Dissertations / Theses on the topic 'Carbon quantum dots'

This thesis presents research into spin-transport in Carbon nanotube quantum dots. Sputtered Permalloy electrodes designed with shape anisotropy were used to contact Carbon nanotubes grown by chemicalvapour deposition in lateral spin-valve structures. The magnetoresistance of these spin-valves were measured at low-temperatures and as a function of the charge state of the quantum dots. Two conductance regimes were measured in a Carbon nanotube spinvalve with Permalloy nucleation pads. At high bias outside of the coulomb blockade regime a ~ 10% magnetoresistance was measured that is analogous to giant-magnetoresistance, in that it is due to spindependent scattering at the ferromagnet-Carbon nanotube interfaces. At lower bias the device enters the coulomb blockade regime and the magnetoresistance observed develops a different structure, over a larger field range, together with the development of an offset in conductance between saturations. The maximum value of this MR was MR ~ 245% and it was attributed to changes in the induced charge on the quantum dot. By modifying the design of the Permalloy electrodes, a single domain state at the point of contact of the Carbon nanotube was achieved. A well defined anti-parallel state of the Permalloy electrodes, with associated changes in the conduction of the devices was observed, yet the conductance offset remained, with a maximum MR of ~ 60%. The positions of the coulomb peaks were measured during magnetic reversal of the electrodes, showing the change in induced charge on the quantum dot, with a maximum MR ~ 350%. Predictions of device transport based on the magneto-coulomb effect and spin-dependent interfacial phase shifts were compared to experimental results and found to not fit the observed behaviour. This led to the conclusion that changes in the charge state of the quantum dots must be due to a fixed spin-quantisation axis intrinsic to the Carbon nanotube.

Graphene quantum dots (GQDs) are small pieces of graphene oxide whose physical dimensions are so confined (a few to a few tens nm) that they have a finite bandgap due to a quantum confinement effect. The finite bandgap of GQDs grants them pronounced absorption bands and a substantial photoluminescence. These optical properties are rarely observed in traditional carbon materials, since most of carbon materials are metallic with a near-zero bandgap and thus have broad absorption spectra with no photoluminescence. The unique optical properties of GQDs, along with GQDs’ inherited advantages from carbon material family (cheap, abundant, non-toxic), make GQDs an attractive material for various applications such as bio-imaging, photoinduced therapy, chemical and metal ion sensors, and photovoltaic devices. Despite of their great potential, several great challenges need to be overcome to enable wider applications. One challenge is the fact that GQDs prepared by typical chemical methods possess significant inhomogeneity, so the precise control of the dimension and surface functionalities is very difficult. Due to the inhomogeneity of GQDs in terms of dimensions and surface functionalities, it is challengeable to establish a precise structure-property relationship. As of today, it is still under debate how surface functional groups of GQDs are responsible for the photoluminescence mechanism, photophysics, and photochemistry. This dissertation is mainly to provide a dedicated study about the photoluminescence mechanism and structure-property relations of GQDs.

This thesis describes experiments on quantum dots made by locally gating one-dimensional quantum wires. The first experiment studies a double quantum dot device formed in a Ge/Si core/shell nanowire. In addition to measuring transport through the double dot, we detect changes in the charge occupancy of the double dot by capacitively coupling it to a third quantum dot on a separate nanowire using a floating gate. We demonstrate tunable tunnel coupling of the double dot and quantify the strength of the tunneling using the charge sensor. The second set of experiments concerns carbon nanotube double quantum dots. In the first nanotube experiment, spin-dependent transport through the double dot is compared in two sets of devices. The first set is made with carbon containing the natural abundance of \(^{12}C\) (99%) and \(^{13}C\) (1%), the second set with the 99% \(^{13}C\) and 1% \(^{12}C\). In the devices with predominantly \(^{13}C\), we find evidence in spin-dependent transport of the interaction between the electron spins and the \(^{13}C\) nuclear spins that was much stronger than expected and not present in the \(^{12}C\) devices. In the second nanotube experiment, pulsed gate experiments are used to measure the timescales of spin relaxation and dephasing in a two-electron double quantum dot. The relaxation time is longest at zero magnetic field and goes through a minimum at higher field, consistent with the spin-orbit-modified electronic spectrum of carbon nanotubes. We measure a short dephasing time consistent with the anomalously strong electron-nuclear interaction inferred from the first nanotube experiment.
Physics

