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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Design and Characterization of ALD-Based Overcoats for Supported Metal Nanoparticle Catalysts

Supported metal nanoparticle (SMN) catalysts are enormously crucial for many catalytic applications. However, catalyst deactivation, caused by sintering and coke formation, is a ubiquitous problem that significantly undermines catalytic processing economics. The application of material overcoating onto supported metal nanoparticles by atomic layer deposition (ALD) offers the solution to inhibit catalyst deactivation. Herein, we discuss examples in which ALD has been used to stabilize SMN catalysts in gaseous and aqueous-phase reactions. We highlight the ALD tools and methods in coating high-surface-area catalysts. Besides, various techniques are introduced to understand better how to characterize the overcoating layer and the catalyst itself. Finally, the outlook for new techniques to characterize the ALD overcoated catalytic materials is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Electro-chemo-mechanical evolution of sulfide solid electrolyte/Li metal interfaces: operando analysis and ALD interlayer effects

Sulfide solid electrolytes (SE) show promise for high-performance solid-state batteries because of their high ionic conductivity and ease of processing. However, sulfide electrolytes have suffered from chemical and electrochemical instability against Li metal anodes. In this paper, we use a suite of in situ/operando microscopy and spectroscopy techniques to demonstrate that Al 2 O 3 interlayers deposited using atomic layer deposition (ALD) delay degradation at the Li/LGPS interface by modifying the solid electrolyte interphase (SEI) chemistry and morphology. Optical and scanning electron microscopy are used to rationalize the electrochemical response of the system, which is attributed to a delayed onset of mechanical degradation at the interface when ALD interlayers are used. Operando X-ray photoelectron spectroscopy demonstrates that the dynamic evolution of SEI chemistry is impacted by the presence of the ALD interlayer. In situ Auger spectroscopy and operando optical microscopy provide visual evidence of spatial heterogeneity of Li plating, which is attributed to the chemo-mechanical degradation of the ALD interphase. The implications of these observations provide valuable insights toward the development of robust interlayers for solid-state batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Enhancing Coking Tolerance and Stability of SOFC Anodes Using Atomic Layer Deposition (ALD) of Oxide Thin Films

The overall objective of this project was to use atomic layer deposition (ALD) to add modifiers to the surfaces of conventional Ni-YSZ cermet, solid oxide fuel cell (SOFC) anodes to enhance both their tolerance to hydrocarbon fuels by decreasing their propensity to form coke deposits, and to increase redox stability. Studies of the use of ALD to modify analogous supported metal powder catalysts were also added to the scope of the project in response to our industrial partner, Atrex going out of business. The initial portion of the program focused on designing and building the ALD reactor required for deposition of the oxide modifier films. Studies of the oxide modifier films on the coking tolerance and of redox properties of Ni-cermet anodes were then carried out. These studies demonstrated that while surface oxide modifiers were able to impart some coking resistance this only occurred for a relatively small range of operating conditions (e.g., temperature, steam-to-fuel ratio, etc.) and not at the level that would be required for operating in methane fuel at low steam-to-methane ratios. In light of this observation, we focused on assessing another approach to enhance anode coking resistance which eliminated bulk Ni from the anode. This approach made use of electronically conducting perovskite films to provide electrical conductivity in the anode, while using small amounts of Ni or other metals, such as Pt, deposited using ALD as the anode oxidation catalyst. This approach proved to be quite promising at both imparting coking resistance and redox stability.

03 NATURAL GAS↗
DOE OSTI2018

A Characterization Study of Reactive Sites in ALD-Synthesized WOx/ZrO2 Catalysts

A series of ZrO2-supported WOx catalysts were prepared using atomic layer deposition (ALD) with W(CO)6, and were then compared to a WOx/ZrO2 catalyst prepared via conventional impregnation. The types of sites present in these samples were characterized using temperature-programmed desorption/thermogravimetric analysis (TPD-TGA) measurements with 2-propanol and 2-propanamine. Weight changes showed that the WOx catalysts grew at a rate of 8.8 × 1017 W atoms/m2 per cycle. Scanning transmission electron microscopy/energy-dispersive spectroscopy (STEM-EDS) indicated that WOx was deposited uniformly, as did the 2-propanol TPD-TGA results, which showed that ZrO2 was completely covered after five ALD cycles. Furthermore, 2-propanamine TPD-TGA demonstrated the presence of three types of catalytic sites, the concentrations of which changed with the number of ALD cycles: dehydrogenation sites associated with ZrO2, Brønsted-acid sites associated with monolayer WOx clusters, and oxidation sites associated with higher WOx coverages. The Brønsted sites were not formed via ALD of WOx on SiO2. The reaction rates for 2-propanol dehydration were correlated with the concentration of Brønsted sites. While TPD-TGA of 2-propanamine did not differentiate the strength of Brønsted-acid sites, H–D exchange between D2O and either toluene or chlorobenzene indicated that the Brønsted sites in tungstated zirconia were much weaker than those in H-ZSM-5 zeolites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2008

