金属纳米团簇复合薄膜Au/BaTiO3与Fe/BaTiO3的PLD制备及其光吸收特征

用脉冲激光沉积技术制备了掺杂纳米金属颗粒Au或Fe的BaTiO₃复合薄膜.用透射电子显微镜和x射线光电子能谱表征了金属颗粒的形态和化学态.330—800nm范围的吸收谱研究表明，掺Au颗粒的BaTiO₃薄膜在580nm附近有一个明显的共振吸收峰，而掺Fe颗粒的BaTiO₃薄膜没有这样的吸收峰.用Mie散射理论对结果进行了分析. 关键词： 复合薄膜 金属颗粒 脉冲激光沉积 吸收谱     

脉冲激光沉积Ag:BaTiO3纳米复合薄膜及其光学特性

在MgO(100)基片上利用脉冲激光沉积技术制备了掺有Ag纳米颗粒的BaTiO3复合薄膜.通过X射线衍射对薄膜的结构进行了表征,利用透射电子显微镜对Ag纳米颗粒的尺寸、形态进行了观测,X射线光电子能谱结果表明Ag呈金属态.在410-500 nm范围内观测到了Ag纳米颗粒引起的等离子振荡峰,随着后处理温度和Ag颗粒浓度的增加,吸收峰发生红移,并出现了双峰现象.     

Au-BaTiO3复合薄膜的脉冲激光沉积制备及其非线性光学效应

利用脉冲激光沉积技术制备了掺杂金纳米颗粒的钛酸钡复合薄膜Au-BaTiO3,用高分辨透射电镜和X射线光电子能谱对薄膜进行了表征。从透射电镜照片可以看出,制备的样品中金颗粒大小约为2~3 nm,呈球形,均匀分布在载体介质中。X射线光电子能谱给出了Ba3d、Ti2p和Au4f电子芯能级结合能,结果表明载体介质是以BaTiO3的形式存在,而Au以金属的状态掺杂其中。330~800 nm范围的线性吸收谱表明样品中Au颗粒的共振吸收峰在500 nm附近。用单光束纵向扫描方法测量了样品的三阶非线性光学效应,使用的光源为调Q的YAG激光器,波长为532 nm,脉宽为10 ns,得到的非线性折射率和非线性吸收系数分别为-2.42×10-6esu和2.22×10-6m/W,表明了Au-BaTiO3复合薄膜有较大的非线性光学响应。     

掺Ag纳米颗粒的BaTiO3复合薄膜的非线性光学特性

通过准分子激光(XeCl,308 nm,20 ns)在MgO(100)单晶衬底上制备了不同掺杂浓度的Ag:BaTiO3纳米复合薄膜,通过X射线衍射和X射线光电子能谱对薄膜的结构和组分进行了表征.在430 nm和470 nm附近观测到了不同浓度Ag纳米颗粒引起的等离子体吸收峰,通过z扫描技术对复合薄膜的三阶非线性光学特性进行了测量,并对其光学非线性的增强机制进行了讨论.     

Au/SiO2纳米多层薄膜的制备及其性质表征

利用多靶磁控溅射技术制备了Au/SiO2纳米颗粒分散氧化物多层复合薄膜.研究了在保持Au单层颗粒膜沉积时间一定时薄膜厚度一定、变化SiO2的沉积时间及SiO2的沉积时间一定而改变薄膜厚度时,多层薄膜在薄膜厚度方向的微观结构对吸收光谱的影响.研究结果表明:具有纳米层状结构的Au/SiO2多层薄膜在560nm波长附近有明显的表面等离子共振吸收峰,吸收峰的强度随Au颗粒的浓度增加而增强,在Au颗粒浓度相同的情况下,复合薄膜光学吸收强度随薄膜厚度的增加而增强.但当金属颗粒的浓度增加到一定程度时,金属颗粒相互接触,没有观察到纳米层状结构,薄膜不显示共振吸收峰特征.用修正后的M-G(Maxwell-Garnett)理论对吸收光谱进行了模拟,得到了与实验一致的结果.     

