Atomic Layer Deposition Treatment Research Articles

Shear Bond Strength to Enamel, Mechanical Properties and Cellular Studies of Fiber-Reinforced Composites Modified by Depositing SiO2 Nanofilms on Quartz Fibers via Atomic Layer Deposition.

Poor interfacial bonding between the fibers and resin matrix in fiber-reinforced composites (FRCs) is a significant drawback of the composites. To enhance the mechanical properties of FRC, fibers were modified by depositing SiO2 nanofilms via the atomic layer deposition (ALD) technique. This study aims to evaluate the effect of ALD treatment of the fibers on the mechanical properties of the FRCs. The quartz fibers were modified by depositing different cycles (50, 100, 200, and 400) of SiO2 nanofilms via the ALD technique and FRCs were proposed from the modified fibers. The morphologies, surface characterizations of nanofilms, mechanical properties, and cytocompatibility of FRCs were systematically investigated. Moreover, the shear bond strength (SBS) of FRCs to human enamel was also evaluated. The SEM and SE results showed that the ALD-deposited SiO2 nanofilms have good conformality and homogeneity. According to the results of FTIR and TGA, SiO2 nanofilms and quartz fiber surfaces had good chemical combinations. Three-point bending tests with FRCs showed that the deposited SiO2 nanofilms effectively improved FRCs' strength and Group D underwent 100 deposition cycles and had the highest flexural strength before and after aging. Furthermore, the strength of the FRCs demonstrated a crescendo-decrescendo tendency with SiO2 nanofilm thickness increasing. The SBS results also showed that Group D had outstanding performance. Moreover, the results of cytotoxicity experiments such as cck8, LDH and Elisa, etc., showed that the FRCs have good cytocompatibility. Changing the number of ALD reaction cycles affects the mechanical properties of FRCs, which may be related to the stress relaxation and fracture between SiO2 nanofilm layers and the built-up internal stresses in the nanofilms. Eventually, the SiO2 nanofilms could enhance the FRCs' mechanical properties and performance to enamel by improving the interfacial bonding strength, and have good cytocompatibility.

Few-cycle atomic layer deposition to nanoengineer polybenzimidazole for H2/CO2 separation

Atomic layer deposition (ALD) creates uniform sub-nanometer films on a variety of surfaces and nanopore walls and has been used to modify polymers to improve surface affinity towards specific molecules, solvent resistance, and barrier properties to gases and vapors. Here, for the first time, we demonstrate that few-cycle ALD can be used to engineer functional polymers at a sub-nanometer scale to improve both molecular size-sieving ability and counterintuitively, gas permeability. Particularly, 1-cycle ALD treatment of polybenzimidazole (PBI) by sequential exposure to trimethylaluminum (TMA) and water vapor remarkably increases H2 permeability by 120% − 270% and H2/CO2 selectivity by 30% at 35–200 °C. The ALD not only deposits an AlOx layer on the surface but also enables the TMA to infiltrate and react with the bulk PBI to form an AlOx network, disrupting polymer chain packing and increasing chain rigidity. The membrane exhibits excellent stability when challenged with simulated syngas, overcoming the permeability/selectivity tradeoff for H2/CO2 separation. This study showcases a facile and scalable way of engineering polymeric membranes at a sub-nanometer level to improve molecular separation performance.

Regulation of thermal conductivity of microencapsulated phase change materials via atomic layer deposition

