposition from First Principles

Atomic layer deposition tackles ever new research questions. Area-selective deposition is one of these recent challenges. Several approaches have been developed to achieve selectivity. One of the most promising is using comparatively small molecules to block the non-growth surface while leaving the growth surface uncovered for the ALD process.This approach requires in-depth knowledge of the surface chemistry of both surfaces involved. In addition, the decomposition pathways of SMI-covered surfaces need to be uncovered to enable stable ALD growth over a maximum number of cycles.These questions are very challenging for lab-based investigations. We present recent progress in the ab initio description of key questions regarding SMI-based ALD processes. At the example of silanol-based SMIs, surface chemistry for Al2O3 growth on Cu while blocking SiO2 will be discussed and compared to experimental findings.[1] Furthermore, the importance of choosing the appropriate surface model will be highlighted. Especially for the challenging question of SMI-layer decomposition.[1 J. Yarbrough, F. Pieck, D. Grigjanis, I.-K. Oh, P. Maue, R. Tonner-Zech, S. F. Bent, "Tuning Molecular Inhibitors and Aluminum Precursors for the Area-Selective Atomic Layer Deposition of Al2O3", Chem. Mater. 2022, 34, 4646-4659.We gratefully acknowledge funding from a Merck KGaA, Darmstadt, Germany 350th Anniversary Research Award. Computations were performed on the CSC Frankfurt, HLR Stuttgart, ZIH Dresden and HPC Regensburg.Figure 1 General structure (a) of the studied SMIs with different reactive and blocking groups (b). Schematic structures of the calculated condensation reactions of the SMIs with OH groups of the SiO2 surface (c). Color code: Si (blue), O (red), and H (white). Figure 1

Complementary spectroscopic and electrochemical analysis of the sealing of micropores in hexamethyldisilazane plasma polymer films by Al2O3 atomic layer deposition

In the present study, the effects of oxygen plasma treatment and subsequent 2 nm thin Al2O3 film deposition by atomic layer deposition on about 30 nm thick hexamethyldisilazane polymer layers are investigated by using a combination of spectroscopic and electrochemical analysis. The investigations focus on the microporosity of the corresponding films and their structural changes. Upon oxygen plasma treatment, the surface near region of the films is converted into SiOx, and the microporosity is increased. Atomic layer deposition of Al2O3 on the plasma oxidized films leads to the decrease of pore sizes and an effective sealing. A correlation between the film microporosity and the change of hydroxyl groups of the films with the adsorption of water was established by ellipsometric porosimetry and in situ Fourier transform infrared (FTIR) spectroscopy. Moreover, electrochemical analysis provided complementary information on the electrolyte up‐take in the differently conditioned thin films.

Thermal laser separation and high-throughput layer deposition for edge passivation for TOPCon shingle solar cells

This work demonstrates the reduction of cutting-induced losses on tunnel-oxide passivated contact (TOPCon) shingle solar cells via edge passivation using high-throughput layer deposition. TOPCon shingle solar cells with a size of 26.46 mm × 158.75 mm are separated from industrial full-square TOPCon host cells either by laser scribing and mechanical cleaving (LSMC) from the emitter-free rear side or by thermal laser separation (TLS) from the front side. TLS yields up to 0.2%abs more efficient shingle cells directly after singulation in comparison to shingle cells that have been separated by LSMC. Passivated edge technology (PET) is applied by depositing aluminum oxide (Al2O3) layers using two different tools: thermal atomic layer deposition (T-ALD) in a lab-scale tool with a throughput of tens of shingle cells per hour and a high-throughput plasma-enhanced ALD (PE-ALD) prototype tool with a throughput of about 60,000 shingle cells per hour. The energy conversion efficiency of the edge-passivated shingle cells after T-ALD Al2O3 PET is found to be 0.4%abs higher than directly after separation. This gain is the same regardless of whether LSMC or TLS is used for cell separation. For PE-ALD Al2O3 and TLS, a gain of 0.5%abs is measured after PET. Stringing tests with electrically conductive adhesive so far indicate that Al2O3 layers do not negatively affect the resistance of cell to cell interconnections. Thus, low-damage cell cutting in combination with high-throughput Al2O3 layer deposition for edge passivation is a very promising approach to maintain high efficiency for industrial TOPCon solar cells in shingled modules.

