Gao M, Scheu C, Tchernychova E, Rühle M
Max-Planck-Institut für Metallforschung, Heisenbergstrasse 3, 70569 Stuttgart, Germany.
J Microsc. 2003 Apr;210(Pt 1):94-101. doi: 10.1046/j.1365-2818.2003.01174.x.
The electron energy-loss near-edge structure (ELNES) of Mo/SrTiO3 interfaces has been studied using high spatial resolution electron energy-loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. Thin films of Mo with a thickness of 50 nm were grown on (001)-orientated SrTiO3 surfaces by molecular beam epitaxy at 600 degrees C. High-resolution transmission electron microscopy revealed that the interfaces were atomically abrupt with the (110)Mo plane parallel to the substrate surface. Ti-L2,3 ( approximately 460 eV), O-K ( approximately 530 eV), Sr-L2,3 ( approximately 1950 eV) and Mo-L2,3 ( approximately 2500 eV) absorption edges were acquired by using the Gatan Enfina parallel EELS system with a CCD detector. The interface-specific components of the ELNES were extracted by employing the spatial difference method. The interfacial Ti-L2,3 edge shifted to lower energy values and the splitting due to crystal field became less pronounced compared to bulk SrTiO3, which indicated that the Ti atoms at the interface were in a reduced oxidation state and that the symmetry of the TiO6 octahedra was disturbed. No interfacial Sr-L2,3 edge was observed, which may demonstrate that Sr atoms do not participate in the interfacial bonding. An evident interface-specific O-K edge was found, which differs from that of the bulk in both position (0.8 +/- 0.2 eV positive shift) and shape. In addition, a positive shift (0.9 +/- 0.3 eV) occurred for the interfacial Mo-L2,3, revealing an oxidized state of Mo at the interface. Our results indicated that at the interface SrTiO3 was terminated with TiO2. The validity of the spatial difference technique is discussed and examined by introducing subchannel drift intentionally.
利用专用扫描透射电子显微镜中的高空间分辨率电子能量损失谱（EELS）对Mo/SrTiO₃界面的电子能量损失近边结构（ELNES）进行了研究。通过分子束外延在600℃下于（001）取向的SrTiO₃表面生长了厚度为50nm的Mo薄膜。高分辨率透射电子显微镜显示，界面在原子尺度上是陡峭的，（110）Mo平面与衬底表面平行。使用带有电荷耦合器件（CCD）探测器的Gatan Enfina并行EELS系统获取了Ti-L₂,₃（约460eV）、O-K（约530eV）、Sr-L₂,₃（约1950eV）和Mo-L₂,₃（约2500eV）吸收边。通过采用空间差分法提取了ELNES的界面特定成分。与块状SrTiO₃相比，界面处的Ti-L₂,₃边向较低能量值移动，并且由于晶体场引起的分裂变得不那么明显，这表明界面处的Ti原子处于较低的氧化态，并且TiO₆八面体的对称性受到了干扰。未观察到界面处的Sr-L₂,₃边，这可能表明Sr原子不参与界面键合。发现了一个明显的界面特定O-K边，其在位置（正移0.8±0.2eV）和形状上均与块状的不同。此外，界面处的Mo-L₂,₃出现了正移（0.9±0.3eV），表明界面处的Mo处于氧化态。我们的结果表明，在界面处SrTiO₃以TiO₂终止。通过有意引入子通道漂移来讨论和检验空间差分技术的有效性。
