Thèses sur le sujet « Electrodic surfaces »
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Lau, Chi Hian. « Chemical, electronic and electrochemical properties of diamond thin films ». Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:53a0886c-14ad-431a-975d-0ecca8fc8968.
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Diamond is of interest as an advanced functional material, since the extreme physical properties of diamond, suggests it is ideally suited to a range of new demanding applications. In this context, the thesis explores basic surface chemical properties of diamond thin films, along with electrochemical, electronic and electron emission processes involving this material. New experiments are reported concerning the nature of surface conductivity on diamond. Measurements clearly show that the conductivity only arises if a hydrogenated diamond surface is exposed to water vapour, in the presence of chemical species capable of acting as electron acceptors. The conduction properties of surface conductive diamond in aqueous solution are also studied, and the first detailed electrochemical investigations of this material are described. Comparative electrochemical studies of nanocrystalline and boron-doped diamond have been performed. Investigations of electrode stability, and the accessible "potential window" are described, as well as the behaviour of a range of 'redox' systems, including transition metal complexes, metal deposition/stripping, and bio-related organic species. Significant differences between the behaviour of nanodiamond and microcrystalline boron-doped material are observed. A range of surface chemical and threshold photoemission studies of diamond thin films are reported. The results indicate that quantum photoyields (QPYs) are insensitive to the diamond "quality", although the wavelength selectivity is dependent on it. The adsorption of oxygen strongly reduces the QPY, although this only occurs slowly in the presence of O2 because of a low reactive sticking probability. Much more rapid uptake of oxygen and consequent reduction of photoyield is observed in the presence of atomic O or electronically excited dioxygen O2*. The presence of alkali metals on the diamond surface increases the QPY, and reduces the sensitivity of the QPY to surface oxygen. Significant differences between the surface chemical properties of Li, and other adsorbed akali metals (K and Cs) are observed.
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Akinbulu, Isaac Adebayo. « Surface properties and electrocatalytic applications of metallophthalocyanines confined on electrode surfaces ». Thesis, Rhodes University, 2011. http://hdl.handle.net/10962/d1005030.
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New cobalt (13, 16 19 and 22), manganese (14, 17, 20 and 23) and iron (15, 18, 21 and 24)phthalocyanine complexes were synthesized and characterized. The UV-Vis spectral properties of the complexes were typical of the nature of central metal and position of substituent on the Pc ligand. Their electrochemical behaviors were signatures of the central metals, with varying influences of the nature and position of substituents. Nanocomposite of complex 18 and single walled carbon nanotubes (SWCNTs) (SWCNT-18)was fabricated. Formation of this nano-composite was confirmed by infrared (IR)spectroscopy, X-ray diffraction (XRD) spectroscopy and transmission electron microscopy (TEM). Self-assembled monolayers (SAMs) of SWCNT-18, complexes 13-15, and 20 were electropolymerized on glassy carbon electrodes (GCE). Complex 14 was also electrodeposited on GCE. Surface properties of the SAMs were consistent with the molecular feature of the substituent and the nature of central metal in the adsorbed species, while those of the MnPc modified GCEs were dependent on point of substitution and number of substituent. The SAM-modified gold electrodes were used for the electrocatalytic oxidation of the carbamate insecticide, carbofuran. Amplification of the current signal of the insecticide, at more energetically feasible oxidation potentials, on the SAM-modified gold electrodes, relative to bare gold electrode,justified electrocatalysis. There was enhanced sensitivity (attributed to the presence of SWCNT) of the SWCNT-18-SAM-modified gold electrode towards carbofuran, relative to the signals observed on the other SAMs. Current response of the insecticide,bendiocarb, was also intensified, at more favorable oxidation potentials, on the MnPc (14 and 17) modified GCEs, relative to the response on bare GCE, substantiating electrocatalysis. Also, catalysis of the oxidation of the herbicide, bentazon, was observed on polymeric film of complex 20. The current response of the herbicide on this film was better than that observed on bare GCE. Electrocatalysis of the analytes, on the respective modified electrodes, occurred via closely related mechanisms.
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Wilks, Justin. « Free Radical Chemistries at the Surface of Electronic Materials ». Thesis, University of North Texas, 2010. https://digital.library.unt.edu/ark:/67531/metadc31552/.
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The focus of the following research was to (1) understand the chemistry involved in nitriding an organosilicate glass substrate prior to tantalum deposition, as well as the effect nitrogen incorporation plays on subsequent tantalum deposition and (2) the reduction of a native oxide, the removal of surface contaminants, and the etching of a HgCdTe surface utilizing atomic hydrogen. These studies were investigated utilizing XPS, TEM and AFM. XPS data show that bombardment of an OSG substrate with NH3 and Ar ions results in the removal of carbon species and the incorporation of nitrogen into the surface. Tantalum deposition onto a nitrided OSG surface results in the initial formation of tantalum nitride with continued deposition resulting in the formation of tantalum. This process is a direct method for forming a thin TaN/Ta bilayer for use in micro- and nanoelectronic devices. Exposure to atomic hydrogen is shown to increase the surface roughness of both air exposed and etched samples. XPS results indicate that atomic hydrogen reduces tellurium oxide observed on air exposed samples via first-order kinetics. The removal of surface contaminants is an important step prior to continued device fabrication for optimum device performance. It is shown here that atomic hydrogen effectively removes adsorbed chlorine from the HgCdTe surface.
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Lotfollahi, Ramin. « Electronic structure of surfaces ». Thesis, Örebro University, Institutionen för naturvetenskap Department of Natural Sciences, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-640.
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For an idealized one-dimensional crystal it is possible to have energy levels whose wave functions are localized at the surface. These states are called surface states. There is one surface state for each energy gap between the ordinary allowed bands of energies. These electron states are called Tamm states. This Tamm state has an energy that lies almost at the middle of the energy gap and is mainly localized at the surface atomic layer. The image potential states are generated by a potential well formed by the Coulomb-like image potential barrier. These image states that are also called Shockley states are localized in a slowly decaying tail in the vacuum.
I also studied the lateral (in-plane) motion of electrons confined to terraces between steps on a vicinal Cu (111) surface. The local density of states showed a number of peaks at energies where electrons can occupy new quantum-well states on a step. I also tested the influence of the electron lifetime on the local density of states.
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Xiu, Yonghao. « Fabrication of surface micro- and nanostructures for superhydrophobic surfaces in electric and electronic applications ». Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26641.
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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Hess, Dennis W.; Committee Chair: Wong, C. P.; Committee Member: Breedveld, Victor; Committee Member: Koros, William J.; Committee Member: Meredith, Carson; Committee Member: Nair, Sankar. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Feng, Yongjia. « First principles studies of transition metal surfaces : the effect of an external field on surface electronic properties and surface energetics / ». View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202003%20FENG.
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Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 106-110). Also available in electronic version. Access restricted to campus users.
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Plachinda, Pavel. « Electronic Properties and Structure of Functionalized Graphene ». PDXScholar, 2012. https://pdxscholar.library.pdx.edu/open_access_etds/585.
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The trend over the last 50 years of down-scaling the silicon transistor to achieve faster computations has led to doubling of the number of transistors and computation speed over about every two years. However, this trend cannot be maintained due to the fundamental limitations of silicon as the main material for the semiconducting industry. Therefore, there is an active search for exploration of alternate materials. Among the possible candidates that can may [sic] be able to replace silicon is graphene which has recently gained the most attention. Unique properties of graphene include exceedingly high carrier mobility, tunable band gap, huge optical density of a monolayer, anomalous quantum Hall effect, and many others. To be suitable for microelectronic applications the material should be semiconductive, i.e. have a non-zero band gap. Pristine graphene is a semimetal, but by the virtue of doping the graphene surface with different molecules and radicals a band gap can be opened. Because the electronic properties of all materials are intimately related to their atomic structure, characterization of molecular and electronic structure of functionalizing groups is of high interest. The ab-inito (from the first principles) calculations provide a unique opportunity to study the influence of the dopants and thus allow exploration of the physical phenomena in functionalized graphene structures. This ability paves the road to probe the properties based on the intuitive structural information only. A great advantage of this approach lies in the opportunity for quick screening of various atomic structures. We conducted a series of ab-inito investigations of graphene functionalized with covalently and hapticly bound groups, and demonstrated possible practical usage of functionalized graphene for microelectronic and optical applications. This investigation showed that it is possible [to] produce band gaps in graphene (i.e., produce semiconducting graphene) of about 1 eV, without degrading the carrier mobility. This was archived by considering the influence of those adducts on electronic band structure and conductivity properties.
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Genua, Maria. « Combinatorial surface-based electronic tongue development : Analytical applications and conception of 2D and 3D biomimetic surfaces ». Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENI044/document.
