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dc.contributor.authorTownsend, Peter Stephen Morris
dc.date.accessioned2018-03-14T15:35:34Z
dc.date.available2018-03-14T15:35:34Z
dc.date.issued2018-01-01
dc.date.submitted2017-11-28
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/274001
dc.description.abstractHelium-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.sponsorshipEPSRC funded, award reference 1363145
dc.language.isoen
dc.rightsAll rights reserved
dc.rightsAll Rights Reserveden
dc.rights.urihttps://www.rioxx.net/licenses/all-rights-reserved/en
dc.subjecthelium-3 surface spin echo spectroscopy
dc.subjectintermediate scattering function
dc.subjectGeneralized Langevin Equation
dc.subjectQuantum Langevin Equation
dc.subjectquantum diffusion
dc.subjectsurface diffusion
dc.subjectincoherent tunneling
dc.titleDiffusion of light adsorbates on transition metal surfaces
dc.typeThesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridge
dc.publisher.departmentDepartment of Physics
dc.date.updated2018-03-14T13:58:48Z
dc.identifier.doi10.17863/CAM.21077
dc.contributor.orcidTownsend, Peter Stephen Morris [0000-0003-1616-4037]
dc.publisher.collegeGonville and Caius
dc.type.qualificationtitlePhD in Physics
cam.supervisorEllis, John
cam.thesis.fundingtrue
rioxxterms.freetoread.startdate2018-03-14


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