Cette étude concerne la caractérisation optique non linéaire (NL) principalement d’ordre 3 dans le visible, l’UV et l’IR en régime picoseconde de différents matériaux tels que certains solvants, le niobate de lithium et les nano-feuilles de graphène. Nous présentons d’abord les expressions des susceptibilités NL. Nous décrivons ensuite la technique de caractérisation Z-scan et ses variantes. Nous présentons une nouvelle méthode qui combine les avantages de Z-scan avec ceux de la microscopie en champ sombre. Nous montrons que cette technique d’imagerie, nommée DFZscan (Dark Field Z-scan), peut mesurer les coefficients de réfraction NL en présence d'une forte absorption NL. Les résultats expérimentaux montrent une importante amélioration de la sensibilité. Finalement, nous comparons les réponses NL des solvants les plus utilisés, dont l’eau qui possède la réfraction NL la plus faible. Ce liquide est utilisé pour caractériser la réponse NL d’une suspension de points quantiques de graphène. Grâce à un modèle simple, nous estimons l'indice de réfraction et d’absorption NL d'une nanofeuille de graphène monocouche. Nous étudions également les non linéarités d’ordres supérieurs dans les matériaux liquides (toluène) et solides (LiNbO3) en vue d’applications potentielles pour la génération de la deuxième harmonique et des modulateurs de guides d'ondes. Ces coefficients peuvent intéresser une grande communauté de chercheurs dans des domaines aussi variés que la filamentation, les solitons, le traitement tout optique du signal et les réseaux de télécommunications. / This study concerns the nonlinear (NL) optical characterization mainly of order 3 in the visible, UV and IR in the picosecond regime of different materials such as solvents, lithium niobate and graphene nanosheets. We first present the expressions of NL susceptibilities. We then describe the Z-scan characterization technique and its variants. We present a new method that combines the advantages of Z-scan with those of dark field microscopy. We show that this imaging technique, called DFZ-scan (Dark Field Z-scan), can measure NL refractive coefficients in the presence of high NL absorption. The experimental results show a significant improvement in the sensitivity. Finally, we compare the NL responses of the most commonly used solvents, including water with the lowest NL refraction. This liquid is used to characterize the NL response of a suspension of graphene quantum dots. Using a simple model, we estimate the refractive index and absorption index NL of a single-layer graphene nanosheet. We also studied higher order non-linearities in liquid (toluene) and solid (LiNbO3) materials for potential applications in second harmonic generation and waveguide modulators. These coefficients can be of interest to a large community of researchers in fields as diverse as filamentation, soliton, all-optical signal processing and telecommunications networks.

[pt] O objetivo deste trabalho foi o desenvolvimento de métodos eletro-analíticos utilizando eletrodos modificados com nanomateriais a base de carbono para determinação de analitos de interesse biológico (creatinina) e farmacológico (primaquina, INHHQ, tiomersal). A determinação de primaquina (antimalárico) e de INHHQ (potencial medicamento para o tratamento de doenças neurodegenerativas) foi proposta usando eletrodo de carbono vítreo (GC) modificado com nanotubos de carbono de paredes múltiplas (MWCNTs) o qual promoveu uma melhora significativa na corrente faradaica e na resolução de pico obtida usando voltametria de onda quadrada (SWV) em tampão Britton-Robinson (BR) 0.02 mol L-1; pH 7.00 e KCl (0.25 mol L-1). Embora vários métodos para quantificar primaquina estejam reportados, muitos deles dependem de procedimentos considerados complexos e trabalhosos, portanto, a modificação proposta de GC usando MWCNTs é comparativamente fácil, levando a uma modificação robusta que produz resultados repetitivos, fornecendo também amplificação do sinal eletroquímico devido à área ativa aumentada e a taxa de transferência eletrônica aprimorada. Os GC/MWCNTs também forneceram, ao trabalhar em um pH adequado, maior resolução na detecção das diferentes etapas eletroquímicas envolvidas no processo redox da primaquina. O eletrodo permitiu o limite de detecção (LOD) de 28 nmol L-1 para a primaquina e, quando associado a um procedimento simples baseado na extração líquido-líquido (LLE) e cromatografia em camada fina (TLC), foi alcançada a seletividade e a capacidade de determinar os níveis mais baixos esperados em amostras de urina. No caso do INHHQ, um método para quantificação por SWV foi relatado pela primeira vez. Além do uso do eletrodo GC/MWCNTs um prévio procedimento de TLC, permitiu a seletividade necessária para determinar o INHHQ no tecido cerebral de ratos Wistar. O LOD foi de 0.85 μmol L-1 e a faixa dinâmica linear cobriu duas ordens de magnitude (10-6 a 10-5 mol L-1). Os pontos quânticos de grafeno (GQDs) foram escolhidos para modificar quimicamente os eletrodos utilizados para determinar tiomersal e creatinina. GQDs são fragmentos nanométricos de grafeno (presentes em dispersões como