Structural studies of the adsorption of molecules on Cu(110)

Thomas, Geoffrey Structural studies of the adsorption of molecules on Cu(110). Doctor of Philosophy thesis, University of Liverpool.

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Abstract

The adsorption of thymine and melamine on Cu(110) has been investigated using a combination of experimental and theoretical techniques. These techniques have allowed the development of an extensive picture of how these molecules may orient on this surface. Many Density Functional Theory (DFT) calculations using the latest version of the Vienna Ab-Initio Simulation Package (VASP) have allowed the production of a series of models which have, in general, corroborated the experimental data. The additional utilisation of semi-empirical techniques (like those used by Grimme), which seek to simulate long-range inter-molecular vdW interactions, have allowed the creation of a firm foundation of, not only how the individual molecules bond to the Cu(110) surface, but of how they arrange themselves into long-range structures. With thymine, two long-range phases were observed; a room temperature structure, which aligned along the [001] direction in 1-D chains, one molecule thick and with the cyclic plane roughly parallel to the [110] direction. The higher temperature phase occurred after annealing between 350-400K and consisted of two distinct 1-D chains, two molecules thick and angled at ~±20o to the [001] direction. In both cases the thymine was deprotonated at the N(1) atom. With melamine, only the room temperature phase is discussed and this consisted of a 2-D “hexagonal” structure arranged on a (6x2) unit cell. Although structural relaxation techniques give good indications of the stability of the models, the technique of Scanning Tunneling Microscopy (STM) simulation has been used extensively with both thymine and melamine systems in order to verify their validity. Although it is not yet possible to directly observe individual atoms in such small molecules it is possible (with STM) to observe their electronic “footprint” and to then re-create this observed image. The similarity of this “simulated STM” to the “experimental STM” combined with a relaxed stable model is a strong indication that the model is in good accordance with the observed (static) system. Combining this analysis technique with experimental data, models are proposed for both the room temperature thymine and melamine phases as well as the annealed thymine phase.

Item Type:	Thesis (Doctor of Philosophy)
Additional Information:	Date: 2013-01-22 (completed)
Subjects:	?? QD ??
Divisions:	Faculty of Science and Engineering > School of Physical Sciences
Depositing User:	Symplectic Admin
Date Deposited:	04 Sep 2013 11:04
Last Modified:	17 Dec 2022 01:19
DOI:	10.17638/00009257
Supervisors:	Rasmita, Raval Darling, George
URI:	https://livrepository.liverpool.ac.uk/id/eprint/9257