Actuellement, la majorité des architectures de processeurs sont fondées sur une mémoire partagée avec cohérence de caches. Des prototypes intégrant de grandes quantités de cœurs, reliés par une infrastructure de transmission de messages, indiquent que, dans un proche avenir, les architectures de processeurs vont probablement avoir ces caractéristiques. Ces deux tendances exigent que les processus s'exécutent en parallèle et rendent la programmation concurrente nécessaire. Cependant, la difficulté inhérente du raisonnement sur la concurrence peut rendre ces nouvelles machines difficiles à programmer. Nous explorons trois approches ayant pour but de faciliter la programmation concurrente. Nous proposons WFR-TM, une approche fondé sur la mémoire transactionnelle (TM), un paradigme de programmation concurrente qui utilise des transactions afin de synchroniser l'accès aux données partagées. Une transaction peut soit terminer (commit), rendant visibles ses modifications, soit échouer (abort), annulant toutes ses modifications. WFR-TM tente de combiner des caractéristiques désirables des TM optimistes et pessimistes. Une TM pessimiste n'échoue jamais aucune transaction; néanmoins les algorithmes existants utilisent des verrous pour exécuter de manière séquentielle les transactions qui contiennent des opérations d'écriture. Les algorithmes TM optimistes exécutent toutes les transactions en parallèle mais les terminent seulement si elles n'ont pas rencontré de conflit au cours de leur exécution. WFR-TM fournit des transactions en lecture seule qui sont wait-free, sans jamais exécuter d'opérations de synchronisation coûteuse (par ex. CAS, LL\SC, etc) ou sacrifier le parallélisme entre les transactions d'écriture. Nous présentons également Dense, une implémentation concurrente de graphe. Les graphes sont des structures de données polyvalentes qui permettent la mise en oeuvre d'une variété d'applications. Cependant, des applications multi-processus qui utilisent des graphes utilisent encore largement des versions séquentielles. Nous introduisons un nouveau modèle de graphes concurrents, permettant l'ajout ou la suppression de n'importe quel arc du graphe, ainsi que la traversée atomique d'une partie (ou de l'intégralité) du graphe. Dense offre la possibilité d'effectuer un snapshot partiel d'un sous-ensemble du graphe défini dynamiquement. Enfin, nous ciblons les futures architectures. Dans l'intérêt de la réutilisation du code il existe depuis quelques temps une tentative d'adaptation des environnements d'exécution de logiciel - comme par ex. JVM, l'environnement d'exécution de Java - initialement prévus pour mémoire partagée, à des machines sans cohérence de caches. Nous étudions des techniques générales pour implémenter des structures de données distribuées en supposant qu'elles vont être utilisées sur des architectures many-core, qui n'offrent qu'une cohérence partielle de caches, voir pas de cohérence du tout. / Though a majority of current processor architectures relies on shared, cache-coherent memory, current prototypes that integrate large amounts of cores, connected through a message-passing substrate, indicate that architectures of the near future may have these characteristics. Either of those tendencies requires that processes execute in parallel, making concurrent programming a necessary tool. The inherent difficulty of reasoning about concurrency, however, may make the new processor architectures hard to program. In order to deal with issues such as this, we explore approaches for providing ease of programmability. We propose WFR-TM, an approach based on transactional memory (TM), which is a concurrent programming paradigm that employs transactions in order to synchronize the access to shared data. A transaction may either commit, making its updates visible, or abort, discarding its updates. WFR-TM combines desirable characteristics of pessimistic and optimistic TM. In a pessimistic TM, no transaction ever aborts; however, in order to achieve that, existing TM algorithms employ locks in order to execute update transactions sequentially, decreasing the degree of achieved parallelism. Optimistic TMs execute all transactions concurrently but commit them only if they have encountered no conflict during their execution. WFR-TM provides read-only transactions that are wait-free, without ever executing expensive synchronization operations (like CAS, LL/SC, etc), or sacrificing the parallelism between update transactions. We further present Dense, a concurrent graph implementation. Graphs are versatile data structures that allow the implementation of a variety of applications. However, multi-process applications that rely on graphs still largely use a sequential implementation. We introduce an innovative concurrent graph model that provides addition and removal of any edge of the graph, as well as atomic traversals of a part (or the entirety) of the graph. Dense achieves wait-freedom by relying on light-weight helping and provides the inbuilt capability of performing a partial snapshot on a dynamically determined subset of the graph. We finally aim at predicted future architectures. In the interest of ode reuse and of a common paradigm, there is recent momentum towards porting software runtime environments, originally intended for shared-memory settings, onto non-cache-coherent machines. JVM, the runtime environment of the high-productivity language Java, is a notable example. Concurrent data structure implementations are important components of the libraries that environments like these incorporate. With the goal of contributing to this effort, we study general techniques for implementing distributed data structures assuming they have to run on many-core architectures that offer either partially cache-coherent memory or no cache coherence at all and present implementations of stacks, queues, and lists.

