Ce:YIG薄膜中氧空位对光吸收性能的影响

讨论了Ce替代石榴石薄膜制备条件对其光吸收性能的影响.通过引入氧空位概念,提出了溅射气氛中的氧含量对薄膜中Ce元素价态影响的理论模型.基于该模型,讨论了Ce：YIG晶体中氧空位的产生机理.研究表明,当晶格中存在过量氧空位时,会导致部分Fe^3＋被还原成Fe^2＋,使得薄膜的光吸收显著增大.实验结果证实,在Ce：YIG薄膜的晶化过程中,采用富氧气氛可以使得薄膜中Ce元素的价态以Ce^3＋离子为主而Ce^4＋离子含量较少,从而有效降低薄膜的光吸收.溅射气氛中的氧含量及后续热处理过程中氧含量的大小均会直接影响Ce：YIG薄膜的光吸收特性.     

Microwave-assisted synthesis of nanostructured perovskite-type oxide with efficient photocatalytic activity against organic reactants in gaseous and aqueous phases

Microwave-assisted synthesis as a straightforward, efficient and time-saving approach is used for the synthesis of LaFeO₃ nanoparticles. The obtained perovskite showed a narrow band gap energy (2.12 eV), high crystallinity, great oxygen adsorption/ desorption ability and mesoporous structure. In order to assess the photocatalytic activity, benzene and reactive black 5 (RB5) dye are used as gaseous and aqueous reactants, respectively. Under visible light irradiation, almost 85% benzene and 96% RB5 degradation are obtained over the perovskite. The reactions are monitored for 60 min using Gas Chromatography (FID&TCD) and UV-VIS spectrophotometer. The dye degradation process is studied thoroughly, from the mechanistic point of view. Surface charge density of LaFeO₃ is measured at different dye concentration to identify the electrical nature of the surface whether it is positive or negative. Moreover, a series of reactions are conducted to monitor the effect of scavengers on the rate of the photocatalytic dye degradation and decipher which active species (hydroxyl and superoxide radicals or the holes) have dominated the dye oxidation reaction. In the present study, hydroxyl radicals are found as the main active species in the photocatalytic degradation reaction.     

Effect of the oxygen vacancy gradient in titanium dioxide on the switching direction of bipolar resistive memory

Resistive memory switching behavior depending on voltage sweep direction is studied by intentionally creating oxygen vacancies within titanium dioxide (TiO₂). By inserting a reactive Ti layer on the TiO₂, oxygen deficient TiO_2−x layer is created, which then causes TiO_2−x/TiO₂ which has an oxygen vacancy gradient. This gradient of oxygen vacancy makes it possible to create an insulating TiO₂ layer on the bottom electrode during the first reset with a negative bias at the top electrode. This insulating layer makes counterclockwise directional bipolar switching more stable. On the other hand, under the clockwise directional voltage sweeping, the first set switching is prevented by the insulating TiO₂ layers created during the first and second reset, which leads to a short circuit due to local heating eventually.     

Influence of oxygen on semi-transparent organic solar cells with gas permeable electrodes

Semi-transparent P3HT:PCBM (poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester) solar cells with high conductivity PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) top electrodes are used to study degradation. Due to the gas permeability of this type of electrode, the simultaneous exposure to oxygen and light leads to a strong decrease of the short circuit current on the timescale of minutes. The losses are not due to a change in the conductivity of the PEDOT:PSS layer, and the short circuit current can be partially recovered by a heating step, indicating that the observed degradation is taking place in the photo-active layer of the cell.     

Effect of oxygen plasma on the properties of tantalum oxide films

The effect of oxygen plasma on the leakage current, permittivity, and the dielectric loss tangent of Ta₂O₅ thin layers (300–400 nm) is studied. It is suggested to treat tantalum oxide films in oxygen plasma to control their electrical and dielectric characteristics.     

First-principles study of the effects of oxygen vacancy on hole tunneling current

The effects of oxygen vacancies on the electronic structure of silicon dioxide and the hole tunneling current were investigated using first-principles calculations. A level related to oxygen vacancy was obtained to be nearly 2.0 eV from the top of valence band within the bandgap of the α-quartz supercell with one oxygen vacancy. And therefore the defect assisted hole (electron) tunneling currents were calculated. The results shows that the hole tunneling current will be dominant for a thinner oxide thickness at low oxide field and the contribution of trap assisted hole tunneling to the total tunneling current decreases with oxide thickness and oxide field increasing. It is concluded that the effects of the oxygen vacancies on the hole tunneling current become smaller with larger oxide thickness and higher electric field.     

