激光能量对反钙钛矿GaCMn_3薄膜结构与物性的影响

本文采用脉冲激光沉积方法在LaAlO3(001)单晶衬底上制备了反钙钛矿GaCMn3薄膜,通过控制制备过程中脉冲激光的能量,研究了不同激光能量条件对GaCMn3薄膜结构与物理性能的影响.分别利用X射线衍射仪、原子力显微镜、超导量子干涉仪和物理性能测试系统,对所制备的薄膜的晶体结构、表面形貌和磁性、电输运性质进行了研究.结果表明,制备的样品均为具有多个晶面取向的反钙钛矿薄膜,且薄膜结构和物性明显随制备激光能量的变化而变化.当激光能量为450mJ时,制备的薄膜多晶面取向性最弱,结晶性和表面形貌最优良.实验所得的薄膜均表现出顺磁-铁磁-反铁磁相转变,然而转变过程比块材较平缓,同时薄膜的电阻率并未表现出块材中的突变特征,我们推测该现象很可能是由衬底的应力及衬底的晶格膨胀对薄膜反常晶格变化的抑制作用造成的.     

氧气氛退火对La0.7Sr0.3MnO3薄膜结构及性能的影响

利用磁控溅射方法,在(100)Si、LaAlO_3(LAO)和SrTiO_3(STO)衬底上制备得到了La_(0.7)Sr_(0.3)MnO_3(LSMO)薄膜,通过X射线衍射仪、原子力显微镜以及磁性测量系统研究了不同温度氧气氛下的后续退火对LSMO薄膜结构及磁学性能的影响.结果表明随着退火温度的升高,LAO和STO衬底上的LSMO薄膜氧含量逐渐增加,Mn4 /Mn3 的比值逐渐趋向于3∶7,表现为面外晶格常数逐渐减少,饱和磁化强度及居里温度都有明显提高,而矫顽力则有所降低;拉曼散射实验结果更直观的给出了退火后LSMO晶格有序性的增加和Jahn-Teller畸变的减弱;而Si单晶上的LSMO薄膜在高温下由于与衬底发生了复杂的化学反应而导致相结构发生改变.     

用激光分子束外延在玻璃衬底上生长La0.67Sr0.33MnO3薄膜

采用激光分子束外延技术,在玻璃衬底上制备了La0.67Sr0.33MnO3 (LSMO) 薄膜,X射线衍射测量结果表明在玻璃衬底上生长的LSMO薄膜沿c轴择优取向生长.在外磁场3 T和88, 220, 300 K条件下,LSMO薄膜的磁电阻变化率分别达到-37.8%, -26.8%和-6.07%.实验结果表明,在廉价的玻璃衬底上制备大面积和具有应用价值的锰氧化物薄膜是可行的.     

用激光分子束外延在玻璃衬底上生长La0.67Sr0.33MnO3薄膜

采用激光分子束外延技术,在玻璃衬底上制备了La_067Sr_033MnO₃ （LSMO） 薄膜,X射线衍射测量结果表明在玻璃衬底上生长的LSMO薄膜沿c轴择优取向生长.在外磁场3 T和88, 220, 300 K条件下,LSMO薄膜的磁电阻变化率分别达到-378%, -268%和-607%.实验结果表明,在廉价的玻璃衬底上制备大面积和具有应用价值的锰氧化物薄膜是可行的. 关键词： 锰氧化物薄膜 玻璃衬底 外延生长     

La1.3Sr1.7Mn2O7/SrTiO3-Nb异质结的整流和光伏特性

采用脉冲激光沉积法在SrTiO₃:0.7%Nb(100)单晶衬底上生长了La_1.3Sr_1.7Mn₂O₇(LSMO)薄膜, 并 研究了LSMO/SrTiO₃-Nb异质结的输运性质和光伏效应. 研究发现, 异质结具有良好的整流特征和明显的光生伏特效应. 在532 nm激光辐照下, 光生电压随温度升高先增大后减小, 并且在150 K达到最大值400 mV, 此温度点与LSMO薄膜发生金属-绝缘体转变的温度一致, 这表明异质结的光生伏特效应受LSMO薄膜内部的输运特征调控. 进一步, 从光生电压随时间的变化曲线中分析发现, 上升沿符合一阶指数函数, 这与载流子的迁移过程相关; 而下降沿符合二阶指数函数, 这与结两侧载流子的外部回路中和以及材料内部的电子-空穴湮灭有关. 值得注意的是, 上升沿和下降沿的时间常数均随着温度先增大后减小, 且最大值均出现在LSMO薄膜的金属-绝缘转变温度.     

