Atomic layer deposition of W on nanoporous carbon aerogels
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In this study, the authors demonstrate the ability to apply precise, conformal W coatings onto all surfaces of nanoporous carbon aerogels using atomic layer deposition (ALD). The resulting material has a filamentous structure in which the W completely encapsulates the carbon aerogel strands. The material mass increases nonlinearly with W coating, achieving a tenfold increase following ten ALD cycles. The aerogel surface area increases by nearly a factor of 2 after ten W ALD cycles. This conformal metal coating of extremely high aspect ratio nanoporous materials by ALD represents a unique route to forming metal functionalized high surface area materials.Keywords:
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Carbon fibers
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Physical vapor deposition
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This report is the first effort to use atomic layer deposition method for deposition of nanosized-thin and highly conformal Al2O3 coatings onto LiMn2O4 cathodes with precise thickness-control at atomic scale. The coated cathodes exhibit significantly enhanced cycleability than bare cathodes, as the dense ALD coating protects the cathode material from severe dissolution.
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Aluminum Oxide
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Atomic layer deposition (ALD) has long been developed for conformal coating thin films on planar surfaces and complex structured substrates based on its unique sequential process and self-limiting surface chemistry. In general, the coated thin films can be dielectrics, semiconductors, conductors, metals, etc., while the targeted surface can vary from those of particles, wires, to deep pores, through holes, and so on. The ALD coating technique, itself, was developed from gas-phase chemical vapor deposition, but now it has been extended even to liquid phase coating/growth. Because the thickness of ALD growth is controlled in atomic level ([Formula: see text]0.1[Formula: see text]nm), it has recently been employed for producing two-dimensional (2D) materials, typically semiconducting nanosheets of transition metal dichalcogenides (TMDCs). In this paper, we briefly introduce recent progress in ALD of multifunctional oxides and 2D TMDCs with the focus being placed on suitable ALD precursors and their ALD processes (for both binary compounds and ternary alloys), highlighting the remaining challenges and promising potentials.
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Transition-metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co-P films were deposited by using PH3 plasma as the phosphorus source and an extra H2 plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self-limited layer-by-layer growth, and the deposited Co-P films were highly pure and smooth. The Co-P films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar Co-P films prepared by the traditional post-phosphorization method. Moreover, the deposition of ultrathin Co-P films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex three-dimensional (3D) architectures.
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Phosphide
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Conformal atomic layer deposition (ALD) inside macroscopic nanoporous solids with aspect ratios greater than 103 can require ALD reactant exposures on the order of 103 Torr-s or greater. For some ALD chemistries, such large exposures raise the concern of non-self-limiting deposition. In the case of ZnO ALD from diethylzinc (DEZ) and H2O, exposures in the 10–103 Torr-s range have resulted in metallic Zn deposition at typical temperatures used for ZnO ALD on wafers (e.g., ∼180 °C). This Zn deposition can be suppressed by lowering the deposition temperature, but this slows H2O desorption and, thus, can necessitate impractically long purge times. In this work, we use static-dose ALD with DEZ and H2O exposures >104 Torr-s to deposit ZnO inside Al2O3 nanoparticle compacts (NPCs) with 50.5 ± 0.3% porosity, 100 nm NP diameter, 1.55 ± 0.05 mm thickness, and an aspect ratio of 7800 ± 200 (based on the half-thickness), and we explore a novel approach to the deposition temperature, T: T is cycled between 160 °C (for H2O purges) and 120 °C (for all other steps). For comparison, we also deposit ZnO with T held constant at 120 or 160 °C. Whereas the T = 160 °C process results in Zn metal deposition and nonuniform infiltration, the temperature-cycled process yields apparently self-limiting ZnO deposition at a growth per cycle (GPC) of ∼2.1 Å/cyc, forming an electrically conductive ZnO network that is uniform throughout the thickness of the NPC, with the exception of some ZnO depletion near the NPC surfaces, possibly due to the (unoptimized) long DEZ purge time. The T = 120 °C process produces similar results, although the GPC is slightly elevated, indicating diminished removal of H2O and/or OH during purges. We employ scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffractometry, electrical resistivity measurements, and ALD chamber pressure analysis in our comparison of the three ALD processes.
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In this study, the authors demonstrate the ability to apply precise, conformal W coatings onto all surfaces of nanoporous carbon aerogels using atomic layer deposition (ALD). The resulting material has a filamentous structure in which the W completely encapsulates the carbon aerogel strands. The material mass increases nonlinearly with W coating, achieving a tenfold increase following ten ALD cycles. The aerogel surface area increases by nearly a factor of 2 after ten W ALD cycles. This conformal metal coating of extremely high aspect ratio nanoporous materials by ALD represents a unique route to forming metal functionalized high surface area materials.
Nanoporous
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Carbon fibers
Deposition
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Atomic layer deposition (ALD) is a self-limited growth method which relies on sequential reactions of gas phase precursor molecules with a solid surface to deposit oxides, metals and other materials in an atomic layer-by-layer fashion. The unique surface-controlled chemistry of ALD enables the conformal coating of high surface area nanoporous materials and provides atomic-level control over the coating thickness. These key advantages offer ALD the ability to precisely tune the pore size and chemical surface composition of nanoporous materials, and therefore render ALD an enabling technology for the controlled atomic-scale design of supported catalysts. Following a short introduction to the basic principles of the ALD technique, experimental studies are presented that demonstrate the ability of ALD for conformal deposition in nanometer-sized mesopores and in the bulk of high surface area powder particles. Selected examples are then discussed, illustrating the versatility of ALD for tailoring nanoporous supports and engineering the presence of catalytic sites or nanoparticles on the pore walls. A specific case study shows the potential of ALD for generating acid sites in ordered mesoporous silica materials. A second case study highlights an ALD-based approach for the synthesis of uniformly dispersed anatase nanoparticles in mesoporous silica thin films, resulting in photocatalytic activity.
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Nanometre
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We present a method to increase the stability of DNA nanostructure templates through conformal coating with a nanometer-thin protective inorganic oxide layer created using atomic layer deposition (ALD). DNA nanotubes and origami triangles were coated with ca. 2 nm to ca. 20 nm of Al 2 O 3 . Nanoscale features of the DNA nanostructures were preserved after the ALD coating and the patterns are resistive to UV/O 3 oxidation. The ALD-coated DNA templates were used for a direct pattern transfer to poly(L-lactic acid) films.
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