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Shao, Jianfei. "STM/STS and BEES Study of Nanocrystals." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10526.
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This work investigates the electronic properties of very small gold and semiconductor particles using Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and Ballistic Electron Emission Spectroscopy (BEES). Complementary theoretical works were also performed. The first theoretical work was to calculate the quantized states in the CdS/HgS/CdS quantum-well-quantum-dot nanocrystals. An eight-band envelope function method was applied to this system. This method treats exactly the coupling between the conduction bands, the light-hole bands, the heavy-hole bands, and the spin-orbit split bands. The contributions of all other bands were taken into account using second order perturbation theory.
Gold nanocrystals with diameters of 1.5 nm have discrete energy levels with energy spacings of about 0.2 eV. These values are comparable to the single electron charging energy, which was about 0.5 eV in our experimental configuration. Since bulk gold doesnt have an energy gap, we expect the electron levels both below and above the Fermi level should be involved in the tunneling. Measured spectroscopy data have rich features. In order to understand and relate these features to the electronic properties of the nanocrystals, we developed a tunneling model. This model includes the effect of excited states that have electron-hole pairs. The relaxation between discrete electron energy levels can also be included in this model. We also considered how the nanocrystals affect the BEES current.
In this work an ultra-high vacuum and low-temperature STM was re-designed and rebuilt. The BEEM/BEES capabilities were incorporated into the STM. We used this STM to image gold nanocrystals and semiconductor nanocrystals. STS and BEES spectra of gold nanocrystals were collected and compared with calculations.
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Lin, Hong. "Etude couplée par TEM/EELS et STM/STS des propriétés structurales et électroniques des nanotubes C et CNx." Paris 6, 2009. http://www.theses.fr/2009PA066494.
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Ce travail de thèse est dédié à l’étude couplée par TEM/EELS et STM/STS des propriétés structurales et électroniques des nanotubes de carbone purs et des nanotubes dopés à l’azote. Nous mettons d’abord en évidence le rôle des effets à N corps sur les spectres électroniques des tubes mesurés par STS et l’influence du substrat métallique. Ensuite nous présentons une étude systématique des fonctions d’ondes électroniques dans les tubes associées aux singularités de Van-Hove. Nous avons mis en évidence la brisure de symétrie de ces états qui est bien décrite par un modèle de liaisons fortes et qui a été confirmée par des calculs ab-initio. La dernière partie concerne l’étude de nanotubes dopés par des atomes d’azote. Des mesures de EELS montrent la présence d’azote dans les tubes et permet d’identifier des liaisons de type pyridinique. Les mesures STM font apparaître plusieurs défauts. Au final nous proposons que les atomes d’azote soient généralement accompagnés de défauts structuraux.
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Verlhac, Benjamin. "Atomic-scale spin-sensing with a single molecule at the apex of a scanning tunneling microscope." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE007/document.
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L’étude présentée dans ce manuscrit s’inscrit dans le domaine du magnétisme de surface, qui a connu de grands développements ces dernières années grâce au microscope à effet tunnel (STM). Elle a pour but de montrer qu’une molécule simple, le nickelocène [Ni(C5H5)2], peut être attachée au sommet d’une pointe STM afin de produire une pointe-sonde magnétique, qui, dans le cadre de l’imagerie magnétique, présente des avantages indéniables comparés à des pointes conventionnelles. À la différence d’autres systèmes moléculaires étudiés avec le STM, nous montrons que les propriétés magnétiques du nickelocène en phase gazeuse sont préservées en présence d’un métal, même lorsque la molécule est attachée au sommet d’une pointe STM. Nous présentons trois résultats marquants avec cette pointe-sonde moléculaire: 1) Nous montrons que l’on peut contrôler le spin du nickelocène, activant à souhait un effet Kondo ; 2) Nous produisons à l’aide du courant tunnel des excitations entre les états de spin du nickelocène, que nous pouvons aisément identifier au travers de la conductance moléculaire. Ces états sont sensibles à toute perturbation magnétique extérieure au nickelocène; 3) Au travers de ces excitations, nous sondons alors le magnétisme de surface. Nous montrons qu’en couplant magnétiquement la pointe-sonde moléculaire avec des atomes, soit isolés soit dans une surface ferromagnétique, nous pouvons mesurer leur polarisation de spin, ainsi que le couplage d’échange nickelocène-atome. Ce dernier permet d’obtenir un contraste magnétique en imagerie STM à l’échelle atomiqueThe study presented in this manuscript is part of the field of surface magnetism, which has undergone major developments in recent years thanks to the scanning tunneling microscope (STM). It aims to show that a single molecule, nickelocene [Ni(C5H5)2], can be attached to the tip of a STM to produce a magnetic probe-tip, which, in the context of magnetic imaging, has undeniable advantages compared to conventional tips. Unlike other molecular systems studied with STM, we show that the magnetic properties of nickelocene in the gas phase are preserved in the presence of a metal, even when the molecule is attached to the tip of a STM. We present three remarkable results with this molecular probe-tip: 1) We show that we can control the spin of nickelocene, activating at will a Kondo effect; 2) We monitor the spin states of nickelocene by producing electrically-driven excitations, which we can easily identify through the molecular conductance. These states are sensitive to the magnetic environment surrounding nickelocene; 3) We use these states to probe surface magnetism. We show that by magnetically coupling the molecular probe tip with single atoms, either isolated or in a ferromagnetic surface, we can measure their spin polarization, as well as the nickelocene-atom exchange coupling. By monitoring this coupling it is possible to obtain a magnetic contrast in the STM images with atomic-scale resolution
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Kubista, Kevin Dean. "Local measurements of cyclotron states in graphene." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39592.
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Multilayer epitaxial graphene has been shown to contain "massless Dirac fermions" and is believed to provide a possible route to industrial-scale graphene electronics. We used scanning tunneling microscopy (STM) and spectroscopy (STS) in high magnetic fields to obtain local information on these fermions. A new STS technique was developed to directly measure graphene's energy-momentum relationship and resulted in the highest precision measurement of graphene's Dirac cone. STS spectra similar to ideal graphene were observed, but additional anomalies were also found. Extra peaks and an asymmetry between electron and hole states were shown to be caused by the work function difference between the Iridium STM tip and graphene. This tip effect was extracted using modeled potentials and performing a least square fit using degenerate perturbation theory on graphene's eigenstates solved in the symmetric gauge. Defects on graphene were then investigated and magnetic field effects were shown to be due to a mixture of potential effect from defects and the tip potential. New defect states were observed to localize around specific defects, and are believed to interact with the STM tip by Stark shifting in energy. This Stark shift gives a direct measurement of the capacitive coupling between the tip and graphene and agrees with the modeled results found when extracting the tip potential.
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Wang, Bo. "An atomistic approach to graphene and carbon clusters grown on a transition metal surface." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2069.
