Magnetostatic Coupling in CoFe2O4/Pb(Zr0.53Ti0.47)O3 Magnetoelectric Composite Thin Films of 2-2 Type Structure

CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃ (CFO/PZT) magnetoelectric composite thin films of 2-2 type structure had been prepared onto Pt/Ti/SiO₂/Si substrate by a sol-gel process and spin coat-ing technique. The structure of the prepared thin film is substrate/PZT/CFO/PZT/CFO. Two CFO ferromagnetic layers are separated from each other by a thin PZT layer. The upper CFO layer is magnetostatically coupled with the lower CFO layer. Subsequent scan-ning electron microscopy (SEM) investigations show that the prepared thin films exhibit good morphologies and compact structure, and cross-sectional micrographs clearly display a multilayered nanostructure of multilayered thin films. The composite thin films exhibit both good magnetic and ferroelectric properties. The spacing between ferromagnetic layers can be varied by adjusting the thickness of intermediate PZT layer. It is found that the strength of magnetostatic coupling has a great impact on magnetoelectric properties of composite thin films, i.e., the magnetoelectric voltage coefficient of composite thin film tends to increase with the decreasing of pacing between two neighboring CFO ferromagnetic layers as a result of magnetostatic coupling effect.     

Influence of High-energy electron-beam on photocatalytic activity of TiO2 films on carbon-fiber deposited by atomic layer deposition

High-energy electron-beam with energy of 1 MeV was used for modifying surface structure of TiO₂ thin films on carbon fiber prepared by using atomic layer deposition under atmospheric pressure. TiO₂ nanoparticles (∼20 nm) on carbon fiber underwent structural modification of the surface upon electron-beam treatment, resulting in enhanced photocatalytic activity. In contrast, a thicker film of TiO₂ did not show such changes in surface structure and photocatalytic activity by electron-beam treatment. We demonstrate that electron-beam can be used for modifying surface structure of photocatalysts consisting of nanoparticles for improvement of their activity.     

The effect of Al2O3-coating coverage on the electrochemical properties in LiCoO2 thin films

The electrochemical properties of nanoscale Al₂O₃-coated LiCoO₂ thin films were examined as a function of the coating coverage. Al₂O₃-coated LiCoO₂ films showed enhanced cycle-life performance with increasing degree of coating coverage, which was attributed to the suppression of Co dissolution and F⁻ concentration in the electrolyte. Moreover, an Al₂O₃-coating layer with partial coverage clearly improved the electrochemical properties, even at 60 °C or with a water-contaminated electrolyte. Even though metal-oxide coating on LiCoO₂ has been actively investigated, the mechanisms of nanoscale coating have yet to be clearly identified. In this article, surface analysis suggested that the Al₂O₃-coating layer had transformed to an AlF₃ ∙3H₂O layer during cycling, which inhibited the generation of HF by scavenging H₂O molecules present in the electrolyte.     

Threshold Al KLL Auger spectra of oxidized aluminium foils

Threshold Al KLL Auger electron spectroscopy and K‐edge x‐ray absorption fine structure spectroscopy have been used to examine technical purity (99.5%) aluminium foil before and after chemical treatment that altered the thickness and degree of hydroxylation of the oxidized layer. Comprehensive surface chemical characterization was effected by means of monochromatized Al Kα‐excited photoelectron spectroscopy. Threshold Al KL_{2, 3}L_{2, 3} spectra were obtained for three of the foils investigated and these spectra were in broad agreement with those observed previously for pure Al foil. The relative intensities of the spectral components for two of the foils were clearly consistent with the previously proposed assignment of the resonantly enhanced Auger component, situated between those arising from the metal and Al(III) oxide, to a thin interfacial layer. The threshold Auger spectra from the aluminium foil bearing the thickest and most hydroxylated oxidized layer were not obviously consistent with the interfacial layer model but O K‐edge spectra revealed that this surface layer was fundamentally different from the others and could have had a greater interfacial surface area. Copyright © 2003 John Wiley & Sons, Ltd.     

