Trimethylaluminum Research Articles

Optimizing Aluminum Oxyhydroxide Vapor Phase Infiltration for the Vapor Phase Mordanting of Natural Dyes to Polyester Fabrics

Industrial textile dyeing and finishing processes are a significant environmental concern producing large quantities of wastewater that require significant treatment to remove unused synthetic chemicals. Polyester fabrics in particular utilize high temperatures and chemical carrier agents in their dyeing processes. In this work, we present a method for attaching natural dye materials derived from madder root to polyethylene terephthalate fabrics via the introduction of aluminum oxyhydroxides through vapor phase infiltration. Vapor phase infiltration (VPI) is an emerging polymer modification technique that exposes a polymer to metalorganic precursors that diffuse into the polymer and become entrapped as inorganic clusters. The resulting hybrids have unique properties of both organic and inorganic materials. The VPI process has found significant use in modifying the properties of textile materials including their mechanical and optical properties. Here, without VPI treatment, the PET fabric cannot be dyed with this natural dye. This talk will discuss how controlling the inorganic loading of hybrid AlOx-PET fabrics infiltrated with trimethylaluminum (TMA) and co-reacted with water vapor at 80 ˚C and 140 ˚C can optimize fabrics for dyeability while minimizing impact on key fabric mechanical properties. At low temperatures (80 ˚C) the resulting hybrid contains inorganic clusters not strongly bound to the polymer chain while at high temperatures (140 ˚C) the inorganic is chemically bound via the carbonyl group. Inorganic loading was controlled by varying the dose pressure of TMA (moles of TMA) and fabric mass (moles of carbonyl functional group) during VPI and quantified using thermogravimetric analysis (TGA). The resulting hybrid AlOx-PET fabrics had various inorganic loadings from one weight percent aluminum oxyhydroxide to above twenty weight percent. The hybrid fabrics were then dyed with Alizarin (derived from madder root) and the dye absorbance was quantified with UV-Vis spectroscopy. At low inorganic loadings for both temperatures, the strength of color varied with inorganic content, but a steady-state absorbance was reached at around 1.8 percent inorganic loading. At these low inorganic loadings, the hybrid fabrics maintain key mechanical behaviors such as stiffness (as measured by drape) which is seen to increase significantly with additional inorganic loading. In addition to optimizing strength of color and fabric stiffness, the time to dye saturation was also explored by varying dye times and quantifying with UV-Vis. By exploring dye saturation curves for different inorganic loadings and infiltration temperatures, kinetic information was gathered to further optimize this dyeing process for industrialization. Overall, using VPI as a vapor phase mordanting process to fix natural dyes to PET fabrics illustrates the impact that even small quantities of the vapor deposited inorganic can create enough of a base for dye to adhere to, highlighting the practical use of these fabrics in the field of textile sustainability.

Using Density Functional Theory and Machine Learning to Predict the Binding Energies of Metal-Organics to Organic Functional Groups for Hybrid Material Creation

Understanding chemical interactions between organic and metal-organic molecules has wide-ranging interest to the vapor deposition community for creating hybrid organic-inorganic materials via techniques such as molecular layer deposition and vapor phase infiltration (VPI). In the case of VPI, a vapor-phase metal-organic precursor is infused into the bulk of a polymer and becomes incorporated at the nanoscale through either chemical interaction with the polymer or the formation of a non-volatile species via the introduction of a co-reactant. VPI has applicability in a number of industrially relevant fields including the creation of novel organic-inorganic hybrid membranes which have shown enhanced stability in organic solvents, while retaining high permeance and selectivity. Motivated by this application, this work uses density functional theory (DFT) to explore chemical interactions occurring during the VPI of polymer of intrinsic microporosity (PIM-1, a polymeric membrane material) with trimethylaluminum (TMA) and its co-reaction with water. These computations revealed that the coordination between the polymer and metal-organic is a critical mechanism for the formation of the hybrid and its resultant solvent stability. To expand understanding of this critical characteristic and accelerate the design of organic-inorganic hybrid materials, a DFT dataset of computed binding energies was generated from suitable and representative atomic-level models of several common polymer functional groups and over 100 metal-organic precursors. From this dataset, a predictive machine learning model for the binding energy of metal-organic molecules to polymers has been developed. This predictive model, along with the chemical guidelines obtained from feature analysis, will aid the selection of potential candidates for novel organic-inorganic hybrid membranes as well as hybrid material creation as a whole.