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L'objectif de cette thèse est le développement d'une langue électronique avec une méthode simplifiée d'obtention de récepteurs à réactivité croisée. Ces récepteurs sont préparés par une approche combinatoire novatrice qui consiste au mélange et à l'auto-assemblage de deux disaccharides. Le couplage de ces récepteurs avec un système de détection d'imagerie par résonance des plasmons de surface nous a permis de réaliser une langue électronique capable de différencier des échantillons de différentes complexités, y compris des protéines pures et des mélanges complexes. Cela se fait grâce aux profils et images d'évolution continue, assimilés à des « empreintes digitales » des échantillons. D'un autre côté, ce système peut être utilisé en tant qu'outil pour la conception de surfaces biomimétiques 2D et 3D. Ce système est prometteur pour l'étude des interactions sucre-protéine et pour la préparation de nanovecteurs biomimétiques qui ciblent de façon spécifique des protéines d'intérêtL'objectif de cette thèse est le développement d'une langue électronique avec une méthode simplifiée d'obtention de récepteurs à réactivité croisée. Ces récepteurs sont préparés par une approche combinatoire novatrice qui consiste au mélange et à l'auto-assemblage de deux disaccharides. Le couplage de ces récepteurs avec un système de détection d'imagerie par résonance des plasmons de surface nous a permis de réaliser une langue électronique capable de différencier des échantillons de différentes complexités, y compris des protéines pures et des mélanges complexes. Cela se fait grâce aux profils et images d'évolution continue, assimilés à des « empreintes digitales » des échantillons. D'un autre côté, ce système peut être utilisé en tant qu'outil pour la conception de surfaces biomimétiques 2D et 3D. Ce système est prometteur pour l'étude des interactions sucre-protéine et pour la préparation de nanovecteurs biomimétiques qui ciblent de façon spécifique des protéines d'intérêt
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Merrick, Ian. « Embedding at electrode surfaces ». Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/55969/.
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Electronic structure calculations are performed on metal surfaces using an embedding method. Firstly, Cu and Ni surfaces with adsorbates are studied. The O/Cu(00T) reconstruction is investigated, and it is found that atomic displacements increase bonding symmetry and is most likely the cause of reconstruction. The interaction between a single graphitic layer and the Ni(III) substrate is also studied, and it is found that interacting states are formed at Ni band gaps. The remainder of the thesis deals with steps on metal surfaces. First, the jellium model is used to calculate the work function dependence on step density. In the low step density limit, the work function varies linearly with step density. Further calculations are performed on realistic Pd and Pt surfaces. When electric fields are applied, the screening charge of stepped surfaces is mostly located at the step edge. This is explained by the increased fields associated with the edge. Field emission from Pd and Pt surfaces is also studied. It is found that Pd is a better emitter than Pt, owing to work function effects. Transmission is dependent on the surface parallel wavevector and decreases with increasing wavevector. The reduced work function also plays a role at stepped surfaces, although the major influence stems from the reduced local work function at the step site. The low effective potential at the step provides a locally reduced barrier to electron removal. In addition, an increase in transmission is seen from non-zero wavevectors for stepped surfaces. The result is that stepped Pd and Pt surfaces, with a step density of one step in every three (001) unit cells, show field emission increased by a factor of four compared with the flat (001) surfaces.
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Cafe, Peter F. « Towards reliable contacts of molecular electronic devices to gold electrodes ». Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3870.
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SYNOPSIS OF THIS THESIS The aim of this thesis is to more fully understand and explain the binding mechanism of organic molecules to the Au(111) surface and to explore the conduction of such molecules. It consists of five discreet chapters connected to each other by the central theme of “The Single Molecule Device: Conductance and Binding”. There is a deliberate concentration on azine linkers, in particular those with a 1,10-phenanthroline-type bidentate configuration at each end. This linker unit is called a “molecular alligator clip” and is investigated as an alternative to the thiol linker unit more commonly used. Chapter 1 places the work in the broad context of Molecular Electronics and establishes the need for this research. In Chapter 2 the multiple break-junction technique (using a Scanning Tunnelling Microscope or similar device) was used to investigate the conductance of various molecules with azine linkers. A major finding of those experiments is that solvent interactions are a key factor in the conductance signal of particular molecules. Some solvents interfere with the molecule’s interaction with and attachment to the gold electrodes. One indicator of the degree of this interference is the extent of the enhancement or otherwise of the gold quantized conduction peak at 1.0 G0. Below 1.0 G0 a broad range for which the molecule enhances conduction indicates that solvent interactions contribute to a variety of structures which could bridge the electrodes, each with their own specific conductance value. The use of histograms with a Log10 scale for conductance proved useful for observing broad range features. vi Another factor which affects the conductance signal is the geometric alignment of the molecule (or the molecule-solvent structure) to the gold electrode, and the molecular alignment is explored in Chapters 3 for 1,10-phenanthroline (PHEN) and Chapter 4 for thiols. In Chapter 3 STM images, electrochemistry, and Density Functional Theory (DFT) are used to determine 1,10-phenanthroline (PHEN) structures on the Au(111) surface. It is established that PHEN binds in two modes, a physisorbed state and a chemisorbed state. The chemisorbed state is more stable and involves the extraction of gold from the bulk to form adatom-PHEN entities which are highly mobile on the gold surface. Surface pitting is viewed as evidential of the formation of the adatom-molecule entities. DFT calculations in this chapter were performed by Ante Bilic and Jeffery Reimers. The conclusions to Chapter 3 implicate the adatom as a binding mode of thiols to gold and this is explored in Chapter 4 by a timely review of nascent research in the field. The adatom motif is identified as the major binding structure for thiol terminated molecules to gold, using the explanation of surface pitting in Chapter 3 as major evidence and substantiated by emergent literature, both experimental and theoretical. Furthermore, the effect of this binding mode on conductance is explored and structures relevant to the break-junction experiment of Chapter 2 are identified and their conductance values compared. Finally, as a result of researching extensive reports of molecular conductance values, and having attempted the same, a simple method for predicting the conductance of single molecules is presented based upon the tunneling conductance formula.
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Cafe, Peter F. « Towards reliable contacts of molecular electronic devices to gold electrodes ». University of Sydney, 2008. http://hdl.handle.net/2123/3870.
Texte intégralRésumé :
PhDSYNOPSIS OF THIS THESIS The aim of this thesis is to more fully understand and explain the binding mechanism of organic molecules to the Au(111) surface and to explore the conduction of such molecules. It consists of five discreet chapters connected to each other by the central theme of “The Single Molecule Device: Conductance and Binding”. There is a deliberate concentration on azine linkers, in particular those with a 1,10-phenanthroline-type bidentate configuration at each end. This linker unit is called a “molecular alligator clip” and is investigated as an alternative to the thiol linker unit more commonly used. Chapter 1 places the work in the broad context of Molecular Electronics and establishes the need for this research. In Chapter 2 the multiple break-junction technique (using a Scanning Tunnelling Microscope or similar device) was used to investigate the conductance of various molecules with azine linkers. A major finding of those experiments is that solvent interactions are a key factor in the conductance signal of particular molecules. Some solvents interfere with the molecule’s interaction with and attachment to the gold electrodes. One indicator of the degree of this interference is the extent of the enhancement or otherwise of the gold quantized conduction peak at 1.0 G0. Below 1.0 G0 a broad range for which the molecule enhances conduction indicates that solvent interactions contribute to a variety of structures which could bridge the electrodes, each with their own specific conductance value. The use of histograms with a Log10 scale for conductance proved useful for observing broad range features. vi Another factor which affects the conductance signal is the geometric alignment of the molecule (or the molecule-solvent structure) to the gold electrode, and the molecular alignment is explored in Chapters 3 for 1,10-phenanthroline (PHEN) and Chapter 4 for thiols. In Chapter 3 STM images, electrochemistry, and Density Functional Theory (DFT) are used to determine 1,10-phenanthroline (PHEN) structures on the Au(111) surface. It is established that PHEN binds in two modes, a physisorbed state and a chemisorbed state. The chemisorbed state is more stable and involves the extraction of gold from the bulk to form adatom-PHEN entities which are highly mobile on the gold surface. Surface pitting is viewed as evidential of the formation of the adatom-molecule entities. DFT calculations in this chapter were performed by Ante Bilic and Jeffery Reimers. The conclusions to Chapter 3 implicate the adatom as a binding mode of thiols to gold and this is explored in Chapter 4 by a timely review of nascent research in the field. The adatom motif is identified as the major binding structure for thiol terminated molecules to gold, using the explanation of surface pitting in Chapter 3 as major evidence and substantiated by emergent literature, both experimental and theoretical. Furthermore, the effect of this binding mode on conductance is explored and structures relevant to the break-junction experiment of Chapter 2 are identified and their conductance values compared. Finally, as a result of researching extensive reports of molecular conductance values, and having attempted the same, a simple method for predicting the conductance of single molecules is presented based upon the tunneling conductance formula.
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Shpilevaya, Inga. « Surface characterisation and functional properties of modified diamond electrodes ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:55c8243f-3779-4bcc-878a-999a067cc9c4.