Dans cette thèse, nous étudions des circuits de boîtes quantiques à base de nanotubes de carbone intégrés dans une cavité micro-onde. Cette architecture générale permet de sonder le circuit en utilisant simultanément des mesures de transport et des techniques propre au domaine de l’Electrodynamique quantique sur circuit. Les deux expériences réalisées durant cette thèse exploitent la capacité des métaux de contact à induire des corrélations de spins dans les boites quantiques. La première expérience est l’étude d’une lame s´séparatrice à paires de Cooper, initialement imaginée comme une source d’électrons intriqués. Le couplage du circuit aux photons dans la cavité permet de sonder la dynamique interne du circuit, et a permis d’observer des transitions de charge habillées par le processus de séparation des paires de Cooper. Le couplage fort entre une transition de charge dans un circuit de boîtes quantiques et des photons en cavité, a été observée pour la première fois dans ce circuit. Une nouvelle technique de fabrication a aussi été développé pour intégrer un nanotube de carbone cristallin au sein du circuit de boîtes quantiques. La pureté et l’accordabilité de cette nouvelle génération de circuit a rendu possible la seconde expérience. Cette dernière utilise deux vannes de spins non colinéaire afin de produire une interface cohérente entre le spin d’un électron dans une double boite quantique, et un photon dans une cavité. Des transitions de spins très cohérentes ont été observée, et nous donnons un modèle sur l’origine de la décohérence du spin comprenant le bruit en charge et les fluctuations des spins nucléaires
In this thesis, we study carbon nanotubes based quantum dot circuits embedded in a microwave cavity. This general architecture allows one to simultaneously probe the circuit via quantum transport measurements and using circuit quantum electrodynamics techniques. The two experiments realized in this thesis use metallic contacts of the circuit as a resource to engineer a spin sensitive spectrum in the quantum dots. The first one is a Cooper pair splitter which was originally proposed as a source of non local entangled electrons. By using cavity photons as a probe of the circuit internal dynamics, we observed a charge transition dressed by coherent Cooper pair splitting. Strong charge-photon coupling in a quantum dot circuit was demonstrated for the first time in such a circuit. A new fabrication technique has also been developed to integrate pristine carbon nanotubes inside quantum dot circuits. The purity and tunability of this new generation of devices has made possible the realization of the second experiment. In the latter, we uses two non-collinear spin-valves to create a coherent interface between an electronic spin in a double quantum dot and a photon in a cavity. Highly coherent spin transitions have been observed. We provide a model for the decoherence based on charge noise and nuclear spin fluctuations

