Author ORCID Identifier:
Date of Graduation
7-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Physics (PhD)
Degree Level
Graduate
Department
Physics
Advisor/Mentor
Salamo, Gregory
Committee Member
Paillard, Charles
Second Committee Member
Manasreh, Bothina
Third Committee Member
Nakamura, Hiro
Fourth Committee Member
Bellaiche, Laurent
Keywords
2D material; DFT; GaSe SnSe GeSe; MBE
Abstract
The controlled synthesis of low-dimensional chalcogenide semiconductors is essential for realizing next-generation optoelectronic and quantum materials in which electronic coherence, interfacial coupling, and symmetry-dependent properties can be engineered at the atomic scale. This dissertation investigates the growth physics, interfacial energetics, and structural evolution of layered GaSe and SnSe synthesized by molecular beam epitaxy (MBE) on three-dimensional substrates, together with the phase stability and growth limitations of Ge–Se compounds. By combining real-time surface diffraction with comprehensive structural, optical, and first-principles analysis, this work establishes fundamental relationships between substrate symmetry, interfacial bonding, and emergent functional behavior in epitaxial chalcogenide heterostructures. For GaSe, systematic control of GaAs surface preparation reveals that the nature of interfacial bonding governs the selection of growth orientation and morphology. Oxide-free surfaces promote chemically bonded, tilted van der Waals planes aligned with substrate dangling bonds, while oxide-terminated interfaces favor c-axis growth and spiral nucleation driven by heterogeneous surface energetics. These findings resolve previously conflicting reports on GaSe epitaxy and demonstrate how interfacial symmetry and surface topology dictate two-dimensional growth pathways on three-dimensional substrates. In ultrathin SnSe films grown on MgO, thickness-dependent symmetry evolution profoundly influences structural ordering and optical transitions. Real-time diffraction measurements reveal the formation of rotational domains during the earliest stages of growth, reflecting the symmetry mismatch between orthorhombic SnSe and the cubic MgO substrate. Subsequent strain relaxation and symmetry breaking give rise to optical responses distinct from bulk SnSe, highlighting the role of epitaxial confinement in modifying the electronic structure and nonlinear optical selection rules. Complementary density functional theory calculations of the Ge-Se system demonstrate that, unlike SnSe, the absence of a thermodynamically and dynamically accessible chalcogen-rich interfacial precursor may contribute to a higher nucleation barrier for GeSe. Convex-hull and phonon analyses reveal that layered GeSe₂ analogues are energetically unfavorable, while low-dimensional tetrahedral configurations are dynamically stable but structurally incompatible with coherent epitaxial film formation. These results provide a plausible thermodynamic explanation for the experimentally observed difficulty in achieving GeSe growth under MBE conditions. Collectively, this work establishes a unified framework linking interfacial chemistry, crystallographic symmetry, and phase stability in layered chalcogenide epitaxy. The insights developed here advance the fundamental understanding of two-dimensional material integration on conventional substrates and provide guiding principles for the design of engineered heterostructures with tailored structural and optical functionality.
Citation
Sheibani, A. (2026). Investigating the Role of the Substrate/Film Interface on the Growth of Layered Chalcogenide Thin Films. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6431