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In this work, the use of modified diamond as an electrode material with superlative physical and electrochemical properties was investigated in a number of electrochemical applications. The surface chemistry of three differing forms of diamond, namely boron-doped microcrystalline diamond, boron-doped diamond powder and detonation nanodiamond powder was modified utilising such strategies as hydrogen plasma treatment, reactive ion plasma etching along with various chemical treatments. The surface and functional properties of the modified diamond electrodes were studied using a wide spectrum of techniques. The electrochemical activity of these materials was concomitantly investigated in order to expand the knowledge of diamond electrochemistry and to establish an understanding of how the surface chemistry of these materials impacts their electrochemical performance. In the first study, the nanostructuring strategies of boron-doped diamond surface with platinum nanoparticles were developed. In particular, two types of diamond nanostructures were produced: one consisting of platinum particles located on the top of diamond nanorods, the other with platinum particles located in the bottom of diamond nanopits. For the first time, the experimental evidence proving the mechanism of the diamond nanostructuring process was reported. The electrochemical activity of these nanostructured diamond electrodes with regard to the electrochemical oxidation of glucose and methanol was investigated. In the second study, the relationship between the surface chemistry of three differing forms of diamond, including microcrystalline boron-doped diamond, boron-doped diamond powder as well as detonation nanodiamond powder, and the electrode fouling in the result of the adsorption processes in methyl viologen and anthraquinonedisulfonate solutions was investigated. The influence of two dissimilar surface terminations: hydrophobic H-terminated and hydrophilic O-terminated on the electrode performance was studied in detail. This work provides a useful insight on the likely reasons for the undesirable adsorption occurrence which may be experienced in many electroanalytical applications that utilise solid and powdered forms of diamond. The third project extends the discussion on the study of the diamond electrodes, modified with detonation nanodiamond and boron-doped diamond powders and investigates the electrochemical behaviour of these materials. In this work, charge transport within the diamond powder films, partition coefficients of different redox mediators along with heterogeneous electron transfer constants were identified. The chemical modification of these electrodes with platinum nanoparticles along with the mechanism of nucleation and growth of the latter were studied. The enhanced electrode performance with regard to methanol electrooxidation reaction was demonstrated. The fourth study investigates the preparation of nickel modified boron-doped diamond electrodes and ascertains the relationship between the surface chemistry of the modified diamond and the associated electrocatalytic performance of nickel nanoparticles in hydrogen peroxide and glucose electrooxidation. The fifth study reports on the development of a novel surface functionalization strategy, based on porphyrin and amide coupling chemistry, which allows the creation of hybrid biomimetic diamond interface that was used as the artificial β-alanine receptor.
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Lowe, V. J. « The modification of electrode surfaces ». Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379931.
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Scenev, Vitalij. « Electronic properties of graphene and other carbon-based hybrid materials for flexible electronics ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2014. http://dx.doi.org/10.18452/17069.
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In dieser Arbeit wurden einerseits die elektronischen Eigenschaften von Graphenen und andererseits die Verwendung von Graphenen und Kohlenstoff-basierten Hybridmaterialien als transparente Elektroden untersucht. Entsprechend ist der erste, umfangreichere Teil der Arbeit Grundlagen-orientiert und fokussiert auf die elektrostatische Wechselwirkung zwischen Graphen und dem Substrat Glimmer. Der zweite, kleinere Teil befasst sich mit der Entwicklung leitfähiger Tinten auf der Basis von Graphenen und anderen Kohlenstoff-basierten Hybridmaterialien für Anwendungen in der druckbaren Elektronik, insbesondere für die Herstellung transparenter Elektroden. Graphen auf Glimmer ist ein sehr wohldefiniertes System, in dem das Graphen über mehrere Quadratmikrometer atomar flach ist. Schichtdickenabhängige Variationen des Oberflächenpotentials von einzel- und mehrlagigen Graphenen auf Glimmer wurden mittels Kelvin Probe Rasterkraftmikroskopie untersucht. Damit konnte die elektrostatische Abschirmlänge von Graphen auf Glimmer bestimmt werden. Lokale Variationen des Oberflächenpotentials innerhalb einer Graphenlage, verursacht durch eingeschlossene Wasserschichten zwischen Graphen und Glimmer, wurden mit Rasterkraftmikroskopie, elektrostatischer Rasterkraftmikroskopie und der Raman-Spektroskopie untersucht. Dies ermöglichte es, die Dotierung von Graphen durch eingeschlossene Wasserschichten zu quantifizieren. Außerdem wurde gezeigt, dass Graphen auf molekular modifiziertem Glimmer lokal auf der Nano-Skala dehnbar ist. Dabei wurde der Glimmer durch das Aufbringen von dendronisierten Polymeren verschiedener Generationen auf Nanometer-Skala modifiziert. Dies eröffnet neue Möglichkeiten, die lokalen elektronischen Eigenschaften von Graphen durch Dehnung zu kontrollieren.Schließlich wurden Kohlenstoff-basierte leitfähige Tinten hergestellt, daraus transparente Elektroden hergestellt, und die Formulierungen der Tinten für das Drucken auf Plastiksubstrate optimiert.This work focusses on the electronic properties of graphene on the one hand, and on the application of graphenes and other carbon-based hybrid materials for transparent electrodes on the other hand. Accordingly, the first part of the work, which is the larger one, is of fundamental nature and focusses on the electronic interaction between graphene and mica as a substrate. The second, smaller part deals with the design of novel conductive inks based on graphene and other carbon-based hybrid materials for applications in printed electronics, in particular for the production of transparent electrodes. Graphene on mica is a very well defined system, which provides atomically flat graphene extending over several square micrometers. Layer-dependent surface potential variations of single and few layered graphenes on mica were probed with Kelvin Probe Force Microscopy. This allowed to estimate the screening length of graphene on mica. Local variations of the surface electrostatic potential above single layer graphene, originating from confined fluid interfacial monolayers of water between the mica and the graphene, were monitored with Scanning Force Microscopy, Electrostatic Scanning Force Microscopy and Raman spectroscopy. This allowed to quantify the doping of graphene by the confined water layers. Exfoliation of graphene onto adsorbed nanostructures on mica allowed to control the strain of graphene at the nano-scale. Nanostructuring was achieved by first coating mica with submonolayers of dendronized polymers of different generations and subsequently depositing graphene. This approach provides new opportunities for the control of the electronic properties of graphene by strain.Finally, novel conducting carbon-based inks were designed and transparent electrodes were fabricated therefrom. The formulations of the inks were optimized for printing on plastic substrates.
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Davarpanah, Abdol Mahmood. « Electronic structure of surface alloys ». Thesis, University of Liverpool, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404704.
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Gennard, Steven John. « Electronic structure properties of metal oxide surfaces ». Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400570.
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Blight, Kyle Raymond. « The electronic structure of indium phosphide surfaces ». Thesis, Blight, Kyle Raymond (1993) The electronic structure of indium phosphide surfaces. PhD thesis, Murdoch University, 1993. https://researchrepository.murdoch.edu.au/id/eprint/51642/.
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Indium phosphide (InP) is a member of a group of compounds known as III-V semiconductors. InP's direct band gap and high carrier mobility, approximately twice that of Si, makes it the ideal candidate for the manufacture of electronic devices such as field effect transistors. However, the wide spread use of InP has been restricted by the lack of a suitable compound or native oxide that could be used to form a passivating film on the surface. To date such films have been shown to contain defects within the film or at the overlayer-substrate interface. These defects trap the charge carriers and inhibit the device performance. The trapping states are also known to be formed by the deposition of metals.
The main objective of the work described in this thesis was to monitor the change in the electronic structure of n and p-InP under a variety of conditions in order to elucidate the physicochemical origin of the extrinsic surface states. In addition, the properties of some inorganic and organic sulphur compounds were investigated for use as passivating agents with which to form an inert and insulating film on the surface. Some of these compounds were found to have potential for use in the construction of electronic devices.
Electrochemical and ultra high vacuum techniques were utilised to monitor the electronic characteristics of the surfaces as a function of oxygen exposure. A simplex curve fitting algorithm was used to fit a model of the electronic structure of the surface to the surface photovoltage spectra. The results are expressed as surface potential curves. In addition to the states tailing into the band gap from the band edges, three midgap states were identified at approximately 0.25, 0.50 and 0.75 of the gap energy. The origin of these surface states was attributed to a disordered surface layer generated by the adsorption processes. A model of the origin and distribution of the surface states is discussed.
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Koda, Ryo. « Electrochemical deposition of metal on microporous silicon electrodes influenced by hydration structures of solutes and electrode surfaces ». 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199323.
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Price, Nicola Jane. « Self-assembled monolayers : electronic properties at the interface ». Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260276.
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Theunissen, W. H. « Reconfigurable contour beam synthesis using a mechanical FEM surface description of dual offset reflector antenna surfaces ». Thesis, University of Pretoria, 1999. http://hdl.handle.net/2263/26784.