Infrared Spectroscopic Analysis of Plasma-Treated Si(100)-Surfaces

 Infrared reflection spectroscopy (specular reflection, attenuated total reflection) has been applied in combination with spectroscopic ellipsometry and electron microscopy to analyze the surface structure of plasma-treated Si(100) surfaces. It is shown that plasma treatments in oxygen and fluorine or chlorine-containing gases cause the formation of a thin surface layer having thicknesses of a few nanometers. The layer was identified to consist of SiO₂ for treatments in an oxygen plasma. Analyses of layers formed by treatments in a fluorine-containing plasma do not confirm the generally assumed model. Different Si-F vibration modes were identified in the surface layer caused by a SF₆ plasma. They correlate, however, with SiF and SiF₂ molecules. There are no indications of the existence of the generally assumed SiF₄. Neither has SiOF₂ been proven in layers produced by etching in a SF₆/O₂ plasma.     

ToF‐SIMS studies of the oxidation of Fe by D2O vapour: comparison with XPS

The oxidation of iron (Fe) by water (D₂O) vapour at low pressures and room temperature was investigated using time‐of‐flight (ToF) SIMS. The results supported those found previously using XPS and the QUASES^? program in that a duplex oxide structure was found containing a thin outer surface hydroxide (Fe(OD)₂) layer over an inner oxide (FeO) layer. The extraordinary depth resolution of the ToF‐SIMS profiles assisted in identifying the two phases; this resolution was achieved by compensation for surface roughness. A substantial concentration of deuterium was found in the subsurface oxide layer. This observation confirmed previous assessments that the formation of FeO was from the reaction of Fe(OD)₂ with outward‐diffusing Fe, leaving deuterium as a reaction product. Copyright © 2005 John Wiley & Sons, Ltd.     

Interface physicochemical processes controlling sulphate anion incorporation in porous anodic alumina and their dependence on the thermodynamic and transport properties of cations

Aluminium was anodised in H₂SO₄, LiHSO₄, NaHSO₄, KHSO₄, Mg(HSO₄)₂ and Al(HSO₄)₃ electrolytes. The kinetics of growth of porous anodic alumina films and of the pore wall oxide dissolution during anodisation was studied. Based on the derived kinetic parameters, suitable physicochemical processes in the barrier layer electrolyte interface controlling the anion incorporation in the barrier layer were suggested and relevant models were formulated. According to these processes Al³⁺ and H⁺ ions are rejected from the pore base surface in the attached double layer, where Al³⁺ ions are solvated, and are transferred to the pore filling solution. The strongly different mobilities of Al³⁺ and H⁺ and the necessary space negative charge density distribution in the double layer result in similar concentration distributions of Al³⁺ and anions inside it, which differ strongly from that of H⁺. These Al³⁺ and anion concentrations increase with decreasing mobility of the main cations in the solution which depends on their hydration enthalpy and transport mechanism. The concentration of incorporated anions inside both a thin surface layer of the barrier layer and the double layer vary similarly. For identical surface density and base diameter of pores the decrease of the above mobility reinforces anion incorporation.     

Anodic oxidation of copper in alkaline solutions: Part IV. Nature of the passivating film

Potentiostatic and X-ray photoelectron spectroscopic (XPS) techniques have been used to study the passivation of copper electrodes in 1.0 mol dm⁻³ LiOH. For potentials <−80 mV (vs. SCE), a porous base layer of Cu₂O is present, and an upper layer of Cu(OH)₂ is formed by nucleation and growth from solution. The dissolved Cu²⁺ ions necessary for Cu(OH)₂ precipitation are produced by metal dissolution in the pores of the Cu₂O layer. Under these conditions, the surface is only partially passivated, since metal dissolution can continue in the pores of the base layer. For potentials >−60 mV (vs. SCE), these pores, and eventually the whole surface, are covered by a layer of CuO identified by XPS. When this layer is formed, the extent of Cu(OH)₂ formation is drastically reduced. In addition the cupric ion dissolution rate is reduced, indicating a much higher degree of surface passivation.     

