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ABREU, FERNANDA DE MELLO. "TIME-DOMAIN OPTICAL MULTIPLEXING IN STM-16, STM-64 AND STM-256 SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2001. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=2361@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROALCATEL TELECOMUNICAÇÕES
Este trabalho tem como foco o up-grade da taxa de bits em enlaces ópticos através da tecnologia OTDM. Os sistemas analisados contemplam os up-grades das taxas de 2,48 Gbps para 10 Gbps e também da taxa de 10 Gbps para 40 Gbps. Para tal, foram introduzidos módulos de transmissão e recepção, capazes de utilizar arquiteturas quase totalmente ópticas. É avaliado então, através de simulações, o comportamento da arquitetura proposta em infra-estruturas de enlaces já instalados no Brasil, destacando os pontos mais críticos. No que se refere ao up-grade de 10 Gbps para 40 Gbps, foi dado enfoque especial para as penalidades relativas à PMD (Polarization Mode Dispersion).
This work aims at up grading the bit rate of optical links through the OTDM technology. The analyzed up-grades change the bit rate of 2,48 Gbps up to 10 Gbps and also from the bit rate of 10 Gbps up to 40 Gbps. To reach these objectives, transmission and reception modules were introduced, using all optical networks topologies. The performance of the proposed architecture was simulated using a infrastructure of links already installed in Brazil. The most critical issues were pointed out. Concerning the up-grade from 10 Gbps to 40 Gbps, a special focus was given to the penalties due to PMD (Polarization Mode Dispersion).
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Celis, Retana Arlensiú Eréndira. "Gap en graphène sur des surfaces nanostructurées de SiC et des surfaces vicinales de métaux nobles." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS417/document.
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L'électronique basée sur le graphène fait face à un verrou technologique, qui est l'absence d'une bande interdite (gap) permettant une commutation entre les états logiques allumé et éteint. Les nano-rubans de graphène rendent possible l'obtention de ce gap mais il est difficile de produire de tels rubans avec une largeur précise à l'échelle atomique et des bords bien ordonnés. Le confinement électronique est une façon élégante d'ouvrir un gap et peut en principe être réglé en ajustant la largeur des nano-rubans. Cette thèse est consacrée à la compréhension de l'ouverture du gap par nano-structuration. Nous avons suivi deux approches: l'introduction d'un potentiel super-périodique sur le graphène par des substrats vicinaux de métaux nobles et le confinement électronique dans des nano-rubans sur des facettes artificielles du SiC. Des potentiels super-périodiques ont été introduits avec deux substrats nano-structurés: l'Ir(332) et un cristal courbé de Pt(111) multi-vicinale. Le graphène modifie les marches initiales des substrats et les transforme en une succession de terrasses (111) et de régions d'accumulation de marches, observés par STM. La nano-structuration du substrat induit alors un potentiel super-périodique dans le graphène entraînant l'ouverture de gaps sur la bande π du graphène observée par ARPES, ce qui est cohérent avec la périodicité structurale observé par STM et LEED. Les gaps peuvent être convenablement expliqués par un modèle de type hamiltonien de Dirac; ce dernier nous permet de retrouver la force du potentiel à la jonction entre les terrasses (111) et la région d'accumulation des marches. La force du potentiel dépend du substrat, de la périodicité associée à la surface et du type de bord des marches (soit type A ou B). Nous avons aussi changé le potentiel de surface en intercalant du Cu sur l'Ir(332), qui reste préférentiellement au niveau de l'accumulation des marches. La surface présente des régions dopées n alors que les régions non-intercalées restent dopées p, conduisant à une succession de rubans dopés n et p pour une même couche de graphène continue. La seconde approche pour contrôler le gap est par confinement électronique dans des nanorubans de graphène synthétisés sur du SiC. Ces rubans sont obtenus sur des facettes du SiC ordonnées périodiquement. Comme l'ouverture d'un gap d'origine inconnue avait été observée par ARPES, nous avons réalisé les premières études atomiquement résolues par STM. Nous démontrons la régularité et la chiralité des bords, nous localisons précisément les nanorubans de graphène sur les facettes et nous identifions des mini-facettes sur du SiC. Afin de comprendre le couplage entre le graphène et le substrat, nous avons étudié une coupe transversale par STEM/EELS, en complément des études par ARPES et STM/STS. Nous observons que la facette (1-107) où le graphène se trouve présente un sub-facettage sur les extrémités haute et basse. Le sub-facettage comprend des mini-terrasses (0001) et des mini-facettes (1-105). Le graphène s'étend tout au long du la région sub-facettée, et est couplé au substrat dans les mini-terrasses (0001), ce qui le rend semi-conducteur. En revanche, le graphène au-dessus des mini-facettes (1-105) est découplé du substrat mais présente un gap observé par EELS, et compatible avec les observations faites par ARPES. L'origine du gap est expliquée par le confinement électronique sur des nano-rubans de graphène de 1 - 2 nm de largeur localisés sur ces mini-facettes (1-105)The major challenge for graphene-based electronic applications is the absence of the band-gap necessary to switch between on and off logic states. Graphene nanoribbons provide a route to open a band-gap, though it is challenging to produce atomically precise nanoribbon widths and well-ordered edges. A particularly elegant method to open a band-gap is by electronic confinement, which can in principle be tuned by adjusting the nanoribbon width. This thesis is dedicated to understanding the ways of opening band-gaps by nanostructuration. We have used two approaches: the introduction of a superperiodic potential in graphene on vicinal noble metal substrates and the electronic confinement in artificially patterned nanoribbons on SiC. Superperiodic potentials on graphene have been introduced by two nanostructured substrates, Ir(332) and a multivicinal curved Pt(111) substrate. The growth of graphene modifies the original steps of the pristine substrates and transforms them into an array of (111) terraces and step bunching areas, as observed by STM. This nanostructuration of the underlying substrate induces the superperiodic potential on graphene that opens mini-gaps on the π band as observed by ARPES and consistent with the structural periodicity observed in STM and LEED. The mini-gaps are satisfactorily explained by a Dirac-hamiltonian model, that allows to retrieve the potential strength at the junctions between the (111) terraces and the step bunching. The potential strength depends on the substrate, the surface periodicity and the type of step-edge (A or B type). The surface potential has also been modified by intercalating Cu on Ir(332), that remains preferentially on the step bunching areas, producing there n-doped ribbons, while the non-intercalated areas remain p-doped, giving rise to an array of n- and p- doped nanoribbons on a single continuous layer. In the second approach to control the gap, we have studied the gap opening by electronic confinement in graphene nanoribbons grown on SiC. These ribbons are grown on an array of stabilized sidewalls on SiC. As a band-gap opening with unclear atomic origin had been observed by ARPES, we carried-out a correlated study of the atomic and electronic structure to identify the band gap origin. We performed the first atomically resolved study by STM, demonstrating the smoothness and chirality of the edges, finding the precise location of the metallic graphene nanoribbon on the sidewalls and identifying an unexpected mini-faceting on the substrate. To understand the coupling of graphene to the substrate, we performed a cross-sectional study by STEM/EELS, complementary of our ARPES and STM/STS studies. We observe that the (1-107) SiC sidewall facet is sub-faceted both at its top and bottom edges. The subfacetting consists of a series of (0001) miniterraces and (1-105) minifacets. Graphene is continuous on the whole subfacetting region, but it is coupled to the substrate on top of the (0001) miniterraces, rendering it there semiconducting. On the contrary, graphene is decoupled on top of the (1-105) minifacets but exhibits a bandgap, observed by EELS and compatible with ARPES observations. Such bandgap is originated by electronic confinement in the 1 - 2 nm width graphene nanoribbons that are formed over the (1-105) minifacets
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Pavera, Michal. "Konstrukce nízkoteplotních ultravakuových rastrovacích sondových mikroskopů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-234579.
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This thesis deals with the development of scanning probe microscopes. Mechanical requirements for microscopes using measuring methods of scanning tunneling microscopy (STM) and atomic force microscopy (AFM) under enviroments of an ultrahigh vacuum (UHV) and variable temperatures are specified. Mechanical designs of two microscopes are discussed and their control electronics described. A special chapter is devoted to description of linear piezo manipulators and mechanical design of these prototypes.
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Müller, Thomas. "Imaging of DNA and DNA-RAP1 assembly by STM, TEM and SFM /." [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10958.
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Holl, Christian [Verfasser], Markus [Akademischer Betreuer] Morgenstern, and Samir [Akademischer Betreuer] Lounis. "High frequency STM and spin polarized STM on magnetic vortices / Christian Holl ; Markus Morgenstern, Samir Lounis." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1192217926/34.
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Wiehlmann, Lutz. "Sequenzspezifizierte Transposonmutagenese (STM) in Pseudomonas aeruginosa." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=96511211X.
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Ruess, Frank Joachim Physics Faculty of Science UNSW. "Atomically controlled device fabrication using STM." Awarded by:University of New South Wales. Physics, 2006. http://handle.unsw.edu.au/1959.4/24855.
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We present the development of a novel, UHV-compatible device fabrication strategy for the realisation of nano- and atomic-scale devices in silicon by harnessing the atomic-resolution capability of a scanning tunnelling microscope (STM). We develop etched registration markers in the silicon substrate in combination with a custom-designed STM/ molecular beam epitaxy system (MBE) to solve one of the key problems in STM device fabrication ??? connecting devices, fabricated in UHV, to the outside world. Using hydrogen-based STM lithography in combination with phosphine, as a dopant source, and silicon MBE, we then go on to fabricate several planar Si:P devices on one chip, including control devices that demonstrate the efficiency of each stage of the fabrication process. We demonstrate that we can perform four terminal magnetoconductance measurements at cryogenic temperatures after ex-situ alignment of metal contacts to the buried device. Using this process, we demonstrate the lateral confinement of P dopants in a delta-doped plane to a line of width 90nm; and observe the cross-over from 2D to 1D magnetotransport. These measurements enable us to extract the wire width which is in excellent agreement with STM images of the patterned wire. We then create STM-patterned Si:P wires with widths from 90nm to 8nm that show ohmic conduction and low resistivities of 1 to 20 micro Ohm-cm respectively ??? some of the highest conductivity wires reported in silicon. We study the dominant scattering mechanisms in the wires and find that temperature-dependent magnetoconductance can be described by a combination of both 1D weak localisation and 1D electron-electron interaction theories with a potential crossover to strong localisation at lower temperatures. We present results from STM-patterned tunnel junctions with gap sizes of 50nm and 17nm exhibiting clean, non-linear characteristics. We also present preliminary conductance results from a 70nm long and 90nm wide dot between source-drain leads which show evidence of Coulomb blockade behaviour. The thesis demonstrates the viability of using STM lithography to make devices in silicon down to atomic-scale dimensions. In particular, we show the enormous potential of this technology to directly correlate images of the doped regions with ex-situ electrical device characteristics.
