Xiangbo Meng

Emerging applications of atomic layer deposition for lithium-ion battery studies.

Lithium-ion batteries (LIBs) are used widely in todays consumer electronics and offer great potential for hybrid electric vehicles (HEVs), plug-in HEVs, pure EVs, and also in smart grids as future energy-storage devices. However, many challenges must be addressed before these future applications of LIBs are realized, such as the energy and power density of LIBs, their cycle and calendar life, safety characteristics, and costs. Recently, a technique called atomic layer deposition (ALD) attracted great interest as a novel tool and approach for resolving these issues. In this article, recent advances in using ALD for LIB studies are thoroughly reviewed, covering two technical routes: 1) ALD for designing and synthesizing new LIB components, i.e., anodes, cathodes, and solid electrolytes, and; 2) ALD used in modifying electrode properties via surface coating. This review will hopefully stimulate more extensive and insightful studies on using ALD for developing high-performance LIBs.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Atomic Layer Deposition of Metal Sulfide Materials

CONSPECTUS: The field of nanoscience is delivering increasingly intricate yet elegant geometric structures incorporating an ever-expanding palette of materials. Atomic layer deposition (ALD) is a powerful driver of this field, providing exceptionally conformal coatings spanning the periodic table and atomic-scale precision independent of substrate geometry. This versatility is intrinsic to ALD and results from sequential and self-limiting surface reactions. This characteristic facilitates digital synthesis, in which the film grows linearly with the number of reaction cycles. While the majority of ALD processes identified to date produce metal oxides, novel applications in areas such as energy storage, catalysis, and nanophotonics are motivating interest in sulfide materials. Recent progress in ALD of sulfides has expanded the diversity of accessible materials as well as a more complete understanding of the unique chalcogenide surface chemistry. ALD of sulfide materials typically uses metalorganic precursors and hydrogen sulfide (H2S). As in oxide ALD, the precursor chemistry is critical to controlling both the film growth and properties including roughness, crystallinity, and impurity levels. By modification of the precursor sequence, multicomponent sulfides have been deposited, although challenges remain because of the higher propensity for cation exchange reactions, greater diffusion rates, and unintentional annealing of this more labile class of materials. A deeper understanding of these surface chemical reactions has been achieved through a combination of in situ studies and quantum-chemical calculations. As this understanding matures, so does our ability to deterministically tailor film properties to new applications and more sophisticated devices. This Account highlights the attributes of ALD chemistry that are unique to metal sulfides and surveys recent applications of these materials in photovoltaics, energy storage, and photonics. Within each application space, the benefits and challenges of novel ALD processes are emphasized and common trends are summarized. We conclude with a perspective on potential future directions for metal chalcogenide ALD as well as untapped opportunities. Finally, we consider challenges that must be addressed prior to implementing ALD metal sulfides into future device architectures.

Controllable synthesis of graphene-based titanium dioxide nanocomposites by atomic layer deposition

Atomic layer deposition (ALD) was used to synthesize graphene-based metal oxide nanocomposites. This strategy was fulfilled on the preparation of TiO(2)-graphene nanosheet (TiO(2)-GNS) nanocomposites using titanium isopropoxide and water as precursors. The synthesized nanocomposites demonstrated that ALD exhibited many benefits in a controllable means. It was found that the as-deposited TiO(2) was tunable not only in its morphologies but also in its structural phases. As for the former, TiO(2) was transferable from nanoparticles to nanofilms with increased cycles. With regard to the latter, TiO(2) was changeable from amorphous to crystalline phase, and even a mixture of the two with increased growth temperatures (up to 250 °C). The underlying growth mechanisms were discussed and the resultant TiO(2)-GNS nanocomposites have great potentials for many applications, such as photocatalysis, lithium-ion batteries, fuel cells, and sensors.

Vapor-Phase Atomic-Controllable Growth of Amorphous Li2S for High-Performance Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries hold great promise to meet the formidable energy storage requirements of future electrical vehicles but are prohibited from practical implementation by their severe capacity fading and the risks imposed by Li metal anodes. Nanoscale Li(2)S offers the possibility to overcome these challenges, but no synthetic technique exists for fine-tailoring Li(2)S at the nanoscale. Herein we report a vapor-phase atomic layer deposition (ALD) method for the atomic-scale-controllable synthesis of Li(2)S. Besides a comprehensive investigation of the ALD Li(2)S growth mechanism, we further describe the high performance of the resulting amorphous Li(2)S nanofilms as cathodes in Li-S batteries, achieving a stable capacity of ∼ 800 mA · h/g, nearly 100% Coulombic efficiency, and excellent rate capability. Nanoscale Li(2)S holds great potential for both bulk-type and thin-film high-energy Li-S batteries.

