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.     

Ceramic thin-film formation on functionalized interfaces through biomimetic processing

Processing routes have been developed for the production of thin ceramic films through precipitation from aqueous solutions. The techniques are based on crystal nucleation and growth onto functionalized interfaces. Surface functionalization routes have been developed by the mimicking of schemes used by organisms to produce complex ceramic composites such as teeth, bones, and shells. High-quality, dense polycrystalline films of oxides, hydroxides, and sulfides have now been prepared from "biomimetic" synthesis techniques. Ceramic films can be synthesized on plastics and other materials at temperatures below 100 degrees C. As a low-temperature process in which water rather than organic solvents is used, this synthesis is environmentally benign. Nanocrystalline ceramics can be produced, sometimes with preferred crystallite orientation. The direct deposition of high-resolution patterned films has also been demonstrated. The process is well suited to the production of organic-inorganic composites.     

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.     

Synthesis and Electronic Transport of Single Crystal K3C60

Sizable single crystals of C(6O) have been synthesized and doped with potassium. Above the superconducting transition temperature T(c), the electrical resistivity p(T) displays a classic metal-like temperature dependence. The transition to the superconducting state at T(c) = 19.8 K is extremely sharp, with a transition width DeltaT < 200 mK. In contrast to transport behavior of doped polycrystalline and granular thin films, no anomalous fluctuations are observed near T(c) in single crystal specimens.     

Growth Mechanism of Sputtered Films of YBa2Cu3O7 Studied by Scanning Tunneling Microscopy

The surface microstructures of c-axis-oriented films of YBa(2)Cu(3)O(7), deposited by off-axis magnetron sputtering on MgO and SrTiO(3) single crystal (100) substrates, have been investigated with scanning tunneling microscopy and atomic force microscopy. There is strong evidence that the films nucleate as islands and grow by adding material to the edge of a spirally rising step. This results in columnar grains, each of which contains a screw dislocation at its center. This microstructure may be of significance in determining superconducting properties such as critical current, and represents a significant difference between thin films (especially those grown in situ) and bulk materials.     

Epitaxial BiFeO3 multiferroic thin film heterostructures

Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.     

化学气相沉积金刚石薄膜的表面过程

采用简单表面反应模式，对化学气相沉积金刚石薄膜的表面动力学过程进行了研究，得到了金刚石薄膜的沉积速率公式，揭示了影响薄膜生长的因素并由此讨论了金刚石薄膜生长的机制和规律。     

Superconductivity modulated by quantum size effects

We have fabricated ultrathin lead films on silicon substrates with atomic-scale control of the thickness over a macroscopic area. We observed oscillatory behavior of the superconducting transition temperature when the film thickness was increased by one atomic layer at a time. This oscillating behavior was shown to be a manifestation of the Fabry-Perot interference modes of electron de Broglie waves (quantum well states) in the films, which modulate the electron density of states near the Fermi level and the electron-phonon coupling, which are the two factors that control superconductivity transitions. This result suggests the possibility of modifying superconductivity and other physical properties of a thin film by exploiting well-controlled and thickness-dependent quantum size effects.     

硫化温度和时间对SnxSy薄膜结构和成分的影响

用热蒸发技术在玻璃基片上沉积一层sn薄膜,在真空条件下,将其在150～300℃下硫化30．60min．对在不同温度和时间下硫化的薄膜进行结构、成分和表面形貌分析,结果表明：在不同温度和不同时间下硫化,所得到的薄膜在物相结构、成分和表面形貌上都存在差异．当硫化温度为240℃、硫化时间为45min时,所制得的薄膜为正交结构的SnS多晶薄膜,其均匀性、致密性以及对基片的附着力都较好,具有（111）方向优先生长,薄膜粒径在200～800nm,且晶格常数与标样的数值吻合很好．     

Microstructural optimization of a zeolite membrane for organic vapor separation

A seeded growth method for the fabrication of high-permeance, high-separation-factor zeolite (siliceous ZSM-5, [Si96O192]-MFI) membranes is reported. The method consists of growing the crystals of an oriented seed layer to a well-intergrown film by avoiding events that lead to a loss of preferred orientation, such as twin overgrowths and random nucleation. Organic polycations are used as zeolite crystal shape modifiers to enhance relative growth rates along the desirable out-of-plane direction. The polycrystalline films are thin (approximately 1 micrometer) with single grains extending along the film thickness and with large in-plane grain size (approximately 1 micrometer). The preferred orientation is such that straight channels with an open diameter of approximately 5.5 angstroms run down the membrane thickness. Comparison with previously reported membranes shows that these microstructurally optimized films have superior performance for the separation of organic mixtures with components that have small differences in size and shape, such as xylene isomers.     