monocamada, poucas camadas ou multicamadas) onde o transporte de elétrons é confinado em suas dimensões. GQDs são estruturas baseadas em carbono que são biocompatíveis e apresentam baixa toxicidade. A pesquisa apresenta uma nova abordagem para a determinação de tiomersal (conservante em vacinas e cosméticos) em vacinas contra influenza usando GQDs como modificador do eletrodo de GC e explorando o efeito sinérgico entre GQDs, radiação visível e a diferença de potencial aplicado. Este sistema promove a oxidação do tiomersal, produzindo um aumento significativo na resposta (par redox Hg/Hg2positivo) em termos de intensidade de corrente usando SWV e tampão BR (0.02 mol L-1; pH 4.00 com KCl a 0.25 mol L-1). O LOD foi de 0.85 μmol L-1 e a faixa dinâmica linear cobriu três ordens de grandeza (10-6 a 10-4 mol L-1). Para a creatinina (um biomarcador para a disfunção renal), um composto de GQDs-cobre foi usado para modificar um eletrodo de ouro. A determinação da creatinina foi realizada utilizando SWV (tampão BR 0.02 mol L-1; pH 4.00 com KCl a 0.25 mol L-1). O método contou com a diminuição do pico de oxidação Cu/Cu2positivo na presença de creatinina, permitindo LOD de 50 nmol L-1 e faixa dinâmica linear, cobrindo três ordens de magnitude (10-6 a 10-4 mol L-1). A resposta SWV da creatinina foi atribuída à formação do complexo creatinina-Cu2+, sendo razoavelmente seletiva em relação a este analito. Todos os procedimentos desenvolvidos por voltametria foram adequadamente comparados com métodos de referência, sendo estatisticamente compatíveis. / [en] The goal of this work was the development of electro-analytical methods using electrodes modified with carbon-based nanomaterials for determination of analytes of biological (creatinine) and pharmacological interest (primaquine, INHHQ, thiomersal). The determination of primaquine (antimalarial) and INHHQ (potential drug for treatment of neurodegenerative diseases) was proposed using glassy carbon (GC) electrode modified with multi-walled carbon nanotubes (MWCNTs) that promoted significant improvement in faradaic current and better peak resolution obtained using square-wave voltammetry (SWV) in Britton-Robinson (BR) buffer 0.02 mol L-1; pH 7.00 and KCl (0.25 mol L-1). Although several methods to quantify primaquine are reported, many of these depend on procedure considered complex and laborious, therefore, the proposed GC modification using MWCNTs is comparatively easy, leading to a robust modification that produce repetitive results also providing amplification of the electrochemical signal due to the increased active area and improved electron-transfer rate. The GC/MWCNTs also provided, when working on a proper pH, higher resolution in detecting the different electrochemical steps involved in the redox process of primaquine. The electrode enabled limit of detection (LOD) of 28 nmol L-1 for primaquine and, when associated with a simple developed procedure, relying of liquid-liquid extraction (LLE) and thin-layer chromatography (TLC), it was achieved the selectivity and the capability to determine the lower levels expected in urine samples. In the case of INHHQ, a method for quantification by SWV was reported for the first time. In addition to the use of GC/MWCNTs electrode, a previous TLC procedure, enabled the selectivity required to determine INHHQ in brain tissue from Wistar rats. The LOD was 0.85 mol L-1 and the linear dynamic range covered two orders of magnitude (10-6 to 10-5 mol L-1). Graphene quantum dots (GQDs) was chosen to chemically modify electrodes used to determine thiomersal and creatinine. GQDs are nanometric fragments of graphene (present in dispersions as monolayer, few layer or multilayer) where electron transport is confined in their dimensions. GQDs are carbon-based structure that are bio-compatible and present low toxicity. The research presents a new approach for the determination of thimerosal (preservative in vaccines and cosmetics) in influenza vaccines using GQDs as a modifier of the GC electrode and exploring the synergistic effect between GQDs, visible radiation and the applied potential difference. This system promotes thiomersal oxidation, producing a significant increase in response (Hg/Hg2 positive redox pair) in terms of current intensity using SWV and BR buffer (0.02 mol L-1; pH 4.00 with KCl at 0.25 mol L-1). The LOD was 0.85 μmol L-1 with linear dynamic range covering three orders of magnitude (10-6 to 10-4 mol L-1). For creatinine, a biomarker for the renal dysfunction, a GQDs-copper composite was used to modify a gold electrode. Determination of creatinine was made using SWV (BR buffer 0.02 mol L-1; pH 4.00 with KCl at 0.25 mol L-1). The method relied on the decreasing of the Cu2+/Cu oxidation peak in the presence of creatinine, enabling LOD of 50 nmol L-1 and linear dynamic range covering three orders of magnitude (10-6 to 10-4 mol L-1). The SWV response of creatinine was attributed to the formation of creatinine-Cu2 positive complex being reasonably selective towards this analyte. All procedures developed by voltammetry were adequately compared with reference methods, being statistically compatible.

