电场作用下铅基阳极表面氧化膜残余内应力产生机理研究

采用SEM、XRD和Raman光谱法研究电场作用下含铬溶液中铅基阳极氧化膜的残余内应力行为、内应力形成, 讨论了氧化膜内应力产生过程与氧化膜表面形貌、物质结构转变的关系。结果表明, 在氧化膜形成初期, Cr₂O₇^2- 和HCrO₄^-离子首先吸附在铅基阳极表面, 电场作用下, 其与铅基体反应并分别形成PbCrO₄和PbO, 同时产生较大内应力。电流密度的增加, 显著提高氧化膜的内应力。随着氧化时间的延长, 阳极析氧行为的加剧, 促进PbO或β-PbO₂形成。同时, 晶粒长大与内应力的不匹配, 导致内应力局部释放, 表现出氧化膜残余内应力减小。铅基氧化膜中不同氧化物组织结构的晶格参数差异, 增加了氧化膜内应力梯度变化, 致使氧化膜破裂。     

The photoresponse of high resistance anatase TiO2 films prepared by the decomposition of titanium isopropoxide

High resistance films of the anatase phase of TiO₂ have been prepared by spray pyrolysis starting with titanium isopropoxide Ti(OPrⁱ)₄. The films were deposited on glass substrates held at 590 K. The TiO₂ films were characterized structurally, optically, and electrically. The photoresponse of these films to prolonged UV radiation in a vacuum and subsequently subjected to O₂, H₂, water vapour, or air environments, has been investigated. When vacuum, O₂ or air is present, the electrical and optoelectronic properties observed can be explained by the induced variations in the oxygen deficiency at the surface of the TiO₂ film and the resulting formation or removal of an enhancement layer at the surface. An equivalent effect on the surface band bending can be induced by an absorbed species. For example, adsorbed water vapour can alter the surface conductance of the films and the result depends on the oxygen-to-titanium ratio present at the surface when the water vapour is introduced.     

应力对蓝宝石衬底上生长二氧化钒薄膜结构和光电性能的调控

利用脉冲激光沉积技术在蓝宝石衬底上生长不同厚度的VO₂薄膜, 对薄膜的结构、表面形貌和光电性能进行研究。结果表明: 所沉积的VO₂薄膜为具有单晶性能、表面平整的单斜晶相的VO₂薄膜, 相变前后, 方块电阻的变化可达到3~4个数量级, 在波长为2500 nm的透过率变化最高可达56%, 优化的可视透过率(T_lum)和太阳能调节率( ∆T_sol )为43.2%和8.7%。薄膜受到的应力对VO₂薄膜有重要影响, 可以通过调节薄膜的厚度对VO₂薄膜光电性能实现调控。当VO₂薄膜厚度较小时, 薄膜受到拉应力, 拉应力能使相变温度显著降低, 金属-绝缘体转变性能(MIT)不但与载流子浓度的变化相关, 而且还受载流子迁移率变化的影响;当VO₂薄膜厚度较大时, 薄膜受到压应力, VO₂薄膜的相变温度接近块体VO₂的相变温度, MIT转变主要来自于载流子浓度在相变前后的变化, 其载流子迁移率几乎不变。     

铝酸盐体系下反应时间对ZrH1.8表面阻氢膜层制备的影响

采用微弧氧化技术在NaAlO₂电解液体系下制备ZrH_1.8表面阻氢膜层, 采用场发射扫描电子显微镜(FE-SEM), X射线衍射(XRD), 真空脱氢实验对膜层进行表征, 考察不同反应时间对ZrH_1.8表面阻氢膜层的厚度、形貌、相结构以及阻氢性能的影响规律。研究结果表明：当反应时间在7.5~15 min变化时, 膜层厚度由78.4 μm增大至152.8 μm。膜层由单斜相M-ZrO₂、四方相T-ZrO₂以及立方相C-ZrO₂组成, 反应时间对膜层的相组成并无明显影响。阻氢膜层由致密层和疏松层构成, 膜层外侧为疏松层, 靠近基体一侧为致密层。当反应时间为10 min时, 获得的膜层表面平整, 致密性较好, 厚度适中, 膜层的氢渗透降低因子PRF值为20。     

阻抗渐变高介电钛酸钡/聚酰亚胺复合薄膜的设计与制备

人体皮肤与空气间在介电常数上有着失配性,可穿戴设备所用的材料需要与人体皮肤有良好的匹配性能,而单一的材料与结构已不能满足这种需求。利用原位聚合法合成了一系列钛酸钡(BaTiO_3)/聚酰亚胺(PI)混合溶液,通过逐层流延涂覆的方法设计制备了一种具有阻抗渐变性质的多层BaTiO_3/PI复合薄膜。结果表明:BaTiO_3纳米粒子可在复合薄膜中均匀分散,调节无机粒子的含量,能够有效地控制复合薄膜的介电常数在2.5~34.0之间变化;同时,BaTiO_3/PI复合薄膜对外加电场的频率具有不敏感性,也具有良好的力学性能,能够满足可穿戴设备对材料的要求。     

Yttrium oxide film deposition by a Langmuir-Blodgett processing technique and its incorpiration into oxide scales by substrate oxidation

Thin films (about 10 nm) of Y₂O₃ have been deposited by a Langmuir-Blodgett processing technique onto a variety of substrates: type 304 stainless steel, low carbon steel, titanium, zirconium and silicon. The substrates were afterwards oxidized in air at 800, 1000 (304 steel), 400 (low C steel), 500 (Ti), 450 (Zr) and 1000 (Si) °C. The effects of the film on the oxide scale thickness and the interaction between Y₂O₃ and the oxide of the substrate have been studied by ion backscattering. In stainless steel, the Y₂O₃ film reduces the oxidation rate by orders of magnitude and Y is distributed throughout the oxide scalw (1–10 at.% level). In other substrates, the effect on oxidation rate was less pronounced, but changes in the visual appearance often took place. The Y₂O₃ incorporation varied for the different substrates, and Y₂O₃ remained as a surface film in the cases of Ti and Si. Such films exhibited good adherence and could not be removed by wiping. The potential use of metal oxide thin films for surface analysis standards and diffusion marker studies is discussed.     

聚酰亚胺/二氧化钛纳米复合薄膜制备与耐电晕性

采用原位聚合法制备不同TiO₂组分聚酰亚胺(PI)/纳米TiO₂复合薄膜, 薄膜厚度50μm。 测试结果表明, TiO₂呈球状颗粒, 直径约为100 nm, 聚酰亚胺呈片状, 尺寸约为2μm×1μm。随着TiO₂含量的增加, 复合薄膜介电常数和介电损耗增大, 击穿场强先增加后降低; 在40 kV/mm电场强度下, 复合薄膜耐电晕老化寿命增加, 纯PI薄膜寿命为3 h, 20wt%TiO₂含量薄膜寿命达到25 h; TiO₂颗粒耐电晕能力强, 与聚合物形成界面相, 改变材料陷阱能级, 有利于空间电荷的扩散和热量的传输, 在薄膜表面形成放电阻挡层, 降低局部放电对薄膜内部的侵蚀, 显著提高薄膜耐电晕老化寿命。     

正向电压对氢化锆微弧氧化阻氢膜层性能的影响

在偏铝酸钠-氢氧化钠-EDTA混合溶液中, 采用恒压模式对氢化锆表面进行微弧氧化处理。借助场发射扫描电镜(FE-SEM)、X射线衍射仪(XRD)及真空脱氢实验, 研究了不同正向电压(350~425 V)对微弧氧化膜层表面、截面、相结构及阻氢渗透性能的影响。分析结果表明: 微弧氧化过程大致由阳极氧化、火花放电、微弧氧化和熄弧四个阶段组成。制备的膜层分为致密层和疏松层, 致密层所占比例约为80%。随着正向电压的增大, 晶粒尺寸增大, 晶面间距减小, 氢化锆表面微弧氧化膜层厚度由122 μm增加至150 μm, 膜层的增长速度也随正向电压的增大而加快。但正向电压的改变对膜层的相结构并无显著影响, 膜层由单斜相氧化锆和四方相氧化锆组成, 当正向氧化电压为400 V时, 氧化膜的PRF值达到最大值20。     

Effect of volume fraction of carbon fibers on wear behavior of Al/Al2O3/C hybrid metal matrix composites

Wear behavior of Al/Al₂O₃/C hybrid metal matrix composites fabricated by squeeze casting method was characterized. The effects of volume fraction of carbon fiber on wear behavior of hybrid composites was investigated. Wear behavior of Al/Al₂O₃/C composites was characterized by the dry spindle wear test under various sliding speeds.

The wear resistance of Al/Al₂O₃/C composites was remarkably improved over Al/Al₂O₃ composites by adding carbon fibers to Al/Al₂O₃/C composites. Specifically, at the intermediate sliding speed the wear resistance of Al/Al₂O₃/C composites containing 8 vol.% carbon fiber was found to be better than that of the rest of the carbon hybrid composites. From fractographic studies, damaged sections in wear surfaces of hybrid composites at intermediate sliding speed were not observed due to the formation of solid lubrication film. The solid lubrication film which was formed as a result of adding carbon fibers improved the wear resistance of carbon hybrid composites because this film reduced the high friction force between MMCs and counter material.     

Magnetic properties of acicular BaFe12O19particles prepared by microwave plasma sintering

Acicular α-FeOOH particles coated with barium ions were irradiated with microwaves under an oxygen pressure of 20 torr to prepare fine BaFe₁₂O₁₉ particles by a plasma reaction. The fine acicular particles has an aspect ratio of about 13 and a magnetization of 43.5 emu/g and contained small amounts of α-Fe₂O₃ and BaFe₂O₄. The particles were mixed with a binder, and the resulting mixture was formed into a coating under a magnetic field of 7 kOe applied vertically to the surface of the film. The squareness ratio in the direction perpendicular to the surface of the coating film was 0.83 without any correction for the demagnetizing field. Transmission electron microscopy (TEM) showed that the long axes of the BaFe₁₂O₁₉ particles all were aligned parallel to the film base. The cross-sections of the particles were rectangular when observed by TEM. It follows that the easy axes of the particles are perpendicular to their long axes     

Fabrication and Optical Properties of Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/Thin Films on Si Substrates Using the PLD Method

Epitaxial 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) thin films with electro-optic effects were fabricated on (La_0.5Sr_0.5)CoO₃(LSCO)/CeO₂/YSZ-buffered Si(001) substrates using double-pulse excitation pulsed laser deposition (PLD) method with a mask placed between the target and the substrate. Epitaxial growth of PMN-PT thin films was undertaken using the two-step growth method of PMN-PT film. The PMN-PT seed layer was deposited at 500degC on the LSCO/CeO₂/YSZ/Si, which temperature was the same as that used for LSCO deposition. The PMN-PT thin films were deposited on the PMN-PT seed layer at 600degC, which enables growth of high-crystallinity PMN-PT films with smooth surfaces. We obtained optimum fabrication conditions of PMN-PT film with micrometer-order thickness. Resultant films showed high crystallinity with full width at half maximum (FWHM)=0.73 deg and 1.6 mum thickness. Electro-optic properties and the refractive index value were measured at 633 nm wavelength using the prism coupling method. The obtained refractive index was 2.59. The electro-optic coefficients r₁₃ and r₃₃ were determined by applying the electrical field between a semitransparent, thin top electrode of Pt and a bottom LSCO electrode. The electro-optic coefficient was r₁₃=17 pm/V at transverse electric field (TE) mode and r₃₃=55 pm/V at transverse magnetic field (TM) mode.     

五层纳米SiO2-Al2O3/聚酰亚胺复合薄膜的制备及性能

采用浸胶法制备了一系列SiO₂-Al₂O₃/聚酰亚胺（SiO₂-Al₂O₃/PI）五层耐电晕薄膜A_m A_n PA_n A_m,其中中间层（P）为纯PI薄膜,外层（A_m）、次外层（A_n）分别为SiO₂-Al₂O₃掺杂不同质量分数的纳米SiO₂-Al₂O₃/PI薄膜。采用TEM、FTIR、宽频介电谱仪、电导电流测试仪、耐电晕测试仪、介电强度测试仪和拉伸实验机对五层纳米复合PI耐电晕薄膜的微观结构、介电性能和力学性能进行了表征和测试。结果表明,SiO₂-Al₂O₃/PI复合薄膜掺杂层形成了分布均匀的有机/无机复合结构;SiO₂-Al₂O₃纳米粒子的保护作用是影响复合材料耐电晕性能的主要因素,复合薄膜A₃₂A₁₆PA₁₆A₃₂的耐电晕寿命最大,为23.4 h;外层掺杂量对五层SiO₂-Al₂O₃/PI复合材料的介电强度影响较大,复合薄膜A₂₀A₂₈PA₂₈A₂₀的介电强度最大,为302.3 kV/mm;通过对五层复合结构的设计,可以在兼顾材料力学性能的同时,提高其耐电晕寿命和介电强度。     