Tailoring the electronic states of Pt by atomic layer deposition of Al2O3 for enhanced CO oxidation performance: Experimental and theoretical investigations

Herein, atomic layer deposition (ALD)-Al2O3 films were applied as a medium to modulate the electronic states of the supported Pt. Based on the sacrificial template of ZIF-67, the ternary Co3O4/Pt/Al2O3 catalyst exhibited better performance in catalytic CO oxidation than the binary Co3O4/Pt catalyst. Both experimental and calculation results indicate the existence of charge transport between the Pt and the ALD-Al2O3 films, leading to electron-rich Pt, enhanced O2 affinity, and reduced activation energy. Interestingly, the oxidation resistance of Pt nanoparticles was visualized when annealing Co3O4/Pt/Al2O3 catalyst at high temperatures. Mechanism studies indicate the typical LH mechanism occurred in CO oxidation, showing that the co-adsorbed CO and O2 could be converted to carbonate-type *OCOO intermediates via low energy barriers. At low temperatures, CO2 was mainly produced by the lattice oxygen-mediated M-vK mechanism based on isotope labeling experiments. Our findings provide an alternative way to regulate the electronic states of noble metals by the ALD technique.

Buried Interface Passivation of Perovskite Solar Cells by Atomic Layer Deposition of Al2O3

Despite having long excited carrier lifetimes and high mobilities in hybrid halide perovskite materials, conventional (n-i-p) devices exhibit significant interfacial nonradiative recombination losses that are little understood but limit the radiative efficiency and the overall open-circuit potential. In this Letter, we reveal that the process of spiro-OMeTAD coating on perovskite gives rise to buried defect states, which are detrimental to the devices’ operational stability. We subsequently report a method to passivate these deleterious buried defect states by atomic layer deposition of Al2O3 through controlled precursor dosages on fully functional devices. The process results in notable improvements in the overall device performance, but the underlying root-cause analysis is what we essentially aimed to elucidate here. The reported passivation technique results in (a) an increase in the efficiency primarily due to an increase of VOC by ∼60–70 mV and consequently (b) enhanced photoluminescence and higher electroluminescence quantum efficiency and (c) overall device operational (MPPT) stability under ambient and, exclusively, even under high vacuum (>300 h) conditions, which is otherwise challenging.

Area-selective atomic layer deposition of Al2O3 using inkjet-printed inhibition patterns and lift-off process

Area-selective atomic layer deposition (AS-ALD) has been studied as an alternative method for metal oxide ALD film patterning in the microelectronics industry. To perform AS-ALD, area-deactivation or -activation processes should be implemented in advance using selective surface modification through a photography-based lift-off process and printing techniques. This study introduces a novel approach for Al2O3 AS-ALD using inkjet-printed inhibition patterns. ALD-inhibition patterns with two-layer structures of fluorocarbon (FC) thin film and photoresist (PR) were patterned by inkjet printing. Low surface energy FC thin films were used to block the Al2O3 nucleation and growth during the ALD process, and PR was patterned to easily remove ALD-inhibition patterns using a lift-off process. To demonstrate AS-ALD, an Al2O3 thin film approximately 10 nm thick was deposited via an in-house built system with a multiple-slit gas source. The proposed AS-ALD method was evaluated for topological analysis using atomic force microscopy and surface composition analysis using a time of flight secondary ion mass spectrometry after Al2O3 deposition and a lift-off process. Finally, a 6 nm thick Al2O3 film was selectively patterned by the lift-off process using an inkjet-printed 1.28 μm thick FC-covered PR inhibition pattern.

