Characterization of Heterojunctions via X-Ray and UV Photoemission Spectroscopy: Energy Level Implications for Single and Mixed Monolayer SAMs, CdSe Nanoparticle Films, and Organic Semiconductor Depositions.

Persistent Link:
http://hdl.handle.net/10150/195913
Title:
Characterization of Heterojunctions via X-Ray and UV Photoemission Spectroscopy: Energy Level Implications for Single and Mixed Monolayer SAMs, CdSe Nanoparticle Films, and Organic Semiconductor Depositions.
Author:
Graham, Amy L.
Issue Date:
2010
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:
This work has centered on the interface dipoles arising at heterojunctions between metals, semiconductor nanoparticles, self-assembled monolayers, and organic semiconductor materials. Alkanethiol self-assembled monolayers, CdSe nanocrystals, and the organic semiconductors zinc phthalocyanine (ZnPc) and Buckminster fullerene (C60) were the basis of these investigations. UV photoemission spectroscopy has proven to be an invaluable tool to observe the vacuum level shifts for these analyses while using XPS to corroborate surface structure. With a full evaluation of these surfaces, the shifts in the vacuum level, valence ionizations, and core ionizations, the impact of these interfaces, as well as their influence on the subsequent deposition of organic semiconductor layers is established.Alkanethiols possessing varying dipole moments were examined on gold and silver substrates. The viability of these alkanethiols was demonstrated to predictively adjust the work function of these metals as a function of their intrinsic dipole moments projected to surface normal, and established differences between Ag--S and Au--S bonds. The capability of the SAMs to modify the work function of gold provided an opportunity for mixed monolayers of the alkanethiols to produce a precise range of work functions by minimal adjustments of solution concentration, which were examined with a simple point dipole model.Photoemission spectroscopy offers a thorough analysis of CdSe nanoparticle films. Despite a plethora of research on these nanocrystals, there still is controversy on the magnitude of the shift in the valence band with diameter. In our research we found the majority of the valence band shift could be attributed to the interface dipole, ignored previously. Meanwhile, the valence band tethered films was obscured by the sulfur of the thiol tether.Finally, organic semiconductor layers deposited on SAMs on gold exhibited various interface dipole effects at these heterojunctions. Charge transfer states of ZnPc did not favor energy level alignment on the SAM/Au substrates used; C60 demonstrated vacuum level shifts on C15 and C12ph alkanethiol monolayers consistent with the interface charge transfer (ICT) model. These results provide credibility to models recently demonstrated in the literature for other passivated metal surfaces, and include the viability of SAMs in these discussions.
Type:
text; Electronic Dissertation
Keywords:
interface dipole; nanocrystals; photoemission spectroscopy; self-assembled monolayers
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Armstrong, Neal R.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleCharacterization of Heterojunctions via X-Ray and UV Photoemission Spectroscopy: Energy Level Implications for Single and Mixed Monolayer SAMs, CdSe Nanoparticle Films, and Organic Semiconductor Depositions.en_US
dc.creatorGraham, Amy L.en_US
dc.contributor.authorGraham, Amy L.en_US
dc.date.issued2010en_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.abstractThis work has centered on the interface dipoles arising at heterojunctions between metals, semiconductor nanoparticles, self-assembled monolayers, and organic semiconductor materials. Alkanethiol self-assembled monolayers, CdSe nanocrystals, and the organic semiconductors zinc phthalocyanine (ZnPc) and Buckminster fullerene (C60) were the basis of these investigations. UV photoemission spectroscopy has proven to be an invaluable tool to observe the vacuum level shifts for these analyses while using XPS to corroborate surface structure. With a full evaluation of these surfaces, the shifts in the vacuum level, valence ionizations, and core ionizations, the impact of these interfaces, as well as their influence on the subsequent deposition of organic semiconductor layers is established.Alkanethiols possessing varying dipole moments were examined on gold and silver substrates. The viability of these alkanethiols was demonstrated to predictively adjust the work function of these metals as a function of their intrinsic dipole moments projected to surface normal, and established differences between Ag--S and Au--S bonds. The capability of the SAMs to modify the work function of gold provided an opportunity for mixed monolayers of the alkanethiols to produce a precise range of work functions by minimal adjustments of solution concentration, which were examined with a simple point dipole model.Photoemission spectroscopy offers a thorough analysis of CdSe nanoparticle films. Despite a plethora of research on these nanocrystals, there still is controversy on the magnitude of the shift in the valence band with diameter. In our research we found the majority of the valence band shift could be attributed to the interface dipole, ignored previously. Meanwhile, the valence band tethered films was obscured by the sulfur of the thiol tether.Finally, organic semiconductor layers deposited on SAMs on gold exhibited various interface dipole effects at these heterojunctions. Charge transfer states of ZnPc did not favor energy level alignment on the SAM/Au substrates used; C60 demonstrated vacuum level shifts on C15 and C12ph alkanethiol monolayers consistent with the interface charge transfer (ICT) model. These results provide credibility to models recently demonstrated in the literature for other passivated metal surfaces, and include the viability of SAMs in these discussions.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectinterface dipoleen_US
dc.subjectnanocrystalsen_US
dc.subjectphotoemission spectroscopyen_US
dc.subjectself-assembled monolayersen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairArmstrong, Neal R.en_US
dc.contributor.committeememberArmstrong, Neal R.en_US
dc.contributor.committeememberPemberton, Jeanne E.en_US
dc.contributor.committeememberSaavedra, Scotten_US
dc.contributor.committeememberMcGrath, Dominicen_US
dc.identifier.proquest11298en_US
dc.identifier.oclc752261144en_US
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