Kinetics of TiCl4 Vapor Phase Infiltration (VPI) into PMMA and the Resulting Thermophysical and Optical Properties of the TiOx -PMMA Hybrids

Vapor phase infiltration (VPI) is a post-polymerization modification technique that imbues inorganic materials into polymers to create organic-inorganic hybrid materials with new properties distinct from the parent polymer. While several VPI precursor-polymer chemistries have been explored, a lack of chemical intuition remains for fully understanding the thermodynamics and kinetics that govern the VPI process. This study seeks to continue to build this knowledge by examining the VPI process kinetics for TiO2 infiltration into PMMA via the use of TiCl4 and H2O precursors. In this research, polymethylmethacrylate / TiO2 hybrid materials are prepared using VPI. The depth of infiltration of the TiO2species into ~200 nm PMMA thin films is studied using x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy and spectroscopic ellipsometry. The kinetics for TiCl4 infiltration increases with both VPI process temperature and TiCl4 exposure time. However, the rates of infiltration are considerably slower than those observed in the more commonly studied trimethylaluminum (TMA) / PMMA system. Even at 150 °C, process times of at least 12 hours are required to fully infiltrate a 200 nm PMMA film whereas using TMA similar films are fully infiltrated within 1 hour at the same process temperature. Films that we believe to be fully infiltrated at 150 °C and 24 hours of TiCl4 exposure have a 6 at% Ti in the innermost bulk, as determined by XPS. Interestingly, unlike AlOx-PMMA hybrids, these TiOx – PMMA hybrids exhibit significant changes in their optical properties. Increased titanium loading leads to a 4% increase in refractive index and increased UV absorbance in the UV range of 270-350nm. Furthermore, films infiltrated at 150 °C and 24 hours of TiCl4 exposure had a 50 % and 70 % reduction in coefficients of thermal expansion (CTE) below and above Tg respectively. Reduced CTE trends with increased titanium loading. We will discuss possible opportunities to use these new properties for various applications.This project is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Enhanced Performance of LiFePO4 Cathodes Protected By Atomic Layer Deposited Ultrathin Alumina Films

The LiFePO4 (LFP) cathode has a theoretical specific capacity of 170 mAh/g. This material is stable, safe, and environmentally benign. Li-ion batteries with LFP cathodes have a long cycle life with excellent charging/discharging performance. In our contribution, we show that the surface modification of the LFP cathode using ultrathin alumina films grown by atomic layer deposition (ALD) can improve Li-ions charge transfer and rate performance of the Li-ion in half-cell configuration with the LFP cathode.We used two types of LFP cathodes in our study with Li-metal as an anode in a half cell configuration. The first LFP electrode had a thickness of 25 μm and consisted of particles of 0.5 - 1 μm in size [1], while the second one (commercial NANOMYTE BE-60E (NEI Corp.)) had a thickness of 70 μm and the average LFP particle size was 2 μm.Ultrathin Al2O3 films were grown on LFP cathodes by ALD at 100 °C using trimethylaluminum (TMA) and water vapors. Due to the self-saturation surface-limited nature of the ALD reaction, even substrates of highly complex morphology can be uniformly coated, where the limitation is the reach of the precursor vapor molecules. The thickness of the ALD layers depends linearly on the number of ALD cycles and ranges from 0.5 to 2 nm for 5 to 20 cycles.Galvanostatic charging/discharging experiments were performed to evaluate the rate capability of the electrodes. Pristine and Al2O3 coated LFP electrodes were laser cut to 18 mm diameter circular electrodes, inserted in the electrochemical test cells PAT-Cell (EL-CELL), and tested using PAT-Tester-x-8 analyzer. LFP with Al2O3 protecting layers was compared to the pristine LFP electrode.For the LFP cathode with the thickness of 25 μm the pristine sample saturates at the specific capacity of 32 mAh/g at 1.8 c-rate, while for the electrode treated with 5 and 20 cycles of Al2O3 the specific capacity dropped to 80 and 60 mAh/g, respectively. The electrodes protected by Al2O3 film always exhibited better rate capability than the pristine sample.A more detailed analysis of the performance was accomplished for the NANOMYTE electrodes. A specific discharge capacity of 160 mAh/g at a c-rate of 0.2 was achieved for both pristine and Al2O3-protected electrodes. Two supercycles with the c-rate 0.2, 0.5, and 1 were applied to the samples. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g for the c-rate 0.2 to about 90 mAh/g at the c-rate 1, while the electrode which was protected by 5 cycles of Al2O3 exhibited a capacity of 120 mAh/g.Investigation of the rate capability fading using electrochemical impedance spectroscopy revealed a gradual increase of the Nyquist plot semicircle diameter as a function of cycles. According to the equivalent circuit model, the semicircle diameter corresponds to the charge transfer at the solid/electrolyte interface. The charge transfer resistance at the solid/electrolyte interface increases with charge/discharge cycling. The charge transfer resistance of the pristine electrode increased more steeply than that of the electrode with 5 cycles of Al2O3. Improvement of the charge transfer resistance of the LFP electrode covered by thin Al2O3 film can be explained by the formation of the Li3.4Al2O3 phase upon lithiation. The diffusivity of the Li ions in the Li3.4Al2O3 phase is several orders of magnitude higher than that of in the Al2O3 film [2]. The results obtained by electrochemical characterization are compared to the X-ray photoelectron spectroscopy performed on samples before and after galvanostatic charging/discharging measurements.[1] A. Fedorkova et al., J. Power Sources 195 (2010) 3907.[2] S. C. Jung et al., J. Phys. Chem. Lett. 4 (2013) 2681.