Investigation of the growth dynamics of pulsed laser-deposited RuO2 films using in situ resistance measurement and atomic force microscopy

RuO₂ thin films were grown on (001) LaAlO₃ utilizing the pulsed laser deposition technique. Atomic force microscopy was used to check the topography of films at different growth stages. The in situ resistivity measurement was used to monitor the resistance change during and post film growth with changes of resistivity associated with the change of film growth mode. Transmission electron microscopy was used to reveal film quality and crystalline information. The layer-plus-island Stranski–Krastanov growth mode is proposed according to above results. The ambient O₂ filled during growth is found to be the main oxygen source for the formed RuO₂.     

Study of the environment effect on the properties of BDN-SA Langmuir–Blodgett films

The chemical and electrical properties of BDN-SA Langmuir–Blodgett films in air and N₂H₄ gas respectively, were studied using X-ray Photoelectron Spectroscopy (XPS) and the electrical resistance measurement. The results indicate that the oxidation effect caused by air leads to the lost of N and partial oxidation of Ni and S in the LB films; while the reduction effect induced by N₂H₄ gas decreases the amount of O in the LB films. The electrical resistance of LB film decreases dramatically after the film being exposed to N₂H₄ gas while increases with the exposure time in air.     

Reduction of field emission in superconducting cavities with high power pulsed RF

A systematic study is presented of the effects of pulsed high power RF processing (HPP) as a method of reducing field emission (FE) in superconducting radio frequency (SRF) cavities to reach higher accelerating gradients for future particle accelerators. The processing apparatus was built to provide up to 150 kW peak RF power to 3 GHz cavities, for pulse lengths from 200 μs to 1 ms. Single-cell and nine-cell cavities were tested extensively. The thermal conductivity of the niobium for these cavities was made as high as possible to ensure stability against thermal breakdown of superconductivity.

HPP proves to be a highly successful method of reducing FE loading in nine-cell SRF cavities. Attainable continuous wave (CW) fields increase by as much as 80% from their pre-HPP limits. The CW accelerating field achieved with nine-cell cavities improved from 8–15 MV/m with HPP to 14–20 MV/m.

The benefits are stable with subsequent exposure to dust-free air. More importantly, HPP also proves effective against new field emission subsequently introduced by cold and warm vacuum “accidents” which admitted “dirty” air into the cavities.

Clear correlations are obtained linking FE reduction with the maximum surface electric field attained during processing. In single cells the maximums reached were E_peak = 72 MV/m and H_peak = 1660 Oe. Thermal breakdown, initiated by accompanying high surface magnetic fields is the dominant limitation on the attainable fields for pulsed processing, as well as for final CW and long pulse operation.

To prove that the surface magnetic field rather than the surface electric fields is the limitation to HPP effectiveness, a special two-cell cavity with a reduced magnetic to electric field ratio is successfully tested. During HPP, pulsed fields reach E_peak = 113 MV/m (H_peak = 1600 Oe) and subsequent CW low power measurement reached E_peak = 100 MV/m, the highest CW field ever measured in a superconducting accelerator cavity.     

Field-induced strain of (Pb, La)(Zr, Ti)O3 epitaxial films grown by metal organic chemical vapor deposition

Two micrometers thick (Pb, La)(Zr, Ti)O₃ [PLZT] films with wide composition range were epitaxially grown on (1 0 0)SrRuO₃ bottom electrode layers epitaxially grown (1 0 0) SrTiO₃ substrates by metal organic chemical vapor deposition. Constituent phase of the films were found to be almost the same with the reported phase diagram for the sintered body except for the wider coexistence region of tetragonal and rhombohedral phases. The change of the measured field-induced strain with the electric field was almost respond to the square of the polarization of the films except the negative strain region, but the magnitude was different. This is due to the increase of the electrostatic coefficient of the film with increasing the La/(Pb + La) ratio. As a results, field induced strain of the PLZT film was found to be controlled by adjusting the composition of PLZT films.     