Using ALD To Bond CNTs to Substrates and Matrices

Atomic-layer deposition (ALD) has been shown to be effective as a means of coating carbon nanotubes (CNTs) with layers of Al2O3 that form strong bonds between the CNTs and the substrates on which the CNTs are grown. ALD is a previously developed vaporphase thin-film-growth technique. ALD differs from conventional chemical vapor deposition, in which material is deposited continually by thermal decomposition of a precursor gas. In ALD, material is deposited one layer of atoms at a time because the deposition process is self-limiting and driven by chemical reactions between the precursor gas and the surface of the substrate or the previously deposited layer.

Wong, Eric W.↗
DOE OSTI2019

Application of time-of-flight secondary ion mass spectrometry to the detection of surface intermediates during the first cycle of atomic layer deposition (ALD) of platinum on silica surfaces

Atomic layer deposition (ALD) has become the method of choice for many applications requiring the controlled growth of thin films on solid surfaces. Yet, the use of metalorganic precursors typical in these depositions adds significant complexity to the chemistry involved. Unfortunately, it is difficult to obtain direct information about the surface species that participate in the reaction mechanisms of ALD. Here we illustrate the value of using time-of-flight secondary ion mass spectrometry (ToF-SIMS) for this purpose. A specific example is provided, a study of the first cycle of deposition of platinum using trimethyl(methylcyclopentadienyl)platinum (IV), or MeCpPt(CH 3 ) 3, on silicon oxide surfaces. In previous investigations of this process, we have determined that the low reactivity of the MeCpPt(CH 3 ) 3 precursor, which hinders fast deposition, can be partially overcome by gas-phase electron-impact activation. What has not been clear is what chemical species form on the solid surface as a result of such activation. Here we show that the MeCp ligand is quite stable and that it remains intact and coordinated to the Pt atoms upon adsorption on the surface. It was also established that some of the methyl groups may remain bound to the Pt center: the main species detected on the silicon oxide surfaces were MeCpPt and MeCpPt(CH 3 ). On the other hand, it appears that no Pt intermediates without MeCp ligands are formed during this initial adsorption. Finally, O 2 treatment of these surfaces at elevated temperature to complete the first ALD cycle leads to the complete removal of all the organic ligands: no evidence for MeCp or methyl groups is seen in the ToF-SIMS traces from the final samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

High-Rate Spinel LiMn 2 O 4 (LMO) Following Carbonate Removal and Formation of Li-Rich Interface by ALD Treatment

Recent work has identified enhanced charge-storage capacity in the spinel lithium manganese oxide (LiMn 2 O 4 ; LMO) lithium-ion battery cathode upon a single atomic layer deposition (ALD) cycle composed of one chemical exposure of trimethylaluminum (TMA) and one exposure of water (H 2 O). In this paper, we report further study of the rate capability following one TMA/H 2 O exposure and identify enhanced rate capability versus pristine LMO. To understand this effect, we experimentally probe the surface composition of LMO with TMA/H 2 O treatment using X-ray photoelectron spectroscopy measurements with inert transfer. This includes a study of the LMO surface properties following TMA exposure before exposure to H 2 O. We identify the removal of a surface carbonate layer from LMO upon TMA exposure and the formation of a Li-rich aluminum oxide surface layer upon subsequent H 2 O exposure. We also observe a previously undescribed phenomenon of Li ions depleting from the LMO surface upon TMA exposure and returning upon H 2 O exposure. These effects are connected with the enhanced rate capability of ALD-coated LMO and are related to a range of emerging studies on carbonate surface layers in battery cathodes, as well as the use of ALD to stabilize battery interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Surface Zeta Potential of ALD-Grown Metal-Oxide Films

Membranes are among the most promising technologies for energy-efficient and highly selective separations, and the surface-charge property of membranes plays a critical role in their broad applications. Atomic layer deposition (ALD) can deposit materials uniformly and with high precision and controllability on arbitrarily complex and large substrates, which renders it a promising method to tune the electrostatics of water/solid interfaces. However, a systematic study of surface-charge properties of ALD-grown films in aqueous environments is still lacking. In this work, 17 ALD-grown metal-oxide films are synthesized, and a comprehensive study of their water stability, wetting properties, and surface-charge properties is provided. Furthermore, this work represents a resource guide for researchers and ultimately for materials and process engineers, seeking to tailor interfacial charge properties of membranes and other porous water treatment components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Degradation & Performance Studies of ALD-Stabilized Nano-Composite SOFC Cathodes