Microencapsulated phase change materials (MEPCMs) have different thermal conductivity requirements under various application conditions. Organic-shell MEPCMs currently dominate the microcapsule due to their easy availability. The aim of this paper is to regulate the thermal properties, especially the thermal conductivity, of organic-shell microcapsules. Herein, with the precision and uniformity of atomic layer deposition (ALD) coating, the thickness of ZnO coating is controlled on the surface of paraffin @ polymethyl methacrylate (PMMA) to realize the regulation of thermal properties of MEPCMs. The experimental results illustrate that the introduction of ALD ZnO shell abates the phase transition enthalpy of MEPCM, but it realizes the optimization of thermal stability and phase transition reversibility for MEPCMs, which is confirmed by the mechanical test results of microcapsules. Furthermore, it is particularly worth mentioning that the thermal conductivity of MEPCM can be adjusted from 0.16 to 1.99 W m−1 K−1 within the ALD cycle range given in this research. The equivalent thermal conductivity of MEPCM was verified by calculation, and the relationship between ALD treatment and thermal conductivity was obtained. This research provides a strategy for accurately regulating the thermal conductivity of phase change microcapsules, breaking through the bottleneck in the application of microcapsules.

Conversion Reactions and Redox Changes on the Surface of Lithium-Ion Battery Cathode Materials during Chemical Vapor Treatment for ALD

Atomic layer deposition (ALD) has emerged as a promising technology for applying ultrathin protective coatings on lithium-ion battery (LIB) cathode surfaces to improve their cycling stability. While there have been numerous reports evaluating the electrochemical performance of these surface-modified cathode materials, the chemical changes induced on the surface of the cathode materials by the ALD coatings and the individual ALD precursors are not fully studied. We performed a systematic investigation to understand the interfacial changes of 12 different cathode materials upon coating with aluminum oxide (Al2O3) using trimethyl aluminum (TMA) and H2O, and aluminum fluoride (AlF3) using TMA and hydrogen fluoride pyridine (HFPy). We also explored the effects of the individual TMA and HFPy precursors on the cathode surfaces. The surface composition and microstructure of these cathode materials, which range from simple transition metal oxides (e.g., NiO and MnO) to complex multi-element cathode materials (e.g., LiNixMn1-x-yCoyO2, NMC), were studied via X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The XPS measurements reveal that the transition metals in the cathode materials undergo selective oxidation/reduction depending upon the nature of the precursor, the coating, and the cathode material. Furthermore, XPS and STEM measurements show the conversion of surface carbonate species to the corresponding metal fluorides upon HF exposure. This conversion reaction is self-limiting but extends hundreds of nanometers below the surface in the case of Li2CO3. ALD and chemical vapor treatment provide new avenues to systematically control the interface of the cathode materials in LIBs that are not possible by conventional coating methods.

Modification of ZIF-8 membranes by atomic layer deposition for high propylene/propane selectivity

Zeolitic-imidazolate framework (ZIF-8) membranes have great potential to separate propylene/propane gas mixtures. Our recent work demonstrated that an excellent propylene/propane separation factor is obtained with a silicalite-seeded ZIF-8 membrane. However, the separation performance was limited due to non-selective defects in the ZIF-8 membranes that adversely affected the membrane separation performance. To further improve membrane performance, zinc oxide (ZnO) was atomically deposited on the synthesized ZIF-8 membrane surface using atomic layer deposition (ALD). ZnO ALD helped to minimize surface defects and inter-crystalline gaps of the membrane and improved the propylene/propane separation factor while maintaining the propylene permanence. After ZnO ALD treatment, ZIF-8 membranes showed significant improvement of the propylene/propane separation factor from 141 to 264, but at the expense of the propylene permeance with a ∼10% reduction. The improvement is likely due to defects healing on the ZIF-8 membrane surface via ZnO ALD. The resulting ZIF-8 membranes were characterized by XRD, XPS, BET, and SEM.