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Blackham, Ian George. « Scanning tunneling microscopy of electrode surfaces ». Thesis, University of Oxford, 1992. https://ora.ox.ac.uk/objects/uuid:f9d27595-1177-406f-89a2-1448ac654dd3.
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A scanning tunneling microscope (STM) suitable for the in-situ study of electrode surfaces under electrochemical control has been developed. The system consists of commercially available software and feedback electronics, with a custom-built stage and electrochemical control. The stage incorporates an automatic coarse approach mechanism for ease of operation. Gold single crystal spheres (SCS) and gold on mica thin films have been studied as surfaces potentially suitable for samples in in-situ electrochemical STM experiments. Characteristic features of each surface have been identified. High resolution in-situ STM imaging of the electro-oxidation of a gold surface in a sulphuric acid electrolyte has been achieved. Surface rearrangement at potentials positive of the double layer region has been observed and correlated with cyclic voltammetry. As yet unexplained features resulting from biasing the surface at potentials negative of the double layer region are reported. In phosphate electrolyte, bulk surface oxide formation and the surface resulting from reduction of the oxide have been imaged. Some aspects of the direct electrochemistry of cytochrome c at 4,4' dithiodipyridine (SSBPY) modified gold electrodes have been investigated. In-situ FTIR showed the potential dependent orientation of adsorbed thiopyridine species, while ex-situ and in-situ STM studies showed a novel surface pitting process to be active. It is hypothesised the STM experiment itself induces the process to take place. Features attributable to cytochrome c molecules have been observed. Rearrangement of gold on mica surfaces, on exposure to certain aqueous solutions has been observed and the process is attributed to the interaction of the solutions with the original surface structure present.
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Fryling, Mark Aaron. « Raman Spectroscopy of Carbon Electrode surfaces / ». The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487859313346783.
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Jaquet, Christopher Denis. « Control surfaces in confined spaces : the optimisation of trailing edge tabs to reduce control surface hinge moments ». Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4327.
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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: This thesis describes the first project relating to the Control Surfaces in Confined Spaces (CoSICS) project at Stellenbosch University. The aim of CoSICS project is to reduce the size of control surface actuators, and this thesis considers the aileron system of commercial aircraft such as the Airbus A320 and A330. Specifically the project aims to reduce the aileron hinge moment, as this will result in smaller actuators. Possible methods are discussed where aerodynamic forces are used to reduce the aileron hinge moment through the use of a wing-aileron-tab configuration. In order to examine the use of the configuration, first order aerodynamic modelling is performed using two-dimensional thin-aerofoil theory, which is also extended to a basic three-dimensional approximation. To determine the maximum reduction in hinge moment several optimisations are performed where only the tab chord length is varied, both tab and aileron chord lengths are varied, and finally the tab chord length and aileron span are varied. The optimisation methods used, namely the gradient-based sequential quadratic programming (SQP) and a real-encoded genetic algorithm (REGA) are discussed in detail and include general implementations which are then applied to the problem. The optimisations performed are dual-layered where optimal deflection angles are determined as well as the optimal geometry. The results of the optimisation are tested using a roll manoeuvre in a specially developed Simulink simulation environment for this purpose. The study produces results where new hinge moment values are an order of magnitude smaller than those of the old configuration, while maintaining suitable lift and rolling moment coefficients. The optimisation and simulation infrastructure developed in this thesis provides a platform for higher-fidelity models and components being developed in future work to provide higher fidelity results.
AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die eerste projek in die Control Surfaces in Confined Spaces-projek1 (CoSICS-projek) uitgevoer by die Universiteit Stellenbosch. Die doel van die COSICs-projek is om die grootte van beheervlak aktueerders te minimeer en hierdie tesis handel oor die aileron stelsel van kommersiële vliegtuie soos die Airbus A320 en A330. Die doel van hierdie tesisis om die skarnier draaimoment van die aileron te minimeer deur aërodinamiese kragte in te span in ’n vlerk-aileron-hulpvlak konfigurasie. Eerste-orde aërodinamiese modelle is afgelei met behulp van twee-dimensionele dunvlerkteorie en is gebruik om die konfigurasie te analiseer. ’n Eerste orde drie-dimensionele benadering is ook ontwikkel. Om die maksimum vermindering in die skarnier draaimoment te bepaal, is verskeie optimerings uitgevoer waar eers die hulpvlak se koordlengte gevarieer word, daarna beide die aileron en hulp-vlak se koordlengtes en laastens die hulp-vlak se koordlengte en wydte. Die twee optimerings metodes wat gebruik is, nl. ’n sekwensiële kwadratiese programmerings (SKP) tegniek, en ’n reële getal-geënkodeerde genetiese algoritme (RGGA), word bespreek en ontwikkel voor hulle toegepas word op die probleem. Twee-vlak optimerings word uitgevoer waar beide die optimale defleksiehoeke en die optimale geometrie bepaal word. Die resultate van die optimering word daarna getoets deur middel van ’n rol maneuver wat uitgevoer word in ’n Simulink simulasie omgewing wat daarvoor geskep is. Hierdie studie lei tot goeie resultate met skarnier draaimoment waardes ’n ordegrootte kleiner as dié van die vorige stelsel, terwyl goeie waardes van rol-moment en verheffingskrag koëffisiënte behou word. Die optimering en simulasie infrastruktuur wat hier ontwikkel word verskaf ’n platform vir meer akkurate modelle en komponente wat ontwikkel word in toekomstige projekte om meer akkurate resultate te lewer.
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McNeil, Robert Peter Gordon. « Surface acoustic wave quantum electronic devices ». Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610718.
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Glans, Per-Anders. « Electronic structure of some SiC and Be surfaces / ». Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek661s.htm.
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Liu, Yan. « Superhydrophobic surfaces for electronic packaging and energy applications ». Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52164.
Texte intégralRésumé :
Superhydrophobic surfaces, which display water contact angles of larger than 150°, have attracted more and more attention due to their importance in both fundamental research and practical applications. This dissertation is mainly focused on the fundamental understanding and exploring applications of superhydrophobic surfaces. First, some specific examples of superhydrophobic surface fabrication were given, which include superoleophobic Si surface, robust superhydrophobic SiC surface, and reversible wettability nanocomposite films. Based on the study of superhydrophobic surfaces, the application of superhydrophobic surfaces in electronic packaging were explored. Superhydrophobic silica/epoxy nanocomposite coating serves as an encapsulant to improve the electronic device reliability. Such superhydrophobic coating showed good stability under humidity at elevated temperatures and was applied on the triple track resistors test coupons. In addition, the applications of superhydrophobic surfaces in solar cells were studied. Two multi-functional hierarchical structure solar cells with self-cleaning, low reflection and high efficiency properties were built up by coating or etching methods.
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Tran, Trung Nam. « Surface discharge dynamics : theory, experiment and simulation ». Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/165509/.
Texte intégralRésumé :
The use of solid insulators in electrical generation, transmission and distribution is widespread. However, the accumulation of charge on the insulator surface has proved to be one of the major factors contributing to system failures. This research work is aimed at studying the dynamics of surface discharge in theory, by simulation and experiment. Different surface charging theories have been reviewed and classiffied according to electric field uniformity. The focus is on basic processes involved in the formation of positive and negative surface discharges. The experimental work utilises the non-destructive quantitative Pockels technique to measure surface charge density distribution. Practical considerations of the Pockels experiment together with image processing techniques are discussed in detail. Using this technique, various factors which influence the surface discharge dynamics have been studied including the effects of the applied voltage waveform, electrode shape and local gaseous environment. Results obtained using positive/negative square wave, ramp and sinusoidal voltages are reported. The impact of using a mushroom electrode instead of a needle electrode is also analysed. In addition, various insulation gases have been experimented namely dry air, N2, CO2 and their mixtures with SF6. Surface discharge measurements have been performed in these gases at various levels of pressure. Surface discharge modelling and simulation studies have also been undertaken. The simulation principles are based on a system of coupled hydrodynamic equations consisting of continuity and Poisson's equations. By solving these equations, the movement and interaction of charged particles and transient electric eld can be simulated and used to verify the discharge theories and experimental results. Due to the asymmetric lamentary nature of positive surface streamers, the development of a positive surface discharge is separated into two phases. The rst phase involves the axial streamer development in the gas gap between the needle electrode and the dielectric surface. This phase is simulated in 2D axial symmetry space dimension by the nite element package COM-SOL. The second phase simulates the streamer propagation in 1D along the dielectric surface by using the eld results from the rst phase. This part of the model is solved by the accurate ux-corrected transport algorithm. The effects of model parameters on the simulation results are discussed and a comparison with experimental data made. Prior to the simulation of a negative surface discharge, a negative corona discharge model in 2D axial symmetry has been analysed (Trichel pulses). The model behaviour is studied with reference to experimental data as model parameters are varied. When the insulators are introduced, the accumulation of surface charge distorts the electric eld leading to the formation of only one discharge current pulse. The simulation charge density distribution is in good agreement with results obtained from the Pockels experiment.