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In this thesis, graphene (i.e. monolayer carbon film) and carbon clusters supported on a transition metal surface are systematically studied by local probe techniques, with respect to their structures, electronic properties and formation mechanisms. The main tools used are low-temperature scanning tunnelling microscopy and spectroscopy (STM and STS), which are introduced in Chapter 2. The mechanism of the resonance tunnelling at electron energies higher than the work function of the surface is discussed in detail, and a qualitative explanation of the Gundlach oscillations in the corresponding spectroscopy is presented. Epitaxial graphene synthesised on the Rh(111) surface by ethylene dehydrogenation is investigated by STM in Chapter 4. Such carbon film exhibits a hexagonal Moiré pattern due to a lattice mismatch between graphene and the rhodium substrate. The periodicity and local registries of the graphene/Rh(111) superstructure are carefully analysed. Based on a thorough discussion about the “commensurate vs. incommensurate” nature of the Moiré pattern in surface science field, the graphene/Rh(111) system is identified to have a non-simple-commensurate superstructure. The surface electronic properties and geometric buckling of graphene/Rh(111) are investigated by resonance tunnelling spectroscopy (RTS) and density functional theory (DFT) calculations in Chapter 5. Spectroscopy measurements reveal a modulation of the electronic surface potential (or work function Φ) across the supercell of epitaxial graphene. Based on the microscopy/spectroscopy data and the extended DFT calculations, we examined the electronic coupling of the various local C-Rh registries, and identified both experimentally and theoretically the local atomic configurations of maximum and minimum chemical bonding between graphene and the rhodium substrate. We studied in Chapter 6 the growth mechanism of graphene on Rh(111) at elevated temperatures. This part starts by investigating the dehydrogenation of ethylene into ethylidyne. When the dehydrogenation process is complete, monodispersed carbon species, identified as 7C6, are found to dominate the cluster population on the rhodium terraces. A significant coalescence of the 7C6 clusters into graphene islands occurs at temperatures higher than 873 K. The structural and electronic properties of the 7C6 carbon clusters are examined by high-resolution STM and STS, and compared with coronene molecules, i.e. the hydrogenated analogues of 7C6. DFT calculations are further used to explain the stability of 7C6 supported on the Rh(111) surface, and also the structural characteristics of such magic-sized carbon clusters.
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Cahlík, Aleš. "Spektrální analýza a charakterizace magnetických atomů a studium supravodivých vrstev pomocí nízkoteplotní STM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254337.
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This work is divided in two thematic parts. The first part shows a refurbishment of a Omicron low temperature STM set-up and its utilization for preparation of superconducting-magnetic interfaces. First, a cleaning procedure of suitable metallic substrates, specifically W(110) and Ir(111), is shown. It is followed by results of iron monolayer deposition on Ir(111) (Fe-Ir(111) interface). The last section deals with study of vanadium growth on pure Ir(111) substrate as well as on mentioned Fe-Ir(111) interface. The second thematic part deals with magnetism of cobalt atoms on a monolayer metal dichalcogenide WS2. It focuses primarily on studying their magnetic moment and magnetic anisotropy using X-ray magnetic circular dichroism (XMCD).
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Vasseur, Guillaume. "Étude par ARPES et STS des propriétés éléctroniques de réseaux métalliques et organiques nanostructurés." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0151/document.
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Dans ce travail nous démontrons, au travers de deux études, l'intérêt fondamental du couplage des techniques de photoémission résolue en angle (ARPES) et de spectroscopie tunnel (STS) dans l'analyse des propriétés électroniques d'interfaces nanostructurées. Dans la première partie, nous présentons une méthodologie permettant de déduire le potentiel de surface induit par la reconstruction triangulaire d'une monocouche d'Ag/Cu(111). Cette méthode est basée sur la mesure des gaps caractérisant la structure de bande de l'état de Shockley du système aux points de haute symétrie de la zone de Brillouin. L'évaporation d'adatomes de potassium permet d'augmenter le nombre de gaps accessibles en photoémission en décalant les bandes vers les états occupés. Dans un modèle d'électrons presque libres, leur amplitude nous donne accès aux premières composantes de Fourier du potentiel. La reconstruction de ce dernier dans l'espace direct nous permet ensuite de calculer la densité d'états locale que nous comparons aux mesures de conductance STS. La seconde partie est consacrée à l'étude de la croissance et des propriétés électroniques des molécules de 1,4-dibromobenzène (DBB) et 1,4-diiodobenzène (DIB) évaporées sur Cu(110). Leur dépôt à température ambiante sur la surface entraîne la déshalogénation des molécules et la formation de phases organométalliques. A 200°C, le système polymérise pour former des chaînes unidimensionnelles de poly(p-phénylène) parfaitement alignées. Les mesures ARPES révèlent l'existence d'une bande pi unidimensionnelle d'états HOMOs dispersant sous le niveau de Fermi. En STS, nous observons également, pour des petites chaînes, le confinement des états LUMOs dans la partie inoccupée du spectre. Le déconfinement de ces états pour les grandes chaînes conduit à la formation d'une bande continue croisant le niveau de Fermi, conférant au polymère un caractère métallique 1D. Le gap HOMO-LUMO est alors mesuré à 1.15 eVIn this work, through two different studies, we demonstrate the fundamental interest in the coupling of angle resolved photoemission (ARPES) and scanning tunneling spectroscopy (STS) to investigate the electronic properties of nanostructured interfaces. In the first part we present a methodology to determine the surface potential of the triangular reconstructed one monolayer of Ag/Cu(111) interface from ARPES. This method is based on the measurement of the Shockley state band structure’s gaps at the high symmetry points of the Brillouin zone. Deposition of potassium adatoms allows us to shift the surface state towards higher binding energies in order to increase the number of accessible gaps in photoemission. From the magnitude of these gaps we deduce the two first Fourier components of the potential felt by electrons using the nearly free electron model. Then we reconstruct it and calculate the local density of states in order to compare it with the conductance maps probed by STS. In the second part we report the study of the growth and the electronic properties of the two molecules 1,4-dibromobenzene (DBB) and 1,4-diiodobenzene (DIB) evaporated on Cu(110). For room temperature deposition, we first observe their deshalogenation and the formation of an intermediate organometallic phase. Then, above 200°C, the system polymerizes into a long-range ordered array of one dimensional poly(p-phenylene) polymer. ARPES intensity maps allowed us to identify a one dimensional graphene-like strongly dispersive pi-band below the Fermi energy. By STS we also observed LUMOs confined states for small chains over the Fermi level. The loss of confinement for long chains induces the formation of a continuous dispersive band which crosses the Fermi energy, conferring a 1D metallic character to the polymer. The HOMO-LUMO gap is found to be 1.15 eV
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Xing, Sarah. "Étude par ARPES et STS des propriétés électroniques d’un supraconducteur haute Tc à base de fer et de chaînes de polymères élaborées à la surface de métaux nobles." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0349/document.
