Ferroelectric Bi3.25La0.75Ti3O12 films of uniform a-axis orientation on silicon substrates

The use of bismuth-layered perovskite films for planar-type nonvolatile ferroelectric random-access memories requires films with spontaneous polarization normal to the plane of growth. Epitaxially twinned a axis-oriented La-substituted Bi4Ti3O12 (BLT) thin films whose spontaneous polarization is entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates using SrRuO3 as bottom electrodes. Even though the (118) orientation competes with the (100) orientation, epitaxial films with almost pure (100) orientation were grown using very thin, strained SrRuO3 electrode layers and kinetic growth conditions, including high growth rates and high oxygen background pressures to facilitate oxygen incorporation into the growing film. Films with the a-axis orientation and having their polarization entirely along the direction normal to the film plane can achieve a remanent polarization of 32 microcoulombs per square centimeter.     

Epitaxial cuprate superconductor/ferroelectric heterostructures

Thin-film heterostructures of Bi(4)Ti(3)O(12)Bi(2)Sr(2)CuO(6+x), have been grown on single crystals of SrTiO(3), LaAlO(3), and MgAl(2)O(4) by pulsed laser deposition. X-ray diffraction studies show the presence of c-axis orientation only; Rutherford backscattering experiments show the composition to be close to the nominal stoichiometry. The films are ferroelectric and exhibit a symmetric hysteresis loop. The remanent polarization was 1.0 microcoulomb per square centimeter, and the coercive field was 2.0 x 10(5) volts per centimeter. Similar results were obtained with YBa(2)Cu(3)O(7-x) and Bi(2)Sr(2)CaCu(2)O(8+x), and single-crystal Bi(2)Sr(2)CuO(6+x)as the bottom electrodes. These films look promising for use as novel, lattice-matched, epitaxial ferroelectric film/electrode heterostructures in nonvolatile memory applications.     

Domain dynamics during ferroelectric switching

The utility of ferroelectric materials stems from the ability to nucleate and move polarized domains using an electric field. To understand the mechanisms of polarization switching, structural characterization at the nanoscale is required. We used aberration-corrected transmission electron microscopy to follow the kinetics and dynamics of ferroelectric switching at millisecond temporal and subangstrom spatial resolution in an epitaxial bilayer of an antiferromagnetic ferroelectric (BiFeO(3)) on a ferromagnetic electrode (La(0.7)Sr(0.3)MnO(3)). We observed localized nucleation events at the electrode interface, domain wall pinning on point defects, and the formation of ferroelectric domains localized to the ferroelectric and ferromagnetic interface. These results show how defects and interfaces impede full ferroelectric switching of a thin film.     

Giant piezoelectricity on Si for hyperactive MEMS

Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO(3) template layer with superior piezoelectric coefficients (e(31,f) = -27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.     

ZnO/Bi_(3.6)Eu_(0.4)Ti_3O_(12)纳米复合薄膜的光致发光性能

采用化学溶液沉积法在石英衬底上制备纳米颗粒ZnO/Bi3.6Eu0.4Ti3O12(BEu T)铁电复合薄膜.光致发光研究结果表明,通过引入ZnO纳米颗粒,BEuT薄膜中Eu3+的发光大大增强,其强度大约是单纯BEu T薄膜的35倍.这种发光强度的极大改善归因于从ZnO到Eu3+的能量传递效率高.     

Giant electrocaloric effect in thin-film PbZr(0.95)Ti(0.05)O3

An applied electric field can reversibly change the temperature of an electrocaloric material under adiabatic conditions, and the effect is strongest near phase transitions. We demonstrate a giant electrocaloric effect (0.48 kelvin per volt) in 350-nanometer PbZr(0.95)Ti(0.05)O3 films near the ferroelectric Curie temperature of 222 degrees C. A large electrocaloric effect may find application in electrical refrigeration.     

Superconductivity in SrCuO2-BaCuO2 Superlattices: Formation of Artificially Layered Superconducting Materials

Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy was used to stabilize SrCuO(2)-BaCuO(2) superlattices in the infinite layer structure. Using this approach, two new structural families, Ba(2)Srn-1,Cun+1 O2n+2+delta and Ba(4)Srn-1 Cun+3O2n+6+delta have been synthesized; these families superconduct at temperatures as high as 70 kelvin.     

Electrically induced ferromagnetism at room temperature in cobalt-doped titanium dioxide

The electric field effect in ferromagnetic semiconductors enables switching of the magnetization, which is a key technology for spintronic applications. We demonstrated electric field-induced ferromagnetism at room temperature in a magnetic oxide semiconductor, (Ti,Co)O(2), by means of electric double-layer gating with high-density electron accumulation (>10(14) per square centimeter). By applying a gate voltage of a few volts, a low-carrier paramagnetic state was transformed into a high-carrier ferromagnetic state, thereby revealing the considerable role of electron carriers in high-temperature ferromagnetism and demonstrating a route to room-temperature semiconductor spintronics.     