Ce travail de thèse s’inscrit dans un programme de recherche européen qui vise à développer de façon rationnelle de nouveaux catalyseurs possédant une activité et une sélectivité élevées pour le vaporeformage du méthanol. L’impact socio-économique de cette réaction est considéré comme très important puisque le méthanol est un vecteur important d’hydrogène pour la production d’énergie dans les piles à combustible via la réaction CH3OH + H2O → CO2 + 3H2. L’objectif principal de la thèse consiste en la détermination des structures géométriques/cristallographiques et électroniques des surfaces d’alliages et de composés intermétalliques dans le système In-Pd, un des nouveaux systèmes prometteurs pour le développement d’une nouvelle génération de catalyseurs. Ces connaissances de base sont essentielles pour pouvoir ensuite appréhender la réactivité chimique de ces intermétalliques et leur spécificité en catalyse / This study is part of an European research program that aims to the rational development of new catalytic materials with high activity and selectivity towards the steam reforming of methanol. The socio-economic impact of this reaction is considered very important because methanol is a major vector for the production of hydrogen energy in fuel cells via the reaction CH3OH + H2O → CO2 + 3H2. The main goal of this thesis is the determination of the geometric/crystallographic and electronic structures of the surfaces of alloys and intermetallic compounds in the In-Pd system, a promising new system for the development of the next generation of catalysts. This basic knowledge is essential to understand the chemical reactivity of these intermetallics and their specificity in catalysis

Samouspořádání organických molekul je spontánní proces tvorby nanostruktur, při kterém je výsledná struktura určena mezimolekulárními and molekulárně-substrátovými interakcemi. Pochopení principů samouspořádávání je klíčem k přípravě funkčních nanostruktur s atomární přesností. Tato diplomová práce se zaměřuje na přípravu a studium samouspořádaných molekulárních struktur 4,4’-diphenyl dikarboxylové kyseliny na povrchu grafenu připraveného na Ir(111). Pro studium vlastností molekulárních struktur je využito rastrovací tunelovací mikroskopie a nízkoenergiové elektronové mikroskopie. Tato kombinace umožňuje získat informace z oblastí o velikosti v řádu nanometrů až milimetrů. V práci je popsána molekulární strukuktura stabilní při pokojové teplotě. Vazebný motiv této struktury je dán interakcí karboxylových skupin sousedních molekul.

The goal of this work is modelling and design of an inverted pendulum prototype. The work presents a mathematical model of a rotary pendulum, modelling of a BLDC motors and also a 3D model of the pendulum prototype is present. The work mentions design of the state space controller and swing up control of the inverted pendulum. Dynamics obtained from the mathematical model is used to create a 3D dynamic model of a pendulum, with the use of the Simscape toolbox. The work deals with control of a BLDC motors with use of vector control. The algorithm is implemented on the CompactRIO platform. Later, hardware is developed, containing STMicroelectronis microcontroller, capable of replacing the CompactRIO platform.

In this work ways of preparation of thin epitaxial cerium oxide film on Cu(110) surface were studied. X-ray photoelectron spectroscopy (XPS), X-ray photoelectron difraction (XPD), low energy electron difraction (LEED), ion scattering spectroscopy (ISS) and scanning tunneling microscopy (STM) were used for the characterization of prepared systems. The island structure of CeO2 was prepared by the method of reactive evaporation in oxygen atmosphere. The influence of temperature on the electronic structure and morphology was studied. At the temperature above 550 ˚C partial reduction to Ce2O3 and reordering of the islands to the CeO2(331) structure was observed. The ceria promoted oxidation of copper surface was approved, since the clean c(6x2) reconstruction of the surface was observed at the oxygen exposure 1,5 order of magnitude lower then on Cu(110) alone. The other model system was prepared by cerium evaporation to the oxygen precovered Cu(110) surface. The mix of (2x1) and c(6x2) surface reconstruction was formed by oxygen exposition at 300 ˚C. Cerium was deposited on this surface, also at 300 ˚C. During the following heating to 500 ˚C the formation of epitaxial film Ce2O3(0001) was observed, accompanied by the formation of large hundreds nm long smooth band structures in the [11̄0] direction.

