Exploring the structural transformation of nonhexagonal rings is of fundamental importance for understanding the thermal stability of nonhexagonal rings and revealing the structure–property relationships. Here, we report on the thermally induced transformation from the fused tetragon-hexagon (4–6) carbon rings to a pair of pentagon (5–5) rings in the graphene-like nanoribbons periodically embedded with tetragon and octagon (4–8–4) carbon rings. A distinct contrast among tetragon, pentagon, hexagon, and octagon carbon rings is provided by noncontact atomic force microscopy with atomic resolution. The thermally activated bond rotation with the dissociation of the shared carbon dimer between the 4–6 carbon rings is the key step for the 4–6 to 5–5 transformation. The energy barrier of the bond rotation, which results in the formation of an irregular octagon ring in the transition state, is calculated to be 1.13 eV. The 5–5 defects markedly change the electronic local density of states of the graphene-like nanoribbon, as observed by scanning tunneling microscopy. Our density functional theory calculations indicate that the introduction of periodically embedded 5–5 rings will significantly narrow the electronic band gap of the graphene-like nanoribbons.

中文翻译：

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石墨烯状纳米带中非六角碳环的热诱导转变

探索非六角环的结构转变对于理解非六角环的热稳定性以及揭示结构与性质的关系至关重要。在这里，我们报道了石墨烯状纳米带中周期性地嵌入了四边形和八边形（4–8–6）的石墨烯状纳米带中的热诱导转变，从熔融的四边形六边形（4–6）碳环转变为一对五边形（5–5）环。 4）碳环。通过具有原子分辨率的非接触原子力显微镜，可以看到四边形，五边形，六边形和八边形碳环之间的明显对比。通过热活化键旋转以及4-6个碳环之间共享的碳二聚体解离，是4-6到5-5转化的关键步骤。键旋转的能垒，导致在过渡态中形成不规则八边形环的计算结果为1.13 eV。通过扫描隧道显微镜观察，5-5缺陷显着改变了石墨烯状纳米带的电子局部密度。我们的密度泛函理论计算表明，周期性嵌入5-5个环的引入将显着缩小石墨烯状纳米带的电子带隙。