Tatiana Savicheva
M.S. FinalMar 26, 2026, 7:00 pm - 8:30 pm
Teams
Effect of Annealing under Ambient and High-Humidity Conditions on the Structural and Optical Properties of a-GeO₂ and 44% a-Ti:GeO₂ Thin-Film Coatings.
Abstract: Amorphous GeO₂ and Ti-Ge-O thin films are promising high-index materials for low-loss optical coatings in gravitational wave detectors and high-power lasers, but their annealing response remains not fully understood due to uncontrolled atmospheric conditions. This thesis goal is to investigate how humidity during annealing affects their structural stability, chemical bonding, and surface morphology, addressing a critical gap in amorphous oxide thin film processing.
Ion-beam sputtered GeO₂, Ti-doped GeO₂, SiO₂, Al₂O₃ and multilayer stacks thin films were annealed at 600°C for 10 hours in controlled ambient air and high-humidity annealing environments. Transformations were characterized using powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), and Nomarski optical microscopy.
Key findings reveal humidity as a dominant factor controlling GeO₂ evolution. PXRD showed pure GeO₂ films crystallized earlier under high humidity, exhibiting peak at 2θ ≈ 26.5° after 600°C for 10h annealing while remaining amorphous in the ambient air. FT-IR confirmed water incorporation through enhanced O-H stretching (3000-3700 cm⁻¹) and H-O-H bending (∼1630 cm⁻¹) bands as well as Ge-O network reorganization. Nomarski microscopy revealed stress-induced micro-cracking and bubbling in high humidity annealed GeO₂, while Ti-doped films remained amorphous at 600°C even under high humidity annealing, demonstrating titanium's network-stabilizing effect. SiO₂ and Al₂O₃ exhibited superior moisture resistance. Multilayer coating stacks showed behavior dependent on their materials: structures containing GeO₂ layers showed sensitivity to humid annealing, while stacks incorporating TiO2 demonstrated improved stability.
These results demonstrate that water vapor as a critical parameter lowering GeO₂ crystallization temperature while Ti doping enhances amorphous stability. Humidity-driven effects previously overlooked in "ambient air" annealing studies explain lack of exact irreproducibility in GeO2-based oxide processing and necessitate controlled atmospheres for reproducible low-loss coatings. Future work includes high-resolution PXRD, ellipsometry, X-Ray Photoelectron Spectroscopy and multilayer stability tests to optimize processing protocols.
Ion-beam sputtered GeO₂, Ti-doped GeO₂, SiO₂, Al₂O₃ and multilayer stacks thin films were annealed at 600°C for 10 hours in controlled ambient air and high-humidity annealing environments. Transformations were characterized using powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), and Nomarski optical microscopy.
Key findings reveal humidity as a dominant factor controlling GeO₂ evolution. PXRD showed pure GeO₂ films crystallized earlier under high humidity, exhibiting peak at 2θ ≈ 26.5° after 600°C for 10h annealing while remaining amorphous in the ambient air. FT-IR confirmed water incorporation through enhanced O-H stretching (3000-3700 cm⁻¹) and H-O-H bending (∼1630 cm⁻¹) bands as well as Ge-O network reorganization. Nomarski microscopy revealed stress-induced micro-cracking and bubbling in high humidity annealed GeO₂, while Ti-doped films remained amorphous at 600°C even under high humidity annealing, demonstrating titanium's network-stabilizing effect. SiO₂ and Al₂O₃ exhibited superior moisture resistance. Multilayer coating stacks showed behavior dependent on their materials: structures containing GeO₂ layers showed sensitivity to humid annealing, while stacks incorporating TiO2 demonstrated improved stability.
These results demonstrate that water vapor as a critical parameter lowering GeO₂ crystallization temperature while Ti doping enhances amorphous stability. Humidity-driven effects previously overlooked in "ambient air" annealing studies explain lack of exact irreproducibility in GeO2-based oxide processing and necessitate controlled atmospheres for reproducible low-loss coatings. Future work includes high-resolution PXRD, ellipsometry, X-Ray Photoelectron Spectroscopy and multilayer stability tests to optimize processing protocols.
Adviser: Carmen Menoni
Co-Adviser: None
Non-ECE Member: Justin Sambur, CHEM
Member 3: Jesse Wilson, ECE
Addional Members: Jorge Rocca, ECE
Co-Adviser: None
Non-ECE Member: Justin Sambur, CHEM
Member 3: Jesse Wilson, ECE
Addional Members: Jorge Rocca, ECE
Publications:
Savicheva T., Davenport A., Rodriguez R., Menoni C. " Crystallization behavior of a-GeO2 and a-44ToGeO/SiO2 coatings annealed in air with different humidity levels.", LVK Meeting, 2025
Savicheva T., Davenport A., Rodriguez R., Menoni C. " Crystallization behavior of a-GeO2 and a-44ToGeO/SiO2 coatings annealed in air with different humidity levels.", LVK Meeting, 2025
Program of Study:
ECE 404
ECE 441
ECE 502
ECE 504
ECE 574
ECE 673
ECE 699
CHEM 550A
ECE 404
ECE 441
ECE 502
ECE 504
ECE 574
ECE 673
ECE 699
CHEM 550A