The aim of this thesis is preparation of inverse model catalyst CeOx/Pt(111) and its investigation using combination of surface physics methods and electrochemistry. New electrochemical cell was designed and built for electrochemical experiments. CeOx/Pt(111) samples were prepared and studied in UHV using STM and XPS methods. After that, samples were transferred to the electrolyte environment and studied by means of cyclic voltammetry and AFM. For high surface coverage of CeOx, new reaction was observed. We have identified this reaction as a combination of the reduction of cerium(IV) oxide by interaction with hydrogen adsorbed on the Pt(111) surface and oxidation of cerium(III) oxide by dissociative adsorption of water molecules. Powered by TCPDF (www.tcpdf.org)

In this work organic molecules, namely derivatives of BODIPY and poly-para-phenyls are investigated on different metal surfaces by means of LT-STM. These molecule are important for the development of molecular electronics and spintronics. I show that aza-BODIPY molecules form a weak chemical bond with the Au(111) substrate and the molecular structure significantly changes upon adsorption. Due to the low corrugation of the Au(111) surface, diffusion of the molecule is observed for applied bias in excess of ±1 V. The temperature dependent formation of different molecular nanostructures formed by polyparaphenyls and Au adatoms is discussed. The diffusing Au adatoms act as coordination centers for the cyano groups present on one end of the molecules. The structure of the super molecular assemblies completely changes in a temperature range of only 60 K. Furthermore, I investigate in this work the hybridization of atomic orbitals within the molecular ligand. The Kondo resonance of a Co atom incorporated into an other aza-BODIPY derivative is investigated in detail on Ag(100). The hybridization of the atomic Co orbital with the organic ligands molecular orbitals is shown by spectroscopy measurements with submolecular resolution. The changing line shape of the Kondo resonance for the molecule-substrate system is discussed. This data is compared to measurements of Co incorporated in another molecular binding motive and on different metal samples to show the importance of the local environment for molecular materials.:Introduction 1 1 Basic Principles 5 1.1 The Scanning Tunneling Microscope 6 1.2 Theory of STM/STS 8 1.2.1 Scanning Tunneling Microscopy 8 1.2.2 Scanning Tunneling Spectroscopy 12 1.2.3 dI/dV-maps and SPECGRIDs 15 1.3 Lateral Manipulation of Adsorbates 15 1.4 The Kondo Effect 17 1.4.1 Investigation of Kondo Systems by STM 19 2 Experimental Setup 23 2.1 LT-STM and UHV System 24 2.2 Substrates 26 2.2.1 Au(111) 26 2.2.2 Ag(100) 28 2.2.3 Cu(110) 28 2.2.4 Surface Preparation 29 2.3 The Molecules 29 2.3.1 aza-BODIPY 29 2.3.2 6Ph-CN 30 2.3.3 Co-(BiPADI)2, Co-BiPADI, and BiPADI 31 2.3.4 Sample Preparation 32 2.4 Organic Photovoltaics 32 3 Aza-BODIPY on Au(111) 35 3.1 Experimental Results 36 3.1.1 STM Images 36 3.1.2 Spectroscopy 38 3.1.3 Lateral Manipulation 38 3.2 Discussion 39 4 6Ph-CN on Au(111) 43 4.1 Experimental Results 44 4.1.1 STM Images 44 4.1.2 Temperature Dependent Nanostructure Formation 44 4.1.3 Spectroscopy 46 4.2 Discussion 47 5 Co-BiPADI on Ag(100) and Cu(110) 55 5.1 Experimental Results 56 5.1.1 Co-BiPADI on Ag(100) 56 5.1.1.1 STM Images and Identification 56 5.1.1.2 Adsorption Geometry 56 5.1.1.3 Spectroscopy and Kondo Resonance 59 5.1.1.4 Temperature Dependent Measurements 63 5.1.1.5 SPECGRID Measurements and Comparison with Molecular Structure 64 5.1.1.6 Interaction of Several Co-BiPADI Molecules and Related Changes of Their Kondo Resonances 67 5.1.1.7 Determination of Adsorption Position of Molecules in SPECGRID Measurements 69 5.1.2 Co-BiPADI on Cu(110) 71 5.1.2.1 STM Images and Identification 71 5.1.2.2 STS Measurements and dI/dV Maps 72 5.2 Discussion 74 6 Co-(BiPADI)2 on Au(111) 81 6.1 Experimental Results 82 6.1.1 STM Images 82 6.1.2 Spectroscopy 82 6.2 Discussion 86 7 Conclusions