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Deshpande, Aparna. "Atomistic interactions in STM atom manipulation." Ohio : Ohio University, 2007. http://www.ohiolink.edu/etd/view.cgi?ohiou169849272.
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Dixon, Richard. "STM studies of semiconducting metal oxides." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365728.
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Revenikiotis, Sackis (Athanasios). "Optimization of STM-tip preparation methods." Thesis, KTH, Materialfysik, MF (Stängd 20120101), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-30873.
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The Scanning Tunneling Microscope (STM) was invented by Gerd Binnig and Heinrich Rohrer and gave them the Nobel Prize in Physics 1986. STM can give us atomic resolution of a surface by applying a voltage between a very sharp tip (STM-tip) and the surface of a material that we want to examine. The STM-tip is moving over the surface and a computer is collecting the tunnel current in every single point to create a digital image. This diploma work is focused on the preparation of the STM-tip. The preparation method that is used is electrochemical etching of a tungsten wire. The sharper the STM-tip is the better resolution in the STM images we can get. With the purpose to get as sharp tip as possible and with a well-defined geometry, we prepared several tips by systematically varying the etching parameters such as voltage, current, concentration and wire length. A new method has been tested to minimize the oxidation on the surface and finally the tips were characterized with scanning electron microscope (SEM).
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Wilson, Jon H. "Silicon surfaces : STM, theory and experiment." Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:64998ae3-9316-42b5-967f-da93ff2bfd6c.
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The fundamental atomic and electronic behaviour of clean silicon surfaces has been studied within a simple tight-binding picture of bonding in solids. Of the various contributions to the surface binding energy, the lowering in the promotion energy (i.e. rehybridization) which accompanies localized Jahn-Teller distortions has been identified as a major electronic driving force underlying the stability of silicon surfaces. The structure of Si(113) has been experimentally determined by the technique of scanning tunnelling microscopy (STM). Despite its high index, the Si(113) surface is found to be highly stable. STM images of both empty and filled states provide strong evidence for a particular structural model with a 3x2 unit cell. The STM results are explained in terms of a general rehybridization principle, suggested by the earlier theoretical study, which accounts for the low surface energy as well as the observed spatial distribution of empty and filled states. In addition, the STM images reveal a high density of domain boundaries which introduce energy states that pin the Fermi level and explain earlier reports of a 3x1 reconstruction for this surface. Voltage-dependent STM image simulations for the Si(113)3x2 surface have been carried out using a simple tight-binding description of surface electronic structure. Quantitative agreement with experiment is obtained confirming the qualitative rehybridization arguments used previously. The local barrier for tunnelling electrons is shown to have an important effect on the interpretation of STM images. The high stability of clean Si(l 13) is shown by STM to be disrupted by adsorption of submonolayer amounts of atomic hydrogen which saturates dangling bonds. Mass transport of silicon occurs and structural models are proposed for the resultant mixed 2x2 and 2x3 surface.
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Clarke, A. R. H. "Quantitative STM imaging of metal surfaces." Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:68cbeba7-d283-498a-9435-b9587e7ef30a.
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Many deductions made about STM images are based upon the model of Tersoff and Hamann, in which images are given in principal by a combination of surface atomic positions and local charge density. There is a now a need for a fuller understanding of this technique in order to explain experimental evidence which indicates that the tip and sample can interact strongly during normal imaging. In order to investigate the fundamental STM imaging process, a method for deducing the tunnel barrier height has been developed which is based on corrugation height measurements of constant current topographs. From experiments on clean Cu(100), values of the tunnel barrier height have been shown to be somewhat below the workfunction (~ 1-2.5eV) but are in good agreement with other reports of atomically resolved barrier height data. At large values of the tunnel conductance (~ 1μS), a fall-off (based upon extrapolation of large separation data) in the corrugation heights is observed with increasing conductance. This effect is quantitatively explained using a Molecular Dynamics simulation of the tip approaching the sample. The simulation gives a good estimate of both the absolute tip-sample separation and site-dependent tip-surface forces. Distributions of corrugation heights indicate that variations in both tip geometry and chemistry are likely to occur in practice and strongly influence the phenomena described above. Similarly, it is found that increased local tunnel barrier heights are measured when the Cu(100) surface is modified with small numbers of single halogen atoms. This data has been used to estimate the contributions to the increase in local barrier height of both adsorbate induced dipoles and geometric topography. Values for the charge transfer between the surface and adsorbate have been established. The process of tip-induced adsorbate manipulation has also been demonstrated at room temperature.
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Dong, Yi. "Single site surface reactions : STM Studies." Doctoral thesis, Université Laval, 2018. http://hdl.handle.net/20.500.11794/30204.
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La demande des composants chimiques énantiopurs dans le secteur pharmaceutique est une des forces qui motive la recherche dans la création des catalyseurs homochiraux à la surface. La catalyse hétérogène est une méthode prometteuse pour la fabrication des produits énantiopurs puisqu'elle porte des avantages tels que la facilité de la séparation des produits désirés, la réutilisation du catalyseur et l'adaptabilité dans différentes conditions de la production en continu. La réaction d'Orito est un des exemples de la réaction hétérogène énantiosélective la plus réussie. Elle concerne l'hydrogénation de α-cétoesters sur des particules de platine modifiées par le cinchona. Il est généralement accepté que des modificateurs cinchona tels que la cinchonidine ou la cinchonine transfère la chiralité en formant des complexes bimoléculaires (complexes 1 :1) avec des réactifs prochiraux sur la surface. La compréhension de la catalyse asymétrique hétérogène au niveau fondamental est insu sante. Par contre, c'est aussi une zone fertile pour la découverte. Du progrès dans le domaine peut être réalisé par des travaux complémentaires en catalyse, en sciences des surfaces et en calcul théorique. Cette thèse décrit les études en science des surfaces inspirées par des rapports dans la littérature sur la réaction d'Orito. En plus des alcaloïdes du cinchona, qui sont des produits naturels, certains nombres de molécules synthétiques sont également des modificateurs chiraux pour la réaction d'Orito. En particulier, Baiker et ses collègues ont enquêté sur la performance du 1-(1-naphtyl)éthylamine (NEA) optiquement pur en tant que modificateur chiral pour l'hydrogénation énantiosélective de cétopantolactone (KPL) en pantolactone sur le Pt/Al2O3.1 Une partie du travail décrit dans cette thèse est l'étude des complexes formés par l'interaction de (R)-NEA et KPL sur la surface de monocristal Pt(111). Le microscope à e et tunnel (STM) est utilisé pour acquérir un grand nombre d'images des complexes KPL/(R)-NEA. Les mesures sont effectuées sur un large rapport de couverture de KPL à (R)-NEA sur la surface. Un algorithme est développé pour accélérer le comptage et la catégorisation de la forme du grand ensemble d'images STM des complexes. L'abondance de plusieurs complexes distincts qui impliquent toute une liaison hydrogène NH···O est déterminée. La prochiralité de KPL dans ces complexes sont attribuées en référant des images STM simulées par théorie de la fonctionnelle de la densité (DFT). Le rapport prochiral global (pr) mesuré dans l'expérience de la surface est comparé au rapport énantiomérique (er) mesuré par Baiker et ses collègues. Un autre algorithme est développé pour l'analyse des événements dynamiques des complexes diastéréomères individuels. Il est appliqué pour tester l'interconversion d'un état à l'autre état pendant la durée de vie de chaque complexe qui est observée par STM. Les résultats sont présentés pour les complexes formés entre 2,2,2-trifluoroacetophenone (TFAP) et (R)-NEA sur le Pt(111). Les complexes TFAP/(R)-NEA montrent des événements dynamiques qui sont décrits comme décomplexation, inversion prochirale sur site et migration intracomplexe. Les résultats sont discutés en référant les barrières énergétiques prédites par DFT pour l'hydrogénation et pour l'inversion prochirale sur site. Un rapport préliminaire présente les données quantitatives sur les interconversions des états aux états des complexes individuels des trois systèmes : TFAP/(R)-NEA, KPL/(R)-NEA et TFAP/8-Me-(R)-NEA. Le dernier modificateur de la surface concerne la substitution d'un méthyle à l'hydrogène à la position 8 du groupe naphtyle du (R)-NEA. Les observations sur les complexes KPL/(R)-NEA et TFAP/(R)-NEA sont résumés dans le contexte des données de science de surface précédemment publiées de notre groupe. La revue met l'accent sur le rôle des interactions secondaires, CH···O et CF···H, dans le contrôle stéréoscopique des molécules prochirales.The demand for enantiopure compounds in the pharmacological sectorsisastrong driving force for research aimed at creating homochiral catalyst surfaces. Heterogeneous catalysts offer potential advantages over homogeneous catalysts including ease of separation of products from the catalyst and greater suitability for operations under continuous ow conditions. One of the most successful examples of a heterogeneous enantioselective reaction is known as the Orito reaction, the hydrogenation of α-ketoesters on cinchona modi ed platinum particles. It is believed that the cinchona modi ers operate chirality transfer by forming bimolecular surface complexes with prochiral reactants. At a fundamental level, heterogeneous asymmetric catalysis is a poorly understood area of surface chemistry. Hence, it is also a fertile area for discovery. Progress in the area can best be made by complementary work in catalysis, surface science and computation. This thesis describes surface science studies that were inspired by reports in the catalysis literature on the Orito reaction. In addition to cinchona alkaloids, which are natural products, a number of synthetic molecules have been shown to be effective chiral modifiers for the Orito reaction. In particular, Baiker and co-workers explored the performance of optically pure 1-(1-naphtyl)-ethylamine (NEA) as a chiral modifier for the enantioselective hydrogenation of ketopantolactone (KPL) to pantolactone on Pt/Al2O3.1 A major part of the work described in this thesis deals with the investigation of surface complexes formed through the interaction of (R)-NEA and KPL on single crystal Pt(111). Scanning tunnelling microscopy (STM) measurements were used to acquire a large number of images of KPL/(R)-NEA complexes. The measurements were performed over a wide ratio KPL to (R)-NEA surface coverage ratios. An algorithm was developed to enable accelerated counting and cataloguing of the large set of STM images of complexes. Therelativeabundancesofmultipledistinctcomplexationstates, allinvolvingNH·· ·O hydrogen bonding, were determined. The prochirality of KPL in these states was assigned by reference to density functional theory (DFT) simulated STM images. The overall prochiral ratio (pr) measured in the surface science experiment was compared to the enantiomeric ratio (er) measured by Baiker and co-workers. An algorithm was developed to investigate uxional events in individual diastereomeric complexes. It was applied to examine state-to-state interconversion occurring during the life times of complexes, as observed using time-lapsed STM measurements. Results are presented for complexes formed by 2,2,2-trifluoroacetophenone (TFAP) interacting with (R)-NEA on Pt(111). The TFAP/(R)-NEA complexes show dynamic events that we describe as decomplexation, on-site prochiral inversion and intracomplex migration. The results are discussed in relation to energy barriers predicted by DFT for hydrogenation and for on-site prochiral inversion. Quantitative data for state-to-state interconversion in single complexes are presented for three systems: TFAP/(R)-NEA, KPL/(R)-NEA and for TFAP interacting with methyl-substituted (R)-NEA. A preliminary analysis of the data is presented. The observations on KPL/(R)-NEA and TFAP/(R)-NEA complexes are reviewed within the context of previously published surface science data from our group. The review emphasizes the role of secondary interactions, CH···O and CF···H bonding, in the stereocontrol of prochiral molecules.
