Electronic Properties of Singvle-Crystal Oxide Films Fabricated on Metal Surfaces

分别在Ru（0001）和Ni（111）金属表面制备了α-Al_2O_3 9A厚和SiO_2 30a厚的高质量单晶薄膜。α-Al_2O_3由γ-相转变为α-Al_2O_3，其结构与Ru（0001）相当。在Ni（111）上形成单晶SiO_2膜的过程中，非晶SiO_2膜初始生长过程中的原子氢和薄膜退火过程中的环境氧是必不可少的。利用扫描隧道光谱（STS）初步观察到氧化层的带隙随氧化层厚度的减小而减小。这一结果被中分辨率电子能量损失谱所证实。在35 A以下，用不同氧化层厚度的α-Al_2O_3薄膜测量了氧化物厚度v对带隙的依赖性。为了在单晶氧化物（即宽禁带晶体）上生长过渡金属超薄膜，我们利用了禁带的缩小，成功地在α-Al_2O_3(9a)/Ru（0001）上制备了单原子层（ML） Pt薄膜。利用反射吸收红外光谱法测量CO吸附在Pt(1ml)/α-Al_2O_3(9a)/Ru（0001）上的C-O振动频率，研究了氧化层的电子特性。另一方面，利用同步辐射掠入射x射线衍射研究了厚度为40a的SiO_2薄膜的晶体结构。制备了厚度为30 A的β-石英单晶膜，并在界面处形成了厚度为10 A的硅化镍多晶膜。这些金属表面的单晶氧化膜是一种新型的表面材料，它将为固体物理和化学的其他领域打开一扇窗。

High-quality single-crystal films of α-Al_2O_3 9A thick and SiO_2 30 A thick have been fabricated on metal surfaces of Ru(0001) and Ni(111), respectively. α-Al_2O_3 was fabricated by a phase transition from γ- to α-Al_]2O_3 having a commensurate structure with Ru(0001). Atomic hydrogen during initial growth of an amorphous SiO_2 film and ambient oxygen atmosphere during annealing of this film were essential in forming the single-crystal SiO_2 film on Ni(111). An extraordinary result that the band gap for the oxide layer decreases with decreasing oxide thickness was preliminarily observed using scanning tunneling spectroscopy (STS). This result was confirmed by medium-resolution electron energy loss spectroscopy, in. which the oxide thickness V. dependence of the band gap was measured by α-Al_2O_3 films with various oxide thicknesses below 35 A. For growing ultra-thin films of transition metals on a single-crystal oxide, i.e. a wide band gap crystal, we have, utilized the band gap narrowing and succeeded in making a monoatomic layer (ML) of a Pt film on α-Al_2O_3(9 A)/Ru(0001). We have investigated electronic properties of the oxide layer using C-O vibrational frequencies of CO adsorbed on Pt(1 ML)/α-Al_2O_3(9 A)/Ru(0001) measured by reflection absorption infrared spectroscopy. On the other hand, the crystal structure of SiO_2 film thick 40 A was investigated by grazing incidence X-ray diffraction using syncrotron radiation. A nice single crystal film of β-quartz is fabricated with a thickness of 30 A and a polycrystalline Ni silicide film 10 A thick is formed with a mosaic structure at the interface. These single-crystal oxide films on metal surfaces are new surface materials, which will open a window against other fields of solid state physics and chemistry.