Elucidating the Growth Kinetics of Hybrid Molecular Beam Epitaxy: An Experimental and Computational Approach
Restricted (Penn State Only)
- Author:
- Fazlioglu Yalcin, Benazir
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 22, 2023
- Committee Members:
- John Mauro, Program Head/Chair
Venkatraman Gopalan, Major Field Member
Sahin Ozdemir, Outside Unit & Field Member
Roman Engel-Herbert, Special Member
Jon-Paul Maria, Major Field Member
Adri van Duin, Chair & Dissertation Advisor - Keywords:
- hybrid molecular beam epitaxy
thin films
oxide
ReaxFF
metal organics
thermogravimetric analysis
chalcogenide - Abstract:
- Since their discovery, thin films have attracted tremendous attention due to their wide range of application areas. The advancements in thin films and thin film growth allow for the study of various electronic phenomena, including transport properties, magnetic ground states, and structural polarization-linked states such as piezoelectricity, pyroelectricity, and ferroelectricity. The remarkable surge in thin film development is expected to persist, given their pivotal role in driving technological progress. However, achieving high-quality and defect-free thin films, which is essential to unlock the full potential of these materials, remains a challenge, despite the utilization of a wide range of growth techniques. This need for better-quality thin films has driven scientists to explore new growth strategies and study ways to improve thin film growth in general. Here, hybrid Molecular Beam Epitaxy stands out as the strategy that has been shown to provide superior control over cation stoichiometry and thus produce higher-quality materials. The primary aim of this dissertation is to uncover ways to enhance the quality of thin films, specifically focusing on BaTiO3 and SrTiO3. Although these materials have been extensively studied, there is still much to discover to fully exploit their potential. As described in this dissertation, 45 nm thick BaTiO3 thin films grown through hybrid molecular beam epitaxy have shown promising optical constants (refractive index= 2.42 and extinction coefficient=0.056) resembling bulk-like BaTiO3. To gain further insights into the decomposition patterns of the metal-organic substance, titanium(IV) isopropoxide, used in growing titanate perovskite structures (BaTiO3, SrTiO3) via hybrid molecular beam epitaxy systems, reactive force field molecular dynamics simulations were employed. Reaction pathways were extracted, and ways to facilitate the decomposition of titanium(IV) isopropoxide molecules were investigated, along with bond energies to determine the rates ratios of bond dissociation reactions. Additionally, titanium(IV) isopropoxide molecules were simulated on SrTiO3 surfaces in a reactive force field simulation environment to study hybrid molecular beam epitaxy growth kinetics on an atomic scale for the first time. In addition, thermogravimetric analysis was performed on metal-organic substances that have been and can potentially be used in thin film growth. Using benzoic acid as a calibration standard, vapor pressure curves were extracted from thermogravimetric measurements using the Langmuir equation. The resulting data was used to discuss the suitability of these metal-organic precursors in chemical vapor deposition-based thin film growth approaches in general, and hybrid molecular beam epitaxy in particular.