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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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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.<br>Physics
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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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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.<br>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 complémentaires<br>Inelastic 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.<br>Includes bibliographical references (leaves 39-43).<br>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.<br>by Michelle Zimmermann.<br>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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Physics<br>Ph.D.<br>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.<br>Temple University--Theses
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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 Zeljkovic<br>We 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<br>Thesis (PhD) — Boston College, 2020<br>Submitted to: Boston College. Graduate School of Arts and Sciences<br>Discipline: Physics
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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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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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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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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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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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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.<br>Science, Faculty of<br>Graduate
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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.<br>xiv, 146 leaves ; 29 cm.
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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 materials<br>In 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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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.<br>10000-01-01
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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 calculations<br>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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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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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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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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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.<br>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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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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GRAZIANETTI, CARLO. "Scanning tunneling microscopy investigation of III-V compound semiconductors and novel 2D nanolattices." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/50028.
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The research activity described in this thesis is mainly devoted to study the fundamental properties of alternate channel materials to bulk silicon. Indeed, there is consensus, in the scientific and industrial community, that silicon is approaching its ultimate scaling limit. Today, increasing the performance of integrated circuits by scaling silicon metal-oxide-semiconductor field effect transistor (MOSFET) is becoming more and more difficult and, therefore, a systematic survey of possible alternate solutions should be considered. This purpose is taken into account by exploring two paradigmatic candidates, namely, a promising III-V semiconductor, In0.53Ga0.47As(001), and a novel two-dimensional (2D) material, silicene, the silicon counterpart of graphene, which does not exist in nature. The former represents a mid-term option fully compatible with silicon-based processing, in a More Moore strategy, while the latter represents a completely different approach that can be envisioned for ultimate device downscaling either in a More Moore perspective or even further for More than Moore prospects. Such a systematic survey has to be carried out with probes which might consider the atomic properties, since the progressive shrinking of devices dimensions is pointing towards atomic-scale. In this framework, the choice of Scanning Tunneling Microscope (STM) represents a suitable probe which can address either the morphological properties or the electronic ones through Scanning Tunneling Spectroscopy (STS), which is the most powerful STM-related capability, since it allows for atomic-scale characterization of the local density of states (LDOS) of the sample. The local electronic properties of In0.53Ga0.47As are investigated at the interface with Al2O3. Two pristine surfaces, the As-rich (2x4) reconstruction and the group-III-rich (In/Ga) (4x2) reconstruction are scrutinized by STM. STS shows that for both n-type doped reconstructions the Fermi level is initially pinned near the valence band. However, upon in situ growth of the Al2O3 thin film by Molecular Beam Epitaxy (MBE), partial unpinning occurs, while post-deposition annealing restores the original pinned condition in a different extent depending on the surface reconstruction. This behavior is rationalized in terms of an interface dipole induced by positive charges in the as-grown oxide, which are suppressed upon annealing. Hence, this comparison shows that the (2x4) reconstruction is more favorable for application-oriented perspectives of In0.53Ga0.47As as an active channel in MOSFET devices. Despite the high expectations, graphene, the nowadays best-known 2D material, has severe limitations for logic electronics due to its gapless nature. These limitations could be possibly overcome by silicene (and germanene). Here, a thoroughly study about the formation by MBE of various 2D phases of silicon on the Ag(111) surface depending on coverage and substrate temperature is reported. The resulting scenario is depicted by several silicene phases showing different periodicities and orientations with respect to the silver substrate. These structural phases stem from the intrinsic flexibility of silicene originated by its buckled structure, in contrast to graphene. The periodically modulated LDOS of silicene superstructures evidenced by STS spectra could be ascribed to the symmetry breaking in the triangular sublattices originated by the presence of buckled honeycomb lattice. The instability of silicene upon air exposure leads to the necessary encapsulation which is provided by an aluminum-based capping layer. This configuration allows the transfer of the samples for ex situ Raman spectroscopy measurements. Both experimental and theoretical Raman spectra show the presence of E2g mode, namely G peak in graphene, which is the fingerprint of honeycomb lattice, and by other vibrational modes activated by the intrinsic disorder related to the buckling. Both theoretical models and experiments proved that silicene phases have different mixture of sp2-sp3 hybridization that means different bond lengths, bond angles, and buckling parameters. Moreover these phases of silicene exhibit different electronic properties, ranging from semiconducting to semi-metal character. The perspective of future high performance logics should probably experience an intermediate step at III-V compound semiconductors, but it is very likely to expect that 2D materials will remain a hot topic in future electronics.
