Sakulsermsuk, Sumet
(2011).
Molecular manipulation with the scanning tunnelling microscope.
University of Birmingham.
Ph.D.
Abstract
This thesis presents two studies into molecular manipulation using scanning tunnelling microscopy (STM), dissociation of chrolobenzene (PhCl) and of 4,4´ dichlorobiphenyl (PCB) manipulation both on Si(111)-7×7 surface. An ab initio investigation is presented on a possible candidate for future atomic manipulation. The dissociation of PhCl process on the Si(111)-7x7 surface was studied using an STM. STM induced dissociation was found to be temperature dependent and requires 1.4 \(\pm\) 0.1 electrons per C-Cl bond breaking event. Based on work and previous work, we suggest this is a mixture of a two-electron temperature independent and one-electron temperature dependent processes. The activation barrier for the thermally assisted one-electron dissociation was measured to be 0.8 \(\pm\) 0.2 eV. This appears to reflect the measured energy barrier of diffusion of 0.84 \(\pm\) 0.08 eV, suggesting that the thermally promoted dissociation process proceeds via a precursor physisorbed state. Electron injection from STM was used to induce atomic manipulation of PCB on Si(111)- 7×7 surface. Four types of manipulation outcomes were observed; desorption, double dark feature, single dark feature and the generation of a bistable adsorbed switching. The PCB bistable switching was voltage independent, but injection tip-site dependent. This suggests that the switching process is driven by thermal excitation, but that the tip-adsorbate interactions play a role. The computational study of naphthalene 1,8-disulfide (NDS) in gas phase was performed by the density functional theory calculations using molecular orbitals. The S-S bond lengths of NDS\(^2\)\(^-\), NDS\(^-\), NDS, NDS\(^+\) and NDS\(^2\)\(^+\) were predicted to be 3.46 Å, 2.74 Å, 2.13 Å, 2.09 Å and 2.06 Å. Therefore the disulfide bond is a strong candidate to undergo vibrational excitation due to respectively short lived ionic molecules created by charge injection from an STM tip.
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