Dissertations / Theses: 'Tunneling (Physics) Tunneling spectroscopy'

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Bautista, Anthony. "TUNNELING SPECTROSCOPY STUDY OF CALCIUM RUTHENATE." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/784.

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The ruthenates are perhaps one of the most diverse group of materials known up to date. These compounds exhibit a wide array of behaviors ranging from the exotic pwave superconductivity in Sr2RuO4, to the itinerant ferromagnetism in SrRuO3, and the Mott-insulating behavior in Ca2RuO4. One of the most intriguing compounds belonging to this group is Ca3Ru2O7 which is known to undergo an antiferromagnetic ordering at 56K and an insulating transition at 48K. Most intriguing, however, is the behavior displayed by this compound in the presence of an external magnetic field. For fields parallel to the a-axis, the compound undergoes a metamagnetic transition into the ferromagnetic region at 6 T. If the external field direction is changed to the b-axis then the result will be different. colossal magnetoresistance occurs and a fall in reistivity of up to three orders of magnitude is recorded at fields of 15T. Most interesting, however, is the energy gap observed for this material. A number of groups have measured such gap with different methods and found conflicting results. For this reason it was of vital importance to perform measurements on this compound and try to resolve this issue. Tunneling spectroscopy is one of the most powerful techniques which can be used to probe the electronic properties of a material. The method is best suited to measure the density of states of a material and hence the nature of the strong correlations which dictate the properties of the compound. We performed a series of tunneling spectroscopy measurements by means of planar tunnel junctions. These types of junctions were chosen because of their stability over a large temperature range and their stability in the presence of an external field. The anisotropies which showed up in the resistivity and magnetization measurements manifested also in our data. For tunneling parallel to the a-axis, we observed a gap opening at 48K with a width a peak to peak width of 2Δa ~258±15meV. As the temperature was lowered, the gap size increased reaching a maximum width of 2Δa ~ 845±38meVat 4.2K. Tunneling parallel to the b-axis, the gap has a much smaller size than the a-axis gap. At 48K the gap width is about 2Δb ~ 201±13 meV and reaches a maximum width of 2Δb ~ 366±33 meV at 4.2K. For the c-axis, the situation is different since the gap opens at 56K instead of 48K. The gap width at 56K is about 2Δc ~ 102±6meV and reaches a maximum width of 2Δc ~ 179±14 meV at 4.2K. In the presence of an external field, we noticed that the overall behavior was always the same in the ab-plane but differed in c-axis direction. In our experiment, an external field was applied along the a-axis and measurements were made at 4.2K. For aaxis tunneling, the gap width decreased to a value of 2Δa ~ 587±27 meV at 4.2 K at 7T. On the other hand, the gap width in the b-axis direction decreased to a value of 2Δb ~ 308±25 meV for the same field. For the c-axis direction, the gap decreased to a value of 2Δc ~ 112±8 meV at 7T. The DOS of the c-axis differs for fields of 6T and above. A third peak emerges inside the gap on the valence side of the DOS. This third peak seems to be a direct consequence of the metamagnetic transition at 6T observed by other groups and may be attributable to a spin-filtering effect.