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Dans ce travail, nous illustrons l’avantage de coupler les techniques de photoémission résolue en angle (ARPES) et de microscopie/spectroscopie tunnel (STM/STS) pour l'étude des propriétés électroniques et structurales des surfaces/interfaces nanostructurées. Dans la première partie, nous présentons l’étude du supraconducteur non conventionnel Eu(Fe0.86Ir0.14)2As2. Ce composé, dopé en Ir de manière optimale, possède une phase supraconductrice réentrante (Tc=22K) qui coexiste avec un ordre ferromagnétique (TM=18K). Nous présentons une étude par ARPES de la structure de bande dans le plan et hors plan ainsi que de la surface de Fermi. Les bandes associées aux états 3d du fer, responsables de la supraconductivité, sont modifiées en présence de la substitution en Ir, mais la topologie de la surface de Fermi est conservée. Le gap supraconducteur est mesuré à 5.5 meV, supérieur à la valeur estimée par la théorie BCS pour une température Tc=22K. La disparition du gap au-dessus de T=10K coïncide avec la phase résistive induite par l’ordre magnétique des moments Eu2+. Les modifications de la surface de Fermi dans le composé substitué indiquent clairement un dopage effectif en trou par rapport au composé parent. La seconde partie est consacrée à l’étude de la croissance, des mécanismes de polymérisation et des conséquences sur les propriétés électroniques de nanostructures moléculaires. Celles-ci sont élaborées par évaporation sous vide des molécules 1,4-dibromobenzène (dBB) et 1,4-diiodobenzène (dIB) sur les surfaces de Cu(110), Cu(111) et Cu(775) en utilisant la réaction catalytique de Ullmann. Nous avons étudié l’influence du type d’halogène et de substrat sur la réaction de polymérisation ainsi que les conséquences sur les propriétés électroniques. En particulier, nous mettons en évidence par des mesures STM et NEXAFS (mesures effectuées à l’aide du rayonnement synchrotron) un mécanisme original de croissance des polymères sur la surface de Cu(775) qui s’accompagne d’une restructuration à l’échelle nanométrique sous la forme d’un « step-bunching ». Celui-ci conduit à la formation de polymères de grande longueur et parfaitement ordonnés à grande échelle. En combinant les mesures ARPES et STS, nous mettons en évidence une évolution du gap HOMO-LUMO caractérisant les chaînes de poly(para)phénylène ainsi formées avec le type d’halogène impliqué dans la réaction catalytique et la géométrie du substrat. Nous montrons ainsi que si le caractère métallique du polymère élaboré sur le Cu(110) trouve son origine dans sa forte interaction avec le substrat, celle-ci diminue fortement lorsque la synthèse a lieu sur les surfaces de Cu(111) et de Cu(775) conduisant à retrouver un comportement semi-conducteur caractérisé par un gap HOMO-LUMO évalué à 2.2 eVIn this work, we highlight the advantage of coupling techniques such as angle resolved photoemission (ARPES), scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) for investigating the electronic and structural properties of nanostructured surfaces/interfaces. In the first part, the electronic structure of the reentrant superconductor Eu(Fe0.86Ir0.14)2As2 (Tc=22K) with coexisting ferromagnetic order (TM=18K) is investigated using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS). We study the in-plane and out-of-plane band dispersions and Fermi surface of Eu(Fe0.86Ir0.14)2As2. The near EF Fe 3d-derived band dispersions near the high-symmetry points show changes due to Ir substitution, but the Fermi surface topology is preserved. The superconducting gap measured at the lowest temperature T=5K (equal to 5.5meV) is beyond the weak-coupling BCS estimation for Tc=22 K. The gap gets closed at a temperature T=10K and this is attributed to the resistive phase which sets in at TM=18K due to the Eu2+ derived magnetic order. The modifications of the FS with Ir substitution clearly indicate an effective hole doping with respect to the parent compound. In the second part, we provide insight into the growth and the electronic properties of 1,4-dibromobenzene (dBB) and 1,4-diiodobenzene on Cu(110), Cu(111) and Cu(775) surfaces. The influence of the substrate is reported in this study: using a copper vicinal surface as support for on-surface Ullmann coupling leads to highly ordered, quasi-infinite polymer growth. Such a new growth mechanism, stemming from vicinal surface reconstructions is observed. The structural composition of different phases obtained in the study is discussed as a concomitant effect of the halogen and the surface geometry. Various interactions such as substrate/molecule, substrate/halogen, molecule/halogen as well as molecule/molecule interactions that took place into the polymerization mechanism are considered for analyzing the electronic properties of the different interfaces. We measured an 1.15 eV HOMO-LUMO gap in dBB/Cu(110), whereas the gap is found to be slightly higher than 1.5eV in dBB/Cu(111) and equal to 2.2eV in dBB/Cu(775). Such a metal-semiconductor transition is shown to occur when the halogen is switched (Br vs I) or the surface geometry is changed (Cu(110) vs Cu(775)) in agreement with the concomitant reduction of the polymer/substrate interaction
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Eilers, Stefan. "Strukturelle und elektronische Eigenschaften von Nanographen-Graphen-Systemen sowie Schnitt- und Faltverhalten von Graphen." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16715.
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Im ersten Teil der Arbeit werden Graphen sowie von Monolagen von auf Nanometer großen Graphenen basierenden Hexa-peri(Dodekyl)-Hexabenzocoronen-Molekülen (HBC-C12), adsorbiert auf Graphen, mit Rastertunnelmikroskopie und –spektroskopie an der Fest-Flüssig-Grenzfläche untersucht. Nanographen-Moleküle selbstaggregieren epitaktisch zu hochgeordneten Monolagen. Die Einheitszellen der Moleküllagen auf Monolage Graphen, Bilage Graphen und auf Graphit sind ununterscheidbar. Die Strukturen der Moleküllagen auf gewellten und flachen Teilen des Graphens stimmen überein. Strom-Spannungs-Kennlinien an Nanographen auf Graphen und auf Graphit weisen auf sehr ähnliche elektronische Eigenschaften hin. Zusammengefasst sind strukturelle sowie elektronische Eigenschaften der Nanographenlage homogen, stabil und definiert. Graphen erweist sich als bestens als Substrat und gleichzeitig als Elektrode für hochgeordnete Lagen von Nanographen-Molekülen geeignet. Im zweiten Teil der Arbeit wird Graphen mit der Sonde eines Rasterkraftmikroskops im Kontaktmodus mechanisch manipuliert. Es wird gezeigt, dass Graphen in nur einem Manipulationsschritt zu Streifen und Spalt geschnitten werden kann. Dieses Verhalten wird mit einem klassischen Modell des Biegens theoretisch erklärt. Das Schnittverhalten liegt in der 2-Dimensionalität des Graphens sowie in dessen Faltbarkeit auf Grund hinreichender Elastizität begründet. Durch mechanische Manipulation mit der Sonde des Rasterkraftmikroskops im Kontaktmodus unter atmosphärischen Bedingungen wird eine Flüssigkeitsschicht zwischen Graphen und dem Siliziumdioxidsubstrat nachgewiesen, welche eine mögliche Erklärung des stark kraftabhängigen Materialkontrasts zwischen Graphen und Siliziumdioxid im Amplitudenmodulationsmodus des Rasterkraftmikroskops darstellt. Weiter wird gezeigt, dass das Falten des Graphens durch mechanische Manipulation eine geeignete Methode zur Herstellung nicht epitaktisch aufeinander gestapelter Graphene darstellt.In the first part of the thesis graphene as well as monolayers of hexa-peri(dodecyl)-hexabenzocoronene molecules (HBC-C12) based on nanometer sized graphenes adsorbed on graphene is investigated by scanning tunnelling microscopy and tunneling spectroscopy at the solid-liquid interface. The nanographene molecules self-assemble on graphene epitaxially to form highly ordered monolayers. The unit cells of the molecular layers on monolayer graphene, bilayer graphene and on graphite appear identical. The structures of the molecular layers occur equal on corrugated and on flat parts of graphene. Current-voltage-characteristics show that the electronic properties of nanographene on graphene and on graphite are very similar. Summarized, structural as well as electronic properties of the nanographene layer are homogeneous, stable and defined. Graphene proves to be excellently qualified for simultaneously being substrate as well as electrode for highly ordered layers of nanographene based molecules. In the second part of the thesis graphene is mechanically manipulated in air in contact mode of a scanning force microscope. It is shown that a single manipulation process can lead to a stripe cut out of graphene. This behaviour is theoretically explained by a classical bending model. The cutting behavior originates from the 2-dimensionality of graphene and its folding ability because of sufficient elasticity. A liquid layer between graphene and the silicon dioxide substrate is verified by mechanical manipulation in contact mode of a scanning force microscope. Hence a possible explanation could be found for the strongly force dependent material contrast between graphene and silicon dioxide in amplitude modulation mode of the scanning force microscope. Further, it is demonstrated that folding graphene by mechanical manipulation is a proper method for the production of graphene stacked on each other non-epitaxially.
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Kramar, John Adam Baldeschwieler John D. Baldeschwieler John D. "Scanning tunneling microscopy and spectroscopy of molybdenum disulphide /." Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-06132007-103520.
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Bigioni, Terry Paul. "Scanning tunneling microscopy and spectroscopy of passivated gold nanocrystals." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30537.
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Frey, Jeffrey T. "Quantum chemical studies of scanning tunneling microscopy and spectroscopy." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file Mb., 245 p, 2006. http://proquest.umi.com/pqdlink?did=1251856811&Fmt=7&clientId=79356&RQT=309&VName=PQD.
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Buchsteiner, Philipp [Verfasser]. "Scanning Tunneling Spectroscopy of Rare Earth Hexaborides / Philipp Buchsteiner." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1224100344/34.
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Yee, Michael Manchun. "Scanning Tunneling Spectroscopy of Topological Insulators and Cuprate Superconductors." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11584.
