How Surface Bonding and Repulsive Interactions Cause Phase Transformations: Ordering of a Prototype Macrocyclic Compound on Ag(111)
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- 作者：Felix Bischoff ; Knud Seufert ; Willi Auw盲rter ; Sushobhan Joshi ; Saranyan Vijayaraghavan ; David 脡cija ; Katharina Diller ; Anthoula C. Papageorgiou ; Sybille Fischer ; Francesco Allegretti ; David A. Duncan ; Florian Klappenberger ; Florian Blobner ; Runyuan Han ; Johannes V. Barth
- 刊名：ACS Nano
- 出版年：2013
- 出版时间：April 23, 2013
- 年：2013
- 卷：7
- 期：4
- 页码：3139-3149
- 全文大小：614K
- 年卷期：v.7,no.4(April 23, 2013)
- ISSN：1936-086X
文摘
We investigated the surface bonding and ordering of free-base porphine (2H-P), the parent compound of all porphyrins, on a smooth noble metal support. Our multitechnique investigation reveals a surprisingly rich and complex behavior, including intramolecular proton switching, repulsive intermolecular interactions, and density-driven phase transformations. For small concentrations, molecular-level observations using low-temperature scanning tunneling microscopy clearly show the operation of repulsive interactions between 2H-P molecules in direct contact with the employed Ag(111) surface, preventing the formation of islands. An increase of the molecular coverage results in a continuous decrease of the average intermolecular distance, correlated with multiple phase transformations: the system evolves from an isotropic, gas-like configuration via a fluid-like phase to a crystalline structure, which finally gives way to a disordered layer. Herein, considerable site-specific molecule鈥搒ubstrate interactions, favoring an exclusive adsorption on bridge positions of the Ag(111) lattice, play an important role. Accordingly, the 2D assembly of 2H-P/Ag(111) layers is dictated by the balance between adsorption energy maximization while retaining a single adsorption site counteracted by the repulsive molecule鈥搈olecule interactions. The long-range repulsion is associated with a charge redistribution at the 2H-P/Ag(111) interface comprising a partial filling of the lowest unoccupied molecular orbital, resulting in long-range electrostatic interactions between the adsorbates. Indeed, 2H-P molecules in the second layer that are electronically only weakly coupled to the Ag substrate show no repulsive behavior, but form dense-packed islands.