Surface functionalization of microporous carbon fibers by vapor phase methods for CO2 capture

The removal of excess CO2 from the atmosphere is expected to play a major role in the mitigation of global warming. Solid-state adsorbents, consisting of CO2-binding functionalities on porous supports, can provide high CO2 capture capacities with low energy requirements. In this contribution, we report on the vapor-phase functionalization of porous carbon fibers with amine functionalities. Functionalization occurs either via direct exposure to cyclic azasilane molecules (2,2-dimethoxy-1,6-diaza-2-silacyclooctane) or by the atomic layer deposition of Al2O3 followed by exposure to azasilane. XPS analysis and SEM/energy-dispersive x-ray spectroscopy (EDX) measurements confirmed Al2O3 deposition and amine functionalization. Yet, the two different functionalization approaches led to different amine loadings and distinct differences in porosity upon functionalization, which affected CO2 capture. Combining Al2O3 and amine functionalization resulted in fast CO2 sorption with superior capturing efficiency. In contrast, direct functionalization resulted in strong reduction of the surface area of the porous support and limited gas exchange. We attribute the superior capture efficiency to the porosity level achieved when combining Al2O3 and amine functionalization demonstrating that this approach might be valuable for compact high-throughput direct air, CO2 capture systems.

Modeling incomplete conformality during atomic layer deposition in high aspect ratio structures

Atomic layer deposition allows for precise control over film thickness and conformality. It is a critical enabler of high aspect ratio structures, such as 3D NAND memory, since its self-limiting behavior enables higher conformality than conventional processes. However, as the aspect ratio increases, deviations from complete conformality frequently occur, requiring comprehensive modeling to aid the development of novel technologies. To that end, we present a model for surface coverage during atomic layer deposition where incomplete conformality is present. This model combines existing approaches based on Knudsen diffusion and Langmuir kinetics. Our model expands the state-of-the art by (i) incorporating gas-phase diffusivity through the Bosanquet formula as well as reaction reversibility in the modeling framework first proposed by Yanguas-Gil and Elam, and (ii) being efficiently integrated within level-set topography simulators. The model is manually calibrated to published results of the prototypical atomic layer deposition of Al2O3 from TMA and H2O in lateral high aspect ratio structures. We investigate the temperature dependence of the H2O step, thus extracting an activation energy of 0.178eV which is consistent with recent experiments. In the TMA step, we observe increased accuracy from the Bosanquet formula and we reproduce multiple independent experiments with the same parameter set, highlighting that the model parameters effectively capture the reactor conditions.

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.

Nucleation and growth mechanism for atomic layer deposition of Al2O3 on two-dimensional WS2 monolayer

Nanoelectronics holds significant promise for two-dimensional (2D) semiconducting transition metal dichalcogenide (TMD) applications. On a polycrystalline WS2 monolayer created by metal-organic chemical vapor deposition (MOCVD) at 950 °C, we studied the nucleation, growth, and development of Al2O3 atomic layer deposition (ALD) on a SiO2/Si substrate. In this investigation, we used various complementary characterization methods, such as Raman spectroscopy, elastic recoil detection, atomic force microscopy, and time-of-flight secondary ion mass spectrometry, to understand thoroughly the intrinsic reactivity of WS2. Strong peak intensity changes at the interfaces in the Raman line scans of the SiO2/Si patterns suggest extremely crystalline WS2. After multiple ALD cycles, triangular WS2 crystals were decorated to provide a two-dimensional growth mode with a great selectivity for grain boundaries and step edges. The results of this work can be used for further exploration of the TMD monolayer structure and properties, which is essential for tailoring 2D materials for a specific application in devices.

Passivating Graphene and Suppressing Interfacial Phonon Scattering with Mechanically Transferred Large-Area Ga2O3.

We demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin amorphous Ga2O3 synthesized on liquid Ga metal. A comparison of temperature-dependent electrical measurements of millimeter-scale passivated and bare graphene on SiO2/Si indicates that the passivated graphene maintains its high field effect mobility desirable for applications. Surprisingly, the temperature-dependent resistivity is reduced in passivated graphene over a range of temperatures below 220 K, due to the interplay of screening of the surface optical phonon modes of the SiO2 by high-dielectric-constant Ga2O3 and the relatively high characteristic phonon frequencies of Ga2O3. Raman spectroscopy and electrical measurements indicate that Ga2O3 passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al2O3.

Influence of oxygen-related defects on In-Ga-Sn-O semiconductor due to plasma-enhanced atomic layer deposition of Al2O3 for low-temperature thin-film transistor in terms of electrical properties

In-Ga-Sn-O (IGTO) thin-film transistors (TFTs) were fabricated with Al2O3 gate insulators by plasma-enhanced atomic layer deposition (PEALD) at a temperature of 150 °C. Electrical performances of IGTO TFTs were significantly affected by plasma conditions when Al2O3 was deposited on IGTO thin films by PEALD. Analyses of X-ray photoemission spectroscopy revealed that excessive oxygen species activated at high plasma power above 150 W were chemisorbed to IGTO films to create excess oxygen bonds such as oxygen interstitials (Oi). Distributions of density of states in IGTO bandgap extracted by photonic capacitance-voltage measurement matched well with positive bias stress (PBS) instability of TFTs. Split-oxygen interstitials [Oi (split)] first created on IGTO by oxygen plasma might migrate to the octahedral site by a constant high gate bias to form octahedral-oxygen interstitials [Oi2- (oct)] by capturing electrons under PBS and reside deep states. Significant changes of subthreshold slope in I-V characteristics during the recovery time after removing PBS indicated that these octahedral-oxygen interstitials such as Oi (oct) and Oi2- (oct) obviously originated from Oi (split) initially formed by plasma and that Oi (oct) defects created by a relaxation process acted as a neutral acceptor-like state above Fermi level and deteriorated electrical properties of IGTO TFT.

Curing defects in plasma-enhanced atomic layer deposition of Al2O3 by six methods

In this paper, the Al2O3 film was fabricated by plasma-enhanced ALD (PEALD) using trimethylaluminium (TMA, Al(CH3)3) precursor. For curing defects such as hydroxyl (OH), Hydrogen, and Carbon inside Al2O3, six types of treatments combining rapid thermal annealing (RTA) or H2 plasma were applied. The comprehensive electrical characteristics such as C-VG, flat-band voltage (Vfb) were quantitatively analyzed by comparing interface trap density (Dit), oxide trapped charge density (Not), permittivity, and breakdown field. RTA is crucial to reduce Dit, Not by ∼78.2% and ∼86.7%, respectively, and enhance the breakdown field from 9 MV/cm to 14 MV/cm or higher by forming the interfacial layer. However, it was not adequate to prevent the severe Vfb shift and decrease of permittivity. H2 plasma pre-treatment could be a solution for these problems as well as slightly improve the breakdown property. But the widening of Vfb variation was still concerned because the amount of carbon reduced by H2 plasma treatment is not consistent. Thus, a more precise H2 plasma treatment is necessary for reliable threshold voltage distribution.

Influence of Oxygen-Related Defects on In-Ga-Sn-O Semiconductor Due to Plasma-Enhanced Atomic Layer Deposition of Al2o3 for Low-Temperature Thin-Film Transistor in Terms of Electrical Properties

Influence of Oxygen-Related Defects on In-Ga-Sn-O Semiconductor Due to Plasma-Enhanced Atomic Layer Deposition of Al2o3 for Low-Temperature Thin-Film Transistor in Terms of Electrical Properties

Extending growth inhibition during area-selective atomic layer deposition of Al2O3 on aminosilane-functionalized SiO2.

During area-selective atomic layer deposition (ALD) based on growth inhibitors, nucleation eventually occurs as the metal precursor reacts with the surface through secondary pathways. We show that ALD of Al2O3 on functionalized SiO2 can be significantly delayed by using a lower reactivity, heteroleptic precursor at well below the saturation dose.