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

从科学上讲，了解应变和电子结构之间的微妙相互作用是极其重要的，这些结构使表面有许多不同的重建；从技术上讲，生长几层厚的结构现在是微电子工业所必需的，并将受到起始表面结构的影响。在这项资助中，我们将研究具有未知但重要结构的Si(110)上的复杂重建，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并为未来的结构研究提供信息。该项目将与两个使用扫描隧道显微镜(STM)的实验小组密切合作进行：一个是日本的一个团队，用于(16x2)重建；另一个是美国的一个小组，用于氢和硅的扩散。我们将建立在实验互动的强大跟踪记录基础上，并与这些小组建立联系，以告知和指导我们的建模。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，并生成模拟的STM图像以及能级数据和扩散常数，以与其他实验技术进行比较。许多正在开发的扩展硅基晶体管技术的技术涉及生长或刻蚀硅基晶体管(001)结构，例如FinFET或图案化原子层外延(ALE)。这一部分的最终目的将是模拟纳米结构OnSi(001)上拐角处的扩散，从而充分理解影响Si(110)和Si(110)面生长和过度生长的问题。Si(001)-(2x1)和Si(111)-(7x7)的重构已经通过实验和模拟相结合的方式解决了，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)还没有被正确地理解，尽管已经提出了一些关于表面特征的建议。这个结构很吸引人，由宽度相同的交替升高和降低的梯田组成，沿着相同的方向延伸，梯田上有复杂的图案；对这种结构(所有梯田在台阶边缘向上或向下)的简单改变就会导致密切相关的Si(17151)表面。这些方面都没有被理解：梯田的宽度；台阶的边缘方向；梯田上的原子结构。

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.