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Silva, Neto Francisco Miranda Soares da. "Rewriting Concurrent Haskell programs to STM." Universidade Federal de Pernambuco, 2014. https://repositorio.ufpe.br/handle/123456789/11435.
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In recent years, the diminishing rate with which we can increase the amount of transistors in a processor core has slowed down the increase of computers’ power. Moore’s Law appears to be drawing to an end. With it, the assumption that software written today will be more efficiently executed in the future simply due to processors’ evolution is being challenged. On the other hand, parallel applications can still be made more efficient by distributing work among different processors to be executed at the same time, thus reducing overall execution time. To enable parallelization, we must have multiple processor cores. This has led to the popularization of multicore architectures. However, writing parallel applications is not trivial. A program must be either written from the start to be executed in parallel, or later adapted for parallel execution. The programmer has the error-prone task of parallelizing the application through use of concurrency and parallelism constructs. Locking, the most common concurrency option, presents risks for inexperienced programmers, such as the famous Deadlock and Livelock problems. As we move from single core architectures to multicore, our programming languages need to make it easier for the programmers to use concurrency. Many researchers have pointed at Software Transactional Memory (STM) as an answer to that issue, as it is a lock-free, abstract way to guarantee isolated access to shared resources. But adapting for STM a program that uses lock is not simple. Besides being an error-prone task, technical details of the language might require special attention to preserve the program’s behavior. In this dissertation, we propose a set of program transformations for concurrency constructs in Haskell, a purely functional programming language. They may be used to refactor a program’s existing locks into transactional constructs from Haskell’s STM implementation. This allows a programmer to gain the benefits of working on STM even for programs which were already developed using locks. Each transformation is accompanied by execution examples and a discussion on its ability to preserve program behavior. We also present a supporting study, in which a controlled experiment was used to evaluate the benefits of locks or STM for the development of Haskell programs. Although subjects’ opinions tended to favor lock-based concurrency, those which used STM overall committed significantly fewer mistakes and required on average 12% less time to finish their assignments.
Recentemente, a queda na taxa de crescimento da quantidade de transístores integráveis em processadores tem desacelerado o crescimento de poder computacional. A lei de Moore parece aproximar-se de seu fim. Com isso, é desafiada a premissa de que software escrito hoje terá melhor desempenho no futuro simplesmente devido à evolução dos processadores. Ainda assim, aplicações paralelas ainda podem se tornar mais eficientes ao se distribuir trabalho entre diferentes processadores para execução simultânea. Para permitir a paralelização, são necessários múltiplos núcleos de processamento, o que tem levado à popularização de arquiteturas multinúcleo. Entretanto, a escrita de aplicações paralelas não é trivial. Deve-se escrever um programa para execução paralela desde sua concepção, ou adaptá-lo posteriormente para execução paralela. O programador tem a difícil tarefa de paralelização da aplicação através do uso de construções de concorrência e paralelismo. Travas, a mais comum opção para concorrência, apresentam riscos para programadores inexperientes, tais quais os famosos problemas de Deadlock e Livelock. Ao adaptarem-se de arquiteturas de um único núcleo para as de multinúcleo, as linguagens de programação precisam facilitar o uso de concorrência para os programadores. Muitos pesquisadores têm indicado Memória Transacional em Software (STM, do inglês Software Transactional Memory) como a resposta para esse problema, por ser uma forma abstrata e não bloqueante para garantia de acesso isolado a recursos compartilhados. Mas adaptar para STM programas que usam travas não é simples. Além de ser uma atividade propensa a erros, detalhes técnicos da linguagem podem requerer cuidados para se preservar o comportamento do programa. Nesta dissertação, é proposto um conjunto de transformações de programas para construções de concorrência em Haskell, uma linguagem de programação puramente funcional. Elas podem ser usadas para refatorar travas de um programa para uso de construções transacionais da implementação de STM em Haskell. Isso permite ao programador aproveitar os benefícios do trabalho com STM mesmo para programas já desenvolvidos com uso de travas. Cada transformação é acompanhada de exemplos de execução e uma discussão sobre sua capacidade de preservar o comportamento do programa. Também é apresentado um estudo de apoio, no qual um experimento controlado foi usado para avaliar os benefícios do uso de travas ou STM no desenvolvimento de programas em Haskell. Apesar das opiniões dos participantes terem favorecido o uso de travas, aqueles que usaram STM cometeram em geral menos erros e em média precisaram de 12% a menos de tempo para terminar suas tarefas.
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Xue, Jiamin. "Scanning Probe Microscopy of Graphene and Carbon Nanotubes." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/238911.
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This dissertation presents research on scanning probe microscopy and spectroscopy of graphene and carbon nanotubes. In total three experiments will be discussed. The first experiment uses a scanning tunneling microscope (STM) to study the topographic and spectroscopic properties of graphene on hexagonal boron nitride (hBN). Graphene was first isolated and identified on SiO₂ substrates, which was later found to be the source of graphene quality degradation, e.g. large surface roughness, increased resistivity and random doping etc. Researchers have been trying to replace SiO₂ with other materials and hBN is by far the most successful one. Our STM study shows an order of magnitude reduction in surface roughness and electrostatic potential variation compared with graphene on SiO₂.The second experiment shows a novel quantum interference effect of electron waves in graphene, loosely referred to as "Friedel oscillations." These arise when incident electron waves interfere with waves scattered from defects in the sample. This interference pattern shows up as a spatial variation in the local density of states, which can be probed by the STM. We measured such Friedel oscillations in graphene near step edges of hBN. Due to its peculiar band structure, the oscillations in graphene have a faster decay rate and their wavelength is an order of magnitude longer than similar oscillations previously observed on noble metal surfaces. By measuring the dependence of the Friedel oscillations on electron energy, we map out the band structure of graphene. The last experiment studies a different system: carbon nanotube quantum dots. By combining scanning probe microscopy and transport measurements, we obtain spatial information about quantum dots formed in a carbon nanotube field effect transistor. We also demonstrate the ability to tune the coupling strength between two quantum dots in series.
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Olthoff, Silke. "High temperature scanning tunnelling microscopy of adsorbate induced phase transitions." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264547.
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Liu, Jun. "Neo--- A new perspective on STM capacity." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5034.
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Exploring the word length effect from the perspective of information density, the current research extended previous findings on cross-linguistic differences in STM capacity with the development of a new strategy that has the potential to double ones digit span with minimal learning and a much shorter training period. Experiments have shown promising results and responses to training differed across language groups. The underlying mechanisms are explored and discussed in relation to strategy usage, capacity estimates and optimization of language systems.
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Shao, Jianfei. "STM/STS and BEES Study of Nanocrystals." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10526.
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This work investigates the electronic properties of very small gold and semiconductor particles using Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and Ballistic Electron Emission Spectroscopy (BEES). Complementary theoretical works were also performed. The first theoretical work was to calculate the quantized states in the CdS/HgS/CdS quantum-well-quantum-dot nanocrystals. An eight-band envelope function method was applied to this system. This method treats exactly the coupling between the conduction bands, the light-hole bands, the heavy-hole bands, and the spin-orbit split bands. The contributions of all other bands were taken into account using second order perturbation theory.
Gold nanocrystals with diameters of 1.5 nm have discrete energy levels with energy spacings of about 0.2 eV. These values are comparable to the single electron charging energy, which was about 0.5 eV in our experimental configuration. Since bulk gold doesnt have an energy gap, we expect the electron levels both below and above the Fermi level should be involved in the tunneling. Measured spectroscopy data have rich features. In order to understand and relate these features to the electronic properties of the nanocrystals, we developed a tunneling model. This model includes the effect of excited states that have electron-hole pairs. The relaxation between discrete electron energy levels can also be included in this model. We also considered how the nanocrystals affect the BEES current.
In this work an ultra-high vacuum and low-temperature STM was re-designed and rebuilt. The BEEM/BEES capabilities were incorporated into the STM. We used this STM to image gold nanocrystals and semiconductor nanocrystals. STS and BEES spectra of gold nanocrystals were collected and compared with calculations.
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Leandro, Silvana Castro [UNESP]. "Batimentos quânticos dependentes do SPIN via STM." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/91985.
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leandro_sc_me_ilha.pdf: 1782827 bytes, checksum: 80c4f27095adfdf0cbd88b99966a75fa (MD5)Neste trabalho investigou-se teoricamente a densidade local de estados (LDOS) sondada por uma ponta de STM de metais hospedando um átomo adsorvido e uma impureza subsuperficial. Modelamos o sistema por meio do Hamiltoniano de Anderson de duas impurezas. Utilizando-se do procedimento da equação de movimento nas funções de Green, derivamos expressões analíticas para a LDOS de dois tipos de hospedeiro: uma superfície metálica e um fio quântico. A LDOS revela oscilações de Friedel e interferência Fano como função da posição da ponta. Essas oscilações dependem fortemente da dimensão do hospedeiro. Encontramos que os números de onda de Fermi dependentes do spin dão origem a batimentos quânticos spin-polarizados na LDOS. Embora a LDOS da superfície mostre um padrão de batimentos amortecidos, ela possui um comportamento oposto no fio quântico. Devido a ausência de amortecimento, o fio opera como um filtro de spins espacialmente resolvido com elevada eficiência.
