外加电场对铁电薄膜相变的影响

采用热力学非线性理论,研究了外加电场对立方基底Pb(Zr_0.3Ti_0.7)O₃(PZT)铁电薄膜相变的影响.通过数值计算,得到了"失配应变-外加电场"相图,及外加电场与极化强度的关系.当外加电场达到186 kV/cm时,能使生长在SrTiO₃ 基底上PZT铁电薄膜从单斜r相转变为c相.在实验上,采用扫描探针显微镜通过对PZT薄膜施加不同的极化电场来研究了它的电畴翻转.从得到的压电响应相图可以看出,绝大多数的电畴是清晰可 关键词： 铁电薄膜 相变 扫描探针显微镜 失配应变     

周期极化掺镁不同组分LiNbO3晶体的研究

利用气相平衡扩散法研制出掺镁不同组分的LiNbO₃晶体，并对其极化特性进行了研究.研究表明晶体的开关电场和自发极化不仅与晶体组分［Li］/［Nb］比有关而且与掺镁量有关，［Li］/［Nb］比为0.973掺入2mol% MgO的近化学比LiNbO₃晶体的开关电场仅为1.8kV/mm，是同成分晶体的1/12，且其极化结构的质量要远好于同成分LiNbO₃晶体和近化学比LiNbO₃晶体. 关键词： 气相平衡扩散 3晶体')" href="#">掺镁LiNbO₃晶体 周期极化     

外延PbZr0.4Ti0.6O3薄膜厚度对其铁电性能的影响

从Landau-Devonshire唯象理论出发，考虑到晶格失配导致的NFDA3位错应力场与极化场的耦合，研究了在SrTiO₃衬底上外延生长的PbZr_0.4Ti_0.6O₃薄膜厚度对其自发极化强度、电滞回线的影响. 结果表明，产生刃位错的PbZr_0.4Ti_0.6O₃薄膜临界厚度为～1.27nm，当薄膜厚度大于临界厚度时，在所形成的位错附近，极化强度出现急剧变化，形成自发极化强度明显减弱的“死层”；随着薄膜厚度的减小，位错间距增大，“死层”厚度与薄膜总厚度之比增加. 由薄膜电滞回线的变化情况可知，其剩余极化强度随着薄膜厚度的减小而逐渐减小. 关键词： 铁电薄膜 自发极化强度 电滞回线 位错     

La0.5Sr0.5CoO3薄膜的外延生长及其机理研究

利用脉冲激光制膜法,在多种衬底和温度条件下,系统研究了La_0.5Sr_0.5CoO₃(LSCO)薄膜的结构和外延生长特性,在LaAlO₃,SrTiO₃和MgO衬底上实现了LSCO薄膜的外延生长.外延生长的薄膜具有低的电阻率和金属性导电特征.研究表明,外延生长的最佳温度范围为700—800℃,最佳衬底为LaAlO₃.并着重探讨了衬底材料和淀积温度等多种因素对LSCO薄膜的生长与性 关键词：     

Pb(Zr0.3Ti0.7)O3铁电薄膜激光感生电压效应

采用脉冲激光沉积(PLD)技术在LaSrAlTaO₃(LSATO),LaAlO₃(LAO)和SrTiO₃(STO)的单晶倾斜衬底上成功制备了Pb(Zr_0.3Ti_0.7)O₃(PZT)薄膜,在三种倾斜衬底上生长的PZT薄膜中都首次发现了LIV效应.对PZT/LSATO薄膜在a,c轴两种不同取向择优生长下的LIV效应做了研究,发现在薄膜c轴取向择优生长 关键词： 激光感生电压效应 铁电薄膜 薄膜生长取向 原子层热电堆     

周期极化LiNbO3晶体中电极布置对反转畴扩张的影响

利用外加电场极化的方法,分别研究了三种不同方式布置的极化电极对C向切割LiNbO_{3< /sub>晶体极化反转畴扩张的影响.实验结果表明在相同极化条件下，当极化电极长度方向与六边 形反转畴一对边呈90°和0°角时，极化扩张速度分别为0.089μm/ms和0.011μm/ms.实验结果揭示，为了有效地控制极化占空比，在制备一维准相位匹配LiNbO3晶体时应 避免极化电极与六边形反转畴壁中一对边呈90°的情况. 关键词： 周期极化 极化扩张 准相位匹配}     

X射线三晶衍射研究YBa2Cu3Oy超导薄膜

应用X射线三晶衍射对LaAlO₃衬底上生长的YBa₂Cu₃O_y薄膜中的应力水平、存在的主要缺陷,以及薄膜与衬底的失配和取向关系等进行了研究。结果表明,薄膜在衬底上几乎完全松弛,应力很小,薄膜存在较严重的晶格取向差缺陷,这是影响薄膜晶体结构完整性的主要因素。此外,衬底与薄膜在垂直于表面和平行于表面方向都存在取向差。 关键词：     

