Modulation of wall thickness of Al-doped ZnO nanotubes by nanolamination of atomic layer deposition for oxygen sensing

The high surface-to-volume ratio and feature dimensions of the gas sensors are the key factors for improving the gas response. In this study, a novel method to prepare an Al-doped ZnO (AZO) nanotube oxygen sensor with tunable wall thickness is reported via the ZnO–Al₂O₃ nanolamination of atomic layer deposition (ALD) using tris(8-hydroxyquinoline) gallium nanowire (GaQ₃NW) as a template. The ALD of Al₂O₃ significantly enhances wall uniformity and decreases the wall thickness of the AZO nanotubes. In addition, the incorporation of Al₂O₃ allows full coverage of AZO on GaQ₃NWs. With an increase in the Al₂O₃ fraction, the carrier concentration increases, but the depth of the depletion layer and gas response of the nanotube sensor are reduced. The gas response of the nanotubes is inversely proportional to wall thickness, suggesting that it is a function of the surface-to-volume ratio. When the wall thickness is decreased to 12 nm, the gas response of AZO nanotubes with 2% Al increases significantly to 7. This can be explained by the grain control model, because thin wall leads to the formation of fully charge-depleted nanotubes.     

Performance improvement of phase-change memory cell using AlSb3Te and atomic layer deposition TiO2 buffer layer

A phase change memory (PCM) cell with atomic layer deposition titanium dioxide bottom heating layer is investigated. The crystalline titanium dioxide heating layer promotes the temperature rise in the AlSb₃Te layer which causes the reduction in the reset voltage compared to a conventional phase change memory cell. The improvement in thermal efficiency of the PCM cell mainly originates from the low thermal conductivity of the crystalline titanium dioxide material. Among the various thicknesses of the TiO₂ buffer layer, 4 nm was the most appropriate thickness that maximized the improvement with negligible sacrifice of the other device performances, such as the reset/set resistance ratio, voltage window, and endurance.     

Al_2O_3/TiO_2纳米抗菌剂的制备及性能

以TiC l4、A l2(SO4)3为原料,控制n(A l2O3)/n(TiO2)=0.2,采用液相共沉淀法制备了A l2O3/TiO2纳米抗菌剂,并用DSC-TG、XRD、UV-vis等手段研究了A l2O3复合对TiO2抗菌性能的影响。结果表明,复合A l2O3后,TiO2纳米抗菌剂经900℃煅烧后完全是锐钛矿结构;950~1 050℃为良好的混晶结构,其中,经950℃煅烧后,混晶结构中锐钛矿相质量分数约占77%,平均粒径约20 nm,可见光吸收带边红移显著,光吸收阈值由纯TiO2的380 nm红移至430 nm左右,抗菌性能好,在荧光灯下对大肠杆菌和金黄色葡萄球菌的抑菌圈直径达15mm左右。     

微乳-水热法合成核壳型TiO2/Al2O3纳米粉体

本文采用微乳-水热法一步合成了核壳型TiO2/Al2O3纳米粉体.通过对产物的Zeta电位研究得出制备Ti(OH)4/Al(OH)3核壳前驱体的最佳pH值.并且采用XRD、TEM及SEM等表征方法与普通一步水热法合成的TiO2/Al2O3纳米粉体的晶形晶貌进行比较.结果表明:微乳-水热法能改善颗粒形状和大小,产品的颗粒大小均匀、平均晶粒粒径为13.68 nm.     

原子层沉积技术在银工艺饰品抗变色中的应用

分析了电镀贵金属、无机钝化膜、有机保护膜等几类常见银合金表面处理方法的特点及存在的问题,概述了原子层沉积技术的发展背景、基本原理、工艺特点、研究及应用状况,介绍了该技术应用于银工艺饰品抗变色上的效果.     