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Pascarella, Nathan William. « Advanced encapsulation processing for low cost electronics assembly ». Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19031.
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Motornyi, Oleksandr. « Ab initio study of electronic surfaces states and plasmons of gold : role of the spin-orbit coupling and surface geometry ». Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX116.
Texte intégralRésumé :
Cette thèse de doctorat est dédiée à l’étude, avec des méthodes de calcul ab initio, desplasmons de surface et des états de surface de surfaces d’or, plate ou comportant desmarches (surface vicinale), par la simulation numérique de spectres de perte d’énergieélectronique (EEL) au moyen de la théorie de la fonctionnelle de la densité (DFT) et de lathéorie de perturbation de la fonctionnelle de la densité dépendant du temps (TDDFPT).L’influence du couplage spin-orbite (CSO) et celle de la géométrie de la surface ont étéétudiées. Dans l’or cristallin, j’ai étudié l’effet des électrons de semicoeur sur les spectresEEL à q = 0. J’ai montré en particulier que pour produire un spectre EEL sur une largegamme de fréquences, de 0 à 60 eV, il est nécessaire de tenir compte des électrons desemicoeur dans le pseudopotentiel, et qu’ils peuvent néanmoins être gelés dans le coeurpour l’étude de la partie basse en énergie du spectre EEL, pour des énergies inférieures à20 eV. J’ai réalisé des développements méthodologiques pour la TDDFPT avec CSO cou-plée à l’emploi de pseudopotentiels ultradoux, qui ont permis l’implémentation pratiquede cette approche dans les algorithmes de Liouville-Lanczos et de Sternheimer. J’ai utiliséavec succès ces approches qui m’ont permis de traiter des systèmes à plusieurs centainesd’atomes. J’ai examiné à nouveau le spectre EEL de l’or cristallin à q = 0, montrant enparticulier les traces d’un plasmon écranté dans le spectre EEL calculé sans inclure leseffets de CSO. J’ai ensuite montré que l’inclusion du CSO a un effet petit mais détectablesur le spectre EEL et le pic de plasmon, donnant un meilleur accord avec l’expérienceà q = 0. J’ai trouvé que la dispersion du plasmon acoustique (PAS) de la surface Au(111) est légèrement modifiée par le CSO, provenant du fait que la structure de bandesest elle-même modifiée par le dédoublement de Rashba de certains niveaux électroniques,dédoublement induit par le CSO. Puis, pour étudier les effets de géométrie, j’ai étudié lessurfaces vicinales (322), (455) et (788) de l’or. J’ai en particulier mené l’étude théoriquedes états électroniques de surface, et analysé l’évolution de l’état de surface de Shockleyentre la surface plate Au(111) et les surfaces ayant des marches dont les terrasses avaientdifférentes largeurs. J’ai montré la transition d’un état de surface résonant pour Au(322)à un état localisé pour Au(455) et pour Au(788), ainsi que le passage d’un état 2D étenduà travers la marche pour Au(322) à un état quasi-1D confiné dans la terrasse de la marchepour Au(455) et pour Au(788). Ces résultats sont en accord avec l’expérience, et avecceux d’un modèle de Kronig-Penney de potentiel périodique. J’ai calculé le spectre EELSpour la surface d’or (455) que j’ai modélisé par une tranche de 5 nm d’or séparée de sesvoisines (répétées périodiquement) par 5 nm de vide. J’ai identifié la signature du plas-mon acoustique de surface. J’ai montré que, pour un moment transféré perpendiculaireà la marche de la surface, la dispersion du PAS n’est pas modifiée par rapport à celle duPAS de la surface plate Au(111) pour q < 0.125 Å −1 . Cependant, pour des valeurs plusgrandes du moment transféré, le pic du PAS a une énergie plus basse que celle du PASde Au(111), montrant les signes du confinement du PAS et suggérant que deux types dePAS peuvent se produire: un plasmon intra(sous)bande, similaire à celui de la surfaceAu(111), et un plasmon inter(sub)band, caractéristique de cette surface vicinaleThe PhD thesis is devoted to the ab initio study of surface plasmons and surface states offlat and vicinal surfaces of Au through the simulation of electron energy loss (EEL) spectraby means of the density functional theory (DFT) and the time-dependent density func-tional perturbation theory (TDDFPT). The influence of the spin-orbit coupling (SOC)and of the surface geometry has been investigated. In bulk Au I have studied the effect ofthe inclusion of semi-core electrons on the EEL spectrum at q = 0 and the plasmon peakposition and intensity. In particular, I have shown that in order to reproduce the EELspectrum on a wide frequency range (0-60 eV) it is important to account for semi-coreelectrons in the pseudopotential although they can be frozen in the core in studies of thelow energy part of the spectrum (below 20 eV). I have made methodological developmentsfor TDDFPT with SOC in the ultrasoft pseudopotential scheme that led to the practicalimplementation of SOC in the Liouville-Lanczos and Sternheimer approaches. I have thensuccessfully applied these approaches that allowed me to model systems with hundreds ofatoms. I have revisited the plasmonic excitations in bulk Au, pointing out that, in partic-ular, one can observe traces of an unscreened s-like bulk plasmon in the EEL spectrum atq = 0 calculated without SOC. I have also demonstrated that SOC has a small but notice-able effect on the Au EEL spectrum and plasmon peak, mainly modifying the unscreeneds-like plasmon peak and thus bringing the calculated spectrum into a better agreementwith experimental results at q = 0. Moreover I have observed that the dispersion ofthe acoustic surface plasmon (ASP) on the Au(111) surface is slightly modified by SOC,because the ASP comes from the surface state that itself is modified by SOC through theRashba splitting. To investigate the effect of geometry I have studied the vicinal (322),(455) and (788) surfaces of Au. In particular I have performed the theoretical study of thesurface states, analyzing the evolution of the Shockley surface state from the flat Au(111)surface towards the surfaces with terraces of different width. I have shown the surfaceresonance-to-surface state transition from (322) to (455) and (788) surfaces. I have shownalso the transition from the average-surface-modulated to the terrace-modulated statefrom (322) to (455) and (788) surfaces, as well as the transition from the extended 2Dstate to the quasi-1D state confined within the terrace. These results are in agreementwith experiments and results obtained with the Kronig-Penney periodic potential model.I have performed the EEL spectrum calculations for the Au(455) surface which I havemodeled with a 5 nm sized slab separated from its periodic neighbors by 5 nm of vacuum.I have identified signatures of the ASP in these spectra, showing that indeed, for the caseof the transferred electron wavevector momentum perpendicular to the step, the ASPdispersion is not changed with respect to the ASP dispersion of the Au(111) surface forq < 0.125 Å −1 . For bigger values of q, however, the ASP peak has a lower energy com-pared to the ASP peak of the Au(111) surface, showing signs of the ASP confinement, andsuggesting that two types of the ASP could occur: an intra(sub)band plasmon, similarto the Au(111) surface plasmon, and an inter(sub)band plasmon, characteristic of thisvicinal surface
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Patchett, Adam John. « The electronic structure of Sc(0001) ». Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240888.
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Marikkar, Fathima Saneeha. « Molecular Design of Electrode Surfaces and Interfaces : For Optimized Charge Transfer at Transparent Conducting Oxide Electrodes and Spectroelectrochemical Sensing ». Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/193952.
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This dissertation has focused on i) optimizing charge transfer rates at indium-tinoxide (ITO) electrodes, and ii) characterization of the supramolecular structure and properties of ultra thin surface modifier films on modified electrodes for various device applications. Commercial ITO surfaces were modified using conducting polymer thin film architectures with and without various chemical activation procedures. Ferrocene derivatives were used as redox probes, which showed dramatic changes in electron transfer rate as the SA-PANI/PAA layers were added to the ITO surface. Highest rates of electron transfer were observed for DMFc, whose oxidation potential coincides with the potential region where these SA-PANI/PAA films reach their optimal electroactivity. Apparent heterogeneous electron transfer rate constants, kS, measured voltammetrically, were ca.10 x higher for SA-PANI/PAA films on ITO, versus clean ITO substrates. These films also showed linear potentiometric responses with retention of the ITO transparency with the capability to create smoothest films using an aqueous deposition protocol, which proved important in other applications. ITO electrodes were also modified via chemisorption of carboxy functionalized EDOTCA and electropolymerization of PEDOTCA/PEDOT copolymers, when properly optimized for thickness and structure, enhance voltammetrically determined electron transfer rates (kS) to solution probe molecules, such as dimethylferrocene (DMFc). Values of kS ≥ 0.4 cm•sec⁻¹, were determined, approaching rates seen on clean gold surfaces. ITO activation combined with formation of these co-polymer films has the effect of enhancing the electroactive fraction of electrode surface, versus a non-activated, unmodified ITO electrode, which acts as a “blocked” electrode. The electroactivity and spectroelectrochemistry of these films helped to resolve the electron transfer rate mechanism and enabled the construction of models in combination with AFM, XPS, UPS and RAIRS studies. The surface topography, structure, composition, work function and contact angle, also revealed other desirable properties for molecular electronic devices. The carboxylic functionality of the EDOTCA molecule adds more desirable properties compared to normal PEDOT films, such as favoring the deposition of smooth films, increasing the optical contrast, participating in hydrogen-bonding, chemisorption to oxide surface, self-doping and providing a linker for incorporation of different functional groups, new molecules, or nanoparticles. Periodic sub-micron electrode arrays can be created using micro-contact printing and electropolymerization. The sinusoidal modulation of the refractive index of such confined conducting polymer nanostructures or nanoparticle stripes allows efficient visible light diffraction. The modulation of the diffraction efficiency at PANI and PEDOT gratings in the presence of an analytical stimulus such as pH or potential demonstrate the sensing capability at these surfaces. The template stripped gold surfaces that are being developed in our lab demonstrate several advantages over commercially available evaporated gold films especially for nanoscale surface modification.