Tunable atomic level surface functionalization of a multi-layered graphene oxide membrane to break the permeability-selectivity trade-off in salt removal of brackish water

To enhance graphene oxide (GO) membrane performance, atomic level surface functionalization was applied via plasma-enhanced atomic layer deposition (ALD) to a GO membrane. Unlike conventional ALD approaches, to functionalize the surface without increasing the membrane thickness, we conducted only a few (3–9) ALD cycles, which allowed for the formation of a tunable ultra-thin (1.44 nm) and uniform hydrophilic metal oxide (Al2O3) layer on the multi-layered membrane. The ALD-treated GO membrane exhibited enhanced water permeability (from 32.9 to 68.0 LMH/bar) and NaCl rejection (from 46.6 up to 63.8%), successfully overcoming the typical trade-off between permeability and rejection efficiency in briskish water desalination. The formed atomic level Al2O3 layer was characterized via Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and d-spacing measurements. The results revealed that this enhanced water permeability can be mainly attributed to the increase in the surface hydrophilicity achieved without narrowing the GO membrane nanochannel structure (dry state 7.5 ~ 7.7 Å). Moreover, healed defects on the two-dimensional GO and improved electrostatic interaction (induced by the ALD treatment) resulted in improved salt rejection. Therefore, the distinctive features of ALD-treated GO membrane may contribute to enhancing its application in brackish water desalination.

Investigation and optimization of HfO2 gate dielectric on N-polar GaN: Impact of surface treatments, deposition, and annealing conditions

UV-assisted capacitance–voltage (C–V) and current–voltage (I–V) measurements were performed on ∼20 nm HfO2/GaN metal–insulator–semiconductor capacitors. The effects of surface preparation, predeposition treatment, HfO2 deposition process, and post-deposition annealing environment on interface characteristics were studied. Surface preparation by etching in diluted BHF and piranha etch prior to atomic layer deposition (ALD) suppressed the interface states compared to the baseline sample possibly due to the removal of the native oxide and impurities. UV/ozone treatment prior to HfO2 deposition reduced the interface states by one order of magnitude compared to the baseline sample possibly due to the formation of a thin Ga2O3 interlayer. In situ ALD pretreatment with tri-methyl-aluminum/N2 plasma was also found to reduce the surface states significantly compared to the baseline sample. In addition, thermal ALD improved the dielectric constant and breakdown voltage of the dielectric as compared to plasma ALD due to less surface damage. The lowest average interface trap density achieved was 1.64 × 1012 cm−2/eV with an HfO2 dielectric constant of 16 on the sample with UV/ozone and piranha treatment with in situ ALD treatment and thermal ALD deposition.

Improvement of fuel cell catalyst performance through zirconia protective layer coating by atomic layer deposition

In this study, the performance of the cathode catalyst of polymer electrolyte membrane fuel cells is improved by the atomic layer deposition (ALD) of a protective layer. An atomic layer-scale zirconia protective layer is coated on the platinum catalyst for surface treatment. The results indicate that a very thin layer deposition with two ALD cycles or less is required to minimize the deterioration of the activity of the catalyst. Further, it is also confirmed that the catalyst aggregation can be effectively suppressed by its encapsulation with the protective layer through several ALD cycles from the analysis of the electrochemical surface area by cyclic voltammetry and the change in the catalyst particle size. According to the results, even two ALD cycles, which provide less than one atom layer, has decreased the deterioration rate to one-fourth of that of the untreated catalyst, with a minor decrease in the fuel cell power. In addition, the I–V data and impedance spectroscopy confirms that the overall stability of the membrane electrode assembly is improved by the ALD treatment. Thus, the ALD of a protective layer is considered to be a very promising strategy to improve the stability and performance of fuel cell catalysts.

Alumina‐Protected, Durable and Photostable Zinc Sulfide Particles from Scalable Atomic Layer Deposition