铁离子掺杂TiO2基自洁净玻璃的制备及性能

用溶胶—凝胶法制备了表面镀有Fe—TiO2光催化薄膜的自洁净玻璃，并利用DTA—TG，XRD，SEM等手段研究了Fe—TiO2光催化薄膜的结构与特征。利用紫外—可见光分光光度计测量了不同镀膜层数的玻璃的透光率。通过光催化降解有机磷农药敌敌畏的水溶液，研究了不同铁含量以及不同镀膜层数对自洁净玻璃光催化活性的影响。研究结果表明：光催化薄膜主要由粒径为几十纳米的Fe3O4和TiO2颗粒构成；铁离子掺杂可以提高自洁净玻璃的光催化活性，在同样镀膜层数(2层)的情况下，[Fe]/[TiO2](摩尔比)＝0．005时的光催化性能最好；当用同样浓度的铁离子掺杂时，镀膜层数为9的光催化活性最高。     

Atomic Control of the SrTiO3 Crystal Surface

The atomically smooth SrTiO(3) (100) with steps one unit cell in height was obtained by treating the crystal surface with a pH-controlled NH(4)F-HF solution. The homoepitaxy of SrTiO(3) film on the crystal surface proceeds in a perfect layer-by-layer mode as verified by reflection high-energy electron diffraction and atomic force microscopy. Ion scattering spectroscopy revealed that the TiO(2) atomic plane terminated the as-treated clean surface and that the terminating atomic layer could be tuned to the SrO atomic plane by homooepitaxial growth. This technology provides a well-defined substrate surface for atomically regulated epitaxial growth of such perovskite oxide films as YBa(2)Cu(3)O(7-delta).     

Observation of antiferromagnetic domains in epitaxial thin films

Antiferromagnetic domains in an epitaxial thin film, LaFeO(3) on SrTiO(3)(100), were observed using a high-spatial-resolution photoelectron emission microscope with contrast generated by the large x-ray magnetic linear dichroism effect at the multiplet-split L edge of Fe. The antiferromagnetic domains are linked to 90 degrees twinned crystallographic regions in the film. The Neel temperature of the thin film is reduced by 70 kelvin relative to the bulk material, and this reduction is attributed to epitaxial strain. These studies open the door for a microscopic understanding of the magnetic coupling across antiferromagnetic-ferromagnetic interfaces.     

Multiferroic BaTiO3-CoFe2O4 Nanostructures

We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO3 (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The films are epitaxial in-plane as well as out-of-plane with self-assembled hexagonal arrays of CoFe2O4 nanopillars embedded in a BaTiO3 matrix. The CoFe2O4 nanopillars have uniform size and average spacing of 20 to 30 nanometers. Temperature-dependent magnetic measurements illustrate the coupling between the two order parameters, which is manifested as a change in magnetization at the ferroelectric Curie temperature. Thermodynamic analyses show that the magnetoelectric coupling in such a nanostructure can be understood on the basis of the strong elastic interactions between the two phases.     

Bulk Superconductivity up to 122 K in the Tl-Pb-Sr-Ca-Cu-O System

New high-temperature superconductors based on oxides of thallium and copper, but not containing barium, have been prepared. A transition temperature (T(c)) of about 85 K is found for (Tl(0.5)Pb(0.5)) Sr(2)CaCu(2)O(7) whereas (Tl(0.5)Pb(0.5))Sr(2)Ca(2)Cu(3)O(9) has a T(c) of about 120 K. Both materials possess tetragonal symmetry with a = 3.80 A, c = 12.05 A for (Tl(0.5)Pb(0.5))Sr(2)CaCu(2)O(7), and a = 3.81 A, c = 15.23 A for (Tl(0.5)Pb(0.5))Sr(2)Ca(2)Cu(3)O(9). A structure refinement of the latter phase has been carried out with single-crystal x-ray diffraction data.     

Ferroelectricity in ultrathin perovskite films

Understanding the suppression of ferroelectricity in perovskite thin films is a fundamental issue that has remained unresolved for decades. We report a synchrotron x-ray study of lead titanate as a function of temperature and film thickness for films as thin as a single unit cell. At room temperature, the ferroelectric phase is stable for thicknesses down to 3 unit cells (1.2 nanometers). Our results imply that no thickness limit is imposed on practical devices by an intrinsic ferroelectric size effect.     

场发射FED器件MIM结构Ta-Ta2O5-Al薄膜的制备及性能

利用直流磁控溅射Ta膜和阳极氧化法制备Ta2O5薄膜,能谱分析（EDS）和X射线衍射仪（XRD）研究表明,在H3PO4电解液中添加少量的乙二醇制备的Ta2O5薄膜,呈非晶态,没有β-Ta2O5晶相出现.利用电击穿场强测试系统研究Ta-Ta2O5-Al复合薄膜制备FED器件（MIM结构）的绝缘性,证明采用磁控溅射和阳极氧化法成功制备了漏电流密度低、耐击穿场强高的Ta2O5薄膜.     