(Invited) Ligand Addition for Thermal Atomic Layer Etching of Metals

Thermal atomic layer etching (ALE) is typically defined by sequential surface reactions. Thermal ALE can be viewed as the reverse of atomic layer deposition (ALD). Thermal ALE is usually performed with two steps: modification of the surface and removal of the modified surface. The modification can be oxidation, fluorination, or chlorination. The removal step is often a ligand-exchange reaction, creating stable volatile species that leave the surface, leading to a net removal of material. For example, aluminum oxide can be etched using thermal ALE with HF to fluorinate the surface and trimethylaluminum (TMA) to exchange methyl ligands for surface fluoride ligands, resulting in volatile Al(CH3)xFy species.Thermal ALE of metals is particularly challenging because the oxidation state of the metal must be changed to match the oxidation state of the volatile metal etch product. This oxidation is performed in the modification step of thermal ALE. After changing the oxidation state, the metal then produces a stable complex during the volatile release reaction. In this work, Ni and Co ALE are developed by modifying the metal via chlorination using SO2Cl2. Subsequently, the metal is removed by addition of an L ligand to the metal center to create a stable, volatile etch product, MClxLy (Figure 1). The L ligands explored in this work were PMe3 and tetramethyl ethylenediamine (TMEDA).The chlorination and ligand-addition approach for metal ALE is based on the Covalent Bond Classification (CBC) method. X ligands are one-electron donors like Cl and other halogens. L ligands are two-electron donors like PMe3. TMEDA is a bidentate ligand. One TMEDA ligand acts as two L ligands since TMEDA binds to the metal center through the lone electron pairs on the two nitrogen groups. According to the CBC method, nickel complexes typically have NiX2L3 or NiX2L2 configurations. Likewise, cobalt complexes are typically found in the CoX2L4, CoX2L2, or CoX3L3 configurations. The goal for Ni or Co ALE is to create these volatile metal compounds using sequential SO2Cl2 and L ligand surface reactions.Both Ni and Co ALE have been studied with in situ quartz crystal microbalance (QCM) and X-ray reflectivity (XRR) to determine the etch rates. Quadrupole mass spectrometry (QMS) was also employed to determine the volatile metal-containing etch species. Using SO2Cl2 and PMe3, Ni etch rates varied from 0.1-3 Å/cycle at temperatures from 75-200 °C. QMS measurements also identified NiCl2(PMe3)2 (NiX2L2) as the stable volatile etch product. Cobalt ALE using SO2Cl2 and TMEDA displayed etch rates from 1-12 Å/cycle at temperatures from 175-300 °C. QMS measurements also detected CoCl2(TMEDA) (CoX2L2) as the stable volatile etch product. In addition, cobalt can be etched using SO2Cl2 and PMe3 from 70-200 °C, with etch rates between 2-4 Å/cycle. These two Co ALE pathways with TMEDA and PMe3 are complementary with TMEDA useful at higher temperatures and PMe3 useful at lower temperatures.Many other X and L ligands could be used for the halogenation and ligand-addition reactions during metal thermal ALE. The CBC method can be used as a guide to develop the X ligands for surface modification and the L ligands for volatile release. This approach should lead to various other metal ALE processes. Selective metal thermal ALE should also be possible using different X and L ligands. Figure 1

Sequential Infiltration Synthesis of Al2O3 in Biodegradable Polybutylene Succinate: Characterization of the Infiltration Mechanism.