We theoretically investigate the local density of states (LDOS) probed by an STM tip of ferromagnetic metals hosting a single adatom and a subsurface impurity. We model the system via the two-impurity Anderson Hamiltonian. By using the equation of motion with the relevant Green’s functions, we derive analytical expressions for the LDOS of two host types: a surface and a quantum wire. The LDOS reveals Friedel-like oscillations and Fano interference as a function of the STM tip position. These oscillations strongly depend on the host dimension. Interestingly, we find that the spin-dependent Fermi wave numbers of the hosts give rise to spin-polarized quantum beats in the LDOS. Although the LDOS for the metallic surface shows a damped beating pattern, it exhibits the opposite behavior in the quantum wire. Due to this absence of damping, the wire operates as a spatially resolved spin filter with a high efficiency.
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Martins, Bruno Vieira da Cunha. "Desenho e construção de um UHV-STM." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277568.
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Orientador: Daniel Mario UgarteTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: O estudo da estrutura de nanosistemas individuais requer o uso de equipamentos capazes de gerar imagens de sistemas com poucos átomos. No caso de nanopartículas metálicas produzidas por síntese química, uma questão relevante e ainda pouco estudada é a organização dos passivantes sobre sua superfície e como isso contribui para a definição de sua estrutura de equilíbrio. Para abordar este tema, devemos ser capazes de gerar imagens de resolução atômica em superfícies com alto grau de curvatura: a microscopia de tunelamento (STM) representa o instrumento mais adequado para este tipo de tarefa. Entretanto, o estudo detalhado requer o uso de métodos não-convencionais de microscopia STM (ex. modulação da tensão de bias ou de setpoint), sendo assim desejável que tenhamos total controle sobre a operação do instrumento. Este domínio preciso sobre as características funcionais consiste na principal razão que justifica a construção de um STM no próprio grupo. Este trabalho descreve o desenho, a construção e a caracterização de um STM de Ultra-Alto Vácuo (UHV). Todo o desenho e a construção foram integralmente realizadas no grupo de pesquisa. Apresentamos e justificamos os parâmetros escolhidos para o projeto, os quais definem o perfil do instrumento. O projeto mecânico consiste em um sistema elástico tipo ¿Parallel-Guiding-Spring Table¿(PSM). O sistema de varredura foi desenvolvido utilizando na configuração tipo tripod para os atuadores piezoelétricos. Desenvolvemos dois protótipos da cabeça STM, ambos compatíveis com UHV. Apresentamos o projeto e a construção da câmara de vácuo e do sistema de amortecimento de vibração. Na parte eletrônica, desenvolvemos um projeto que envolve blocos anal'ogicos de precisão e componentes digitais de 16 bits. O sistema funciona com baixa tensão, o que o torna mais estável e menos suscetível ao ruído e a variações térmicas. O sistema de controle embarcado e seu modelo analítico são analisados de modo a se determinar os parâmetros para operação estável. Caracterizamos todo o sistema e obtivemos imagens para superfícies de Grafite e Au como forma de verificar a performance do equipamento construído. Por fim discutimos as dificuldades do projeto e apresentamos soluções para os pontos que requerem certa otimização
Abstract: The study of the structure of individual nanosystems requires the use of equipments capable of generating images of systems containing just a few atoms. In the case of metallic nanoparticles produced by chemical synthesis, a relevant and not much studied question is the organization of the passivant molecules over the surface and how they contribute to the definition of the equilibrium structure. To adress this issue, we must be capable of generating atomic resolution images on surfaces with a high level of curvature: the Scanning Tunneling Microscopy (STM) represents the most adequate instrument for this job. Nevertheless, the detailed study requires the use of non-conventional methods of STM microscopy (ex. bias voltage and setpoint modulation), then it is desirable to have total control over the instrument operation. This precise domain over the functional characteristics consists in the main reason that motivated the construction of a STM in our group. This work describes the design, construction and characterization of an Ultra-High Vacuum (UHV) STM. The design and construction were both integrally done in our research group. We present and justify the chosed project parameters, which define the profile of the instrument. The mechanical project consists of an elastic system of the ¿Parallel-Guiding- Spring-Table Mechanism¿(PSM) type. The scanning system was developed using the tripod configuration for the piezoelectric actuators. We have developed two prototypes for the STM head, both compatible with UHV. We present the project and construction of the vacuum chamber and the vibration isolating system. For the electronics, we have developed a project that involves precision analog blocks and 16 bits digital components. The system works with low voltage, what turns it more stable e less succeptible to noise and thermal variations. The embedded control system and its model are analysed in order to determine the stable operation parameters. We have characterized the system in detail and obtained images for Graphite and Gold surfaces as a way to verify the performance of the constructed equipment. Finally, we discuss the difficulties of the project and present solutions for the points that require optimization
Doutorado
Física da Matéria Condensada
Doutor em Ciências
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Leandro, Silvana Castro. "Batimentos quânticos dependentes do SPIN via STM /." Ilha Solteira, 2013. http://hdl.handle.net/11449/91985.
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Orientador: Antonio Carlos Ferreira SeridonioBanca: Devaney Ribeiro do Carmo
Banca: Guillermo Gerardo Cabrera Oyarzun
Resumo: Neste trabalho investigou-se teoricamente a densidade local de estados (LDOS) sondada por uma ponta de STM de metais hospedando um átomo adsorvido e uma impureza subsuperficial. Modelamos o sistema por meio do Hamiltoniano de Anderson de duas impurezas. Utilizando-se do procedimento da equação de movimento nas funções de Green, derivamos expressões analíticas para a LDOS de dois tipos de hospedeiro: uma superfície metálica e um fio quântico. A LDOS revela oscilações de Friedel e interferência Fano como função da posição da ponta. Essas oscilações dependem fortemente da dimensão do hospedeiro. Encontramos que os números de onda de Fermi dependentes do spin dão origem a batimentos quânticos spin-polarizados na LDOS. Embora a LDOS da superfície mostre um padrão de batimentos amortecidos, ela possui um comportamento oposto no fio quântico. Devido a ausência de amortecimento, o fio opera como um filtro de spins espacialmente resolvido com elevada eficiência.
Abstract: We theoretically investigate the local density of states (LDOS) probed by an STM tip of ferromagnetic metals hosting a single adatom and a subsurface impurity. We model the system via the two-impurity Anderson Hamiltonian. By using the equation of motion with the relevant Green's functions, we derive analytical expressions for the LDOS of two host types: a surface and a quantum wire. The LDOS reveals Friedel-like oscillations and Fano interference as a function of the STM tip position. These oscillations strongly depend on the host dimension. Interestingly, we find that the spin-dependent Fermi wave numbers of the hosts give rise to spin-polarized quantum beats in the LDOS. Although the LDOS for the metallic surface shows a damped beating pattern, it exhibits the opposite behavior in the quantum wire. Due to this absence of damping, the wire operates as a spatially resolved spin filter with a high efficiency.
Mestre
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Robertson, Derek. "Variable processing of flavours in rat STM." Thesis, University of St Andrews, 1985. http://hdl.handle.net/10023/14682.
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The research reported in this thesis examines factors that affect the willingness of rats to ingest novel flavour solutions. Emphasis is placed on the memorial processes assumed to underlie the decision as to whether or not a solution is "safe" to drink. Rats exhibit caution (neophobia) in consuming an unfamiliar (target) solution. This unconditional response to novelty habituates as the rat acquires experience with the target solution (provided that ingestion of the target solution has no noxious consequences!). Neophobia to the target solution may be restored, however, if another (distractor) solution is presented during the interval separating pre-exposure to, and testing of, the target solution (Green & Parker, 1975). In Section 1, the phenomena of habituation to an iterated target stimulus and the disruption of this process by a distractor are introduced. Theoretical explanations of the "dishabituation" effect of a distractor stimulus are described and assessed. The possibility of an empirical test of the relative validity of the Robertson and the Wagner hypotheses using the attenuation of flavour neophobia procedure of Green and Parker provided the impetus for the experiments reported in Section 2. In Section 3, attention is drawn to the similarity of the procedure designed to establish habituation and that Intended to establish latent inhibition to a stimulus. A limited review of empirical data is presented testifying to the fact that habituation and latent inhibition are affected similarly by identical parameter manipulations. The Wagner (1976) model views habituation and latent inhibition as the outcome of a common underlying process, Expts. 10a and 10b, therefore, sought to determine whether latent inhibition of a conditioned taste aversion (CTA) to lemon or sucrose solution would be affected by a coffee distractor in a manner consonant with predictions derived from the results of the neophobia experiments reported in Section 2. The distractor, however, had no effect on strength of latent inhibition in either experiment. Expt. 11c demonstrated that it is possible for a distractor (30% vanilla) to disrupt attenuation of neophobia to a target flavour (3% cider vinegar) without affecting latent inhibition to the target flavour, i.e., there is no direct correspondence between measures of habituation and latent inhibition to the same stimulus. In Section 4, the phenomena of overshadowing and potentiation of a CTA are introduced. At least one explanation of potentiation (c.f., Durlach & Rescorla, 1980) stresses the importance of an association between the elements of a compound CS. Rescorla and Furrow (1977) found interstimulus associations were formed more rapidly between similar rather than dissimilar stimuli. Given these results, Expts. 12a and 12b sought to determine whether a single sequential presentation of lemon and coffee (similar solutions) paired with LiCl would result in potentiation of a conditioned aversion to the lemon solution and whether a single sequential presentation of sucrose and coffee (dissimilar solutions) paired with LiCl would result in overshadowing of a conditioned aversion to the sucrose solution. These experimental predictions were confirmed. In Section 5, a potential confound in the neophobia experiments is addressed. Interpretation of attenuated neophobia as a habituation process is defended and alternatives to the Wagner (1976) theory of habituation are considered for their ability to encompass the data reported in Section 2. Only the Wagner model, however, appears able to account for all the data. Nevertheless, some limitations of the model are indicated. Finally, the conditions promoting overshadowing and potentiation of a CTA are discussed.
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Pavelec, Jiří. "Vývoj lineárního posuvu pro UHV STM/AFM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229812.