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Chan, Ho Bun 1969. "Tunneling spectroscopy of the two-dimensional electron gas." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9387.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999.
Includes bibliographical references (p. 155-161).
We measure the single particle density of states (DOS) of a two-dimensional electron system (2DES) in a GaAs/AlGaAs heterostructure. Using a technique that we call "Time Domain Capacitance Spectroscopy" (TDCS), we measure the complete current-voltage characteristics for tunneling into the 2DES without making ohmic contacts to it. TDCS detects the tunneling current in regimes difficult to access by conventional methods, such as when the in-plane conductance is low. For the first time we detect the contributions of localized states to the tunneling current. The DOS of an interacting 2DES in the diffusive limit displays logarithmic energy dependence near the Fermi level. Using TDCS, we measure the voltage dependence of the tunneling conductance of a semiconductor 2DES and observe the logarithmic Coulomb anomaly for the first time in 2D systems other than thin metal films. As we increase the density, this suppression in tunneling conductance narrows and recedes. Nevertheless suppression reappears when we apply a magnetic field perpendicular to the 2D plane. We find that the tunneling conductance depends linearly on voltage near zero bias for all magnetic field strengths and electron densities. Moreover, the slopes of this linear gap are strongly field dependent. The data are suggestive of a new model of the tunneling gap in the presence of disorder and screening. We also use TDCS to study the interactions among electronic spins. By applying excitations less than kT, we observe that equilibrium tunneling into spin-polarized quantum Hall states (v=l, 3, 1/3) occurs at two distinct tunneling rates for samples of very high mobility. Some electrons tunnel into the 2DES at a fast rate while the rest tunnel at a rate up to 2 orders of magnitude slower. Such novel double-rate tunneling is not observed at even-integer filling fractions where the 2DES is not spin-polarized. The dependence of the two rates on magnetic field, temperature and tunnel barrier thickness suggests that slow in-plane spin relaxation, possibly related to formation of Skyrmions, leads to a bottleneck for tunneling of electrons.
by Ho Bun Chan.
Ph.D.

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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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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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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
Ph.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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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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Ji, Tao. "Inelastic electron tunneling spectroscopy in molecular electronic devices from first-principles." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96883.

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In this thesis, we present the first-principle calculations of inelastic electron tunneling spectroscopy(IETS) in single molecular break junctions. In a two-probe electrode-molecule-electrode setup, density functional theory(DFT) is used for the construction of the Hamiltonian and the Keldysh non-equilibrium Green's function(NEGF) technique will be employed for determining the electron density in non-equilibrium system conditions. Total energy functional, atomic forces and Hessian matrix can be obtained in the DFT-NEGF formalism and self-consistent Born approximation(SCBA) is used to integrate the molecular vibrations (phonons) into the framework once the phonon spectra and eigenvectors are calculated from the dynamic matrix. Geometry optimization schemes will also be discussed as an indispensable part of the formalism as the equilibrium condition is crucial to correctly calculate the phonon properties of the system.To overcome the numerical difficulties, especially the large computational time demand of the electron-phonon coupling problem, we develop a numerical approximation for the electron self-energy due to phonons and the error is controlled within numerical precision. Besides, a direct IETS second order I-V derivative expression is derived to reduce the error of numerical differentiation under reasonable assumptions. These two approximations greatly reduce the computation requirement and make the calculation feasible within current numerical capability.As the application of the DFT-NEGF-SCBA formalism, we calculate the IETS of the gold-octanedithiol(ODT) molecular junction. The I-V curve, conductance and IETS from ab-inito calculations are compared directly to experiments. A microscopic understanding of the electron-phonon coupling mechanism in the molecular tunneling junctions is explained in this example. In addition, comparisons of the hydrogen-dissociative and hydrogen-non-dissociative ODT junctions as well as the different charge transfer behaviors are presented to show the effects of thiol formation in the ODT molecular junction.
Dans cette thèse, nous présentons des calculs ab initio de la spectroscopie à effet tunnel par électron inélastique (IETS)appliqués à des jonctions moléculaires. Dans le cadre d'une configuration électrode-molécule-électrode,la théorie de la fonctionnelle de la densité (DFT) est utilisée pour construire l'hamiltonien et les fonctions de Green hors-équilibres(NEGF) sont employées pour déterminer la densité électroniquedans des conditions hors-équilibre. Le cadrede la DFT-NEGF nous permet de calculer des quantités telles que la fonctionnelle d'énergie totale,les forces atomiques ainsi que la matrice de Hessian. L'approximationauto-consistante de Born (SCBA) est employée afin d'intégrer les vibrations moléculaires (phonons) dans le formalisme DFT-NEGF,une fois que le spectre des phonons et les vecteurs propres ont été calculés à partir de la matrice dynamique. Des méthodes d'optimisations géométriques sont aussi discutées en tant que part indispensable du formalisme,étant donné que la condition d'équilibre mécanique est essentielle afin de calculer correctement les propriétés des phonons du système.Afin de surmonter les difficultés numériques, particulièrement concernant la grande demandecomputationnelle requise pour le calcul du couplage électron-phonon, nous développons une approximation numérique pour la self-énergie associée aux phonons. De plus, en employant quelques hypothèses raisonables, nous dérivons une expression pour l'IETS calculée à partir de laseconde dérivée de la courbe I-V dans le butde réduire l'erreur associée à la différentiation numérique. L'utilisation de ces deux approximations diminuent grandement les exigences computationnelles et rendent les calculs possibles avec les capacités numériques actuelles.Comme application du formalisme DFT-NEGF-SCBA, nous calculons l'IETS de la jonction moléculaire or-octanedithiol(ODT)-or. La courbe I-V, la conductance et l'IETS obtenues par calculs ab initio sontdirectement comparées aux données expérimentales. Une compréhension microscopique du couplage électron-phonon pour une jonction moléculaire à effet tunnel est élaborée dans cet exemple. De plus, des comparaisons entre les jonctions ODT à hydrogène dissociatif et à hydrogène non-dissociatif ainsi queles différents comportements de transfert de charges sont présentés afin de montrer les effets de la formation du thiol dans la jonction moléculaire ODT.