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Over the past twenty-five years, condensed matter physics has been developing materials with novel electronic characteristics for a wide range of future applications. Two research directions have shown particular promise: topological insulators, and high temperature copper based superconductors (cuprates). Topological insulators are a newly discovered class of materials that can be manipulated for spintronic or quantum computing devices. However there is a poor spectroscopic understanding of the current topological insulators and emerging topological insulator candidates. In cuprate superconductors, the challenge lies in raising the superconducting transition temperature to temperatures accessible in non-laboratory settings. This effort has been hampered by a poor understanding of the superconducting mechanism and its relationship with a mysterious pseudogap phase. In this thesis, I will describe experiments conducted on topological insulators and cuprate superconductors using scanning tunneling microscopy and spectroscopy, which provide nanoscale spectroscopic information in these materials.Physics
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Chen, Ching-Tzu Yeh Nai-Chang. "Scanning tunneling spectroscopy studies of high-temperature cuprate superconductors /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-05222006-124257.
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Tomic, Aleksandra T. "Scanning tunneling microscopy of complex electronic materials." Diss., Connect to online resource - MSU authorized users, 2008.
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Thesis (Ph.D.)--Michigan State University. Dept. of Physics and Astronomy, 2008.Title from PDF t.p. (viewed on Mar. 27, 2009) Includes bibliographical references (p. 95-102). Also issued in print.
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Burema, Shiri. "Inelastic Electron Tunneling Spectroscopy with the Scanning Tunneling Microscope : a combined theory-experiment approach." Thesis, Lyon, École normale supérieure, 2013. http://www.theses.fr/2013ENSL0821.
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La Spectroscopie par Effet Tunnel Inélastique (IETS) avec un Microscope à Effet Tunnel (STM) est une nouvelle technique de spectroscopie vibrationnelle, qui permet de caractériser des propriétés très fines de molécules adsorbées sur des surfaces métalliques. Des règles de selection d’excitation vibrationnelle basées sur la symétrie ont été proposées, cependant, elles ne semblent pas exhaustives pour expliquer la totalité du mécanisme et des facteurs en jeu; elles ne sont pas directement transposables pour les propriétés d'un adsorbat et sont lourdes d'utilisation. Le but de cette thèse est donc d'améliorer ces règles de selection par une étude théorique. Un protocole de simulation de l'IETS a été développé, paramétré, et évalué, puis appliqué pour calculer des spectres IETS pour différentes petites molécules, qui sont systématiquement liées, sur une surface de cuivre. Des principes additifs de l'IETS ont été developpés, notamment concernant l’extension dans le vide de l’état de tunnel, l'activation/ quench sélectif de certains modes du aux propriétés électroniques de certains fragments moléculaires, et l'application de certaines règles d'addition de signaux IETS. De plus, des empreintes vibrationnelles par des signaux IETS ont été determinées pour permettre de différentier entre les orientations des adsorbats, la nature chimique des atomes et les isomères de structures. Une stratégie simple utilisant les propriétés de distribution de la densité électronique de la molécule isolée pour prédire les activités IETS sans des couts importants de calculs a aussi été développée. Cette expertise a été utilisée pour rationaliser et interpréter les mesures expérimentales des spectres IETS pour des métalloporphyrines et métallophtalocyanines adsorbées. Ces études sont les premières études IETS pour des molécules aussi larges et complexes. L'approche expérimentale a permis de déterminer les limitations actuelles des simulations IETS. Les défauts associés à l'identification ont été résolus en faisant des simulations d'images STM complémentairesInelastic Electron Tunneling Spectroscopy (IETS) with the Scanning Tunneling Microscope (STM) is a novel vibrational spectroscopy technique that permits to characterize very subtle properties of molecules adsorbed on metallic surfaces. Its proposed symmetry-based propensity selection rules, however, fail to fully capture its exact mechanism and influencing factors; are not directly retraceable to an adsorbate property and are cumbersome. In this thesis, a theoretical approach was taken to improve them. An IETS simulation protocol has been developed, parameterized and benchmarked, and consequently used to calculate IETS spectra for a set of systematically related small molecules on copper surfaces. Extending IETS principles were deduced that refer to the tunneling state’s vacuum extension, the selective activating/quenching of certain types of modes due to the moieties’ electronic properties, and the applicability of a sum rule of IETS signals. Also, fingerprinting IETS-signals that enable discrimination between adsorbate orientations, the chemical nature of atoms and structural isomers were determined and a strategy using straightforward electronic density distribution properties of the isolated molecule to predict IETS activity without (large) computational cost was developed. This expertise was used to rationalize and interpret experimentally measured IETS spectra for adsorbed metalloporphyrins and metallophthalocyanines, being the first IETS studies of this large size. This experimental approach permitted to determine the current limitations of IETS-simulations. The associated identification shortcomings were resolved by conducting complementary STM-image simulations
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Zimmermann, Michelle (Michelle Anne). "Scanning tunneling spectroscopy of lead-substituted bismuth strontium copper oxide." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40919.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (leaves 39-43).
The hole-doped cuprate Bi ... is doped with lead to the solubility limit of x = 0.38 and studied using STM/STS in the overdoped regime where Tc < 2K. Despite the high lead content, residual supermodulations are observed in the BiO plane. In agreement with previous studies on (Pb,Bi)-2201, there is no separation of the sample into Pb-rich and Pb-poor domains, nor is there a spectral correlation with Pb location. Differential tunneling conductance is modeled using the van Hove scenario, wherein modulated regions are shown to have higher values of EVHS than flat regions. The consistency of parameters matching theoretical predictions to tunneling spectra suggest that EVHS describes a significant part of the density of states.
by Michelle Zimmermann.
S.B.
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Moore, Steven Alan. "Scanning Tunneling Microscopy and Spectroscopy Measurements of Superconductor/Ferromagnet Hybrids." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/359662.
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PhysicsPh.D.
The focus of this thesis work is the study of the nanoscale electronic properties of magnetically coupled superconductor/ferromagnet hybrid structures using low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) under ultra-high vacuum conditions. There are a number of novel effects that can occur due to the non-homogenous magnetic field from the ferromagnet, which directly influence the global and local superconducting properties. These effects include the generation of vortices/anti-vortices by the non-uniform magnetic stray field, local modulations in the critical temperature, filamentary superconductivity close to the transition temperature, and superconducting channels that can be controlled by external magnetic fields. Prior to this dissertation the subject of superconductor/ferromagnet hybrid structures has been mainly studied using global measurements (such as transport and magnetization) or scanning probe techniques that are sensitive to the magnetic field. Scanning tunneling microscopy probes the local electronic density of states with atomic resolution, and therefore is the only technique that can study the emergence of superconductivity on the length scale of the coherence length. The novel results presented in this dissertation show that magnetically coupled superconductor/ferromagnet heterostructures offer the possibility to control and tune the strength and location of superconductivity and superconducting vortices, which has potential for promising technological breakthroughs in computing and power applications.
Temple University--Theses
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Amokrane, Anis. "Tunneling spectroscopy of mono- and di-nuclear organometallic molecules on surfaces." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE006/document.
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La recherche actuelle sur les composants électroniques à l'échelle nano s'oriente vers les matériaux organométalliques. Dans ce contexte, le travail présenté ici s'est focalisé sur la molécule de TbPc2 qui a été étudiée sur différents substrats, afin de déterminer l'effet de ses propriétés géométriques, électroniques et magnétiques en fonction de son environnement. Ainsi, il a été observé qu'au-dessus du substrat d'Au (111) la TbPc2 contient un électron excédentaire délocalisé sur le ligand supérieur qui, en intéragissant avec les électrons de surface, produit une résonance Kondo. Lorsqu'il s'agit de domaines moléculaires, une manipulation moléculaire montre qu'une localisation de spin est générée aux intersections produisant une résonance magnétique. Pour aller plus loin dans la détermination de l'effet de voisinage, un second lanthanide (cérium) a été déposé au-dessus de la molécule de TbPc2, la réponse géométrique, électronique et magnétique du nouveau complexe a été examinée sur différents substratsToday's research on the best electronic components at the nanoscale has focused on organometallic materials. In this context, the research presented in this thesis has been performed on TbPc2 molecules that were investigated on various substrates, in order to highlight the environment effect on both geometric, electronic and magnetic properties. It has been observed that on Au (111), the TbPc2 has an excedentary electron delocalized over the upper ligand. This electron interacts with the surface electron sea creating a Kondo resonance.When it comes to a molecular domain, it has been demonstrated throughout a molecular manipulation that a spin localization is made at the molecular intersection regions creating also a magnetic resonance. In order to further investigate the environmental modification, a second lanthanide (cerium) has been deposited over the TbPc2 molecule. The properties of the new complex were deeply investigated on various substrates
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Gyamfi, Mike [Verfasser]. "Scanning Tunneling Microscopy and Spectroscopy of Adatoms on Graphene / Mike Gyamfi." München : Verlag Dr. Hut, 2012. http://d-nb.info/1025821254/34.
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Shantyr, Roman. "Scanning tunneling microscopy, scanning tunneling spectroscopy on growth, atomic and electronic structure of Co oxide and Mn oxide films on Ag(001)." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972530487.
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Zhao, He. "Probing the Strongly Correlated Quantum Materials with Advanced Scanning Tunneling Microscopy/Spectroscopy:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:108971.
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Thesis advisor: Ilija ZeljkovicWe used spectroscopic-imaging scanning tunneling microscopy (SI-STM) and spin-polarized STM (SP-STM) to unveil new electronic phenomena in several different quantum systems. We explored: (1) a potential topological superconductor heterostructure Bi₂Te₃/Fe(Te, Se), (2) high-Tc superconductors − Bi₂Sr₂CaCu₂O₈₊ₓ and Fe(Te, Se), and (3) doped spin-orbit Mott insulators Sr₂IrO₄ and Sr₃Ir₂O₇. In Bi₂Te₃/Fe(Te, Se), we observed superconductivity (SC) on the surface of Bi₂Te₃ thin film, induced by the iron-based superconductor substrate. By annealing the optimally-doped cuprate superconductor Bi₂Sr₂CaCu₂O₈₊ₓ, we drastically lowered the surface hole doping concentration to detect a unidirectional charge stripe order, the first reported charge order on an insulating (defined by the spectral gap with zero conductance spanning the Fermi level) cuprates surface. In the high-Tc SC Fe(Te, Se) single crystal, we found local regions of electronic nematicity, characterized by C₂ quasiparticle interference (QPI) induced by Fermi surface anisotropy and inequivalent spectral weight of dyz and dxz orbitals near Fermi level. Interestingly, the nematic order is locally strongly anti-correlated with superconductivity. Finally, utilizing SP-STM, we observed a short-range antiferromagnetic (AF) order near the insulator-metal transition (IMT) in spin-orbital Mott insulators Sr₂IrO₄ and Sr₃Ir₂O₇. The AF order inhomogeneity is found not to be strongly correlated with the charge gap. Interestingly, the AF order in the bi-layered Sr₃Ir₂O₇ shows residual memory behavior with temperature cycling. Overall, our work revealed new phenomena in a range of today’s most intriguing materials and set the stage for using SP-STM in other complex oxides
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Bouvron, Samuel [Verfasser]. "Gate-controlled scanning tunneling spectroscopy of CoPc molecules on graphene / Samuel Bouvron." Konstanz : Bibliothek der Universität Konstanz, 2014. http://d-nb.info/1057842346/34.
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Schackert, Michael Peter [Verfasser]. "Scanning Tunneling Spectroscopy on Electron-Boson Interactions in Superconductors / Michael Peter Schackert." Karlsruhe : KIT Scientific Publishing, 2015. http://www.ksp.kit.edu.
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Liu, Weiming, and University of Lethbridge Faculty of Arts and Science. "Scanning tunneling microscopy and spectroscopy simulations of the silicon (111)-(7x7) surface." Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2006, 2006. http://hdl.handle.net/10133/543.
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Since 1982, the Si (111)-(7x7) surface has been extensively studied both theoretically and experimentally with the modern powerful tools of STM and Scanning Tunneling Spectroscopy (STS). In this work, a simple atomic orbital model for the Si (111)-(7x7) surface is developed to simulate the experimental results of STM and STS. Based on Tersoff-Hamann’s theory for the tunneling current, simulations of clean Si (111)-(7x7) constant-current images are presented. The direct, real-space simulated topographic images of the surface are compared to experimental results qualitatively and quantitatively. The simulation of spectroscopic imaging and normalized conductance spectra are also included. The adsorption of atomic hydrogen atoms onto the Si (111)-(7x7) surface is also simulated.xiv, 146 leaves ; 29 cm.
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Maltezopoulos, Theophilos. "Wave-function mapping of electronic states in nanostructures by scanning tunneling spectroscopy." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971435375.
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Delaney, Robert. "A dilution refrigerator based scanning tunneling microscope for high resolution nanoscale spectroscopy." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/59090.
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This thesis describes the design, construction and fabrication of a complete ultra-high vacuum (UHV) Dilution refrigerator based scanning tunneling microscope (STM). Data taken at a base temperature of 114 mK is presented and electrical, mechanical and vacuum design features are described for both the STM and the UHV system. Topographic images and spectroscopy on Au(111), graphene and other materials are presented to detail the performance of the STM. Techniques involving coherence and finite element analysis are used to address acousto-mechanical interaction between the STM and an acoustic room mode. The design and fabrication of an electron beam heater sample plate and complete UHV sputtering and annealing stage are presented.Science, Faculty of
Graduate
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Meyer, Jörg. "Electronic Properties of Organic Nanomaterials Studied by Scanning Tunneling Microscopy and Spectroscopy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-200781.
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In this work organic molecules, namely derivatives of BODIPY and poly-para-phenyls are investigated on different metal surfaces by means of LT-STM. These molecule are important for the development of molecular electronics and spintronics. I show that aza-BODIPY molecules form a weak chemical bond with the Au(111) substrate and the molecular structure significantly changes upon adsorption. Due to the low corrugation of the Au(111) surface, diffusion of the molecule is observed for applied bias in excess of ±1 V. The temperature dependent formation of different molecular nanostructures formed by polyparaphenyls and Au adatoms is discussed. The diffusing Au adatoms act as coordination centers for the cyano groups present on one end of the molecules. The structure of the super molecular assemblies completely changes in a temperature range of only 60 K. Furthermore, I investigate in this work the hybridization of atomic orbitals within the molecular ligand. The Kondo resonance of a Co atom incorporated into an other aza-BODIPY derivative is investigated in detail on Ag(100). The hybridization of the atomic Co orbital with the organic ligands molecular orbitals is shown by spectroscopy measurements with submolecular resolution. The changing line shape of the Kondo resonance for the molecule-substrate system is discussed. This data is compared to measurements of Co incorporated in another molecular binding motive and on different metal samples to show the importance of the local environment for molecular materialsIn dieser Arbeit werden organische Moleküle, Derivate von BODIPY und poly-para-Phenyl, auf verschiedenen Metalloberflächen mittels Tief-Temperatur Rastertunnelmikroskopie (LT-STM) untersucht. Diese Moleküle sind wichtig für die Entwicklung von molekularer Elektronik und Spintronik. Ich zeige, dass aza-BODIPY-Moleküle eine schwache chemische Bindung mit dem Au(111)- Substrat eingehen und die molekulare Struktur bei der Adsorption deutlich verändert wird. Wegen der geringen Rauigkeit der Au(111)-Oberfläche wird bereits bei einer angelegten Spannungen über ±1 V die Diffusion der Moleküle beobachtet. Die temperaturabhängige Bildung verschiedener molekularer Nanostrukturen aus poly-para-Phenyl und frei beweglichen Goldatomen wird diskutiert. Die diffundierenden Goldatome agieren hierbei als Koordinationszentren für die Cyanogruppen am einen Ende der Moleküle. Die Struktur der supramolekularen Anordnungen verändert sich dabei in einem Temperaturbereich von nur 60 K vollkommen. Außerdem beschäftige ich mich in dieser Arbeit mit der Hybridisierung atomare Orbitale im molekularen Verbund. Die Kondo-Resonanz eine Co-Atoms, welches in einem anderen aza-BODIPY-Derivat gebunden ist, wird detailliert auf der Ag(100)-Oberfläche untersucht. Die Hybridisierung des atomaren Co-Orbitals mit den molekularen Orbitalen des organischen Liganden wird an Hand von Spektroskopiemessungen mit submolekularer Auflösung gezeigt. Die veränderte Form der Kondo-Resonanz für dieses Molekül-Substrat-System wird diskutiert. Diese Daten werden mit Messungen an Co-Atomen in anderen molekularen Bindungsschemen und auf anderen Substraten verglichen um dieWichtigkeit der lokalen Umgebung für molekulare Materialien zu verdeutlichen
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Hackley, Jason. "A Liquid-Helium-Free High-Stability Cryogenic Scanning Tunneling Microscope for Atomic-Scale Spectroscopy." Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/19211.
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This dissertation provides a brief introduction into scanning tunneling microscopy, and then Chapter III reports on the design and operation of a cryogenic ultra-high vacuum scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Other performance characteristics such as thermal drift analysis and a cool-down analysis are reported. Scanning tunneling spectroscopy (STS) measurements based on the lock-in technique were also carried out and showed no detectable presence of noise from the CCC. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic-scale.
A study of electron transport in single-walled carbon nanotubes (SWCNTs) was also conducted. In Chapter IV, STS is used to study the quantum-confined electronic states in SWCNTs deposited on the Au(111) surface. The STS spectra show the vibrational overtones which suggest rippling distortion and dimerization of carbon atoms on the SWCNT surface. This study experimentally connects the properties of well-defined localized electronic states to the properties of their associated vibronic states.
In Chapter V, a study of PbS nanocrystals was conducted to study the effect of localized sub-bandgap states associated with surface imperfections. A correlation between their properties and the atomic-scale structure of chemical imperfections responsible for their appearance was established to understand the nature of such surface states.
This dissertation includes both previously published/unpublished and co-authored material.
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Taber, Benjamen. "Real-Space Visualization of Organic Molecular Electronic Structure: Scanning Tunneling Microscopy and Spectroscopy." Thesis, University of Oregon, 2018. http://hdl.handle.net/1794/23711.
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Organic electronics are becoming an increasingly important part of the semiconductor industry, with myriad applications enabled by their low cost, solution processability, and electrical conductivity. Charge transport in electronic applications involving organic semiconductor materials depends strongly on the electronic properties of nanoscale interfaces. Local variations in molecular environments can have a significant impact on the interfacial electronic properties, and subsequently the organic semiconductor electronic structure. Here, we use scanning tunneling microscopy and spectroscopy, supported by theoretical calculations, to investigate the impact of the local adsorption environment on the local density of states of oligothiophenes, carbon nanohoops, and carbon nanotubes. First, we present work showing that, for alkyl-substituted quaterthiophenes, molecular packing and electronic structure at interfaces differ substantially from the bulk, and a significant degree of structural and electronic variation occurs even in this relatively simple system. Then, we report on investigations of longer alkyl-substituted oligothiophenes, were we found a variety of planar molecular conformations that surprising exhibited similar, particle-in-a-box-like progressions of unoccupied molecular orbitals. Next, we share our research that found, for the first time, metal surface electrons confined within single adsorbed molecules. Finally, we study the impact of electrostatic defects in both metal and dielectric substrates on single-walled carbon nanotubes. The research presented in this dissertation increases our understanding of organic semiconductor interfaces and the impact of said interfaces on local molecular electronic structure, thereby aiding future organic semiconductor technological development.10000-01-01
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Ge, Xin [Verfasser]. "Scanning tunneling microscopy and spectroscopy of functional molecules on metal surfaces / Xin Ge." Kiel : Universitätsbibliothek Kiel, 2008. http://d-nb.info/1019755075/34.
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Craes, Fabian [Verfasser], CARSTEN [Akademischer Betreuer] BUSSE, and Achim [Akademischer Betreuer] Rosch. "Scanning Tunneling Spectroscopy on Graphene Nanostructures / Fabian Craes. Gutachter: Carsten Busse ; Achim Rosch." Köln : Universitäts- und Stadtbibliothek Köln, 2014. http://d-nb.info/1051077354/34.
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Meier, Focko Karl. "Co on Pt(111) studied by spin-polarized scanning tunneling microscopy and spectroscopy." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982018266.
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Jandke, Jasmin Maria [Verfasser]. "Elastic and Inelastic Scanning Tunneling Spectroscopy on Iron-Based Superconductors / Jasmin Maria Jandke." Karlsruhe : KIT Scientific Publishing, 2019. http://d-nb.info/1184402590/34.
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Jandke, Jasmin [Verfasser]. "Elastic and Inelastic Scanning Tunneling Spectroscopy on Iron-Based Superconductors / Jasmin Maria Jandke." Karlsruhe : KIT Scientific Publishing, 2019. http://d-nb.info/1184402590/34.
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Kersell, Heath R. "Alternative Excitation Methods in Scanning Tunneling Microscopy." Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1449074449.
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Herden, Tobias [Verfasser]. "Combined Scanning Tunneling and Atomic Force Microscopy and Spectroscopy on Molecular Nanostructures / Tobias Herden." Konstanz : Bibliothek der Universität Konstanz, 2014. http://d-nb.info/1079071865/34.
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Balashov, Timofey [Verfasser], and W. [Akademischer Betreuer] Wulfhekel. "Inelastic scanning tunneling spectroscopy : magnetic excitations on the nanoscale / Timofey Balashov. Betreuer: W. Wulfhekel." Karlsruhe : KIT-Bibliothek, 2009. http://d-nb.info/1014099013/34.
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Subramaniam, Dinesh [Verfasser]. "Scanning tunneling spectroscopy on graphene nanoislands, iron nanoislands and phase change materials / Dinesh Subramaniam." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1026454417/34.
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Schlenk, Tobias [Verfasser]. "Spin-Resolved and Inelastic Scanning Tunneling Spectroscopy of Magnetic Atoms and Clusters / Tobias Schlenk." München : Verlag Dr. Hut, 2013. http://d-nb.info/1045126039/34.
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Nag, Pranab Kumar. "Unusual electronic properties in LiFeAs probed by low temperature scanning tunneling microscopy and spectroscopy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-231628.
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In this thesis, the electronic properties in superconducting LiFeAs single crystal are investigated using low temperature scanning tunneling microscopy and spectroscopy (STM/S) at various temperatures. For this purpose, the differential conductance (dI/dV) measured by STS which is directly proportional to the local density of states (LDOS) of the sample to the sub-atomic precision, is used together with the topography information. The dI/dV spectra within the ±1 V energy range reveal a characteristic feature at around -350 mV to -400 mV in stoichiometric LiFeAs. This feature seems to be a universal property among all the Fe-based high temperature superconductors, because it is also found in Fe0.965Se1.035 and NaFe0.975Co0.025As single crystals at the energy of -210 mV and -200 mV, respectively.
The temperature dependent spectroscopy data averaged over a spatially fixed clean area of 2 nm × 2 nm are successfully executed between 5 K and 20 K. The two distinct superconducting phases with critical temperatures Tc = 16 K and 18 K are observed. In addition, the distance between the dip position outside the superconducting gap and the superconducting coherence peak in the spectra remains temperature independent which confirms that it is not connected to an antiferromagnetic (AFM) spin resonance. The temperature dependent spectra have been measured between 5 K and 61 K within the energy range of ±100 mV as well. The hump structure at 42 mV tends to disappear around 60 K from unknown origin.
