Bismuth selenide belongs to a class of topological insulators---materials characterized by a intriguing electronic band structure, with a characteristic Dirac conical band on the surface. In this master thesis, the optical response of this material is explored in the infrared spectral range and in a broad range of magnetic fields. We mainly focus on the absorption of light due to free charge carriers having, when the magnetic field is applied, a form of cyclotron resonance. We find that the experimentally observed response is consistent with expectations for massive electrons in bulk rather than massless particles on the surface.

This thesis deals with surface analysis and characterization of optical features of thin films created by hexamethyldisiloxane (HMDSO) plasma polymerization on silicon wafers. The RF plasma industrial deposition equipment was used for the thin layers formation. These thin films serve as protective coatings on the reflective layer in the car light or solar panels. Theoretic part gives basic information about plasma, its occurrence, features, diagnostics and applications. Thin layers, their production and characterization are discussed here, too. Theoretic description of monomer material (including the group of other organosilicones) is also presented here. The FTIR spectroscopy and elipsometry are mentioned as the main methods for thin films characterisation. Because material during its practical use degrades due to external conditions, the influence of them on the thin layer properties is studied using the accelerated aging of created films. Industrial deposition chamber AluMet 1800V made by Leybold Optics, Ltd. installed in Zlin Precision company was used for the thin films production. Thin films were created under different conditions that were selelected near to the real conditions used in technology. Various applied powers (2-5 kW) were used for the deposition under different monomer flows. Further, the influence of oxygen addition on the created film properties was investigated. The deposition process was monitored by optical emission spectroscopy. The spectrometer Jobin Yvon Triax 320 with CCD detector was used. The selected part from every samples set was exposed by UV radiation (48 hours at radiation density of 0.68 W/m2 at 340 nm) to simulate the probable conditions during the layers real use. The surface properties were investigated by measurement of reflected light spectral intensity in the visible range at different angles. The angle between incident and reflected beam was varied in the interval of 40 - 150° with 10° step. The influence of sample preparation conditions as well as their aging effect was studied at the selected angles. Spectral reflectance doesn´t depend significantly on applied discharge power and oxygen addition. The significant shift of reflectance into the red part of spectrum was observed at UV exposed samples more or less independently on the applied discharge power of monomer flow rate. Addition of oxygen during the deposition suppresses this effec significantly. Characterization of thin layer structure was done by FTIR spectroscopy. No significant changes were observed in the structure at different discharge powers of monomer flow rates except total absorption intensities that are proportional to the layr thickness. The oxygen addition, of course, changes the structure significantly. These results are only preliminary because the layers were very thin (deposition conditions were near to the common process standard) and thus the signal/noise ratio was relatively low.

Diploma thesis studies the effect of temperature (75 and 105 °C) and the effect of 3 kinds of liquids (silicone and hydraulic oil and coolant) at room temperature and at 105 °C on change of the structure of 3 species butadiene-acrylonitrile (NBR) seals (o-ring and two types of bolts). The seals are inspected by the thermogravimetric analysis, differential scanning calorimetry and infrared spectroscopy, the influence of 105 °C on the o-rings is also evaluated in terms of changes in tensile properties. The greatest changes in the composition and structure are observed on o-rings particularly due to temperature of 105 °C, there was a significant reduction in dilatability and an increase in stiffness and glass transition temperature. The root cause is the surface and centre additive decomposition and oxidation. The bolts have suffered from decomposition of the protective surface layer and the additives in the centre, structural change was minor. Exposure to 75 °C has resulted in a gradual loss of low molecular weight substances. Liquids at room temperature didn‘t affect the structure of the seals, at 105 °C it caused a loss of weight due to decomposition of the protective surface layer and release of additives and the products of their decomposition. Results showed that the common use of the NBR seals at 105 °C is unsuitable, at 75 °C it leads to gradual changes, loss in mechanical and sealing properties.

