All-carbon materials based on sp²-hybridized atoms, such as fullerenes¹, carbon nanotubes² and graphene³, have been much explored due to their remarkable physicochemical properties and potential for applications. Another unusual all-carbon allotrope family are the cyclo[n]carbons (C_n) consisting of two-coordinated sp-hybridized atoms. They have been studied in the gas phase since the twentieth century^4,5,6, but their high reactivity has meant that condensed-phase synthesis and real-space characterization have been challenging, leaving their exact molecular structure open to debate^7,8,9,10,11. Only in 2019 was an isolated C₁₈ generated on a surface and its polyynic structure revealed by bond-resolved atomic force microscopy^12,13, followed by a recent report¹⁴ on C₁₆. The C₁₈ work trigged theoretical studies clarifying the structure of cyclo[n]carbons up to C₁₀₀ (refs. ^{15,16,17,18,19,20}), although the synthesis and characterization of smaller C_n allotropes remains difficult. Here we modify the earlier on-surface synthesis approach to produce cyclo[10]carbon (C₁₀) and cyclo[14]carbon (C₁₄) via tip-induced dehalogenation and retro-Bergman ring opening of fully chlorinated naphthalene (C₁₀Cl₈) and anthracene (C₁₄Cl₁₀) molecules, respectively. We use atomic force microscopy imaging and theoretical calculations to show that, in contrast to C₁₈ and C₁₆, C₁₀ and C₁₄ have a cumulenic and cumulene-like structure, respectively. Our results demonstrate an alternative strategy to generate cyclocarbons on the surface, providing an avenue for characterizing annular carbon allotropes for structure and stability.

基于sp ²杂化原子的全碳材料，例如富勒烯¹ 、碳纳米管²和石墨烯³ ，由于其卓越的物理化学性质和应用潜力而得到了广泛的探索。另一个不寻常的全碳同素异形体家族是由两个配位的sp杂化原子组成的环[ n ]碳（ _Cn ）。自二十世纪以来，人们一直在气相中研究它们^4,5,6 ，但它们的高反应性意味着凝聚相合成和真实空间表征一直具有挑战性，使得它们的确切分子结构有待争论^{7,8, 9,10,11} 。仅在 2019 年，表面上才生成了一个孤立的 C ₁₈ ，并且通过键分辨原子力显微镜揭示了其多聚结构^12,13 ，随后又发表了关于 C ₁₆的最新报告¹⁴ 。 C ₁₈工作引发了理论研究，阐明了 C ₁₀₀以内的环[ n ]碳的结构（参考文献^{15,16,17,18,19,20} ），尽管较小的 C _n同素异形体的合成和表征仍然很困难。在这里，我们修改了早期的表面合成方法，通过尖端诱导脱卤和全氯化萘（C ₁₀ Cl）的逆伯格曼开环来生产环[10]碳（C ₁₀ ）和环[14]碳（C ₁₄ ） ₈ ）和蒽（C ₁₄ Cl ₁₀ ）分子。 我们使用原子力显微镜成像和理论计算表明，与C ₁₈和C ₁₆相比，C ₁₀和C ₁₄分别具有积聚烯和类积聚烯结构。我们的结果展示了一种在表面生成环碳的替代策略，为表征环状碳同素异形体的结构和稳定性提供了途径。