新型电极材料Sb掺杂BaSnO_3薄膜的外延生长及其在铁电薄膜电容器中的应用

本文利用脉冲激光沉积技术在SrTiO_3单晶衬底上生长了Sb掺杂BaSnO_3(BSSO)外延薄膜.结构和输运性质测量结果显示BSSO薄膜是一种具有立方钙钛矿结构导电性很好的薄膜材料,80K时呈现金属绝缘体转变,室温下薄膜的电阻率、载流子浓度和迁移率分别为ρ=2.43 mΩcm,n=1.65×1021 cm~(-3)和μ=1.75 cm~2/Vs.以BSSO薄膜为底电极制备了具有比较好电滞回线的Pb(Zr_(0.52)Ti_(0.48))O_3和Bi(Mn_(0.05)Fe_(0.95))O_3铁电电容器,表明BSSO薄膜是一种具有应用前景的新型电极材料.     

La2/3Sr1/3MnO3/BaTiO3复合薄膜的制备及其电致磁电效应研究

使用脉冲激光沉积技术,在LaAlO₃(001)单晶基片上制备了La_2/3Sr_1/3MnO₃(LSMO)/BaTiO₃(BTO)双层薄膜.X射线衍射分析显示,LSMO层和BTO层呈现纯(001)取向.原子力显微镜研究表明,薄膜表面晶粒大小均匀,排列致密,表面均方根粗糙度为1.4 nm.复合薄膜的磁学、电学性能研究表明,其具有良好的磁学和介电性能.电输运测试显示,与在BTO层上施加正方向 关键词： 磁电效应 铁电/铁磁异质结构 脉冲激光沉积     

不同生长方向的La0.7Sr0.3MnO3薄膜结构及性能研究

利用磁控溅射方法,在(100),(110)和(111)LaAlO3(LAO)衬底上制备得到了不同生长方向的La0.7Sr0.3MnO3(LSMO)薄膜并对其结构及磁电学性能进行了系统研究.结果表明:LSMO薄膜完全按LAO衬底取向生长;(111)生长方向的薄膜由于晶格畸变程度最小,磁畴方向能较好的保持一致性,从而具有最大的磁饱和强度值;高的磁有序度减弱了巡游电子eg的自旋无序相关散射,有效降低了电阻.但外加磁场后电阻变化不明显,最大磁电阻值只有5.1%.     

La0.67Ca0.33MnO3薄膜中的各向异性应变与电荷有序

本文采用脉冲激光沉积法在NdGaO3(001)单晶衬底上制备了一系列的La0.67Ca0.33MnO3薄膜,实验主要研究了薄膜的输运性质.La0.67Ca0.33sMnO3块材是铁磁金属基态,而La0.67Ca0.33MnO3/NdGaO3(001)薄膜由于各向异性应变的存在,可以观测到电荷有序绝缘相的出现.薄膜样品表...     

沉积氧压对La0.8Sr0.2MnO3/0.7wt%Nb:SrTiO3异质结的整流伏安特性及输运性的调控

采用脉冲激光沉积法在(100)0.7wt%Nb:SrTiO3(NSTO)衬底上制备了La0.8Sr0.2MnO3(LSMO)/NSTO(100)异质结,仔细研究了原位沉积氧压和真空退火对LSMO/NSTO异质结的结构及其整流伏安特性的调控.X-射线线性扫描和原子力显微镜测量显示,低氧压制备的LSMO/NSTO(100)异质结具有良好的外延结构和平整的表面.电流-电压(I～V)曲线显示,沉积氧压为100mTorr的异质p～n结展现出极好的整流伏安特性;而氧压为240mTorr的异质p～n结平缓增加的电流可解释为异质p～n结在界面处晶格缺陷的增加.作为对比,沉积氧压调控的LSMO/SrTiO3(100)薄膜的输运性也被研究.电阻率结果显示,低氧压制备的LSMO薄膜,其电阻率的增加及金属-半导体转变温度Tp的降低归因于氧空位增加诱导的Mn4+离子减少及MnO6八面体的畸变.     