原子层沉积技术在钛改性多孔氧化铝上的应用

采用原子层沉积技术进行Al₂O₃表面钛改性,利用N2吸附-脱附、X射线衍射、X射线荧光分析、透射电镜和热重-微分热重-差示扫描量热等表征手段对改性前后的Al₂O₃载体进行表征。结果表明,钛分散到Al₂O₃表面,Al₂O₃载体表面氧化钛为锐钛矿结构,改性后的载体具有良好的热稳定性。钛分散性与Al₂O₃表面化学环境有关,钛对多孔Al₂O₃表面改性可以通过原子层沉积技术实现。     

Synthesis of high‐molecular weight poly(trimethylene terephthalate) catalyzed by MoO3 supported Al2O3‐TiO2 catalysts

Poly(trimethylene terephthalate) (PTT) is an excellent fiber materials. Although it was synthesized as early as 1940s, obtaining high‐molecular weight PTT suitable for spinning is not easy due to no evident breakthrough in the catalysts for PTT synthesis. Patents and literatures disclosed a lot of the catalysts of preparing PTT, but which are more or less disadvantageous. Based on acid catalytic mechanism of PTT preparation, a series of solid acid as x% MoO₃/(50% Al₂O₃ ? 50% TiO₂) (briefly written as xM/(A ? T), x = 0, 10, 15, 20 by weight) were prepared by sol–gel coprecipitation and wetting impregnation methods, and first used for PTT synthesis in this work. When 50% Al₂O₃ ? 50% TiO₂ (briefly written as A ? T) was supported by MoO₃ using wetting impregnation technique of (NH₄)₆Mo₇O₂₄.4H₂O aqueous solution, a lot of Brφnsted acid and Lewis acid sites were formed on xM/(A ? T) catalyst surfaces, which was confirmed by the characteristics of their NH₃‐TPD (temperature programmed desorption). All the prepared catalysts were highly active ones toward synthesis of PTT. PTT with high‐intrinsic viscosity (IV) was obtained in the presence of trace amount of the catalysts. IV ranging of the PTT synthesized from 0.66 to 0.95 dL g^?1 corresponds to weight average molecular weight from 49,197 to 73,004. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

钛酸铝／氧化铝复合材料的制备及其抗铝液浸渗性能

以Al2O3,TiO2,MgO和Fe2O3粉末为起始原料制备出不同氧化铝含量的钛酸铝／氧化铝复合材料;通过考察浸于熔融铝液中试样断面显微结构和特征元素分布研究了复合材料抗铝液浸渗性能。研究表明,反应烧结得到的是含5％MgTi2O5（质量分数）和1％Fe2TiO5（质量分数）的钛酸铝复合固溶体与氧化铝组成的复合材料,复合材料的烧结致密度随试样中氧化铝含量的增加而增加。高钛酸铝含量的钛酸铝／氧化铝复合材料具有良好的抗铝浸渗性能。     

二氧化钛纳米管稳定Pickering乳液制备PS/TiO2纳米管复合微球

利用γ-甲基丙烯酰氧基丙基三甲氧基硅烷（KH-570）,对水热法制备的TiO₂纳米管进行了表面改性,并用改性的纳米管为稳定剂,采用Pickering乳液聚合法制备了聚苯乙烯/TiO₂纳米管复合微球。采用红外光谱（IR）、光学显微镜、高分辨透射电镜（HRTEM）、高分辨扫描电子显微镜（FESEM）、X射线光电子能谱（XPS）等分析手段,对改性前后TiO₂纳米管以及复合微球的结构和形貌进行了表征,用三相接触角仪测试并优化了TiO₂纳米管的表面润湿性。研究结果表明,当m_KH-570/m_TiO2=15%时,改性TiO₂纳米管表面润湿性最佳,能很好地稳定Pickering乳液聚合,聚合后可以得到壳层为致密均匀TiO₂纳米管,核为聚苯乙烯的复合微球。     

Anticorrosion assessment of Al2O3‐TiO2 composite thin films derived from sol‐gel dipping technique

Metal surface protection by means of nanostructured ceramic coatings is considered an issue, which is variously scrutinized, and more efforts are made to improve steel performance in accordance with this method. In this respect, this study sought to examine the protective effects of a nanostructured coating containing TiO₂ and Al₂O₃. The optimization approach for obtaining a coating without any cracks with the highest efficiency of corrosion resistance is reported. The variables under assessment were as follows: weight ratio of the oxides, calcination temperature, and preparation parameters. The synthesized samples were analyzed utilizing XRD, FESEM, AFM, Tafel test, EIS, and microhardness measurement. The results revealed that the optimized conditions were as follows: (i) Ti:Al precursor mixture with a weight ratio of 75:25, (ii) heat treatment at 1000°C. This process yielded a uniform composite coating without any cracks with 5.1 nm roughness, containing crystalline rutile phase and amorphous alumina. Not only the intended coating improves the corrosion resistance of steel up to 97%, but it also increases its surface hardness up to 10 units.     