Zero-dimensional graphene (carbon) quantum dots have been drawing attention in bio-related applications since their discovery, especially for their optical properties, chemical stability, and easily modifiable surface.  This thesis focuses on the green synthesis of nitrogen-doped graphene quantum dots (GQDs) for dual-mode bioimaging with X-ray fluorescence (XRF) and optical fluorescence. Both conventional and microwave- (MW-)assisted solvothermal methods were followed to investigate the precursors’ effect on the synthesized GQDs. The MW-assisted method permitted the synthesis of uniform GQDs with an excitation-independent behavior, due to highly controllable reaction conditions. It was demonstrated that the molecular structure of the precursors influenced the optical fluorescence properties of the GQDs. Thus, both blue- (BQDs) and red-emitting (RQDs) GQDs were obtained by selecting specific precursors, leading to emission maxima at 438 and 605 nm under the excitation wavelengths of 390 and 585 nm, respectively.  Amine-functionalized Rh nanoparticles (NPs) were chosen as the X-ray fluorescence (XRF) active core, synthesized via MW-assisted hydrothermal method with a custom designed sugar ligand as the reducing agent. These NPs were conjugated with BQDs using EDC-NHS treatment. The hybrid Rh-GQDs NPs exhibited green emission (520 nm) under 490 nm excitation and led to a reduced cytotoxicity with respect to bare Rh NPs, highlighting the passivation role of the GQDs via the real-time cell analysis (RTCA) assay. The hybrid complex constituted a multimodal bioimaging contrastagent, tested with confocal microscopy (in vitro) and XRF phantom experiments. / Sedan deras upptäckt har nolldimensionella kvantprickar av grafen (kol) uppmärksammats inom biorelaterade applikationer, särskilt för deras optiska egenskaper, kemiska stabilitet och enkelt modifierbara yta. Denna avhandling fokuserar på en grön syntesmetod av kvävedopade grafen-kvantprickar för bimodal bioavbildning med röntgenfluorescens och optisk fluorescens. Både konventionella och mikrovågs-assisterade solvotermiska syntesmetoder användes för att undersöka metodernas effekt på de syntetiserade kvantprickarna. Den mikrovågs-assisterade metoden möjliggjorde syntes av uniforma kvantprickar med exciteringsoberoende egenskaper på grund av mycket kontrollerbara reaktionsförhållanden. Det demonstrerades att den molekylära strukturen hos prekursorerna påverkade de optiska fluorescensegenskaperna hos grafen-kvantprickarna. Genom att välja specifika prekursorer erhölls kvantprickar som emitterar i både blått och rött ljus, motsvarande emissionsmaxima vid 438 respektive 605 nm under excitering vid 390 respektive 585 nm. Amin-funktionaliserade Rh-nanopartiklar valdes som en aktiv kärna för röntgenfluorescens, syntetiserad genom en mikrovågs-assisterad hydrotermisk metod med en specialdesignad sockerligand som reduktionsmedel. Dessa nanopartiklar konjugerades med blåemitterande kvantprickar genom EDC-NHS-behandling. De hybrida nanopartiklarna uppvisade grön emission (520 nm) under 490 nm excitation och ledde till en minskad cytotoxicitet uppmätt genom cellanalys i realtid (RTCA) jämfört med endast Rh-nanopartiklar, vilket framhävde passiveringsrollen som kvantprickarna spelar. Hybridkomplexet utgjorde ett multimodalt kontrastmedel för bioavbildning, vilket demonstrerades med konfokalmikroskopi (in vitro) och fantomexperiment med röntgenfluorescens.