AbstractZinc sulfide has unique and easily modifiable photophysical properties and is a promising candidate for photocatalysis and optoelectronic devices. However, ZnS suffers from corrosive decomposition during excitation processes like UV irradiation, which drastically limits its field of potential applications. For the first time, complete photostabilization of individual ZnS particles by a dense, durable, and only 3‐nm‐thick Al2O3 layer, produced by rotary atomic layer deposition (ALD) is reported. In contrast to bare ZnS, the coated particles do not suffer from photocorrosive degradation even under long‐term or high power UV irradiation. The presence of a protection layer covering the entire ZnS surface is additionally confirmed by microscopic and spectroscopic investigations of particle cross‐sections. Further, complete inhibition of the reaction between Ag+ ions added as the analyte and the ZnS surface is observed. Durability tests of the as‐prepared Al2O3 layer upon prolonged exposure to water reveal a significant decrease in the protection capability of the layer, which is ascribed to the hydrolysis of the amorphous Al2O3. A calcination step at 1000 °C after the ALD treatment, which leads to crystallization of the amorphous Al2O3 layer, successfully suppresses this hydrolysis and produces an insulating, dense, and inert protection layer.

Improved High-Energy Na-NCM Cathode Prepared by Ion Exchange Route via Application of Various ALD Treatments

The application of layered oxide compounds as cathode materials for sodium-ion batteries is considered a promising direction for the development of high-energy Na-ion batteries. However, despite many efforts, practical implementation of such electrodes is still challenging, mainly due to structural and surface instabilities associated with the high operating voltage of these cathodes. One of the most effective ways to mitigate these undesirable phenomena is the use of atomic layer deposition (ALD) to form a Nano-sized protective layer on the electrode surface. Application of ALD treatment results in increased electrode stability by preventing irreversible interactions between the electrolyte and cathode material. In search of optimal coating formulations, the effect of various ALD coatings viz. sodium-aluminate, lithium-aluminate, and alumina on the electrochemical performance of Na-NCM cathode synthesized by ion-exchange method. While the initial capacity loss attributed to oxygen release was significantly suppressed in all coated samples, better stability was observed for NaxAlyOz coating. The stabilization mechanism of the NaxAlyOz coating further investigated by XPS, XRD, and TEM revealed improved surface properties that prevent irreversible oxygen loss and migration of manganese from the electrode bulk toward the surface.

Angstrom-Thick Oxide Overcoat on Decorated Nanoclusters for Enhanced Performance and Durability of SOFC Cathodes

A solid oxide fuel cell (SOFC) is an energy conversion system with high conversion efficiency, high power density and fuel flexibility.1 Since its durability and cost issues are largely originated from the high temperature operation, intense efforts have been made to reduce the operational temperature to an intermediate range of 600 – 800 °C.2 The decrease in temperature, however, results in a significant decrease in the electrochemical kinetics in particular of the oxygen reduction reaction (ORR) occurring at the cathode.3,4 Atomic layer deposition (ALD) is an emerging low-temperature chemical vapor deposition variant that can deposit well-dispersed islands or uniform films at the atomic scale even on a highly corrugated geometry.8,9 By leveraging the capability, researchers have successfully improved SOFC durability mainly by suppressing the agglomeration of high-surface-area electrodes10–13 and/or dopant segregation to the surface of perovskite-based cathodes.14,15 Considering the capability of ALD to perform a conformal atomic-scale treatment on complex geometry, an ALD treatment can be best leveraged when applied to a structure of extreme surface area as opposed to conventional porous backbone structures. However, its application to a high-surface-area electrodes (e.g. infiltrated electrodes) and associated analysis is rarely reported.In this presentation, we demonstrate that a uniform atomic-scale oxide overcoat (either ceria or yttria with a nominal thickness of 0.7 – 1.5 Å) by ALD is highly effective not only in the enhancement of thermal stability of underlying ceria nanoparticles (5 – 20 nm) infiltrated on LaNi0.6Fe0.4O3- d (LNF) backbone (~100 nm) but also in the facilitation of oxygen reduction kinetics. Since LNF does not suffer from Sr segregation, a major degradation mechanism,17 the analysis of cell performance degradation is simplified. Based upon electrochemical and physical characterization of a series of infiltrated and/or ALD-treated samples, we discuss the impact of surface treatment on the nanoscale morphology, surface chemistry and electrode performance.We provide a quantitative analysis of the thermal agglomeration of NPs with and without ALD treatment and prove the close correlation between the NP agglomeration and electrode performance degradation. To the best of our knowledge, this is the first work showing the correlation in a quantitative manner. In addition, we demonstrate that an angstrom-scale ALD overcoat dramatically enhances the electrode performance in terms of polarization resistance and its activation energy for both bare LNF and ceria-infiltrated LNF electrodes. The improved electrode activity from ALD treatment is mainly ascribed to a significant facilitation of O2 dissociative adsorption with a partial reduction, with the aid of surface-specific oxygen-deficient and catalytically active ceria.The authors acknowledge the support from the Korea Institute of Industrial Technology (KITECH) and U.S. National Science Foundation CAREER Award (DMR 1753383). The use of TEM at the Molecular Foundry was supported by the U.S. Department of Energy (Contract No. DE-AC02-05CH11231). The XPS work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (Contract DE-AC52-07NA27344). Sossina M. A high-performance cathode for the next generation of solid-oxide fuel cells, 431, 170, 2004Kang H., Grewal S., Li H., Lee M. H. Effect of Surface-Specific Treatment by Infiltration into LaNi6Fe4O3-δ Cathodic Backbone for Solid Oxide Fuel Cells, 166, 255, 2019

Heteroatom Doping By Atomic Layer Deposition for Cathodic Interface Treatment of Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are widely studied due to its high efficiency and fuel flexibility.1,2 In SOFCs, cathodic reaction is known to be the main source of voltage losses due to the sluggishness of oxygen reduction reaction (ORR), which led intense research efforts to develop high-performance cathodes. The main approaches include surface treatments for facilitated surface exchange and surface area enhancement by various wet processes and/or vacuum-based deposition scheme.In this study, we demonstrate the significant impact of atomic layer deposition (ALD) treatment on the cathodic performance and operational durability. ALD has significant advantages in providing atomic scale surface overcoat with an accurate control over thickness and stoichiometry with excellent reproducibility. We use LaNi0.6Fe0.4O3- δ (LNF) as the cathodic backbone and CeO2 (ceria) as a priori infiltrated species. Two different oxides (CeO2 and Y2O3) were used as the atomic-scale coating materials.First, the cell with bare porous LNF cathode showed a high polarization resistance (Rp ) of 1.24 Ω cm2 at 700 °C, but with a single-step ceria infiltration (with 1 M cerium nitrate solution), a significantly lower Rp of 0.27 Ω cm2 was obtained. An ALD-coated ceria right on top of the LNF backbone also resulted in a dramatic decrease in Rp (0.54 Ω cm2) even with a nominal overcoat thickness of 6 Å (6 cycles of cerium and deionized water). A 6-cycle ALD coating of ceria on a ceria-infiltrated LNF showed a further improvement of cathodic performance (Rp = 0.19 Ω cm2). A similar effect was demonstrated with an ALD coating of different material (Y2O3; 3 cycles; nominal thickness = ~3 Å , Rp = 0.20 Ω cm2).More interestingly, a significantly enhanced operational durability was demonstrated by ALD treatments. A sample with a single-step infiltration of ceria showed an increase of Rp by 55% in 150 h at 700 ℃. However, a ceria ALD treatment on a ceria-infiltrated LNF resulted in a milder increase of Rp by 33% in 150 h at 700 ℃. An yttria (Y2O3) ALD overcoat suppressed the degradation even further; only 22% increase in Rp demonstrated in 150 h at 700 ℃.These observations suggest that an atomic scale surface coating by ALD can be an effective approach to enhance not only the kinetics of cathodic reactions but also the operational durability at high temperatures. This is conjectured to be originated from the capability of ALD overcoat in suppressing the sintering of either backbone or infiltrated oxide nanoparticles, and partially from a change in surface chemistry facilitating surface exchange. Electron microscopy and X-ray photoelectron spectroscopy results will be discussed in this respect.This work acknowledges the support from the U.S. National Science Foundation CAREER Award (DMR1753383) and NASA MIRO Program (NNX15AQ01A). SG and MHL also acknowledge NASA ASTAR fellowship (NNX15AW57H). The use of TEM at the Molecular Foundry was supported by the U.S. Department of Energy (Con- tract No. DE-AC02-05CH11231) 1 Z. Shao and S.M. Haile, Nature 431, 170 (2004). 2 H. Kang, S. Grewal, H. Li, and M.H. Lee, 166, 255 (2019).