The temperature dependent quasiparticle interference (QPI) has been studied within the temperature range between 6.7 K and 25 K and analyzed by the Fourier transformation of the measured spectroscopic maps. The dispersion plots in momentum space as a function of temperature show an enhancement of QPI intensity (±5.5 mV) within the superconducting gap at the Fermi level at 6.7 K near q ~ 0. This is interpreted on the basis of Andreev bound state. In both polarities outside of this, a depletion of QPI intensity is noticed between 5.5 mV and around 9 mV. At positive energies, the QPI intensity becomes very rich above 9 mV. The size of the enhanced QPI intensity near the Fermi level, and the edge of the rich QPI intensity beyond 9 mV are found to behave like superconducting order parameter with rising of temperature.
Furthermore, an energy mode peaked at around 14 mV appears in the integrated QPI intensity below superconducting Tc (6.7 K). This is consistent with the observed peak at 1st derivative of the dI/dV spectra. In both of these cases, such 14 mV peak is suppressed at normal state (25 K). This mode is therefore directly related to superconductivity in LiFeAs. The off-stoichiometric LiFeAs single crystal with superconducting Tc of 6.5 K has a 10 mV rigid band shift of the Fermi level towards electron doping. The absence of the rich QPI intensity between 9 mV and 17 mV is found compared to the stoichiometric LiFeAs, and hence the 14 mV mode is absent here. This brings us to conclude once more time that such 14 mV energy mode is relevant for superconductivity in LiFeAs.
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Törker, Michael. "Tunneling spectroscopy of highly ordered organic thin films." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2003. http://nbn-resolving.de/urn:nbn:de:swb:14-1056446807640-19877.
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In this work, a Au(100) single crystal was used as substrate for organic molecular beam epitaxy. Highly ordered organic thin films of the molecules 3,4,9,10-perylenetetracarboxylic-3,4,9,10-dianhydrid (PTCDA) and hexa-peri-hexabenzo-coronene (HBC) as well as organic-organic heterostructures on reconstructed Au(100) were prepared. The molecular arrangement was characterized in Scanning Tunneling Microscopy and Low Energy Electron Diffraction investigations. Scanning Tunneling Spectroscopy data were recorded on monolayer and submonolayer PTCDA films. Measurements on closed PTCDA layers at different fixed tip sample separations revealed a peak +0.95V. Other measurements performed consecutively on a PTCDA island and on uncovered Au(100) areas showed that this peak is indeed caused by the PTCDA molecules. Another set of consecutive measurements on herringbone and square phase PTCDA islands indicates that in the normalized differential conductivity the peak shape and peak position depend on the molecular arrangement. The STS data are compared to UPS and IPES results, already published. In the case of highly ordered films of HBC on Au(100) it was possible to derive the energetic positions of the HBC frontier orbitals and the energies of the molecular states next to these frontier orbitals from Tunneling Spectroscopy measurements. These measurements were performed using two different tip materials. The results are compared to UPS measurements, to theoretical calculations of the electronic conductance based on a combination of the Landauer transport formalism with a density-functional-parametrized tight-binding scheme within the Local Density Approximation (LDA) as well as semiempirical quantum chemistry calculationsFür die hier dargestelleten Arbeiten wurde ein Au(100) Einkristall als Substrat für die organische Molekularstrahlepitaxie verwendet. Hochgeordnete organische Dünnschichten der Moleküle 3,4,9,10-Perylen-tetracarbonsäure-3,4,9,10-dianhydrid (PTCDA) und Hexa-peri-hexabenzo-coronen (HBC) sowie organisch-organische Heteroschichten wurden auf der Au(100) Oberfläche abgeschieden. Die Struktur der Schichten wurde mittels Rastertunnelmikroskopie (STM) und Niederenergetischer Elektronenbeugung (LEED) untersucht. Tunnelspektroskopiedaten wurden für Monolagen sowie Submonolagen von PTCDA aufgenommen. Messungen an geschlossenen PTCDA Filmen zeigen für verschiedene Probe-Spitze-Abstände ein Maximum in der normierten differentiellen Leitfähigkeit bei +0.95V. Aufeinanderfolgende Messungen auf PTCDA-Inseln und unbedeckten Gebieten der Au(100) Oberfläche zeigen eindeutig, dass dieses Maximum auf die PTCDA Moleküle zurückzuführen ist. Weitere Messungen an PTCDA Inseln unterschiedlicher Struktur (Fischgrätenstruktur bzw. quadratische Struktur) belegen einen Zusammenhang zwischen der Anordnung der Moleküle und der Peakposition bzw. Peakform in der normierten differentiellen Leitfähigkeit. Die STS Daten werden mit UPS und IPES Ergebnissen aus der Literatur verglichen. Im Falle hochgeordneter HBC Schichten auf Au(100) war es möglich, neben dem höchsten besetzten und niedrigsten unbesetzten Molekülorbital auch die energetische Position der jeweils nächsten Orbitale zu bestimmen. Diese Messungen wurden mit zwei unterschiedlichen Spitzenmaterialien durchgeführt. Die Ergebnisse für HBC auf Au(100) werden mit UPS Daten sowie mit theoretischen Rechnungen verglichen
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Törker, Michael. "Tunneling spectroscopy of highly ordered organic thin films." Doctoral thesis, Technische Universität Dresden, 2002. https://tud.qucosa.de/id/qucosa%3A24233.
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In this work, a Au(100) single crystal was used as substrate for organic molecular beam epitaxy. Highly ordered organic thin films of the molecules 3,4,9,10-perylenetetracarboxylic-3,4,9,10-dianhydrid (PTCDA) and hexa-peri-hexabenzo-coronene (HBC) as well as organic-organic heterostructures on reconstructed Au(100) were prepared. The molecular arrangement was characterized in Scanning Tunneling Microscopy and Low Energy Electron Diffraction investigations. Scanning Tunneling Spectroscopy data were recorded on monolayer and submonolayer PTCDA films. Measurements on closed PTCDA layers at different fixed tip sample separations revealed a peak +0.95V. Other measurements performed consecutively on a PTCDA island and on uncovered Au(100) areas showed that this peak is indeed caused by the PTCDA molecules. Another set of consecutive measurements on herringbone and square phase PTCDA islands indicates that in the normalized differential conductivity the peak shape and peak position depend on the molecular arrangement. The STS data are compared to UPS and IPES results, already published. In the case of highly ordered films of HBC on Au(100) it was possible to derive the energetic positions of the HBC frontier orbitals and the energies of the molecular states next to these frontier orbitals from Tunneling Spectroscopy measurements. These measurements were performed using two different tip materials. The results are compared to UPS measurements, to theoretical calculations of the electronic conductance based on a combination of the Landauer transport formalism with a density-functional-parametrized tight-binding scheme within the Local Density Approximation (LDA) as well as semiempirical quantum chemistry calculations.Für die hier dargestelleten Arbeiten wurde ein Au(100) Einkristall als Substrat für die organische Molekularstrahlepitaxie verwendet. Hochgeordnete organische Dünnschichten der Moleküle 3,4,9,10-Perylen-tetracarbonsäure-3,4,9,10-dianhydrid (PTCDA) und Hexa-peri-hexabenzo-coronen (HBC) sowie organisch-organische Heteroschichten wurden auf der Au(100) Oberfläche abgeschieden. Die Struktur der Schichten wurde mittels Rastertunnelmikroskopie (STM) und Niederenergetischer Elektronenbeugung (LEED) untersucht. Tunnelspektroskopiedaten wurden für Monolagen sowie Submonolagen von PTCDA aufgenommen. Messungen an geschlossenen PTCDA Filmen zeigen für verschiedene Probe-Spitze-Abstände ein Maximum in der normierten differentiellen Leitfähigkeit bei +0.95V. Aufeinanderfolgende Messungen auf PTCDA-Inseln und unbedeckten Gebieten der Au(100) Oberfläche zeigen eindeutig, dass dieses Maximum auf die PTCDA Moleküle zurückzuführen ist. Weitere Messungen an PTCDA Inseln unterschiedlicher Struktur (Fischgrätenstruktur bzw. quadratische Struktur) belegen einen Zusammenhang zwischen der Anordnung der Moleküle und der Peakposition bzw. Peakform in der normierten differentiellen Leitfähigkeit. Die STS Daten werden mit UPS und IPES Ergebnissen aus der Literatur verglichen. Im Falle hochgeordneter HBC Schichten auf Au(100) war es möglich, neben dem höchsten besetzten und niedrigsten unbesetzten Molekülorbital auch die energetische Position der jeweils nächsten Orbitale zu bestimmen. Diese Messungen wurden mit zwei unterschiedlichen Spitzenmaterialien durchgeführt. Die Ergebnisse für HBC auf Au(100) werden mit UPS Daten sowie mit theoretischen Rechnungen verglichen.