Effect of molecular weight on gas selectivity of oriented thin polyimide membrane

In this study, we focused on effect of the molecular weight of polyimide on the gas selectivity of the asymmetric membrane with an oriented surface skin layer prepared at different shear stresses. Asymmetric polyimide membranes, which have a defect‐free surface skin layer supported by a porous substructure, were prepared by a dry/wet phase inversion process. The structures of the asymmetric polyimides consisted of a thin skin layer and a porous substructure characterized by the presence of finger‐voids. The gas selectivities of the asymmetric polyimide membranes increased with an increase in the shear rate or a decrease in the molecular weight, indicating that the oriented polyimide structure in the surface skin layer provided a high size and shape discrimination between the gas molecules. The selectivity values of (O₂/N₂) and (CO₂/CH₄) in the asymmetric polyimide membrane prepared from the 7.2 × 10⁴ molecular weight material at 1000 sec^?1 shear rate were 12 and 143, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

有机物单层分散在相关材料制备中的应用

与无机氧化物和盐类在载体表面自发单层分散相类似, 许多有机物也可以在载体表面自发单层分散.有机物在载体表面单层分散行为和分散后的存在状态与有机物分子形状和结构特点及载体表面性质和孔结构有关. 利用有机物在载体表面的单层分散, 可以设计制备具有优异性能的材料. 本文简要综述了近年来这方面研究工作取得的相关进展, 主要介绍了有机物单层分散在碳/氧化物复合物、氧化物和薄壁中孔碳材料的制备和织构调控方面的一些应用实例. 单层分散的有机物热分解后可在载体表面形成均匀的薄碳层, 以无机多孔氧化物为载体可制备出包覆均匀碳薄层的碳/氧化物复合物, 这种碳/氧化物复合物在染料吸附、催化剂载体和光催化方面显现出好的性能. 以溶胶-凝胶法制备氧化物时, 分散的有机物可以隔离溶胶颗粒, 从而制备出高比表面积的氧化物并可对孔容进行调控, 以此方法制备的γ-氧化铝比表面积可达506 m²·g^-1. 在惰性气氛中加热上述碳/氧化物复合物, 碳层可抑制氧化物的相变; 而在氧气中, 碳层燃烧发热会促进相变, 由此可快速制备超细α-氧化铝. 包覆均匀碳薄层的氧化物载体对碳起支撑作用, 在将氧化物溶解去除后, 可便捷制得高比表面积、大孔容、高中孔率的薄壁中孔碳材料, 碳材料的形貌、孔径分布等可通过选用不同织构的氧化物载体进行调控.     

Revealing the Role of Gold in the Growth of Two-Dimensional Molybdenum Disulfide by Surface Alloy Formation

The formation of Mo/Au surface alloy during Au-assisted chemical vapor deposition (CVD) of MoS₂ is confirmed by a series of control experiments. A metal–organic chemical vapor deposition (MOCVD) system is adapted to conduct two-dimensional MoS₂ growth in a controlled environment. Sequential injection of Mo and S precursors, which does not yield any MoS₂ on SiO₂/Si, grows atomically thin MoS₂ on Au, indicating the formation of an alloy phase. Transmission electron microscopy of a cross-section of the specimen confirms the confinement of the alloy phase near the surface only. These results show that the reaction intermediate is the surface alloy, and that the role of Au in the Au-assisted CVD is the formation of an atomically thin reservoir of Mo near the surface. This mechanism is clearly distinguished from that of MOCVD, which does not involve the formation of any alloy phases.     