MgB2 superconducting thin films with a transition temperature of 39 kelvin

We fabricated high-quality c axis-oriented epitaxial MgB2 thin films using a pulsed laser deposition technique. The thin films grown on (1 i 0 2) Al2O3 substrates have a transition temperature of 39 kelvin. The critical current density in zero field is approximately 6 x 10(6) amperes per cubic centimeter at 5 kelvin and approximately 3 x 10(5) amperes per cubic centimeter at 35 kelvin, which suggests that this compound has potential for electronic device applications, such as microwave devices and superconducting quantum interference devices. For the films deposited on Al2O3, x-ray diffraction patterns indicate a highly c axis-oriented crystal structure perpendicular to the substrate surface.     

地膜的水热效应与麦田土壤N2O排放

通过两个小麦生长期田间试验,研究了地膜覆盖对耕层土壤N_2O排放的影响.结果表明,无论是否耕种小麦,地膜覆盖均能明显提高耕层土壤含水量,且对休耕地的保水作用高于小麦田.小麦田覆膜后增温幅度小于休耕地,但在孕穗期前和成熟期后增温效果大,而小麦生长中期小;尤其能显著提高0～5 cm耕层土壤温度,甚至10 cm深土壤温度.地膜覆盖后小麦田耕层土壤中NO_3~--N平均含量增加5.34 mg·kg~(-1),且小麦生长旺盛期增加量明显.覆膜使大多数小麦生育期土壤N_2O排放通量高于常规耕作,其增排效应与土壤水分、温度、NO_3~--N含量、有机质增加量存在较好的线性关系;小麦田土壤N_2O增排的最大影响因子是耕层5 cm处土壤温度的变化,其次与土壤养分有效性增加密切相关;而休耕地土壤N_2O的增排作用主要受控于覆膜对水热条件及微生物能量供给的改善.     

聚合物电致发光二极管发光层中的电场分布

以单层聚对苯乙炔（PPV）薄膜发光二极管为例，研究其薄膜中的电场分布，探讨其电场分布对载流子注入、输运和复合的影响，研究结果有助于揭示其发光机理，为提高发光效率提供了有益的启示。     

High-Density Nanosecond Charge Trapping in Thin Films of the Photoconductor ZnODEP

An electrooptical memory effect is observed with solid thin films of the photoconductor zinc-octakis(beta-decoxyethyl) porphyrin (ZnODEP) sandwiched between two optically transparent electrodes. Upon irradiation with the simultaneous application of an electric field, electron-hole pairs are generated and separated within the photoconductive layer. These electron-hole pairs become "frozen" within the films when the irradiation is interrupted. These trapped charges can be released by irradiation of the cell, resulting in a transient short-circuit photocurrent. No cross talk between adjacent memory elements separated by approximately 0.2 micrometer (a density of 3 gigabits per square centimeter) was detected. The charge storage system is robust and nonvolatile. The response time for the write-read beam is in the subnanosecond range, and no refreshing is required for long-term retention of trapped charges.     

不同类型钙化合物对污染土壤水稻吸收累积Ｃｄ Ｐｂ的影响及机理

以潮泥田和红黄泥为供试土壤,利用盆栽试验研究了施用不同类型钙化合物(CaO、CaCO3、CaSO4)对水稻吸收累积Cd、Pb的影响及机理。结果表明,潮泥田施用CaO和CaCO3后,土壤pH值明显升高。当CaO施用量达到0.36gCa·kg-1时土壤有效态Cd含量显著降低,水稻糙米Cd含量也随之显著下降,降幅达26.3%;施用CaCO(30.24gCa·kg-1)和CaSO(40.24gCa·kg-1)后水稻糙米Cd含量降幅分别为23.7%(P0.05)和18.4%(P0.05)。红黄泥施用CaO、CaCO3和CaSO4后,土壤pH值变化趋势与潮泥田相同。当CaO施用量达到0.24gCa·kg-1时土壤有效态Cd含量显著降低,但水稻糙米Cd含量反而上升,当CaO施用量达到0.36gCa·kg-1时,与对照相比水稻糙米Cd含量增加34.5%(P0.05);当CaO施用量增至0.48gCa·kg-1时土壤有效态Pb含量明显增加,水稻糙米Pb含量也随之显著增加,增幅达41.7%。在等钙(0.24gCa·kg-1)条件下,潮泥田及红黄泥施用CaO、CaCO3和CaSO4后因pH变幅较小导致水稻糙米Cd、Pb含量无明显差异。综合分析认为,利用钙化合物控制污染土壤上水稻对Cd、Pb的吸收累积时,需要根据土壤Cd、Pb含量和pH综合考虑合理的钙化合物类型和用量。