基于柔性基底异质结有机薄膜的光伏器件

研究了基于柔性基板的有机薄膜太阳能电池,实验以聚3,4-乙撑二氧噻吩/聚苯乙烯磺酸盐作为阳极修饰层,1,4-亚苯基亚乙烯基（MEH-PPV）材料作为给体层以及富勒烯（C60）材料作为受体层制备异质结柔性有机太阳能电池。实验结果表明:增加阳极修饰层,虽然会阻挡光的吸收,但是可以大幅度地提高短路电流、开路电压、填充因子和能量转换效率4个参数。并发现MEH-PPV受体层的厚度对有机太阳能电池的性能有较大影响,当受体层厚度为90 nm时能量转换效率达到最大,为1.29%。     

Sulphur isotope fractionation during the reduction of elemental sulphur and thiosulphate by Dethiosulfovibrio spp

Stable sulphur isotope fractionation was investigated during reduction of thiosulphate and elemental sulphur at 28°C by growing batch cultures of the sulphur- and thiosulphate-reducing bacteria Dethiosulfovibrio marinus (type strain DSM 12537) and Dethiosulfovibrio russensis (type strain DSM 12538), using citrate as carbon and energy source. The cell-specific thiosulphate reduction rate in the growth phase was 7.4±3.9?fmol?cell(-1)?d(-1). The hydrogen sulphide produced was enriched in (32)S by 10.3±1?‰ compared with total thiosulphate sulphur, close to previous experimental results observed for other sulphate- and non-sulphate-reducing bacteria. Elemental sulphur reduction yields sulphur isotope enrichment factors between-1.3 and-5.2?‰ for D. russensis and-1.7 and-5.1?‰ for D. marinus. The smaller fractionation effects are observed in the exponential growth phase (cellular rates between 5 and 70?fmol?S°?cell(-1)?d(-1)) and enhanced discrimination under conditions of citrate depletion and cell lysis (cellular rates between 0.3 and 3?fmol?S°?cell(-1)?d(-1)).     

Surface plasmon coupled fluorescence in deep-ultraviolet excitation by Kretschmann configuration

We report the experimental demonstration of fluorescence of CdSe quantum dots with surface plasmon excitation in deep-ultraviolet （deep-UV） region. Surface plasmon resonance in deep-UV is excited by aluminum thin film in the Kretschmann-Raether geometry. Considering the oxidation thickness of aluminum, the experimental results of incident angle dependence of reflectance show good agreement with Fresnel theory. Surface plasmon resonance with 19 nm-thick aluminum and 5 nm-thick almnina was excited at the incident angle of 48 degrees for 266 nm excitation. Fluorescence of CdSe quantum dots coated on this aluminum film was observed by the surface plasmon excitation.     

Current-dependent positive magnetoresistance in La_(0.8)Ba_(0.2)MnO_3 ultrathin films

We report an investigation into the magnetoresistance(MR) of La_(0.8) Ba_(0.2) Mn O_3 ultrathin films with various thicknesses. While the 13 nm-thick film shows the commonly reported negative magnetoresistive effect, the 6 nm-and 4 nmthick films display unconventional positive magnetoresistive(PMR) behavior under certain conditions. As well as the dependence on the film's thickness, it has been found that the electrical resistivity and the PMR effect of the thinner films are very dependent on the test current. For example, the magnetoresistive ratio of the 4 nm-thick film changes from +46%to-37% when the current is increased from 10 n A to 100 n A under 15 k Oe at 40 K. In addition, the two thinner films present opposite changes in electrical resistivity with respect to the test current, i.e., the electroresistive(ER) effect, at low temperatures. We discuss the complex magnetoresistive and ER behaviors by taking account of the weak contacts at grain boundaries between ferromagnetic metallic(FMM) grains. The PMR effect can be attributed to the breaking of the weak contacts due to the giant magnetostriction of the FMM grains under a magnetic field. Considering the competing effects of the conductive filament and local Joule self-heating at grain boundaries on the transport properties, the dissimilar ER effects in the two thinner films are also understandable. These experimental findings provide an additional approach for tuning the magnetoresistive effect in manganite films.     