and Outlook 89 Bibliography 93 List of Publications 101 Acknowledgments 103 A Appendices 105 A.1 Fitting Routine for Kondo STS 105 A.2 Background Subtraction in Kondo STS 107 A.3 MATLAB Fitting Tool fit.m 107 A.4 Import Routine and Fitting Script for SPECGRID Files 111 A.5 Calibration of Piezo Constants from Atomically Resolved Images 112 A.5.1 Au(111) 112 A.5.2 Ag(100) 112 Confirmation 113 / In dieser Arbeit werden organische Moleküle, Derivate von BODIPY und poly-para-Phenyl, auf verschiedenen Metalloberflächen mittels Tief-Temperatur Rastertunnelmikroskopie (LT-STM) untersucht. Diese Moleküle sind wichtig für die Entwicklung von molekularer Elektronik und Spintronik. Ich zeige, dass aza-BODIPY-Moleküle eine schwache chemische Bindung mit dem Au(111)- Substrat eingehen und die molekulare Struktur bei der Adsorption deutlich verändert wird. Wegen der geringen Rauigkeit der Au(111)-Oberfläche wird bereits bei einer angelegten Spannungen über ±1 V die Diffusion der Moleküle beobachtet. Die temperaturabhängige Bildung verschiedener molekularer Nanostrukturen aus poly-para-Phenyl und frei beweglichen Goldatomen wird diskutiert. Die diffundierenden Goldatome agieren hierbei als Koordinationszentren für die Cyanogruppen am einen Ende der Moleküle. Die Struktur der supramolekularen Anordnungen verändert sich dabei in einem Temperaturbereich von nur 60 K vollkommen. Außerdem beschäftige ich mich in dieser Arbeit mit der Hybridisierung atomare Orbitale im molekularen Verbund. Die Kondo-Resonanz eine Co-Atoms, welches in einem anderen aza-BODIPY-Derivat gebunden ist, wird detailliert auf der Ag(100)-Oberfläche untersucht. Die Hybridisierung des atomaren Co-Orbitals mit den molekularen Orbitalen des organischen Liganden wird an Hand von Spektroskopiemessungen mit submolekularer Auflösung gezeigt. Die veränderte Form der Kondo-Resonanz für dieses Molekül-Substrat-System wird diskutiert. Diese Daten werden mit Messungen an Co-Atomen in anderen molekularen Bindungsschemen und auf anderen Substraten verglichen um dieWichtigkeit der lokalen Umgebung für molekulare Materialien zu verdeutlichen.:Introduction 1 1 Basic Principles 5 1.1 The Scanning Tunneling Microscope 6 1.2 Theory of STM/STS 8 1.2.1 Scanning Tunneling Microscopy 8 1.2.2 Scanning Tunneling Spectroscopy 12 1.2.3 dI/dV-maps and SPECGRIDs 15 1.3 Lateral Manipulation of Adsorbates 15 1.4 The Kondo Effect 17 1.4.1 Investigation of Kondo Systems by STM 19 2 Experimental Setup 23 2.1 LT-STM and UHV System 24 2.2 Substrates 26 2.2.1 Au(111) 26 2.2.2 Ag(100) 28 2.2.3 Cu(110) 28 2.2.4 Surface Preparation 29 2.3 The Molecules 29 2.3.1 aza-BODIPY 29 2.3.2 6Ph-CN 30 2.3.3 Co-(BiPADI)2, Co-BiPADI, and BiPADI 31 2.3.4 Sample Preparation 32 2.4 Organic Photovoltaics 32 3 Aza-BODIPY on Au(111) 35 3.1 Experimental Results 36 3.1.1 STM Images 36 3.1.2 Spectroscopy 38 3.1.3 Lateral Manipulation 38 3.2 Discussion 39 4 6Ph-CN on Au(111) 43 4.1 Experimental Results 44 4.1.1 STM Images 44 4.1.2 Temperature Dependent Nanostructure Formation 44 4.1.3 Spectroscopy 46 4.2 Discussion 47 5 Co-BiPADI on Ag(100) and Cu(110) 55 5.1 Experimental Results 56 5.1.1 Co-BiPADI on Ag(100) 56 5.1.1.1 STM Images and Identification 56 5.1.1.2 Adsorption Geometry 56 5.1.1.3 Spectroscopy and Kondo Resonance 59 5.1.1.4 Temperature Dependent Measurements 63 5.1.1.5 SPECGRID Measurements and Comparison with Molecular Structure 64 5.1.1.6 Interaction of Several Co-BiPADI Molecules and Related Changes of Their Kondo Resonances 67 5.1.1.7 Determination of Adsorption Position of Molecules in SPECGRID Measurements 69 5.1.2 Co-BiPADI on Cu(110) 71 5.1.2.1 STM Images and Identification 71 5.1.2.2 STS Measurements and dI/dV Maps 72 5.2 Discussion 74 6 Co-(BiPADI)2 on Au(111) 81 6.1 Experimental Results 82 6.1.1 STM Images 82 6.1.2 Spectroscopy 82 6.2 Discussion 86 7 Conclusions and Outlook 89 Bibliography 93 List of Publications 101 Acknowledgments 103 A Appendices 105 A.1 Fitting Routine for Kondo STS 105 A.2 Background Subtraction in Kondo STS 107 A.3 MATLAB Fitting Tool fit.m 107 A.4 Import Routine and Fitting Script for SPECGRID Files 111 A.5 Calibration of Piezo Constants from Atomically Resolved Images 112 A.5.1 Au(111) 112 A.5.2 Ag(100) 112 Confirmation 113