La majeure partie de mon travail de thèse a porté sur l’étude de la composition chimique de la surface d’Europe. Afin d’apporter une plus-value par rapport aux résultats de l’instrument NIMS à bord de la sonde Galileo qui orbita dans le système jovien de 1995 à 2003, une campagne d’observations depuis le sol a été menée avec le spectromètre imageur infra-rouge SINFONI au VLT. Cinq observations en optique adaptative possédant une résolution spatiale d’environ 160 km et une résolution spectrale R=1500 dans le proche infra-rouge furent acquises. Une procédure complexe de réduction des données a été mise en place afin de construire un cube hyperspectral global en réflectance de la surface. La modélisation linéaire de chacun des spectres du cube a permis d’aboutir aux premières cartes d’abondances absolues jamais obtenues pour la surface d’Europe. Ces cartes confirment la présence des deux espèces majoritaires, la glace d’eau et l’acide sulfurique hydraté. La distribution de l’acide sulfurique est centrée sur l’hémisphère orbital arrière qui est préférentiellement impacté par un flux d’ions de soufre originaires du tore de plasma produit par l’activité volcanique d’Io. Cependant, deux résultats inattendus ont été obtenus. Le premier concerne la glace d’eau, dont la forme cristalline est près de deux fois plus abondante que la forme amorphe selon les résultats de la modélisation. Ce résultat, surprenant compte tenu du taux d’irradiation très élevé auquel la surface est soumise, pourrait s’expliquer par l’existence d’un fort gradient de cristallinité au sein de la couche de glace, mais aussi par l’existence d’une activité endogène relativement soutenue qui se traduit visuellement par une surface peu cratérisée, donc jeune. La corrélation entre la distribution des grains cristallins et la géomorphologie semble accréditer la seconde hypothèse. Le second résultat concerne la détection de sels chlorés à partir de la modélisation des spectres hautement résolus de SINFONI, et non de sulfates, remettant en cause les détections marginales annoncées par les observations de l’instrument NIMS/Galileo. La distribution des sels chlorés, tout comme celle de la glace d’eau cristalline, est corrélée à la géomorphologie, ce qui confirme le rôle important des apports endogènes. Des processus tectoniques et cryovolcaniques mis en évidence récemment pourraient être à l’origine de cette distribution. L’autre versant de ma thèse a été consacré aux caractéristiques physiques des grains cométaires de 67P/C-G. L’instrument COSIMA embarqué sur l’orbiter de la sonde Rosetta a permis la collecte, l'imagerie et l'analyse chimique élémentaire des grains présents dans l’environnement proche de 67P/C-G. Une approche automatisée de la détection des grains à partir des images prises par la caméra « COSISCOPE » a été mise en place et a permis de détecter environ 35000 grains ayant une surface de plus de 100 µm2 entre août 2014 et mai 2016. La résolution de 13.7 µm/pixel a rendu possible la caractérisation en détail de la forme et de la structure des grains, et le nombre important de détections a permis d’obtenir des statistiques robustes concernant la distribution en taille et l’évolution de celle-ci au cours du temps. Deux grandes familles de grains ont été identifiées : les grains compacts, qui ne représentent qu’une faible minorité des grains et qui ont été majoritairement collectés en début de mission, et les agrégats, qui ont une structure très poreuse similaire à celle des IDPs et des micrométéorites collectées en Antarctique. La distribution en taille obtenue suit une loi de puissance intégrale en r-2.66. La comparaison avec des lois obtenues à des échelles différentes par d’autres instruments met en évidence des différences qui peuvent être interprétées par des mécanismes d’éjection dépendant de la taille associés à un biais du processus de collecte en orbite. / The major part of my work focused on the study of the chemical composition of Europa’s surface. In order to provide additional insights in comparison to the results of the NIMS instrument onboard the Galileo spacecraft that orbited in the Jovian system from 1995 to 2003, a ground-based observations campaign was conducted with the infrared imaging spectrometer SINFONI on the VLT. Several observations using adaptive optics with a spatial resolution of about 160 km and a spectral resolution R = 1500 in the near-infrared were acquired and then combined. A specific data reduction pipeline was developed to build a global hyperspectral cube in surface reflectance. The linear modeling of each spectra of this cube leads to the first global abundance maps ever obtained for the surface of Europa. These maps confirm the presence of the two major species, namely water ice and hydrated sulfuric acid. The distribution of the hydrated sulfuric acid is centered on the trailing orbital hemisphere preferentially affected by a sulfur ion flux coming from the plasma torus produced by Io volcanic activity. Two surprising results were obtained. The first one concerns water ice, which crystalline form