| AVS 60th International Symposium and Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+AS+BI+EM+SE+SS-WeA |
| Session: | Applications of Self-Assembled Monolayers and Nano-Structured Assemblies |
| Presenter: | A. Enders, University of Nebraska Lincoln |
| Authors: | A. Enders, University of Nebraska Lincoln D. Kunkel, University of Nebraska Lincoln S. Beniwal, University of Nebraska Lincoln P.A. Dowben, University of Nebraska Lincoln S. Simpson, State University of New York at Buffalo E. Zurek, State University of New York at Buffalo |
| Correspondent: | Click to Email |
The self-assembly of organic molecules on flat metal surfaces can differ considerably from the well-known solution-based supramolecular chemistry. Substrates may set limits to the mobility of molecular adsorbates, and interactions across the organic/inorganic interface may perturb the electronic structure of the molecules and the substrate considerably. As a result, their diffusivity, the strength of chemical bonds, charge, protonation and deprotonation may all be dependent on the substrate itself. This can be exploited to engineer unique structures and properties that may not exist naturally in the respective crystalline phase.
One of the central questions in organic self-assembly is the role of an intrinsic molecular electric dipole and how the resulting electrostatic interaction competes with other chemical bonds. We studied small molecules with large intrinsic electrical dipole as model system for molecular films adsorption on surfaces for altering the interface dipole screening. For instance, we investigated the self-assembly and interface properties of zwitterionic molecules of type C6H2(…NHR)2(…O)2 (R = H, ...), adsorbed on Cu(111), Ag(111), Au(111) surfaces with scanning tunneling microscopy in UHV [1]. These molecules carry positive and negative charges on opposite parts of the molecule, resulting in a huge electric dipole of typically 10 Debye. We find that the dipole of the surface-supported molecule is decreased with respect to free species and of order of 1 - 2 Debye, depending on the substrate material. The molecules self-assemble into 2D structures upon adsorption, where the substrate-dependent strength of the dipolar interactions between the adsorbed molecules can dictate the network architecture. DFT calculations were performed to analyze adsorption geometry, charge transfer and dipole moment. By systematic comparison of the self-assembly of those molecules on different metal substrates we were able to show that the intrinsic dipole mainly plays a role in the structure formation if the interaction strength with the substrate is very weak, otherwise epitaxial fit to the substrate dictates the molecular arrangement.