Fe3O4/MgO(100)薄膜外场诱导电阻变化特性

采用激光分子束外延（L-MBE）方法,以MgO(100)为基底生长了Fe3O4单晶薄膜, 研究了Fe3O4/MgO(100)薄膜外场（温度、磁和激光场）诱导电阻变化特性。X射线衍射(XRD)分析表明Fe3O4薄膜是沿MgO(200)晶面外延生长的单晶薄膜;反射高能电子衍射（RHEED）强度振荡曲线分析表明Fe3O4薄膜表面平整,而且生长模式为2维层状生长;原子力显微镜（AFM）分析表明Fe3O4薄膜表面粗糙度为0.201 nm,说明薄膜表面达到原子级平整度。外场作用下Fe3O4薄膜的电阻测试表明：薄膜样品的电阻在120 K(Verwey转变温度)出现一峰值,略微下降后继续增大, 展现出半导体型的导电特性; 在激光作用下,整个测量温度范围内薄膜样品的电阻减小,样品展示出瞬间光电导的特性;从降温曲线可以看出, Verwey转变温度由无激光作用时的120 K上升到有激光作用时的140 K; 光致电阻变化率随着温度的降低而增大,这主要是由于激光作用导致电荷有序态的退局域化。     

Fe3O4薄膜的电输运及光诱导特性研究

用脉冲激光沉积法在(111)Si衬底上成功制备了高度择优取向的Fe₃O₄薄膜.电阻-温度关系表明Fe₃O₄薄膜的Verwey转变(T_V)约在122 K,低温段(T_V)输运特征满足Mott变程跳跃模型,高温段(T>T_V)为小极化子输运.激光作用下的光电导实验发现,在整个温区表现为光致电阻率减小,而且低温段的电阻变化率比高温段要大很多.分析认为Fe₃O₄薄膜的光致电阻率变化主要与激光激发t_2g电子的转移有关. 关键词： 3O₄薄膜')" href="#">Fe₃O₄薄膜 小极化子 光诱导特性     

Fe3O4磁性纳米颗粒的催化性能研究进展

综述了国内外这一领域科研工作者的研究成果,以紫外光谱（UV）和电化学传感器为主要手段阐述了Fe₃O₄MNPs对H₂O₂的催化作用并对Fe₃O₄MNPs利用其催化性质在H₂O₂的检测领域的进一步发展和应用进行了展望。     

Fe3O4/MgO(100)薄膜的激光分子束外延与磁电学性能

 采用激光分子束外延方法,以烧结α-Fe₂O₃/为靶材,在MgO（100）基底上制备了Fe₃O₄薄膜。通过反射高能电子衍射原位观察了薄膜生长前后的表面结构,结果表明所生长的Fe₃O₄薄膜表面平整。经显微激光拉曼光谱和X光电子能谱分析证实所得薄膜表面成分为纯相Fe₃O₄。磁电学性能采用多功能物性系统测量,结果表明：当温度降至100 K附近时,薄膜电阻率有较大增加,Verwey相转变的范围变宽而且不明显,说明反向晶粒边界的存在;在7 160 kA·m^-1的磁场下,室温磁电阻达到-6.9%,在80和150 K温度下磁电阻分别达到-10.5%和-16.1%;薄膜的室温饱和磁化强度约为260 kA·m^-1,其矫顽磁场约为202 kA·m^-1。     

Fe3O4纳米粒子对P3HT:PCBM电池的影响

为了提高太阳能电池的性能,研究磁性纳米粒子在外加磁场的作用下对聚合物太阳能电池有源层P3HT:PCBM成膜及太阳能电池性能的影响。本文采用热分解法制备了磁性Fe₃O₄纳米粒子,将不同质量分数的Fe₃O₄纳米粒子掺入到P3HT:PCBM溶液中,旋涂后在外加磁场的作用下自组成膜。通过TEM、XRD对制备的Fe₃O₄纳米粒子进行表征,并利用偏光显微镜、原子力显微镜对成膜质量进行探究。结果表明,采用热分解法制备的Fe₃O₄纳米粒子直径在10 nm左右,在外加磁场作用下,Fe₃O₄纳米粒子对成膜有一定的调控作用。当Fe₃O₄纳米粒子掺杂质量分数为1%时,太阳能电池器件的开路电压增加3.77%,短路电流增加24.93%,光电转换效率提高7.82%。     

海藻酸改性的空心Fe3O4纳米颗粒的制备与应用

不使用任何模板一步制得空心Fe₃O₄纳米颗粒,然后将海藻酸钠嫁接在氨基化的空心Fe₃O₄表面,再利用海藻酸盐与钙离子的作用,在空心Fe₃O₄表面形成一个凝胶化层,制得海藻酸盐凝胶化的空心Fe₃O₄纳米颗粒,粒径约为400～500 nm．采用TEM、XRD、XPS、VSM等手段对纳米微球进行表征．VSM表征结果表明在室温下样品磁性材料为超顺磁性．改性Fe₃O₄纳米颗粒成功地用于柔红霉素的载负和缓释,最大载负率和载药量分别为28.4%和14.2%．缓释结果表明,海藻酸盐凝胶化层的存在,能更有效控制柔红霉素缓慢地释放．     