is about twice more abundant than the amorphous form according to the modeling results. This result, unexpected given the very high radiation rate on the surface, could be explained by a strong crystallinity gradient through the ice slab. However, it could also point out an endogenous activity possibly strong as first suggested by its poorly well-known cratered surface. The correlation between the crystalline grains distribution and the geomorphology seems in favor to the second hypothesis. The second result is related to the detection of chlorinated salts from the modeling of highly resolved spectra from SINFONI. Sulfates, first reported by several analyses of NIMS observations are marginal in the modeled composition, hence challenging their presence on the surface of Europa. The chloride distribution, as well as the one of the crystalline water ice, is correlated to geomorphology, potentially confirming significant endogenous contributions as the result of tectonic and cryovolcanic processes recently highlighted. The second part of my PhD was dedicated to the physical characteristics of the 67P/C-G’s cometary grains. The COSIMA instrument onboard the Rosetta orbiter allowed the collection, imaging and elemental chemical analysis of grains present in the immediate environment of 67P/C-G. An automated approach of the grains detection based on images taken by the camera "COSISCOPE" was set up and able to detect about 35.000 grains having an area of more than 100 µm² between August 2014 and May 2016. The resolution of 13.7 µm/pixel allowed to perform a detailed characterization of the shape and the structure of the grains, and the large number of detections permitted to obtain significant statistics on the size distribution and its evolution over the time. Two large families of grains have been identified: the compact grains, which represent only a small minority of grains mostly collected at the beginning of the mission, and aggregates, which have a very porous structure similar to those of IDPs and micrometeorites collected in Antarctica. The size distribution obtained follows an integrated power law in r-2.66. The comparison with the laws obtained at different scales by other instruments highlights differences that can be interpreted by ejection mechanisms depending on the size associated with a selection bias during the collection process in orbit.

L’étude en laboratoire d’échantillons extraterrestres, issus d’objets primitifs, est fondamentale aussi bien pour améliorer notre connaissance de la formation et de l’évolution de notre Système Solaire que pour interpréter les observations faites par les missions spatiales.Des analyses précises en laboratoire de ces échantillons sont essentielles pour comprendre les conditions physico-chimiques qui ont mené à la formation des petits corps et des planètes. Le but de cette thèse interdisciplinaire a été d’exploiter l’imagerie infrarouge et de développer un dispositif de microtomographie en spectroscopie infrarouge à transformée de Fourrier.Nous étudierons des fragments de météorites et de poussières astéroïdales. De plus, la tomographie en rayons X a été utilisée pour contraindre précisément la forme de l’échantillon. Avec ces analyses, nous avons caractérisé la composition de matériaux extraterrestres à très petite échelle sans les détruire. Nous avons étudié l’effet des processus post-accrétionels, comme l’altération spatiale, à l’intérieur du corps parent, ou l’altération spatiale, à la surface de l’astéroïde, à la fois sur les parties minérale et organique. En particulier,nous avons pu grâce à cette expérience,étudier la corrélation spatiale de la matière minérale et organique, ce qui est fondamental pour comprendre l’origine et l‘évolution de la matière organique. / Laboratory based studies of extraterrestrialmaterials derived from primitive objectsis fundamental to improve our knowledgeabout the formation and the evolutionof the Solar System as well as for interpretingobservations collected by spacecraftand landers. Precise laboratory analysesof samples obtained from sample returnmissions are essential to understand theconditions and the physico-chemical processes,which lead to the formation of thesmall bodies and planets. The aim of thisinterdisciplinary thesis was to exploit theinfrared imaging and to implement threedimensionalFourier transform infrared microtomographyto study different extraterrestrialmaterials (meteorites and asteroidaldust). Moreover, X-ray tomographywas used to determine the precise shape ofthe samples. With these analytical methods,we have characterized the compositionof extraterrestrial materials withoutdestroying them at very high resolution.We have studied the post-accretional effects,such as aqueous alteration inside theparent’s bodies or space weathering at thesurface of asteroids, on both the mineraland the organic components. In particular,we studied the correlations between the organicmaterials and the minerals observedin the sample, which is fundamental to understandthe origin and the evolution of theorganic matter.

