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Adsorbate-induced nanoscale faceting of rhenium surfaces
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Title
Adsorbate-induced nanoscale faceting of rhenium surfaces
Identifier
ETD_1305
Identifier
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http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000050465
Language
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eng
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theses
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Physics and Astronomy
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(authority = ETD-LCSH)
Topic
Nanostructured materials
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(authority = ETD-LCSH)
Topic
Rhenium
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(ID = SBJ-1);
(authority = ETD-LCSH)
Topic
Metals--Surfaces
Abstract
In this dissertation, we report the first systematic study of adsorbate-induced faceting of hexagonal close-packed (hcp) metal surfaces. Focusing on two atomically rough rhenium surfaces: Re(12-31) and Re(11-21), we reveal the dependence of their surface morphology on adsorbate coverage and species by means of low energy electron diffraction (LEED), scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), temperature programmed desorption (TPD) and high resolution soft X-ray photoemission spectroscopy (HRSXPS) based on synchrotron radiation.
Re(12-31) becomes completely faceted when oxygen coverage is greater than 0.7 monolayer (ML) and the surface is annealed at T > 700K. As oxygen coverage further increases, the surface morphology evolves from long ridges formed by (01-10) and (11-21) facets, to truncated ridges due to sequential emergence of (10-10) and (01-11), and eventually to complex structures formed by (01-10) (10-10) (01-11) and (10-11) facets. All facets disappear when the surface is annealed at T > 1300K due to oxygen desorption and the surface reverts to planar.
Drastic differences have also been found between oxygen and nitrogen-induced faceting of Re(11-21). For O/Re(11-21), the morphology evolves as a function of oxygen coverage from a partially faceted surface with zigzag chains formed by (01-10) and (10-10) to a completely faceted surface with four-sided pyramids formed by (01-10) (10-10) (01-11) and (10-11). Two metastable facets, (33-64) and (2x1) reconstructed (11-22) are also observed in the evolution process. In contrast, for N/Re(11-21), a fully faceted surface shows ridges formed by (13-42) and (31-42) facets upon exposure to ammonia at 800-900K; ammonia dissociates on Re and only nitrogen remains on the surface at T > 600K. A (2x1) reconstructed N/Re(11-21) surface is also observed in LEED when the surface is annealed at 600-700K. Temperature-pressure phase diagrams from first principles calculations are consistent with the experimental results.
Our work has implications for Re-based catalysts that operate under oxygen or nitrogen-rich conditions because the structure of the catalysts often affects their performance. The results show great promise of tailoring the surface morphology at the nanometer scale by choosing appropriate adsorbate-substrate combinations, adsorbate coverages and annealing conditions.
Re(12-31) becomes completely faceted when oxygen coverage is greater than 0.7 monolayer (ML) and the surface is annealed at T > 700K. As oxygen coverage further increases, the surface morphology evolves from long ridges formed by (01-10) and (11-21) facets, to truncated ridges due to sequential emergence of (10-10) and (01-11), and eventually to complex structures formed by (01-10) (10-10) (01-11) and (10-11) facets. All facets disappear when the surface is annealed at T > 1300K due to oxygen desorption and the surface reverts to planar.
Drastic differences have also been found between oxygen and nitrogen-induced faceting of Re(11-21). For O/Re(11-21), the morphology evolves as a function of oxygen coverage from a partially faceted surface with zigzag chains formed by (01-10) and (10-10) to a completely faceted surface with four-sided pyramids formed by (01-10) (10-10) (01-11) and (10-11). Two metastable facets, (33-64) and (2x1) reconstructed (11-22) are also observed in the evolution process. In contrast, for N/Re(11-21), a fully faceted surface shows ridges formed by (13-42) and (31-42) facets upon exposure to ammonia at 800-900K; ammonia dissociates on Re and only nitrogen remains on the surface at T > 600K. A (2x1) reconstructed N/Re(11-21) surface is also observed in LEED when the surface is annealed at 600-700K. Temperature-pressure phase diagrams from first principles calculations are consistent with the experimental results.
Our work has implications for Re-based catalysts that operate under oxygen or nitrogen-rich conditions because the structure of the catalysts often affects their performance. The results show great promise of tailoring the surface morphology at the nanometer scale by choosing appropriate adsorbate-substrate combinations, adsorbate coverages and annealing conditions.
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xvi, 136 p. : ill.
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Ph.D.
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Includes bibliographical references (p. 130-135)
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by Hao Wang
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Wang
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Hao
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1975 May 2-
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Hao Wang
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Madey
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Theodore
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chair
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Theodore E Madey
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Yuzbashyan
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Emil
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Emil Yuzbashyan
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Thomson
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Gordon
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Gordon Thomson
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Zimmermann
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Frank
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Frank Zimmermann
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Hulbert
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Steven
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Steven L Hulbert
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Rutgers University
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Graduate School - New Brunswick
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2008
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2008-10
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xx
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Rutgers University Electronic Theses and Dissertations
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doi:10.7282/T3HX1CZJ
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ETD doctoral
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The author owns the copyright to this work.
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Open
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.
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