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Acharya, Danda Pani. "Atomic Manipulation and Tunneling Spectroscopy on Metal and Semiconductor Surfaces." View abstract, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3292889.

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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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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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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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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
Ph.D.
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.
Temple University--Theses

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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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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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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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Nicholls, Dylan. "Scanning Tunneling Microscopy and Spectroscopy studies of zinc-phthalocyanine adsorption on SiC(0001) and iridium-modified silicon surfaces." Thesis, The University of North Dakota, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3626206.

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Studies were performed on two seemingly different topics, molecular thin films on graphite/graphene and metal induced changes in various cuts of silicon (Si) surfaces. However, both projects share the underlying theme of self-assembly. Since nature can rely upon self-assembly at the nano-scale, all that is needed is to discover functional means to create components for integrated circuits as well as electronic and photonic devices.

Scanning Tunneling Microscopy and Spectroscopy (STM/STS) studies were carried out to characterize the morphology of thin porphyrin films on graphite and the effects of Zn-Phthalocyanine (Zn-Pc) adsorption on the electronic properties of graphene. It was found that the metal atom complex of porphyrin molecules can determine the morphology, intermolecular forces and ability to create thin films on a graphite surface. Zn-Pc adsorption onto graphene shifts the position of the Dirac point with respect to Fermi level which leads to localized p- and n-type doping effects in the graphene substrate.

STM, STS and Low-Energy Electron Diffraction (LEED) measurements were carried out on iridium (Ir) modified Si(111) and Si(100) surfaces. The Ir-modified Si(111) surface exhibited a √7×√7 R 19.1° domain formation that was composed of Ir-ring clusters. LEED measurements showed that on Ir-modified Si(100), a p(2×2) structure arose after annealing at ~700°C. The proposed model for the Ir-silicide nanowires shows that an Ir atom replaces every other Si dimer along the Si dimer rows of Si(100)-2×1.

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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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Clark, Kendal W. "STM Study of Molecular and Biomolecular Electronic Systems." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1282363151.

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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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Arbelo, Jorge Elena [Verfasser]. "Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy / Elena Arbelo Jorge." Mainz : Universitätsbibliothek Mainz, 2011. http://d-nb.info/1018331166/34.

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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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Fillis-Tsirakis, Evangelos [Verfasser], and Jochen [Akademischer Betreuer] Mannhart. "Investigating superconductivity by tunneling spectroscopy using oxide heterostructures / Evangelos Fillis-Tsirakis ; Betreuer: Jochen Mannhart." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1138630756/34.

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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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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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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.

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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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Jandke, Jasmin Maria [Verfasser], and W. [Akademischer Betreuer] Wulfhekel. "Elastic and Inelastic Scanning Tunneling Spectroscopy on Iron-Based Superconductors / Jasmin Maria Jandke ; Betreuer: W. Wulfhekel." Karlsruhe : KIT-Bibliothek, 2017. http://d-nb.info/1148551247/34.

