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Nanolithography on H:Si(100)-(2 x 1) using combined Scanning Tunneling Microscopy and Field Ion Microscopy techniquesVesa, Cristian Unknown Date
No description available.
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Spectroscopies locales sur des nanostructures hybrides hors équilibreQuaglio, Thomas 19 January 2012 (has links) (PDF)
Nous utilisons un microscope combinant microscopie à force atomique (AFM) et microscopie à effet tunnel (STM) à très basse température (~100 mK) afin d'étudier des nanocircuits mésoscopiques. Pour effectuer l'AFM dans ces conditions, nous utilisons un diapason en quartz recouvert de deux électrodes sur l'une desquelles est collée la pointe. Lorsque le diapason vibre on peut alors localiser en AFM un échantillon conducteur sur un substrat isolant, puis stopper les vibration pour réaliser des spectroscopies tunnel le long de la partie conductrice. Nous utilisons des pointes de platine-iridium ce qui nous permet de mesurer la densité d'états électronique locale. Nous nous sommes intéressés aux jonctions Josephson hybrides composées d'un îlot d'environ 1 µm de métal normal (cuivre) séparant deux supraconducteurs (aluminium). Ces échantillons sont réalisées par lithographie électronique et évaporation sous angle.Les courbes courant-tension de ces jonctions deviennent hystérétiques à très basse température ce qui est vraisemblablement dû à la dissipation thermique dans la partie normale. Nous avons pu localiser de manière fiable des échantillons uniques et effectuer simultanément des mesures en transport et des spectroscopies locales. Nous avons vu que la densité d'états du supraconducteur varie continuement à proximité du métal normal. Nous avons également observé un chauffage du supraconducteur avec le courant traversant la jonction. La mesure de la densité d'états du supraconducteur permet alors d'estimer la température électronique dans l'échantillon. La comparaison avec notre modèle thermique montre que l'énergie thermique produite dans le métal normal semble être évacuée mieux que prévu.
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Titania Nanoscale Films and Surfaces : Surface Science Investigation of Structure and PropertiesRagazzon, Davide January 2014 (has links)
This thesis presents surface science studies, investigating several aspects of titanium dioxide at the atomic scale. The greater part of this work is devoted to the preparation by chemical vapor deposition (CVD) of titanium(IV) tetraisopropoxide (TTIP) of ultrathin TiO2 or TiOx films on Au(111). Four ordered structures were growth and characterized. It was also demonstrated how the morphology of the film (wetting film vs island) can be tailored. The acquired knowledge about the CVD process was exploited to load nano porous gold with titania, enhancing its catalytic activity. The reactivity towards water adsorption of the titania structures on Au(111) was also investigated. Finally, part of this work concerned the studying of the behavior of water on the stoichiometric rutile TiO2(110) surface, combining the experiments with density-functional theory (DFT) calculations and (kinetic) Monte Carlo simulations. The main experimental techniques used in this work are low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and photoelectron spectroscopy (PES).
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Rewriting Concurrent Haskell programs to STMSilva Neto, Francisco Miranda Soares da 27 February 2014 (has links)
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Previous issue date: 2014-02-27 / 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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Spectroscopic imaging STM study of the interplay between magnetism and superconductivity in iron-based superconductorsAluru, Rama K. P. January 2017 (has links)
The discovery of high-temperature superconductivity in 1986 in copper-oxide materials have opened up new avenues to investigate new families of quantum materials that were previously not known. Understanding the mechanism of superconductivity in high-T[sub]c superconductors has been an important research theme in condensed matter physics, as it is believed to be essential to realize the next generation engineered materials that become superconducting at room temperature. Discovered in 2006, iron based superconductors are a new addition to the family of high-T[sub]c superconductors, these materials exhibit several interesting properties and show some vivid similarities with cuprates and other families of high-temperature superconductors. In this thesis, I will present the spin-polarized scanning tunneling microscopy (SPSTM) study carried out on the parent compound of iron chalcogenide high temperature superconductor Fe[sub](1+y)Te to investigate the bi-collinear antiferromagnetic order. Magnetic tips in this work are prepared using a novel preparation technique by picking up excess iron atoms and clusters of FeTe from the surface of the sample. Next, I will present the SP-STM results obtained in the spin glass phase of Fe[sub](1+y)SeₓTe₁₋ₓ visualizing the interplay between the short ranged bi-directional bi-collinear antiferromagnetic order and superconductivity at the atomic scale. In this thesis, I will also present the scanning tunneling microscopy and spectroscopy (STM/STS) study of the native and engineered defect bound states in the iron-pnictide superconductor LiFeAs. This study addresses the pairing symmetry of the superconducting order parameter and understanding of dip-hump features seen in STM spectra outside the superconducting gap in iron pnictide superconductor LiFeAs.