Diffusion barrier performance of TiVCr alloy film in Cu metallization

In this study, 15 nm-thick sputter-deposited TiVCr alloy thin films were developed as diffusion barrier layers for Cu interconnects. The TiVCr alloy film tends to form a solid solution and a simple crystal structure from the constituted elements. Under TEM, the 15 nm-thick as-deposited TiVCr alloy film was observed to have a dense semi-amorphous or nanocrystalline structure. In conjunction with X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy analyses, the Si/TiVCr/Cu film stack remained stable at a high temperature of 700 °C for 30 min. The electrical resistance of Si/TiVCr/Cu film stack remained as low as the as-deposited value. These indicated that the mixed TiVCr refractory elements’ alloy barrier layer is very beneficial to prevent Cu diffusion.     

把“拉倒法测量薄膜附着力”引入大学物理实验

介绍了如何把"拉倒法测量薄膜附着力"的实验引入到大学物理实验教学中.用简单的直流溅射镀膜仪在玻璃衬底上沉积银薄膜,用设计制作的拉倒法测量薄膜附着力的实验装置测量了银薄膜在衬底上单位面积的附着力.本实验是对已经在北京科技大学国家工科物理基础课程教学基地开设的大学物理实验内容的新的扩充.     

Growth and magnetic properties of ultra-thin Co(0001) films on patterned {\rm Mo(110)/Al_2O_3(11\overline{2}0)} substrates

Single crystalline patterned Mo(110) films have been prepared on ${\rm Al_2O_3(11\overline{2}0)}$ using standard lithographical techniques, that can be used as a substrate for 3d magnetic metals epitaxy. The preparation procedure, and the structural and morphological characteristics are presented. We show that the patterned Mo(110) films may be used in a similar way than single crystal Mo(110) substrates. The structural and magnetic properties of a 3 nm-thick cobalt film deposited on the patterned Mo(110) film have been studied. The epitaxial Co layer reveals a uniaxial in-plane magnetic anisotropy as measured by Kerr magnetometry.     

金属Fe薄膜的PLD制备及其非线性光学性质研究

采用脉冲激光沉积（PLD）技术在MgO基片上制备了金属Fe薄膜.利用原子力显微镜研究了不同制备温度对薄膜表面形貌的影响.x射线衍射分析表明沉积温度大于500℃时，Fe薄膜在MgO基片上有很好的结晶性，并有单一取向.通过z扫描方法测量了超薄Fe膜的光学非线性，得到了Fe薄膜的非线性折射率n₂＝709×10^-5cm²/ kW，非线性吸收系数 β＝-552×10^-3cm/W. 关键词： Fe薄膜 非线性 脉冲激光沉积     

面外应变对1-3型垂直异质P(VDF-TrFE)基复合薄膜电热性能的调控

考虑1-3型垂直异质铁电P（VDF-TrFE）基复合薄膜结构,利用非线性的热力学理论分析和讨论了平面外应变对复合薄膜电热性能的调控作用. 结果表明,在施加的垂直电场下,平面外应变可以有效地调控电极化、热释电系数、绝热温差等铁电、电热性能. 通过合理的调控平面外应变可以在很大的温度区域范围内获得比纯平面外延薄膜结构更高的绝热温差. 研究结果预示着垂直异质P（VDF-TrFE）基复合薄膜结构在一定的工作温度范围内具有优异的电热性能,在微电源、光通信二极管、红外传感器等微型元件方面有着广泛的应用前景. 关键词： 电热效应 平面外应变 P(VDF-TrFE)复合薄膜 绝热温差     

Influence of Au thickness on the optical and electrical properties of transparent and conducting TiO2/Au/TiO2 multilayer films

Au-intermediate TiO₂/Au/TiO₂ (TAT) multilayer films were deposited by RF magnetron sputtering onto glass substrates. Changes in the optical and electrical properties of the films were investigated with respect to the thickness of the Au interlayer.The observed optical and electrical properties were dependent on the thickness of the Au interlayer. The resistivity decreased to 3.3 × 10⁻⁴ Ω cm for TiO₂ films with a 20 nm-thick Au interlayer and the optical transmittance was also influenced by the Au interlayer. Although optical transmittance deteriorated as Au thickness increased, TiO₂ films with a 5 nm-thick Au interlayer showed a relatively high optical transmittance of 80% at a wavelength of 550 nm. In addition, since a TAT film with a 5 nm-thick Au interlayer showed a relatively high work function value, it is an alternative candidate for use as a transparent anode in OLEDs and flat panel displays.     

