Author

Kareem Gameel

Abstract

Density functional theory (DFT) has been regularly exploited for meticulous studying of complex surface interactions at a molecular orbital scale. However, DFT calculations usually yield inaccurate thermodynamics results that contradict experimental findings. A clear example is the CO adsorption puzzle caused by the wrong estimation of adsorption sites, especially for the (111) transition metal surfaces. The puzzle is still not fully resolved and a complete adsorption picture is yet to be reported. Herein, we demonstrate the reliability of DFT calculations for the study of local bond properties, despite the wrong energetics predictions. We also highlight the importance of considering a comprehensive analysis of all the possible adsorption sites over distinctive surface facets. Each surface facet, with its unique arrangement of atoms, results in a varying adsorbate behavior, although the same adsorption site is studied. Investigating these variations gives insights about the influence of surface atomic arrangement on the orbitals' interactions. Within the investigation, it is found that the varying density of orbitals, with the matching symmetry for interaction at different adsorption sites, affects the magnitude of orbital interaction, and thus, acts as an additional factor for determining the site preference. Based on the frontier (5σ and 2π*) orbital energy description, calculated using RPBE functional, new perceptions to the understanding of the adsorption puzzle have been exposed. In addition, we emphasize the significance of considering a holistic analysis of adsorbate orbitals, not only limited to the main CO frontier orbitals. This approach leads to a better understanding of the surface bonding and CO final structure. This investigation can help in providing guidelines for innovating design principles for materials, based on the required adsorbate behavior and charge transport phenomena, to be used for catalysis and sensors applications.

Department

Physics Department

Degree Name

MS in Physics

Date of Award

2-1-2019

Online Submission Date

September 2018

First Advisor

Allam, Nageh

Committee Member 1

Elshakre, Mohamed

Committee Member 2

Awad, Adel

Document Type

Thesis

Extent

127 p.

Rights

The author retains all rights with regard to copyright. The author certifies that written permission from the owner(s) of third-party copyrighted matter included in the thesis, dissertation, paper, or record of study has been obtained. The author further certifies that IRB approval has been obtained for this thesis, or that IRB approval is not necessary for this thesis. Insofar as this thesis, dissertation, paper, or record of study is an educational record as defined in the Family Educational Rights and Privacy Act (FERPA) (20 USC 1232g), the author has granted consent to disclosure of it to anyone who requests a copy.

IRB

Not necessary for this item

Comments

This work would have never been presented before the reader without the support and funding I was given by the American University in Cairo, which provided the educational and research atmospheres required for excelling in the field of physics. I am grateful for the great professors who assisted in building the necessary theoretical knowledge that constitutes the foundation of a genuine scientist. On the research side, I am sincerely grateful for working with a top-quality professor like Prof. Nageh Allam, as my thesis advisor. From day one, he provided guidance with sincere care, while building strong work ethics and research skills. Dr. Nageh’s availability never ceased to stop 24 hours and throughout the whole week including weekends and holidays; indeed, he is a one pronounced example for dedication and devotion for science and research, and for building a powerful research generation of successful leaders who can survive and even excel in their fields at the most harsh and stressful environments. I would also like to acknowledge the generous support I received from Prof. Mohammad Shakre, who provided valuable and meticulous comments on my thesis work within a very short period of time. I would also like to acknowledge the support I got from my team-mates at the Energy Materials Laboratory (EML). I am particularly grateful for having the chance to collaborate with the theoretical sub-group of the EML in the learning and publishing processes. Moreover, I would like to express my sincere gratitude to my cheering wife (Nadine) for her loving support. Finally, I would like to express my gratefulness for my family, particularly my father, who implanted the love of science in me and to whom I appreciatively dedicate this work.

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