Fabrication, analysis and patterning of sol-gel based silica ultrathin films

Persistent Link:
http://hdl.handle.net/10150/280795
Title:
Fabrication, analysis and patterning of sol-gel based silica ultrathin films
Author:
Robertson, Joseph William F.
Issue Date:
2004
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:
A novel approach to sol-gel thin film fabrication has been developed which leads to the production of ultrathin ∼2 nm to 100 nm thick silica and conductively-doped silica films on metal and semiconductor substrates. The research described herein focuses on the development, characterization and potential application of these thin films in current technology. These ultrathin films were fabricated by a sol-gel procedure, which utilized highly diluted silica precursor compounds. The [H₂O]:[Si] ratio ranged from 50 to 1000, far above the typical values (4-10) used in sol-gel film preparation. This dilution leads to highly densified silica when spin-cast onto an appropriately compatible surface. The surface examined included Si(111)/SiO₂; ITO; and 3-(mercaptopropyl)trimethoxysilane (3MPT) modified Au and Ag. These surfaces must act as wetting control agents for the sol-gel precursor, while simultaneously providing adhesion to the nm sized sol-gel aggregates. The 3MPT-Ag monolayer was examined in detail by Tl, Pb and Cd underpotential deposition electrochemistry, to understand the interfacial structure of the molecule. These results show that the 3MPT monolayer is very stable to outside influences (i.e. Tl and Pb reversibly deposit monolayers at the metal surface). The UPD of metal ions is highly size dependent with Tl depositing with fewer kinetic limitations than Pb and Cd not depositing at all. Raman spectral characterization shows that 3MPT undergoes some reversible rearrangement during the UPD process. The electronic properties of the pure silica films were examined in great detail. The results suggested that in solution, a solvated gel layer at the film-solution interface gives rise to an anomalously low capacitance <100 pF/cm², which has no comparison in the current literature. In the dry state, these silica films have a dielectric constant of ε = 3.5, which is close to that of thermally-grown silica on silicon (3.9). These films were doped with 1,1'-bistriethoxysilylferrocene, an electrochemically-active sol-gel material. The results suggest that under the proper precursor solution conditions, thin ( <10 nm), uniform films can be fabricated. By simply adjusting the ratio of the ferrocene moiety in solution, the film composition can be adjusted. XPS verifies that the atom ratio in solution is near to the observed atom ratio in the films, with some indication of surface segregation of the ferrocene moiety. Electrochemical analysis of these films suggests that electron hopping between the ferrocene centers drives the electrochemical response only when there are pinhole defects, to support counterion conduction to the surface. (Abstract shortened by UMI.)
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Chemistry, Analytical.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Pemberton, Jeanne

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleFabrication, analysis and patterning of sol-gel based silica ultrathin filmsen_US
dc.creatorRobertson, Joseph William F.en_US
dc.contributor.authorRobertson, Joseph William F.en_US
dc.date.issued2004en_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.abstractA novel approach to sol-gel thin film fabrication has been developed which leads to the production of ultrathin ∼2 nm to 100 nm thick silica and conductively-doped silica films on metal and semiconductor substrates. The research described herein focuses on the development, characterization and potential application of these thin films in current technology. These ultrathin films were fabricated by a sol-gel procedure, which utilized highly diluted silica precursor compounds. The [H₂O]:[Si] ratio ranged from 50 to 1000, far above the typical values (4-10) used in sol-gel film preparation. This dilution leads to highly densified silica when spin-cast onto an appropriately compatible surface. The surface examined included Si(111)/SiO₂; ITO; and 3-(mercaptopropyl)trimethoxysilane (3MPT) modified Au and Ag. These surfaces must act as wetting control agents for the sol-gel precursor, while simultaneously providing adhesion to the nm sized sol-gel aggregates. The 3MPT-Ag monolayer was examined in detail by Tl, Pb and Cd underpotential deposition electrochemistry, to understand the interfacial structure of the molecule. These results show that the 3MPT monolayer is very stable to outside influences (i.e. Tl and Pb reversibly deposit monolayers at the metal surface). The UPD of metal ions is highly size dependent with Tl depositing with fewer kinetic limitations than Pb and Cd not depositing at all. Raman spectral characterization shows that 3MPT undergoes some reversible rearrangement during the UPD process. The electronic properties of the pure silica films were examined in great detail. The results suggested that in solution, a solvated gel layer at the film-solution interface gives rise to an anomalously low capacitance <100 pF/cm², which has no comparison in the current literature. In the dry state, these silica films have a dielectric constant of ε = 3.5, which is close to that of thermally-grown silica on silicon (3.9). These films were doped with 1,1'-bistriethoxysilylferrocene, an electrochemically-active sol-gel material. The results suggest that under the proper precursor solution conditions, thin ( <10 nm), uniform films can be fabricated. By simply adjusting the ratio of the ferrocene moiety in solution, the film composition can be adjusted. XPS verifies that the atom ratio in solution is near to the observed atom ratio in the films, with some indication of surface segregation of the ferrocene moiety. Electrochemical analysis of these films suggests that electron hopping between the ferrocene centers drives the electrochemical response only when there are pinhole defects, to support counterion conduction to the surface. (Abstract shortened by UMI.)en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectChemistry, Analytical.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorPemberton, Jeanneen_US
dc.identifier.proquest3165794en_US
dc.identifier.bibrecord.b47210424en_US
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