Enhanced photocatalytic activity of graphene oxide/titania nanosheets composites for methylene blue degradation

In the present work, we report enhanced photocatalytic degradation of methylene blue dye in aqueous solution by using ultra-thin anatase TiO₂ nanosheets (NSs) combined with graphene oxide (GO) as a photocatalyst. The two-dimensional ultra-thin anatase TiO₂ NSs are fabricated via chemical exfoliation. By completely delaminating a lepidocrocite-type layered protonic titanate H_xTi_2−x/4□_x/4O₄·H₂O (x=0.7, □: vacancy) into individual layers through ion exchange with tetrabutylammonium (TBA⁺) cations, well-dispersed ultra-thin colloidal Ti_0.91O₂ NSs with a lateral size up to a few micrometers are obtained. Subsequent acid treatment induces colloidal Ti_0.91O₂ to reassemble and precipitate into a gelation form, followed by thermal annealing to convert the Ti_0.91O₂ gelation into anatase TiO₂ nanosheets as photocatalyst for methylene blue degradation. TiO₂ NSs show a high photocatalytic degradation efficiency of 53.2% due to the ultra-thin thickness for facile electron transfering and large surface area for methylene blue absorption. Moreover, photocatalytic effect can be further improved by simply adding GO suspension to achieve colloidal self-assembly of GO and TiO₂ NSs. An optimal GO content of 3 wt% further increases the photocatalytic degradation efficiency to 91.2% due to faster electron–hole seperation and improved surface area provided by GO. This work provides a simple but effective approach by combing graphene oxide with TiO₂ nanosheets synthesized via the exfoliation method for methylene blue degradation.     

Facile sonochemical synthesis of BiOBr-graphene oxide nanocomposite with enhanced photocatalytic activity for the degradation of Direct green

The BiOBr-graphene oxide (BiOBr-GO) nanocomposite was successfully synthesized by sonochemical method. The as-synthesized nanocomposite was characterized by Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The effect of incorporation of graphene-oxide with BiOBr on photocatalytic performance of BiOBr under exposure of UV–Visible light irradiation was systematically investigated. The percent removal of Direct green by BiOBr-GO at pH 7 was found to be 91.9% while by pure BiOBr it was 37%. This exhibits that BiOBr-GO shows enhanced adsorption and photocatalytic performance for removal of Direct green under UV–Visible light irradiation. Mechanism of Direct green degradation can be explained by AOP involving heterogeneous photocatalysis. The probable mechanism of photocatalytic degradation and mineralization of Direct green also explained by LC–MS analysis. The mineralization efficiency indicates the 91.7% TOC removal for the degradation of Direct green by BiOBr-GO.     

FPD气相色谱法测定液晶材料中微量有机膦杂质

建立了一种液晶材料中微量有机膦杂质的FPD气相色谱分析测试方法,可以同时测试液晶材料中微量三苯基氧膦和三苯基膦杂质。方法重现性好,结果相对标准偏差(RSD,n=5)分别为4.4%和5.6%,有机膦杂质的添加回收率为80%~110%。实验对于液晶材料工业化过程中膦成分的分析方法建立具有较好的指导意义。     

Effect of interfacial and bulk organic contamination on the quality of thin silicon oxide

The effect of organic contamination of silicon (HF-last cleaned) and silicon dioxide (as-received) wafer surfaces on the quality of gate oxide was studied. Controlled contamination by model organics as well as cleanroom contamination conditions were investigated. Wafers were oxidized under oxidizing or inert ramp-up ambient to grow ultrathin thermal oxides (30 /spl Aring/). Surface and electrical characterization of the oxides was done by Auger sputter profiling, tunneling atomic force microscopy (TAFM) and gate oxide integrity (GOI) measurements. For oxides grown in an inert ambient during ramp-up, HF-last cleaned wafers had a large number of carbon-based defects as compared to as-received wafers. Oxygen in the ramp-up ambient oxidized and volatilized organics resulting in good quality thin gate oxides for HF-last cleaned wafers. However, for as-received wafers, the defect density was increased in an oxidizing ramp-up ambient. A probable mechanism for degradation of the gate oxide quality on HF-last wafers in an inert ramp-up ambient is investigated.     

