dc.contributor.author Townsend, Peter Stephen Morris dc.date.accessioned 2018-03-14T15:35:34Z dc.date.available 2018-03-14T15:35:34Z dc.date.issued 2018-01-01 dc.date.submitted 2017-11-28 dc.identifier.uri https://www.repository.cam.ac.uk/handle/1810/274001 dc.description.abstract Helium-3 surface spin echo spectroscopy (HeSE) has been used to measure the diffusive dynamics of adsorbates on close-packed metal surfaces, namely hydrogen on Cu(111), Pd(111) and Ru(0001), carbon and oxygen on Ru(0001), and oxygen on Cu(111). Chapter 2 reviews the HeSE technique and describes the relevant dynamical models and statistical methods used to interpret data in later chapters. The performance of the ionizing detector is analysed, with a focus on the signal-to-noise ratio. In Chapter 3 expressions for the classical intermediate scattering function (ISF) are introduced for open and closed systems. The effects of corrugation and surface-perpendicular motion on the amplitude of different components in the ISF are modelled analytically and compared with simulation. The exact ISF for a particle on a flat surface, obeying the Generalized Langevin Equation with exponential memory friction, is calculated analytically. In Chapter 4 the analytical ISF is calculated for quantum Brownian motion and for coherent tunneling dynamics in a tight binding system. The bounce method for calculating quantum mechanical hopping rates in dissipative systems is applied to model diffusion of hydrogen on Ru(0001). Chapter 5 presents the first HeSE measurements of carbon and oxygen diffusion. C/Ru(0001) diffusion is assigned to a small carbon cluster. The jump rate has an activation energy $E_{A}=292\pm7\,$meV in the temperature range $550\,\textrm{K}\leq T \leq 1300\,$K. Oxygen diffusion is significantly slower. By comparison of literature data with the new HeSE results, the activation energy for oxygen diffusion at low coverage is estimated as $650\pm10$meV. Oxygen measurements at high coverage $\theta\approx0.22\,$ML are consistent with strong mutual O-O interactions. Surface diffusion is also observed after exposing Cu(111) to oxygen. Chapter 6 presents low-coverage measurements of protium (H) and deuterium (D) diffusion on Ru(0001), Pd(111) and Cu(111). In the quantum activated regime there is evidence for multiple jumps in all three systems, suggesting a low dynamical friction. The measurements on Ru(0001) indicate that the deep tunneling rate is much slower for D than for H. dc.description.sponsorship EPSRC funded, award reference 1363145 dc.language.iso en dc.rights All rights reserved dc.rights All Rights Reserved en dc.rights.uri https://www.rioxx.net/licenses/all-rights-reserved/ en dc.subject helium-3 surface spin echo spectroscopy dc.subject intermediate scattering function dc.subject Generalized Langevin Equation dc.subject Quantum Langevin Equation dc.subject quantum diffusion dc.subject surface diffusion dc.subject incoherent tunneling dc.title Diffusion of light adsorbates on transition metal surfaces dc.type Thesis dc.type.qualificationlevel Doctoral dc.type.qualificationname Doctor of Philosophy (PhD) dc.publisher.institution University of Cambridge dc.publisher.department Department of Physics dc.date.updated 2018-03-14T13:58:48Z dc.identifier.doi 10.17863/CAM.21077 dc.contributor.orcid Townsend, Peter Stephen Morris [0000-0003-1616-4037] dc.publisher.college Gonville and Caius dc.type.qualificationtitle PhD in Physics cam.supervisor Ellis, John cam.thesis.funding true rioxxterms.freetoread.startdate 2018-03-14
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