Slight Co-doping tuned magnetic and electric properties on cubic BaFeO3 single crystal

The single crystal of cubic perovskite BaFeO$_{3}$ shows multiple magnetic transitions and external stimulus sensitive magnetism. In this paper, a 5%-Co-doped BaFeO$_{3}$ (i.e. BaFe$_{0.95}$Co$_{0.05}$O$_{3})$ single crystal was grown by combining floating zone methods with high-pressure techniques. Such a slight Co doping has little effect on crystal structure, but significantly changes the magnetism from the parent antiferromagnetic ground state to a ferromagnetic one with the Curie temperature $T_{\rm C} \approx 120$ K. Compared with the parent BaFeO$_{3}$ at the induced ferromagnetic state, the saturated magnetic moment of the doped BaFe$_{0.95}$Co$_{0.05}$O$_{3}$ increases by about 10% and reaches 3.64 $\mu_{\rm B}$/f.u. Resistivity and specific heat measurements show that the ferromagnetic ordering favors metallic-like electrical transport behavior for BaFe$_{0.95}$Co$_{0.05}$O$_{3}$. The present work indicates that Co-doping is an effective method to tune the magnetic and electric properties for the cubic perovskite phase of BaFeO$_{3}$.     

Microstructures and electrical properties of La0.8Sr0.2MnO3 films synthesized by sol-gel method

La_0.8Sr_0.2MnO₃ (LSMO) thin films were fabricated on alumina substrates by an improved sol-gel dip-coating process. It was found that multiple dip-coating process could not be performed until the pre-firing temperature reached 600 °C. Different amounts of LSMO powders were added to precursor solution with an aim to avoid cracks in LSMO thin films during calcining caused by the shrinkage mismatch between the film and the substrate. The structure and surface morphology of the films prepared from precursors with and without LSMO powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the addition of 56.4 wt.% LSMO powders into the sol-gel precursor solution significantly modified the microstructure of films. A single LSMO perovskite phase was obtained on alumina substrate after calcining at 800 °C for 4 h by the improved sol-gel method. The sheet resistance of the films prepared with different processing parameters was measured by four-point dc method. Results indicated that the sheet resistance of films decreased with increasing the number of coating applications and the amount of LSMO powders.     

La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> thin films on SrTiO<Subscript>3</Subscript> and CaTiO<Subscript>3</Subscript> buffered Si substrates: structural,static, and dynamic magnetic properties

Nearly 50-nm thick La_0.7Sr_0.3MnO₃ (LSMO) films were grown on Si substrates using molecular beam epitaxy on (001) Si substrates over-layered by a 20 nm thick SrTiO₃ (STO) or by a 20 nm thick CaTiO₃ (CTO) film. In addition, a reference LSMO film was directly deposited on a (001) STO substrate by pulsed laser deposition. For all the samples, X-ray diffraction revealed an excellent epitaxy of the LSMO film and small mosaicity around (001), with in-plane [100] and [010] cubic axes. The LSMO/CTO films are in-plane compressed while the LSMO/STO ones are in-plane extended. The temperature dependence of their static magnetic properties was studied using a SQUID, showing a Curie temperature overpassing 315 K for all the samples. Hysteresis loops performed at room temperature (294 K) with the help of a vibrating sample magnetometer (VSM) are also discussed. At 294 K Micro-strip ferromagnetic resonance (MS-FMR) was used to investigate the dynamic magnetic properties. It allows concluding to a strong anisotropy perpendicular to the films and to a weak fourfold in-plane anisotropy with easy axes along the [110] and [1[`1]0 1\bar{1}0 ] directions. Their values strongly depend on the studied sample and are presumably related to the strains suffered by the films.     