Rapid Proton Transmission through Nafion | Graphene | ALD Alumina | Nafion Membranes

Recent reports from several laboratories indicate that proton transmission through graphene and other 2D materials in contact with proton-conducting electrolytes can occur rapidly with a much lower activation energy than expected from a wide range of computational studies on the proton / graphene interaction energy, and a much higher selectivity relative to transmission of other ions than would be expected based only on ion size. It would be desirable to be able to control transport through the graphene, and many approaches have been tried to rationally control transport rates through graphene via chemical treatments applied to the graphene. One such approach involves use of atomic layer deposition (ALD), in which single layers of inorganic materials, often oxides, are coated in a self-limiting way onto a surface by a series of pulsed reaction steps delivered in series. A common ALD implementation involves coatings of aluminum oxide, or alumina, created by sequential dosing of a surface with trimethyl aluminum and water vapor. We report here on use of the ALD method to coat single-layer CVD graphene supported on copper foil or on Nafion membranes with layers of alumina. Coatings resulting from 50 ALD cycles are found to be thick enough and homogeneous enough to block photoelectron emission from the underlying substrates (copper or Nafion) when the coatings are analyzed by X-ray photoelectron spectroscopy. Electrochemical hydrogen pump experiments were then performed to assess the degree to which ALD treatment of the graphene on Nafion, delivered prior to preparing Nafion | graphene | Nafion sandwich membranes, could change the rate of proton transmission through the graphene that is embedded within the Nafion. As little as two ALD treatment cycles are sufficient to reduce proton transmission currents through graphene by approximately half relative to graphene that is not treated by ALD. Surprisingly, fifty ALD cycles has almost the same effect as two cycles. This finding indicates that that ALD alumina coating is a relatively good proton conductor which is thought to reflect the action of transport pathways on the hydrated surface of the porous ALD alumina layer. The insensitivity of proton transmission to the number of ALD cycles applied suggests that the function of the ALD is to change the transport rates at interfaces, perhaps by creating a new ALD alumina / Nafion interface that protons must traverse in order to pass through the membrane.

High-Rate Spinel LiMn2O4 (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 (LiMn2O4; LMO) lithium-ion battery cathode upon a single atomic layer deposition (ALD) cycle compos...

Tough and Immunosuppressive Titanium-Infiltrated Exoskeleton Matrices for Long-Term Endoskeleton Repair.

Although biodegradable membranes are essential for effective bone repair, severe loss of mechanical stability because of rapid biodegradation, soft tissue invasion, and excessive immune response remain intrinsically problematic. Inspired by the exoskeleton-reinforcing strategy found in nature, we have produced a Ti-infiltrated chitin nanofibrous membrane. The membrane employs vapor-phase infiltration of metals, which often occurs during metal oxide atomic layer deposition (ALD) on organic substrates. This metal infiltration manifests anomalous mechanical improvement and stable integration with chitin without cytotoxicity and immunogenicity. The membrane exhibits both impressive toughness (∼13.3 MJ·m-3) and high tensile strength (∼55.6 MPa), properties that are often mutually exclusive. More importantly, the membrane demonstrates notably enhanced resistance to biodegradation, remaining intact over the course of 12 weeks. It exhibits excellent osteointegrative performance and suppresses the immune response to pathogen-associated molecular pattern molecules indicated by IL-1β, IL-6, and granulocyte-macrophage colony-stimulating factor expression. We believe the excellent chemico-biological properties achieved with ALD treatment can provide insight for synergistic utilization of the polymers and ALD in medical applications.