纳米Fe3 O4 颗粒的正电子湮没谱学研究

测量了磁性纳米Fe₃O₄颗粒的X射线衍射谱(XRD)、正电子湮没寿命谱(PALS)和符合多普勒展宽谱(CDBS),研究了不同压力和退火温度对磁性纳米Fe₃O₄颗粒物相、电子结构、缺陷及电子动量分布等的影响. XRD,PALS,CDBS测量结果表明:纳米Fe₃O₄颗粒的缺陷浓度随压力的增加而增大,但物相和缺陷类型并未发生变化;磁性纳米Fe₃O_{4< 关键词： 正电子 3}O₄')" href="#">Fe₃O₄ 寿命谱 多普勒展宽谱     

多孔SiO2包裹磁性纳米颗粒Fe3O4的制备与表征

采用加热分解油酸铁法制备了Fe₃O₄磁性纳米颗粒,并用有机模板和反相微乳液相结合的方法将磁性纳米颗粒包裹在多孔二氧化硅中.用红外光谱(FTIR)研究了不同的处理方式对油酸铁表面官能团的影响及油酸的反应浓度和加热分解油酸铁的过程中升温速率对Fe₃O₄纳米颗粒的影响.结果表明,用乙醇和丙酮处理后的固态蜡状油酸铁表面的油酸基团会受到损害,将不利于加热分解时形成单分散性的Fe₃O₄纳 关键词： 3O₄纳米颗粒')" href="#">Fe₃O₄纳米颗粒 2包裹')" href="#">多孔SiO₂包裹 反相微乳液法 油酸铁     

Si基Bi4Ti3O12铁电薄膜的制备与特性研究

采用sol-gel工艺, 在分层快速退火的工艺条件下成功地制备了高质量Si基Bi_{4Ti3O12铁电薄膜. 研究了Si基Bi4Ti3O12薄膜的生长行为、铁电性能、C-V特性和疲劳特性. 研究表明: Si基Bi4Ti3O12薄膜具有随退火温度升高沿c轴择优生长的趋势; 退火温度通过影响薄膜的晶粒尺寸、生长取向和薄膜中载流子的浓度来改变Si基Bi关键词： sol-gel法 铁电薄膜 4Ti3O12')" href="#">Bi4Ti3O12 C-V特性}     

SrBi2Ta2O9/Bi4Ti3O12复合铁电薄膜的制备与特性研究

采用溶胶凝胶工艺在p-Si衬底上制备了SrBi₂Ta₂O₉/Bi₄Ti₃O₁₂复合铁电薄膜. 研究了SrBi₂Ta₂O₉/Bi₄Ti₃O₁₂复合薄膜的微观结构与生长行为、铁电性能和疲劳特性. 研究表明: Si衬底Bi₄Ti< 关键词： 2Ta₂O₉')" href="#">SrBi₂Ta₂O₉ 4Ti₃O₁₂')" href="#">Bi₄Ti₃O₁₂ 复合铁电薄膜 溶胶凝胶工艺     

Growth, morphology, and crystalline structure of ultrathin Fe films on Cu3Au(100)

The growth mode, morphology, and crystalline structure of Fe films on Cu₃Au(100) are studied for different growth temperatures (300 and 160 K), using in situ scanning tunneling microscopy and low energy electron diffraction. Multilayer growth is found to be predominant for both growth temperatures. Only in films of 3–4 monolayers (ML) grown at 300 K is a mixed mode of layer-by-layer growth and island growth observed. An fcc-to-bcc structural transformation, accompanied by a distinct change in the surface topography, starts at about 3.5 ML and 5.5 ML for the growth temperatures of 300 and 160 K, respectively. For both growth temperatures bcc-like Fe in Fe/Cu₃Au(100) assumes, most likely through a Bain path, a surface plane with the (100) rather than the (110) orientation found in the Fe/Cu(100) system. Both the surface morphology and the onset thickness of the fcc–bcc structural transformation are shown to be strongly affected by the growth temperature.     

Magnetic anisotropy manipulation and interfacial coupling in Sm3Fe5O12 films and CoFe/Sm3Fe5O12 heterostructures

The magnetic anisotropy manipulation in the Sm₃Fe₅O₁₂ (SmIG) films and its effect on the interfacial spin coupling in the CoFe/SmIG heterostructures were studied carefully. By switching the orientation of the Gd₃Ga₅O₁₂ substrates from (111) to (001), the magnetic anisotropy of obtained SmIG films shifts from in-plane to out-of-plane. Similar results can also be obtained in the films on Gd₃Sc₂Ga₃O₁₂ substrates, which identifies the universality of such orientation-induced magnetic anisotropy switching. Additionally, the interfacial spin coupling and magnetic anisotropy switching effect on the spin wave in CoFe/SmIG magnetic heterojunctions have also been explored by utilizing the time-resolved magneto-optical Kerr effect technique. It is intriguing to find that both the frequency and effective damping factor of spin precession in CoFe/SmIG heterojunctions can be manipulated by the magnetic anisotropy switching of SmIG films. These findings not only provide a route for the perpendicular magnetic anisotropy acquisition but also give a further path for spin manipulation in magnetic films and heterojunctions.     