Micromirror with large-tilting angle using Fe-based metallic glass

For enhancing the micromirror properties like tilting angle and stability during actuation, Fe-based metallic glass (MG) was applied for torsion bar material. A micromirror with mirror-plate diameter of 900?μm and torsion bar dimensions length 250?μm, width 30?μm and thickness 2.5?μm was chosen for the tilting angle tests, which were performed by permanent magnets and electromagnet setup. An extremely large tilting angle of over -270° was obtained from an activation test by permanent magnet that has approximately 0.2?T of magnetic strength. A large mechanical tilting angle of over -70° was obtained by applying approximately 1.1?mT to the mirror when 93?mAwas applied to solenoid setup. The large-tilting angle of the micromirror is due to the torsion bar, which was fabricated with Fe-based MG thin film that has large elastic strain limit, fracture toughness, and excellent magnetic property.     

高效率金属微腔OLEDs性能

以半透明Ag膜为阳极出光面,利用MoO₃作为空穴注入层,在普通玻璃衬底上制备了底发射微腔OLEDs器件,其中微腔由接近全反射厚度为100nm的Al阴极和反射率约为50%左右厚度为22nm的半透明Ag阳极构成,由于采用了有效的空穴和电子注入层MoO₃和LiF,以Alq₃作为发光材料,器件的起亮电压为2.5V,在10V外加电压下正向亮度超过了15000cd/m²,最大电流效率接近6cd/A,大约是制备于ITO玻璃衬底阳极上的常规器件的两倍(3.2cd/A),并研究了光谱窄化以及随观测角度变化的微腔效应。     

Structural transition of secondary phase oxide nanorods in epitaxial YBa2Cu3O7−δ films on vicinal substrates

A theoretical study of a structural transition of secondary phase oxide nanorods in epitaxial YBa₂Cu₃O_7?δ films on vicinal SrTiO₃ substrates is presented. Two possible types of film/substrate interface are considered, with one assuming complete coherence, while the other is defective as manifested by the presence of antiphase grain boundaries. Only in the former case does the increase of the vicinal angle of the substrate lead to a substantial change of the strain field in the film, resulting in a transition of the nanorod orientation from the normal to the in-plane direction of the film. The calculated threshold vicinal angle for the onset of the transition and lattice deformation of the YBa₂Cu₃O_7?δ film due to the inclusion of the nanorods is in very good agreement with experimental observations. This result sheds lights on the understanding of the role of the film/substrate lattice mismatch in controlling self-assembly of dopant nanostructures in matrix films.     

Control of the interfacial reactivity in the Ni/Si system

The reactivity at the Ni/Si interface is studied as a function of the sputtering conditions of the nickel film. Four systems are considered, by combining two different sputtering rates and two distinct base pressures for the deposition of the nickel 10 nm-thick film. The formation of Ni₂Si is revealed at the four interfaces by an X-ray emission spectroscopy study of the interfacial Si 3p occupied valence states. Increasing the sputtering rate is herein evidenced to decrease the quantity of silicide formed at the interface. Moreover, the combination of a high sputtering rate and a low base pressure advantageously prevents against the oxidization of the silicon surface during the metal deposition.     

Ab initio study of shear strain effects on ferroelectricity at PbTiO3 thin films

Ferroelectric thin film with the perovskite ABO₃ structure have been widely used in technology applications, e.g., actuators in MEMS/NEMS and nonvolatile random access memories (FeRAM). In order to clarify the effect of the shear strain on the ferroelectricity, the PbTiO₃ thin film as a typical one is chosen. The focus of this study is to put on the PbO-terminated (1? × ?1) and c(2? × ?2) surfaces and the TiO₂-terminated (1? × ?1) surface. Based on ab initio density functional theory calculations with the local density approximation, we have found out that in both the PbO and TiO₂-terminated (1? × ?1) models, the ferroelectricity in the PbO layers was enhanced under the positive shear strain while it was suppressed under the negative one. For the TiO₂ layers, the ferroelectricity was slightly enhanced and sharply suppressed under the positive and negative shear strains, respectively. In the PbO-terminated (2? × ?2) model, the AFE phase was suppressed by the FE phase under the positive shear strain while the opposite trend was found under the negative shear strain. For the PbO layers, the ferroelectricity was enhanced under the positive and negative shear strains. For the TiO₂ layers, the influence of the negative shear strain on the ferroelectricity was larger than that of the positive one. In addition, the ideal strength of the PbTiO₃ thin film with the different terminations was investigated as well.     

