On-surface synthesis of graphene clusters from a Z-bar-linkage precursor with quaterphenylbranches
On-surface synthesis of graphene clusters from a Z-bar-linkage precursor with quaterphenylbranches
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由具有四联苯支链的 Z 杆连接前体表面合成石墨烯簇
DOI：
10.1039/c7qm00577f
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发表时间：
2018
影响因子：
7
通讯作者：
H. Sakaguchi
中科院分区：
文献类型：
--
作者：
Z. Xu;T. Kojima;W. Wang;K. Kaushik;A. Saliniemi;T. Nakae;H. Sakaguchi
用扫描隧道显微镜、拉曼光谱和理论计算研究了含四苯基支链的Z-链前驱体在Au（111）表面的双区化学气相沉积产物。在400 °C下退火产生分子内脱氢前体的线性阵列，并且超过450 °C的温度导致分子间脱氢和石墨烯簇的形成。该反应途径与先前报道的具有三联苯分支的Z-杆连接前体的结果形成显著对比，其中进行纯手性聚合并允许形成并苯型石墨烯纳米带。其原因可能源于四苯基支化前体的双自由基形式的构象，其通过在250 °C退火期间在Au（111）上脱溴而产生。四苯基支化的前体可能有利于对称构象，两个自由基指向Au（111）表面，而我们以前的结果表明，三联苯支化的前体可能有利于不对称（手性）构象，一个自由基指向和另一个远离Au（111）表面。由于双自由基对Au的强亲和力，推测四苯基支化前体的对称构象的空间位阻阻止聚合（111）。这种对称的前体构象通过分子内脱氢导致融合的脱溴前体，并最终通过表面上的分子间融合导致转化为石墨烯簇。
The products of two-zone chemical vapor deposition on Au(111) from a Z-bar-linkage precursor with quaterphenyl-branches were investigated by scanning tunneling microscopy, Raman spectroscopy, and theoretical calculations. Annealing at 400 °C produced linear arrays of intramolecular-dehydrogenated precursors, and temperatures over 450 °C led to intermolecular dehydrogenation and to the formation of graphene clusters. This reaction pathway contrasts remarkably with the previous results reported for a Z-bar-linkage precursor with terphenyl branches, where homochiral polymerization proceeded and allowed the formation of acene-type graphene nanoribbons. The reason might originate from the conformation of the biradical form of the quaterphenyl-branched precursor, produced by debromination on Au(111) during 250 °C annealing. The quaterphenyl-branched precursor might favor a symmetric conformation with both the radicals pointing toward the Au(111) surface, whereas our previous results showed that the terphenyl-branched precursor might favor asymmetric (chiral) conformations, with one radical pointing toward and the other one away from the Au(111) surface. Steric hindrance of the symmetric conformations of the quaterphenyl-branched precursor is presumed to prohibit polymerization due to the strong affinity of the biradical to Au(111). Such symmetric precursor conformations lead to fused debrominated precursors via intramolecular dehydrogenation, and finally result in the conversion to graphene clusters via on-surface intermolecular fusion.