Graphene-like materials can be viewed as promising storage media for hydrogen as they are lightweight, durable, and scalable. For practical use, doping is required to overcome the kinetic limitations for diffusion and recombination on surfaces due to the required rehybridization of atoms. We studied the synthesis of nitrogen-doped graphene on Ru(0001) by chemical vapor deposition (CVD) of pyridine and N-doping through ion irradiation. Using the combination of scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy, and density functional theory (DFT) we unambiguously identify the structure and location of the N species within the graphene moiré. The pyridine CVD leads only to a low concentration (<0.1 at%) of N-related sites. Higher concentrations of N-dopants (>10 at%) are subsequently introduced by low-energy ion irradiation. The concentration of graphitic (GN) and pyridinic nitrogen (PN) can be tuned by varying the ion dose and annealing temperature. DFT calculations provide detailed information about the relative thermodynamic stability of GN and PN within the graphene moiré. Measured and simulated STM images of GN and PN yield an excellent agreement, allowing us to confidently establish that GN is preferentially located near the center of the Atop region of the graphene moiré, while PN is located at the boundary between the FCC and HCP region, which are defined by the registry between C and Ru atoms. This report explicitly confirms the site assignments and provides a foundation for the site synthesis and analysis of their structural and electronic properties that drive the thermodynamic stability and reactivity of N-doped graphene.

中文翻译：

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Ru 上石墨烯莫尔条纹中石墨和吡啶氮的热力学稳定性和位点特异性分布


类石墨烯材料可以被视为有前途的氢储存介质，因为它们重量轻、耐用且可扩展。在实际应用中，由于需要原子的再杂化，需要掺杂来克服表面扩散和复合的动力学限制。我们研究了通过吡啶的化学气相沉积 （CVD） 和离子照射的 N 掺杂在 Ru（0001） 上合成氮掺杂石墨烯。结合使用扫描隧道显微镜 （STM）、X 射线光电子能谱和密度泛函理论 （DFT），我们明确地确定了石墨烯莫尔条纹中 N 物种的结构和位置。吡啶 CVD 仅导致低浓度 （<0.1 at%） 的 N 相关位点。随后通过低能离子照射引入更高浓度的 N 掺杂剂 （>10 at%）。石墨 （GN） 和吡啶氮 （PN） 的浓度可以通过改变离子剂量和退火温度来调节。DFT 计算提供了有关石墨烯莫尔条纹中 GN 和 PN 的相对热力学稳定性的详细信息。GN 和 PN 的测量和模拟 STM 图像产生了极好的一致性，使我们能够自信地确定 GN 优先位于石墨烯莫尔条纹 Atop 区域的中心附近，而 PN 位于 FCC 和 HCP 区域之间的边界，这由 C 和 Ru 原子之间的注册定义。本报告明确确认了位点分配，并为位点合成和分析其结构和电子特性提供了基础，这些特性驱动 N 掺杂石墨烯的热力学稳定性和反应性。