直接氧化法制备TiO2-Al2TiO5复相陶瓷

以Ti—Al—C和TiC—Ti—Al体系为反应体系,采用直接氧化法制备Al2TiO3-TiO2复相陶瓷。研究了氧化温度对体系合成产物组成的影响。结果表明,两种体系的合成产物都由Al2TiO3和TiO2相组成,没有杂质相存在。碳高温氧化成CO2向外扩散,在坯体内形成疏松通道,利于O2的渗入,提高了氧化反应程度。     

原子层沉积构建高性能催化剂的研究进展

催化剂在能源化工领域具有重要应用,精确设计及调控催化剂结构可有效改善催化剂的性能。原子层沉积（ALD）是基于饱和自限制的气-固界面反应技术,被认为是调控活性相的组成、尺寸及落位最有效的方式之一。本文综述了ALD技术在调控催化剂活性相结构、设计多功能型催化剂及提高催化剂稳定性等方面的研究进展。重点阐述了ALD技术在调控催化剂活性相颗粒尺寸和表界面结构、设计多功能核壳结构及多孔材料限制性催化剂等方面的应用。ALD设计及控制金属沉积的技术优势可实现对催化剂活性、产物选择性和稳定性的有效调控,但其在复杂结构载体的沉积机理方面仍未得到充分研究,是今后研究工作重点。此外,利用ALD技术设计结构清晰、功能多样的催化剂来进一步提高催化性能及认识其反应机理也是未来的研究方向。     

Solid-state sintering of core-shell ceramic powders fabricated by particle atomic layer deposition

The properties of technical ceramics are highly dependent on their microstructure, which evolves during sintering. Sintering is the process by which ceramic parts are subjected to high temperatures to activate chemical diffusion and the consumption of porosity. During the initial stage of sintering, interparticle necks between neighboring particles form and subsequently increase in size, consuming porosity as the particle centers move closer together. To experimentally determine how this process depends on particle surface composition, particle atomic layer deposition (ALD) was used to deposit a thin film of amorphous aluminum oxide (Al₂O₃) onto yttria-stabilized tetragonal zirconia (3YSZ) particles, producing core-shell structured powders. The uniformity of the Al₂O₃ film was confirmed with transmission electron microscopy and energy dispersive spectroscopy. Scanning electron microscopy was used to observe microstructural evolution during sintering, and the dihedral angles of Al₂O₃ and 3YSZ grains were measured to determine the ratio of interfacial energies between the 3YSZ|3YSZ, 3YSZ|Al₂O₃, and Al₂O₃|Al₂O₃ interfaces. Analysis of the densification kinetics revealed that the initial stage of densification is dependent on the material at the surface of the particles (ie, the Al₂O₃ film) and is controlled by the diffusion of Al³⁺ cations through Al₂O₃. Once the Al₂O₃ film has coalesced, the sintering behavior is controlled by the densification of the core material (3YSZ). Thus, core-shell powders fabricated by particle ALD sinter by a two-step process where the kinetics are dependent on the material present at interparticle contacts.     