The introduction of inorganic materials into biopolymers has been envisioned as a viable option to modify the optical and structural properties of these polymers and promote their exploitation in different application fields. In this work, the growth of Al2O3 in freestanding ∼30-μm-thick poly(butylene succinate) (PBS) films by sequential infiltration (SIS) at 70 °C via trimethylaluminum (TMA) and H2O precursors was investigated for the first time. The incorporation of Al2O3 into the PBS matrix was clearly demonstrated by XPS analysis and SEM-EDX cross-sectional images showing a homogeneous Al2O3 distribution inside the PBS films. Raman measurements on infiltrated freestanding PBS show a reduction of the signal related to the ester carbonyl group as compared to pristine freestanding PBS films. Accordingly, FTIR and NMR characterization highlighted that the ester group is involved in polymer–precursor interaction, leading to the formation of an aliphatic group and the concomitant rupture of the main polymeric chain. Al2O3 mass uptake as a function of the number of SIS cycles was studied by infiltration in thin PBS films spin-coated on Si substrates ranging from 30 to 70 nm. Mass uptake in the PBS films was found to be much higher than in standard poly(methyl methacrylate) (PMMA) films, under the same process conditions. Considering that the density of reactive sites in the two polymers is roughly the same, the observed difference in Al2O3 mass uptake is explained based on the different free volume of these polymers and the specific reaction mechanism proposed for PBS. These results assessed the possibility to use SIS as a tool for the growth of metal oxides into biopolymers, paving the way to the synthesis of organic–inorganic hybrid materials with tailored characteristics.

Low-Temperature Atomic Layer Deposition of AlN Using Trimethyl Aluminum and Plasma Excited Ar Diluted Ammonia

Low-Temperature Atomic Layer Deposition of AlN Using Trimethyl Aluminum and Plasma Excited Ar Diluted Ammonia

Thickness-dependent physical and nanomechanical properties of [formula omitted] thin films

A set of undoped AlxGa1−xN epilayers with different thicknesses were grown on (0001) sapphire substrates using metal-organic chemical vapor deposition (MOCVD) technique, using the same gas-phase composition of trimethylaluminum (TMAl) and trimethylgallium (TMGa). Giving that the first growth stage is crucial for the successful fabrication of AlxGa1-xN epilayers; thus, SiN nano-mask, as an alternative method to nanoimprint lithography (NIL) which is used for patterning substrates, was deposited on sapphire substrate. Indeed, SiN treatment initiates the three-dimensional (3D) growth mode to efficiently decrease the threading dislocation density. It was found that depending on the film surface coalescence degree, the physical and nanomechanical properties are thoroughly dependent. As the non-coalescent surface is present, the porosity effects are dominant. As soon as the film thickness attains the surface coalescence, the Al incorporation is enhanced and convoyed with it point defects. Despite the decrease of the threading dislocations along with the film thickness evolution, it was observed that the physical properties are slightly decreased and the nanomechanical properties are improved. This is likely related to point defect interaction with nucleated dislocations. Moreover, the defects did not severally affect the plastic deformation capacity (ductility) of AlxGa1-xN films, where high indentation force was applied and no failure was revealed. Therefore, the balance between AlxGa1−xN physical and nanomechanical performances devotes to manufacture a wider range of efficient UV devices.

Understanding Physicochemical Mechanisms of Sequential Infiltration Synthesis toward Rational Process Design for Uniform Incorporation of Metal Oxides.

Sequential infiltration synthesis (SIS) is a novel technique for fabricating organic–inorganic hybrid materials and porous inorganic materials by leveraging the diffusion of gas-phase precursors into a polymer matrix and chemical reactions between the precursors to synthesize inorganic materials therein. This study aims to obtain a fundamental understanding of the physicochemical mechanisms behind SIS, from which the SIS processing conditions are rationally designed to obtain precise control over the distribution of metal oxides. Herein, in situ FTIR spectroscopy was correlated with various ex situ characterization techniques to study a model system involving the growth of aluminum oxides in poly(methyl methacrylate) using trimethyl aluminum (TMA) and water as the metal precursor and co-reactant, respectively. We identified the prominent chemical states of the sorbed TMA precursors: (1) freely diffusing precursors, (2) weakly bound precursors, and (3) precursors strongly bonded to pre-existing oxide clusters and studied how their relative contributions to oxide formation vary in relation to the changes in the rate-limiting step under different growth conditions. Finally, we demonstrate that uniform incorporation of metal oxide is realized by a rational design of processing conditions, by which the major chemical species contributing to oxide formation is modulated.

Resolving the Heat of Trimethylaluminum and Water Atomic Layer Deposition Half-Reactions.

Atomic layer deposition (ALD) is a surface synthesis technique that is characterized by self-limiting reactions between gas-phase precursors and a solid substrate. Although ALD processes have been demonstrated that span the periodic table, a greater understanding of the surface chemistry that affords ALD is necessary to enable greater precision, including area- and site-selective growth. We offer new insight into the thermodynamics and kinetics of the trimethylaluminum (TMA) and H2O ALD half-reactions with calibrated and time-resolved in situ pyroelectric calorimetry. The half-reactions produce 3.46 and 2.76 eV/Al heat, respectively, which is greater than the heat predicted by computational models based on crystalline Al2O3 substrates and closely aligned with the heat predicted by standard heats of formation. The pyroelectric thin-film calorimeter offers submillisecond temporal resolution that uniquely and clearly resolves precursor delivery and reaction kinetics. Both half-reactions are observed to exhibit multiple kinetic rates, with average TMA half-reaction rates at least 2 orders of magnitude faster than the H2O half-reaction kinetics. Comparing the experimental heat with published computational literature and additional first-principles modeling highlights the need to refine our models and mechanistic understanding of even the most ubiquitous ALD reactions.

Vapor-Phase Infiltration of Polymer of Intrinsic Microporosity 1 (PIM-1) with Trimethylaluminum (TMA) and Water: A Combined Computational and Experimental Study.

Vapor-phase infiltration, a postpolymerization modification process, has demonstrated the ability to create organic-inorganic hybrid membranes with excellent stability in organic solvents while maintaining critical membrane properties of high permeability and selectivity. However, the chemical reaction pathways that occur during VPI and their implications on the hybrid membrane stability are poorly understood. This paper combines in situ quartz crystal microbalance gravimetry (QCM) and ex situ chemical characterization with first-principles simulations at the atomic scale to study each processing step in the infiltration of polymer of intrinsic microporosity 1 (PIM-1) with trimethylaluminum (TMA) and its co-reaction with water vapor. Building upon results from in situ QCM experiments and SEM/EDX, which find TMA remains within PIM-1 even under long desorption times, density functional theory (DFT) simulations identify that an energetically stable coordination forms between the metal-organic precursor and PIM-1's nitrile functional group during the precursor exposure step of VPI. In the subsequent water vapor exposure step, the system undergoes a series of exothermic reactions to form the final hybrid membrane. DFT simulations indicate that these reaction pathways result in aluminum oxyhydroxide species consistent with ex situ XPS and FTIR characterization. Both NMR and DFT simulations suggest that the final aluminum structure is primarily 6-fold coordinated and that the aluminum is at least dimerized, if not further "polymerized". According to the simulations, coordination of the aluminum with at least one nitrile group from the PIM-1 appears to weaken significantly as the final inorganic structure emerges but remains present to enable the formation of the 6-fold coordination species. Water molecules are proposed to complete the coordination complex without further increasing the aluminum's oxidation state. This study provides new insights into the infiltration process and the chemical structure of the final hybrid membrane including support for the possible mechanism of solvent stability.

A toolbox for easy entry low wavenumber in situ atomic layer deposition transmission FTIR spectroscopy studies.

A detailed description of a flexible and portable atomic layer deposition (ALD) system is presented for conducting in situ Fourier transform infrared (FTIR) absorption spectroscopy studies during the evolution and growth of ALD films. The system is directly integrated with a commercial FTIR spectrometer (Bruker Vertex 80V) to avoid the necessity of an external optical path to the instrument, thereby mitigating complexity and optical losses. In this work, we use potassium bromide (KBr) with a 5nm layer of sputtered Si as a substrate due to higher infrared transmittance when compared to a single-side polished Si wafer. The FTIR absorption study is conducted at normal incidence in transmission mode using a deuterated L-alanine doped triglycine sulfate (DTGS) detector owing to its potential applicability for reliable measurements at wavenumbers below ∼700cm-1. We demonstrate this by measuring ex situ the transverse optical phonon of bulk Al2O3 centered at 680cm-1. The integrity and functionality of the system to track the nucleation stage are validated by conducting in situ FTIR absorption measurements of Al2O3 using tri-methyl aluminum (TMA) and H2O. The measured IR absorption spectra for the Al2O3 growth after each cycle of TMA and H2O show the formation and removal of CH3 (2800-3000cm-1) groups on the substrate surface and CH4 (3016 and 1306cm-1) molecules in the reactor, thus confirming the successful tracking of ligand exchange. Thus, this instrument, together with the choice of KBr as substrate, can enable straightforward ALD nucleation studies using a DTGS detector having sufficient signal without additional optical setup and modifications to off-the-shelf FTIR systems that allow low wavenumber experiments.

