title: Competition between Hexagonal and Tetragonal Hexabromobenzene Packing on Au(111).
abstract: 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.
authors.affiliation: 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.
authors.forename: Han
authors.initials: H
authors.lastname: Huang
authors.forename: Zhiyu
authors.initials: Z
authors.lastname: Tan
authors.forename: Yanwei
authors.initials: Y
authors.lastname: He
authors.affiliation: Institute of Physics, Chinese Academy of Sciences , Beijing 100190, People's Republic of China.
authors.forename: Jian
authors.initials: J
authors.lastname: Liu
authors.affiliation: Institute of Physics, Chinese Academy of Sciences , Beijing 100190, People's Republic of China.
authors.forename: Jiatao
authors.initials: J
authors.lastname: Sun
authors.forename: Kang
authors.initials: K
authors.lastname: Zhao
authors.forename: Zhenhong
authors.initials: Z
authors.lastname: Zhou
authors.forename: Guo
authors.initials: G
authors.lastname: Tian
authors.affiliation: Institute of Materials Research and Engineering, Agency for Science Technology and Research , 3, Research Link, Singapore 117602, Singapore.
authors.forename: Swee Liang
authors.initials: SL
authors.lastname: Wong
authors.affiliation: 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.
authors.forename: Andrew Thye Shen
authors.initials: AT
authors.lastname: Wee
keywords: Au(111)-22×√3; DFT calculations; LT-STM; halogen bonding; molecular arrangement