Growth and electric properties of (100)-oriented Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 thin film by pulsed laser deposition

Mn-doped (Bi_0.5Na_0.5)TiO₃-BaTiO₃ (BNBMT) thin film with the composition near the morphotropic phase boundary was grown on (La_0.6Sr_0.4)CoO₃-electroded SrTiO₃ single-crystal substrate by using pulsed laser deposition method. Ascribed to the crystal structure and lattice similarity, (100)-oriented BNBMT film with pure single-phase perovskite structure was obtained through carefully controlling the growth conditions. Enhanced ferroelectric and dielectric properties were obtained with large remanent polarization P _r of ～21 μC/cm², coercive field E _c of ～7.4 kV/mm and dielectric constant $\varepsilon_{33}^{T}/\varepsilon_{0}$ of ～750 at 1 kHz. The excellent global electrical properties of the BNBMT film are promising for environmentally friendly ferroelectric devices.     

Evolution of the interfacial structure of LaAlO3 on SrTiO3

The evolution of the atomic structure of LaAlO_{3} grown on SrTiO_{3} was investigated using surface x-ray diffraction in conjunction with model-independent, phase-retrieval algorithms between two and five monolayers film thickness. A depolarizing buckling is observed between cation and oxygen positions in response to the electric field of polar LaAlO_{3}, which decreases with increasing film thickness. We explain this in terms of competition between elastic strain energy, electrostatic energy, and electronic reconstructions. Based on these structures, the threshold for formation of a two-dimensional electron system at a film thickness of 4 monolayers is quantitatively explained. The findings are also qualitatively reproduced by density-functional-theory calculations.     

Origin of ultraviolet photovoltaic effect in Fe3O4 thin films

We have investigated the transport and ultraviolet photovoltaic properties of Fe$_{3}$O$_{4}$ thin films grown on glass substrates by facing-target sputtering technique. The nonlinear dependence of current-density on voltage suggests that the transport process is most likely the tunnelling process and grain boundaries act as barriers. Furthermore, nonequilibrium electron-hole pairs are excited in the grains and grain boundary regions for Fe$_{3}$O$_{4}$ film under ultraviolet laser, since the energy gap of Fe$_{3}$O$_{4}$ is smaller than the ultraviolet photon energy. And then the built-in electric field near the grain boundaries will separate carriers, leading to the appearance of an instant photovoltage.     

Study of the elastic constants in a La0.6Sr0.4MnO3 film by means of laser-generated ultrasonic wave method

Two dimensional (2D) displacement field of the laser-generated ultrasonic wave is detected in a two-layered structure of La(0.6)Sr(0.4)MnO(3) (LSMO)/MgO system by means of the optical difference detection method. In order to obtain the elastic constants of the La(0.6)Sr(0.4)MnO(3) thin film, the displacement field of the laser-generated ultrasonic wave for the La(0.6)Sr(0.4)MnO(3)/MgO system is analyzed with finite element method (FEM). We further compare the theoretical simulations with the experimental results, and the elastic constants for the LSMO film, i.e., the Young's modulus and Poisson ratio, are obtained.     

High-Pressure Synthesis of SeCu 1− x Zn x O 3 Perovskites

The SeCu 1 m x Zn x O 3 solid solution, with a distorted perovskite-type structure, has been synthesized under high pressures and temperatures. X-ray diffraction analysis indicates that the zinc ions occupy the copper sites, a solid solution being formed. It seems that high-pressure stabilises a small cation such as Se 4+ in the A site of the perovskite structure ABO 3 although the material is better described as formed by selenite anions \rm{SeO}_{3}^{-} and Cu 2+ /Zn 2+ cations.     

Deposition mechanism of nano-structured single-layered C36 film on a diamond （100） crystal plane

The Brenner-LJ potential is adopted to describe the interaction between C36 clusters and diamond surface, and the deposition mechanism of multi-C36 clusters on the diamond surface is also studied by using the method of molecular dynamics simulation. The simulation results show that the competition effects of two interactions, i.e. the interaction between cluster and cluster and the interaction between cluster and crystal plane, are studied, and then the influence of these competition effects on C36 cluster deposition is analysed. The finding is that when an incident energy is appropriately chosen, C36 clusters can be chemically adsorbed and deposited steadily on the diamond surface in the form of single-layer, and in the deposition process the multi-C36 clusters present a phenomenon of energy transmission. The experimental result shows that at a temperature of 300K, in order to deposit C36 clusters into a steady nanostructured single-layered film, the optimal incident energy is between 10 and 18 eV, if the incident energy is larger than 18 eV, the C36 clusters will be deposited into an island nano-structured film.