Adsorption and surface reaction of isopropyl alcohol on SiO2 surfaces

In this study, we investigated the adsorption and surface reaction of isopropyl alcohol (IPA) gas on silicon dioxide (SiO2) surfaces. The temperature dependence of the decomposition behavior of IPA and the effect on the SiO2 surface, such as reduction of SiO2 during IPA treatment, were studied. The chemical structures of the SiO2 surfaces before and after IPA treatment were analyzed by x-ray photoelectron spectroscopy (XPS). The decomposition behavior of IPA was investigated using an in-line evaluation system equipped with a SiO2 reactor and Fourier-transform infrared spectroscopy (FT-IR). During IPA treatment at temperatures above 150 °C, different types of organic matter were deposited on the SiO2 surfaces depending on the temperature. SiO2 was not reduced, and its surface states were not changed at temperatures below 350 °C. In addition, we investigated the amount of trimethylaluminium (TMAl) adsorbed on SiO2 surface with and without IPA treatment. As a result, the amount of TMAl adsorbed on SiO2 surface was reduced by about 25% by the IPA treatment. We found that the organic matter obtained by IPA treatment partially inhibited the adsorption of the TMAl gas on SiO2 surfaces. These findings will be useful for the use of IPA in the advanced semiconductor manufacturing such as in area-selective processes.

Formation of Free Hydrogen Gas By Annealing ALD-Al2O3/Si Stacked Structure

1. IntroductionAtomic layer depositions (ALD) of Al2O3 films are very essential technique to realize next generation electronic devices thanks to their high-k properties [1]. However, ALD-Al2O3 films usually suffer blistering during thermal treatments, which have caused serious problems for decades in the field of device fabrication [2]. Many groups have studied the cause of this phenomenon, and various models have been proposed. such as, stress at the interface between Al2O3 and Si [3], diffusion of Si atoms at the interface[4], residual H2O in the film after the ALD process [5], and aggregation of hydrogen atoms at the Al2O3/Si interface [6], and so on. However, the actual mechanism has hitherto remained unclear due to a lack of conclusive evidence. Here, in this study, we have tried to reveal the origin of this phenomenon using spectroscopic measurements [7]. As a result, we have succeeded in directly identifying the gas inside the blisters, which can be a concrete evidence to reveal the roots of a phenomenon that has long been obscured.2. Experimental ProcedureIn the experiment, (100) oriented Si substrates with resistivity of 0.1-0.5 W∙cm were carried out. After cleaning the substrates by acetone, sulfuric-acid hydrogen-peroxide mixture solution, and hydrofluoric acid solution, all the substrates were loaded into ALD chamber which was heated up to 300oC. Then, Al2O3 layer with ~108 nm thickness was deposited on the substrates with conventional thermal ALD process using trimethylaluminum (TMA) and H2O as precursor gasses. After deposition, samples were annealed in rapid thermal annealing (RTA) furnace for 5 min with 400 – 1000 oC at N2 ambient. Finally the samples were characterized by laser microscopy, field emission scanning electron microscopy (FE-SEM), spectroscopic ellipsometry, and Raman spectroscopy.3. Results and DiscussionsFigs. 1(a) and 1(b) show typical microscopic image of sample before, and after RTA (500oC, 5 min), respectively. We can clearly see that several blisters appear by annealing the samples, while there was no such sign before annealing. From the microscopic observations, we have summarized density of blisters as a function of RTA temperature in Fig. 2. Here, we can clearly see that by increasing RTA temperature, blister density increases, which is largely consistent with a previous result reported by O. Beldarrain et al, where 400-cycle Al2O3 layers were grown at 200 oC.To discuss the origin of the blister, we have conducted cross-sectional SEM observations of the formed blisters. Fig. 3 shows a typical SEM image of a blister after annealed at 500oC. The cross-sectional SEM observations clearly show that the blisters are completely hollow underneath. The surface of the flat Si substrate can also be seen under the blister, indicating that the upper Al2O3 film has completely delaminated from the interface between Si and Al2O3. From these results, we have speculated that blistering of Al2O3 after annealing is due to outgassing from the Al2O3/Si interface. Here, we came up with an idea that by identifying the gas inside the blisters, we can clarify the cause of this phenomenon.To identify the content inside blisters, Raman spectroscopy was carried out. The 532 nm wavelength laser used for Raman measurements can pass completely through Al2O3, making it possible to measure the gas inside without destroying the blisters. Fig. 4 shows a typical result of the Raman measurement of a blister of a sample after RTA (500oC). Here, as a result, characteristic spectra with peaks at positions ~4126, ~4144, ~4156, and ~4162 cm-1 were successfully observed. These four peaks can be assigned as peaks due to the difference in the rotational-quantum-number (J) of H2 as shown in Fig. 4, which is typical spectra of free H2 gas. These results provide evidence that blister formation is caused by the generation of hydrogen gas from the Al2O3/Si interface, a finding that is of great importance in clarifying the physics of blister formation mechanisms.In the presentation, we will also present details on the physics of hydrogen gas generation and methods to suppress blister formation.[References][1] R. Zhang, et al., IEEE Trans. Electron Devices 59, 335-341, (2012).[2] G Dingemans, et al., J. Vac. Sci. Technol. A, 30, 040802, (2012).[3] J. Thurn., et al., J. Mater. Sci. 39, 4799, (2004)[4] M. Broas, et al., Appl. Phys. Lett. 111, 141606, (2017)[5] O. Beldarrain, et al., J. Vac. Sci. Technol. A, 31, 01A128 (2013)[6] D. G. Xie, et al., Nat. Mater., 14, 899, (2015).[7] R. Matsumura, et al., accepted to ACS Applied Materials & Interfaces, https://doi.org/10.1021/acsami.1c20660 Figure 1