Mesopore differences between pillared lamellar MFI and MWW zeolites probed by atomic layer deposition of titania and consequences on photocatalysis

Abstract The pillared MWW (PMWW or MCM-36) and pillared MFI (PMFI) are two prominent representatives of meso-/microporous lamellar zeolites, which are made by pillaring of layered MCM-22(P) and multilamellar MFI precursors, respectively. They both consist of a 10-membered ring sinusoidal micropore channel within each zeolitic layer and mesopore voids created by pillars between two adjacent zeolitic layers. Although catalytic activities of PMWW and PMFI have been compared, identification of mesopore differences between these two pillared lamellar zeolites has not been attempted. In this work, we report the differences in mesopore characteristics between PMWW and PMFI zeolites probed by atomic layer deposition (ALD) of titania (ALD-TiO2) species and a combination of structural, textural, composition and catalytic property analyses of the samples before and after ALD treatment, respectively. The results suggest PMFI has cylindrical mesopores with uniform sizes from pore entrance to main body, while PMWW has ink-bottle mesopores with the neck size much smaller than pore body. The communication between micropore and mesopore in PMFI is direct, but no communication exists in PMWW zeolites. The ALD-TiO2 process considerably modified external surface composition of PMFI and PMWW zeolites, which consequently led to a new application of the pillared lamellar zeolite materials, i.e., photo-catalytically active meso-/microporous zeolites for environmental remedy reactions.

Atomic Layer Deposition Treatment on Infiltrated Cathodes for Solid Oxide Fuel Cells

A solid oxide fuel cell (SOFC) is considered one of the most promising power generation technologies for the future because of its high efficiency, low emission and fuel flexibility. To avoid durability and cost issues originated from high-temperature operation, intermediate temperature SOFCs (IT-SOFCs) operating between 600 – 750 °C has been extensively studied. As an approach to maximize the cathodic surface area and surface-sensitive catalytic activity at the reduced temperature, wet impregnation (i.e. infiltration) of various active catalysts has been widely used. Infiltrated cathodic nanoparticles with the size of few nanometers have indeed proved to be highly effective in boosting the electrochemical activity toward oxygen reduction reaction (ORR).1 In this study, we first applied various infiltrates on a porous LaNi0.6Fe0.4O3 (LNF) cathode. The infiltrated materials were chosen based upon their merits in a specific aspect such as surface exchange rate, ionic conductivity and electronic conductivity. The infiltrated materials of choice include LNF, (La1−xSrx)1−yMnO3 (LSM), Pr6O11, Pr-doped ceria and gadolinia-doped ceria (GDC). It was found that an infiltration of LNF (the same material with the backbone cathode material) reduced the electrode polarization by more than an order of magnitude at 700 °C, indicating the significant impact of surface area itself on the cathodic performance. Among all the cathodes, Pr6O11-infiltrated cathode rendered the lowest cathodic polarization. On the other hand, infiltrated nanoparticles are highly susceptible to thermal agglomeration during operation due to their tiny size and resulting high surface energy. The agglomeration process results in a significant loss of catalytically active surface area, leading to a performance degradation over time.2 To address the issue, an ultrathin oxide layer (ceria, Y-dope ceria (YDC), zirconia and Y-doped zirconia (YSZ)) was coated by the atomic layer deposition (ALD) on the infiltrated cathode. While the application of ALD overcoat on porous cathode material itself is not new,3,4 its application to infiltrated cathodes has rarely been reported. To achieve a proper doping for oxygen conduction, Y2O3 sub-cycles for YDC and YSZ were performed once for every 4 ceria and zirconia sub-cycles, respectively. The electrochemical performance between 600 – 750 °C, short-term durability (~100 h) of the resulting structures (performed at 700 °C under a cell polarization of 0.5 V) and relevant discussions will be presented. This work was supported by the NASA MIRO Program (NNX15AQ01A). References 1 D. Ding, X. Li, S. Y. Lai, K. Gerdes and M. Liu, Energy Environ. Sci., 2014, 7, 552. 2 Y. Zhang, R. Knibbe, J. Sunarso, Y. Zhong, W. Zhou, Z. Shao and Z. Zhu, Adv. Mater., 2017, 29, 1700132. 3 A. Karimaghaloo, A. M. Andrade, S. Grewal, J. H. Shim and M. H. Lee, ACS Omega, 2017, 2, 806–813. 4 Y. Gong, D. Palacio, X. Song, R. L. Patel, X. Liang, X. Zhao, J. B. Goodenough and K. Huang, Nano Lett., 2013, 13, 4340–5.