Au/SiO2纳米复合薄膜的微结构及光吸收特性研究

用多靶磁控溅射技术制备了Au/SiO2纳米多层薄膜.利用透射电子显微镜以及吸收光谱对Au/SiO2复合薄膜的微观结构、表面形貌及光学性能进行了表征和测试.研究结果表明:单层Au/SiO2薄膜中Au沉积时间小于10s时,分散在SiO2中的Au颗粒随Au的沉积时间的延长而增大;当沉积时间超过10s后,Au颗粒的尺寸几乎不随沉积时间变化,但Au颗粒的形状由网络状结构变为薄膜状结构.[Au(t1)SiO2(600)]×5多层薄膜在540-560nm波长附近有明显的表面等离子共振吸收峰,且吸收峰的强度随Au的沉积时间增加而增强.基于修正后的Maxwell-Garnett (M-G)有效媒质理论,讨论了金属颗粒的形状对等离子共振吸收峰的峰位和强度的影响.模拟的吸收光谱与实验吸收光谱形状、趋势及吸收峰位相符合.     

Co:BaTiO3/Si(100)纳米复合薄膜制备、微结构及其紫外光电子能谱研究

采用脉冲激光气相沉积(PLD)方法,在Si(100)晶面上制备了Co:BaTiO3纳米复合薄膜.采用X射线衍射(XRD)结合透射电镜(TEM)方法研究了两种厚度Co:BaTiO3纳米复合薄膜的晶体结构,当薄膜厚度约为30 nm时,薄膜为单一择优取向;当薄膜厚度约为100 nm时,薄膜呈多晶结构.原子力显微镜(AFM)分析表明,当膜厚为30 nm时,薄膜呈现明显的方形晶粒.采用紫外光电子能谱(UPS)研究了Co的价态和Co:BaTiO3纳米复合薄膜的价带谱.研究表明:当Co浓度很高时其态密度(DOS)与晶体BaTiO3明显不同.此外,嵌埋纳米Co颗粒的BaTiO3薄膜的能带结构可用纳米颗粒的浓度来调制,从而也可对其光学和电学性质进行改性.     

脉冲激光沉积Ag:BaTiO3纳米复合薄膜及其光学特性

在MgO(100)基片上利用脉冲激光沉积技术制备了掺有Ag纳米颗粒的BaTiO₃复合薄膜.通过X射线衍射对薄膜的结构进行了表征,利用透射电子显微镜对Ag纳米颗粒的尺寸、形态进行了观测,X射线光电子能谱结果表明Ag呈金属态.在410—500nm范围内观测到了Ag纳米颗粒引起的等离子振荡峰,随着后处理温度和Ag颗粒浓度的增加,吸收峰发生红移,并出现了双峰现象. 关键词： 金属纳米复合薄膜 激光沉积 光吸收     

Au/SiO2纳米多层薄膜的制备及其性质表征

利用多靶磁控溅射技术制备了Au/SiO₂纳米颗粒分散氧化物多层复合薄膜.研究了在保持Au单层颗粒膜沉积时间一定时薄膜厚度一定、变化SiO₂的沉积时间及SiO₂的沉积时间一定而改变薄膜厚度时，多层薄膜在薄膜厚度方向的微观结构对吸收光谱的影响.研究结果表明：具有纳米层状结构的Au/SiO₂多层薄膜在560 nm波长附近有明显的表面等离子共振吸收峰，吸收峰的强度随Au颗粒的浓度增加而增强，在Au颗粒浓度相同的情况下，复合薄膜 关键词： 2纳米复合薄膜')" href="#">Au/SiO₂纳米复合薄膜 多靶磁控溅射 吸收光谱 有效介质理论     

纳米BaTiO3陶瓷的Raman光谱研究

高压能增加陶瓷烧结的致密驱动力和抑制陶瓷晶粒的长大。用高压辅助烧结的方法得到了晶粒尺寸约为60和30 nm的致密纳米BaTiO3陶瓷。BaTiO3陶瓷的晶体结构随温度的变化由变温Raman光谱来研究。在温度范围-190℃到200℃内,与粗晶的BaTiO3陶瓷相比,纳米BaTiO3陶瓷Raman散射结果表明,随着晶粒尺寸的减小,Raman峰的强度变弱,相变越来越弥散,出现了相变峰的消失;而且随着温度的升高,在纳米BaTiO3陶瓷甚至在30 nm BaTiO3陶瓷中都有与粗晶相同的从三方相到正交相到四方相到立方相的连续相变。变温Raman散射也表明,当晶粒大小减小到纳米尺寸时,纳米BaTiO3陶瓷表现出与粗晶不同的新颖性质。在一定的温度范围内,存在多种铁电相的共存。     