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32

Jandke, Jasmin [Verfasser], and W. [Akademischer Betreuer] Wulfhekel. "Elastic and Inelastic Scanning Tunneling Spectroscopy on Iron-Based Superconductors / Jasmin Maria Jandke ; Betreuer: W. Wulfhekel." Karlsruhe : KIT-Bibliothek, 2017. http://d-nb.info/1148551247/34.

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33

Al-Brithen, Hamad A. H. "Scanning Tunneling Microscopy Investigation of Rock-salt and Zinc-blende Nitrides Grown by Molecular Beam Epitaxy." Ohio University / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1107274641.

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34

Mühlenberend, Svenja [Verfasser]. "Metals and organic adsorbates on GaAs(110) : a scanning tunneling microscopy, spectroscopy and luminescence study / Svenja Mühlenberend." Kiel : Universitätsbibliothek Kiel, 2016. http://d-nb.info/1096220903/34.

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35

Jochmann, Kira [Verfasser]. "Scanning tunneling microscopy and femtosecond laser photoemission spectroscopy of supported cluster structures: A new experimental approach / Kira Jochmann." Ulm : Universität Ulm. Fakultät für Naturwissenschaften, 2015. http://d-nb.info/1075253179/34.

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36

Kersell, Heath Ryan. "Investigations on the Complex Rotations of Molecular Nanomachines." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1307126123.

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37

Hanneken, Christian [Verfasser], and Roland [Akademischer Betreuer] Wiesendanger. "Observation of Non-Collinear Magnetoresistance by Scanning Tunneling Spectroscopy on Skyrmions in PdFe/Ir(111) / Christian Hanneken. Betreuer: Roland Wiesendanger." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2016. http://d-nb.info/1093411333/34.

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38

Hanneken, Christian Verfasser], and Roland [Akademischer Betreuer] [Wiesendanger. "Observation of Non-Collinear Magnetoresistance by Scanning Tunneling Spectroscopy on Skyrmions in PdFe/Ir(111) / Christian Hanneken. Betreuer: Roland Wiesendanger." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2016. http://nbn-resolving.de/urn:nbn:de:gbv:18-77548.

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39

Smeenk, Christopher. "Imaging Atoms and Molecules with Strong Laser Fields." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24023.

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We study multi-photon ionization of rare gas atoms and small molecules by infrared femtosecond laser pulses. We demonstrate that ionization is accurately described by a tunnelling model when many infrared photons are absorbed. By measuring photo-electron and photo-ion spectra, we show how the sub-Ångstrom spatial resolution of tunnelling gives information about electron densities in the valence shell of atoms and molecules. The photo-electron and photo-ion momentum distributions are recorded with a velocity map imaging (VMI) spectrometer. We describe a tomographic method for imaging a 3-D momentum distribution of arbitrary symmetry using a 2-D VMI detector. We apply the method to measure the 3-D photo-electron distribution in elliptically polarized light. Using circularly polarized light, we show how the photo-electron momentum distribution can be used to measure the focused laser intensity with high precision. We demonstrate that the gradient of intensities present in a focused femtosecond pulse can be replaced by a single average intensity for a highly nonlinear process like multi-photon ionization. By studying photo-electron angular distributions over a range of laser parameters, we determine experimentally how the photon linear momentum is shared between the photo-electron, photo-ion and light field. We find the photo-electron carries only a portion of the total linear momentum absorbed. In addition we consider how angular momentum is shared in multi-photon ionization, and find the photo-electron receives all of the angular momentum absorbed. Our results demonstrate how optical and material properties influence the photo-electron spectrum in multi-photon ionization. These will have implications for molecular imaging using femtosecond laser pulses, and controlling the initial conditions of laser generated plasmas.

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40

Nag, Pranab Kumar [Verfasser], Bernd [Akademischer Betreuer] Büchner, and Rüdiger [Gutachter] Klingeler. "Unusual electronic properties in LiFeAs probed by low temperature scanning tunneling microscopy and spectroscopy / Pranab Kumar Nag ; Gutachter: Rüdiger Klingeler ; Betreuer: Bernd Büchner." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/1150310332/34.

