The chemistry of carbon surfaces has regained traction in recent years in view of its applicability towards covalent modification of a variety of (2D) materials. A general requisite is the formation of a dense and well-defined monolayer of aryl groups covalently bound to the surface. Given the use of reactive chemistries however, it is often not easy to achieve precise control over the monolayer growth while maintaining high grafting densities. Here we present a straightforward experimental protocol for the fabrication of well-defined covalent monolayers onto the surface of graphite. Using a combination of surface analytical tools, we demonstrate that the ascorbic acid mediated dediazoniation of aryldiazonium salts leads to self-limiting growth of monolayers with high grafting densities. The aryl radicals preferentially attach to the basal plane of the substrate and once the surface is covered with a covalent monolayer, the surface reaction does not proceed further to an appreciable extent. The layer thickness of the covalent films was measured using atomic force microscopy whereas the grafting efficiencies were assessed using Raman spectroscopy. The chemical composition of the grafted films was studied using X-ray photoelectron spectroscopy whereas scanning tunneling microscopy provided nanometer scale insight into the structure of the covalent films. Mechanistic aspects of the process are also discussed. The self-terminating chemistry described here is a new addition to the synthetic armory for covalent modification of materials and sets a strong foundation for achieving precise nanoscale control over the covalent functionalization process.

中文翻译：

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碳表面的自限共价修饰：重氮化学反应。

鉴于碳表面对多种（2D）材料进行共价改性的适用性，近年来碳表面化学已重新受到关注。一般要求是形成共价键合到表面上的致密且定义明确的芳基单层。然而，考虑到使用反应性化学物质，在保持高接枝密度的同时，要实现对单层生长的精确控制通常并不容易。在这里，我们为石墨表面上定义明确的共价单层的制造提供了一个简单的实验方案。使用表面分析工具的组合，我们证明了抗坏血酸介导的芳基重氮盐的去重氮化作用导致具有高接枝密度的单分子层的自限性生长。芳基自由基优先附着在基材的基面上，一旦表面被共价单层覆盖，表面反应就不会进一步进行到可观的程度。使用原子力显微镜测量共价膜的层厚度，而使用拉曼光谱法评估接枝效率。使用X射线光电子能谱研究了接枝膜的化学组成，而扫描隧道显微镜则提供了对共价膜结构的纳米级洞察力。还讨论了过程的机械方面。