First-principles study of electronic properties of amine ligand-capped CsPbBr3 surface with organo-metallic alumina precursor treatment

Water and oxygen stability has been one of the major bottlenecks in practical application of perovskite quantum dots (PeQDs). Recently, ultra-thin alumina via atomic layer deposition (ALD) has been used as protective coating to improve the stability of PeQDs. However, the use of organo-metallic trimethylaluminum (TMA) precursor is typically accompanied by undesirable photoluminescence quenching of PeQDs. We investigate in detail the interaction mechanism between TMA and amine ligands-capped PeQDs to shed light on the origin of such quenching. First-principles calculations reveal that TMA is highly reactive to insert into amine ligands and PeQDs, which disrupts the bonding between ligand and the PeQDs surface. The demethylation of the insertion product would induce substantial trap states on the PeQDs surface, resulting in the degradation of photoluminescence. Methyl aluminum diisopropoxide (MADI) with asymmetric structure is proposed as an ALD precursor for the treatment of PeQDs. Due to the tight binding of the isopropyl groups to the Al atom, MADI can effectively avoid successive dissociation after reaction with surface ligands, avoiding the formation of trap states. This work highlights the importance of precursor engineering for ligand passivation and provides guidance to the design of precursors with minimal trap-states for highly efficient and stable PeQDs.

Multiple layers of aluminum silicate and silicon dioxide deposited by room-temperature atomic layer deposition for enhanced cation sorption

Multiple layers of aluminum silicate and SiO2 are deposited at room temperature (RT) by repeating a combination of aluminum-silicate atomic layer deposition (ALD) and a plural number of SiO2 ALDs. The RT-ALD is performed by using precursors of tris(dimethylamino)silane and trimethyl aluminum (TMA). The oxidizing gas is plasma excited humidified Ar. A cross-sectional transmission electron microscope and angle resolved x-ray photoelectron spectroscopy suggest that aluminum from the TMA molecule is diffused to SiO2 to form an aluminum silicate layer with the Al rich surface at RT. The deposited film shows an enhanced Na sorption in an NaCl aqueous solution of 10 mM, compared with the pure aluminum silicate layer without the SiO2 layer. It is assumed that the bond formation of Al–O–Al in the aluminum silicate film is suppressed by limiting the thickness of the aluminum silicate layer. Multiple films are also applicable for Cs and K ion sorption. The effects of the multiple layers on the ion sorptivity are discussed in the paper.

Al2O3-Coated Si-Alloy Prepared by Atomic Layer Deposition as Anodes for Lithium-Ion Batteries.

Silicon-based anodes can increase the energy density of Li-ion batteries (LIBs) owing to their large weights and volumetric capacities. However, repeated charging and discharging can rapidly deteriorate the electrochemical properties because of a large volume change in the electrode. In this study, a commercial Fe-Si powder was coated with Al2O3 layers of different thicknesses via atomic layer deposition (ALD) to prevent the volume expansion of Si and suppress the formation of crack-induced solid electrolyte interfaces. The Al2O3 content was controlled by adjusting the trimethyl aluminum exposure time, and higher Al2O3 contents significantly improved the electrochemical properties. In 300 cycles, the capacity retention rate of a pouch full-cell containing the fabricated anodes increased from 69.8% to 72.3% and 79.1% depending on the Al2O3 content. The powder characterization and coin and pouch cell cycle evaluation results confirmed the formation of an Al2O3 layer on the powder surface. Furthermore, the expansion rate observed during the charging/discharging of the pouch cell indicated that the deposited layer suppressed the powder expansion and improved the cell stability. Thus, the performance of an LIB containing Si-alloy anodes can be improved by coating an ALD-synthesized protective Al2O3 layer.

Atomic and Molecular Layer Deposition of Chiral Thin Films Showing up to 99% Spin Selective Transport.