Highly conductive mesoporous hierarchical carbon hollow fibers fabricated via confinement of TiO2 coating by ALD

A polysulfone (PSF) hollow fiber composed of interconnected nanofibers within its wall was employed as a template to deposit with a layer of TiO₂ by atomic layer deposition. Direct nitridation of the TiO₂-coated PSF hollow fiber at 800 and 1000°C was conducted, and a new hierarchical structure of TiO_xN_1−x and TiN@nitrogen-doped carbon hollow fibers, respectively, was formed. The PSF fiber served as the source of carbon and was directly transformed to a nitrogen-doped carbon fiber because the shape change was confined by the TiO₂ coating. In the meantime, TiO_xN_1−x or TiN was formed after the nitridation of TiO₂. X-ray photoelectron spectrometric analysis indicated that there was no chemical bonding between the nitridized coating and the carbon nanofibers. It implies that the nitridation of TiO₂ and carbonization of PSF proceed independently and simultaneously in the nitridation process. Raman spectroscopic analysis also confirmed the formation of graphitic lattice and Ti–N bonding. Electrical measurement indicated that both fibers were highly conductive, with the electrical resistivity in the order of 10⁻⁵ Ω m, which is lower than those of amorphous carbon and graphite along the direction perpendicular to the basal plane.     

Gd~(3+)掺杂TiO_2纳米纤维的制备、表征及其光催化性能

采用静电纺丝技术并结合溶胶-凝胶方法制备TiO2和TiO2/Gd2O3纳米纤维,采用差热-热重分析(TG-DTA)?场发射扫描电镜(FE-SEM)、红外光谱(FTIR)、X射线粉末衍射(XRD)对材料进行表征,通过亚甲基蓝光降解反应研究其催化性能。结果表明,掺杂Gd3+可以强烈抑制TiO2由锐钛矿相向金红石相的转变,抑制晶粒生长,减少晶粒尺寸;Gd3+掺杂TiO的纳米纤维对亚甲基蓝的光催化活性明显提高。     

Thermal conductivity of yttria-stabilized zirconia thin films grown by plasma-enhanced atomic layer deposition

Zirconia doped with yttrium, widely known as yttria-stabilized zirconia (YSZ), has found recent applications in advanced electronic and energy devices, particularly when deposited in thin film form by atomic layer deposition (ALD). Although ample studies reported the thermal conductivity of YSZ films and coatings, these data were typically limited to Y₂O₃ concentrations around 8 mol% and thicknesses greater than 1 μm, which were primarily targeted for thermal barrier coating applications. Here, we present the first experimental report of the thermal conductivity of YSZ thin films (∼50 nm), deposited by plasma-enhanced ALD (PEALD), with variable Y₂O₃ content (0–36.9 mol%). Time-domain thermoreflectance measures the effective thermal conductivity of the film and its interfaces, independently confirmed with frequency-domain thermoreflectance. The effective thermal conductivity decreases from 1.85 to 1.22 W m⁻¹ K⁻¹ with increasing Y₂O₃ doping concentration from 0 to 7.7 mol%, predominantly due to increased phonon scattering by oxygen vacancies, and exhibits relatively weak concentration dependence above 7.7 mol%. The effective thermal conductivities of our PEALD YSZ films are higher by ∼15%–128% than those reported previously for thermal ALD YSZ films with similar composition. We attribute this to the relatively larger grain sizes (∼23–27 nm) of our films.     

Photocatalytic functional coatings of TiO2 thin films on polymer substrate by plasma enhanced atomic layer deposition

We prepared photocatalytic TiO₂ thin films which exhibited relatively high growth rate and low impurity on polymer substrate by plasma enhanced atomic layer deposition (PE-ALD) from Ti(NMe₂)₄ [tetrakis (dimethylamido) Ti, TDMAT] and O₂ plasma to show the self-cleaning effect. The TiO₂ thin films with anatase phase and bandgap energy about 3.3 eV were deposited at growth temperature of 250 °C and the photocatalytic effects were compared with commercial Activ glass. From contact angles measurement of water droplet and photo-induced degradation test of organic liquid, TiO₂ thin films with anatase phases showed superhydrophilic phenomena and decomposed organic liquid after UV irradiation. The anatase TiO₂ thin film on polymer substrate showed highest photocatalytic efficiency after 5 h UV irradiation. We attribute the highest photocatalytic efficiency of TiO₂ thin film with anatase structure to the formation of suitable crystalline phase and large surface area.     