SO2-4/Fe2O3-Al2O3纳米固体酸的红外光谱研究

用IR光谱研究了SO4^2-/Fe2O3-Al2O3纳米固体酸在不同焙烧温度下表面结构与酸性的变化，结果表明，当焙烧温度在450－500℃时，双齿螯合配位结构特征谱带齐全，酸性强，小于450℃时，双齿螯合配位特征谱带不齐全，酸性不强，而大于500℃时，随着温度的升高，特性谱带区域宽化，特征峰消失，酸性变弱。此外，从Fe-O纳米颗粒的特征振动带显示可得知，样品的粒径小于30nm。     

Verwey相变处Fe3O4的结构、磁性和电输运特性

作为典型的金属–绝缘体转变,Fe3O4的Verwey相变蕴涵的丰富物理现象与微观机制,因而受到了人们的广泛关注.在Verwey相变处,Fe3O4的晶体结构、电子结构以及磁各向异性等均发生转变,但其磁基态并未发生改变.与其他强关联体系相比,Fe3O4的Verwey相变不需要考虑磁交换耦合作用的变化,有利于揭示强关联体系中金属–绝缘体转变的物理本质.本文从晶体结构、电荷有序、电输运特性、磁性和铁电特性等方面简要地介绍了Fe3O4的Verwey相变的研究历史和现状.     

Effect of thickness on the microstructure of GaN films on Al2O3 (0001) by laser molecular beam epitaxy

Heteroepitaxial GaN films are grown on sapphire (0001) substrates using laser molecular beam epitaxy. The growth processes are in-situ monitored by reflection high energy electron diffraction. It is revealed that the growth mode of GaN transformed from three-dimensional (3D) island mode to two-dimensional (2D) layer-by-layer mode with the increase of thickness. This paper investigates the interfacial strain relaxation of GaN films by analysing their diffraction patterns. Calculation shows that the strain is completely relaxed when the thickness reaches 15 nm. The surface morphology evolution indicates that island merging and reduction of the island-edge barrier provide an effective way to make GaN films follow a 2D layer-by-layer growth mode. The 110-nm GaN films with a 2D growth mode have smooth regular hexagonal shapes. The X-ray diffraction indicates that thickness has a significant effect on the crystallized quality of GaN thin films.     

Magnetization reversal asymmetry in Fe/MgO(0 0 1) thin films

We study the in-plane magnetization process in 200 Å Fe(0 0 1) thin films grown by sputtering at normal incidence. In spite of this growth geometry, a small uniaxial in plane magnetic anisotropy, whose origin is not totally understood, is found superimposed to the expected cubic biaxial one. This has a dramatic effect both on the reversal process and the domain structure. A combined longitudinal and transversal Kerr study shows the different switching processes (180° walls along the main easy axis versus 90° along the secondary easy axis) depending on the relative orientation of the magnetic field with respect to the Fe crystallographic axes. Remarkably, this two- and sometimes three-step switching process appears only when the field is applied along certain crystallographic directions. These findings are corroborated by domain observations.     

Design of a novel correlative reflection electron microscope for in-situ real-time chemical analysis

A novel instrument that integrates reflection high energy electron diffraction (RHEED), electron energy loss spectroscopy (EELS), and imaging is designed and simulated. Since it can correlate the structural, elemental, and spatial information of the same surface region via the simultaneously acquired patterns of RHEED, EELS, and energy-filtered electron microscopy, it is named correlative reflection electron microscopy (c-REM). Our simulation demonstrates that the spatial resolution of this c-REM is lower than 50 nm, which meets the requirements for in-situ monitoring the structural and chemical evolution of surface in advanced material.     

Synthesis of ZnAl2O4/α-Al2O3 complex substrates and growth of GaN films

With the solid phase reaction between pulsed-laser-deposited (PLD) ZnOfilm and α-Al2O3 substrate, ZnAl2O4/α-Al2O3 complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl2O4 changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding scanning electron microscope (SEM)images indicate that the surface morphology of ZnAl2O4 transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRDspectra present that ZnAl2O4 prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl2O4/α-Al2O3 substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD). XRD spectra indicate that GaN film on this kind of complex substrate changes from c-axis single crystal to poly-crystal as ZnAl2O4 layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results indicate that islands on thin ZnAl2O4 layer can promote nucleation at initial stage of GaN growth, which leadsto the (0001)-oriented GaN film.