[pt] Uma sonda fotoluminescente do tipo turn-off foi avaliada para a detecção de Hg(2+) usando pontos quânticos de grafeno (GQDs). Diferentes nanopartículas de carbono fotoluminescentes foram preparadas usando a abordagem bottom-up, usando ácido cítrico ou ácido cítrico misturado com algum composto contendo enxofre (tioureia, tioacetamida ou glutationa). Dispersões desses GQDs foram comparadas em termos de comportamento fotofísico na presença de Hg(2+). Observou-se que as nanopartículas preparadas com ácido cítrico e tioureia (GQDs- TU) apresentaram melhor perfil de supressão fotoluminescente (resposta analítica) na presença de Hg(2+). As condições experimentais foram ajustadas para o melhor perfil de resposta e para obter os parâmetros analíticos de mérito. Um estudo para avaliar possíveis interferências na presença de outros íons de metais pesados além de íons alcalinos e alcalino-terrosos, comumente presentes em amostras de água natural. A curva analítica normalizada (concentração L0/L versus Hg(2+) foi linear (R(2) = 0,998) até 0,20 microgramas L(-1). O limite de quantificação (LOQ) foi de 10 microgramas L(-1) e o limite de detecção (LOD) foi de 3 microgramas L(-1) para o ensaio em batelada. Além disso, a estratégia proposta para a determinação indireta de Hg(2+) foi adaptada para um sistema de análise por injeção em fluxo (FIA). Após a otimização do ensaio, com a faixa linear cobrindo o intervalo até 900 microgramas L(-1) (R(2)= 0,999), os valores de LOD e LOQ foram 24 microgramas L(-1) e 80 microgramas L(-1), respectivamente. A recuperação na amostra simulada de água fortificada foi de 99,4 por cento mais ou menos 1,2. / [en] A photoluminescent turn-off probe was evaluated for the detection of Hg(2+) based on graphene quantum dots (GQDs). Different photoluminescent carbon nanoparticles were prepared using the bottom-up approach, with citric acid and with citric acid mixed with some sulfur compound (thiourea, thioacetamide or glutathione). Dispersions of these GQDs were compared in terms of photophysical behavoior in the presence of Hg(2+) . It was observed that the nanoparticles prepared with citric acid and thiourea (GQDs-TU) presented a better linear photoluminescent suppression (analytical response) in the presence of Hg(2+). Experimental conditions were adjusted to improve analytical response and to obtain analytical figures of merit. A study to evaluate potential interferences in the presence of other heavy metal ions and alkaline and alkaline-earth ions, commonly present in natural water samples. The normalized analytical curve (L0/L versus Hg(2+) concentration) was linear (R(2) = 0.998) up to 0.20 micrograms (L-1). The limit of quantification (LOQ) was 10 micrograms L(-1) and the limit of detection (LOD) was 3 micrograms L(-1) for the batch assay. In addition, the proposed strategy for indirect determination of Hg2+ was applied in a flow injection analysis system (FIA). After optimization of the assay, linear range covered a range up to 900 micrograms L(-1) (R(2) = 0.999) with LOD of 24 micrograms L(-1) and LOQ of 80 micrograms L(-1). The recovery in the fortified water sample was 99.4 percent.

