Studying novel material properties using synchrotron-based soft x-ray spectroscopy

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Date
2015-09-08Author
Pitman, Amy
Type
ThesisDegree Level
MastersMetadata
Show full item recordAbstract
This thesis is centred around the study materials with novel electronic properties, including transition metals interacting with semiconductors and unique molecular systems. The idea of advancing modern computing is the basis for motivating the work in that the projects all have potential to be used in novel applications that would impact the efficiency and/or execution of current technology. We have studied two variations of transition metals as they appear in materials and two molecular systems. As for the transition metals interacting with semiconductors, we first discuss transition metal atoms introduced as impurities to a semiconductor lattice, and second, we discuss transition metal oxides that are naturally semiconducting.
We have used a number of experimental and theoretical techniques to better understand
these groups of materials. Materials prepared through high quality synthesis techniques were
studied using x-ray spectroscopy made possible by synchrotron light sources. Computational software then allowed for the experiments to be interpreted by comparing them to the simulations.
In the study of transition metals as impurities, we chose the Co:MoS2 system because MoS2 has had promising results with other transition metal dopants. We examined the electronic structure for two purposes: (1) to determine the local bonding environment and locations of the cobalt atoms in order to better understand the behaviour of Co as an impurity; and (2) the overall band gap of the system so that we could evaluate the system’s potential for use in applications. Experimental results combined with our theoretical simulations led us to conclude that the samples available were all metallic, and at low concentrations cobalt atoms were able to substitute directly into the MoS2 lattice.
An examination of copper (II) oxide allowed us to investigate the ability to tune the band gap of a known semiconductor through a synthesis process that applied axial pressure to the sample. For a collection of samples prepared at different pressures, x-ray spectroscopy
methods showed an increasing band gap with increasing synthesis pressure, a result that is
most encouraging for the field of band gap engineering.
Using soft x-ray spectroscopy to examine the conduction and valence bands of the two molecular systems, the potassium-doped hydrocarbons and Li2RuO3, was important for drawing conclusions about the materials’ composition and behaviour. Results showed the introduction of new states at the lower edge of the conduction band of K:phenanthrene, a possible reason for its low-temperature superconductivity. Li2RuO3’s electronic structure was examined and compared to calculations performed by collaborators.
Degree
Master of Science (M.Sc.)Department
Physics and Engineering PhysicsProgram
PhysicsSupervisor
Moewes, AlexanderCommittee
Dick, Rainer; Chang, Gap Soo; Kasap, SafaCopyright Date
July 2015Subject
XAS
XES
RIXS
x-ray spectroscopy
electronic materials
DOS
band structure
band gap
crystal field
transition metal
DMS
spintronics
spin electronics