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41

Nag, Pranab Kumar [Verfasser], Bernd Akademischer Betreuer] Büchner, and Rüdiger [Gutachter] [Klingeler. "Unusual electronic properties in LiFeAs probed by low temperature scanning tunneling microscopy and spectroscopy / Pranab Kumar Nag ; Gutachter: Rüdiger Klingeler ; Betreuer: Bernd Büchner." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-231628.

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42

Perraud, Simon. "Etude de puits quantiques semiconducteurs par microscopie et spectroscopie à eﬀet tunnel." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00606632.

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Des puits quantiques à base d'hétérostructures In0.53 Ga0.47 As/In0.52 Al0.48 As, fabriqués par épitaxie par jets moléculaires sur substrats InP(111)A, sont étudiés par microscopie et spectroscopie à eﬀet tunnel à basse température et sous ultra-vide. La première partie est consacrée à une étude de la surface épitaxiée (111)A de In0.53 Ga0.47 As de type n. Il est découvert que le niveau de Fermi de surface est positionné dans la bande de conduction, à proximité du niveau de Fermi de volume, et peut être partiellement contrôlé en variant la concentration d'impuretés de type n dans le volume. Ce résultat est conﬁrmé en déterminant la relation de dispersion de la bande de conduction en surface. Un tel dépiégeage partiel du niveau de Fermi de surface indique que la densité d'états de surface accepteurs est faible. Il est proposé que ces états proviennent de défauts ponctuels natifs localisés à la surface. La deuxième partie, basée sur les résultats obtenus dans la première partie, est consacrée à une étude de puits quantiques In0.53 Ga0.47 As de surface, déposés sur des barrières In0.52 Al0.48 As selon la direction (111)A. Les mesures sont conduites sur la surface épitaxiée (111)A du puits quantique In0.53 Ga0.47 As, de manière à pouvoir sonder à l'échelle du nanomètre la distribution de densité locale d'états électroniques dans le plan du puits quantique. Il est conﬁrmé que des sous-bandes électroniques sont formées dans le puits quantique, et que la concentration d'électrons dans le puits peut être contrôlée du fait du dépiégeage partiel du niveau de Fermi de surface. Il est découvert qu'un phénomène de percolation d'états localisés survient dans la queue de chaque sous-bande, ce qui indique la présence d'un potentiel désordonné dans le puits quantique. Les seuils de percolation sont déterminés en utilisant un modèle semi-classique. L'origine du potentiel désordonné est attribuée à une distribution aléatoire des défauts ponctuels natifs à la surface du puits quantique. Il est également découvert qu'un état lié apparaît au bas de chaque sous-bande à proximité d'un défaut ponctuel natif de type donneur. L'énergie de liaison et le rayon de Bohr des états liés peuvent être directement déterminés. De plus, il est démontré que l'énergie de liaison et le rayon de Bohr sont fonctions de l'épaisseur du puits quantique, en accord quantitatif avec des calculs variationnels d'impuretés dans le modèle de l'atome d'hydrogène.

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43

Corbetta, Marco [Verfasser], J. [Akademischer Betreuer] Kirschner, W. [Akademischer Betreuer] Widdra, and C. M. [Akademischer Betreuer] Schneider. "Spin-polarized scanning tunneling microscopy and spectroscopy study of Fe and Co nanostructures on Cu(111) / Marco Corbetta. Betreuer: J. Kirschner ; W. Widdra ; C. M. Schneider." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2013. http://d-nb.info/1038211212/34.

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44

Wedekind, Sebastian [Verfasser], Jürgen [Akademischer Betreuer] Kirschner, Wolf [Akademischer Betreuer] Widdra, and Bene [Akademischer Betreuer] Poelsema. "A spin-polarized scanning tunneling microscopy and spectroscopy study of individual nanoscale particles grown on copper surfaces / Sebastian Wedekind. Betreuer: Jürgen Kirschner ; Wolf Widdra ; Bene Poelsema." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2009. http://d-nb.info/1024976785/34.