This work showed, definitively, for the first time, that zirconia Atomic Layer Deposited (ALD) overcoats improve the stability of Solid Oxide Fuel Cell (SOFC) cathodes by chemically gettering interfacial Sr that has segregated out of lanthanum strontium cobalt iron oxide (LSCF). The optimum ALD ZrO 2 overcoat thickness was found to be ≥5 nm and <10 nm. Gadolinium doped ceria (GDC) pre-infiltration was also shown, for the first time, to improve SOFC cathode stability through the chemical getting of Sr at the LSCF-backbone and LSCF-gas interfaces. Due to the fact that it can be performed easily in air on large-area electrodes, GDC pre-infiltration is likely more commercially viable than ALD ZrO 2 overcoating as an interfacial Sr gettering technique. Combining ZrO 2 overcoating with GDC pre-infiltration was not successful because the GDC nano-particles gettered the ZrO 2 overcoat instead of the interfacial Sr.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2018

Modification of Radiator Pigments by Atomic Layer Deposition (ALD)

The optical and physical properties of spacecraft radiator coatings are dictated by orbital environmental conditions. For example, coatings must adequately dissipate charge buildup when orbital conditions, such as polar, geostationary or gravity neutral, result in surface charging. Current dissipation techniques include depositing a layer of ITO (indium tin oxide) on the radiator surface in a high temperature process. Other examples include the application of variable emittance coatings such as the use of VO2 to optimize radiator size, allowing for a decrease in heater power budget. The application of these enhanced coatings must be such that the properties in question are tailored to mission-specific requirements. Modification of these coatings can be accomplished during coating application preprocessing by using a deposition technique prevalent in the semiconductor micro processing industry called Atomic Layer Deposition (ALD). The preprocessing is rendered directly on the coating dry pigment before binding. ALD is a cost effective nano-manufacturing technique that allows for the conformal coating of substrates with atomic-level thickness control in a benign temperature and pressure environment. Through the introduction of paired precursor gases, thin films can be deposited on a myriad of substrates ranging from glass, polymers, aerogels, metals, powders, and other high aspect-ratio micro- and nano-structures. By providing atomic-level control, where single layers of atoms can be deposited, the fabrication of metal transparent films, precise nano-laminates, and coatings of nano-channels and pores is achievable. We have demonstrated a method for the ALD of In2O3 and ITO films on a variety of substrates from Si(100) wafers, glass slides, and on Z93P pigments (patent pending). The results indicate excellent growth of 4-22 nm thick films demonstrating an order of magnitude decrease in resistivity on the pigments.

ITO↗
DOE OSTI2024

Method of making thin films of sodium fluorides and their derivatives by ALD

A method of making thin films of sodium fluorides and their derivatives by atomic layer deposition (“ALD”). A sodium precursor is exposed to a substrate in an ALD reactor. The sodium precursor is purged, leaving the substrate with a sodium intermediate bound thereon. A fluorine precursor is exposed to the bound sodium intermediate in the ALD reactor. The fluorine precursor is purged and a sodium fluoride film is formed on the substrate.

Mane, Anil U.↗
DOE OSTI2021

Reactor scale simulations of ALD and ALE: Ideal and non-ideal self-limited processes in a cylindrical and a 300 mm wafer cross-flow reactor

Here, we have developed a simulation tool to model self-limited processes such as atomic layer deposition (ALD) and atomic layer etching inside reactors of arbitrary geometry as well the output of in situ quartz crystal microbalance and mass spectrometry. We have applied this model to two standard types of cross-flow reactors: a cylindrical tube reactor and a model 300 mm wafer reactor, and explored both ideal and nonideal self-limited kinetics. The model results are in agreement with experimental results and analytic expressions obtained using a simple plug-flow model for the cylindrical tube reactor. We also extended the simulations to consider two nonideal self-limited processes: soft-saturating processes characterized by a slow reaction pathway and processes where surface by-products can compete with the precursor for the same pool of adsorption sites. Our results show that it is possible to have a self-limited process with saturated yet inhomogeneous growth profiles due to the competition of reactor by-products. This is in agreement with experimental observations for titanium dioxide ALD from titanium tetraisopropoxide and titanium tetrachloride precursors.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

Band diagram and rate analysis of thin film spinel LiMn 2 O 4 formed by electrochemical conversion of ALD-grown MnO

