Neste trabalho utilizamos métodos computacionais ab initio, baseados na Teoria do Funcional da Densidade (DFT), para simular em nível atomístico propriedades estruturais, eletrônicas e magnéticas de nanoestruturas de grafeno. Estudamos nanoflocos de grafeno (GNFs) em estado pristino e GNFs com defeitos intrínsecos (monovacância, divacância e Stone-Wales). Escolhemos GNFs com diferentes terminações e formas, e estudamos também empilhamentos duplos - biflocos - em diferentes composições. Empregamos dois enfoques diferentes de DFT, a aproximação de gradiente generalizado simples no nível teórico de Perdew-Burke-Ernzerhof (PBE), e PBE híbrida (PBEh), incorporando uma fração de troca de Hartree-Fock. Todos os cálculos foram realizados através do código all-electron AIMS, incluindo correções de van der Waals. Nossos GNFs foram escolhidos com simetrias específicas: D2h, D3h e D6h, e com diferentes bordas, armchair (AC), zigue-zague (ZZ) e misturas das duas. Os flocos hexagonais D6h apresentam um gap de energia e nao apresentam spin, enquanto flocos perfeitos com bordas zigue-zague e mistas apresentam spin intrínseco. Esse spin não nulo é devido à diferença no numero de átomos entre uma e outra subrede do grafeno (Liebs imbalance). Defeitos em materiais de carbono sao frequentes, e tem sido estudados experimental e teoricamente. Aqui, estudamos a monovaçancia, através de modelos de cluster e supercélulas, e obtemos para esse defeito o momento magnético de = 2B, (B ´e o magneton de Bohr). Mostramos que as diferenças entre resultados anteriores são oriundas do erro de auto-interação presente na DFT simples, amenizado através do uso de PBEh. Através da mesma metodologia estudamos a interação de nanoestruturas de grafeno com moléculas de água, focalizando em propriedades estruturais. A grafite é um material hidrofóbico, mas a nanoestrutura poderia favorecer a interação com a água. Obtemos que pequenos agregados de água são adsorvidos na superfície de GNFs e biflocos, entretanto a inclusão desses agregados na região interna dos biflocos é altamente desfavorável. Assim podemos esperar que essas nanoestruturas empilhadas sejam também hidrofóbicas. / In this work, computational ab initio methods based on density functional theory (DFT) are used to simulate on an atomistic level the structural, electronic and magnetic properties of graphene nanostructures. We study pristine graphene nanoflakes (GNFs), and GNFs with intrinsic defects (monovacancy, divacancy, Stone-Wales). We design GNFs with different terminations and shapes and also studied stacked forms -biflakes- in different compositions. We employed two DFT approaches, plain generalized gradient approximation in the Perdew-Burke-Ernzerhof (PBE) level of the theory, and hybrid PBE (PBEh) incorporating a fraction of Hartree-Fock exchange. All calculations were performed with the all-electron code AIMS, including van der Waals corrections. Our GNFs were chosen from three symmetry groups: D2h, D3h and D6h, and with different edges, armchair (AC), zigzag (ZZ) and a mixture of both. Our chosen D6h- hexagonal flakes present an energy gap and no spin, while perfect trigonal zigzag and mixed edges GNFs have an intrinsic spin. This non-zero spin is due to the graphene sublattice imbalance (Liebs imbalance). Defects are common in carbon materials, and have been experimentally and theoretically studied in graphene. Here, the single vacancy in graphene was studied, by cluster and supercell approaches, finding that the vacancy induces a magnetic moment = 2B (Bohr magneton). We show that conflicting results for the magnetic moment coming from theoretical studies come from the self-interaction error present in plain PBE, cured through the use of PBEh. Using the same methodology we studied the interaction of carbon nanostructures with water molecules, focusing on structural properties. Graphite is a hydrophobic material but nanostructuring could favor the interaction with water. We obtained that small water groups are adsorbed on the surface of GNFs and biflakes, however the inclusion of these groups in the internal region of biflakes is highly unfavorable, thus we can expect these stacked nanostructures to be also hydrophobic.

Un des défis majeurs auquel la communauté de la nano-optique aura à répondre dans les années à venir sera de concentrer l'énergie lumineuse à l'échelle du nanomètre de façon à créer une nanosource optique ou thermique intense à même d'alimenter de futurs dispositifs. Les nanoparticules métalliques, supportant une résonance plasmon de surface, sont idéales pour de telles applications. Dans ce contexte, cette thèse a pour vocation d'apporter un élément de réponse aux problématiques d'optimisation thermique aux échelles nanométriques et de proposer une nouvelle technique de nanothermométrie. A l'aide de simulations numériques, nous avons pu mettre en évidence les propriétés de génération de chaleur des nitrures de titane et de zirconium, dépassant celle de l'or, qui en font alors des matériaux de choix pour concevoir et fabriquer des nanosources thermiques dans le visible. Nous avons également obtenu une morphologie de particules induisant un échauffement maximal pour une longueur d'onde donnée : une nanoétoile à trois branches. Nous avons ensuite fabriqué des nanostructures d'or par lithographie électronique afin de les caractériser par holographie photothermique. En utilisant les deux types d'informations accessibles avec cette technique, l'amplitude et la phase optique, nous nous sommes alors efforcés à quantifier l'élévation de température de nanobâtonnets d'or. L'holographie photothermique d'amplitude a permis d'obtenir des mesures de température semi-quantitatives et, la technique de phase, encore préliminaire, se révèle intéressante et innovante pour étudier les propriétés thermoplasmoniques de nanostructures plasmoniques. / Focusing light on the nanoscale in order to create intense optical or thermal nanosources is probably the main challenge facing the nano-optics community, in order to power up future devices. Metallic nanoparticles and their surface plasmon resonance are ideal optical or thermal nanosources.In this context, this thesis aims at providing a possible solution to the issues of thermal optimization at the nanoscale and nanothermometry.By carrying out numerical simulations, we were able to highlight the heat generation properties of titanium and zirconium nitrides, exceeding those of gold, which make them ideally suited in order to conceive and fabricate heat nanosources in the visible. We also managed to obtain a particle morphology inducing a maximum heating at a given wavelength : a three-branchs nanostar.We fabricated gold nanostructures by e-beam lithography in order to characterize them with photothermal holography. By exploiting the two kind of informations available with this far-field optical technique, the amplitude and the optical phase, we strove to quantify the temperature variations of gold nanorods. The photothermal holography setup based on amplitude delivered semi-quantitative temperature measurements, and the phase based-technique, still at a preliminary stage of developpement, proves to be a new and promising tool for the study of optical and thermal properties of plasmonic nanostructures.

La composition chimique du film d'oxyde natif formé à l'air ambiant et du film passif formé en milieu acide (0,05 M H2SO4) à 500 mV/ESH sur une surface d'alliage monocristallin Fe-17Cr-14,5Ni-2,3Mo orientée (100) a été étudiée par Spectrométrie de masse d'ions secondaires à temps de vol (ToF-SIMS) et Spectroscopie de photoélectrons induits par rayons X (XPS). Ces films peuvent être considérés comme ayant une structure duplex avec une couche externe enrichie en Fe et une couche interne enrichie en Cr. La passivation provoque un net enrichissement en Mo concentré dans la couche externe des films passifs. Le vieillissement à l'état passif promeut l'enrichissement en molybdène et sa localisation vers l'extrême surface du film passif. Les propriétés électroniques de ces films ont été étudiées par Spectroscopie à effet tunnel (STS). La comparaison des valeurs de Eg mesurées par STS montre que la largeur de la bande interdite devient beaucoup plus élevée après passivation et vieillissement à l'état passif de la surface, en accord avec l'enrichissement en Cr3+, démontré par nos mesures ToF-SIMS et XPS. Les modifications nanostructurales induites par passivation en milieu acide de la surface Fe-17Cr-14,5Ni-2,3Mo(100) couverte par un film d'oxyde natif ont été étudiées par Microscopie à effet tunnel (STM) ex situ et in situ, et par Microscopie à force atomique (AFM). Un effet observé du Mo est de promouvoir l'homogénéité nanostructurale de la surface passivée. Un autre effet du Mo serait de former une couche externe amorphe. / The chemical composition of the air-formed native oxide film and the passive film formed in acidic medium (0.05 M H2SO4) at 500 mV/SHE on the (100)-oriented Fe-17Cr-14.5Ni-2.3Mo single crystal stainless steel surface was studied by Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). These films can be considered as having a duplex structure with an outer layer enriched in Fe and an inner layer enriched in Cr. The passivation causes a net enrichment of Mo concentrated in the outer layer of the passive films. Aging in the passive state promotes the enrichment of molybdenum and its localization to the outermost surface of the passive film. The electronic properties of these films were studied by Scanning tunneling spectroscopy (STS). The comparison of the Eg values measured by STS shows that the width of the band gap becomes much higher after passivation and aging in the passive state of the surface, in agreement with the enrichment of Cr3+, demonstrated by our ToF-SIMS and XPS measurements. The nanostructural modifications induced by passivation in acidic medium of the Fe-17Cr-14.5Ni-2.3Mo(100) surface covered by a native oxide film were studied by Scanning tunneling microscopy (STM) ex situ and in situ, and Atomic force microscopy (AFM). An observed effect of Mo is to promote the nanostructural homogeneity of the passivated surface. Another effect of Mo could be to form an amorphous outer layer.