New model for the role of oxygen in the emitting surface of the impregnated tungsten cathode

Based on the analysis and synthesis of recent experimental results—in particular, on the role of oxygen in the surface of a tungsten substrate—previous suggestions are examined and disproved. Furthermore, a new model for the role of oxygen in the thermionic emitting surface of an impregnated tungsten cathode is proposed. The model assumes that, at oxygen concentrations of approximately 5 × 10¹⁴ atoms cm^?2 or less, oxygen atoms are incorporated into the outermost layer of the tungsten substrate; this accompanies the surface roughening that lowers the work function, enhances the barium-substrate bond, and forms a compacted Ba-(W,O) atomic configuration that is most stable and has the lowest work function. At higher oxygen concentrations, the excess oxygen lies on a surface site between the barium adsorbate and the tungsten substrate, forming a less stable Ba-O-(W,O) configuration that increases the work function and poisons the emitting surface. This model can effectively explain all the observed experimental results.     

Effect of annealing-induced oxidation of molybdenum oxide on organic photovoltaic device performance

Molybdenum oxide (MoO_x) has been widely used as a hole transport layer in organic photovoltaic cells (OPVs), whose performance can be improved by inserting a MoO_x layer between an organic active layer and a transparent anode because of efficient carrier dissociation. In this study, the influence of thermally annealed MoO_x on the photovoltaic performance of OPVs was first investigated using low-bandgap polymer and [6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) blend films as the active layer. We used three low-bandgap polymers: poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl) (PTB7), and poly([2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b,3,3-b]dithiophene]3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl) (PTB7-Th). Power conversion efficiencies were drastically increased for all investigated polymers when the as-deposited MoO_x layer was annealed at 160 °C for 5 min. In particular, a high efficiency of 6.57% was achieved when PTB7 was used; for comparison, the efficiency of a reference device with an as-deposited MoO_x layer (not subjected to annealing) was 1.40%. Specifically, the short-circuit current density and fill factor were remarkably improved after annealing, which means that efficient carrier dissociation was achieved in the active layer. We evaluated optical absorption and surface morphology to elucidate reasons behind the improved photovoltaic performance, and these parameters only slightly changed after annealing. In contrast, angle-dependent X-ray photoelectron spectroscopy revealed that the MoO_x layer was oxidized after annealing. In general, the oxygen vacancies of MoO_x act as carrier traps; a reduction in the number of carrier traps causes high hole mobility in the organic layer, which, in turn, results in an improved photovoltaic performance. Therefore, our results indicate that the annealing-induced oxidation of MoO_x is useful for achieving high photovoltaic performance.     

Effect of morphology on the photocatalytic activity of g-C3N4 photocatalysts under visible-light irradiation

Graphite-like carbon nitride (g-C₃N₄) photocatalysts with different morphologies have been synthesized using melamine as a precursor using a template-free wet chemical method. The as-prepared g-C₃N₄ nanorods, g-C₃N₄ microcones and porous g-C₃N₄ quadruple prisms were characterized by XRD, FESEM, FT-IR and UV–vis absorption spectrophotometer. These nanostructured g-C₃N₄ photocatalysts show better photocatalytic activity than bulk g-C₃N₄ under visible light irradiation in view of degrading Rhodamine B (RhB). The porous g-C₃N₄ quadruple prisms show the highest photocatalytic efficiency. We deduce that the surface area of the catalysts and their adsorption ability of target molecules play important roles in improving the photocatalytic activity of the g-C₃N₄ photocatalysts.     

Models of the formation of oxide phases in nanostructured materials based on lead chalcogenides subjected to treatment in oxygen and iodine vapors

Model concepts concerning control over the formation of oxide layers during the course of oxidation are developed on the basis of experimental results of studies of systematic features of the formation of nanostructured layers after diffusion annealing. Data on a variation in the composition of oxide phases as the extent of deviation from stoichiometry is changed in the initial lead chalcogenide are presented. Model concepts related to the possibility of varying the thickness of the coating oxide phases using annealing in an oxygen-containing medium are developed. It is shown that annealing in an iodine atmosphere ensures the effective penetration of oxygen into the grains, which is necessary for an increase in the photoluminescence efficiency.     