Shallow doping effect of ZnO treatment using atomic layer deposition process on p-type In0.53Ga0.47As

The number of atomic layer deposition (ALD) cycles for ZnO treatment was changed to study its merits and demerits as a passivation layer prior to the deposition of a HfO2 film on a p-type In0.53Ga0.47As substrate. Even a few cycles of ZnO ALD treatment was effective in improving the capacitance–voltage (C–V) characteristics by suppressing strong Fermi-level pinning, which occurred because of a high interface state density near the lower half of the In0.53Ga0.47As band gap. Increases in the number of ZnO ALD cycles induced an increase in the minimum capacitance and response of minority carriers at higher frequencies in the inversion region of the C–V characteristics. According to various temperature- and frequency-dependent C–V analyses, these changes were explained by the shallow p-type doping effect of Zn atoms in the In0.53Ga0.47As substrate. As a disadvantage, ZnO ALD treatment caused a slight increase in the dielectric leakage current.

Improved Stability of Porous Silicon in Aqueous Media via Atomic Layer Deposition of Oxides

In this work, porous silicon (PSi) samples were conformally coated with ultrathin films of aluminum oxide (Al2O3) and hafnium oxide (HfO2) using atomic layer deposition (ALD) to passivate their internal surface and improve their overall stability in aqueous media. Their porosity and optical properties were characterized before and after ALD treatment. The stability over time in aqueous media of the ALD passivated porous layers was then evaluated and compared to PSi layers oxidized at 800 °C (PSiO2), which is a treatment widely used in the literature for biosensing applications. The ALD oxide-covered samples performed equally to the oxidized PSi samples, but exhibited a higher mean refractive index, which results in a better contrast. These improved optical properties resulted in a signal exhibiting a significantly decreased noise. This in turn leads to a theoretical limit of detection improved by a factor 13 and 16 for PSi/Al2O3 and PSi/HfO2, respectively, compared to the standard PSiO2. This could thus r...

Ultrathin ALD coating on TiO2 photoanodes with enhanced quantum dot loading and charge collection in quantum dots sensitized solar cells

TiO2 nanocrystals are widely used in photoanodes for quantum dot solar cells (QDSCs) owing to their chemical stability and suitable energy band structure. However, surface defects and grain boundaries of TiO2 nanocrystals photoanodes allow high surface charge recombination, which limits the performance of QDSCs. In this work, an ultrathin TiO2 layer is introduced to the surface of TiO2 photoanodes by atomic layer deposition (ALD). The ultrathin layer not only reduces the surface defects of TiO2 nanoparticles and strengthens the connection between adjacent nanoparticles to suppress the charge recombination for improving the electron collection efficiency (ηcc), but also increases the surface energy of photoanodes to load more quantum dots (QDs) for enhancing the light harvesting efficiency (LHE). As a result, the solar cell based on CdS/CdSe QDs with ALD treatment exhibits an efficiency of 5.07% that is much higher than that of the cells without modification (4.03%).