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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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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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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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Clark, M. L. "The adsorption of the aurocyanide ion onto carbon: An investigation using scanning tunneling spectroscopy." Thesis, Clark, M.L. (2000) The adsorption of the aurocyanide ion onto carbon: An investigation using scanning tunneling spectroscopy. PhD thesis, Murdoch University, 2000. https://researchrepository.murdoch.edu.au/id/eprint/52706/.
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The carbon-in-pulp process uses activated carbon to win gold from gold-bearing solutions. This process is very effective in winning the gold, and has been used commercially for many decades. Despite numerous studies into the adsorption mechanism, no consensus has yet been reached as to how the gold is adsorbed onto the carbon.
Scanning tunneling spectroscopy is a technique that makes use of the electronic information contained in a scanning tunneling microscope image, to gain information about the material being studied on an atom-by-atom basis. Although STS has had considerable use in UHV studies, very little use has been made of the technique in air or under liquid. Yet STS has the potential to be a valuable tool for in situ studies where other surface analysis techniques cannot be used.
In this work, STS has been used to study the adsorption of gold onto carbon in situ. The principle method of STS used was I/V spectroscopy. In this method, the bias voltage of the tip is ramped over a specified range and the tunneling current is recorded and plotted out on a graph. The type of material on the surface beneath the tip determines the shape of the graph.
A number of different materials were successfully examined in air and under liquid by this method. This established a baseline of which materials could be distinguished in situ.
The technique was applied to material adsorbed onto HOPG from a solution of potassium aurocyanide and calcium chloride. The spectra were then compared to the spectrum of elemental gold and the spectrum of AuCN. The composition of the adsorbed material was then identified. This identification made possible some conclusions concerning the various proposed methods of aurocyanide adsorption.
Some investigations into aurocyanide adsorption onto activated carbon were also conducted using I/V spectroscopy, with less clear results. Reasons for this are discussed.
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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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Holder, Jonathan Paul. "Resonant tunnelling spectroscopy of vertical GaAs/AlGaAs structures." Thesis, University of Exeter, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312281.
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Mahapatra, Ojas. "A scanning probe microscopy (SPM) study of Bi(110) nanostructures on highly oriented pyrolytic graphite (HOPG)." Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8042.
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This research work is aimed at understanding the electronic properties of Bi(110) nanostructures. This study chiefly uses Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS) and Non Contact Atomic Force Microscope (NCAFM) to investigate the geometric and electronic structure of Bi(110) islands on highly oriented pyrolytic graphite (HOPG) substrate.
STM measurements are the primary focus of the thesis which involves imaging the bismuth islands and study of its atomic structure. STM images of the Bi(110) islands reveal a ‘wedding cake’ profile of the bismuth islands that show paired layers on top of a base. I(V) (Current vs voltage) data was acquired via STS techniques and its first derivative was compared to DFT calculations. The comparison implied the presence of a dead wetting layer which was present only underneath the bismuth islands. We observed bilayer damped oscillations in the surface energy that were responsible for the stability of paired layers in Bi(110) islands. Interesting Moiré pattern arising out of misorientation between the substrate and the overlayer are also observed in STM images on some bismuth islands.
Bright features pertaining to enhanced LDOS (local density of states) were observed on the perimeter of the bismuth islands and stripes in the STM images and STS dI/dV maps which appear at energies around the Fermi level. The bright features which we termed as ‘bright beaches (BB)’ are also observed on grain boundaries and defects that suggest that they are related to termination of the chain of bismuth atoms.
The Bi(110) islands and stripes were observed to form preferred widths with a well defined periodicity. This peculiar phenomenon was attributed to a lateral quantum size effect (QSE) that results from a Fermi wave vector with appropriate shifts in Fermi energy. The widths of the islands prefer to adjust themselves at the nodes of this in-plane Fermi wavelength.
NaCl deposited on a HOPG substrate forms cross shaped islands which were used as spacers to limit the interaction between the bismuth films and the underlying HOPG substrate. The NaCl islands are transparent to the flow of tunneling current and allow STS measurements. The LDOS of Bi/HOPG was very similar to the LDOS of Bi deposited on NaCl/HOPG which suggests that the wetting layer underneath the bismuth islands plays an important role in decoupling the film from the underlying substrate.
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Trainer, Daniel Joseph. "INVESTIGATION OF THE QUASIPARTICLE BAND GAP TUNABILITY OF ATOMICALLY THIN MOLYBDENUM DISULFIDE FILMS." Diss., Temple University Libraries, 2019. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/559773.
