Epitaxial Bi2Sr2CuOy thin films as p-type transparent conductors

Development of p-type transparent conducting thin films is tireless due to the trade-off issue between optical transparency and conductivity. The rarely concerned low normal state resistance makes Bi-based superconducting cuprates the potential hole-type transparent conductors, which have been realized in Bi₂Sr₂CaCu₂O_y thin films. In this study, epitaxial superconducting Bi₂Sr₂CuO_y and Bi₂Sr_1.8Nd_0.2CuO_y thin films with superior normal state conductivity are proposed as p-type transparent conductors. It is found that the Bi₂Sr_1.8Nd_0.2CuO_y thin film with thickness 15 nm shows an average visible transmittance of 65% and room-temperature sheet resistance of 650 Ω/sq. The results further demonstrate that Bi-based cuprate superconductors can be regarded as potential p-type transparent conductors for future optoelectronic applications.     

Nonvolatile Resistive Switching and Physical Mechanism in LaCrO_3 Thin Films

Polycrystalline LaCrO_3(LCO) thin films are deposited on Pt/Ti/SiO_2/Si substrates by pulsed laser deposition and used as the switching material to construct resistive random access memory devices. The unipolar resistive switching(RS) behavior in the Au/LCO/Pt devices exhibits a high resistance ratio of ~104 between the high resistance state(HRS) and low resistance state(LRS) and exhibits excellent endurance/retention characteristics.The conduction mechanism of the HRS in the high voltage range is dominated by the Schottky emission, while the Ohmic conduction dictates the LRS and the low voltage range of HRS. The RS behavior in the Au/LCO/Pt devices can be understood by the formation and rupture of conducting filaments consisting of oxygen vacancies,which is validated by the temperature dependence of resistance and x-ray photoelectron spectroscopy results.Further analysis shows that the reset current I_R and reset power P_R in the reset processes exhibit a scaling law with the resistance in LRS(R_0), which indicates that the Joule heating effect plays an essential role in the RS behavior of the Au/LCO/Pt devices.     

La1-xNaxMnO3/YSZ膜的化学溶液法制备及输运性能研究

本文采用化学溶液法在钇稳定的二氧化锆(Y-stabilized ZrO2,YSZ)单晶基板上制备了La1-xNaxMnO3(LNMO)膜并对其输运性能进行了研究.X-射线衍射(XRD)结果表明,所获得的LNMO膜为高度(h00)取向;输运结果表明,所制备的LNMO膜表现为外延膜的性能,且La0.7Na0.3MnO3薄膜在300K、0.5T磁场下可获得～5%磁阻值.     

铜铁矿基p-TCO材料的制备与物性研究

采用溶胶-凝胶法和高温固相反应法进行了铜铁矿结构单相CuBO2(B=Al,Cr,La)多晶陶瓷的制备,并采用脉冲激光沉积法(Pulsed laser deposition,PLD)制备了CuCrO2薄膜。结果表明:溶胶-凝胶法可以成功制备高纯CuAlO2和CuCrO2多晶材料。该方法还可以显著降低烧结温度且使烧结时间显著缩短;所制备的名义组分CuAlO2和CuCrO2样品均呈p型半导体导电行为,CuBO2的电导率随着B位离子半径的增大而明显减小;PLD法制备的CuCrO2薄膜呈高度c轴取向,厚度～200nm的薄膜在可见光区的平均透射率～80%。     

溶胶凝胶法制备铜铁矿结构p型透明导电氧化物薄膜

铜铁矿结构p型透明导电氧化物(transparent conducting oxide, TCO)薄膜是一类在电子学领域具有广泛应用前景的新材料,因其可与n-TCO薄膜形成真正意义上的“透明器件”而备受关注。本文介绍了铜铁矿结构p-TCO的结构特性以及溶胶凝胶法的基本原理和特点;系统地介绍了溶胶凝胶法制备铜铁矿结构p-TCO薄膜的工艺;分析比较了有机醇盐、无机盐溶胶体系的优缺点;最后讨论了进一步的发展方向,指出溶胶凝胶法是一种高效可行的制备p-TCO薄膜的方法。     

Modulation of Insulator-Metal Transition Temperature by Visible Light in La7/8Sr1/8MnO3 Thin Film

Effects of magnetic field and light illumination on the electrical transport properties of La7/8Sr1/8MnO3 thin film grown on a Si substrate are investigated. The film shows an insulator-metal transition at Tp - 191.9 K and a low-temperature resistance minimum at Tmin ≈ 48 K in darkness. Both magnetic field and light illumination shift the insulator-metal transition temperature Tp to be higher, while the low-temperature transport properties of the film induced by them show different trends. That is, the magnetic field and light illumination make the Tmin shift to lower and higher temperatures, respectively. The enhancement of both Tp and Train under light illumination could be explained in terms of photoinduced hole-doping and demagnetization effects of La7 /8Sr1/8MnO3.     

(Bi,Pb)_2Sr_2CaCu_2O_y单晶的磁通钉扎研究

我们通过对重Pb掺杂的Bi-2212((Bi,Pb)-2212)单晶磁化性质的测量来研究磁通钉扎性能,发现样品中存在与温度有明显依赖关系的鱼尾效应,且此鱼尾效应不仅体现在磁滞洄线上,还体现在不同磁场下零场冷的M～T曲线的交叠上.同时我们采用非线性磁通蠕动模型,并考虑表面位垒和体钉扎的影响,运用数值模拟分析了样品的磁化性质,结果表明(Bi,Pb)-2212单晶的鱼尾效应源于重Pb掺杂导致样品各向异性的降低所引起的强的体钉扎效应,而高温的磁化性质主要取决于表面位垒的作用.     

Improvement of dielectric （Ba,Sr）TiO3 thin tunability and loss tangent of films with K doping

Ba0.6Sr0.4 TiO3 thin films doped with K were deposited on Pt/Ti/SiO2 /Si substrates by the chemical solution deposition method. The structure, surface morphology and the dielectric and tunable properties of Ba0.6Sr0.4 TiO 3 thin films have been studied in detail. The K content in Ba0.6Sr0.4TiO3 thin films has a strong influence on the material’s properties including surface morphology and the dielectric and tunable properties. It was found that the Curie temperature of K-doped Ba0.6Sr0.4 TiO3 films shifts to a higher value compared with that of undoped Ba0.6Sr0.4TiO3 thin films, which leads to a dielectric enhancement of K-doped Ba0.6Sr0.4 TiO3 films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices.