Since the discovery of superconductivity, its fantastic properties have fascinated the scientific community. The discovery of high critical temperature (Tc) superconducting compositions further inspires the wide applications of superconductors with relatively inexpensive liquid nitrogen cooling. Recently, the integration of superconductivity and optical waveguides has put forward the potential for ultrasensitive, ultra-fast and ultralow noise light detectors. However, simple and cost effective superconductor designs and fabrication processes are still required to enable wide implementation. The objective of this research was to study the fabrication of the superconductor core fibers with a fused silica cladding via the melt-draw approach, as well as develop appropriate characterization techniques to describe the fibers produced. In addition, a further objective was to determine the cooling efficiency of ordered holes around a superconductor core and construction of a one dimensional (1-D) single-phase steady state model to predict the heat transfer during cryogenic liquid transfer inside glass tube. In this thesis, both Pb and YBCO superconductor core fibers with fused silica cladding have been demonstrated. The fibers were fabricated via the melt-draw technique and maintained overall diameters ranging from 200-900 μm and core diameters of 100-800 μm. Surface morphology, chemical composition, interface effect, and superconductivity were further investigated. Surface morphology analysis confirmed that the Pb and YBCO core fibers possessed good circularity and clean interfaces between the core and cladding. Both the Pb and YBCO cores were relatively dense after the melt-draw process. The melt-draw process avoided contamination during fabrication as indicated by the composition analysis. Limited PbO was examined on the Pb core surface but further action will be required to detect the source of oxygen. The YBCO core maintained a stoichiometric ratio comparable to the superconducting phase even after the melt forming process. The elemental mapping showed that limited cross-diffusion occurred between the Pb core and fused silica cladding. Conversely significantly more elemental cross interaction between the core and cladding was noted for the YBCO core fiber. Superconductivity of the Pb core was verified by a custom designed four-probe technique in liquid helium. The YBCO core was also confirmed to be superconductive after heat treatment with O₂ present. The feasibility of efficient cooling by the holey glass tubes was confirmed. A 1-D single-phase steady state model was constructed to evaluate the heat transfer mechanism. The experimental results are in reasonable agreement to the theoretical calculation. / Master of Science

En la presente memoria se describe el método para la medida de la variación térmica de la resistividad entre 10 y 300 K que hemos puesto a punto en nuestros laboratorios de la Universidad de Cantabria. Dicho método es el de cuatro puntas con corriente alterna y detección síncrona. También se analizan, mediante el método de los elementos finitos, los efectos de la geometría de la muestra y posición de los contactos en la relación entre la resistividad observada experimentalmente y la resistividad real, haciendo hincapié en el caso de muestras anisótropas. Posteriormente aplicamos esta técnica al estudio de diversas series de materiales: 1) Los compuestos RPt que cumplen la Ley de De Gennes y en los que hemos podido determinar los valores de la masa efectiva m* y de la constante de canje. 2) Los compuestos RNi2Si2 en las que se puede observar una relación entre la resistividad magnética y las estructuras magnéticas. 3) Los compuestos CeyLa1-yNixPt1-x, en las que se estudia el efecto Kondo 4) Los amorfos metálicos (Co1-x(Fe5Ni5)x)75Si15B10 en los que se observa un mínimo en la resistividad a bajas temperaturas así como variaciones en lnT, T2 y T a temperaturas bajas, intermedias y altas respectivamente / The present report describes the method for measuring the temperature dependence of the resistivity between 10 and 300 K that we have developed in our laboratories at the University of Cantabria. This is a four-probe method using ac current and synchronous detection. Also it is analyzed, using the finite element method, the effects of the sample geometry and contacts position in the relationship between the real resistivity and resistivity observed experimentally, even in the case of anisotropic samples. Subsequently we apply this technique to the study of different family of materials: 1) RPt compounds which follow the De Gennes Law, allowing us to determine the values of the effective mass m * and exchange constant. 2) The compounds RNi2Si2 in which it is possible to establish a relationship between the magnetic resistivity and the magnetic structures. 3) The compounds CeyLa1-yNixPt1-x, in which we study the Kondo effects. 4) The amorphous Co1-x(Fe5Ni5)x)75Si15B10 metals, in which there is a minimum in the resistivity at low temperatures as well as variations in LnT, T2 and T at low, intermediate and high temperatures respectively.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The petroleum industry produces significant amounts of residues in several of its processes, from the perforation of wells, production, storage, transport and refining, to the distribution of its derivatives. The wastewater generated in the oil extraction step is known as produced water and, when stored in flotation tanks, if generates a residue called oily sludge . In a previous report, carbon-clay composites were obtained from this oily sludge and it was found this the material shows semiconductor properties. Thus, here we aimed to further evaluate the electrical properties of the carbon-clay composites using a home-made four probe apparatus. The carbon-clay composites have been prepared using the pyrolysis conditions reported in the previous study, changing here the precursor granulometry then afterwards characterizing the samples by FTIR, XRD, Raman and SEM. The presence of clays-mineral phases as well as carbon rich phases was evidenced from FTIR spectroscopy. Raman spectra revealed the presence of graphitic crystallites in addition to a disordered carbon matrix. XRD data allowed us to properly identify the mineral phases. SEM images have shown a clear effect of the precursor granulometry on the microstructure of the final pellets. Compact pellets can be expected when using a precursor with smaller particle size. The electrical measurements were accomplished using both a current source especially built for this and alternatively a Keithey 237 electrometer coupled to the four-probe apparatus. Satisfactory current values in terms of stability and reproducibility were obtained with both sources in the range of 640 μA (minimum potential) 37 mA (maximum potential). Applying current values in this range for the carbon-clay composite samples it was possible to confirm their semiconductive properties, since conductivities were found to lie in the range ≈10-4 (Ω*cm)-1. Finally the sample compactness was found to play a significant role in the electrical conductivity since the higher conductivity values were found for more compact samples. / A indústria petrolífera produz quantidades significativas de resíduos em vários dos seus processos, desde a perfuração de poços até a distribuição de seus derivados. Nesse ambiente industrial surge a chamada água produzida, que ao ficar em tanques de flotação, gera um resíduo chamado de borra de petróleo . A partir de uma observação preliminar, realizada por Andrade et al, do compósito carbono-argila, utilizando a espectroscopia de impedância eletroquímica, foi possível identificar que o material em estudo é um semicondutor. Desta maneira, surgiu o interesse de estudar com mais profundidade as características elétricas do mesmo. O objetivo deste trabalho é realizar um estudo das propriedades elétricas do compósito, destacando seus parâmetros principais como condutividade e resistividade elétricas, pelo método de quatro pontas e caracterizar a borra de petróleo gerada no tratamento de água produzida. A borra de petróleo foi seca inicialmente por 48 horas a 110ºC, foram feitas pastilhas com material peneirado a granulometrias diferentes e depois sinterizadas sob atmosfera inerte de nitrogênio, até 800ºC com isoterma de 2h. Em seguida, foi realizada a montagem do aparato de quatro terminais utilizando eletrodos de latão e de platina, para medição de resistividade elétrica do material e a montagem de uma fonte de corrente constante. Através do espectro FTIR, observou-se banda referentes aos estiramento O-H de argilominerais; bandas de resíduos orgânicos; e banda dos componentes minerais. As análises de DRX apresentaram como constituintes a montmorilonita, quartzo, calcita e barita, bem como a cristobalita, ghelenita, anortita e magnetita. O Raman apresentou banda devido à presença de carbono grafite e banda devido à desordem na estrutura do carbono grafite. A análise por MEV apresentou em algumas amostras superfície mais compactada com a presença de grãos e aglomerados. Tanto com a fonte construída, quanto com um eletrômetro obteve-se uma estabilidade de corrente na faixa de 640μA a 37mA. Foi possível comprovar com ambas as medidas que o material em estudo é um material que apresentou um valor de condutividade na faixa da semicondução (≈10-4 Ω.cm)-1.

In this thesis, I explore model systems for planar atomic and molecular scale electronics on surfaces. The nanoscale systems are experimentally investigated by combining scanning tunneling microscopy (STM) with atomic and molecular manipulation. Furthermore, the on-surface chemical synthesis of molecules, as well as the construction of atomic wires on selected surfaces is applied. Polycyclic aromatic hydrocarbon (PAH) molecules play a key role in this work, as they can provide the functionality of the molecular scale devices. In the first part of this work, I investigate different PAH´s on the Au(111) surface. The precursor molecules form supramolecular assemblies and the on-surface synthesis approach to obtain the desired molecular products is used. In particular, bisanthene molecules via a cyclodehydrogenation reaction and the non-alternant polyaromatic hydrocarbon diindenopyrene after a thermally induced debromination followed by selective ring-closure to form a five-membered ring are obtained. An interesting surface for future applications is the passivated silicon Si(001)-(2x1):H. I prepare this surface and characterize the substrate. The surface has a band gap and molecules are electronically decoupled from the semiconducting substrate due to the passivation layer. Furthermore, atomic defects on this substrate, so called dangling bonds (DB´s), have defined electronic states. I show that it is possible to produce DB defects controllably by applying voltage pulses using the tip of the STM and achieve with this method atomic wires with DB´s. The third part of this thesis deals with the investigation of molecular structures on Si(001)-(2x1):H. I present the generation of hexacene by a surface assisted reduction. This result can be generalized for the generation of PAH´s after deoxygenation on passivated silicon and can open new routes to design functional molecules on this substrate. Secondly, one-dimensional chains of acetylbiphenyl (ABP) molecules are explored. They interact via its pi-stacked phenyl rings that are considered as conducting channel. Finally, I demonstrate that a single ABP molecule acts as a switch, as one can reversibly passivate and depassivate a single DB by a hydrogen transfer. In the last part of this work, I test the new low-temperature four-probe STM located at CEMES-CNRS in Toulouse. This machine is constructed for the development of molecular scale devices. For this purposes an atomic precision is needed for all the different tips at the same time and a high stability of this scanning probe microscope must be achieved. I perform a manipulation experiment of molecules to test the necessary submolecular precision. For that reason, supramolecular assemblies of ABP molecules on Au(111) are imaged and manipulated by any of the four tips using the lateral manipulation mode as well as by voltage pulses. The stability of the system is shown, as all tips of the four-probe STM work independently in parallel.:1 Introduction 2 Fundamentals of scanning tunneling microscopy 2.1 The working principle 2.2 Scanning tunneling spectroscopy 2.3 Manipulation modes 2.4 Modeling 3 Experimental setup, materials and methods 3.1 The scanning tunneling microscope 3.2 The Au(111) surface 3.3 Further experimental details 4 On-surface synthesis of molecules 4.1 Introduction 4.2 Generation of a periacene 4.3 Investigating a non-alternant PAH 4.4 Conclusion 5 The passivated silicon surface 5.1 Introduction 5.2 Preparation of passivated silicon 5.3 Characterization of Si(001)-(2x1):H 5.4 Tip-induced formation of dangling bonds 5.5 Conclusion 6 Organic molecules on passivated silicon 6.1 Introduction 6.2 Hexacene generated on passivated silicon 6.3 Acetylbiphenyl on passivated silicon 6.4 Conclusion 7 Testing a low temperature four-probe STM 7.1 Introduction 7.2 The four-probe STM 7.3 Performance test of the four-probe STM on Au(111) 7.4 Manipulation of ABP assemblies 7.5 Conclusion 8 Summary and outlook 9 Appendix 9.1 Dibromo-dimethyl-naphtalene on Au(111) 9.2 Epiminotetracene on Au(111) Bibliography Curriculum vitae Scientific contributions Acknowledgement Statement of authorship / In dieser Arbeit untersuche ich Modellsysteme für planare atomare und molekulare Elektronik auf Oberflächen. Die Systeme auf der Nanoskala werden experimentell durch die Kombination