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45

Lindner, Philipp [Verfasser]. "Thermal properties of atomic-scale skyrmions in PdFe nanoislands on Ir(111) investigated by variable-temperature and time-resolved scanning tunneling microscopy and spectroscopy / Philipp Lindner." Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/1236695054/34.

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46

Teichmann, Karen [Verfasser], Rainer G. [Akademischer Betreuer] Ulbrich, and Hans W. [Akademischer Betreuer] Schumacher. "Scanning tunneling spectroscopy of space charge regions in semiconductors: From single donor to heterostructure systems / Karen Teichmann. Gutachter: Rainer G. Ulbrich ; Hans W. Schumacher. Betreuer: Rainer G. Ulbrich." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1043611398/34.

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47

Somma, Carmine. "Coherent Multidimensional Off-resonant THz Spectroscopy on Semiconductors." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18512.

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Zum ersten Mal konnte die kohärente Erzeugung von ultrakurzen Pulsen mit Feld stärken im MV/cm Bereich mit einem Spektralbereich von 0.1-30 THz im organischen Kristall DSTMS. Kohärente mehrdimensionale Terahertzspektroskopie (CMTS) hat sich zu einer wichtigen Methode zur Untersuchung der niederenergetischen Anregungen von Halbleitern and deren kohärenter Dynamik entwickelt. Eine neuartige CMTS Methode mit drei phasenstarren, zueinander zeitverzögerten Terahertzpulsen wurde entwickelt. Sie beruht auf der kollinearen Wechselwirkung der Pulse mit der Probe, sodass verschiedene Ordnungen des nichtlinearen Signals in gleicher Richtung emittiert werden und deshalb gleichzeitig gemessen werden können. Amplitude und Phase des nichtlinearen Signals können durch elektro-optisches Abtasten vermessen werden, wodurch die zeitliche Entwicklung der kohärenten Wechselwirkungen in Echtzeit untersucht werden kann. CMTS erlaubt zusätzlich die eindeutige Zerlegung des nichtlinearen Signals in die verschiedenen nichtlinearen Ordnungen in der jeweiligen mehrdimensionalen Frequenzdomäne. Die nichtlineare, nicht-resonante Antwort zweier undotierter Halbleiter, des Ferroelektrikums Lithiumniobat (LiNbO3) und Indiumantimonids (InSb) kann mit dieser neuartigen Methode untersucht werden. In LiNbO3 wird das nichtlineare Signal durch einen Femtosekunden nichtlinearen Verschiebestrom (SC) hervorgerufen. SC wird durch die gebrochene Inversionssymmetrie des Kristalls in Verbindung mit einer ultraschnellen Dephasierung der feldinduzierten, kohärenten interband-Polarisation hervorgerufen. Die Dephasierung der interband-Polarisation erlaubt das Tunneln von Elektronen vom Valenzband in das Leitungsband. In InSb wird das kohärente Signal durch sowohl zwei-Phonen als auch zwei-Photonen interband-Anregungen erzeugt. Die impulsive Anregung einer kohärenten zwei-Phononen Polarisation wird durch das große Übergangsdipolmoment von InSb verstärkt, was zu deutlich größeren Amplituden der Polarisation als im linearem Regime führt.
For the first time, the coherent generation of ultrashort MV/cm field pulses with a spectrum covering the frequency range 0.1-30 THz is demonstrated in the organic crystal DSTMS. Coherent multidimensional terahertz spectroscopy (CMTS) has become a prominent technique for, e.g., driving low-energy excitations in semiconductors and monitoring their coherent dynamics. A novel CMTS technique using three phase-locked inter-delayed THz pulses is implemented. It relies on a collinear interaction of the pulses with a sample, so that different contributions to the nonlinear signal are emitted in the same direction, and thus can be measured all at once. Phase-resolved detection by electro-optic sampling allows for measuring amplitude and absolute phase of the nonlinear signal, thereby enabling to investigate the evolution of coherent interactions between quantum excitations in real time. In CMTS, the nonlinear signal is dissected into the distinct nonlinear contributions in the corresponding multidimensional frequency domain. This novel technique is applied to study the nonlinear off-resonant response of two undoped bulk semiconductors, the wide-bandgap ferroelectric lithium niobate (LiNbO3) and the narrow-bandgap indium antimonide (InSb). In LiNbO3, the nonlinear signal is generated by a femtosecond nonlinear shift current (SC), a distinctive characteristic of the bulk photovoltaic effect. The SC stems from the lack of inversion symmetry and the ultrafast dephasing of the field-induced interband coherent polarization due to a sufficiently high decoherence rate, which enables tunneling of electrons from the valence to the conduction band. In InSb, the nonlinear signal is caused by the coherent response on both the two-phonon and two-photon interband excitations. The impulsive generation of the two-phonon coherent polarization is enhanced by the large interband transition dipole of InSb, resulting in much larger polarization amplitudes than in the regime of linear response.