Cette thèse porte sur l’étude de la radio-sensibilité de Molécules AromatiquesHétérocycliques (MAH) à basse température exposées à une irradiation avec des ionslourds rapides. La présence de ces molécules dans les météorites carbonées sur Terre estune forte indication pour l’existence de cette catégorie de molécules dans l’espace.L’objectif de ce travail est de simuler l’effet des rayons cosmiques sur des MAH enphase solide et d’estimer leur résistance à l’irradiation. Les lignes de faisceaux deGANIL et de GSI permettent de simuler cet effet. L’évolution des MAH en phase solidea été monitorée par spectroscopie infrarouge à transformée de Fourier. Cela permet dequantifier la destruction des MAH, de déterminer leur section efficace de destruction etde détecter les molécules produites. Les sections efficaces de destruction de l’adénine etde la cytosine suivent une loi puissance en fonction du pouvoir d’arrêt électronique :σd~ Se1.2. Les nouvelles bandes d’absorption observées après l’irradiation des MAH sontprincipalement attribuées à des nitriles (R-C≡N), des isonitriles (R-N≡C) et (R-C≡C).L’évolution de la section efficace en fonction du pouvoir d’arrêt électronique a permisd’estimer la durée de vie de l’adénine dans l’espace : (14×106) années. Ces résultatspermettront de comprendre la stabilité et la chimie de ces molécules complexes dansl’espace. / The thesis concerns the study of the radio sensitivity of aromatic heterocyclic molecules(AHMs) at low temperature (12 K) exposed to swift heavy ion radiation. The presenceof aromatic heterocyclic molecules in carbonaceous meteorites on Earth is a strongindication that this class of molecules exists in outer space.The aim of this work was to study the effects of cosmic ray analogues on solid AHMsand to estimate their survival under radiation. The beam lines of GANIL and GSI allowto simulate the effects of cosmic rays in AHMs. The evolution of the solid AHMs underirradiation was monitored by Fourier transformed infrared absorption spectroscopy; thisallows to quantify the disappearance of AHMs, to determine their apparent destructioncross section and to detect their radioproducts. Furthermore, it was found that adenineand cytosine destruction cross sections (σd) follow a power law with the electronicenergy loss: σd~ Se1.2 .New IR absorption peaks arising from the AHMs degradationswere observed; these peaks can be attributed to nitriles (R-C≡N), isonitriles (R-N≡C),and (R-C≡C).The observed power law allowed the estimation of the lifetime of adeninein space exposed to galactic cosmic rays as (14×106) years. These findings may help tounderstand the stability and chemistry related to complex organic molecules in space.

Au cours de cette étude, nous avons montré que dans les oxydes de fer type perovskite, les ions sulfates (SO42-) pouvaient être utilisés à escient pour apporter de l'anisotropie cristalline et électronique ou bien au contraire pour casser les mises en ordre à longue distance et provoquer l'isotropie du matériau. Ainsi, ce travail a permis d'isoler les composés bidimensionnels : Sr4Fe2.5-x□xO7.25-(3x/2)(SO4)0.5 (avec x=0, 0.25 et 0.5). Ils peuvent être décrits comme une intercroissance SrO/SrFeO2,5/SrFe0,5-x□xO1,25-(3x/2)(SO4)0,5/SrFeO2,5 et cristallisent dans une maille moyenne quadratique I4/mmm (a=ap et c≈29 Å). Les tétraèdres de sulfates non-pontés se présentent de façon transversale par rapport à c ⃗ pour x=0,5 et longitudinale pour x=0 et 0,25 parce que pontés aux pyramides de fer de la couche partagée. Les atomes de fer des couches non-mixtes SrFeO2,5 se situent eux en coordinence pyramidale pour x=0 et pyramidale et octaédrique pour x=0.5 et x=0.25 afin de respecter la trivalence du fer. Quel que soit x, les composés sont antiferromagnétiques de type G (les spins se situant dans le plan (a,b)). Cependant, pour x=0,5, deux configurations magnétiques sont observées, tandis que les composés x=0 et x=0.25 n'en montrent qu'une seule. Dans le composé Sr4Fe2.5□xO7.25(SO4)0.25(CO3)0.25, l'influence des carbonates (CO32-) se ressent directement sur le paramètre d'empilement, qui est plus petit. Cela n'entraîne cependant aucun changement sensible dans les propriétés physiques. Les composés sont des semi-conducteurs présentant de fortes valeurs de résistivité électronique (de l'ordre de 106Ω.cm) et ne sont pas conducteurs ioniques.La phase ordonnée "15R" SrFe0.6Cr0.4O2.8 se désordonne lorsque l'on substitue 10% du fer par des sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) et adopte une structure pseudo-cubique. Ses propriétés physiques sont alors bouleversées puisque l'on passe d'un comportement ferromagnétique à antiferromagnétique (TN=800K). Ce composé très