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Physics<br>Ph.D.<br>Two dimensional (2D) materials, including graphene, hexagonal boron nitride and layered transition metal dichalcogenides (TMDs), have been a revolution in condensed matter physics and they are at the forefront of recent scientific research. They are being explored for their unusual electronic, optical and magnetic properties with special interest in their potential uses for sensing, information processing and memory. Molybdenum disulfide (MoS2) has been the flagship semiconducting TMD over the past ten years due to its unique electronic, optical and mechanical properties. In this thesis, we grow mono- to few layer MoS2 films using ambient pressure chemical vapor depositions (AP-CVD) to obtain high quality samples. We employ low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) to study the effect of layer number on the electronic density of states (DOS) of MoS¬2. We find a reduction of the magnitude of the quasiparticle band gap from one to two monolayers (MLs) thick. This reduction is found to be due mainly to a shift of the valence band maxima (VBM) where the conduction band minimum (CBM) does not change dramatically. Density functional theory (DFT) modeling of this system shows that the overlap of the interfacial S-pz orbitals is responsible for shifting the valence band edge at the Γ-point toward the Fermi level (EF), reducing the magnitude of the band gap. Additionally, we show that the crystallographic orientation of monolayer MoS2 with respect to the HOPG substrate can also affect the electronic DOS. This is demonstrated with five different monolayer regions having each with a unique relative crystallographic orientation to the underlying substrate. We find that the quasiparticle band gap is closely related to the moiré pattern periodicity, specifically the larger the moiré periodicity the larger the band gap. Using DFT, we find that artificially increasing the interaction between the film and the substrate means that the magnitude of the band gap reduces. This indicates that the moiré pattern period acts like a barometer for interlayer coupling. We investigate the effect of defects, both point and extended defects, on the electronic properties of mono- to few layer MoS¬2 films. Atomic point defects such including Mo interstitials, S vacancies and O substitutions are identified by STM topography. Two adjacent defects were investigated spectroscopically and found to greatly reduce the quasiparticle band gap and arguments were made to suggest that they are Mo-Sx complex vacancies. Similarly, grain boundaries were found to reduce the band gap to approximately ¼ of the gap found on the pristine film. We use Kelvin probe force microscopy (KPFM) to investigate the affect of annealing the films in UHV. The work function measurements show metastable states are created after the annealing that relax over time to equilibrium values of the work function. Scanning transmission electron microscopy (STEM) is used to show that S vacancies can recombine over time offering a feasible mechanism for the work function changes observed in KPFM. Lastly, we report how strain affects the quasiparticle band gap of monolayer MoS2 by bending the substrate using a custom built STM sample holder. We find that the local, atomic-scale strain can be determined by a careful calibration procedure and a modified, real-space Lawler Fujita algorithm. We find that the band gap of MoS2 reduces with strain at a rate of approximately 400 meV/% up to a maximum strain of 3.1%, after which the film can slip with respect to the substrate. We find evidence of this slipping as nanoscale ripples and wrinkling whose local strain fields alter the local electronic DOS.<br>Temple University--Theses
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Yankowitz, Matthew Abraham. "Local Probe Spectroscopy of Two-Dimensional van der Waals Heterostructures." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/594649.
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A large family of materials, collectively known as "van der Waals materials," have attracted enormous research attention over the past decade following the realization that they could be isolated into individual crystalline monolayers, with charge carriers behaving effectively two-dimensionally. More recently, an even larger class of composite materials has been realized, made possible by combining the isolated atomic layers of different materials into "van der Waals heterostructures," which can exhibit electronic and optical behaviors not observed in the parent materials alone. This thesis describes efforts to characterize the atomic-scale structural and electronic properties of these van der Waals materials and heterostructures through scanning tunneling microscopy measurements. The majority of this work addresses the properties of monolayer and few-layer graphene, whose charge carriers are described by massless and massive chiral Dirac Hamiltonians, respectively. In heterostructures with hexagonal boron nitride, an insulating isomorph of graphene, we observe electronic interference patterns between the two materials which depend on their relative rotation. As a result, replica Dirac cones are formed in the valence and conduction bands of graphene, with their energy tuned by the rotation. Further, we are able to dynamically drag the graphene lattice in these heterostructures, owing to an interaction between the scanning probe tip and the domain walls formed by the electronic interference pattern. Similar dragging is observed in domain walls of trilayer graphene, whose electronic properties are found to depend on the stacking configuration of the three layers. Scanning tunneling spectroscopy provides a direct method for visualizing the scattering pathways of electrons in these materials. By analyzing the scattering, we can directly infer properties of the band structures and local environments of these heterostructures. In bilayer graphene, we map the electrically field-tunable band gap and extract electronic hopping parameters. In WSe₂, a semiconducting transition metal dichalcogenide, we observe spin and layer polarizations of the charge carriers, representing a coupling of the spin, valley and layer degrees of freedom.