Spin electronics is delivering a much desired combination of properties such as high speed, low power, and high device densities for the next generation of memory devices. Utilizing chiral-induced spin selectivity (CISS) effect is a promising path toward efficient and simple spintronic devices. To be compatible with state-of-the-art integrated circuits manufacturing methodologies, vapor phase methodologies for deposition of spin filtering layers are needed. Here, we present vapor phase deposition of hybrid organic-inorganic thin films with embedded chirality. The deposition scheme relies on a combination of atomic and molecular layer deposition (A/MLD) utilizing enantiomeric pure alaninol molecular precursors combined with trimethyl aluminum (TMA) and water. The A/MLD deposition method deliver highly conformal thin films allowing the fabrication of several types of nanometric scale spintronic devices. The devices showed high spin polarization (close to 100%) for 5 nm thick spin filter layer deposited by A/MLD. The procedure is compatible with common device processing methodologies.

Structurally characterized aluminum alkoxide derivatives for aerosol spray materials production

The synthesis of a family of aluminum alkoxides was undertaken via the reaction of trimethyl aluminum (Al(CH3)3) using a series of sterically varied ortho-substituted phenols (H-OAr), including: 2-methyl phenol (H-oMP), 2-isopropyl phenol (H-oPP), 2-phenyl phenol (H-oPhP), 2,6-di-methyl phenol (H-DMP), 2,6-di-isopropyl phenol (H-DIP), and 2,6-di-phenyl phenol (H-DPhP). The products isolated using the least sterically encumbered phenoxides proved to generate the homoleptic compounds: [(oMP)Al((μ-oMP)2Al(oMP)2)2] (1), and [Al(μ-oPP)(oPP)2]2 (2), [Al(μ-oPP)(oPP)2(THF)]2 (2-THF), and [Al(μ-oPhP)(oPhP)2]2 (3). As the steric bulk was increased only partial substitution was achieved forming the alkyl, alkoxide compounds: [Al(μ-OAr)(CH3)(OAr)]2 (OAr = trans-DMP (4a), cis-DIP (5a), trans-DPhP (6a)). Sub-stoichiometric metathesis reactions for the smaller OAr ligands were undertaken to produce a series of [Al(CH3)3-x(OAr)x]2 where × = 2: OAr = trans-oMP (1a); x = 1, OAr = oMP (1b), and DMP (4b). Alternatively, the use of neo-pentanol (H-ONep) led to the homoleptic species [(ONep)Al((μ-ONep)2Al(ONep)2)2] (7) and heteroleptic [Al(μ-ONep)(CH3)2]2 (7b). Efforts to generate 7 from [Al(OPri)3]4 resulted in the production of the mixed ligated species [Al4(μ-OPri)6(ONep)6] (8). The compounds were fully characterized using a variety of analytical tools as well as multinuclear NMR (1H, 13C, 27Al) spectroscopy. Select species were used for aerosol spray pyrolysis for the anticipated production of alumina (Al2O3) materials. The final products from 1, 1b, 7, and 7b proved to generate amorphous mesoparticles of size 2.1(0.1), 2.6(0.2), 2.7(0.2), and 2.5(0.2) μm, respectively as determined by SEM and pXRD analyses. Data collected using Single Particle Aerosol Mass Spectrometry (SPAMS) revealed that Al0 particles had been produced instead of the expected Al2O3 ceramic materials.

Atomic Layer Engineering of Aluminum‐Doped Zinc Oxide Films for Efficient and Stable Perovskite Solar Cells

AbstractAtomic layer deposition (ALD) has been considered as an efficient method to deposit high quality and uniform thin films of various electron transport materials for perovskite solar cells (PSCs). Here, the effect of deposition sequence in the ALD process of aluminum‐doped zinc oxide (AZO) films on the performance and stability of PSCs is investigated. Particularly, the surface of AZO film is terminated by diethylzinc (DEZ)/H2O (AZO‐1) or trimethylaluminum (TMA)/H2O pulse (AZO‐2), and investigated with surface‐sensitive X‐ray photoelectron spectroscopy technique. It is observed that AZO‐2 significantly enhances the thermal stability of the upcoming methylammonium lead iodide (MAPbI3) layer and facilitates charge transport at the interface as evidenced by photoluminescence spectroscopes and favorable interfacial band alignment. Finally, planar‐type PSC with AZO‐2 layer exhibits a champion power conversion efficiency of 18.09% with negligible hysteresis and retains 82% of the initial efficiency after aging for 100 h under ambient conditions (relative humidity 40 ± 5%). These results highlight the importance of atomic layer engineering for developing efficient and stable PSCs.