Physical mechanisms responsible for the water-induced degradation of PC61BM P3HT photovoltaic thin films

We show that [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM) at the surface of thin film blends of poly(3-hexylthiophene) (P3HT):PC₆₁BM can be patterned by water. Using a series of heating and cooling steps, water droplets condense onto the blend film surface. This is possible due to the liquid-like, water swollen layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Breath pattern water deformation and subsequent drying on the film surface results in isolated PC₆₁BM structures, showing that migration of PC₆₁BM takes place. This was confirmed by selective wavelength illumination to spatially map the photoluminescence from the P3HT and PC₆₁BM. Within a device, redistribution of the surface PC₆₁BM into aggregates would be catastrophic, as it would markedly alter device performance. We also postulate that repeated volume change of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate layer by water swelling may be, in part, responsible for the delamination failure mechanism in thin film solar cells devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 141–146     

Determination of X-ray compression efficiency of a thin film X-ray waveguide structure using marker layer fluorescence

We demonstrate that a thin marker layer, sandwiched in the guiding medium of a thin film planner X-ray waveguide structure, can be used to determine X-ray compression efficiency for a particular excitation mode. It can also be used in evaluating the transmission efficiency of waveguide structure and for the determination of X-ray intensities reaching the waveguide exit. This approach has been applied for determining X-ray compression and transmission efficiency of a Mo/B₄C/Mo based X-ray waveguide structure, by inserting a thin Fe marker layer.     

Influence of YSZ buffer layer on the electric properties of compositionally graded (Ba,Sr)TiO<Subscript>3</Subscript> thin film

Compositionally graded Ba_1−x Sr _x TiO₃ (BST) (0 ≤ x ≤ 0.4) thin films were fabricated on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by a modified sol–gel technique. The YSZ buffer layer was prepared by RF magnetron sputtering. The microstructure of the graded BST films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that all the films have uniform and crack-free surface with a perovskite structure. The graded BST film with an YSZ buffer layer has larger dielectric constant and lower dielectric loss. The leakage current density of the graded BST film with an YSZ buffer layer lowers two orders than the film without buffer layer. The improved electric properties of the graded films with an YSZ buffer layer was attributed to the YSZ buffer layer act as an excellent seeding layer to enhance the graded BST film growth.     

表面修饰的TiO_2太阳能电池界面特性研究

用水热法制备了具有典型锐钛矿晶型的TiO2纳米材料,采用Cr(NO3)3对TiO2薄膜电极进行修饰改性。用X射线衍射(XRD)、扫描电子显微镜(SEM)和光电子能谱(XPS)测试电极的物相及表面结构,结果显示TiO2薄膜表面包覆一层粒径较大的氧化铬颗粒,整个电极仍保持均匀的多孔结构。电流-电压(I-V)曲线测试结果显示,改性后最佳电极的短路电流和光电转换效率分别比改性前提高了31.1%和40.4%。用电化学阻抗谱(EIS)测试电池的界面特性,从测试结果可以看出,相同偏压下,改性后电池的TiO2/染料/电解质界面电阻更大,说明氧化铬包覆层在一定程度上抑制了界面的电子复合,改善了电池的光电输出特性。     

Single-step fabrication of asymmetric dual-phase composite membranes for oxygen separation

Asymmetric dual-phase composite membranes for oxygen separation were conveniently fabricated by an acid leaching technique. A thin dense layer of Ce_0.85Sm_0.15O_1.925/Sm_0.6Sr_0.4FeO_3−δ was left by controlling the degree of acid leaching, and a porous substrate of Ce_0.85Sm_0.15O_1.925 with a fluorite structure was formed after dissolution of Sm_0.6Sr_0.4FeO_3−δ with a perovskite structure in HCl. Thus, a thin dense layer and a porous substrate can be fabricated in a single step in which traditional shrinkage mismatch and chemical reaction between thin dense layers and porous substrates can be avoided. The thickness of the dense layer can be controlled by varying the acid leaching time. Hence, dual-phase composite membranes with high oxygen flux can be obtained.     