氧化钒薄膜微观结构的研究

采用直流磁控反应溅射在Si(100)衬底上溅射得到(001)取向的V₂O₅薄膜.x射线衍射(XRD)、扫描电镜(SEM)和傅里叶变换红外光谱(FTIR)的结果表明，氧分压影响薄膜的成分和生长取向，在氧分压0.4Pa时溅射得到(001)取向的纳米V₂O₅薄膜，即沿c轴垂直衬底方向取向生长的薄膜.V₂O₅薄膜经过真空退火得到(001)取向的VO₂薄膜，晶体颗 关键词： 微观结构 氧化钒薄膜 择优取向 直流磁控溅射     

外电场辅助化学气相沉积方法制备网格状β-Ga2O3纳米线及其特性研究

利用外电场辅助化学气相沉积（CVD）方法,在蓝宝石衬底上制备出了由三组生长方向构成的网格状β-Ga₂O₃纳米线.研究了不同外加电压大小对β-Ga₂O₃纳米线表面形貌、晶体结构以及光学特性的影响.结果表明：外加电压的大小对样品的表面形貌有着非常大的影响,有外加电场作用时生长的β-Ga₂O₃纳米线取向性开始变好,只出现了由三组不同生长方向构成的网格状β-Ga₂O₃纳米线;并且随着外加电压的增加,纳米线分布变得更加密集、长度明显增长.此外,采用这种外电场辅助的CVD方法可以明显改善样品的结晶和光学质量.     

外加电场法制备LiNbO3周期畴的反转电流特性研究

采用外加电场法制备了LiNbO₃单晶周期畴结构. 在对不同尺寸周期畴的反转电流进行比较研究的基础上,提出了一种确定反转畴成核时间和纵向贯穿速率的方法. 根据这一方法,得到在电场强度为25.1kV/mm,脉冲宽度为50 ms的脉冲方波作用下,LiNbO₃单晶反转畴的成核时间约为80ns,纵向贯穿速率约为0.1667m/s. 关键词： 3单晶周期极化')" href="#">LiNbO₃单晶周期极化 反转电流 反转畴成核时间 反转畴纵向贯穿速率     

Pulsed laser deposition of NdNiO3 thin films

We report the structural and transport properties of NdNiO₃ thin films prepared via pulsed laser deposition over various substrates. The films were well textured and c-axis oriented with good crystalline properties. The electrical resistivity of the films undergoes a metal-insulator transition, depending on the deposition process. Well-defined first order metal-insulator phase transition (T_MI) was observed in the best quality films without high pressure processing. Various growth conditions such as substrate temperature, oxygen pressure and thickness were varied to see their influence on T_MI. Deposition temperature was found to have a great impact on the electrical and structural properties of these films. Further the films deposited on LaAlO₃ substrate were found to be highly oriented with uniform grain size as observed from X-ray diffraction and atomic force microscopy, whereas those on Si substrate were polycrystalline, dense and randomly oriented.     

Effect of substrate temperature on the properties of LiNbO<Subscript>3</Subscript> nanocrystalline films during pulsed laser deposition

The results are presented from studying the effect substrate temperature has on the morphological, electrophysical, and optical parameters of LiNbO₃ films obtained via pulsed laser deposition. It is established that films formed at temperatures of 300 to 600°C have a nanocrystalline structure with crystallites predominantly oriented in planes (110), (1010), and (220). The refractive index of the obtained films in the wavelength range of 500–800 nm varies from 2.13 to 2.26.     

Size and interface effects on Curie temperature of perovskite ferroelectric nanosolids

A simple and unified model, without any adjustable parameter, is established for size effect on Curie temperature of low-dimensional ferroelectrics (thin films, nanowires and nanoparticles), T _c(D), where D denotes size of low-dimensional ferroelectrics. T _c(D) function is based on consideration on the size dependence of spontaneous polarization of low-dimensional ferroelectrics P _s(D), which is determined by the misfit strain at the ferroelectrics/substrate interface. It is shown that P _s(D) and T _c(D) functions decrease or increase when the misfit strain is tensile or compressive. The numerically predicted results are in agreement with the available experimental results of BaTiO₃ and PbTiO₃ nanoparticles and thin films.     

Composition, XRD and morphology study of laser prepared LiNbO3 films

LiNbO₃ films were deposited by PLD from LiNbO₃ crystalline or from three different stoichiometric or Li-enriched LiNbO₃ targets. Polycrystalline films were prepared on SiO₂/Si or sapphire substrates at temperatures T _S ～650–750 °C. Main attention was paid to the influence of targets preparation and the deposition conditions on films composition, morphology and crystallinity. The thin-film morphology was determined by SEM microscopy. The composition was measured by SIMS, RBS, PIXE and PIGE methods. Highly oriented, smooth and stoichiometric LiNbO₃ films were synthesized.     

