Philosophiae Doctor - PhD / The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in VO2 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-VO2 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of VO2 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of VO2 thin films. A reversible thermal tunability of the optical/dielectric constants of VO2 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in VO2 host matrix. / South Africa

[pt] As nanopartículas, atualmente, têm sido alvo de pesquisas em diversas áreas devido as suas exclusivas propriedades magnéticas, fotônicas, optoeletrônicas e catalíticas. O presente trabalho teve como objetivo estudar a resposta SERS, bem como as possíveis interações existentes entre as nanopartículas de ouro com ácido etilenodiaminotetraacético e o seu respectivo complexo com cromo (III). Este complexo foi sintetizado e caracterizado pelas técnicas de análise elementar (espectrometria de absorção atômica e CHN), espectroscopia de infravermelho, espectroscopia Raman e espectroscopia de ultravioleta-visível. Foi possível verificar que, neste caso, o ligante EDTA se coordenou de maneira pentadentada com o íon Cr(3 mais); e que uma molécula de água ocupou a sexta posição de coordenação. Foram também sintetizadas em meio aquoso, suspensões coloidais de nanopartículas de ouro pelo método físico de ablação laser. Este método é interessante pois permite que as partículas sejam formadas sem a presença de quaisquer outros reagentes, utilizando unicamente ouro e água. Em seguida, elas foram caracterizadas pelas técnicas de espectroscopia de ultravioleta-visível, SERS, SEM e TEM. Os dados mostraram que as partículas possuíam diâmetros relativamente pequenos, entre 10 e 30 nm e que havia a presença de moléculas de monóxido de carbono adsorvidas em sua superfície, possivelmente oriundas do CO2 presente no ar que se solubiliza com facilidade em água e que em alguma etapa da ablação foi reduzido. A fim de estudar e apresentar a sensibilidade da técnica SERS, foram preparadas soluções de EDTA e do complexo sintetizado de modo que ao serem adicionadas às suspensões de nanopartículas, obtivessem concentração final igual a 10(-5) mol/L. Para serem analisadas via SERS, essas misturas foram gotejadas em uma placa de vidro previamente revestida com uma camada de alumínio, de modo que fosse extinta qualquer possível interferência da fluorescência oriunda do vidro. As bandas SERS obtidas foram, então, estudadas e os dados sugerem que as interações ocorridas na superfície das nanopartículas, tanto com o ligante quanto com o complexo, sejam do tipo ligação de hidrogênio. / [en] Nowadays, the nanoparticles have been target of searches in several in various areas due its magnetic, photonic, optoelectronic and catalytic exclusive proprieties. The present work aimed to study the SERS response and the possible interaction between the gold nanoparticles and ethylenediamninetatraacetic acid and its chromium (III) complex. This complex was synthesized and characterized by elemental analyses ( atomic absorption spectrometry and CHN ), infrared spectroscopy, Raman spectroscopy and Ultraviolet-visible spectroscopy techniques. It was possible to see that, in this case, the ligand EDTA coordenates as a quinquidentate with the chromium íon, and one water molecule occupied the sixty valence position. In this paper was synthesized also a aqueous colloidal solution of gold nanoparticle by the physic method pulsed laser ablation. This method is very interesting because allow the formation of the particles without the action of another reagent, utilizing just gold and quarter. After that, its was characterized by ultraviolet-visible spectroscopy, SERS, SEM and TEM. The dates showed that the particles had relatively small diameters, near 10 to 30 nm and there was the presence of carbon monoxide molecules adsorbed in its surfaces, possibility from CO2 present in the air that is so much soluble in water and in some stage of ablation was reduced. In order that study and present the sensibility of the SERS techniques, solutions of EDTA and synthesized complex was prepared in such a manner as when its added inside the colloidal solutions its final concentration was 10(-5) mol / L. In order to analyzed by SERS, these mixtures was deposited in a glass plate that before was covered by a aluminum layer so as to extinct some interference from glass fluorescence. The SERS bands got was studied and we believe that the interaction occurred in the nanoparticles surface with a both ligand and complex was by hydrogen bond.