Van der Waals Epitaxial Growth of agr-Alumina Nanocrystals on Mica

Lattice mismatch stresses, which severely restrict heteroepitaxial growth, are greatly minimized when thin alumina films are grown by means of van der Waals forces on inert mica substrates. A 10-nanometer-thick epitaxial film exhibits crystallographic sixfold symmetry, a lattice constant close to that of the basal plane [0001] of alpha-alumina (sapphire), and an aluminum: oxygen atomic ratio of 1:1.51 +/- 0.02 (measured by x-ray photoelectron spectroscopy), again the same as for bulk sapphire. The film is free of steps and grain boundaries over large areas and appears to be an ideal model system for studying adhesion, tribology, and other surface phenomena at atomic scales.     

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.     

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.     

Growth and erosion of thin solid films

Thin films that are grown by the process of sputtering are, by and large, quite unlike the smooth, featureless structures that one might expect. In general, these films have a complicated surface morphology and an extended network of grooves and voids in their interiors. Such features can have a profound effect on the physical properties of a thin film. The surface irregularities and the bulk defects are the result of a growth instability due to competitive shadowing, an effect that also plays a role in geological processes such as erosion. For amorphous thin films, the shadow instability can be described by a remarkably simple model, which can be shown to reproduce many important observed characteristics of thin film morphology.     

Bond selectivity in silicon film growth

Hydrogen atoms can selectively eliminate strained bonds that form during the growth of amorphous silicon films. By periodically interrupting the growth and exposing the grown material to hydrogen, the film composition can be varied continuously from a non-equilibrium amorphous structure to that of a crystalline solid. Furthermore, by tuning the hydrogen exposure it is possible to discriminate between Si-Si bonds formed on different substrates, thereby allowing substrate-selective growth. The evolution of the film structure during hydrogen exposure is directly observed by scanning tunneling microscopy, and a model describing the role of hydrogen is presented.     

Growth of uniformly oriented silica MFI and BEA zeolite films on substrates

Applications of zeolite films benefit from alignment of the integrated channels, but methods for film growth have nearly always introduced orientational randomization in the direction normal to the substrate. We now report facile methods to grow silicalite-1 films and pure silica beta zeolite films on substrates with straight or sinusoidal channels positioned uniformly upright at a thickness of up to 8 micrometers. Precise gel compositions and processing temperatures are critical to promote secondary growth on pre-formed oriented crystal monolayers while suppressing self-crystallization in the bulk medium. Preliminary results highlight the potential of these uniformly oriented films in the nonlinear optical response and separation of xylene isomers.     

A combinatorial approach to materials discovery

A method that combines thin film deposition and physical masking techniques has been used for the parallel synthesis of spatially addressable libraries of solid-state materials. Arrays containing different combinations, stoichiometries, and deposition sequences of BaCO(3), Bi(2)O(3), CaO, CuO, PbO, SrCO(3), and Y(2)O(3) were generated with a series of binary masks. The arrays were sintered and BiSrCaCuO and YBaCuO superconducting films were identified. Samples as small as 200 micrometers by 200 micrometers in size were generated, corresponding to library densities of 10,000 sites per square inch. The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.     

Atomic-Scale Images of the Growth Surface of Ca1-xSrxCuO2 Thin Films

The surface microstructure of c-axis (Ca,Sr)CuO(2) thin films, grown by laser molecular beam epitaxy on SrTiO(3)(001) substrates, was studied by ultrahigh-vacuum scanning tunneling microscopy (STM). Images were obtained for codeposited Ca1-xSrxCuO(2) thin films, which show a layered-type growth mode. The surfaces consist of atomically flat terraces separated by steps that are one unit cell high. A pronounced dependence of the growth mechanism on the Sr/Ca ratio of the films was observed. Atomic resolution STM images of the CuO(2) sheets in the ab plane show a square lattice with an in-plane spacing of 4 angstroms; the lattice contains different concentrations of point defects, depending on the polarity of the sample-tip bias.     

壳聚糖涂膜对大蒜保鲜效果的研究

采用壳聚糖作为涂膜保鲜材料,在常温条件下研究不同浓度壳聚糖的单膜和复合膜对大蒜贮藏期间主要理化特性的变化.结果表明,1.50%壳聚糖单膜和壳聚糖-玉米淀粉复合膜均可有效抑制大蒜的呼吸强度,保持大蒜的水分含量、硬度、可溶性同形物含量和总糖含量,以壳聚糖-玉米淀粉复合膜的保鲜效果最为理想.     

Direct observation of structural defects in laser-deposited superconducting y-ba-cu-o thin films

The defect structure of in situ pulsed, laser-deposited, thin films of the high-transition temperature superconductor Y-Ba-Cu-O has been observed directly by atomic resolution electron microscopy. In a thin film with the nominal composition YBa(2)Cu(3)O(7) (123), stacking defects corresponding to the cationic stoichiometry of the 248, 247, and 224 compounds have been observed. Other defects observed include edge dislocations and antiphase boundaries. These defects, which are related to the nonequilibrium processing conditions, are likely to be responsible for the higher critical currents observed in these films as compared to single crystals.