Si(110): (16x2) Reconstruction and Adatom Diffusion

半导体表面表现出各种各样的重建（原子位置的变化和由于表面的键合），这往往是复杂和有趣的；从科学和技术的角度来看，它们也非常重要。科学地理解应变和电子结构之间微妙的相互作用是极其重要的，这些相互作用使表面具有许多不同的重建；从技术上讲，对于微电子工业来说，几个原子层厚度的结构的增长是必要的，并且将受到初始表面结构的影响。在这项资助中，我们将研究具有未知但重要结构的Si（110）的复杂重建，并研究硅和氢原子在表面上的扩散，这将允许表面的受控生长以及为未来的结构研究提供信息。该项目将与使用扫描隧道显微镜（STM）的两个实验小组密切合作：日本的一个小组进行（16x2）重建；以及美国的氢和硅扩散小组。我们将建立在实验互动的良好记录上，并与这些群体建立联系，为我们的建模提供信息和指导。该项目将使用高度复杂的电子结构方法来模拟重建和扩散，并生成模拟STM图像以及能级数据和扩散常数，以便与其他实验技术进行比较。许多扩展硅基晶体管技术的技术都涉及在si（001）上生长或蚀刻结构，例如finfet或图像化原子层外延（ALE）。这将产生具有Si（110）侧面的Si（001）结构，而其他研究途径包括直接在Si（110）上制造晶体管，以提高其迁移率。因此，了解和控制这种表面上的生长的能力在技术上是非常重要的，它依赖于硅和氢的扩散（取决于生长源）。我们将模拟这两种原子在简单Si（110）表面上沿衬底的行和跨行扩散，然后考虑阶边。该部分的最终目标是模拟Si（001）上纳米结构的拐角扩散，从而全面了解影响Si（110）生长和过度生长的问题以及Si（110）表面结构。Si(001)-(2x1)和Si(111)-(7x7)的重构已经通过实验和建模的结合得到了解决，尽管Si（001）的某些方面仍然存在争议，并且是正在进行的低温实验的主题；然而，Si(110)-(16x2)尚未被正确理解，尽管已经提出了一些关于表面特征的建议。它的结构非常迷人，由高低交错的阶地组成，这些阶地宽度相同，方向相同，阶地上有复杂的图案；这种结构的简单变化（所有的阶地在台阶边缘向上或向下）导致密切相关的Si（17 15 1）表面。这些方面都没有被理解：阶地宽度；一步edgedirection;梯田上的原子结构。我们将使用仔细的电子结构建模，与STM和光电发射光谱（PES）实验密切合作，提出表面结构，并解释其重要特征。这将加深我们对半导体重建及其背后机制的理解，并加强英国在该领域的材料建模能力。

Semiconductor surfaces show a wide variety of reconstructions (thechange in atomic positions and bonding due to the surface) which areoften complex and intriguing; they are also enormously important bothfrom scientific and technological viewpoints. Scientifically,understanding the subtle interplay between strain and electronicstructure which give the surfaces many different reconstructions isextremely important; technologically, the growth of structures a fewatomic layers thick is now necessary for the microelectronicsindustry, and will be affected by the starting surface structure. Inthis grant, we will investigate a complex reconstruction on Si(110)with unknown but important structure and also study diffusion ofsilicon and hydrogen atoms across the surface, which will allowcontrolled growth of the surface as well as informing futurestructural studies.The project will be carried out in close collaboration with twoexperimental groups using scanning tunneling microscopy (STM): a teamin Japan for the (16x2) reconstruction; and a group in USA for thehydrogen and silicon diffusion. We will build on a strong trackrecord of experimental interaction and established links with thesegroups to inform and guide our modelling. The project will use highlysophisticated electronic structure methods to model the reconstructionand diffusion, and generate simulated STM images as well as energylevel data and diffusion constants for comparison with otherexperimental techniques.Many of the techniques being developed to extend silicon-basedtransistor technology involve growth or etching of structures onSi(001), e.g. FinFETs or patterned atomic-layer epitaxy (ALE). Thesewill yield structures on Si(001) with Si(110) sides, while otheravenues of research involve fabricating transistors directly onSi(110) for its improved mobility. An ability to understand andcontrol growth on this surface is therefore enormously importanttechnologically, and relies on diffusion of silicon and hydrogen(depending on growth source). We will model the diffusion of bothadatoms on the simple Si(110) surface, along and across the rows inthe substrate and then consider step edges. The final aim of the partwill be to model diffusion around a corner on nano-structure onSi(001), leading to a full understanding of issues affecting growthand overgrowth of Si(110) and structures with Si(110) faces.The reconstructions of Si(001)-(2x1) and Si(111)-(7x7) have alreadybeen solved by a combination of experiment and modelling, though someaspects of Si(001) remain controversial and are the subject ofon-going low temperature experiments; Si(110)-(16x2), however, has notbeen properly understood though some proposals have been made forfeatures on the surface. The structure is fascinating, consisting ofalternately raised and lowered terraces all the same width and runningin the same direction with complex patterns on the terraces; a simplechange to this structure (with all terraces either going up or down atstep edges) leads to the closely related Si(17 15 1) surface. None ofthese aspects have been understood: the terrace width; step edgedirection; the atomic structure on the terraces. We will use carefulelectronic structure modelling in close collaboration with STM andphoto-emission spectroscopy (PES) experiments to propose a surfacestructure, and explain its important features. This will deepen ourunderstanding of semiconductor reconstructions and the mechanismsbehind them, as well as strengthening the UK materials modellingcapability in this area.