No description available.

1-D and 2-D organic nanostructures formed by supramolecular self-assembly on HOPG(0001)from molecules containing amide and carboxylic moieties have been investigated with scanning tunneling and force microscopy operated in ambient conditions. A Precise determination of the structure of the monolayer of arachidic acid on graphite was found from moire pattern resulting from tunneling current contributions from both the monolayer and the substrate. Wedge-shaped benzamide amphiphilic molecules deposited on HOPG mainly showed 1-D structures. Systematically varied molecular geometry and head groups reveal the architecture of nanowires which are distinctly different from their columnar mesophase in solution.

In multiband superconductors, different bands at the Fermi surface contribute to the superconductivity with different magnitudes of superconducting gaps on different portions of the Fermi surface. Each band in a multiband superconductor has a condensate with an amplitude and phase that weakly interacts with the other bands’ condensate. The coupling strength between the bands determines whether one or two superconducting transition temperatures are observed, and it is the key to many peculiar properties. In general, if there are two gaps of different magnitude, there are two different length scales associated with the suppression of these gaps in applied magnetic fields, for example. Therefore, effects of multigap superconductivity can be observed in superconducting vortices, which are twirls of supercurrents that are generated when a superconductor is placed in a magnetic field. Furthermore, the two superconducting order parameters in different bands are characterized by a magnitude and phase. In multiband superconductors, there are collective excitations corresponding to fluctuations of the relative phase of two order parameters, so-called the Leggett mode. The first material identified as multiband superconductor is Magnesium Diboride (MgB2) in 2001 with a critical temperature Tc of 39 K. MgB2 is a superconducting material with the highest transition temperature among all conventional BCS superconductors. It has two superconducting gaps \Delta_\pi ~ 2 meV and \Delta_\sigma\ ~ 7 meV and they arise from the existence of two bands \pi and \sigma bands of boron electrons. The discovery of superconductivity in MgB2 renewed interest in the field of multiband superconductivity. MgB2 has attracted many scientists’ attention both for the fundamental importance of understanding the multiband superconductivity and possible applications such as magnets, power cables, bolometers, Josephson junction-based electronic devices, and radio-frequency cavities. Afterward, other materials have been identified as multiband superconductors such as NbSe2, the family of iron-based superconductors, heavy fermion superconductors, multilayer cuprates, borocarbides, etc. This dissertation uses tunneling experiments to highlight multiband superconductivity features in two systems, namely MgB2 thin films and ultrathin films of Pb. Further, we use multiple techniques to study a superconducting material, nitrogen-doped niobium, used for superconducting radio-frequency cavities. For the project on MgB2, MgB2/Native-Oxide/Ag planar junctions are fabricated and characterized down to 2.1 K and in the magnetic field parallel to the sample surface up to 6 Tesla. This work investigates how pairbreaking affects the magnitude and phase of the order parameter in a multiband superconductor. The tunneling spectra are analyzed in the framework of a two-band model developed by our theory collaborator Prof. Alex Gurevich, Old Dominion University. The model allows the extraction of the pair-breaking parameters among other quantities. The analysis shows that the order parameter