Controlled fabrication of quantum dots and nanostructures by controlling high-index surfaces of group IV semiconductors

控制在Si（001）衬底上形成的锗量子点的尺寸和形状对其应用具有重要的技术意义。表面活性剂的作用被认为是实现量子点可控生长的一种很有前途的方法。其中，目前研究较多的氢吸附效应抑制了在4个Ge{105}面上形成的“hut”结构的形成。我们利用STM和AFM方法研究了在Si（105）衬底上形成的Ge（105）表面的结构。基于实验和理论STM图像的对比，我们提出了该表面的应变结构模型，并通过原子分辨AFM图像进行了验证。利用STM研究了该体系对氢的吸附，揭示了表面应变对Ge（105）在氢吸附条件下稳定性的影响。基于新建立的Ge（105）的原子结构，理解了吸附氢原子的Ge（105）表面的STM图像。我们观察了不同Ge量的氢包覆Ge（105）表面的稳定性，发现Ge包覆量小于1.4 ML的Ge（105）表面对氢的吸附使其表面非常不稳定，导致表面粗糙化。这一事实表明，氢在Ge（105）表面的吸附是通过阻止在Ge（105）表面形成sp^2杂化二聚体的应变释放机制而增加表面应变的。因此，在吸附氢的存在下，Ge（105）的形成将受到抑制。

Controlling the size and shape of Ge quantum dots formed on the Si(001) substrate is great technological importance for their application. Surfactant effects on this system are regarded as one of promising methods to achieve the controlled growth of quantum dots. Among them, hydrogen-adsorption effect, which has been studied intensively these days, is known to suppress the formation of the "hut" structure formed upon four Ge{105} facets. We have investigated the structure of the Ge(105) surface formed on a Si(105) substrate using STM and AFM to establish the surface structure. The strained structure model for this surface, which we have proposed based on comparison between experimental and theoretical STM images, is confirmed by an atomically resolved AFM image. Hydrogen adsorption on this system has been studied using STM, to show the role of surface strain on the stability of the Ge(105) under hydrogen-adsorption condition. The STM images of the Ge(105) surfaces with adsorbed hydrogen atoms are understood based on the newly-established atomic structure of Ge(105). We observed the stability of hydrogen-covered Ge(105) surface with different amounts of Ge to find that the hydrogen adsorption on the Ge(105) surfaces with Ge coverages of less than 1.4 ML makes the surface remarkably unstable and results in the roughening of the surface. This fact indicates that the hydrogen adsorption on Ge(105) increases the surface strain by arresting the strain-relief mechanism via the formation of sp^2-hybridized dimers on the Ge(105) surface. Thus, the formation of Ge(105) will be unfavorable and suppressed under the existence of adsorbed hydrogen.