Matching Items (2)
Description
In this dissertation, combined photo-induced and thermionic electron emission from low work function diamond films is studied through low energy electron spectroscopy analysis and other associated techniques. Nitrogen-doped, hydrogen-terminated diamond films prepared by the microwave plasma chemical vapor deposition method have been the most focused material. The theme of this research is represented by four interrelated issues. (1) An in-depth study describes combined photo-induced and thermionic emission from nitrogen-doped diamond films on molybdenum substrates, which were illuminated with visible light photons, and the electron emission spectra were recorded as a function of temperature. The diamond films displayed significant emissivity with a low work function of ~ 1.5 eV. The results indicate that these diamond emitters can be applied in combined solar and thermal energy conversion. (2) The nitrogen-doped diamond was further investigated to understand the physical mechanism and material-related properties that enable the combined electron emission. Through analysis of the spectroscopy, optical absorbance and photoelectron microscopy results from sample sets prepared with different configurations, it was deduced that the photo-induced electron generation involves both the ultra-nanocrystalline diamond and the interface between the diamond film and metal substrate. (3) Based on results from the first two studies, possible photon-enhanced thermionic emission was examined from nitrogen-doped diamond films deposited on silicon substrates, which could provide the basis for a novel approach for concentrated solar energy conversion. A significant increase of emission intensity was observed at elevated temperatures, which was analyzed using computer-based modeling and a combination of different emission mechanisms. (4) In addition, the electronic structure of vanadium-oxide-terminated diamond surfaces was studied through in-situ photoemission spectroscopy. Thin layers of vanadium were deposited on oxygen-terminated diamond surfaces which led to oxide formation. After thermal annealing, a negative electron affinity was found on boron-doped diamond, while a positive electron affinity was found on nitrogen-doped diamond. A model based on the barrier at the diamond-oxide interface was employed to analyze the results. Based on results of this dissertation, applications of diamond-based energy conversion devices for combined solar- and thermal energy conversion are proposed.
ContributorsSun, Tianyin (Author) / Nemanich, Robert (Thesis advisor) / Ponce, Fernando (Committee member) / Peng, Xihong (Committee member) / Spence, John (Committee member) / Treacy, Michael (Committee member) / Arizona State University (Publisher)
Created2013
Description
The performance of accelerator applications like X-ray free electron lasers (XFELs)and ultrafast electron diffraction (UED) and microscopy (UEM) experiments is limited
by the brightness of electron beams generated by photoinjectors. In order to
maximize the brightness of an electron beam it is essential that electrons are emitted
from photocathodes with the smallest possible mean transverse energy (MTE).
Metallic photocathodes hold the record for the smallest MTE ever measured at 5
meV from a Cu(100) single crystal photocathode operated near the photoemission
threshold and cooled to 30 K. However such photocathodes have two major limitations:
poor surface stability, and a low quantum efficiency (QE) which leads to
MTE degrading non-linear photoemission effects when extracting large charge densities.
This thesis investigates the efficacy of using a graphene protective layer in order
to improve the stability of a Cu(110) single crystalline surface. The contribution to
MTE from non-linear photoemission effects is measured from a Cu(110) single crystal
photocathode at a variety of excess energies, laser fluences, and laser pulse lengths.
To conclude this thesis, the design and research capabilities of the Photocathode and
Bright Beams Lab (PBBL) are presented. Such a lab is required to develop cathode
technology to mitigate the practical limitations of metallic photocathodes.
ContributorsKnill, Christopher John (Author) / Karkare, Siddharth (Thesis advisor) / Drucker, Jeffery (Committee member) / Kaindl, Robert (Committee member) / Teitelbaum, Samuel (Committee member) / Arizona State University (Publisher)
Created2023