aus Rastertunnelmikroskopie (RTM) und atomarer sowie molekularer Manipulation untersucht. Moleküle werden durch die oberflächenchemische Synthese generiert und atomare Drähte auf ausgewählten Oberflächen hergestellt. Polyzyklisch aromatische Kohlenwasserstoff (PAK) Moleküle spielen bei dieser Arbeit eine Schlüsselrolle, da sie die passiven und aktiven Elemente auf molekularem Maßstab darstellen können. Im ersten Teil dieser Arbeit untersuche ich verschiedene PAK´s auf der Au(111)-Oberfläche. Die Präkursoren bilden dabei supramolekulare Anordnungen und ich nutze die Oberflächensynthese, um die gewünschten molekulare Produkte zu erhalten. Im Speziellen habe ich Bisanthen-Moleküle über eine Zyklodehydrogenationsreaktion und das nicht-alternierende PAK Diindenopyren erzeugt. Dieses entsteht nach einer thermisch-induzierten Debromierung gefolgt von selektivem Ringschluss, sodass ein fünfgliedriger Ring gebildet wird. Eine interessante Oberfläche für zukünftige Anwendungen ist das passivierte Silizium Si(001)-(2x1):H. Ich habe diese Oberfläche erfolgreich präpariert und das Substrat charakterisiert. Die Oberfläche hat eine Bandlücke und Moleküle sind elektronisch von dem halbleitenden Substrat durch die Passivierungsschicht entkoppelt. Desweiteren haben atomare Defekte dieser Oberfläche, sogenannte Dangling-Bond´s (DB’s), definierte elektronische Zustände innerhalb der Bandlücke. Ich habe DB´s kontrolliert durch Spannungspulse mithilfe der Spitze des RTM erzeugt und stelle so atomare Drähte mit DB Defekten her. Der dritte Teil dieser Arbeit befasst sich mit der Untersuchung molekularer Strukturen auf Si(001)-(2x1):H. Die Erzeugung von Hexacen auf passivierten Silizium durch eine oberflächenunterstützte Reduktion wird gezeigt. Dieses Ergebnis ist eine neue Strategie für die Herstellung von PAK´s nach der Deoxygenierung und eröffnet neue Wege um funktionelle Moleküle auf diesem Substrat zu entwerfen. Zweitens zeige ich, dass Acetylbiphenyl (ABP) Moleküle eindimensionale Ketten auf dieser Oberfläche bilden. Diese interagieren über ihre Phenylringe, welche als leitender Kanal gesehen werden können. Zudem kann ein einzelnes ABP Molekül wie ein Schalter genutzt werden, da es reversibel einzelne DB´s durch Wasserstoffübertragung passivieren und depassivieren kann. Im letzten Teil dieser Arbeit wird das neue Tieftemperatur Vier-Sonden RTM, welches sich in CEMES-CNRS in Toulouse befindet, getestet. Diese Maschine ist für die Herstellung und Untersuchung von Geräten im molekularem Maßstab konstruiert worden. Zu diesem Zweck ist eine atomare Präzision für die verschiedenen Spitzen zur gleichen Zeit erforderlich und eine hohe Stabilität des Rastersondenmikroskops muss gewährleistet sein. Ich führe ein Manipulationsversuch an Molekülen durch, um die notwendige submolekulare Präzision zu testen. Dafür werden supramolekulare Anordnungen von ABP-Molekülen auf Au(111) abgebildet und die Strukturen mit jeder der vier Spitzen im lateralen Manipulationsmodus und durch Spannungpulse bewegt. Damit habe ich die Stabilität des Systems getestet und konnte zeigen, dass alle Spitzen des Systems unabhängig voneinander parallel arbeiten.:1 Introduction 2 Fundamentals of scanning tunneling microscopy 2.1 The working principle 2.2 Scanning tunneling spectroscopy 2.3 Manipulation modes 2.4 Modeling 3 Experimental setup, materials and methods 3.1 The scanning tunneling microscope 3.2 The Au(111) surface 3.3 Further experimental details 4 On-surface synthesis of molecules 4.1 Introduction 4.2 Generation of a periacene 4.3 Investigating a non-alternant PAH 4.4 Conclusion 5 The passivated silicon surface 5.1 Introduction 5.2 Preparation of passivated silicon 5.3 Characterization of Si(001)-(2x1):H 5.4 Tip-induced formation of dangling bonds 5.5 Conclusion 6 Organic molecules on passivated silicon 6.1 Introduction 6.2 Hexacene generated on passivated silicon 6.3 Acetylbiphenyl on passivated silicon 6.4 Conclusion 7 Testing a low temperature four-probe STM 7.1 Introduction 7.2 The four-probe STM 7.3 Performance test of the four-probe STM on Au(111) 7.4 Manipulation of ABP assemblies 7.5 Conclusion 8 Summary and outlook 9 Appendix 9.1 Dibromo-dimethyl-naphtalene on Au(111) 9.2 Epiminotetracene on Au(111) Bibliography Curriculum vitae Scientific contributions Acknowledgement Statement of authorship