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# Molecular manipulation with the scanning tunnelling microscope

Sakulsermsuk, Sumet (2011)
Ph.D. thesis, University of Birmingham.

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## 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.

Type of Work: Ph.D. thesis. Palmer, Richard E. Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Physics & Astronomy QC Physics University of Birmingham 1337
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