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The aim of this diploma thesis is to develop a linear positioning stage for Ultra High Vacuum (UHV) environment. Simple prototypes of the linear positioning stage were designed and incorporated as part of a multiaxis sample manipulator for a UHV Scanning Tunneling Microscopy / Atomic Force Microscopy (STM/AFM). Different types of position encoders and linear guideways are discussed. Implementation of the homodyne interferometer as an optimization tool for a slip-stick based linear stage is described. Scalar diffraction theory is used to model the diffraction grating optical position encoder behavior.
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Zan, Recep. "Microscopy and spectroscopy of graphene : atomic scale structure and interaction with foreign atom species." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/microscopy-and-spectroscopy-of-graphene-atomic-scale-structure-and-interaction-with-foreign-atom-species(7ff75244-c81a-414f-88d2-e614297f0390).html.
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Since its discovery, the one atom thick material graphene has been at the centre of growing interest in two-dimensional materials. Due to its exceptional properties, graphene is a rich topic to explore by physicists, chemists, engineers and materials scientists. In addition to its use in the fundamental research, graphene is also a promising candidate for future electronics, photonics and energy storage devices.The project presented in this thesis was carried out to explore the structure of suspended graphene in particular in order to probe the metal-graphene interaction via Transmission Electron Microscopy, as most graphene applications require interfacing with metals. As the work was based on free standing graphene, graphene layers obtained by mechanical cleavage or growth on a substrate were transferred onto TEM-grids. Therefore, fabrication, suspended sample preparation and identification of graphene layers were first discussed for a better understanding of how to obtain high quality graphene, as this was essential for the rest of the project.Structural, topographic and chemical analysis of pristine suspended graphene layers were investigated in detail via Transmission Electron Microscopy and Scanning Tunnelling Microscopy. The latter technique was also employed for graphene on a substrate along with establishing annealing conditions for residue free graphene.Metal deposited suspended graphene layers were then investigated in the electron microscopes. Different metal behaviours were observed on the graphene surfaces for the same amount of metal evaporation. Generally, metals interact only weakly with graphene as they are not observed on clean (residue free) parts and are mainly clustered. On the other hand, graphene etching has been observed in the presence of metals. The etching was initiated with graphene vacancy formation as a result of the interaction between metal and carbon atoms on clean graphene. Once a vacancy was created, a hole quickly formed and eventually the graphene layers were destroyed. However, those holes created by metals were healed spontaneously either by non-hexagonal or perfect hexagonal rings. The possible etching and healing mechanisms of the suspended graphene were also discussed.
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Gregoriev, Ross. "DEVELOPMENT OF A SILICON NANOWIRE MASK USING SCANNING PROBE MICROSCOPY." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1283.
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Scanning probe microscopy techniques were used to investigate the desorption of hydrogen passivated silicon to form SiO2 etch masks The application of the etch masks were planned on being used to manufacture silicon nanowires. Low concentration hydrofluoric acid was used to passivate the surface. The surface was selectively depassivated by SPM techniques. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) were used to create the masks. The STM system used was found to desorb hydrogen from the surface faster than the STM could image and was considered incapable in the configuration investigated. This led to the use of atomic force microscopy (AFM). Using a conductive tip in contact mode, lithography on the passivated surface was performed. The topography of the lithography was compared to similar works and found to be similar in size. The width was found to be 80nm and the thickness 1nm. The depassivated layers were confirmed to be oxide through electronic force microscopy (EFM). Finally, voltages were swept with the tip in contact with the surface to find the bandgap of the oxide. It was found that the voltage sweeps were severely modifying the tip along with producing inconsistent desorption thicknesses ranging from 0.2 to 12nm. Despite the results from the voltage sweeps, the lithography procedure performed using the AFM was found to be successful.
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Calupitan, Jan Patrick Dela Cruz. "Térarylènes photo réactifs : synthèse et études par microscopie à effet tunnel." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30016/document.
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Les diaryléthènes et leurs dérivés terrylènes sont prometteurs pour la prochaine génération de dispositifs optoélectroniques en raison de leurs excellentes propriétés photochimiques. Pour les rendre viables pour les appareils électroniques miniaturisés, il est nécessaire d'étudier cette classe de molécules au niveau unimoléculaire avec le microscope à tunnel sous vide ultra-élevé (UHV STM). Cette thèse comporte trois parties: 1) développement de terarylènes hautement sensibles à la commutation; (2) leur modification pour les études STM; et 3) les résultats de ces études STM. Pour être étudié à l'échelle de la molécule unique par STM, des terarylènes ayant une sensibilité de commutation élevée ont été sélectionnés. Ces composés présentent des rendements quantiques élevés allant jusqu'à 100%. Cependant, la réaction de cycloréversion reste faible, de sorte qu'une voie alternative, grâce à un mécanisme oxydatif à réaction en chaîne, a été recherchée. Dans une première partie, nous montrons que l'efficacité et la vitesse de cette réaction peuvent être contrôlées par la fixation de groupes aromatiques sur les carbones réactifs. Dans la deuxième partie, nous avons fonctionnalisé ces molécules afin de les étudier par STM en introduisant des groupes tert-butyle et chlorure. Tout en préservant leurs excellentes propriétés photochimiques, les groupes tert-butyle présentent un excellent contraste lumineux dans les images STM, ils minimisent aussi l'agrégation de ces molécules sur la surface et découplent légèrement les molécules de la surface. Les atomes de chlore permettent de contrôler les assemblages moléculaires sur des substrats isolants de type bicouche de NaCl cristalline précédemment déposés sur un substrat métallique. Dans la troisième partie, les résultats de STM sont présentés. Nous avons développé une nouvelle approche ascendante pour la formation reproductible de nano-assemblages du terarylène non modifié à 77 K. Quant au terarylène modifié par les groupes tert-butyle, il présente à 5 K sur une surface d'Ag (111) différentes formes qui, grâce à la position des groupes tertbutyles à contraste élevé et à l'aide de calculs DFT, ont pu être assignées comme étant différentes conformations de surface de la molécule. Sur NaCl / Ag (111), il a été possible de visualiser les états occupés et inoccupés de la molécule. Cela illustre que, pour ces applications, des molécules avec des propriétés appropriées peuvent être des candidates intéressantes pour des études STM afin d'obtenir des informations sur leurs propriétés à l'échelle de la molécule unique. De telles molécules peuvent être optimisées pour tenir compte de la surface, car sa simple présence peut induire un comportement bien différent de celui obtenu en solution. Cette thèse ouvre les terarylènes à des applications futures nécessitant une surface solidePhotoswitching diarylethenes, and their terarylene derivatives, are promising for the next generation optoelectronic devices because of their excellent photochemical properties. To make them viable for miniaturized electronic devices, it is necessary to study this class of molecules at the single molecular level by scanning tunneling microscopy under ultra-high vacuum (UHV STM). This thesis has three parts: 1) development of terarylenes highly sensitive to switching; (2) their modification for STM studies; and 3) results of STM investigations. To be studied at the single molecular level by STM, terarylenes with high switching sensitivity have been selected. These compounds display high quantum yields of up to 100 %. However, the cycloreversion reaction remains low so an alternative route, through a chain-reaction oxidative mechanism, has been sought. In the first part, we show that the efficiency and speed of this reaction may be controlled by attachment of aromatic groups on the reactive carbons. In the second part, we functionalized these molecules for STM studies by attaching tert-butyl and chloride groups. These substituents preserve their excellent photochemical and switching properties while tert-butyl groups show bright contrast in STM images, minimize aggregation of these molecules on the surface, and slightly decouple the molecule from the surface. The chlorine group has been introduced to direct their surface assembly on insulating substrates composed of crystalline NaCl bilayer previously grown over a metallic substrate. In the third part, results of STM are presented. We developed a new bottom-up approach for forming reproducible nanoassemblies of the unmodified terarylene at 77 K. Meanwhile, at 5 K, the terarylene functionalized with tert-butyl groups present different forms on the Ag(111) surface. From the positioning of the high-contrast tert-butyl groups and with the aid of DFT calculations, we assign different conformations of the molecule on the surface. On NaCl/Ag(111), direct visualization of the occupied and unoccupied states could be achieved. This illustrates that for these applications, molecules with appropriate properties can be interesting candidates for STM studies to obtain information at the single molecular level. Such molecules may be redesigned with a consideration of the surface as its mere presence may induce behavior previously unobserved or neglected if they were studied in solution. This thesis opens terarylenes to future applications which require a solid surface
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Zhang, Tianzhen. "Limite d'Anderson et états de bords topologiques." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS240/document.
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Cette thèse décrit la fabrication de systèmes hybrides basés sur le semi-conducteur InAs et leur étude par spectroscopie STM et la mesure de jonctions Josephson. Dans une première expérience, je montre que des nanocristaux (NC) de plomb (Pb) supraconducteurs de haute qualité peuvent être réalisés sur la surface (110) d'InAs. Lorsque la taille latérale des NC est inférieure à la longueur d'onde de Fermi du gaz d'électrons bidimensionnel accumulé à la surface de InAs, les NC ne sont que faiblement couplés à ce gaz électronique et se retrouvent donc dans le régime de blocage de Coulomb. Ce phénomène a permis la première étude de l'effet de parité supraconducteur par spectroscopie STM, que nous avons utilisée pour vérifier la validité de la limite d'Anderson. Dans une seconde expérience, je montre que des NC de Bismuth (Bi) de haute qualité peuvent également être réalisés sur la surface (110) d'InAs. Contrairement aux NC de Pb, une couche de mouillage de Bi sépare les NC de la surface InAs, conduisant à un fort couplage entre les NC de Bi et le substrat. A partir de la spectroscopie STM, nous avons identifié des états de bord sur le plan (111) des NC avec une symétrie C3. En supposant que le bismuth est un isolant topologique de second ordre comme suggéré théoriquement, les états de bords observés peuvent être interprétés naturellement comme les états de charnière prédits dans cette dernière théorie de bande topologiqueThis thesis describes the fabrication of hybrid systems based on the narrow-gap semiconductor InAs and their study through STM spectroscopy and measure of the Josephson characteristics. In the first experiment, I show that high quality superconducting Lead (Pb) nanocrystals can be grown on the (110) surface of InAs. When the lateral size of the Pb nanocrystals is smaller than the Fermi wavelength of the two-dimensional electron gas accumulated at the surface of InAs, the nanocrystals are only weakly coupled to this electron gas and, consequently, are found in the regime of Coulomb blockade. This phenomenon enabled the first study of the superconducting parity effect through STM spectroscopy, which we employed to check the validity of the Anderson limit. In the second experiment, I show that high quality Bismuth (Bi) nanocrystals can also be grown on the (110) surface of InAs. In contrast to Pb nanocrystals, a wetting layer of Bi separates the nanocrystals from the InAs surface, leading to a strong coupling between the Bi nanocrystals and the substrate. From STM spectroscopy, we have identified edge-states on the (111) plane of the nanocrystals with C3 symmetry. Assuming that Bismuth is a 2nd order topological insulator as suggested theoretically, the observed edge-states can be interpreted naturally as the hinge-states predicted in this last topological band-theory. Finally, I will present the methods that I developed for the fabrication of hybrid Josephson junctions on bulk InAs and InAs/GaSb heterostructures, together with preliminary measurements of Josephson characteristics
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Le, Sueur Hélène. "Un AFM-STM cryogénique pour la physique mésoscopique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00261434.
