Competition between Hexagonal and Tetragonal Hexabromobenzene Packing on Au(111)

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• 作者：Han Huang ; Zhiyu Tan ; Yanwei He ; Jian Liu ; Jiatao Sun ; Kang Zhao ; Zhenhong Zhou ; Guo Tian ; Swee Liang Wong ; Andrew Thye Shen Wee
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：March 22, 2016
• 年：2016
• 卷：10
• 期：3
• 页码：3198-3205
• 全文大小：495K
• ISSN：1936-086X

文摘

Low-temperature scanning tunneling microscope investigations reveal that hexabromobenzene (HBB) molecules arrange in either hexagonally closely packed (hcp) or tetragonal 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.