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Taktiskt ruttutbyte / Tactical route exchangeThornberg, Markus, Manukyan, David January 2017 (has links)
Den tekniska utvecklingen har gjort att nya möjligheter har tillkommit för att säkra framförandet av fartyg och effektivisera ruttplaneringen. Ett av de effektiviseringssäten som för närvarande utvecklas är ruttutbyte. Syftet med studien är att med hjälp av ett simulerat scenario samt frågeformulär belysa eventuella risker förknippade med ruttutbyte till sjöss. Studien speglar deltagarnas upplevelse av den kritiska situationen som simuleringen återger och visar även skillnaden i beslutsfattandet mellan erfarna och oerfarna navigatörer. Tidigare forskning betonar till stor del fördelar med taktiskt ruttutbyte men mindre angående nackdelar med systemet. Med hjälp frågeformulär insamlades deltagarnas erfarenheter och upplevelser angående taktiskt ruttutbyte. Enligt scenariot var det planerat att ett av fartygen i trafikflödet skulle avvika från sin planerade rutt. Ruttutbyte har simulerats genom att visa fartygsrutter i ECDIS. Resultatet av studien visar att det finns ett klart mönster mellan olika gruppers beslutsfattande och graden av pålitlighet till de i ECDIS visade rutterna för andra fartyg. Studien visar även att det finns en påtaglig risk för kollision om navigatörer följer ruttutbytet utan vidare kritisk granskning på grund av falsk trygghet. / The technical advances in the maritime sector have led to new possibilities to secure the safe passage of the vessels and improve the process of route planning. One example of such advances is route exchange. The purpose of this study was by means of simulation to pinpoint whether there are any probable risks connected with the tactical route exchange. This study reflected the experience of the participants of the critical situation portrayed in the simulation. It also takes in to account the difference of the decision-making between the different groups. These groups are composed of experienced navigators and unexperienced navigators. The study also describes the simulation from a fact-based standpoint. Earlier research describes mostly advantages of the tactical route exchange and in less degree the disadvantages of the tactical route exchange. The study has been composed by means of simulation at several occasions. With the help of questionnaires, a general picture has been compiled of the participants’ background, experience and the general opinion about the tactical route exchange. According to the prepared scenario there was one vessel which was intended to deviate from its intended route. The route exchange was projected in the ECDIS console. The result shows that there is a pattern between the different groups´ decision-making and the degree of reliability of the projected routes. The study also points out the obvious risk of collision dependent on the incompleteness of the system and weaknesses for the worst-case scenario which should be taken into account in the future upgrades of the system.
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Nízkoteplotní rastrovací tunelová mikroskopie / Low temperature scanning tunneling microscopySojka, Antonín January 2017 (has links)
The diploma thesis is divided into two main parts. The first part describes the production of chrome and cobalt tips for SP-STM with subsequent testing of chrome tips on the Fe-Ir system (111). Furthermore, the first results from the growth studies of niobium on iridium(111) are presented. In the second part is described in detail the experimental LT-STM microscope of the Faculty of Physical Engineering. The chapter deals with the development of the microscope and its testing on a HOPG sample under atmospheric and vacuum conditions. The chapter describes the biggest problems which were solved when the microscope was puting into operation state. The second part also introduces the design of a new vacuum transport system, which consists of a tip and sample transport pallet. At the end of the second part is described the testing of cooling systems for LT-STM and the design of their modifications.
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Užití kovových materiálů pro selektivní růst / Application of metallic materials for selective growthNěmeček, Tomáš January 2008 (has links)
The Si(100) surface and Ga surface phases up to 1 ML on their oxidation have been studied by XPS and LEED. The selective growth of Ga on the SiO2/Si structures fabricated by EBL has been analyzed using SEM and AFM methods. It was proved that Ga clusters grow in structures beside the oxide. The structure of alumina on Ni3Al(111) and NiAl(110) substrates was fully determined by combining the results of STM measurements and DFT simulations. It was determined the alumina/NiAl(110) does not form a suitable template for ordered Fe and Co clusters growth. However, the next research confirmed the alumina/Ni3Al(111) forms template appropriate to clusters growth purpose.
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The Atomic Structure of Ultrathin Germania FilmsLewandowski, Adrián Leandro 11 December 2019 (has links)
Die Herstellung von ultradünnen Germaniumdioxidfilmen auf Metallsubstraten ist erstmals erfolgreich gelungen. Die Filmstruktur konnte mittels oberflächensensitiven Techniken mit atomarer Präzision und chemischer Sensitivität aufgelöst werden. Zur Untersuchung werden STM-Bilder analysiert und durch niederenergetische Elektronenbeugung (LEED), eine dynamischen LEED-Studie und extern ausgeführte Dichtefunktionaltheorieberechnungen (DFT) ergänzt.