De par leurs nombreuses applications potentielles, de nombreux efforts de recherche ontété poursuivis dans le domaine de la synthèse de nanoparticules. Cependant le mécanisme àl'origine des formes anisotropes de nanoparticules d'or, pour une taille et une structure biendéfinies, reste encore un sujet controverse.L'objectif général de cette thèse est de comprendre l'origine de cette anisotropie, lors dela formation de nanoparticules d'or, en particulier sous la forme de nano-bâtonnets d'or, enphase liquide. Parmi les nombreux procédés de synthèse existants, la "synthèse de particulesanisotropes par croissance à partir de germes" a été retenu, car il permet un contrôle précis dela taille et de la structure des nanoparticules. Lors de la synthèse de nanoparticules, les germesjouent un rôle de précurseur et permettent ainsi de maitriser la structure cristalline desnanoparticules finales. Si le rôle crucial des germes a déjà pu être étudié par différentsgroupes de recherche, une étude systématique sur la genèse de l'anisotropie par rapport à lataille et la structure initale des germes restait à réaliser. Ce travail a ainsi pour objectif derépondrre aux deux questions :i. Comment contrôler la structure cristalline et de la taille des germes?ii. Quelles sont les influences de la taille des germes et de leur structure sur la cinétique dela croissance? / Between the ongoing research on various type of nanomaterials to tune the particle sizeand crystal design in nanoscale for their potential applications, anisotropic gold nanoparticleshas attracted the most intention not only because of their divine color but also their enhancedcatalytic activities, optical properties and electrical conductivities. Event though, many effortshave been already made in the field of synthesis of anisotropic gold nanoparticles, withdefined sizes and structures, growth mechanism of many unique anisotropic shapes is still acontroversial subject.Overall objective of this thesis is to understand the origin of anisotropy during theformation of anisotropic gold nanoparticles, especially gold nanorods, in liquid phase. For ourenvisaged aim, between numerous synthetic methods developed for production ofnanoparticles, seed mediated approach is chosen for the fabrication of final anisotropic goldnanoparticles from small seeds which is grown into final nanoparticle later on. During thesynthesis of nanoparticles, those seeds play critical role as precursors to control the yield ofand the crystal structure of final anisotropic nanoparticle. Here we offer a systematical studyon the origin of anisotropy with respect to “seed size” and “crystal morphology”. Since thesesmall particles are the genesis of anisotropic metal nanoparticle synthesis, in this thesis weanswer following questions to explain the origin of anisotropy;i. How to control the crystal structure and the size of the seeds?ii. What are the influences of controlled seed size and structure on the kinetics ofnanoparticle growth?

Cette thèse présente la synthèse et la caractérisation de nanoparticules d’or bi-fonctionnelles. Plusieurs voies de synthèse de nanoparticules d’or sphériques sont présentées afin d’obtenir des nanoparticules de 2 nm, 5 nm, 15 nm ou 35 nm de diamètre. La couronne de ligands peut être rendue bi-fonctionnelle par deux procédés : les synthèses bi-ligands ou les échanges de ligands. Dans les deux cas, la composition de la couronne de ligands est étudiée par résonance magnétique nucléaire et elle s’avère être systématiquement différente de la composition du milieu réactionnel, chaque ligand introduisant des interactions intermoléculaires particulières qui lui confèrent des propriétés de complexation propres vis-à-vis de la surface d’or. La ségrégation des ligands en surface est étudiée par nucléation hétérogène et régiosélective de silice et aboutit à la formation de nanostructures or/silice asymétriques, révélant une séparation de phase des ligands sous forme de patches dans certains cas. Enfin, une influence particulière des ligands aromatiques sur les propriétés optiques des nanoparticules d’or est observée, se traduisant par un fort décalage de la position de la bande plasmon de surface localisé vers les grandes longueurs d’onde. Une étude théorique montre l’influence de ces ligands sur les transitions interbandes de l’or au sein des nanoparticules. / This thesis shows the synthesis and the characterization of bi-functional gold nanoparticles. Several synthesis of spherical gold nanoparticles are presented in order to obtain nanoparticles with a diameter of 2 nm, 5 nm, 15 nm or 35 nm. The ligand shell can become bi-functional from two processes: bi-ligand synthesis or ligand exchange. In both cases, the composition of the ligand shell is studied by nuclear magnetic resonance and is shown to be systematically different from the reaction medium’s composition, each ligand introducing particular intermolecular interactions which provide it proper complexing abilities against the gold surface. The ligand segregation on the surface is studied thanks to regioselective heterogeneous nucleation of silica, leading to the formation of asymmetric gold/silica nanostructures, thus revealing a phase separation of the ligands in certain cases. Then, a particular influence of aromatic ligands on the optical properties of the gold nanoparticles is observed, showing a strong shift of the localized surface plasmon band to higher wavelengths. A theorical study shows the influence of this kind of ligands on the gold interband transitions in the nanoparticles.Keywords: gold nanoparticles, functionnalization, ligand exchange, segregation, gold/silica hybrid nanostructures, plasmonics, nuclear magnetic resonance.

