Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117542, Singapore.
Centre for Advanced 2D Materials, National University of Singapore , Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore.
ACS Nano. 2016 Mar 22;10(3):3198-205. doi: 10.1021/acsnano.5b04970. Epub 2016 Feb 29.
Low-temperature scanning tunneling microscope investigations reveal that hexabromobenzene (HBB) molecules arrange in either hexagonally closely packed (hcp) [Formula: see text] or tetragonal [Formula: see text] structure on Au(111) dependent on a small substrate temperature difference around 300 K. The underlying mechanism is investigated by density functional theory calculations, which reveal that substrate-mediated intermolecular noncovalent C-Br···Br-C attractions induce hcp HBB islands, keeping the well-known Au(111)-22×√3 reconstruction intact. Upon deposition at 330 K, HBB molecules trap freely diffusing Au adatoms to form tetragonal islands. This enhances the attraction between HBB and Au(111) but partially reduces the intermolecular C-Br···Br-C attractions, altering the Au(111)-22×√3 reconstruction. In both cases, the HBB molecule adsorbs on a bridge site, forming a ∼15° angle between the C-Br direction and [112̅]Au, indicating the site-specific molecule-substrate interactions. We show that the competition between intermolecular and molecule-substrate interactions determines molecule packing at the subnanometer scale, which will be helpful for crystal engineering, functional materials, and organic electronics.
低温扫描隧道显微镜研究表明，六溴苯（HBB）分子在 Au(111)上的排列方式取决于 300K 左右的微小衬底温度差，要么是六边形紧密堆积（hcp）[公式：见文本]，要么是四方[公式：见文本]结构。通过密度泛函理论计算研究了其内在机制，结果表明，由底物介导的分子间非共价 C-Br···Br-C 吸引诱导了 hcp HBB 岛，从而保持了众所周知的 Au(111)-22×√3 重构的完整性。在 330K 下沉积时，HBB 分子会捕获自由扩散的 Au adatoms 形成四方岛。这增强了 HBB 与 Au(111)之间的吸引力，但部分降低了分子间的 C-Br···Br-C 吸引力，改变了 Au(111)-22×√3 重构。在这两种情况下，HBB 分子都吸附在桥位上，C-Br 方向与[112̅]Au 之间形成约 15°的夹角，表明了特定于位置的分子-底物相互作用。我们表明，分子间和分子-底物相互作用之间的竞争决定了亚纳米尺度上的分子堆积，这将有助于晶体工程、功能材料和有机电子学。
