Exploration of new spintronics materials by vapor phase epitaxy approach

(1) Co掺杂TiO_2薄膜的微观结构分析和磁圆二色性研究采用Co k -壳层x射线吸收近边结构（XANES）和扩展x射线吸收精细结构（EXAFS）研究了Co在锐钛矿Co_xTi_<1-x>O_2薄膜中的局部结构和电子态。常观察到两种Co在+2形式氧化态和金属小团簇。磁性圆二色性（MCD）研究表明，TiO_2基体材料的铁磁性与电子能带结构之间存在显著的相关性。此外，通过同步辐射XMCD实验，Co: TiO_2钛矿膜的铁磁性来源于Co^<2+>态，而非金属Co。(2)Co掺杂金红石薄膜在超光滑TiO_2单晶衬底上的低温生长。在超光滑衬底上，TiO_2的均匀外延生长在300℃时仍能继续进行，远低于传统阶梯状蓝宝石衬底上TiO_2的生长。低温生长可以生长出无杂质相的高质量共掺杂TiO_2薄膜。x射线光电子能谱和x射线吸收精细结构表明，掺杂的Co在薄膜中以2+价态取代了Ti位。然而，由于薄膜的高度绝缘性质，在4K以下没有检测到铁磁性。(3)在高绝缘Co: TiO_2薄膜中注入载流子首先制备了基于Co: TiO_2皱褶有源沟道的场效应晶体管（FET）。顶栅晶体管具有非晶结构。在a.1102（110）超光滑衬底上生长的Co: TiO_2薄膜上制备了LaA103绝缘子。然而，薄膜的高漏电流特性阻碍了TFT器件的适当性能。然后，在绝缘和导电TiO_2交替生长的过程中，调制氧分压PO_2。人工晶格中的铁磁性通过减少PO_2来提高TiO_2的生长。Co: TiO_2/Nb: TiO_2界面的同步辐射XPS实验证明，这种铁磁性增强可能是由于载流子从导电层1102注入到绝缘层Co: TiO_2。(4)高c轴取向Ru(Eu1.5Ce0.5)Sr2Cu2O10_d薄膜的通量辅助反应固相外延研究采用一种新的生长技术——紫外辅助反应固相外延技术在SrTiO3（001）衬底上生长出了高c轴取向的Ru(Eu1.5Ce0.5)Sr2Cu2O10_d （Ru-1222）薄膜。lms外延生长为（100）Ru-1222//(100)SrTiO3，具有良好的结晶度和原子结构。磁化数据与大量Ru-1222样品的磁化数据一致。lms被认为是grant超导的。虽然在低于5 K的温度下没有获得零电阻，但在铁磁阶内约25 K时观察到超导转变的开始。(5)用于固态材料完全三相图的组合阴影掩模的设计设计了一种用于组合合成三元成分扩散库的新型掩模，该掩模允许将这些库通过一系列简单的掩模沉积在可旋转的底座上。这消除了使用加热基板的复杂驱动。在我们的配置中，这种设计通过在衬底上的三角形区域几乎线性地从0到100%改变每个组成部分的生长速率来产生标准的线性相图。薄膜生长发生在一系列循环中，在这些循环中，通过掩膜运动、靶交换和激光脉冲的同步，材料的一个分子层沉积在整个扩散区域

(1)Micro-structural analyses and Magnetic circular dichroism study of Co doped TiO_2 thin filmsThe local structure and electronic state of Co in anatase Co_xTi_<1-x>O_2 films were investigated by Co K-shell x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). There are often observed two kinds of Co in +2 formal oxidation state and metallic small clustering. A significant correlation between the observed ferromagnetism and the electronic band structure of TiO_2 host material was suggested by magnetic circular dichroism (MCD) study. Furthermore, synchrotron-radiation XMCD experiment for Co : TiO_2 anatase film concluded that the origin of the ferromagnetism was from Co^<2+> state but not from metallic Co.(2)Low temperature growth of Co-doped rutile thin film on the ultra-smooth TiO_2 single crystal substrateAn ultra-smooth TiO_2 single crystal substrate was developed to exhibit a step and terrace structure. On the ultra-smooth substrate, the … More homo-epitaxial growth of TiO_2 was found to proceed even at 300℃, relatively much lower than that for the TiO_2 growth on a conventionally used stepped □-sapphire substrate. The low temperature growth enabled to grow a high-quality Co-doped TiO_2 film with no impurity phase. X-ray photoelectron spectroscopy and x-ray absorption fine structure revealed that the doped Co in the films took 'a valence state of 2+ and substituted for Ti site. However, the ferromagnetism was not detected down to 4K, owing to the highly insulating nature of the films.(3)Carrier injection into highly insulating Co : TiO_2 filmsAt first, field-effect transistor (FET) was fabricated based on a Co : TiO_2 ruffle active channel. Top-gate transistor structure with amorphous. LaA103 insulator was fabricated on the Co : TiO_2 film grown on a.1102(110) ultra-smooth substrate. However, the high-leakage current property in the film prevented the appropriate performance of the TFT device. Next, during the alternate growth of insulating Co : TiO_2 and conductive TiO_2, an oxygen partial pressure PO_2 was modulated. The ferromagnetism in the artificial lattice was found to increase by decreasing the PO_2 for the growth of TiO_2. This enhancement of the ferromagnetism might be due to carrier injection from the conductive 1102 layer to the insulating Co : TiO_2 layer, as was evidenced by synchrotron-radiation XPS experiments of the Co : TiO_2/Nb : TiO_2 interface.(4)Flux-assisted reactive solid phase epitaxy of highly c-axis oriented Ru(Eu1.5Ce0.5)Sr2Cu2O10_d thin filmsHighly c-axis oriented epitaxial Ru(Eu1.5Ce0.5)Sr2Cu2O10_d (Ru-1222) thin lms were grown on SrTiO3 (001) substrates by a novel growth technique,ux-assisted reactive solid phase epitaxy. The lms grew epitaxially as (100)Ru-1222//(100)SrTiO3 with excellent crystallinity and atomically at terraces and steps. The magnetization dala are consistent with that reported for bulk Ru-1222 samples. The lms are suggested to be grantlar superconducting. Although zero resistance was not obtained at temperatures down to 5 K, the onset of superconducting transition was observed at about 25 K within the ferromagnetic order.(5)Design of Combinatorial Shadow Masks for Complete Ternary-Phase Diagramming of Solid State MaterialsA novel mask was designed for the combinatorial synthesis of a ternary composition spreads library, which allows such libraries to be deposited through a series of simple masks on a rotatable mount. This eliminates the use of complicated actuation of a heated substrate. In our configuration, this design leads to a standard linear phase diagram by varying the growth rate of each constituent nearly linearly from 0 to 100% at a triangular area on the substrate. Film growth occurs as a series of cycles in which one molecular layer of the material is deposited over the entire area of the spread by a synchronization of the mask movement, target exchange, and laser pulses: Less