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La spectroscopie électronique basée sur l'effet tunnel donne accès à la densité d'états des électrons (DoS) dans les matériaux conducteurs, et renseigne ainsi en détail sur leurs propriétés électroniques. Au cours de cette thèse, nous avons développé un microscope permettant d'effectuer la spectroscopie tunnel résolue spatialement (10 nm) de nanocircuits individuels, avec une résolution en énergie inégalée (10 µeV). Cet appareil combine les fonctions de Microscopie par Force Atomique (mode AFM) et de spectroscopie Tunnel locale (mode STM), et fonctionne à 30 mK. Dans le mode AFM, la topographie de l'échantillon est imagée grâce à un diapason en quartz piézoélectrique, ce qui permet de repérer les circuits. La spectroscopie tunnel peut ensuite être faite sur les zones conductrices.
Avec ce microscope, nous avons mesuré la DoS locale dans une structure hybride Supraconducteur-métal Normal-Supraconducteur (S-N-S). Dans un tel circuit, les propriétés électroniques de N et de S sont modifiées par l'effet de proximité supraconducteur. Notamment, pour des fils N courts, nous avons pu observer -comme prédit- la présence d'un gap dans sa DoS, indépendant de la position dans la structure : le “minigap”. De plus, en modulant la phase supraconductrice entre les deux S, nous avons mesuré la modification de ce gap, et sa disparition lorsque la différence de phase vaut π.
Nos résultats expérimentaux pour la DoS, ainsi que ses dépendances en phase, en position, et en longueur de N sont en accord quantitatif avec les prédictions de la théorie quasiclassique de la supraconductivité. Certaines de ces prédictions sont observées pour la première fois.
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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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Pham, Van Dong. "STM characterization of functionalized carbon nanotubes and graphene." Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCC245.
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Dans cette thèse, nous avons étudié l'interaction entre des molécules organiques et des nanomatériaux de carbone. En utilisant un microscope à effet tunnel (STM) à basse température et sous ultra-vide, nous avons mesuré les propriétés de molécules de porphyrine physisorbées sur du graphène ou des nanotubes de carbone. Nous avons d'abord étudié l'injection d'électrons dans le graphène sur des défauts (joints de grains et atomes d'azote insérés). Une étude d'états image résonants nous a également permis de mettre en évidence une variation locale du travail de sorite dans le graphène dopé. Nous avons ensuite étudié les propriétés de molécules de porphyrine (H2TPP) adsorbées sur une surface Au(111). En utilisant la pointe du microscope nous avons induit des réactions de tautomérisation et de déshydrogénation et montré comment cela modifie les états moléculaires et l'interaction molécule-surface. Nous avons ensuite étudié l'interaction du graphène avec des molécules de porphyrine. Nous avons montré que le couplage électronique est faible entre les molécules et le graphène. Nous avons ensuite montré comment un atome d'azote inséré dans le réseau de carbone du graphène modifie l'interaction molécule-surface. Une diminution de l'énergie des états moléculaires au niveau des sites dopants révèle un transfert de charge partiel entre les sites d'azote et les molécules. Dans la dernière partie, nous avons étudié les propriétés de nanotubes de carbone monoparois fonctionnalisés par un polymère de porphyrine. Les mesures ont révélé que le polymère couvre partiellement les nanotubes. La spectroscopie locale a indiqué que la densité d'états locale est modifiée au niveau du polymèreIn this thesis we studied the interaction between organic molecules and carbon nanomaterials. Using scanning tunneling microscopy (STM) at low temperature and in ultra-high vacuum, we measured the properties of porphyrin molecules at the surface of graphene and single-walled carbon nanotubes. We first studied electron injection in graphene at defect sites (grain boundaries and nitrogen doping atoms). Using image-potential states, we evidenced the variation of local work function in doped graphene. Secondly, we investigated the properties of free-base porphyrin (H2TPP) molecules adsorbed on a Au(111) surface. We performed tip-induced tautomerization and dehydrogenation of the molecules, and revealed how these operations modify the molecular states and molecule-substrate interaction. Following these two preliminary studies, we studied the interaction of graphene with porphyrin molecules. We evidenced a weak electronic coupling between the molecules and graphene. We then showed how a nitrogen dopant on doped graphene can tune the molecule-surface interaction. The comparison between molecules adsorbed on nitrogen doping sites with those adsorbed on carbon sites clearly reveals a downshift of the energy of the molecular states at the doping sites. This downshift reveals a partial electron transfer from the nitrogen sites of graphene to the adsorbed molecules. In the last part of this thesis, we studied the properties of single-walled carbon nanotubes functionalized with a porphyrin polymer. The STM measurements revealed that the polymer is partially covering the nanotubes. Local spectroscopy indicated that the local density of states are modified at the polymer location
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Vinet, Maud. "Etude par stm de nanostructures supraconductrices par proximite." Université Joseph Fourier (Grenoble), 2001. http://www.theses.fr/2001GRE10047.
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Cette these a ete motivee par le desir d'etudier l'effet de proximite entre un metal normal (n) et un supraconducteur (s). Pour cela, nous avons construit un microscope a effet tunnel (stm) pour mesurer la densite d'etats electroniques locale d'un metal. Celui-ci fonctionne a 100 mk dans un cryostat a dilution renverse. Pour respecter la philosophie de ce cryostat original, le stm est thermalise par contacts mecaniques sur la boite de melange sans gaz d'echange. Avant de coupler le stm a la dilution, nous avons procede a une mise au point prealable dans un cryostat a 4he a des temperatures comprises entre 4,2 k et 1,5 k. Nous avons donc etudie l'effet de proximite entre de l'or (n) en bon contact electrique avec du niobium (s) a 1,5 k. La reflexion d'andreev est le mecanisme microscopique qui regit cet effet de proximite. Elle permet a electron incident d'energie au dessus du niveau de fermi qui arrive sur une interface avec un supraconducteur d'etre retro-reflechit en un trou d'energie -. La paire electron-trou correles ainsi creee dans le metal normal se propage de maniere coherente sur une distance l hd/. Ces correlations conduisent a un affaiblissement de la densite d'etats a une particule dans le metal normal. Lorsque l'or est de taille infinie, 1 m dans notre cas, nous observons un affaiblissement de la densite d'etats electroniques locale dont l'extension spectrale diminue lorsque l'on s'eloigne de l'interface. Physiquement, c'est une manifestation de la longueur l. Les spectres mesures sont quantitativement expliques par le formalisme quasi-classique de l'equation d'usadel. Lorsque l'or est en contact avec le niobium est de faibles dimensions, quelques dizaines de nanometres, la densite d'etats montre un minigap
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Willis, Mary L. "STM Studies of Oxygen Etching of Silicon Surfaces." VCU Scholars Compass, 2005. http://scholarscompass.vcu.edu/etd/1008.
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This study uses atomic force microscopy (AFM) to investigate the oxygen etching behavior of the following silicon surface orientations: (001), (111), (113), (5 5 12) and (112). Most etching was performed at sample temperatures between 650 °C and 800 °C, at pressures of 3.3×10-7 and 1.5×10-7 Torr, and at an exposure of 200 L. Surface orientation strongly influences the morphology resulting from extended etching. The surface orientations that are stable against etching and remain flat include Si(001), Si(111), and Si(113). Such surfaces also include island structures, which result from etching around oxide-induced pinning sites. The density of these islands increases at lower temperatures and higher pressures. The surface orientations that are unstable against oxygen etching and facet to other orientations include Si(5 5 12) and Si(112). These surfaces form sawtooth facets that are primarily composed of more stable (111) and (113) planes. By controlling the temperature and exposure during oxygen etching, it is therefore possible to form a variety of surface morphologies.
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Voňka, Jakub. "Návrh a ověření nízkoteplotní části UHV - STM mikroskopu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230611.
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The diploma thesis addresses the design and experimental verification of cooling system and low temperature part of UHV - STM working in temperature range of 20K - 300K. Due to the demand of variable temperature, the flow cooling system with cryogenic (~5 K) helium (He) is used. Two variants of the low temperature part of the microscope are studied. First the version with cooling only the sample holder, and second with cooling of the whole STM. Designed cooling system consists of He flow cryostat allowing to connect it to the Dewar vessel with liquid helium (LHe) using a low-loss transfer line. The cryostat consists of He inlet and outlet, heat exchangers and copper strains (i.e. braids) for the thermal connection of the sample holder/STM and radiation shield around the STM with the heat exchangers. The thesis describes the design of the flow cryostat and its initial tests in the designed vacuum chamber. Heat flow through a spot contact is also discussed to estimate thermal conductance of insulation supports based on thermal resistance of spherical contacts. The thesis was elaborated in collaboration with the Institute of Scientific Instruments of the ASCR, v.v.i.
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Dao, Tomáš. "Návrh nosné platformy pro nízkoteplotní UHV STM mikroskop." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231317.
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Diploma thesis deals with the design of a vibration isolated platform for low temperature scanning tunneling microscope working under ultra high vacuum (UHV STM). Cooling of the microscope is done by liquid helium using a flow cryostat designed in Institute of Scientific Instruments of the AS CR. In the thesis, general requirements of designing of an ultra high vacuum compatible devices are discussed, as well as the ways of vibrational isolation and damping. Also some ways how to restrict the transfer of vibration between vacuum devices and surroundings are mentioned. This knowledge is then applied to the design of the antivibrational microscope platform compatible with low temperature usage. For better understanding of vibrational transfer and damping, a real model of the designed platform is made and vibrational transfer characteristics are measured and compared with the theory.
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McHardy, Robert John. "Surface diffusion of electrodes investigated by scanning tunnelling microscopy." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366719.