storage devices in micro sizes are receiving more and more attention. One of them, on-paper Microsupercapacitors (MSCs), has become a key energy storage device because of its good mechanical flexibility and high power density. In this project, a triphase system with electrochemically exfoliated graphene and graphene quantum dots to synergistically stabilize PEDOT:PSS in ethylene glycol/water solvent was developed for scalable and reliable inkjet printing. Without any post-treatment, the printed patterns with a large thickness (up to 9 μm, about 0.4 μm per layer) attain a sheet resistance of as low as 4 Ω2−1 and high resolution at a small drop spacing of 10 μm. Thanks to these feature, the areal capacitance of the on-paper MSCs can reach >2 mF cm−2 at a high scan rate of 1000 mV s−1. The device also exhibits excellent mechanical flexibility, long cycle life (>95% capacitance retention after 10000 cycles CV test) and long service time (retain 84% capacitance after 4 months in air without any encapsulation). Moreover, we can directly print the interconnect to connect 4 devices on paper substrate in series or in parallel and thus get rid of metal current collector. / Med den snabba utvecklingen av flexibel och bärbar elektronik får energilagringsenheter i mikrostorlek allt mer uppmärksamhet. En av dem, mikrosuperkondensatorer (MSC) på papper, har blivit en viktig energilagringsenhet på grund av sin goda mekaniska flexibilitet och höga effekttäthet. I det här projektet utvecklades ett trefasigt system med elektrokemiskt exfolierad grafen och grafenkvantprickar för att synergistiskt stabilisera PEDOT:PSS i etylenglykol/vattenlösningsmedel för skalbar och tillförlitlig bläckstråleutskrift. Utan någon efterbehandling uppnår de tryckta mönstren med stor tjocklek (upp till 9 μm, ca 0,4 μmper lager) ett arkmotstånd på så lågt som 4 Ω2−1 och hög upplösning vid ett litet droppavstånd på 10 μm. Tack vare dessa egenskaper kan den ytliga kapacitansen hos MSC på papper nå >2 mF cm−2 vid en hög skanningshastighet på 1000 mV s−1. Anordningen uppvisar också utmärkt mekanisk flexibilitet, lång livslängd (>95% kapacitansbehållning efter 10000 cykler i CV-test) och lång livslängd (behåller 84% kapacitans efter 4 månader i luft utan inkapsling). Dessutom kan vi direkt skriva ut kopplingen för att ansluta fyra enheter på papperssubstratet i serie eller parallellt och på så sätt bli av med metallströmkollektorn.

Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery. This motivated our present research work on QDIPs, DWELLs, and graphene like QDs. The intention of this research was to study the size dependent achievements of QDIPs, DWELLs, and graphene like QDs with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on the device performance. In this dissertation four research studies pertaining to optical properties of quantum dot and dot-in-a-well infrared photodetectors, I-V characteristics of graphene quantum dots, and energy and spin texture of germanene quantum dots are presented. Improving self-assembled QD is a key issue in the increasing the absorption and improving the performance. In the present research work, an ideal self-assembled QD structure is analyzed theoretically with twenty-hole levels (Intraband optical transitions within the valence band) and twenty-electron energy levels (DWELL). Continuing the efforts to study self-assembled QDs we extended our work to graphene like quantum dots (graphene and germanene) to study the electronic transport properties. We study numerically the intraband optical transitions within the valence band of InxGa1-xAs/GaAs pyramidal quantum dots. We analyze the possibility of tuning of corresponding absorption spectra by varying the size and composition of the dots. Both ‘x ’ and the size of the quantum dot base are varied. We have found that the absorption spectra of such quantum dots are more sensitive to the in-plane incident light. We present numerically obtained absorption optical spectra of n-doped InAs/In0.15Ga0.85As/GaAs quantum dot-in-a-well systems. The absorption spectra are mainly determined by the size of the quantum dot and have weak dependence on the thickness of the quantum well and position of the dot in a well. The dot-in-a-well system is sensitive to both in-plane and out-of-plane polarizations of the incident light with much stronger absorption intensities for the in-plane-polarized light. We also present theoretically obtained I-V characteristics of graphene quantum dots, which are realized as a small piece of monolayer graphene. We describe graphene within the nearest-neighbor tight-binding model. The current versus the bias voltage has typical step-like shape, which is due to discrete energy spectrum of the quantum dot. The current through the dot system also depends on the position of the electrodes relative to the quantum dot. In relation to graphene quantum dots, we present our study of buckled graphene-like materials, like germanene and silicene. We consider theoretically germanene quantum dot, consisting of 13, 27, and 35 germanium atoms. Due to strong spin-orbit interaction and buckled structure of the germanene layer, the direction of the spin of an electron in the quantum dot depends on both the electron energy and external perpendicular electric field. With variation of energy, the direction of spin changes by approximately 4.50. Application of external electric field results in rotation of electron spin by approximately 0.50, where the direction of rotation depends on the electron energy.