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Paniagua, Barrantes Sergio. « Interfacial engineering of transparent electrodes and nanoparticles with phosphonic acids and metal-organic dopants for organic electronic applications ». Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52920.
Texte intégralRésumé :
This thesis focuses on understanding the chemistry involved in a variety of surface modification reactions, both on metal oxides and graphene. In this work, the rates of chemisorption of a prototypical phosphonic acid on ITO under several processing protocols are measured using XPS to determine the optimal procedure. UPS is used to track the dependence of the electronic structure of the system, specifically of the work function and position of the valence band maximum on coverage. Phosphonic acid monolayers with appropriate tail groups can also be used to initiate chemistry from surfaces, which has potential for building layers of organic-electronic devices, including organic solar cells and capacitors. The growth of non-conjugated polymers from BaTiO₃ nanoparticles using a facile ATRP technique is studied via solution-phase and solid-state techniques to determine its applicability to make matrix-free composites for hybrid dielectrics. In addition, the surface chemistry involved in Kumada Catalyst-Transfer to grow polythiophene derivatives from ITO is examined via XPS. Finally, the newly emerged alternative for replacement of ITO as transparent electrode, graphene, is n- and p-doped using redox-active, solution-processable metal-organics, which increased its conductivity and allowed the work function to be tuned over a range of 1.8 eV. The systems are characterized in a systematic study, and the results are promising for future applications of graphene.
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Önsten, Anneli. « Surface Reactivity and Electronic Structure of Metal Oxides ». Doctoral thesis, KTH, Materialfysik, MF, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33667.
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The foci of this thesis are the metal oxides Cu2O, ZnO and Fe3O4 and their interaction with water and sulfur dioxide (SO2). The intention is to study SO2-induced atmospheric corrosion on a molecular level. All studies are based on photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM) measurements. The band structure of Cu2O in the Γ-M direction has been probed by angle-resolved PES (ARPES). It reveals a more detailed picture of the bulk band structure than earlier data and gives the first experimental evidence of a dispersive hybridized Cu 3d-Cu 4s state. The experimental data is compared to band structure calculations. The structure of clean metal oxide surfaces and impact of sample preparation have been studied. Oxygen vacancies can form a (√3x√3)R30° reconstruction on Cu2O(111). Oxygen atoms adjacent to copper vacancies, steps or kinks are shown to be adsorption sites for both water and SO2. Annealing temperature influences the defect density and hydrogen content in ZnO, which can have large impact on the surface properties of ZnO(0001). Water is shown to adsorb dissociatively on ZnO(0001) and partly dissociatively on Cu2O(111). The dissociation occurs at undercoordinated oxygen sites on both surfaces. Water stays adsorbed on ZnO(0001) at room temperature but on Cu2O(111), all water has desorbed at 210 K. SO2 interacts with one or two undercoordinated O-sites on all studied oxide surfaces forming SO3 or SO4 species respectively. SO4 on Fe3O4(100) follows the (√2x√2)R45° reconstruction. On Cu2O(111) and ZnO(0001), SO2 adsorbs on defect sites. An SO3 to SO4 transition is observed on Cu2O(111) when heating an SO3 adsorbate layer from 150 K to 280K. Coadsorption of water and SO2 on ZnO(0001) and Fe3O4(100) has been studied briefly. Water blocks SO2 adsorption sites on ZnO(0001). On Fe3O4(100) and on one type of reduced ZnO(0001) sample, SO2 dissociation to atomic sulfur or sulfide occurs to a higher extent on water exposed surfaces than on clean surfaces. Water thus appears to increase the charge density on some surfaces. Further studies are needed to reveal the cause of this unexpected effect.QC 20110516
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Fretwell, H. M. « Positron annihilation studies of electronic and defect structures in metallic systems ». Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357787.
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Ndieyira, Joseph Wafula. « X-ray diffraction studies of electrode surfaces ». Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624193.
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Chumillas, Sara. « Enzymatic Bioelectrocatalysis on well-defined electrode surfaces ». Doctoral thesis, Universidad de Alicante, 2017. http://hdl.handle.net/10045/81990.
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Los neurotransmisores, las quinonas y las enzimas redox desempeñan un papel muy importante en muchos procesos biológicos. Todos ellos tienen en común su importante papel en diferentes reacciones redox biológicas. Los neurotransmisores participan en los procesos de transmisión de impulsos nerviosos de organismos multicelulares; las enzimas redox actúan como catalizadores de un gran número de procesos biológicos basados en reacciones de transferencia de electrones que permiten obtener la energía necesaria para el sustento de la vida, tales como la reducción de oxígeno (O2) a agua (H2O) durante la respiración, la oxidación de azúcares a CO2 u otras vías metabólicas como la glicólisis o la fosforilación oxidativa. Esta tesis se centra en la caracterización de neurotransmisores (dopamina), quinonas (4-etilcatecol, 4-metilcatecol y catecol) y enzimas redox (CueO, lacasa perteneciente al grupo de las multicobre oxidasas) desde un punto de vista fundamental utilizando la electroquímica como herramienta de trabajo. Para ello, se han empleado como principales técnicas experimentales la voltametría cíclica (CV), el desplazamiento de carga con CO, las espectroscopías infrarroja (FTIR y ATR), Ultravioleta-Visible (UV-vis) y Raman, así como la microscopía de efecto túnel (STM). En el primer capítulo el trabajo de la tesis se contextualiza dentro del campo de la bioelectrocatálisis y de las biopilas de combustible. Además, se describen también los diferentes procedimientos utilizados para la funcionalización de electrodos y la inmovilización de enzimas. De la misma forma, también se resumen las propiedades de las catecolaminas y multicobre oxidasas, así como sus estructuras típicas, reacciones, mecanismos de transferencia de electrones y métodos de síntesis. Los contenidos principales de la tesis están estructurados en dos partes diferentes. La primera parte describe la reactividad de las catecolaminas sobre electrodos de oro, platino y carbón tipo diamante, prestando especial atención a los procesos de adsorción y oxidación registrados a bajos y altos potenciales, respectivamente. La segunda parte describe las condiciones óptimas para la catálisis de la reacción de reducción de O2 por parte de la CueO y su comportamiento electroquímico y espectroscópico. El efecto de compuestos comúnmente descritos en la literatura como inhibidores también está recogido en los capítulos 6 y 8.
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Becker, Udo. « The electronic structure of galena and hematite surfaces : applications to the interpretations of STM images, XPS spectra and heterogeneous surface reactions ». Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/40159.
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Scanning tunneling microscopy (STM) images and scanning tunneling spectroscopy (STS)
spectra of galena (PbS) and hematite (a-Fe203) were calculated using ab-initio methods in order to interpret experimental images and spectra that were taken in previous studies. These calculations have helped to understand which states of the mineral surfaces were imaged depending on the bias voltage and tip-sample separation. The computational results also gave insight in electron transfer processes that take place during surface adsorption/oxidation/reduction processes. In this context, different oxidation (using O2 and ferric iron as oxidants) and gold adsorption/reduction mechanisms on galena were evaluated at an atomic level. On hematite, the main emphasis was determining the differences in the local electronic structure of specific sites above the surface and the electronic structure of the bulk. Hereby, step sites turned out to have an increased local density of states at certain electron binding energies that are absent on flat surfaces. states can explain the highly increased reactivity of step sites as compared to terraces.
X-ray photoelectron spectra (XPS) were calculated to compare the photoelectron peaks of the calculated specific surface structures (that do not have a bulk equivalent) with experimentally
obtained XPS spectra. Most of the calculated peak chemical shifts coincided with those that were found in experiments and that were previously interpreted in terms of known bulk structures. Therefore, it can be inferred that the conventional way of interpreting XPS spectra might be incomplete if specific surface structures are neglected.
In order to understand step velocities on a gypsum (010) surface, step energies of different step directions were calculated using an ab-initio approach. An approximately linear relationship was found between the calculated step energies and the experimentally
detemined step velocities.Ph. D.