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Zheng, Husong. "STM Study of Interfaces and Defects in 2D Materials." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/97440.
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Two-dimensional (2D) materials show novel electronic, optical and chemical properties and have great potential in devices such as field-effect transistors (FET), photodetectors and gas sensors. This thesis focuses on scanning tunneling microscopy and spectroscopy (STM/STS) investigation of interfaces and defects 2D transition metal dichalcogenides (TMDCs).
The first part of the thesis focuses on the synthesis of 2D TiSe2 with chemical vapor transport (CVT). By properly choosing the growth condition, Sub-10 nm TiSe2 flakes were successfully obtained. A 2 × 2 charge density wave (CDW) was clearly observed on these ultrathin flakes by scanning tunneling microscopy (STM). Accurate CDW phase transition temperature was measured by transport measurements. This work opens up a new approach to synthesize TMDCs.
The second part of the thesis focuses on monolayer vacancy islands growing on TiSe2 surface under electrical stressing. We have observed nonlinear area evolution and growth from triangular to hexagonal driven by STM subjected electrical stressing. Our simulations of monolayer island evolution using phase-field modeling and first-principles calculations are in good agreement with our experimental observations. The results could be potentially important for device reliability in systems containing ultrathin TMDCs and related 2D materials subject to electrical stressing.
The third part of the thesis focuses on point defects in 2D PtSe2. We observed five types of distinct defects from STM topography images and measured the local density of states (LDOS) of those defects from scanning tunneling spectroscopy (STS). We identified the types and characteristics of these defects with the first-principles calculations. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or varying growth condition in few-layer 1T-PtSe2 and other related 2D materials.Doctor of Philosophy
Since the discovery of graphene in 2004, two-dimensional (2D) materials have attracted more and more attentions. When the thickness of a layered material thinned to one or few atoms, it shows interesting properties different from its bulk phase. Due to the reduced dimensionality, interfaces and defects in 2D materials will significantly affect the electronic property and chemical activity. However, such nanometer scale features are several orders of magnitude smaller than the wavelength of visible light, which is the limit of resolution for optical microscope. Scanning tunneling microscope (STM) is widely used in study of 2D materials not only because it can provide the topography and local electronic information at atomic scale, but also because of the possibility of directly fabricate atomic scale structure on the surface. The first part of the thesis focuses on the synthesis of 2D TiSe2 with chemical vapor transport (CVT). TiSe2 belongs to the transition metal dichalcogenides (TMDCs) family, showing a sandwiched layered structure. When the temperature goes down to 200K, a 2 × 2 superlattice called charge density wave (CDW) will show up, which is clearly observed in our STM images. The second part of the thesis focuses on monolayer vacancy islands growing on TiSe2 surface controlled by electrical stressing. During continuous STM scanning, we have observed nonlinear area growth of the vacancy islands. The shape of those islands transfers from triangular to hexagonal. We successfully simulated such growth using phase-field modeling and first-principles calculations. The results could be potentially important for device reliability in systems containing ultrathin TMDCs and related 2D materials subject to electrical stressing. The third part of the thesis focuses on defects in 2D PtSe2. We observed five types of distinct defects in our STM topography images. By comparing them with DFT-calculated simulation images, we identified the types and characteristics of these defects. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering in few-layer 1T-PtSe2 and other related 2D materials.
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Ericsson, Leif KE. "Growth and Characterization of ZnO Nanocrystals." Doctoral thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-27156.
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The understanding of surfaces of materials is of crucial importance to all of us. Considering nanocrystals (NCs), that have a large surface to bulk ratio, the surfaces become even more important. Therefore, it is important to understand the fundamental surface properties in order to use NCs efficiently in applications. In the work reported in this thesis ZnO NCs were studied. At MAX-lab in Lund, synchrotron radiation based Spectroscopic Photoemission and Low Energy Electron Microscopy (SPELEEM) and X-ray Photoelectron Spectroscopy (XPS) were used. At Karlstad University characterization was done using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Scanning Tunnelling Microscopy (STM), Auger Electron Spectroscopy (AES), and XPS. The fundamental properties of ZnO surfaces were studied using distributions of ZnO NCs on SiO2/Si surfaces. The conditions for distribution of ZnO NCs were determined to be beneficial when using ethanol as the solvent for ultrasonically treated dispersions. Annealing at 650 °C in UHV cleaned the surfaces of the ZnO NCs enough for sharp LEEM imaging and chemical characterization while no sign of de-composition was found. A flat energy band structure for the ZnO/SiO2/Si system was proposed after 650 °C. Increasing the annealing temperature to 700 °C causes a de-composition of the ZnO that induce a downward band bending on the surfaces of ZnO NCs. Flat ZnO NCs with predominantly polar surfaces were grown using a rapid microwave assisted process. Tuning the chemistry in the growth solution the growth was restricted to only plate-shaped crystals, i.e. a very uniform growth. The surfaces of the NCs were characterized using AFM, revealing a triangular reconstruction of the ZnO(0001) surface not seen without surface treatment at ambient conditions before. Following cycles of sputtering and annealing in UHV, we observe by STM a surface reconstruction interpreted as 2x2 with 1/4 missing Zn atoms.Baksidestext The understanding of the surfaces of materials is of crucial importance to all of us. Considering nanocrystals (NCs), that have a large surface to bulk ratio, the surfaces become even more important. In the work in this thesis ZnO NCs were studied. The fundamental properties of ZnO surfaces were studied using distributions of ZnO NCs on SiO2/Si surfaces. Annealing at 650 °C in UHV cleaned the surfaces of the ZnO NCs enough for sharp LEEM imaging and chemical characterization while no sign of de-composition was found. A flat energy band structure for the ZnO/SiO2/Si system was proposed after 650 °C. Increasing the annealing temperature to 700 °C causes a de-composition of the ZnO that induce a downward band bending on the surfaces of ZnO NCs. Flat ZnO NCs with predominantly polar surfaces were grown using a microwave assisted process. Tuning the chemistry in the growth solution the growth was restricted to only plate-shaped crystals, i.e. a very uniform growth. The surfaces of the NCs were characterized using AFM, revealing a triangular reconstruction of the ZnO(0001) surface not seen without surface treatment at ambient conditions before. Following cycles of sputtering and annealing in UHV, we observe by STM a surface reconstruction interpreted as 2x2 with 1/4 missing Zn atoms.
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Ccori, Pablo César Calcina. "Avaliação de desempenho do sistema de memória transacional de Clojure como biblioteca de sincronização na linguagem Java." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/45/45134/tde-18082011-134122/.
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Neste trabalho apresenta-se uma avaliação do desempenho da implementação de memória transacional da linguagem Clojure, utilizada como biblioteca de sincronização para uso em conjunto com outras aplicações dentro da máquina virtual de Java. É implementada uma camada de interface entre as estruturas de dados de Clojure e o benchmark STMBench7 e são discutidos alguns aspectos que geram sobrecarga no desempenho.In this work a performance evaluation of Clojure transactional memory implementation is presented, using it as a synchronization library to work together with other applications on Java virtual machine. It is implemented an interface layer between Clojure data structures and STMBench7 benchmark, and issues about overhead in performance are discussed.
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Juteräng, David. "STM Study of PTCDA on Pb/Si(111) 1×1." Thesis, Karlstads universitet, Fakulteten för teknik- och naturvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-16179.
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The interaction and orbital energy levels of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules on a Pb/Si(111) 1x1 substrate have been investigated. A Si(111) sample was annealed to form the 7x7 configuration. 1.5 monolayer of Pb was evaporated onto the surface, which was then annealed. 0.5 monolayer of PTCDA was applied to the substrate through molecular beam epitaxy (MBE). The surface configuration of the substrate was monitored step by step by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Scanning tunneling spectroscopy (STS) was used to pinpoint the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules. It was found that the PTCDA molecules formed a herringbone pattern on the substrate. The PTCDA electronic energy levels corresponding to the HOMO and the LUMO were obtained. From these values the energy gap between these orbitals, the molecular bandgap of PTCDA on Pb/Si(111) 1x1, was determined.
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Ferlauto, Andre Santarosa. "Construção e aplicações de um microscópio de tunelamento (STM)." Universidade de São Paulo, 1996. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-02082013-144215/.
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O objetivo deste trabalho foi a construção de um microscópio de tunelarnento (STM) e sua aplicação a alguns tipos de materiais. Todas suas partes constituintes - cabeça de medida, sistema de isolamento contra vibrações, circuito eletrônico de retroalirnentação e programa computacional de controle - foram desenvolvidas c montadas em nosso laboratório. O aparelho foi testado e calibrado por medidas de interferência óptica e através de imagens da estrutura cristalina de grafite obtidas com o próprio instrumento. Foi realizado um estudo sobre filmes finos de ouro, otirnizando-se o processo de deposição por sputtering, para sua utilização corno cobertura de amostras isolantes a serem investigadas por microscopia eletrônica de varredura (SEM) ou de tunelarnento. Um método de preparo de amostras sernicondutoras foi proposto e utilizado no estudo inicial de pontos quânticos de InAs crescidos pela técnica de epitaxia por feixe molecular (MBE).The aim of this work was the construction of a scanning tunneling microscope (STM) and its application to some interesting physical systems. All its parts- measurement head, antivibration system, electronic feedback circuit and control software were developed and mounted in our laboratory. The instrument was tested and calibrated by optical interferometry and using images of the atomic structure of graphite obtained with the microscope itself. A systematic study of thin sputtered Au films was carried out in order to optimize the sputtering process for its use in the coverage of insulating samples to be investigated by scanning electron microscopy (SEM) and STM. We also proposed a new method to prepare semiconducting surfaces for STM measurements in air, which was used to study InAs quantum dots grown by molecular beam epitaxy (MBE).
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吳誼暉 and Yee-fai Ng. "Optimization of etching parameters for STM tips and an STM study of SiC (0001) [square root]3 x [square root]3 reconstruction." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B29797834.
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Ng, Yee-fai. "Optimization of etching parameters for STM tips and an STM study of SiC (0001) [square root]3 x [square root]3 reconstruction /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20567583.
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Walton, John Moorcroft. "The acquisition, analysis and processing of Scanning Auger Microscopy (SAM) and Scanning Tunneling Microscopy (STM) data." Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387184.
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Ishii, Masaru. "Nanofabrication and STM/XPS Studies of Automotive Model Catalysts." Thesis, University of Reading, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485372.