Nanoscale spinel lithium manganese oxide is of interest as a high-rate cathode material for advanced battery technologies among other electrochemical applications. In this work, the synthesis of ultrathin films of spinel lithium manganese oxide (LiMn 2 O 4 ) between 20 and 200 nm in thickness by room-temperature electrochemical conversion of MnO grown by atomic layer deposition (ALD) is demonstrated. The charge storage properties of LiMn 2 O 4 thin films in electrolytes containing Li + , Na + , K + , and Mg 2+ are investigated. A unified electrochemical band-diagram (UEB) analysis of LiMn 2 O 4 informed by screened hybrid density functional theory calculations is also employed to expand on existing understanding of the underpinnings of charge storage and stability in LiMn 2 O 4 . It is shown that the incorporation of Li + or other cations into the host manganese dioxide spinel structure (λ-MnO 2 ) stabilizes electronic states from the conduction band which align with the known redox potentials of LiMn 2 O 4 . Furthermore, the cyclic voltammetry experiments demonstrate that up to 30% of the capacity of LiMn 2 O 4 arises from bulk electronic charge-switching which does not require compensating cation mass transport. As a result, the hybrid ALD-electrochemical synthesis, UEB analysis, and unique charge storage mechanism described here provide a fundamental framework to guide the development of future nanoscale electrode materials for ion-incorporation charge storage.

36 MATERIALS SCIENCE↗
DOE OSTI2022

3D LiMn 2 O 4 nThin Film Deposited by ALD: A Road toward High-Capacity Electrode for 3D Li-Ion Microbatteries

Miniaturized electronics suffer from a lack of energy autonomy. In that context, the fabrication of lithium-ion solid-state microbatteries with high performance is mandatory for powering the next generation of portable electronic devices. Here, the fabrication of a thin film positive electrode for 3D Li-ion microbatteries made by the atomic layer deposition (ALD) method and in situ lithiation step is demonstrated. The 3D electrodes based on spinel LiMn 2 O 4 films operate at high working potential (4.1 V vs Li/Li + ) and are capable of delivering a remarkable surface capacity (approximate to 180 mu Ah cm -2 ) at low C-rate while maintaining more than 40 mu Ah cm -2 at C/2 (time constant = 2 h). Both the thickness of the electrode material and the 3D gain of the template are carefully tuned to maximize the electrode performance. Further, advanced characterization techniques such as transmission electron and X-ray transmission microscopies are proposed as perfect tools to study the conformality of the deposited films and the interfaces between each layer: no interdiffusion or segregation are observed. This work represents a major issue towards the fabrication of 3D-lithiated electrode by ALD-without any prelithiation step by electrochemical technique-making it an attractive solution for the fabrication of 3D Li-ion solid-state microbatteries with semiconductor processing methods.

3D Li-ion micro-batteries↗
DOE OSTI2025

Carboxyl-functionalized perovskite enables ALD growth of a compact and uniform ion migration barrier

Mixed-halide wide-band-gap perovskites are critical components of highly efficient tandem cells, but their operating stability is limited by halide migration. Metal oxides deposited via atomic layer deposition (ALD) have been shown to block halide migration; however, previously pursued methods result in inhomogeneous nucleation and growth. We hypothesized that functionalizing the perovskite surface with ALD-active carboxyl groups could promote nucleation and enable higher-temperature metal oxide growth. We find that 5-ammonium valeric acid iodide (5-AVAI) facilitates the formation of a compact and uniform aluminum oxide (Al 2 O 3 ) layer and allows growth at 100°C compared with the previous limit of 75°C. We demonstrate that halide migration into the C 60 electron transport layer is reduced by a factor of 10 compared with the reference case. Finally, Al 2 O 3 -capped perovskite solar cells with a band gap of 1.78 eV retain 90% of their initial power conversion efficiency after 1,000 h of continuous operation under 1-sun illumination at 55°C.