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Schackert, Michael Peter [Verfasser], and W. [Akademischer Betreuer] Wulfhekel. "Scanning Tunneling Spectroscopy on Electron-Boson Interactions in Superconductors / Michael Peter Schackert. Betreuer: W. Wulfhekel." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1053703910/34.
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Brede, Jens Herwig [Verfasser]. "Spin-Polarized Scanning Tunneling Microscopy and Spectroscopy of Phthalocyanine Molecules on Surfaces / Jens Herwig Brede." München : Verlag Dr. Hut, 2011. http://d-nb.info/1018983023/34.
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Pietzsch, Oswald. "Magnetic imaging by spin-polarized scanning tunneling spectroscopy applied to ultrathin Fe/W(110) films." [S.l.] : [s.n.], 2001. http://www.sub.uni-hamburg.de/disse/444/Disse.pdf.
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Hofe, Thomas von. "Electron dynamics of Cs covered Cu(111) a scanning tunneling spectroscopy investigation at low temperatures /." kostenfrei, 2006. http://e-diss.uni-kiel.de/diss_1614/d1614.pdf.
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Shawulienu, Kezilebieke. "Scanning tunneling microscopy and spectroscopy of metal organic complexes : from single atoms to extended networks." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE005/document.
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La recherche actuelle dans le domaine des nanosciences, l’assemblage supramoléculaire d’atomes métalliques et de molécules sur des surfaces ouvre la voie à des composants fonctionnels, utiles dans une multitude d’applications comme l’Optoélectronique, le magnétisme et la catalyse. Il a été démontré que dans certains cas, l’état de Spin Haut et une forte anisotropie magnétique apparaissent suite à un transfert d’électron entre ligands, surface et atome métallique. Le but de cette thèse porte sur l’auto-assemblage des 1,2,4,5-Tetracyanobenzene (TCNB) et des coordinations nanostructurelles des Fe-TCNB sur une surface d’Au(111). La formation de ces structures est conduite par les interactions non-covalentes. La spectroscopie à effet tunnel (STS) révèle que la molécule de TCNB est physisorbée sur la surface d’Au(111). Une analyse détaillée des spectres dI/dV effectués sur une monocouche de TCNB sur une surface d’Au(111) montre que la molécule de TCNB a un transfert de charge négligeable sur ce substrat avec une énergie d’adsorption de 0,5 eV par molécule. Les mesures STS révèlent un gap HOMO-LUMO de 3 eV, comme le prédit la théorie. En contrôlant les paramètres de fabrication, des composants nanostructurels avec différentes compositions chimiques ou des arrangements moléculaires ont été synthétisés. Les propriétés électroniques ont été caractérisées par une analyse spectroscopique dI/dV locale sur les centres métalliques à différentes étapes de formation des complexes Fe-(TCNB)x (x=4, 2). La déposition à très basse température forme un état intermédiaire métastable. Les données STM montrent que l’angle que forment le trièdre Fe-N-C est de 120°. La spectroscopie tunnel révèle que le Fe et la molécule de TCNB gardent leur identité spectroscopique, le Fe garde ses états de surface de la même façon que s’il avait été déposé seul sur une surface d’Au(111). Ceci indique que les molécules de TCNB sont virtuellement dans le même état électronique qu’avant la déposition du Fe. La situation change lorsque ce dépôt est effectué à température ambiante. Une augmentation de température agit sur l’interaction des composants transformant ainsi la formation en un complexe monomère de Fe(TCNB)4 avec un angle Fe-N-C de 180°. La spectroscopie STS sur ce complexe suggère fortement que la liaison de coordination est formée entre le Fe et la molécule de TCNB. Les calculs DFT soutiennent ces conclusions. Plus loin, une structure a été réalisée par la synthèse d’un réseau Fe(TCNB)2. Ce réseau a une structure carrée avec une séparation régulière entre les atomes de Fe. Les informations électroniques de la structure sont données par la molécule de FePc (où Pc représente la molécule de Phthalocyanine) pour identifier les pics de résonnance du spectre du réseau de Fe(TCNB)2. Une similitude apparait dans les spectres dI/dV effectués sur l’atome de Fe et sur les ligands dans les deux systèmes, indiquant que le Fe ressent un environnement similaire quand il est entouré de TCNB ou quand il est à l’intérieur d’une Phthalocyanine. Une analyse plus détaillée basée sur la formation des liaisons métal-ligands a été discutéeIn the bottom up approach of today’s nanoscience, the supramolecular assembly of metal atoms and molecules on surfaces is leading to functional compounds, relevant to many applications in optoelectronics, magnetism, and catalysis. It has been found that in some cases high magnetic spin states and strong magnetic anisotropy appear as a result of electron transfer between ligands, surface and metal atom. The focus of this thesis lies on the self assembling of 1,2,4,5-Tetracyanobenzene (TCNB) and Fe-TCNB coordination nanostructures on the Au(111) surface. The structural formation is directed by the non covalent interactions. Scanning tunneling spectroscopy (STS) reveal that the TCNB molecules are physisorbed on Au(111) surface. By detail analysis of the dI/dV spectra above the TCNB monolayer on the Au(111) surface, we found that the TCNB molecules on Au(111) shows a negligible charge transfer with Au(111) substrate and a small adsorption energy of 0.5 eV per TCNB molecules. STS measurement provide a HOMO-LUMO gap of 3 eV in agreement with DFT calculations. By controlling the fabrication parameters, surface coordination nanostructures with different chemical composition or molecular packing have been synthesized. The electronic properties have been characterized by the local dI/dV analysis of the metal centers at different steps of a Fe-(TCNB)x (x=4, 2) complexes formation. At low temperature deposition, first form an ordered metastable intermediate. STM data yield the bond angle between the Fe-N-C is 120°. The scanning tunneling spectroscopy reveal that Fe atoms and the TCNB molecules keep their identity while the Fe atoms localize the surface-state electrons similar to what they do on the bare Au(111) surface. This result indicates that the TCNB molecules are virtually in the same electronic state as before the Fe adsorption. The situations are different when the deposition performance at room temperature. When the temperature is changed, to room temperature, the original entities transform into the Fe(TCNB)4 monomer complexes with 180° Fe-N-C bond angles. The STS above the Fe(TCNB)4 complex strongly suggest that the coordination bond had been formed between the Fe atom and the TCNB ligands. DFT calculations support the conclusions and drawn from experimental studies and assist the interpretations of experiment. Further structural complexation is achieved by the synthesis of Fe(TCNB)2 network. The network has a square structure with a regular separation of the magnetic Fe atoms in the network. The electronic information is gathered from the spectroscopic labeling of FePc to identify some of the resonances of the Fe(TCNB)2 network. There are similar features are found in the dI/dV spectra above the Fe atoms and ligand in both system, indicating that the Fe somehow feels a similar environment from the TCNB ligands in the network and in the FePc molecules. Further analysis of this feature have been disused by means of metal-ligand bond formation
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Neils, Christopher Martin. "Laser scanning microscopy of broad freezing interfaces with applications to biological cells /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004349.
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