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Szamota-Leandersson, Karolina. « Electronic structure of clean and adsorbate-covered InAs surfaces ». Doctoral thesis, KTH, Materialfysik, MF, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-24423.
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This thesis is the result of investigations regarding the processes in InAs III-V semiconductor surfaces induced by additional charge incorporated by adsorbates. The aim of the project is to study the development of the accumulation layer on the metal/InAs(111)A/B surfaces and its electronic structure. InAs(111)A is indium-terminated and InAs(111)B is arsenic-terminated. In addition, InAs(100) is also studied. These three substrates are different; InAs(111)A has a (2x2)-termination, explained by an indium vacancy model, and the clean surface exhibits a two-dimensional electron gas (2DEG). InAs(111)B(1x1) is bulk-truncated and unreconstructed and does not host a 2DEG. InAs(100)(4x2)/c(8x2) exhibits a more covalent character of the surface bonds compared to InAs(111)A/B, and the surface is terminated by a complex reconstruction. Photoelectron spectroscopy and LEED (low energy electron diffraction) have been used as the main tools to study surfaces with sub-monolayer to monolayer amounts of adsorbates. A photoemission peak related to a two-dimensional electron gas appears close to the Fermi level. This 2DEG has in most cases InAs bulk properties, since it is located in the InAs conduction band. A systematic study of core levels and valence bands reveals that the appearance of the 2DEGs is a complex process connected to the surface order. Adsorption of lead, tin or bismuth on InAs(111)B(1x1) induces emission from a 2DEG, but only at monolayer coverage and when the surface is ordered. Cobalt reacts strongly with InAs forming InCo islands and no accumulation is observed. Examination of Cs/InAs(111)B does not reveal any 2DEG and the surface reaction is strongly related to the clean surface stabilization process. Examination of the In-terminated InAs(111)A(2x2) surface shows that In reacts strongly with cobalt and tin adatoms and with oxygen in cases of large exposure, which decreases the 2DEG intensity, while adatoms of cesium and small doses of oxygen enhance the emission from the 2DEG. InAs(100) is terminated with one kind of atom - the InAs(100)(4x2)/c(8x2) is indium terminated. Bismuth creates dimers on the surface and a 2DEG is observed. More generally, this thesis describes some of the general physical background applied to surface science and 2DEG. The first part is a general overview of the processes on the surface. The second part concentrates on the methods related to preparation of samples, and the third part on the measurement methods. The photoelectron spectroscopy part concerns the theory used in mapping electronic structure. The inserted figures are taken from different experiments, including results for InAs(111)A not previously published.QC 20100910
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Tallarida, Massimo. « Electronic properties of semiconductor surfaces and metal, semiconductor interfaces ». [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/196/index.html.
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Rad, M. Goshtasbi. « Electronic structure and reactions at some tetrahedral semiconductor surfaces / ». Stockholm : Tekniska högsk, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3069.
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Okeke, Gregory Nwoye. « Studies of the electronic porperties of clean metal surfaces ». Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356955.
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Persson, Kristin. « Electronic Control of Cell Cultures Using Conjugated Polymer Surfaces ». Doctoral thesis, Linköpings universitet, Fysik och elektroteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-106254.
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In the field of bioelectronics various electronic materials and devices are used in combination with biological systems in order to create novel applications within cell biology and medicine. A famous example of a successful bioelectronics application is the pacemaker. Metals are the most common electrical conductors, whereas polymers are generally considered being insulators. However, in the late 1970s it was shown that a special class of polymers with conjugated double bonds, could in fact, after some chemical modifications, conduct electricity. This was the start of the research field known as conducting polymers, and then later on organic electronics, a research area that has grown rapidly during the last decades. Conjugated polymers are also suitable to interact and interface with cells and tissues, as they are generally soft, flexible and biocompatible. In addition, their chemical properties can be tailor-made through synthesis to fit biological requirements and functions. During the last years applications using organic bioelectronics have become numerous. This thesis describes applications based on different conjugated polymers aiming to stimulate and control cell cultures. When culturing cells it is of interest to be able to control events such as adhesion, spreading, proliferation, differentiation and detachment. First, the impact of different polymer compositions and redox states on the adhesion of bacteria and subsequent biofilm formation was investigated. Similar polymer electrodes were also used to steer differentiation of neural stem cells, through changes in the surface exposure of a relevant biomolecule. Controlled delivery of molecules was achieved by coating nanoporous membranes with polymers that swell and contract when changing the redox state. Finally, electronic control over cell detachment using a water-soluble polymer was achieved. When applying a positive potential to this polymer, it swells, cracks and finally detaches, taking the cells that was cultured on top along with it. Together, the work and results presented in this thesis demonstrate a versatile conjugated polymer technology to achieve electronic control of the different growth stages of cell cultures as well as cellular functions.
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Traub, Matthew C. Gray Harry B. « Chemical functionalization and electronic passivation of gallium arsenide surfaces / ». Diss., Pasadena, Calif. : California Institute of Technology, 2008. http://resolver.caltech.edu/CaltechETD:etd-07172007-124916.
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Irrera, Simona. « Structural and electronic properties of chiral molecules on surfaces ». Doctoral thesis, La Sapienza, 2006. http://hdl.handle.net/11573/917346.
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Searle, Christopher. « The surface electronic structure of Y(0001) ». Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367246.
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Bjelkevig, Cameron. « Surface Chemical Deposition of Advanced Electronic Materials ». Thesis, University of North Texas, 2010. https://digital.library.unt.edu/ark:/67531/metadc67938/.
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The focus of this work was to examine the direct plating of Cu on Ru diffusion barriers for use in interconnect technology and the substrate mediated growth of graphene on boron nitride for use in advanced electronic applications. The electrodeposition of Cu on Ru(0001) and polycrystalline substrates (with and without pretreatment in an iodine containing solution) has been studied by cyclic voltammetry (CV), current-time transient measurements (CTT), in situ electrochemical atomic force microscopy (EC-AFM), and X-ray photoelectron spectroscopy (XPS). The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. XPS measurements confirmed the presence and stability of adsorbed I on the Ru surface following pre-treatment in a KI/H2SO4 solution and following polarization to at least −200 mV vs. Ag/AgCl. CV data of samples pre-reduced in I-containing electrolyte exhibited a narrow Cu deposition peak in the overpotential region and a UPD peak. The kinetics of the electrodeposited Cu films was investigated by CTT measurements and applied to theoretical models of nucleation. The data indicated that a protective I adlayer may be deposited on an air-exposed Ru electrode as the oxide surface is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electroplating process. A novel method for epitaxial graphene growth directly on a dielectric substrate of systematically variable thickness was studied. Mono/multilayers of BN(111) were grown on Ru(0001) by atomic layer deposition (ALD), exhibiting a flat (non-nanomesh) R30(3x3) structure. BN(111) was used as a template for growth of graphene by chemical vapor deposition (CVD) of C2H4 at 1000 K. Characterization by LEED, Auger, STM/STS and Raman indicate the graphene is in registry with the BN substrate, and exhibits a HOPG-like 0 eV bandgap density-of-states (DOS).
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Williams, A. A. « The chemistry and electronic structure of surfaces of ionic compounds ». Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370273.
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Herranz-Lancho, Coral. « Synthesis and characterization of molecules for electronic devices ». Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAE037.