Advances in the design of organic resist materials

The resist materials used today in the fabrication of semiconductor devices were not expressly designed for this application. They were originally developed for use in the printing industry and were simply adopted by the electronics industry with relatively minor modifications. The performance of these resists was more than adequate for initial applications and, as a result, it was not necessary completely understand the chemistry responsible for lithographic behavior. However, the current resolution requirements and severe processing conditions in device manufacturing make it necessary to understand resist chemistry not only to maximize the performance of available materials but also to allow for the rational design of new materials.The paper discusses three topics which demonstrate that one can specifically design a resist system for optimal performance. The first deals with the generation of a negative tone image from a positive photoresist. The second topic addresses techniques for significantly reducing the time required to expose a resist. And finally, the materials requirements for the next generation of multilayer resist (MLR) systems will be discussed.     

氧分压对铟镓锌氧薄膜晶体管性能影响

采用标准的液晶显示屏基板制备工艺制备出铟镓锌氧薄膜晶体管(IGZO-TFT),通过调节IGZO薄膜工艺中氧分压,研究不同氧分压对TFT器件电学性能的影响。实验结果表明,所有器件都展现出良好的电学特性,随着氧分压从10%增加到50%,TFT的阈值电压由0.5 V增加到2.2 V,而亚阈值摆幅没有发生变化。在栅极施加30 V偏压3600 s后,随着氧分压的增加,阈值电压向正向的漂移量由1 V增加到9 V。经过分析得出高氧分压的IGZO-TFT器件中载流子浓度低,建立相同导电能力的沟道时所需要栅极电压会更大,阈值电压会增加。而在金属-绝缘层-半导体(MIS)结构中低载流子浓度会导致有源层能带弯曲的部分包含更多与电子陷阱相同的能态,栅介质层(GI)会俘获更多的电子,造成阈值电压漂移量较大的现象。     

Effect of the state of vacancy equilibrium on diffusion of chromium impurity in gallium arsenide

The results of studying the diffusion of Cr impurity in GaAs according to electrical measurements are reported. Dependences of the diffusion coefficient and limiting solubility of electrically active Cr atoms in GaAs on temperature (at fixed pressures of As vapors) and on the pressure of As vapors (at fixed temperatures) are determined. The dependence of the Cr diffusion coefficient in GaAs on the ratio between the volume of the sample under study to the volume of the cell in the case of pronounced deviation from the crystal’s stoichiometry towards Ga excess is established. The obtained experimental data are analyzed on the basis of concepts concerning the dissociative mechanism of migration of Cr atoms in the GaAs crystal lattice; according to this mechanism, the diffusion coefficient depends heavily on the concentration of Ga vacancies.     

Effect of zirconium oxide nanopowder on the thermal,chemical and gas barrier properties of starch

Starch/zirconium oxide (Starch/ZrO₂) bionanocomposites were prepared using various percentages of nano-ZrO₂ by a solution technique. The interaction of ZrO₂ nanocomposites with starch was studied by Fourier transform infrared spectroscopy (FTIR) and their structural behavior was investigated by X-ray diffraction (XRD). The dispersion of ZrO₂ within virgin starch was investigated by a field emission scanning electron microscope (FESEM), a high resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED). Thermal properties of starch/ZrO₂ bionanocomposites were studied by thermogravimetric analysis (TGA). An increase in thermal stability was observed with increase in filler loading. The conductivity of starch/ZrO₂ bionanocomposites was measured and an increase in conductivity was observed due to the increase in ZrO₂ concentration. Starch/ZrO₂ bionanocomposites were more resistant towards chemicals like dilute acid and alkali. The oxygen barrier property of composites was studied and a substantial reduction in permeability was observed. Further, the biodegradability of starch/ZrO₂ bionanocomposites was reduced. Thermally stable, chemical resistant, and gas barrier starch bionanocomposites with conducting property may enable the materials for manufacturing packaging materials and semiconducting devices.