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Scanning Tunnelling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS) have been used in this work at various temperatures to study the mechanism of NOx storage reaction using model catalysts based mainly on the li02 (110) and the Pt (111) surfaces. The metals Pd and 8a were deposited using metal vapour deposition (MVD». The key findings of this work are summarised below. Prior to the investigation of the 8a/Pdm02 (110) model catalyst, the NOx reactivity with the clean li02 (110) surface and Sa reactivity with li02 (110) were studied. NO and N02was adsorbed on the clean li02 (110)-(1 X2) surface in the molecule state at room temperature and dissociated 'at 373 K in the XPS. However, the amount of adsorbed NO or N02 was small, - less than 0.1 ML, and there was no evidence of or~ered structure of any reactivity between NO and li02 (110) in the STM. Upon increasing the·annealing temperature, liN was formed at 873 K by reaction of dissociated N with interstitialli3 + diffused from the bulk. On the other hand, for a small amount of 8a deposition on the li02 (110) surface, the surface was disordered, but rows of 8a were seen running in the [001] direction of the li02 substrate. Upon sintering at 1073K in UHV, a (2x2) pattern was seen in LEED that originated from the Sa, although no ordering could be seen with STM. NO and O2were adsorbed on the Pd/Sarn02 (110) model catalysts, which was prepared by the 8a deposition and then Pd deposition at 673 K. However it was less reactive due to a low NO sticking probability and it was impossible to obtain atomic resolution images of model catalysts. A new approach, using inverse catalysts, was adopted, that is, Pt (111) was used as the support and Sa was deposited at room temperature. A locally ordered (2x2) structure was obtained. In the case of the annealing temperature at 1273 K, the variety of structures were formed, which these structures might be Sa overlayer, Sa/Pt alloy and BaO. One of these structures is the banded zig-zag structure on the terrace, with the unit cell can be defined as (8 ~ J. After the introduction of O2 at· 573 K, large scale images of BaO were obtained. The average spacing is - 8.6 A, twice that expected for the (111) plane of BaO, which is due to reconstruction, resulting in the formation of (2x2) structure. There was a metastable state of a top layer of BaO/Pt (111) model catalyst at 573 K in the presence of O2, which is likely to be due to the formation of Ba02 confirmed by the atomic structure of Ba02 in the STM. Upon dosing NO and O2 at 573 K, the BaO particles grew and some growth was confirmed at step edges, especially O2 rich state. This effect is observed by an approximate increase in particle volume of 100%, which is consistent with about half of the oxide being converted to the nitrate. It is therefore postulated that a film of the nitrate effectively encapSUlates the oxide. This surface is unreactive to S02' However, when both S02 and O2 were co-dosed, the , ; atomic structure of BaO has rapidly disappeared which might be converted to the SUlphate, 8aS04, Which would result in poisoning of the real catalyst.
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Jemander, Thorbjörn. "STM studies of overlayers on semiconductor or insulator surfaces /." Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek686s.pdf.
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Zotti, Linda Angela. "Molecular ordering and STM imaging of functionalized organic molecules." Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479082.
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Rokni, Fard Mahroo. "Study of fullerenes on Au (111) surfaces using STM." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/7974/.
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A variable temperature scanning tunnelling microscope (VTSTM) was used to study (C₆₀)m-(Au)n magic number clusters as well as the sputtering Au (111) surface. Formation of C₆₀-Au magic clusters was previously reported. Here a more in depth study of the clusters as well as conditions required to control the sizes and positions are presented. This is then followed by studies of topographical changes after sputtering Au (111) surface, with and without C₆₀ islands. Results obtained from this investigation indicated the stronger binding of broken fullerence cages with each other or the gold surface.
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Ovramenko, Tamara. "STM studies of single organic molecules on silicon carbide." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112315.
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L’interaction de molécules organiques avec les surfaces semiconductrices permet de contrôler les propriétés physiques de ces dernières et ce, soit à travers une modification locale en utilisant des molécules individuelles, soit par la passivation de la surface par une mono-couche complète. Aussi, le contrôle de l’interaction moléculaire nous permet de modifier les propriétés intrinsèques des molécules à travers un découplage électronique partiel ou complet entre les orbitales moléculaires et la surface. Pour atteindre ces objectifs, cette thèse présente l’étude expérimentale de l’adsorption de molécules sur la surface semiconductrice à large gap de 6H-SiC(0001)-3x3. Les expériences ont été réalisées à l’aide d’un microscope à effet tunnel opérant dans les conditions d’Ultra-Haut Vide et de température ambiante (UHV RT-STM). Les résultats ont été comparés à des études théoriques employant des calculs selon la théorie de la fonctionnelle de la densité (DFT). Trois molécules on été étudié durant ce travail de thèse : C60, Caltrope et Trima. Les études STM et DFT montre que les molécules individuelles de C60 sont chimisorbé à la surface de carbure de silicium SiC(0001)-3x3 à travers la formation d’une seule liaison Si-C avec un seul adatome de silicium, contrairement aux autres surfaces semiconductrices où la molécule se chimisorbe en formant plusieurs liaisons. Trois sites d’adsorption par rapport à l’adatome de Si de la maille de surface ont été observés. Pour expliquer les observations STM, les forces de Van der Waals entre la molécule de C60 et les atomes de la surface voisins ont du être pris en compte dans les calculs DFT. Il a été observé aussi que les molécules de C60 forment de petits clusters même à de faibles taux de couverture ce qui indique la présence d’un état précurseur de la molécule et des interactions intermoléculaires non négligeable. La molécule de Caltrope, nouvellement synthétisée, a été étudié aussi bien sur la surface de Silicium que celle de SiC. Le dépôt de cette molécule complexe ne peut être réalisé selon la méthode d’évaporation classique sans induire sa dissociation et a donc nécessité l'emploi de techniques d’évaporation spécifiques. Nos résultats expérimentaux montrent un comportement remarquable: le dépôt de molécule individuelle est induit sur la surface de manière efficace par la pointe du STM démontrant ainsi l’idée d’imprimerie moléculaire. Suite à son adsorption sur la surface de silicium à travers une seule liaison, la molécule de Caltrope se comporte comme un moteur moléculaire activé thermiquement. La troisième molécule a être étudié est la molécule de Trima. Elle a été sélectionnée à cause de sa taille comparable à la distance des ad-atomes de silicium de la surface de SiC. La structure chimique de la molécule qui se termine par un groupement cétone rend possible la fonctionnalisation de la surface. Ceci est révélé par les calculs DFT de la densité de charge. La distribution de charge montre qu’il n’y a pas de partage entre les atomes d’oxygènes de la molécule et les ad-atomes de la surface et donc nous avons un évidence claire pour la formation d’une liaison dativeThe interaction of organic molecules with a semiconductor surface enables the physical properties of the surface to be controlled, from a local modification using individual isolated molecules to passivation using a complete monolayer. Controlling the molecular interaction also allows us to modify the intrinsic properties of the molecules by partial or complete electronic decoupling between the molecular orbitals and the surface. To this end, this thesis presents experimental studies of the adsorption of molecules on the wide band gap 6H-SiC(0001)-3×3 substrate. The experiments were performed using Ultra-High Vacuum Room Temperature Scanning Tunneling Microscopy (UHV RT STM) and the results were compared with comprehensive theoretical Density Functional Theory (DFT) calculations. Three different molecules were studied in this thesis: C60, Caltrop and Trima. The STM and DFT studies show that individual C60 fullerene molecules are chemisorbed on the silicon carbide SiC(0001)-3×3 surface through the formation of a single Si-C bond to one silicon adatom, in contrast to multiple bond formation on other semiconducting surfaces. We observed three stable adsorption sites with respect to the Si adatoms of the surface unit cell. To explain the STM observations, Van der Waals forces between the C60 molecule and the neighboring surface atoms had to be included in the DFT calculations. The C60 molecules are also observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and non negligible intermolecular interactions. The second newly designed Caltrop molecule was studied on both the Si and SiC surfaces. Intact adsorption of this complex organic molecule cannot be realized using classical adsorption methods and requires the use of specific evaporation techniques. Our experimental results show remarkable behavior: The STM tip efficiently deposits single molecules one at a time, demonstrating the concept of single molecule printing. After adsorption on the Si surface through one bond, the Caltrop operates as a thermally activated molecular rotor. The third molecule to be studied is the Trima molecule. This molecule was chosen because it is commensurable in size with the surface Si adatom distance. The chemical termination of the molecule with a ketone group enables the successful functionalization of the SiC surface. The Trima molecule provides a rare and clear-cut example of the formation of two dative bonds between the oxygen atoms of the carbonyl groups and the Si adatoms of the SiC surface. This is revealed by the DFT calculations of the charge density. The charge distribution shows that there is no sharing of electrons between the oxygen atoms of the molecule and the surface which is clear evidence for the formation of a dative bond
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Губкіна, Євгенія Олександрівна. "Дизайн веб-сайту для сфери послуг компанії «STM services»." Бакалаврська робота, ЗНУ, 2021. https://dspace.znu.edu.ua/jspui/handle/12345/5231.
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Губкіна Є. О. «Дизайн web-сайту для сфери послуг компанії «STM services» : кваліфікаційна робота бакалавра спеціальності 022 «Дизайн» освітньо-професійної програми «Графічний дизайн» / наук. керівник Л. М. Коваль. Запоріжжя : ЗНУ, 2021. 68 с.EN : The work is presented on 68 pages of printed text. The list of links includes 39 sources. The object of research is the development of the web-site "STM services. The subject of research – methods and technologies of web-site development. The purpose of the study is a theoretical analysis of web-site design. The following software was used in the work: Adobe Illustrator; Adobe Photoshop; Figma; Microsoft Word; Microsoft PowerPoint. Additional tools: Adobe Color; Content watch; Languagetool.
UA : Робота викладена на 68 сторінках друкованого тексту. Перелік посилань включає 39 джерел. Об'єктом дослідження є розробка web-сайту «STM services. Предмет дослідження – методи й технології розробки web-сайту. Мета дослідження – теоретичний аналіз проєктування web-сайтів. В роботі було використане наступне програмне забезпечення: Adobe Illustrator; Adobe Photoshop; Figma; Microsoft Word; Microsoft PowerPoint. Додаткові інструменти: Adobe Color; Сontent-watch; Languagetool.
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Perera, Uduwanage Gayani E. "STM Investigation of Charge-Transfer and Spintronic Molecular Systems." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1300141817.
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