An atomistic investigation of CO adsorption on a weakly interacting substrate

Abstract

This thesis presents a low-temperature scanning tunnelling microscopy (LT-STM) investigation of CO interactions on Cu(110). In the first instance, lateral CO−CO interactions were investigated at low coverage (∼ 0.06 ML) . These interactions were found to be highly anisotropic (attractive and repulsive in the [001] and [11̅0] directions respectively). Atom-resolved microscopy revealed formation of linear chains strictly aligned in the [001] direction. These molecular arrangements are found to arise from substrate mediation effects. Step edge sites are often found to be the arrangement of atoms responsible for active catalysis. Thus CO interactions at Cu(110) step edges were studied. The adsorption of CO at the upper terrace of the step edge, was observed to modulate the nature of the highly coordinated atoms neighbouring them at the lower terrace, effectively ’activating’ them towards CO adsorption. This has important implications to the fundamental understanding of catalytic processes at the atomic level. CO adsorption structures were investigated at increasing coverages. At low coverage due to the attractive nature of the CO−CO interaction linear chains are formed in the favourable [001] direction. As more CO is packed onto the surface the separation between these chains in the unfavourable [11̅0] direction decreases in a step-wise manner. At a saturation coverage of just over 0.75 ML the compression due to close packing relieves itself by introducing a ‘wiggling’ periodicity along the [001] direction. These novel structures at high coverage are possible configurations CO molecules could adopt on active catalyst surfaces. STM-IETS measurements were performed to obtain vibrational spectra of CO on Cu(110). Whilst certain vibrational modes could be resolved, further parameter optimisation is needed to observe the C−O stretching peak. Lastly, a preliminary study into the co-adsorption of CO and H is presented. Whilst this investigation is still in its early stages, the results show promising avenues for further work.

Date of Award	29 Jul 2020
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Renald Schaub (Supervisor) & Paul Webb (Supervisor)