lacunaire en oxygène montre des défauts structuraux plus ou moins étendus et un comportement de type semi-conducteur. Aucun phénomène de conduction ionique n'est observé. / In this study, we have shown that in perovskite-type iron oxides, sulfate ions (SO42-) can be used to bring structural and electronic anisotropy, or on the contrary to break long distance ordering and cause the isotropy of the material.Thus, this work made it possible to isolate the two-dimensional compounds: Sr4Fe2.5-x□x07.25-(3x/2)(SO4)0.5 (with x = 0.25 and 0.5). They can be described as an intergrowth SrO/SrFeO2,5/SrFe0,5-x□xO1,25-(3x/2)(SO4)0.5/SrFeO2,5 and crystallize in a quadratic mean cell I4/mmm (a=ap et c≈29 Å). The unbridged sulfates tetrahedra are oriented transversely with respect to c ⃗ for x=0.5 and longitudinal for x=0 and 0.25 because bridged to the iron pyramids of the shared layer. The iron atoms of the non-mixed layers SrFeO2,5 are in pyramidal coordination for x=0 and pyramidal and octahedral coordination for x=0.5 and x=0.25, in order to respect the trivalence of iron. However, for x=0.5, two magnetic configurations are observed whereas the compounds x=0 and x=0.25 show only one. In the compound Sr4Fe2.5□xO7.25(SO4)0.25(CO3)0.25, the influence of the carbonates (CO32-) is directly felt on the stacking parameter, which is smaller. The compounds are semiconductors with high electronic resistivity values (of the order of 106Ω.cm) and are not ionic conductors.The ordered phase "15R" SrFe0.6Cr0.4O2.8 becomes disordered when 10% of the iron is substituted with sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) and adopts a pseudo-cubic structure. Its physical properties are then modified because we switch from a ferromagnetic to an antiferromagnetic behavior (TN=800K). This oxygen-deficient compound shows more or less large structural defects and a semiconductor behavior. No ionic conduction phenomenon is observed.

In this thesis we investigate experimentally certain aspects of the interaction of terahertz (THz) radiation with intersubband transitions and excitonic transitions in semiconductor quantum wells. The first part deals with a more fundamental view on an intersubband transition in a symmetric, undoped GaAs/AlGaAs multiple quantum well. After optical excitation of carriers, the considered electronic conduction intersubband transition is probed in the low-intensity linear regime using broadband THz pulses. These pulses are detected via field-resolved electro-optic sampling. While the sample’s terahertz absorption shows the expected single peak of the resonant intersubband transition, the differential transmission spectra, i.e. the photoexcitation-induced changes in transmission, display strong Fano signatures. On the basis of a microscopic theory, we show that they originate from a phase sensitive superposition of THz current and ponderomotive current. The latter one results from the wiggling motion of carriers induced by the accelerating THz field. Our findings demonstrate for the first time that the ponderomotive contribution has to be taken into account also at the lowest THz intensities. The following issues consider the interaction with THz pulses of higher intensity from the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf. In one experiment we investigate efficient second order sideband generation in the GaAs/AlGaAs multiple quantum well mentioned above. To this end a near-infrared laser tuned to excitonic interband transitions is mixed inside the sample with the inplane polarized FEL beam to create the sum- and difference-frequencies between them. We compare the sideband efficiencies for the THz beam tuned to the interexcitonic heavy-hole light-hole transition and to the intraexcitonic heavy-hole 1s-2p transition. In the latter case we achieve a ten times higher n=+2 low-temperature efficiency around 0.1%. This value is comparable to previous studies in the literature, but our approach involves different transitions in a much simpler geometry. At room temperature the efficiency drops only by a factor of 7 for low THz powers. The last part of this thesis addresses another fundamental quantum-mechanical phenomenon: the splitting of an absorption line in a strong THz field. In the same abovementioned quantum well sample the FEL wavelength is tuned near the intraexcitonic 1s-2p heavy-hole transition. The THz radiation induces a power-dependent splitting of the heavy-hole 1s exciton absorption line which manifests itself in the transmitted spectrum of a broadband near-infrared probe beam. The FEL-wavelength-dependent strength of this so-called Autler-Townes splitting is discussed on the basis of a simple two-level model.