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La miniaturisation toujours plus poussée des composants électroniques a atteint une limite en arrivant à l’échelle atomique. Afin de fabriquer des circuits à cette échelle, il est nécessaire de intéresser aux plus petits composants pouvant être intégrés : les molécules individuelles et les groupes d’atomes. Dans cette optique, les molécules de 1,4-bis(pyridin-4-ylethynyl) benzène (BPEB), Dibenzo[a,h]thianthrene (DBTH), de Bis{82,92,152,162,222,232- hexa-(2,4,6-trifluorophenoxy)[g,l,q]-5,10,15,20-tetraazaporphyrino)}[b,e]-benzene (H4Pc2) ont été conçues, synthétisées et caractérisées afin d’en étudier le transport de charges et les changements induits proche de la surface. Des techniques de SPM, tels que le STM, le nc-AFM et l’usage conjoint de l’AFM avec le STM ont été mises en pratique pour analyser les molécules reposant intégralement ou partiellement sur un substrat. L’interprétation des résultats expérimentaux a été faite au moyen de calculs de DFT. De plus, l’autoassemblage en solution de nouvelles mono-phthalocyanines métalliques fluorées, MPc (M= Mg2+, 2H+, Co2+) a été étudié.Tout d’abord, les mesures de conductance mirent en évidence, lors d’expériences de manipulation de fils moléculaires (BEPB), les changements de conformation associés aux transport des électrons à travers les molécules. De plus, le mouvement dit de “retournement papillon” (anglais: butterfly flapping) ayant lieu dans la classe des thianthrènes fut bloqué à basse température grâce à l’interaction avec le substrat. Ce blocage a permit de conduire la première étude stéréochimique de dérivés de thianthrènes chiraux (DBTH). Les analyses STM du DBTH ont montrées que le passage entre deux configurations de DBTH est reproductible et non-destructif. Par ailleurs, le nc-AFM utilisé à résolution sub-moléculaire a constitué un outils important pour réaliser une caractérisation complète et distinguer entre les différents isomères de configuration et de constitution déposés sur une surface. D’autre part, la structure moléculaire de la phthalocyanine binucléaire (H4Pc2) a été confirmée en utilisant un STM en mode “courant constant” et un AFM en mode “fréquence constante”. Ces résultats jettent les bases d’une prochaine étude de transport (travail en cours). En outre, l’étude de l’agrégation dans les molécules de MPc mit en évidence le rôle important de la capacité de coordination de l’atome central de la cavité Pc sur la formation d’agrégat. Finalement, des mesures électrochimiques ont démontrées que l’agrégation moléculaire peut bloquer le nature active de l’atome Co2+. Dans ce travail, il a été clairement montré que le SPM est une technique adéquate pour étudier les changements de conformations et de configurations associés aux courant tunnel d’électrons à travers des molécules, qu’elles soient planaire ou pas. Les études d’agrégation des interrupteurs magnétiques ont permis de mieux comprendre l’organisation supramoléculaire. Cette organisation est un point crucial pour le développement de futurs circuits basés sur une fabrication “bottom-up”The demand of downscaling of technology will reach its limit at the atomic length scale. This claim creates the necessity of investigating the smallest components suitable to become devices, single molecules or group of atoms. Therefore, 1,4-bis(pyridin-4-ylethynyl) benzene (BPEB), Dibenzo[a,h]thianthrene (DBTH) and Bis{82,92,152,162,222,232-hexa-(2,4,6-trifluorophenoxy)[g,l,q]-5,10,15,20-tetraazaporphyrino)}[b,e]-benzene (H4Pc2) have been designed, synthesized and characterized to investigate transport of charge through molecules and surface confined molecular switching. Scanning Probe Microscopy (SPM), such as STM, nc-AFM and combined STM/AFM were used to study the molecules on near-surface conditions. Density Functional Theory (DFT) calculations were used to interpret the experimental results. Moreover, the self-assembly of new fluorinated metalo mono-phthalocyanines, MPc (M= Mg2+, 2H+, Co2+) was investigated in solution.Firstly, conductance experiments performed while a molecular wire (BPEB) was being lifted up from a surface revealed the conformational changes associated to the transport of electrons through molecules. Secondly, the “butterfly” flapping motion in the class of the thianthrenes was blocked due to the interaction with a surface at low temperature. This block leads to the first stereochemical study of a quiral thianthere derivative (DBTH). The STM experiments on DBTH revealed a reproducible and non-destructive switching between two surface confined configurations of DBTH. In addition, nc-AFM with submolecular resolution has been proved to be a powerful tool for the full characterization and distinction of configurational and constitutional isomers on surfaces. Thirdly, the molecular structure of a binuclear phthalocyanine (H4Pc2) was confirmed through constant current STM and constant high _f AFM experiments. These results set the state of future spintronic transport experiments (ongoing work). On the other hand, the aggregation studies on MPc revealed that the coordination character of the central atom of the Pc cavity has an important effect on the formation of aggregates. Additionally, electrochemical experiments demonstrated that molecular aggregations can lead to the quenching of the electrochemical-active nature of a Co2+ atom.Herein it has been demonstrated that SPM are suitable techniques to study the conformational and configurational changes associated with the tunneling of electrons through planar and non-planar molecules in real space. Aggregation studies of magnetic switches were carried out to better understand the supramolecular organization under near surface conditions, a key point for the design of future devices based on the bottom up approach
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Zu, Fengshuo. « Electronic properties of organic-inorganic halide perovskites and their interfaces ». Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20396.
Texte intégralRésumé :
Über die besonders hohe Effizienz von Halid-Perowskit (HaP)-basierten optoelektronischen Bauteilen wurde bereits in der Literatur berichtet. Um die Entwicklung dieser Bauteile voranzutreiben, ist ein umfassendes und verlässliches Verständnis derer elektronischen Struktur, sowie der Energielevelanordnung (ELA) an HaP Grenzflächen von größter Bedeutung. Demzufolge beschäftigt sich die vorliegende Arbeit mit der Untersuchung i) der Bandstruktur von Perowskit-Einkristallen, um ein solides Fundament für die Darlegung der elektronischen Eigenschaften von polykristallinen Dünnschichten zu erarbeiten, und mit ii) den Einflüssen von Oberflächenzuständen auf die elektronische Struktur der Oberfläche, sowie deren Rolle bei der Kontrolle von ELA an HaP Grenzflächen. Die Charakterisierung erfolgt überwiegend mithilfe von Photoelektronenspektroskopie (PES) und ergänzenden Messmethoden wie Beugung niederenergetischer Elektronen an Oberflächen, UV-VIS-Spektroskopie, Rasterkraftmikroskopie und Kelvin-Sonde.
Erstens weist die Banddispersion von zwei prototypischen Perowskit-Einkristallen eine starke Dispersion des jeweiligen oberen Valenzbandes (VB) auf, dessen globales Maximum in beiden Fällen am R-Punkt in der Brillouin-Zone liegt. Dabei wird eine effektive Lochmasse von 0.25 m0 für CH3NH3PbBr3, bzw. von ~0.50 m0 für CH3NH3PbI3 bestimmt. Basierend auf diesen Ergebnissen werden die elektronischen Spektren von polykristallinen Dünnschichten konstruiert und es wird dadurch aufgezeigt, dass eine Bestimmung der Valenzbandkantenposition ausgehend von einer logarithmischen Intensitätsskala aufgrund von geringer Zustandsdichte am VB Maximum vorzuziehen ist.
Zweitens stellt sich bei der Untersuchung der elektronischen Struktur von frisch präparierten Perowskit-Oberflächen heraus, dass die n-Typ Eigenschaft eine Folge der Bandverbiegung ist, welche durch donatorartige Oberflächenzustände hervorgerufen wird. Des Weiteren weisen die PES-Messungen an Perowskiten mit unterschiedlichen Zusammensetzungen aufgrund von Oberflächenphotospannung eine Anregungslichtintensitätsabhängigkeit der Energieniveaus von bis zu 0.7 eV auf. Darüber hinaus wird die Kontrolle von ELA durch gezielte Variation der Oberflächenzustandsdichte gezeigt, wodurch sich unterschiedliche ELA-Lagen (mit Abweichungen von über 0.5 eV) an den Grenzflächen mit organischen Akzeptormolekülen erklären lassen. Die vorliegenden Ergebnisse verhelfen dazu, die starke Abweichung der in der Literatur berichteten Energieniveaus zu erklären und somit ein verfeinertes Verständnis des Funktionsprinzips von perowskit-basierten Bauteilen zu erlangen.Optoelectronic devices based on halide perovskites (HaPs) and possessing remarkably high performance have been reported. To push the development of such devices even further, a comprehensive and reliable understanding of their electronic structure, including the energy level alignment (ELA) at HaPs interfaces, is essential but presently not available. In an attempt to get a deep insight into the electronic properties of HaPs and the related interfaces, the work presented in this thesis investigates i) the fundamental band structure of perovskite single crystals, in order to establish solid foundations for a better understanding the electronic properties of polycrystalline thin films and ii) the effects of surface states on the surface electronic structure and their role in controlling the ELA at HaPs interfaces. The characterization is mostly performed using photoelectron spectroscopy, together with complementary techniques including low-energy electron diffraction, UV-vis absorption spectroscopy, atomic force microscopy and Kelvin probe measurements. Firstly, the band structure of two prototypical perovskite single crystals is unraveled, featuring widely dispersing top valence bands (VB) with the global valence band maximum at R point of the Brillouin zone. The hole effective masses there are determined to be ~0.25 m0 for CH3NH3PbBr3 and ~0.50 m0 for CH3NH3PbI3. Based on these results, the energy distribution curves of polycrystalline thin films are constructed, revealing the fact that using a logarithmic intensity scale to determine the VB onset is preferable due to the low density of states at the VB maximum. Secondly, investigations on the surface electronic structure of pristine perovskite surfaces conclude that the n-type behavior is a result of surface band bending due to the presence of donor-type surface states. Furthermore, due to surface photovoltage effect, photoemission measurements on different perovskite compositions exhibit excitation-intensity dependent energy levels with a shift of up to 0.7 eV. Eventually, control over the ELA by manipulating the density of surface states is demonstrated, from which very different ELA situations (variation over 0.5 eV) at interfaces with organic electron acceptor molecules are rationalized. Our findings further help to explain the rather dissimilar reported energy levels at perovskite surfaces and interfaces, refining our understanding of the operational principles in perovskite related devices.
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Cowen, Simon. « Optical studies of surface-modified electrodes ». Thesis, University of Exeter, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279731.
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