Persistent Link:
http://hdl.handle.net/10150/194860
Title:
LOCAL ELECTRONIC PROPERTIES OF ORGANIC SEMICONDUCTOR INTERFACES
Author:
Blumenfeld, Michael Lewis
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:
Understanding organic semiconductor interfaces is critical to developing organic photovoltaics (OPV). OPV interfaces are disordered due to weak intermolecular interactions, resulting in diverse charge transfer micro-environments. I present experimental data isolating high-order intermolecular interactions controlling interfacial energy level alignment and describe new instrumental capabilities providing access to the local electronic and kinetic landscape at organic semiconductor interfaces. Interface formation between vanadyl naphthalocyanine (VONc) and highly ordered pyrolytic graphite (HOPG) is investigated. Ultraviolet photoemission spectroscopy (UPS) shows that the VONc binding energy (BE) decouples from the work function, shifting in an opposite direction and contradicting the standard interface dipole model. This effect is quantitatively described using an electrostatic depolarization model and confirmed by simulations which show an inhomogeneous potential at the interface. New data and literature values suggest orthogonality between polarizability and molecular dipole in polar porphyrazines. Their potential for interface engineering is discussed. The electron-rich Au(111)/VONc interface is investigated. The organic layer induces a large interface dipole in Au(111) which can be fit to a depolarization model. Ionization potential and depolarization data suggest that the second VONc layer on Au(111) adopts a tilted geometry. Electrostatic differences between Au(111)/VONc and HOPG/VONc are discussed, demonstrating that interface dipole contributions are not interchangeable. The surface states of the Au(111)/VONc interface are characterized by angle resolved 2-photon photoemission to determine the magnitude of the perturbation. The measured free-electron-like effective mass and BE destabilization of the Shockley state is attributed to step edges caused by lifting the Au(111) (22 x √3) reconstruction. The Shockley state is accessible primarily through resonance with the n = 1 image state. Another resonance between the image state and a molecular state of VONc is tentatively identified. Design and construction of a confocal fluorescence microscope capable of single molecule detection in ultrahigh vacuum is described. Initial images and fluorescence trajectories demonstrate the ability to measure charge transfer kinetics between an individual organic semiconductor molecule and well-characterized insulating surfaces. Progress towards completion of a scanning photoionization microscope is presented. The microscope demonstrates diffraction-limited imaging capabilities using fs-laser-generated photoelectron current as contrast. Recommendations are given towards achieving spectral resolution and for future experimental systems.
Type:
text; Electronic Dissertation
Keywords:
charge transfer; microscopy; photoelectron spectroscopy; photovoltaics; polarizability; thin films
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Monti, Oliver L. A.
Committee Chair:
Monti, Oliver L. A.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleLOCAL ELECTRONIC PROPERTIES OF ORGANIC SEMICONDUCTOR INTERFACESen_US
dc.creatorBlumenfeld, Michael Lewisen_US
dc.contributor.authorBlumenfeld, Michael Lewisen_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.abstractUnderstanding organic semiconductor interfaces is critical to developing organic photovoltaics (OPV). OPV interfaces are disordered due to weak intermolecular interactions, resulting in diverse charge transfer micro-environments. I present experimental data isolating high-order intermolecular interactions controlling interfacial energy level alignment and describe new instrumental capabilities providing access to the local electronic and kinetic landscape at organic semiconductor interfaces. Interface formation between vanadyl naphthalocyanine (VONc) and highly ordered pyrolytic graphite (HOPG) is investigated. Ultraviolet photoemission spectroscopy (UPS) shows that the VONc binding energy (BE) decouples from the work function, shifting in an opposite direction and contradicting the standard interface dipole model. This effect is quantitatively described using an electrostatic depolarization model and confirmed by simulations which show an inhomogeneous potential at the interface. New data and literature values suggest orthogonality between polarizability and molecular dipole in polar porphyrazines. Their potential for interface engineering is discussed. The electron-rich Au(111)/VONc interface is investigated. The organic layer induces a large interface dipole in Au(111) which can be fit to a depolarization model. Ionization potential and depolarization data suggest that the second VONc layer on Au(111) adopts a tilted geometry. Electrostatic differences between Au(111)/VONc and HOPG/VONc are discussed, demonstrating that interface dipole contributions are not interchangeable. The surface states of the Au(111)/VONc interface are characterized by angle resolved 2-photon photoemission to determine the magnitude of the perturbation. The measured free-electron-like effective mass and BE destabilization of the Shockley state is attributed to step edges caused by lifting the Au(111) (22 x √3) reconstruction. The Shockley state is accessible primarily through resonance with the n = 1 image state. Another resonance between the image state and a molecular state of VONc is tentatively identified. Design and construction of a confocal fluorescence microscope capable of single molecule detection in ultrahigh vacuum is described. Initial images and fluorescence trajectories demonstrate the ability to measure charge transfer kinetics between an individual organic semiconductor molecule and well-characterized insulating surfaces. Progress towards completion of a scanning photoionization microscope is presented. The microscope demonstrates diffraction-limited imaging capabilities using fs-laser-generated photoelectron current as contrast. Recommendations are given towards achieving spectral resolution and for future experimental systems.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectcharge transferen_US
dc.subjectmicroscopyen_US
dc.subjectphotoelectron spectroscopyen_US
dc.subjectphotovoltaicsen_US
dc.subjectpolarizabilityen_US
dc.subjectthin filmsen_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.advisorMonti, Oliver L. A.en_US
dc.contributor.chairMonti, Oliver L. A.en_US
dc.contributor.committeememberBrown, Michael F.en_US
dc.contributor.committeememberSanov, Andreien_US
dc.contributor.committeememberCorrales, L. Reneen_US
dc.identifier.proquest11263en_US
All Items in UA Campus Repository are protected by copyright, with all rights reserved, unless otherwise indicated.