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PLASMON PHOTOABSORPTION AND SURFACE IONIZATION
OF METAL NANOCLUSTERS
by
Chunlei Xia
________________________________________________________________________
A Dissertation Proposal Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PHYSICS)
December 2009
Copyright 2009 Chunlei Xia
Object Description
| Title | Plasmon photoabsorption and surface ionization of metal nanoclusters |
| Author | Xia, Chunlei |
| Author email | cxia@usc.edu; xiachunlei@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Physics |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2009-05-11 |
| Date submitted | 2009 |
| Restricted until | Unrestricted |
| Date published | 2009-12-15 |
| Advisor (committee chair) | Kresin, Vitaly |
| Advisor (committee member) |
Bozler, Hans Kalia, Rajiv Thomson, Richard Bradforth, Stephen |
| Abstract | The ionization and fragmentation of alkali clusters as a result of (1) absorption of ultraviolet light by volume plasmons and (2) collisions with a surface were studied.; The volume plamson is an important elementary excitation, it could not couple to light waves in the bulk and thus could not be investigated by optical spectroscopy, however the situation is different for clusters due to the presence of the boundary. What is more, it is fundamental to study the interaction between light and matter, but the photoabsorption of simple metal clusters in the UV region has remained unexplored experimentally. We have carried out experiments on the photoabsorption of Na₂₀ and Na₉₂ covering the near UV part as well as visible range (~ 2.0 - 5.5 eV) employing the photodepletion technique. The absorption cross sections for clusters of some other sizes in the near UV range have also been studied. The experimental data for Na₂₀ in the visible part agree with existing data very well. In addition to the strong surface plasmon absorption peaks in the visible, we observed appreciable photoabsorption in the UV region. These cross section spectra have been fitted by Lorentzian line shapes and revealed broad peaks slightly above 4 eV. The frequency and weight of these peaks match the theoretical predictions and are identified as the nanocluster "volume plasmon" resonance. The photoabsorption spectra provide the first experimental observation of optically excited "volume plasmon" collective electronic states in metal nanocluster particles, a phenomenon unique to finite systems.; The plasma resonance measurement of pure sodium clusters was extended to mixed clusters in a beam including Na₂₁Cl and Na₂₂Cl₂ and the spectra were compared with that of Na₂₀. For Na₂₀ and Na₂₁Cl, the resonance positions are close, suggesting that the Cl⁻ ion in Na₂₁Cl does not locate at the center of the metallic droplet and does not strongly modify the effective valence electron density. The spectrum of Na₂₂Cl₂ is noticeably dissimilar to the other two, raising the possibility of structural differences and/or incomplete charge transfer.; We also experimentally studied the surface-impact ionization of sodium clusters. Large sodium nanoparticles (~ 10 nm in radius), generated in a vapor condensation source, produce copious amounts of positive ions upon colliding with a surface. The ion flux does not display an exponential surface temperature dependence, is present for both conducting and non-conducting surfaces, and carries a substantial kinetic energy. On the basis of these characteristics it is concluded that the signal arises from dissociative ionization produced by energetic impact, rather than from thermal charge transfer to the surface. |
| Keyword | volume plasmon; nanocluster; photoabsorption; surface plasmon; surface ionization |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2791 |
| Contributing entity | University of Southern California |
| Rights | Xia, Chunlei |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Xia-3024 |
| Archival file | uscthesesreloadpub_Volume23/etd-Xia-3024-0.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Full text | PLASMON PHOTOABSORPTION AND SURFACE IONIZATION OF METAL NANOCLUSTERS by Chunlei Xia ________________________________________________________________________ A Dissertation Proposal Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (PHYSICS) December 2009 Copyright 2009 Chunlei Xia |
