Characterization of the Photosensitive Response in Polysilane-based Organic/Inorganic Hybrid Materials

Persistent Link:
http://hdl.handle.net/10150/195442
Title:
Characterization of the Photosensitive Response in Polysilane-based Organic/Inorganic Hybrid Materials
Author:
Chandra, Haripin
Issue Date:
2007
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The motivation for the current work stems from a unique application, i.e. the photopatterning of optical functionality in a photosensitive material immediately prior to use. In this case, optical devices such as diffraction gratings and optical interconnects are produced in thin films using integrated photonic sources under relatively uncontrolled environmental conditions. The compatibility of the material photoexcitation mechanism with wavelength and fluence levels available from compact solid-state optical sources and the need to understand the impact of local atmospheric composition and temperature on the photosensitive material response are therefore of primary concern. The primary goal of the current study was to investigate photoexcitation mechanisms and photoinduced optical and structural changes in promising candidate material systems for this application: polysilane and polygermane-based molecular hybrid polymers. The work pursued the development of a fundamental understanding of the key photophysical and photostructural responses of thin films composed of both pure, linear-chain polysilanes and of a Ge-Si copolymer. The effects of molecular modifications to the polymers, including polymer backbone catenate structure and side-group identity, on the optical and photosensitive behavior observed in these systems are examined. Through such effort, an understanding of how such structural characteristics influence key photosensitive properties, i.e. the excitation wavelength and the resulting photoinduced optical property changes, was attained. A related objective in the present work was to characterize the thermal stability of these hybrid polymers, specifically in terms of the effect of thermal treatment on as-deposited and photomodified materials. In this case, an evaluation of the similarities and differences in structural modification in response to both thermal and optical fields was pursued. The primary mechanism associated with the photoinduced phenomena observed in both polysilane and polygermane involves backbone chain scissioning and the formation of silane-radicals upon absorption of near-UV (λ ≈ 300 to 400 nm) photons, resonant with the lowest energy, σ - σ* (HOMO-LUMO) transition of the Group IVA backbone. The final photoproducts obtained result from a mixture of different competing processes which occur subsequent to this initial photoscissioning. In aerobic atmospheric environments, the radicals formed capture oxygen and form oxide linkages forming the dominant photoproducts. On the other hand, under anaerobic conditions, photooxidation is suppressed while hydride passivation of the radical dominates the response. The oxidized product, resulting from irradiation under the aerobic environment, exhibited higher refractive index changes than irradiation under anaerobic conditions. Photoexcitation using higher energy photons (typically λ ≈ 230 to 300 nm) are resonant with side-group transitions associated with π-conjugated states of the cyclic moieties. Under these conditions, the excitation accesses both these organic side-groups as well as the Group IVA backbone structure. Such excitation conditions resulted in a larger photoinduced structural modification in the irradiated polymer, as observed both in terms of its electronic structure as well as the resulting refractive index change. Thermally induced structural modification to the backbone and side-group moieties were found to be qualitatively similar those produced under optical irradiation. For example, the primary structural changes were again associated with backbone chain scissioning. Photoinduced structural modifications through resonant optical excitation of the material, however, tended to be more focused on the specific structural moieties accessed.
Type:
text; Electronic Dissertation
Keywords:
Polysilane; photosensitive; polysilylene; photoinduced; photopatterning
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Materials Science & Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Potter, Barrett G.; Potter, Kelly S.
Committee Chair:
Potter, Barrett G.

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleCharacterization of the Photosensitive Response in Polysilane-based Organic/Inorganic Hybrid Materialsen_US
dc.creatorChandra, Haripinen_US
dc.contributor.authorChandra, Haripinen_US
dc.date.issued2007en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe motivation for the current work stems from a unique application, i.e. the photopatterning of optical functionality in a photosensitive material immediately prior to use. In this case, optical devices such as diffraction gratings and optical interconnects are produced in thin films using integrated photonic sources under relatively uncontrolled environmental conditions. The compatibility of the material photoexcitation mechanism with wavelength and fluence levels available from compact solid-state optical sources and the need to understand the impact of local atmospheric composition and temperature on the photosensitive material response are therefore of primary concern. The primary goal of the current study was to investigate photoexcitation mechanisms and photoinduced optical and structural changes in promising candidate material systems for this application: polysilane and polygermane-based molecular hybrid polymers. The work pursued the development of a fundamental understanding of the key photophysical and photostructural responses of thin films composed of both pure, linear-chain polysilanes and of a Ge-Si copolymer. The effects of molecular modifications to the polymers, including polymer backbone catenate structure and side-group identity, on the optical and photosensitive behavior observed in these systems are examined. Through such effort, an understanding of how such structural characteristics influence key photosensitive properties, i.e. the excitation wavelength and the resulting photoinduced optical property changes, was attained. A related objective in the present work was to characterize the thermal stability of these hybrid polymers, specifically in terms of the effect of thermal treatment on as-deposited and photomodified materials. In this case, an evaluation of the similarities and differences in structural modification in response to both thermal and optical fields was pursued. The primary mechanism associated with the photoinduced phenomena observed in both polysilane and polygermane involves backbone chain scissioning and the formation of silane-radicals upon absorption of near-UV (λ ≈ 300 to 400 nm) photons, resonant with the lowest energy, σ - σ* (HOMO-LUMO) transition of the Group IVA backbone. The final photoproducts obtained result from a mixture of different competing processes which occur subsequent to this initial photoscissioning. In aerobic atmospheric environments, the radicals formed capture oxygen and form oxide linkages forming the dominant photoproducts. On the other hand, under anaerobic conditions, photooxidation is suppressed while hydride passivation of the radical dominates the response. The oxidized product, resulting from irradiation under the aerobic environment, exhibited higher refractive index changes than irradiation under anaerobic conditions. Photoexcitation using higher energy photons (typically λ ≈ 230 to 300 nm) are resonant with side-group transitions associated with π-conjugated states of the cyclic moieties. Under these conditions, the excitation accesses both these organic side-groups as well as the Group IVA backbone structure. Such excitation conditions resulted in a larger photoinduced structural modification in the irradiated polymer, as observed both in terms of its electronic structure as well as the resulting refractive index change. Thermally induced structural modification to the backbone and side-group moieties were found to be qualitatively similar those produced under optical irradiation. For example, the primary structural changes were again associated with backbone chain scissioning. Photoinduced structural modifications through resonant optical excitation of the material, however, tended to be more focused on the specific structural moieties accessed.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectPolysilaneen_US
dc.subjectphotosensitiveen_US
dc.subjectpolysilyleneen_US
dc.subjectphotoinduceden_US
dc.subjectphotopatterningen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineMaterials Science & Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorPotter, Barrett G.en_US
dc.contributor.advisorPotter, Kelly S.en_US
dc.contributor.chairPotter, Barrett G.en_US
dc.contributor.committeememberLucas, Pierreen_US
dc.contributor.committeememberPotter, Kelly S.en_US
dc.contributor.committeememberDeymier, Pierre A.en_US
dc.identifier.proquest2499en_US
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