A general empirical formula of current-voltage characteristics for point-to-plane geometry corona discharges

With a point-to-plane geometry, the experimental investigation of the current–voltage characteristics in corona discharges demonstrated that existing empirical formulae met with some physical difficulties in explaining the results. By mathematically processing the experimental data and applying the updated knowledge of corona inception, a new general formula in characterizing the relationship of corona current–voltage was derived and expressed as I = K(V − V0)n. It was demonstrated that the exponent n falls into a limited scope of 1.5–2.0, and there always exists an optimal exponent n in the scope, which can be determined by maximizing the R-square of regression. Of all the potentially influential factors, it was disclosed that the point radius has the strongest influence on the optimal exponent n, and the effects of ambient conditions and corona polarities are not noticeable. The optimal exponent n holds a fixed value of 2.0 for microscopic points and of 1.5 for large points with a radius in millimetres, but changes decreasingly with the radius for the points of microns. For given experimental conditions, the optimal exponent n almost does not change with the inter-electrode distance. Furthermore, it was demonstrated that the formula is applicable not only for both negative and positive coronas in point-to-plane geometries but also for both polarities in point-to-ring geometries. With the optimal exponent n, the formula can well explain the inconsistencies met by other existing formulae and best represent the characteristics of corona current–voltage with an accuracy of 1 µm.

Three growth modes and mechanisms for highly structure-tunable SnO2 nanotube arrays of template-directed atomic layer deposition

This article presents a vapor-phase strategy to synthesize highly structure-tunable SnO2 nanotube arrays of high aspect ratio, which features atomic layer deposition of SnO2 on anodic aluminium oxide templates using SnCl4 and H2O as precursors. This systematic study disclosed that there are three distinctive temperature-dependent growth modes, i.e., layer-by-layer, layer-by-particle, and evolutionary particles contributing to the structural uniqueness of the resultant SnO2 nanotubes. The layers were identified in an amorphous phase while the particles in a crystalline phase. As a consequence, the synthesized SnO2 nanotubes are not only phase-controllable but also morphology-transferable with growth temperatures. In a following effort to explore the underlying mechanisms, as another contribution of this study, three growth models were proposed and clarified. Thus, this study offers not just a precise alternative for synthesizing structurally novel nanotubes but scientific insights into fundamentals as well.

Atomic layer deposition for nanomaterial synthesis and functionalization in energy technology

Atomic layer deposition (ALD) has been receiving more and more research attention in the past few decades, ascribed to its unrivaled capabilities in controlling material growth with atomic precision, manipulating novel nanostructures, tuning material composition, offering multiple choices in terms of crystallinity, and producing conformal and uniform film coverage, as well as its suitability for thermally sensitive substrates. These unique characteristics have made ALD an irreplaceable tool and research approach for numerous applications. In this review, we summarize the recent advances of ALD in several important areas including rechargeable secondary batteries, fuel cells, solar cells, and optoelectronics. With this review, we expect to exhibit ALDs versatile potential in providing unique solutions to various technical challenges and also hope to further expand ALDs applications in emerging areas.

Atomic layer deposited Li4Ti5O12 on nitrogen-doped carbon nanotubes

Atomic layer deposition was used for the synthesis of ternary spinel Li4Ti5O12 compounds on nitrogen-doped carbon nanotubes, featuring its accurate tunability of elemental compositions.

Atomic Layer Deposition of MnS: Phase Control and Electrochemical Applications.

Manganese sulfide (MnS) thin films were synthesized via atomic layer deposition (ALD) using gaseous manganese bis(ethylcyclopentadienyl) and hydrogen sulfide as precursors. At deposition temperatures ≤150 °C phase-pure γ-MnS thin films were deposited, while at temperatures >150 °C, a mixed phase consisting of both γ- and α-MnS resulted. In situ quartz crystal microbalance (QCM) studies validate the self-limiting behavior of both ALD half-reactions and, combined with quadrupole mass spectrometry (QMS), allow the derivation of a self-consistent reaction mechanism. Finally, MnS thin films were deposited on copper foil and tested as a Li-ion battery anode. The MnS coin cells showed exceptional cycle stability and near-theoretical capacity.