In dieser Arbeit werden atomar aufgelöste Rastertunnelmikroskopiebilder (STM) von ultradünnen Germaniumdioxid- und Siliziumdioxidfilmen direkt verglichen. Ziel der Analyse ist es, den Einfluss des Metallsubstrats auf die Struktur von Oxidfilmen zu untersuchen. Zu diesem Zweck werden ultradünne Germaniumdioxid-Filme auf Ru(0001), Pt(111) und Au(111) abgeschieden und mit Siliziumdioxid-Filmen auf verschiedenen Substraten verglichen, die in früheren Studien untersucht wurden. Germaniumdioxid und Siliziumdioxid sind eng miteinader verknüpft. Hierbei sind Struktur und chemische Eigenschaften als äquivalent anzusehen.
Es wurden drei verschiedene Netzwerkstrukturen aufgeklärt: Monolagen-, Zickzack- und Bilagenfilme. Die einzelnen Bausteine in diesen Filmsystemen bestehen aus verzerrten Tetraedern, in denen ein Germaniumatom von vier Sauerstoffatomen umgeben ist. Benachbarte Tetraeder sind durch Ge-O-Ge-Bindungen miteinander verknüpft und binden im Fall der Monolagenfilme an das darunterliegende Metallsubstrat. In Bilagenfilmen hingegen gibt es keine chemischen Bindungen zum Substrat, wodurch die Filmstruktur flexibler wird. Durch Variation der Herstellungsbedingungen kann man rein kristalline, amorphe oder Phasen mittlerer Ordnung erhalten. Es ist wichtig hervorzuheben, dass der amorphe Germaniumdioxid-Bilagenfilm ein neues amorphes zweidimensionales Material darstellt. / The preparation of metal-supported ultrathin films of germanium dioxide, termed also germania, has been successfully achieved for the first time. The structure of the films is elucidated with atomic precision and chemical sensitivity using surface science techniques. The investigation is performed by analyzing STM images and is complemented by low-energy electron diffraction (LEED) patterns, a dynamical LEED study, and external support from density functional theory (DFT) calculations.
In this work, we compare side-by-side atomically-resolved scanning tunneling microscopy (STM) images of ultrathin films of germania and silica. The analysis aims to investigate the impact of the metal support on the structure of oxide films. For that purpose, ultrathin germania films are grown on Ru(0001), Pt(111) and Au(111), and compared with previously reported silica ultrathin films supported on different substrates. Germania has been widely associated with silica since they are considered to be structural and chemical equivalent materials.
Three main network structures have been characterized: monolayer, zigzag and bilayer films. In all systems, the building block consists of a distorted tetrahedron with a germanium atom surrounded by four oxygen atoms. Adjacent tetrahedra connect to each other through Ge-O-Ge bonds and, in the case of the monolayer films, they also bind to the metal support. Conversely, in bilayer films there are no chemical bonds to the metal substrate, thus providing more flexibility to the film structure. Through a meticulous control of the preparation conditions one can obtain a purely crystalline phase, an amorphous one, or one with intermediate order. It is important to highlight that the amorphous germania bilayer film represents a new 2-dimensional amorphous material.
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PCI-Einsteckkarte für ATM-NetzwerkanalyseZieschang, Michael 04 March 2001 (has links)
Development of a PCI card for PCI bus based host systems, which allows for analysis of ATM data streams on ATM transmission links with a data rate of 622Mbit/s.
Implementation and previous deliberations and therefrom and from given specifications arisen partial tasks
Fields of application of the ATM-Analyzer board
Depiction of particular development steps
Functional description of the ATM-Analyzer
Explanations on how to put the PCB and the employed test software into operation
Assessment of test results / Entwicklung einer Einsteckkarte für PCI-Bus-basierte Hostsysteme zur Analyse von Datenströmen auf ATM-Übertragungsstrecken mit einer Geschwindigkeit von 622 Mbit/s.
Realisierung und damit verbundene Vorüberlegungen und daraus und aus gegebenen Spezifikationen erwachsene Teilaufgaben
Anwendungsgebiete der Analyzer-Karte
Darstellung der einzelnen Entwicklungsschritte
Funktionsbeschreibung des ATM-Analyzers
Erläuterungen zur Inbetriebnahme der Leiterkarte und der verwendeten Testsoftware
Bewertung der Testergebnisse
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