Depuis plus de 30ans, les chercheurs essaient de combiner le silicium et le GaAs. Le potentiel de l'intégration du GaAs sur Si est en effet considérable pour le remplacement des substrats coûteux de GaAs ou de Ge dans la fabrication de cellules PV, de photodétecteurs, de LED, de lasers…. Il en est de même pour le développement de nouveaux dispositifs opto- et électroniques par l'intégration monolithique de GaAs sur circuit silicium. Des défis majeurs persistant jusqu'à aujourd'hui doivent toutefois être surmontés.Dans le but de surmonter ces difficultés, nous proposons un concept intéressant qui permet l'hétéroépitaxie de III-V sur Si. Ce concept est basé sur la technique d’épitaxie latérale (ELO) par CBE depuis des ouvertures nanométriques réalisées dans un masque de silice ultra-mince. Cette technique nous a permis d’obtenir des microcristaux de GaAs sans défaut et parfaitement intégrés sur Si grâce à une nucléation depuis des ouvertures de très petits diamètres qui évitent la génération de dislocations dues au désaccord de maille. Le concept étant validé, nous avons poursuivi l’étude en utilisant une 2ème approche de nanostructuration technologique du masque et permettant la localisation des cristaux. L’obtention in fine d’une pseudo-couche de GaAs sur Si sans défaut ni contrainte serait particulièrement utile pour les diverses applications mentionnées. Seront donc présentés le concept d’intégration, puis les résultats de croissance par ces techniques, et des analyses matériaux complémentaire. Pour finir, sera détaillée la structure d’une cellule PV de GaAs/Si devant permettre d’atteindre un rendement de conversion de 29,2%, ainsi que les premiers résultats obtenus. / For over thirty years researchers have attempted to combine Si and GaAs. Alternative GaAs-on-Si substrates have a considerable market potential for replacing the costly GaAs or Ge substrate in producing traditional GaAs devices such as solar cells, photodetectors, LEDS, lasers, and microwave devices, and as a new technology for monolithic integration of GaAs elements and silicon integrated circuits. However, major challenges remaining until now must be overcome.In that way, we propose an interesting concept that allows III-V heteroepitaxy on silicon. This concept is based on the Epitaxial Lateral Overgrowth (ELO) by CBE from nanoscale holes through an ultra-thin silica layer. This technique allows us to obtain GaAs microcrystals without any defect and perfectly integrated on Si thanks to nanoscaled nucleation seeds which prevent dislocation generation due to lattice mismatch. The concept being validated, the study has continued using a 2nd approach of nanostructuration to allow crystal localization. The achievement of getting a GaAs pseudo-layer on silicon substrate without any defect or stain would be of great interest for the formerly mentioned applications.So the integration concept of III-V materials on silicon will be introduced, then growth resultants by these techniques, and material characterizations in order to qualify the integrated GaAs on silicon regarding to the opto- and electronic applications. Finally, the structure of a GaAs/Si tandem solar cell will be discussed. After proving this solar cell could reach a 29.2% conversion efficiency, first achievements will be revealed.

