Physik Department E20, Technische Universität München, 85748 Garching, Germany.
ACS Nano. 2012 Mar 27;6(3):2477-86. doi: 10.1021/nn204863p. Epub 2012 Mar 2.
We address the interplay of adsorption, chemical nature, and self-assembly of uracil on the Ag(111) and Cu(111) surfaces as a function of molecular coverage (0.3 to 1 monolayer) and temperature. We find that both metal surfaces act as templates and the Cu(111) surface acts additionally as a catalyst for the resulting self-assembled structures. With a combination of STM, synchrotron XPS, and NEXAFS studies, we unravel a distinct polymorphism on Cu(111), in stark contrast to what is observed for the case of uracil on the more inert Ag(111) surface. On Ag(111) uracil adsorbs flat and intact and forms close-packed two-dimensional islands. The self-assembly is driven by stable hydrogen-bonded dimers with poor two-dimensional order. On Cu(111) complex structures are observed exhibiting, in addition, a strong annealing temperature dependence. We determine the corresponding structural transformations to be driven by gradual deprotonation of the uracil molecules. Our XPS study reveals unambiguously the tautomeric signature of uracil in the contact layer and on Cu(111) the molecule's deprotonation sites. The metal-mediated deprotonation of uracil and the subsequent electron localization in the molecule determine important biological reactions. Our data show a dependence between molecular coverage and molecule-metal interaction on Cu(111), as the molecules tilt at higher coverages in order to accommodate a higher packing density. After deprotonation of both uracil N atoms, we observe an adsorption geometry that can be understood as coordinative anchoring with a significant charge redistribution in the molecule. DFT calculations are employed to analyze the surface bonding and accurately describe the pertaining electronic structure.
我们研究了嘧啶在 Ag(111)和 Cu(111)表面的吸附、化学性质和自组装随分子覆盖率（0.3 到 1 单层）和温度的变化。我们发现，两种金属表面都充当模板，而 Cu(111)表面还充当了生成自组装结构的催化剂。通过 STM、同步辐射 XPS 和 NEXAFS 研究，我们揭示了 Cu(111)表面上的明显多晶型性，与嘧啶在更惰性的 Ag(111)表面上的情况形成鲜明对比。在 Ag(111)上，嘧啶吸附是平坦且完整的，并形成紧密堆积的二维岛。自组装由稳定的氢键二聚体驱动，二维有序性差。在 Cu(111)上，除了观察到复杂的结构外，还观察到对退火温度强烈的依赖性。我们确定相应的结构转变是由嘧啶分子的逐渐去质子化驱动的。我们的 XPS 研究明确揭示了嘧啶在接触层和 Cu(111)上的互变异构特征，以及分子的去质子化部位。嘧啶的金属介导去质子化和随后分子中的电子定位决定了重要的生物反应。我们的数据表明，在 Cu(111)上，分子覆盖率和分子-金属相互作用之间存在依赖性，因为分子在更高覆盖率下倾斜以适应更高的堆积密度。在嘧啶的两个 N 原子都去质子化后，我们观察到一种可以理解为配位锚定的吸附几何形状，其中分子中的电荷重新分布显著。DFT 计算被用来分析表面键合，并准确描述相关的电子结构。