in the ? band is quickly suppressed in the field, the ? band is cleaner than the ? band. The ratio of pairbreaking parameter in the ? band to the ? band rapidly increases at fields higher than ~0.1 T and then plateau at higher fields. This transition around 0.1 T magnetic field suggests a phase decoupling in the two bands of MgB2. Below the transition, the two bands are phase-locked, so mostly, the superconductivity in the ? band is affected, and after phase decoupling, both bands are affected by the applied field. These results are important for a basic understanding of multiband superconductors and the application implications of this material. This phase decoupling has a new and profound consequence on the superconducting state of a multiband superconductor that has been theoretically predicted and never observed experimentally. For the Pb project, ultrathin films of Pb in ultrahigh vacuum conditions are deposited by e-beam evaporation and characterized with low-temperature scanning tunneling microscopy and spectroscopy (STM/STS). The STM/STS allows measuring the electronic density of states with the highest spatial resolution down to atomic scale. The shape of a superconducting vortex core is determined by the superconducting gap and the Fermi velocity, and the STM allows to map anisotropies of these quantities spatially. The vortex cores of Pb film show a complex shape that evolves from triangular at short distances from the center to a six-fold symmetric star shape farther away from the center. These details are very subtle, and they can be highlighted only if one works within the clean limit (to avoid the averaging effect of the scattering) and by fabricating the heterostructure that pins the vortices spatially. The complex vortex core shape reflects the anisotropy of the two bands that contribute to superconductivity in this material. For the project on Niobium, cold and hot spots from nitrogen-doped Nb cutouts are characterized by low temperature scanning tunneling microscopy and spectroscopy (STM/STS) combined with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The radiofrequency (RF) measurements of the quality factor and temperature mapping on an N-doped Nb superconducting resonator cavity are carried out at Jefferson Laboratory before cutting out the samples. This work aims to identify possible sources of excess dissipation in hot spots and relate them to the surface chemical composition and superconducting properties. The temperature mapping revealed a strong effect of the cavity cooldown rate on the intensities of hot spots and their spatial distribution, which indicates a significant contribution of trapped vortices to the RF dissipation. SEM images acquired on the cold and hot spots using a secondary electron detector show absence of residual hydride scars and niobium nitrides on their surface. Angle-resolved XPS measurements on the native surface of these samples revealed higher oxidized Nb 3d states on the N-doped Nb cold spots, which is supported by XPS depth profiles done on the samples by Argon ion sputtering. Argon ion sputtering of oxidized Nb removes oxygen preferentially from Nb2O5 and diffuses to bulk, thickening the lower oxidation state layers. The proximity theory framework’s tunneling spectra analysis suggests hot spots have stronger pairbreaking due to a weakly reduced pair potential, a thicker metallic suboxide layer, and a wide distribution of the contact resistance. STM imaging of vortex cores shows a triangular vortex lattice in both samples, and the coherence length is nearly the same in hot and cold spots. The experimental data analysis suggests weakly degraded superconducting properties at the surface of hot spot regions are not the primary sources of RF losses. Instead, they are the regions where vortices nucleate first and get trapped during cooling down. These experimental techniques and findings will be crucial in helping to qualify new recipes for SRF cavity production and to boost their performance. / Physics