The intercalation of surfactant anions, namely sodium dodecyl sulphate, sodium benzene sulphonate and lauric acid, into commercial layered double hydroxides (LDH-CO3) with approximate composition [Mg0.654AI0.346 (OH)2](CO3)0.173.0.5H2O] was explored. LDH-CO3 is commercially available in bulk form owing to its large scale applications as a PVC stabiliser and acid scavenger in polyolefins. It is therefore of interest to investigate intercalation methods using LDH-CO3 as starting material. The intercalation method used was compared with the pre existing procedures, for instance the co-precipitation, ion exchange and regeneration methods. Due to the tenacity with which the carbonate ion is held in LDH-CO3, direct ion exchange is an intricate matter. Hence, in the regeneration method the carbonate ion is removed by thermal treatment and the LDH-surfactant is obtained by reaction of the LDH and surfactant in an aqueous medium. Nevertheless, the resulting products are impure and poorly crystallised, and only partial intercalation is achieved. The underlying principle of the current method is protonation of the carbonate anion to a monovalent anion that is easily exchanged with surfactant anions. Improved results were obtained when water-soluble organic acids were used, the most suitable being lower aliphatic carboxylic acids, e.g. acetic, butyric and hexanoic acid. In contrast, higher linear aliphatic carboxylic acids are preferentially intercalated to the anionic surfactants. In both cases the carboxylic acids are assumed to assist intercalation by facilitating the elimination of the carbonate ions present in the anionic clay galleries. X-ray diffraction analysis, thermal analysis and infrared spectroscopy confirmed the monolayer intercalation of LDH-dodecyl sulphate and LDH-dodecylbenzene sulphonate. In contrast, LDH-laurate featured a bilayer structure. / Dissertation (MSc)--University of Pretoria, 2009. / Chemistry / unrestricted

Frequency Domain Diffuse Optical Spectroscopy (FD-DOS) is an emerging optical technique that uses near infrared light to probe the hemodynamics of biological tissue. Compared to more common Continuous Wave (CW) methods, FD-DOS uses light that is temporally modulated on the order of MHz to quantify the absorption and scattering of tissue. FD-DOS can also be used to obtain absolute concentration of tissue chromophores such as oxy- and deoxy-hemoglobin, which allow for quantitative measurements of tissue hemodynamics. This dissertation focuses on the evolution of our lab’s custom digital FD-DOS as a platform for taking optical measurement of biological tissue for respiratory and cardiovascular applications. Several important instrumentation improvements will be reviewed that have enhanced the performance of the system while making it more portable and clinic ready. Two translational applications will be described in detail: 1) the use of high-speed FD-DOS for the non-invasive extraction of venous oxygen saturation (SvO2) and 2) the use of FD-DOS to monitor the hemodynamics of the sternocleidomastoid (SCM) muscle towards the non-invasive monitoring of patients on mechanical ventilation. The custom FD-DOS system parameters were adjusted for each application, with a focus on high speed to extract the cardiac signal for the SvO2 project, and a focus on high SNR to measure the highly absorbing SCM. Measurements on healthy volunteers and rabbits were used to assess the feasibility of using FD-DOS for these applications. Finally, preliminary work was conducted to characterize a miniature FD-DOS source and detector with the goal of moving towards a wearable version of FD-DOS. / 2022-05-15T00:00:00Z