Theoretical and experimental secondary electron spin polarisation studies and 3D theory of field emission for nanoscale emitters

Spin-polarised electron beams are an invaluable probe of spin-dependent phenomena in fields of atomic and molecular physics, magnetism and biophysics. For this purpose, this work explores both theoretical and experimental aspects of field emission properties of point-like nano-scale emission sources with special emphasis on their spin-polarising ability. Firstly, the development of a novel multi-scale field emission simulation procedure is introduced and its capability to successfully combine classically calculated boundary conditions with quantum mechanical density functional theory (DFT) simulations are demonstrated. This technique is then applied to two emission tips based on a capped (5,5) carbon nanotube and a small tungsten-pyramid. In so doing, this thesis demonstrates how this novel simulation method can provide insights into material properties, such as the spatial distribution of charge density, the physical distribution and energies of individual orbitals for different applied fields and the changes in total potential energy with varying fields. Secondly, to investigate the interactions between spin-polarised electron beams with ferromagnetic materials experimental work on several magnetic heterostructures was conducted using a spin-polarised low-energy electron microscope. The analysis of the energy and spin-dependent energy loss and newly-developed secondary electron yield experiments have insights into inelastic scattering mechanisms. Measuring the energy-dependent reflectivity in conjunction with DFT simulation further gives indications about the material’s spin-dependent electronic band structure a few electronvolts above the Fermi level. Furthermore, this work includes the design, fabrication, and integration of specialised experimental equipment into a pre-existing ultra-high vacuum system to analyse nano-sized field emitters. As these emitters are based on ultra-thin magnetic Fe and Fe3O4 nano-disks, theoretical studies using micromagnetic simulations were performed to analyse their magnetic behaviour. Based on the resulting phase diagrams suitable dimensions that enable the fabrication of robust spin-polarised field emitter systems, which have a stable in-plane magnetisation and long Néel relaxation times, were found.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2021

Author dc:creator

• Masur, Sabrina

Advisors dc:contributor.advisor

• Barnes, Crispin
• Ionescu, Adrian
• Edgcombe, Chris

• DFT
• Carbon nanotube
• Field emission
• spin polarisation
• Secondary electrons

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/c751ad33-61fb-4c19-89ab-d7ede6bf4db5/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0001-7337-7245
0000-0003-0265-5281

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/329942