Formation of cadmium sulfide (CdS) nanofilm on a Cd(OH)2/SiO2 precursor layer

Dense thin nanostructured films of cadmium sulfide CdS obtained by chemical deposition from aqueous solutions are strongly bound to a substrate due to the formation of cadmium hydroxide Cd(OH)₂ in the system. By X-ray reflectometry and grazing incidence diffraction it is found that at the beginning of the deposition a dense Cd(OH)₂/SiO₂ layer is produced on the surface of a silicon or glass substrate. This layer is formed through the atomic-layer adsorption of crystalline 1–3 nm thick Cd(OH)₂ film by the oxygencontaining substrate surface. During sulfidation of this cadmium-containing substrate layer, a surface nucleation layer of CdS/Cd(OH)₂/SiO₂ forms, which provides the growth, denseness, and strong adhesion to the substrate of nanostructured CdS film with a disordered structure. According to the obtained experimental data, a “hydroxide scheme” of film deposition is confirmed and refined, and the stages of CdS nanofilm formation are determined.     

SAXS study of polymer adsorption on porous ZrO2

The small‐angle X‐ray scattering method (SAXS) has been used for the analysis of polymer adsorption on porous ZrO₂. Particular attention has been paid to the adsorption of polyacrylic acid (PAA) and polyacrylamide (PAM) on the surface of porous ZrO₂. It has been established that the SAXS method determines whether the polymer has penetrated the carrier's pores, and that polymers of low molecular weight create a thin transition layer on the surface of ZrO₂ (understood in the context of a change in the electron density). The creation of this layer is clearly reflected in the run of SAXS curves (Porod's plot). Ruland–Vonk's method has been used to determine the thickness of the transition layer. The results are consistent with those obtained when the viscosity method was used. Copyright © 2003 John Wiley & Sons, Ltd.     

Layer‐by‐Layer Assembled Conductive Metal–Organic Framework Nanofilms for Room‐Temperature Chemiresistive Sensing

The utility of electronically conductive metal–organic frameworks (EC‐MOFs) in high‐performance devices has been limited to date by a lack of high‐quality thin film. The controllable thin‐film fabrication of an EC‐MOF, Cu₃(HHTP)₂, (HHTP=2,3,6,7,10,11‐hexahydroxytriphenylene), by a spray layer‐by‐layer liquid‐phase epitaxial method is reported. The Cu₃(HHTP)₂ thin film can not only be precisely prepared with thickness increment of about 2 nm per growing cycle, but also shows a smooth surface, good crystallinity, and high orientation. The chemiresistor gas sensor based on this high‐quality thin film is one of the best room‐temperature sensors for NH₃ among all reported sensors based on various materials.     

Optimizing the Atomic Layer Deposition of Alumina on Perovskite Nanocrystal Films by Using O2 As a Molecular Probe

Encapsulation methods have shown to be effective in imparting improved stability to metal-halide perovskite nanocrystals (NCs). Atomic layer deposition (ALD) of metal oxides is one of the promising approaches for such encapsulation, yet better control on the process parameters are required to achieve viable lifetimes for several optoelectronic and photocatalytic applications. Herein, we optimize the ALD process of amorphous aluminum oxide (AlO_x) as an encapsulating layer for CsPbBr₃ NC thin films by using oxygen (O₂) as a molecular diffusion probe to assess the uniformity of the deposited AlO_x layer. When O₂ reaches the NC surface, it extracts the photogenerated electrons, thus quenching the PL of the CsPbBr₃ NCs. As the quality of the ALD layer improves, less quenching is expected. We compare three different ALD deposition modes. We find that the low temperature/high temperature and the exposure modes improve the quality of the alumina as a gas barrier when compared with the low temperature mode. We attribute this result to a better diffusion of the ALD precursor throughout the NC film. We propose the low temperature/high temperature as the most suitable mode for future implementation of multilayered coatings.