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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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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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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 discutée<br>In 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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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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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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Kislitsyn, Dmitry. "Spectroscopic Studies of Nanomaterials with a Liquid-Helium-Free High-Stability Cryogenic Scanning Tunneling Microscope." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22281.
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This dissertation presents results of a project bringing Scanning Tunneling Microscope (STM) into a regime of unlimited operational time at cryogenic conditions. Freedom from liquid helium consumption was achieved and technical characteristics of the instrument are reported, including record low noise for a scanning probe instrument coupled to a close-cycle cryostat, which allows for atomically resolved imaging, and record low thermal drift. Subsequent studies showed that the new STM opened new prospects in nanoscience research by enabling Scanning Tunneling Spectroscopic (STS) spatial mapping to reveal details of the electronic structure in real space for molecules and low-dimensional nanomaterials, for which this depth of investigation was previously prohibitively expensive.
Quantum-confined electronic states were studied in single-walled carbon nanotubes (SWCNTs) deposited on the Au(111) surface. Localization on the nanometer-scale was discovered to produce a local vibronic manifold resulting from the localization-enhanced electron-vibrational coupling. STS showed the vibrational overtones, identified as D-band Kekulé vibrational modes and K-point transverse out-of plane phonons. This study experimentally connected the properties of well-defined localized electronic states to the properties of associated vibronic states.
Electronic structures of alkyl-substituted oligothiophenes with different backbone lengths were studied and correlated with torsional conformations assumed on the Au(111) surface. The molecules adopted distinct planar conformations with alkyl ligands forming cis- or trans- mutual orientations and at higher coverage self-assembled into ordered structures, binding to each other via interdigitated alkyl ligands. STS maps visualized, in real space, particle-in-a-box-like molecular orbitals. Shorter quaterthiophenes have substantially varying orbital energies because of local variations in surface reactivity. Different conformers of longer oligothiophenes with significant geometrical distortions of the oligothiophene backbones surprisingly exhibited similar electronic structures, indicating insensitivity of interaction with the surface to molecular conformation.
Electronic states for annealed ligand-free lead sulfide nanocrystals were investigated, as well as hydrogen-passivated silicon nanocrystals, supported on the Au(111) surface. Delocalized quantum-confined states and localized defect-related states were identified, for the first time, via STS spatial mapping. Physical mechanisms, involving surface reconstruction or single-atom defects, were proposed for surface state formation to explain the observed spatial behavior of the electronic density of states.
This dissertation includes previously published co-authored material.
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Åhlund, John. "Electronic and Geometrical Structure of Phthalocyanines on Surfaces : An Electron Spectroscopy and Scanning Tunneling Microscopy Study." Doctoral thesis, Uppsala universitet, Fysiska institutionen, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7802.
Full textAbstract:
Core- and Valence Photoelectron Spectroscopy (PES), X-ray- and Ultraviolet-Visible Absorption Spectroscopy (XAS and UV-Vis), Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) calculations are used to study the electronic and geometrical structure of a class of macro-cyclic molecules, Phthalocyanines (Pc), on surfaces. These molecules are widely studied due to their application in many different fields. Multilayer and monolayer coverages of Iron Phthalocyanine (FePc) and metal-free Phthalocyanine (H2Pc) deposited on different surfaces are investigated in order to get insight in the electronic and geometrical structure of the obtained overlayers, of crucial importance for the understanding of the film functionality. Sublimation of molecular thick films on Si(100) and on conducting glass results in films with molecules mainly oriented with their molecular plane orthogonal to the surface. Ex-situ deposited H2Pc films on conductive glass show different molecular orientation and morphology with respect to the vacuum sublimated films. We study the monolayer adsorption structure of FePc and H2Pc and compare our results with other Pc’s adsorbed on graphite. We find that the molecular unit cell and the superstructure is characteristic for each Pc adsorbed on graphite, even if the geometrical size of the compared molecules is the same. The PE- and XA- spectra of FePc on graphite are essentially identical for the mono- and multilayer preparations, evidencing weak intermolecular and molecular-substrate interactions of van der Waals nature. Furthermore, we characterize Pc’s on InSb (001)-c(8x2). The substrate In rows are observed to be the adsorption site for Pc’s. We find that the growth of the two-dimensional islands of FePc is prolonged in the [-110] direction, in contrast to ZnPc adsorbed on the same substrate at room temperature. We interpret this result as an indication that the adsorption is controlled by the substrate corrugation observed at 70 K.
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Åhlund, John. "Electronic and geometrical structure of phthalocyanines on surfaces : an electron spectroscopy and scanning tunneling microscopy study /." Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7802.
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