Al2O3↗
DOE OSTI2019

Formation of Unsaturated Hydrocarbons and Hydrogen: Surface Chemistry of Methyltrioxorhenium(VII) in ALD of Mixed-Metal Oxide Structures Comprising Re(III) Units

We present the full investigation of the atomic layer deposition (ALD) of a mixed rhenium-aluminum oxide, namely ReAl 2 O 3 CH 3 , a material with tunable resistance, comprising the building unit of conductive rhenium oxides, ReOx. The deposition, involving methyltrioxorhenium(VII) (MeReO 3 , MTO) and trimethylaluminum (TMA), was analyzed by employing complementary in situ diagnostic quartz-crystal microbalance (QCM), Fourier-transform infrared (FT-IR) spectroscopy, and quadrupole mass spectrometry (QMS) to explore and reveal the underlying growth mechanism of this material. A proposed mechanism includes reductive elimination steps, thereby creating a stable Re(III)-containing thin film, making this ALD process unique regarding its growth. In addition, as proven by QMS, the surface reactions include the formation of hydrogen and unsaturated hydrocarbons. From this straightforward process, an extraordinarily high growth rate of 4.5 angstrom cycle -1 at temperatures as low as 150 °C was obtained. This material was found to exhibit highly promising electrical properties in terms of low thermal coefficient of resistance (TCR) in combination with high resistivity. By blending thin films of ReAl 2 O 3 CH 3 with additional layers (1, 2, or 3) of Al 2 O 3 , we were able to fine-tune the electrical resistivity in the range of 3.9 x 10(6) -1.5 x 10 11 Ω.cm. Simultaneously, the TCR was lowered to about -0.014 degrees °C -1 , making this material highly resistive over a broad temperature range and a promising candidate for advanced detector applications, e.g., multichannel plates (MCPs).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Thermal Chemistry of Nickel Diketonate Atomic Layer Deposition (ALD) Precursors on Tantalum and Silicon Oxide Surfaces

The mechanism of the thermal conversion of both bis(2,2,6,6-tetramethyl-3,5-heptanedionato)nickel(II) (Ni(TMHD) 2 ) and the protonated ligand (TMHD-H) adsorbed on TaO x and SiO 2 /TaO x surfaces was characterized under ultrahigh vacuum (UHV) by a combination of temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) experiments. In this work, A stepwise decomposition was observed with Ni(TMHD) 2 encompassing at least four different stages: (1) a ligand loss, to release TMHD-H; (2) a surprising ligand fractioning via the scission of an inner C–C bond within the central β-diketonate moiety to produce an aldehyde (pivaldehyde) and a ketone (pinacolone); (3) further ligand splitting following a more extensive cracking to yield an olefin (from dehydrogenation of the terminal tert-butyl group), carbon monoxide, and adsorbed methylene groups; and finally, (4) the loss of one oxygen atom from the remaining ligands to produce the corresponding enone. As these conversions take place, the Ni ion is reduced, first to a partially oxidized intermediate, as the first ligand is removed, and then to its metallic state as the remaining organic fragments migrate to the surface. A similar sequence was seen on both surfaces, but with the transitions taking place at higher temperatures on SiO 2 . The implications of these results to the surface chemistry of other ALD precursors and to the design of ALD processes are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

ALD with Alternative Coreactants: Which Work, Which Do Not, and Why

In this paper, we present a combined experimental and theoretical study that systematically evaluates a series of alcohols (i.e., primary, secondary, and tertiary) as coreactants for trimethylaluminum (TMA)-based atomic layer deposition (ALD) of Al 2 O 3 . We employed in situ quartz crystal microbalance techniques and ex situ X-ray photoelectron spectroscopy to probe growth across a range of temperatures from T = 120 to 285 °C. Dispersion-inclusive hybrid density functional theory was employed to identify potential reaction pathways and compute corresponding Gibbs free-energy barriers and rate coefficients. Experimentally on an Al 2 O 3 surface, sustained thin-film growth, where the rate is constant over many cycles, was only observed with tertiary alcohols (tert-butanol and 2-methyl-2-butanol) at elevated temperatures (e.g., T = 285 °C); for tert-butanol specifically, sustained growth also occurred at T = 240 °C, with no sustained growth at or below T = 210 °C. Growth using primary and secondary alcohols decayed to a negligible value after only 2–3 cycles on an Al 2 O 3 surface at all tested temperatures. Intentional trace additions of H 2 O to anhydrous alcohols restored sustained growth but at reduced deposition rates relative to pure H 2 O. Theoretical analysis supports a bimolecular alkoxy β-H elimination mechanism as the primary reaction pathway: initiated by the formation of a bound alkoxy species, the subsequent β-H elimination step is rate-determining, with a barrier that systematically decreases as the degree of the alcohol coreactant is increased from primary to secondary to tertiary. Computed rate coefficients (k) also indicate a strong temperature dependence (with k increasing by ∼4–5 orders of magnitude from T = 120 to 285 °C) and are consistent with the experimental observation that only tertiary alcohols lead to steady thin-film growth at elevated temperatures. This integrated approach establishes why only certain alcohols can sustain Al 2 O 3 ALD and delivers a predictive framework for identifying effective alcohol coreactants.

36 MATERIALS SCIENCE↗