Modulation of the absorption coefficient at 1.3 μm in Ge/SiGe multiple quantum well heterostructures on silicon

We report modulation of the absorption coefficient at 1.3?μm in Ge/SiGe multiple quantum well heterostructures on silicon via the quantum-confined Stark effect. Strain engineering was exploited to increase the direct optical bandgap in the Ge quantum wells. We grew 9?nm-thick Ge quantum wells on a relaxed Si0.22Ge0.78 buffer and a contrast in the absorption coefficient of a factor of greater than 3.2 was achieved in the spectral range 1290-1315?nm.     

Photovoltaic performance of flexible Cu(In,Ga)Se2 thin-film solar cells with varying Cr impurity barrier thickness

We report the effect of Cr impurity barrier on Cu(In,Ga)Se₂ (CIGS) thin-film solar cells prepared on flexible substrates. The Cr films with varying the thickness (t_Cr) were deposited on stainless steel substrates using direct-current magnetron sputtering. The solar cell performance was improved by increasing t_Cr since the diffusion of Fe impurities from the substrate to CIGS was suppressed. Although the elemental composition, grain size, and strain of CIGS film showed little change with varying Fe content, the fill factor and the short-circuit current density increased as decreasing Fe. The Fe increased the series resistance, shunt paths, and saturation current density. The reduction of Fe caused a steeper bandgap grading in CIGS which enhances current collection due to higher electric fields in bulk CIGS. CIGS solar cells with 1000 nm-thick Cr barrier showed the best conversion efficiency of 9.05%.     

Characteristics of Ni films deposited on SiO2/Si(1 0 0) and MgO(0 0 1) by direct current magnetron sputtering system with the oblique target

280 nm-thick Ni films were deposited on SiO₂/Si(1 0 0) and MgO(0 0 1) substrates at 300 K, 513 K and 663 K by a direct current magnetron sputtering system with the oblique target. The films deposited at 300 K mainly have a [1 1 0] crystalline orientation in the film growth direction. The [1 1 0]-orientation weakens and the [1 1 1]- and [1 0 0]-orientations enhance with increasing deposition temperature. The lattice constant of the Ni films is smaller than that of the Ni bulk, except for the film grown on MgO(0 0 1) at 663 K. Furthermore, as the deposition temperature increases, the lattice constant of the films grown on the SiO₂/Si(1 0 0) decreases whereas that of the films grown on the MgO(0 0 1) increases. The films deposited at 300 K and 513 K grow with columnar grains perpendicular to the substrate. For the films deposited at 663 K, however, the columnar grain structure is destroyed, i.e., an about 50 nm-thick layer consisting of granular grains is formed at the interface between the film and the substrate and then large grains grow on the layer. The Ni films deposited at 300 K consist of thin columnar grains and have many voids at the grain boundaries. The grains become thick and the voids decrease with increasing deposition temperature. The resistivity of the film decreases and the saturation magnetization increases with increasing deposition temperature.     

Measurement of the energetics of metal film growth on a semiconductor: Ag/Si(100)-(2 x 1)

The first direct calorimetric measurements of the energetics of metal film growth on a semiconductor surface are presented. The heat of adsorption of Ag on Si(100)-(2 x 1) at 300 K decreases from approximately 347 to 246 kJ/mol with coverage in the first monolayer (ML) due to overlap of substrate strain from nearby Ag islands. It then rises quickly toward the bulk sublimation enthalpy (285 kJ/mol) as 3D particles grow. A wetting layer grows to 1.0 ML, but is metastable above approximately 0.55 ML and dewets when kinetics permit. This may be common when adsorbate islands induce a large strain in the substrate surface nearby.     

Self-organized growth of nanoparticles on a surface patterned by a buried dislocation network

The self-organized growth of Co nanoparticles is achieved at room temperature on an inhomogenously strained Ag(001) surface arising from an underlying square misfit dislocation network of 10 nm periodicity buried at the interface between a 5 nm-thick Ag film and a MgO(001) substrate. This is revealed by in situ grazing-incidence small-angle x-ray scattering. Simulations of the data performed in the distorted wave Born approximation framework demonstrate that the Co clusters grow above the dislocation crossing lines. This is confirmed by molecular dynamic simulations indicating preferential Co adsorption on tensile sites.