GaAs(100)衬底上C60单晶膜的取向生长

利用双温区真空蒸发沉积技术成功地在GaAs（100）衬底上实现了完全（111）取向的C₆₀单晶膜的生长．用扫描电子显微镜和Ｘ射线衍射技术对C₆₀单晶膜的形貌和结构进行了分析．结果表明：能实现C₆₀取向生长的衬底温度范围很窄，温度过高或过低都易造成晶粒的取向无序．对实验结果做出了合理的解释，并讨论了C₆₀单晶膜的生长机制 关键词：     

Intricacies of strain and magnetic field induced charge order melting in Pr0.5Ca0.5MnO3 thin films

Thin films of the half-doped manganite Pr_0.5Ca_0.5MnO₃ were grown on (1 0 0) oriented MgO substrates by pulsed laser deposition technique. In order to study the effect of strain on the magnetic field induced charge order melting, films of different thicknesses were prepared and their properties were studied by X-ray diffraction, electrical resistivity and magnetoresistance measurements. A field induced charge order melting is observed for films with very small thicknesses. The charge order transition temperature and the magnetic field induced charge order melting are observed to depend on the nature of strain that is experienced by the film.     

Control of a- and c-plane preferential orientations of ZnO thin films

We report orientation-controllable growth of ZnO thin films and their orientation-dependent electrical characteristics. ZnO thin films were deposited on single-crystalline (1 0 0) LaAlO₃ and (1 0 0) SrTiO₃ substrates using pulsed laser deposition (PLD) at different substrate temperatures (400-800 °C). It was found that the orientation of ZnO films could be controlled by using different substrates of single-crystalline (1 0 0) LaAlO₃ and (1 0 0) SrTiO₃. The a-plane () and c-plane (0 0 0 2) oriented ZnO films are formed on LaAlO₃ and SrTiO₃, respectively. In both cases, the degree orientation increased with increasing deposition temperature T_s. Both the surface free energy and the degree of lattice mismatch are ascribed to play an important role for the orientation-controllable growth. Further characterization show that the grain size of the films with both orientations increases for a substrate temperature increase (i.e. from T_s = 400 °C to T_s = 800 °C), whereas the electrical properties of ZnO thin films depend upon their crystalline orientation, showing lower electrical resistivity values for a-plane oriented ZnO films.     

Growth of ultrathin layers of Au on LiNbO3(0 0 0 1) measured with atomic force microscopy

Atomic force microscopy (AFM) has been used to characterize the growth of Au deposited via evaporation onto the positive face of single crystalline, lithium niobate, LiNbO₃(0 0 0 1) surface. In order to study the mechanisms for the ordering and aggregation of a noble metal on this ferroelectric surface, topographic and phase contrast imaging of the fractional surface coverage of Au were performed. Atomically flat, uniformly poled LiNbO₃ surfaces were prepared via an ambient high temperature anneal and served as a support for the thin gold films. These gold atomic layers were grown using electron bombardment evaporation sources under ultra-high vacuum (UHV) conditions and subsequently characterized under both vacuum and ambient environments. Using AFM it was found that gold preferentially nucleates at the top of LiNbO₃ substrate step edges. With increased coverage, island formation proceeds due to local aggregation of adsorbed gold on each substrate terrace. Based on local imaging of the growth morphology, the data is discussed in terms of thin film growth mechanisms as well as the influence of native surface features such as defects and charge distribution. Understanding growth mechanisms for gold layers on ferroelectric surfaces allows for a fuller appreciation of how atomic deposition of metal atoms on patterned poled LiNbO₃ surfaces would occur as well as yielding greater insight on the atomic characteristics of metals on ferroelectric interfaces.     

Pulsed laser deposition of ZnO as conductive buffer layer of (001)-LiNbO3 thin films

1 (LO) mode peak at 579 cm^-1, indicating oxygen deficiency in the films. Significant dependence of the electrical property for the films on substrate temperature was shown. The I–V relation of the films exhibited non-ohmic behavior. Whereas the films deposited above 500 °C showed a metal-like property, at a lower substrate temperature semiconducting thin films were achieved. The (001)-oriented LiNbO₃/ZnO heterostructure was successfully prepared on quartz fused and (001) sapphire plates. Received: 6 April 1998/Accepted: 26 May 1998     

Influence of the thickness on structural,magnetic and electrical properties of La0.7Ca0.3MnO3 thin film

We have studied the effect of thickness on the structural, magnetic and electrical properties of La_0.7Ca_0.3MnO₃ thin films prepared by pulsed laser deposition method using X-ray diffraction, electrical transport, magneto-transport and dc magnetization. X-ray diffraction pattern reflects that all films have c-axis epitaxial growth on LaAlO₃ substrate. The decrease in out-of-plane cell parameter specifies a progressive relaxation of in the plane compressive strain as the film thickness is increases. From the dc magnetization measurements, it is observed that ferromagnetic to paramagnetic transition temperature increases with increase in the film thickness. Magneto-resistance and temperature coefficient of resistance increases with film thickness and have maximum value near its metal to insulator transition temperature.