Adatoms and defects in graphene

石墨烯是一种由碳原子排列成六边形晶格的二维原子晶体。自2004年首次对这种材料进行实验观察以来，它一直以其不同寻常的电子、结构、化学、光学、机械和其他特性而令人惊叹。石墨烯令人兴奋的主要原因有三个：(i)它是我们已知的第一个二维原子晶体，因此它将被用来回答诸如二维稳定性、晶体缺陷、裂纹扩展等基本问题；（ii）这种材料的电子结构非常不寻常，石墨烯中的准粒子服从线性色散关系，从而允许在台式装置中进入量子电动力学的微妙场；（iii）石墨烯的特殊性质使其具有广泛的应用，从超高速高频晶体管和高效光传感器到复合材料和电子显微镜研究中生物分子的支持。最近，来自曼彻斯特的研究人员开创了一个新的研究方向——可以使用石墨烯作为骨架，脚手架来合成具有预定义属性的新型二维晶体。从某种意义上说，石墨烯是一种独特的材料，它有两个表面，没有体积，因此石墨烯表面的任何化学或结构变化都会极大地改变其性能。第一个例子是2009年由曼彻斯特小组尝试的石墨烯——一种每个碳原子上都附着一个氢原子的材料——与石墨烯不同，它是一种具有显著带隙的绝缘体。在本提案中，我们将尝试扩展这一想法，并致力于合成其他具有预定义电子和结构特性的二维材料。为此，我们将研究各种ad-原子的吸附，它们的相互作用，迁移，再分配，以及它们引入石墨烯结构和电子特性的变化。特别令人感兴趣的是在某些临界浓度的ad原子下形成各种自组装结构。例如，已经证明氢可以在石墨烯表面形成周期链，这可能是在原子水平上构造石墨烯的新方法。我们将研究当不同浓度的ad-原子在不同温度下沉积在石墨烯晶体的一侧或两侧时，这种结构是如何形成的。进一步的问题是：我们能否将元素（例如，B）替代地合并到工程频带结构中？接触生长或外延生长产生的杂质在石墨烯上的位置，它们的影响是什么？另一个令人兴奋的研究方向是操纵二维晶体中的缺陷。研究石墨烯中各种缺陷的形成、相互作用和湮灭是非常令人兴奋的。TEM原则上可以允许由于敲除损伤而形成缺陷，此外，在具有非常小的电子探针（1埃数量级）的STEM中，这开辟了缺陷工程的令人兴奋的主题，通过创建可以用杂质原子装饰的缺陷的特定排列，并将转化为这种晶体的新颖电子和结构特性。必须强调的是，如果没有SuperSTEM，则无法监测所建议程序的成功，SuperSTEM由于其亚+图像分辨率和类似的光谱分辨率，结合低至60 keV的操作，提供了单原子灵敏度成像和光谱评估石墨烯原子结构的手段，即能够监测单个原子的位置，性质和键合。在曼彻斯特，我们最近证明了在石墨烯上实现亚纳米分辨率的单原子光谱是可能的；现在我们有机会将其应用于基于石墨烯的一系列令人兴奋的新结构。

Graphene is a two dimensional atomic crystal which consists of carbon atoms arranged in a hexagonal lattice. Since the first experimental observation of this material in 2004 it continues to amaze with its unusual electronic, structural, chemical, optical, mechanical and other properties. There are three major reasons for excitement with graphene: (i) it is the first two-dimensional atomic crystal known to us, so it will be used to answer such fundamental questions as stability in two-dimensions, defects in such crystals, crack propagation, etc; (ii) the electronic structure of this material is very unusual, with quasi-particles in graphene obeying linear dispersion relation, thus allowing an access to the subtle field of quantum electrodynamics in a bench-top set-up; (iii) graphene's peculiar properties make it favorable for a number applications, ranging from ultra-fast high frequency transistors and high-efficiency photosensors to composite materials and supports for biomolecules in electron microscopy research.Recently, a new direction of study has been pioneered by researchers from Manchester - one could use graphene as a back-bone, scaffolding to synthesize novel two-dimensional crystals with predefined properties. Graphene is a unique material in a sense that it has two surfaces and no bulk, thus any chemistry or structural changes on graphene's surface would change its properties dramatically. The first example, attempted in 2009 by the Manchester group, was graphane - a material in which one hydrogen atom is attached to each of the carbons - which, in contrast to graphene, is an insulator with a significant band-gap.In this proposal we will try to extend this idea and work towards synthesis of other two-dimensional materials with predefined electronic and structural properties. To this end we will study adsorption of various ad-atoms, their interaction, migration, redistribution, changes they introduce into structural and electronic properties of graphene. Of particular interest is the formation of various self-assembled structures at some critical concentrations of ad-atoms. For instance, it has been demonstrated that hydrogen can form periodic chains on the graphene surface, which might be a new way for structuring graphene on an atomic level. We will study how such structures will form when different concentration of ad-atoms are deposited at different temperatures either only from one or from both sides of graphene crystal. Further issues are: Can we incorporate elements (e.g., B) substitutionally, to engineer bandstructure? Where do impurities resulting from contacting or epitaxial growth reside on graphene, and what is their influence?Another exciting direction of research is to manipulate defects in two-dimensional crystals. It is particular exciting to study the formation, interaction and annihilation of various types of defects in graphene. A TEM in principal can allow formation of defects due to knock-out damage, moreover, in a STEM with a very small electron probe (of the order of 1 Angstrom) this opens up the exciting topic of defect engineering by creation of specific arrangements of defects which can be decorated with impurity atoms, and will be translated into novel electronic and structural properties of such crystals. It has to be emphasised that the success of the suggested procedures could not be monitored if it were not for the SuperSTEM, which, owing to its sub-+ image resolution and a similar spectroscopic resolution, combined with operation down to 60 keV, provides the means to image and spectroscopically assess graphene atomic landscapes with single-atom sensitivity, i.e., enables to monitor position, nature and bonding of individual atoms. At Manchester we have recently proven that single-atom spectroscopy with sub nm resolution on graphene is possible; now we have the opportunity to apply this to a host of exciting novel structures based on graphene.