Morphology dependence of the dielectric properties of epitaxial BaTiO3 films and epitaxial BaTiO3/SrTiO3 multilayers

Epitaxial BaTiO₃ films and epitaxial BaTiO₃/SrTiO₃ multilayers were grown by pulsed laser deposition on vicinal surfaces of (001)-oriented Nb-doped SrTiO₃ (SrTiO₃:Nb) single-crystal substrates. Atomic force microscopy was used to investigate the surface topography of the deposited films. The morphology of the films, of the BaTiO₃/SrTiO₃ interfaces, and of the column boundaries was investigated by cross-sectional high-resolution transmission electron microscopy. Measurements of the dielectric properties were performed by comparing BaTiO₃ films and BaTiO₃/SrTiO₃ multilayers of different numbers of individual layers, but equal overall thickness. The dielectric loss saturates for a thickness above 300 nm and linearly decreases with decreasing film thickness below a thickness of 75 nm. At the same thickness of 75 nm, the thickness dependence of the dielectric constant also exhibits a change in the linear slope both for BaTiO₃ films and BaTiO₃/SrTiO₃ multilayers. This behaviour is explained by the change observed in the grain morphology at a thickness of 75 nm. For the thickness dependence of the dielectric constant, two phenomenological models are considered, viz. a series-capacitor model and a dead-layer model. PACS 77.22.-d; 77.22.Ch; 77.55.+f; 77.22.Gm; 77.84.Dy; 81.15.-z ; 81.16.Mk; 81.65.-b; 68.55.-a; 68.37.-d     

Size effect on SrRuO3/BaTiO3/SrRuO3 ferroelectric ultrathin film capacitor

We have carried out a detailed investigation on the size effect on SrRuO₃/BaTiO₃/SrRuO₃ ferroelectric ultrathin film capacitors with film thickness fully strained with a SrTiO₃ substrate. We employ the transverse field Ising model, taking into account the incomplete charge compensation of the realistic SrRuO₃ electrode and the misfit strain imposed by the SrTiO₃ substrate in the Hamiltonian, to quantitatively explain the experimental observation in the literature. It is found that BaTiO₃ ultrathin films between two metallic electrodes lose their ferroelectric properties below a critical thickness of about 4.17 nm due to the enhancement of the quantum effect under the influence of the incomplete charge compensation of the electrode.     

Twin-seeded BaTiO3 ceramics

Grain size is important in the barium titanate ceramics used as capacitors and thermistors. Normally this is controlled by chemical additives and firing schedules, but growth twins also lead to increased grain size. Seeding experiments described in this paper demonstrate how the twins can be used to produce large-grained BaTiO₃ ceramics.     

Properties of BaTiO3/BaZrO3 ferroelectric superlattices with competing instabilities

Properties of (BaTiO₃)₁/(BaZrO₃) _n ferroelectric superlattices (SLs) with n = 1?7 grown in the [001] direction are calculated from first principles within the density functional theory. It is revealed that the quasi-two-dimensional ferroelectricity occurs in these SLs in the barium titanate layers with a thickness of one unit cell; the polarization is oriented in the layer plane and weakly interacts with the polarization in neighboring layers. The ferroelectric ordering energy and the height of the barrier separating different orientational states of polarization in these SLs are sufficiently large to provide the formation of an array of independent polarized planes at 300 K. The effect of the structural instability on the properties of SLs is considered. It is shown that the ground state is a result of simultaneous condensation of the Γ₁₅ polar phonon and phonons at the M point (for SLs with even period) or at the A point (for SLs with odd period); it is a polar structure with out-of-phase rotations of the octahedra in neighboring layers, in which highly polarized layers are spatially separated from the layers with strong rotations. The competition between the ferroelectric and structural instabilities in biaxially compressed SLs manifests itself in that the switching on of the octahedra rotations leads to an abrupt change of the polarization direction and can cause an improper ferroelectric phase transition to occur. It was shown that the experimentally observed z-component of polarization in the SLs can appear only as a result of the mechanical stress relaxation.     