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48

Bidermane, Ieva. "Structure and Electronic Properties of Phthalocyanine Films on Metal and Semiconductor Substrates." Doctoral thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-217086.

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The current thesis presents fundamental studies of phthalocyanines (Pcs), a group of organic macro-cycle molecules. The use of phthalocyanine molecular films in devices with a variety of possible technological applications has been the reason of the many studies dedicated to such molecules during the last decades. Core and valence photoelectron spectroscopies (PES), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) techniques are used to study phthalocyanine molecules in gas phase and adsorbed on gold (111) and silicon Si(100)-2x1 substrates. Density functional theory (DFT) is used to obtain further insights in the electronic structure of the phthalocyanines. The aim of our studies is to get a deeper understanding into the molecule-molecule and molecule-substrate interactions, a fundamental requirement for improving the devices based on such molecular materials. Gas phase PES and XAS studies and single molecule DFT calculations are performed on the valence band (VB) of iron phthalocyanine (FePc), manganese phthalocyanine (MnPc) and metal-free phthalocyanine (H2Pc). The VB simulations have shown how the metal atom of the Pc influences the inner valence states of the molecules. The HOMO of the H2Pc and FePc is formed by mostly C2p states, whereas the HOMO of MnPc has mainly Mn3d character. PES studies of H2Pc on Au(111) have revealed the influence of the surface on the adsorption of the monolayer. XAS studies indicate formation of ordered monolayer with the Pc ligands parallel to the surface and the change of the molecular tilt angle with increasing thicknesses. For LuPc2 adsorbed on Au(111), STM study demonstrates a formation of bilayer instead of a monolayer. A comparison between the results of LuPc2 adsorbed on pristine or passivated Si(100)-2x1 confirmes the different reactivities of these surfaces: LuPc2 retains many molecular-like characters, when adsorbed on the innert passivated Si. Instead, on the more reactive pristine Si surface, the spectroscopic results have indicated a more significant interaction, possible hybridization and charge redistribution between the molecules and the surface. Moreover, STM images show a modification of the geometrical shape of the molecules, which are proposed to adsorb in two different geometries on the pristine Si surface.

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49

Oh, Seung Cheol [Verfasser], Johannes [Akademischer Betreuer] Barth, and Markus [Akademischer Betreuer] Lackinger. "Single layer films of functional molecules on noble metal surfaces visited by scanning tunneling microscopy and X-ray spectroscopy / Seung Cheol Oh. Gutachter: Johannes Barth ; Markus Lackinger. Betreuer: Johannes Barth." München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1060825449/34.

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50

Prüser, Henning [Verfasser], Rainer G. [Akademischer Betreuer] Ulbrich, Thomas [Akademischer Betreuer] Pruschke, and Richard [Akademischer Betreuer] Berndt. "Scanning tunneling spectroscopy of magnetic bulk impurities: From a single Kondo atom towards a coupled system / Henning Prüser. Gutachter: Rainer G. Ulbrich ; Thomas Pruschke ; Richard Berndt. Betreuer: Rainer G. Ulbrich." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/1044767782/34.

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Dissertations / Theses on the topic 'Tunneling (Physics) Tunneling spectroscopy'

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