Volatile organic compounds (VOCs) in the indoor air have adverse effects on the dwellers residing in a building or a vehicle. One of these effects is called sick building syndrome (SBS). SBS refers to situations in which the users of a building develop acute health effects and discomfort depending on the time they spend inside some buildings without having any specific illness. Furthermore, monitoring volatile organic compounds could lead to early diagnosis of specific illnesses through breath analysis. Among those VOCs formaldehyde, acetaldehyde can be listed. In this thesis, VOC detecting thin film sensors have been investigated. Such sensors have been manufactured using semiconducting metal oxides, ligand activated gold nanoparticles and Graphene/TiO2 mixtures. Advanced gas deposition unit, have been used to produce NiO thin films and Au nanoparticles. DC magnetron sputtering has been used to produce InSnO and VO2 thin film sensors. Graphene/TiO2 sensors have been manufactured using doctor-blading. While presenting the results, first, material characterization details are presented for each sensor, then, gas sensing results are presented. Morphologies, crystalline structures and chemical properties have been analyzed using scanning electron microscopy, X-ray diffraction and X-ray photo electron spectroscopy. Furthermore, more detailed analyses have been performed on NiO samples using extended X-ray absorption fine structure method and N2 adsorption measurements. Gas sensing measurements were focused on monitoring formaldehyde and acetaldehyde. However, responses ethanol and methane were measured in some cases to monitor selectivity. Graphene/TiO2 samples were used to monitor NO2 and NH3. For NiO thin film sensors and Au nano particles, fluctuation enhanced gas sensing is also presented in addition to conductometric measurements.

Dans ce travail de thèse nous avons étudié les propriétés de fluorescence de films minces d’or dopés avec des molécules organiques Nous avons montré par imagerie électroniques MEB et TEM qu’ils sont structurés en agglomérats de nanocristaux (5 à 10nm) recouverts de molécules formant un gap nanométrique. Dans les spectres d’extinction nous avons observé la présence de la résonance plasmon du métal ainsi que d’une autre résonance à 600nm que nous attribuons au plasmon de gap.Les spectres d’émission et d’excitation de fluorescence ont confirmé que ces films dopés fluorescents avec une composante venant de la fluorescence de l’or, et une autre caractéristique de la présence des molécules fluorescentes. Les décalages spectraux en excitation et en émission à la fois de l’or et des molécules sont les signes d’un couplage fort entre leurs états électroniques, ce qui serait en accord avec la très forte concentration de molécules dans le film (1/100 molaire)L’observation non intuitive de la fluorescence des molécules insérées dans la couche d’or aurait pour origine l’augmentation considérable de leur taux radiatifs qui a été récemment observé dans les nanogaps. / In this thesis work we studied the fluorescence properties of gold thin films doped with organic molecules. We have shown by electronic imaging SEM and TEM that they are structured in agglomerates of nanocrystals (5 to 10 nm) covered with molecules forming a nanometric gap. In the quenching spectra we observed the presence of the plasmon resonance of the metal as well as another resonance at 600nm that we attribute to the gap plasmon.The fluorescence emission and excitation spectra confirmed that these fluorescent doped films with a component coming from the fluorescence of gold, and another characteristic of the presence of fluorescent molecules. The spectral shifts in excitation and in emission of both the gold and the molecules are the signs of a strong coupling between their electronic states, which would be in agreement with the very high concentration of molecules in the film (1/100 molar)The non-intuitive observation of the fluorescence of the molecules inserted into the gold layer is due to the considerable increase in their radiative levels that has recently been observed in nanogaps.

When an electromagnetic wave illuminates metal nanostructure under right circumstances, it can couple to the motion of electrons and thus give rise to so-called LSPR. When these collective oscillations non-radiatively decay, they excite charge carriers that can have, for a short moment of time, highly non-thermal energy distribution. These so-called "hot" electrons and holes can then take part in photochemical applications, e.g. in reactions on photoactive electrodes where hot electrons act as catalysts. Gold nanoparticles seem to be a good candidate for fabrication of such electrodes because they exhibit resonantly enhanced absorption due to plasmon excitation in the visible and near infrared spectral range, which could make the solar energy harvesting more efficient. In this work we present electrohemical experiments that should help to clarify the underlying principles of photochemical reactions involving hot electrons. Our model system consists of indium tin oxide electrodes covered with tungsten disulphide nanotubes that were previously decorated by gold nanoparticles. By comparing the results of chronoamperometric measurements on individual components of this system it was shown that excitation of plasmonic nanoparticles indeed leads to photocurrents and that electrochemical methods can serve as a valuable tool for analysis of photochemical reactions catalyzed by hot electrons.

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This diploma thesis deals with comparison of experimental and simulated low energy ion scattering spectra. There is a theoretical description of basic principles of low energy ion scattering and description of the spectrometer, which is situated at Institute of physical engineering. It is shown, how to prepare samples using the colloidal gold solution. The deposition of gold nanoparticles is characterized. The usage and meaning of time and energy spectra of low energy ion scattering is explained. There is also shown the effect of channeling in Si substrate.

This thesis deals with metal nanostructures and their use in detection of biomolecules. A protocol for stabilizing solutions of gold nanoparticles was developed for better usage in biological samples or biochemical processes, where different pH or salt concentrations can be used. A model of optical properties of the nanoparticles was presented and supported by spectroscopic experiments. A possible utilization of plasmonic nanostructures on surfaces for detection of biomolecules was also demonstrated.