诱导纳晶石墨烯生长的电子能量分布与碳基团密度在线诊断研究

Research and development of sensors based on the excellent photo-electromagnetic characteristics of nanocrystalline graphene have attracted enormous attentions in recent years. As an important means of controllable preparation of nanocrystalline graphene, plasma electron irradiation becomes the focus of academic research. However, due to the lack of online diagnostic of irradiation electron energy distribution in the graphene growth process, size and content control of nanocrystalline graphene is difficult to achieve, hindering the development of new generation of nanocrystalline graphene sensors. Therefore, this project proposed a core scientific problem of "Electron-irradiation-induced nanocrystalline graphene growth mechanism", will use online plasma diagnostics techniques as the research method, take electrons’ heating effect on carbon atoms and damage effect on covalent bonds as the theoretical fundamental, aim at the size and content control of nanocrystalline graphene by electron energy distribution, and eventually achieve controllable manufacturing of nanocrystalline graphene. In particular, a retarding field energy analyzer and a Langmuir probe will be used to measure electron energy distribution, high resolution transmission electron microscopy combined with Raman spectroscopy will be utilized to analyze rules of size and content control of nanocrystalline graphene, the energy transfer mechanism between electrons and carbon atoms will be verified by external laser beam and electron beam irradiation. The research outcome is of scientific significance for revealing the electron-irradiation-induced nanocrystalline graphene growth mechanism, and of great practical value for the design and manufacturing of nanocrystalline graphene sensors.

近年来，基于纳晶石墨烯优异光电磁特性的传感器研发得到了业界极大关注。等离子体电子照射作为一种可控制备纳晶石墨烯的重要手段而成为学界研究焦点。然而，由于缺乏石墨烯生长过程中照射电子能量分布的在线诊断研究，难以实现纳晶石墨烯尺度和含量调控，阻碍了新一代纳晶石墨烯传感器的发展。为此，本项目提出“电子照射诱导纳晶石墨烯生长机制”这一核心科学问题，以等离子体在线诊断技术为研究手段，以电子对碳原子的加热效应和对共价键的破坏效应为理论分析基础，以电子能量分布调控纳晶石墨烯尺度和含量为研究目标，最终实现纳晶石墨烯可控制造。具体而言，通过能量分析器和朗缪尔探针在线测量电子能量分布；结合高分辨透射电子显微镜与拉曼光谱分析纳晶石墨烯尺度和含量调控规律；利用外加激光束与电子束照射验证电子与碳原子的能量转移机理。研究成果对揭示电子照射诱导纳晶石墨烯生长机制具有科学意义，对纳晶石墨烯传感器设计制造具有重要实用价值。

本项目利用实验与理论方法研究了用于等离子体电子照射沉积纳晶石墨烯薄膜过程中的电子能量分布和碳基团成分，研究了直流电流对碳薄膜的摩擦学特性的影响，开发了一种快速在线诊断多射频电容耦合等离子体带电粒子能量分布的半解析迭代模型，并且研究了纳晶石墨烯碳薄膜的光电特性。.主要结论包括：.1．微波电子回旋共振等离子体电子照射沉积纳晶石墨烯薄膜过程中，薄膜内石墨烯纳晶的尺寸和含量随着照射电子的能量和通量增加。电荷在偏置的石墨烯纳晶边缘累积使得边缘形成一个局域强电场。局域电场吸引更多的电子，诱导石墨烯晶体的进一步生长，导致更强烈的电荷累积和电场增强。这种“滚雪球”效应导致电子强烈地激发表面碳碳共价键使其自发弛豫到sp2杂化态。沉积过程中，碳原子是主要的碳基团成分。.2．通直流电流时，碳薄膜内部的电子在电场驱动下碰撞激发碳原子诱导薄膜内部产生类似等离子体电子照射产生的石墨烯纳晶，最终降低了薄膜的摩擦系数。.3．多射频电容耦合等离子体中由于低频功率的存在，传统的高频鞘层假设和解析模型不成立。本项目提出的半解析迭代方式可以准确快速地获得多射频电容耦合等离子体鞘层内的带电粒子密度和能量，大大缩短了计算时间，实现了在线分析诊断。.4. 纳晶石墨烯薄膜中小尺寸、高含量的石墨烯晶体有利于形成晶体边缘电子捕获中心，从而提高异质结的光电特性。