嵌埋Ni颗粒的BaTiO_3/SrTiO_3薄膜的相变特性

采用高温X射线原位衍射和变温介电谱对SrTiO3基底上外延生长的BaTiO3(嵌埋Ni颗粒)薄膜进行了相变特性分析。从X射线衍射和介电谱的分析结果得出,BaTiO3的相变温度点转变为弥散的温度区间。在这个弥散的相变温度区间内,由于基底和薄膜之间的失配,以及嵌埋Ni颗粒的应力作用,薄膜的介电响应弥散剧烈,并偏离德拜弛豫。分析Cole-Cole图获知,BaTiO3薄膜在四方相转变为立方相的相变过程中同时存在几种极化机制,在高温状态下介电损耗随温度增大而增大。降温过程中,薄膜没有立即恢复四方相,可能是基底和Ni颗粒的共同作用影响了相变弛豫。     

Ba TiO3/SrTiO3超晶格Bragg衍射及其理论模拟

用X射线全外反射掠入射衍射和通常Bragg衍射,研究了Ba TiO³/SrTiO³(BTO/STO)超晶格的界面应变.X射线衍射动力学理论用于模拟Bragg衍射.发现与一般半导体外延膜或超晶格不同,BTO/STO超晶格的垂直和水平晶格常数的关系不完全遵守四方畸变的规律.这种偏离可能与钙钛矿型氧化物材料的结构复杂性有关.     

溶胶-凝胶法制备BaTiO3/SrTiO3多层膜的介电增强效应

采用溶胶凝胶法,在PtTiSiO2Si衬底上逐层制备了BaTiO3SrTiO3多层膜.从多层膜的XRD图可看出明显的双峰,分别对应为BaTiO3和SrTiO3的特征峰,表明样品已形成了多层膜结构.与同厚度的Ba05Sr05TiO3单层膜比较,BaTiO3SrTiO3多层膜的介电系数得到了明显的增强,在频率为10kHz时,周期为66nm的BaTiO3SrTiO3多层膜相对于同厚度的Ba05Sr05TiO3薄膜的介电系数从245增强到595,而损耗依然保持较低,分别为0029和0033.研究同时表明,BaTi 关键词： 溶胶-凝胶法 多层膜 介电增强     

Stoichiometry of BaTiO3 nanoparticles

Barium titanate nanoparticles with various nominal Ba/Ti ratios were prepared through direct synthesis from solution (DSS) and further annealed at different temperatures. Their deviation from stoichiometry was studied through XRD analysis, and a large deviation from stoichiometry has been observed. The grain size we studied ranges from 50 nm to 1 μm. For the as-prepared particles, the grain size is about 50 nm, and the maximum excess of Ti is over 15%. For the samples annealed at 800 °C, the grain size is increased to 100 nm, and the maximum excesses of Ba and Ti are 8 and 9%, respectively. The defects formed during synthesis and surface effect of nanoparticles are both estimated for their contributions to the deviation from stoichiometry, and the defects have been found to be mainly responsible for the large deviation observed.     

Electrical and dynamic mechanical behavior of BaTiO3/VGCF/LDPE composite

The electrical and dynamic mechanical behavior of barium titanate (BaTiO₃)/vapor-grown carbon fiber (VGCF)/Low Density Polyethylene (LDPE) composites has been studied. The measurement of electrical conductivity exhibits a lower percolation threshold and a more distinct two-stage percolation region, especially with a wide plateau between the two stages, for BaTiO₃/VGCF/LDPE composites compared to the two-component system of VGCF/LDPE. This can be attributed to increase of the effective concentration of VGCF and the obstruction of BaTiO₃ particles on VGCF networks. The dynamic mechanical spectra of BaTiO₃/VGCF/LDPE composites present a distinctive α relaxation region with its peak value nearly remaining constant at its high temperature side in contrast to the abrupt decrease of LDPE. Moreover, the loss factor in the α relaxation region reaches its largest value for the composite of 8 vol% VGCF content. This means that the piezo-damping effect really functions in BaTiO₃/VGCF/LDPE composites and only in certain conditions can this effect have practical significance. Further examination of the damping behavior in a different relaxation region demonstrates that the piezo-damping effect is directly related to the relaxation behavior of the polymeric matrix. Also, the piezo-damping effect is highly temperature and frequency dependent. The dielectric measurements suggest that, before the formation of a certain critical conducting state, the energy dissipation approach of the piezo-damping effect may be mainly determined by the interfacial polarization effect in the composite. Thus, it may be inferred that the piezo-damping effect also contributes to the dramatic increase of the loss factor at the high temperature side of the α relaxation peak for the BaTiO₃/LDPE composite and functions practically even if there is no presence of VGCF.