Orientador: Marisa Masumi Beppu / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-18T11:40:54Z (GMT). No. of bitstreams: 1 Vasconcellos_FernandodaCruz_D.pdf: 16906370 bytes, checksum: f307344fa0f9ccb976c0dbb73c5bf226 (MD5) Previous issue date: 2011 / Resumo: O trabalho trata da produção de filmes nanoestruturados multicamadas de biopolímeros sobre substratos sólidos com a técnica de deposição layer-by-layer (LbL). A técnica de montagem layer-by-layer é uma ferramenta adequada para produção controlada de filmes de multicamadas com propriedades importantes tais como: a biocompatibilidade, a biodegrabilidade, a baixa toxicidade, a hidrofilicidade e a baixa citotoxicidade, concedendo a estes filmes grande versalitidade em suas aplicações. O foco principal da pesquisa foi estudar multicamadas dos polieletrólitos naturais quitosana e ácido hialurônico e sua aplicabilidade para: 1) promover a adesão de linfócitos B, 2) gerar superfícies antibacterianas. Os testes da preparação e o estudo da variação de parâmetros de montagem de filmes dos biopolímeros, assim como sua caracterização foram úteis para a avaliação dessas aplicações. O estudo também incluiu a produção de filmes multicamadas contendo outros biopolímeros (alginato de sódio e carboximetilcelulose), assim como polímeros sintéticos e nanopartículas. A caracterização dos filmes envolveu diversas técnicas de análise, dentre elas: microscopia de força atômica (MFA), que permitiu obter informações sobre a topologia e elasticidade dos filmes, e microbalança de cristal de quartzo com dissipação (QCM-D), que permitiu fazer uma análise em tempo real das características dos filmes durante a deposição dos biopolímeros. Os resultados obtidos neste trabalho mostram a viabilidade da fabricação de filmes multicamadas a base de biopolímeros para uso na imobilização de linfócitos B. Os resultados mapeiam e otimizam as variáveis de preparação dos filmes de multicamadas dos polieletrólitos (PEMs) de HA e CHI através do pH, força iônica, e última camada depositada, que influenciam a imobilização seletiva dos linfócitos. Estes filmes exploram as interações CD44-ácido hialurônico sem a necessidade de utilização de reações químicas agressivas e promovem a adesão seletiva de linfócitos assegurando a viabilidade, habilidade de replicação e funções dos linfócitos, após a imobilização. Filmes assim construídos tem aplicação em biossensores a base de células, engenharia do sistema imune, sistemas de diagnóstico e tratamento de doenças entre outras. Os resultados mostraram também que a técnica LbL é viável para a construção de superfícies antibacterianas. As propriedades antibacterianas e de imobilização de linfócitos da superfície desses filmes são passíveis de aplicações biotecnológicas / Abstract: This thesis is on the production of biopolymer nanostructured multilayered thin films deposited on solid substrates utilizing the layer-by-layer (LbL) deposition technique. The layer-by- layer deposition technique of assembly is a simple yet versatile and powerful tool for the controlled production of biopolymer multilayered thin films carrying important properties, such as: biocompatibility, biodegradability, low toxicity, hydrophilicity, low cytotoxicity, which entice them as candidates for a wide variety of applications. The main focus of the research was the study of natural biopolymer polyelectrolytes such as chitosan and hyaluronic acid, and their applicability in: 1) promoting the adhesion of B lymphocytes, and 2) generating antibacterial surfaces. The film preparation process in itself and the study of the film properties as a function of deposition parameters, such as pH and ionic strength, during assembly, were very important in tailoring the multilayer film for specific applications. The study also included the production of multilayered films composed by other biopolymers (sodium alginate, carboxymethylcellulose), as well as by synthetic polymers and nanoparticles. The characterization of the films involved various techniques, such as: atomic force microscopy (AFM) - which allowed the acquisition of information regarding film topology and elasticity, and the quartz crystal microbalance with dissipation (QCM-D), which permitted an analysis, in real time, of the film characteristics during deposition of the biopolymers. The results obtained in this work show the feasibility of fabricating multilayered thin films based on biopolymers for their use in the adhesion of B lymphocytes. The results map out and optimize the preparation of polyelectrolyte multilayered (PEMs) composed of HA and CHI through the variation of pH, ionic strength, and choice of last layer deposited, all factors that influence the selective immobilization of lymphocytes. These films explore the CD44- hyaluronic acid interactions without the use of aggressive chemical reactions to promote the selective adhesion of lymphocytes, maintaining their viability, meaning, maintaining their ability to replicate and their native functions after being immobilized. The results also show the feasibility of the LbL technique in producing biopolymer films having antibacterial properties. Both film characteristics - the adhesion and the antibacterial properties - find applicability in the area of bionanotechnology. These films may be used in the fabrication of cell based sensors, in immune system engineering, in diagnostics systems and in disease treatments, among others / Doutorado / Engenharia de Processos / Doutor em Engenharia Química