Structural features and thermoelectric properties of Al‐doped (ZnO)5In2O3 homologous phases

In this work, we investigated the influence of Al doping on the structure of the (ZnO)₅In₂O₃ homologous phase and the thermoelectric characteristics of (ZnO)₅(In_1?xAl_x)₂O₃ ceramics for x=0, 0.01, 0.03, 0.05, 0.1, and 0.2, prepared using a classic ceramic procedure and sintering at 1500°C for 2 hours. The Al substituted for In on both the primary sites in the Zn₅(In_1?xAl_x)₂O₈ homologous phase, the octahedral sites in the basal‐plane inversion boundaries and the trigonal bi‐pyramidal sites in the zig‐zag inversion boundaries, which resulted in a uniformly increased shrinkage of the unit cell with the additions of Al. The a and c parameters were reduced for x=0.2 by a maximum 0.8%. All the samples had similar microstructures, so the differences in the TE characteristics mainly resulted from the effects of the substitution of Al for In, decreasing the charge‐carrier concentration and affecting their mobility. Slightly improved TE characteristics were only observed for Al additions with x=0.01‐0.05, while larger additions of Al only resulted in a reduced electrical conductivity and decreased ZT values in comparison to the un‐doped composition.     

Atomic layer deposition (ALD) of nanoscale coatings on SrAl2O4-based phosphor powders to prevent aqueous degradation

The aqueous degradation of Eu²⁺-activated and Dy³⁺-codoped strontium aluminate (SrAl₂O₄:Eu²⁺, Dy³⁺, SA2-Green) long afterglow phosphors synthesized from solid-state reaction and coated with nanoscale metal oxide protective layers (≤12 nm) via atomic layer deposition (ALD) is investigated. Uncoated phosphor powders degrade rapidly upon water immersion and lose their green phosphorescence within 48 hours of water exposure. Postmortem investigations reveal hydration and decomposition of the SrAl₂O₄ phase. ALD of ~10 nm Al₂O₃ or ~12 nm TiO₂ is found to significantly improve the powder's resistance to aqueous degradation. All ALD-coated powders show minimal structural and chemical degradation and retain phosphoresence after 48 hours of water immersion. This enhanced durability offers a new pathway for applying long afterglow phosphors to outdoor applications like roadway markings or safety signage and for their incorporation into more eco-friendly waterborne coatings.     

Pool boiling fouling and corrosion properties on liquid‐phase‐deposition TiO2 coatings with copper substrate

Fouling on the heat transfer surfaces of industrial heat exchangers is an intractable problem, and several techniques have been suggested to inhibit fouling. Surface coatings are of such techniques by which the adhesion force between fouling and heat transfer surface can be reduced with low surface free energy thin films. In this article, liquid phase deposition was applied to coat titanium dioxide thin films on the red copper substrates with film thickness in micro‐ or nano‐meter scale. Coating thickness, contact angle, roughness, surface topography, and components were measured with X‐ray diffraction, contact angle analyzer, stylus roughmeter, scanning electron microscopy, and energy dispersive X‐ray spectroscopy, respectively. Surface free energy of coating layers was calculated based on the contact angle. Heat transfer and fouling characteristics in pool boiling of distilled water and calcium carbonate solution on coated surfaces were investigated. Heat transfer enhancement was observed on coated surfaces compared with untreated or polished surfaces due to the micro‐ and nano‐structured surfaces which may increase the number of nucleation sites. The nonfouling time on the coated surfaces is extended than that on the untreated or polished surfaces due to the reducing of the surface free energy of coated surfaces. Corrosion behavior of coated surfaces soaked in the corrosive media of hydrochloric acid, sodium hydroxide alkali, and sodium chloride salt solutions with high concentration at room temperature a few hours was also explored qualitatively. Anticorrosion results of the coated surfaces were obtained. The coatings resisted alkali corrosion within 7.2 × 10⁵ s, acidic corrosion within 3.6 × 10⁵ s and salt corrosion within 2.16 × 10⁶ s. The present work may open a new coating route to avoid fouling deposition and corrosion on the heat transfer surfaces of industry evaporators, which is very important for energy saving in the related industries. © 2010 American Institute of Chemical Engineers AIChE J, 2011