双铁电复合材料的制备及其光电化学性能研究

通过模板法制备钒酸铋(BiVO₄)薄膜, 用溶胶-凝胶法制备铁电材料铁酸铋(BiFeO₃)并对BiVO₄进行修饰, 以半导体复合的方式提高BiVO₄的光电化学性能。电化学测试结果表明, 经BiFeO₃修饰后, BiVO₄薄膜的光电化学性能有所提高, 其中经BiFeO₃旋涂5次后的BiVO₄薄膜具有最优的光电化学性能, 光电流密度达到0.72 mA·cm^-2, 较未修饰样品提高了67.4%。利用外场极化调节能带弯曲可以显著地提高BiVO₄/nBiFeO₃铁电复合物的光电化学性能, 复合物经正极化20 V电压处理后的光电流密度最高为0.91 mA·cm^-2, 比BiVO₄薄膜提升了1倍以上, 具有良好的光电化学性能。BiFeO₃与BiVO₄复合后有利于形成异质结, 促进光生电子、光生空穴的产生与分离, 并且外场极化调节能带弯曲使光生电荷加速转移, 是铁电复合物光电化学性能提高的主要原因。     

Memory switching in amorphous Ge---Se---Tl chalcogenide semiconductor films

The switching effects in amorphous GeSe₂, GeSe₄, GeSe₂Tl and GeSe₄Tl thin films have been investigated. The observed switching phenimenon for these compositions was of the memory type. The threshold switching voltage was found to increase linearly with increasing film thickness (80–740 nm), while it decreased exponentially with increasing temperature (T < T_g).

The effect of adding thallium to both amorphous GeSe₂ and amorphous GeSe₄ results in decreasing the values of the threshold electric field, the activation energy of switching, as well as the thermal activation energy of conduction. The results obtained are explained in accordance with the electrothermal model of breakdown.     

纳米Ni60-TiB2复合涂层的超音速火焰喷涂制备及600℃循环氧化特性

采用超音速火焰喷涂技术在45#钢基体表面制备纳米Ni60-TiB2复合涂层,研究了纳米和常规微米Ni60-TiB2复合涂层在静态大气环境下600℃的循环氧化行为。结果表明：纳米Ni60-TiB2涂层具有晶粒纳米化和微观组织均匀化的特点,其氧化膜由完整连续SiO2膜构成,在其上均匀地分布着细小的TiO_2颗粒和B_2O_...     

Characterization of intermetallic phases and oxides formed in annealed Ni/Al multilayer structures

Two different multilayer structures composed of ten alternating Ni and Al thin films were sputter deposited on Si (111) substrates. These multilayers with individual Ni and Al thin film thicknesses of about 25 nm and 38 nm and of 25 nm and 13 nm, respectively, have the average compositions of Ni_0.50Al_0.50 and Ni_0.75Al_0.25. The samples were heat treated in a differential scanning calorimeter instrument with a constant heating rate of 40 °C min ⁻¹ in Ar from room temperature to 550 °C. The compositions of as-deposited and heat-treated samples were studied with high-resolution Auger electron spectroscopy (AES) rotational depth profiling. X-ray photoelectron spectroscopy (XPS) analyses show an excess of Ni in both annealed samples. X-ray diffraction measurements of annealed multilayers show the formation of Ni₂Al₃ and NiAl₃ phases in the Ni_0.50Al_0.50 sample and the presence of Ni₃Al and Ni A1₃ phases with some excess of Ni in the Ni_0.75Al_0.75 sample. AES and XPS investigations of the reacted layers after 15 min annealing in air at 500 °C disclose considerably different surface oxide thin films: on the Ni_0.50Al_0.50 layer the oxide thin film consists of Al₂O₃ with a small amount of NiO, whereas that on the top of the Ni_0.75Al_0.25 layer is thicker and consists of NiO on top and some Al₂O₃ below.