Vďaka ich vysokej verzatilite a nízkej priestorovej náročnosti sú metapovrchy sľubným nasledovníkom tradičných optických komponentov. Táto práca sa upriamuje na metapovrchy, ktoré môžu nahradiť polvlnné doštičky a difraktívne deliče zväzku. Práca prezentuje dve stratégie výroby nanoštruktúr z oxidu titaničitého s vysokým pomerom strán -- jedna používa reaktívne iónové leptanie vrstvy TiO2 skrz kovovú masku, kým druhá používa štrukturovaný elektrónový rezist ako formu pre depozíciu atomárnych vrstiev TiO2. V závere práce sú charakterizované a analyzované optické vlastnosti vyrobených štruktúr, predovšetkým ich fázový posun a transmisivita.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22087号 / エネ博第395号 / 新制||エネ||76(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 森井 孝, 教授 木下 正弘, 教授 片平 正人 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

PhD (Physics) / Department of Physics / Understanding how and why superconductivity (SC) occurs in a given material has been very challenging for physicists for more than a hundred years, notwithstanding the major milestones, such as the London theory, the Landau-Ginzburg theory, and the BCS theory. The extreme challenge to predict the occurrence of SC is symbolized by the long string of unanticipated but breathtaking advances, i.e., the unexpected discoveries of cuprates and Fe-pnictides being the dramatic modern examples. Because of their incompatibility, the nucleation of SC near a ferromagnet is di cult and has never been realized except for the case that another superconductor provides proximity-boosted Cooper pairs. This perceived necessity to start with another superconductor is engrained in the exten- sive study of the proximity e ect in superconductor/ferromagnet (S/F) powder sample, where all the structures involve a superconductor with either stable or metastable struc- ture. Compounding the di culty, it is also generally recognized that SC with substantial Tc is favourable in low dimensionality because of strong quantum uctuation. In this thesis, we report a serendipitous nding of SC that emerges under the most implausible circumstances in low eld microwave absorption measurement. This new revelation may lead to unconventional avenues to explore novel SC for applications in superconducting spintronics. By means of a varienty of techniques, including EPR, SEM, FTIR, PPMS/VSM and XRD, nanonickel incorporated YBCO in di erent weighting factors have been studied. With its complex chemical structure and magnetic properties, Ni-YBCO is far from well understood and the magentic behavior of the system under di erent conditions is investi- gated. From the dilute mixture of nanonickel particles, it is found that groups of normal Josephson junctions (JJs) and JJs due to YBCO-nickel-YBCO interparticle weaklinks form as nickel is ferromagnetic. We experimentally show, for the rst time multiple phase reversals in the non-resonant microwave absorption (NRMA) spectra from Ni-YBCO pos- sibly, due to the formation of JJs. We also show that these multiple phase reversals then vii depend on microwave power and temperature. We argue that microwave power induced coherence among some groups of JJs and breaking of some of the weaker JJs can then lead to the disappearance of multiple phase reversals at higher microwave power levels. Further, we also report a role of pair breaking e ects that shall give a linear eld de- pendence of the derivative microwave absorption signal, which is essentially the NRMA signal. This pair-breaking e ect dominates at temperatures closer to Tc as expected thermodynamically. The presence of two peaks in the system, results in high permeability ferromagnet which acts as a magnetic short circuit for magnetic ux density and creates low reluctance path. A transition from normal to anomalous does not occur in this work, because of the possibility of junction in the sample. As predictable at the region around the origin where the weaklinks are supposed to be very strong for a very low doping or low nanonickel addition ( 0.5 % wt), not much e ect was observed. However, when the nanonickel addition is increased to 2 % and 3% we see a signi cant change in the magnetization and the associated hysteresis, indicating ux pinning. / NRF

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