Carbon quantum dots (CQDs) are the latest generation of carbon nanomaterials in applications where fullerenes, carbon nanotubes, and graphene are abundantly used. With several attractive properties such as tunable optical property, edge-functionalization, and defect-rich chemical structure, CQDs have the potential to revolutionize optoelectronics, electro- and photocatalysis, and biomedical applications. Chemical modifications through the addition of heteroatoms, chemical reduction, and surface passivation are found to alter the band gap, spectral position, and emission pathways of CQDs. Despite extensive studies, fundamental understanding of structure-property relationship remains unclear due to the inhomogeneity in chemical structure and a complex emission mechanism for CQDs. This dissertation outlines a series of works that investigate the structure-property relationship of CQDs and its impact in a variety of applications. First, this relationship was explored by modifying specific chemical functionalities of CQDs and relating them to differences observed in optical, catalytic, and pharmacological performance. While a number of scientific articles reported that top-down or bottom-up synthesized CQDs yielded similar properties, the results herein present dissimilar chemical structures as well as photoluminescent and metal sensing properties. Second, the role of nitrogen heteroatoms in top-down synthesized CQD was studied. The effect of nitrogen atoms on spectral position and fluorescence quantum yield was considerably studied in past reports; however, thorough investigation to differentiate various nitrogen related chemical states was rarely reported. By finely tuning both the quantity of nitrogen doping and the distribution of nitrogen-related chemical states, we found that primary amine and pyridine induce a red-shift in emission while pyrrolic and graphitic nitrogen produced a blue-shift in emission. The investigation of nitrogen chemical states was extended to bottom-up synthesized CQDs with similar results. Finally, top-down, bottom-up, nitrogen-doped and chemically reduced CQDs were separately tested for their ability to act as photodynamic anti-cancer agents. This series of experiments uncovered the distribution of reactive oxygen species produced during light exposure which elucidated the photodynamic mechanisms of cancer cytotoxicity. The results presented in this dissertation provide key insight into engineering finely-tailored CQDs as the ideal nanomaterial for a broad range of applications.

Biocompatible and photostable fluorescent probes are crucial yet challenging to develop for visualizing and tracking biological functions and interactions that occur in living organisms. We synthesized biocompatible carbon quantum dots (CQDs) with 15% quantum yield (QY) and tested them for cellular and scaffold imaging at variable depths. The CQDs, synthesized from collagen under controlled and benign conditions in a hydrothermal reactor, were characterized for their fundamental physicochemical properties. The fluorescence characteristics were determined using two-photon microscopy and based on our results we propose a mechanism for CQD luminescence by combining the carbogenic core and edge-effect contributions to the photoluminescent (PL) behavior. The bioimaging of cells embedded in a luminescent 3D printed scaffold showed that CQDs enable imaging at depths of about 1500 μm under biomimetic conditions. Real-time videography and imaging tests showed a differential visualization of individual cells and scaffold. The excellent photostability and non-photobleaching characteristics of CQDs make them suitable for long-term whole cell and tissue imaging via multi-photon microscopy. Nanoparticles are key vehicles for targeted therapies because they can pass through biological barriers, enter into cells, and distribute within cell structures. We investigated the synthesis of blue and green emissive hexagonal boron nitride quantum dots (hBNQDs) using a liquid-exfoliation technique followed by hydrothermal treatment. A distinct shift from blue to bright-green emission was observed upon surface passivating the dots using poly (ethylene glycol) or PEG200 under the same UV irradiation. The quantum yield of the hBNQDs increased with the surface passivation. Multiplexed imaging was accomplished using the hBNQDs in conjunction with organic dyes. The hBNQDs provided images with distinctive emission wavelengths and fluorescence lifetimes. Although the fluorescence signals of blue- and green-emissive hBNQDs overlap spectrally with those of the emission wavelengths of the organic dyes, the fluorescence lifetime data were resolved temporally using software-based time gates. The blue-emissive hBNQD-b quantum dots were validated as sensitive platforms for detecting intracellular ferric ions with a low limit of detection (20.6 nM). The green-emissive hBNQD-g quantum dots successfully identified intracellular variations in pH, and the localization in human breast cancer cells was determined during their life cycles via fluorescence lifetime imaging. Sensitive and selective detection of Fe3+ merits attention since its deficiency can cause significant physiological dysfunction. Herein, we explored the interplay of synthesis parameters and size of the Spirulina derived carbon dots to optimize and develop a bright (51% quantum yield), selective and ultra-sensitive sensor to detect variations in intracellular Fe3+ ion concentrations. The final product showed a lower detection limit of 380pM and a response time of only 30 seconds. Several spectroscopic methods were used to elucidate the fluorescence and quenching mechanism of the carbon dots (CDs). Fluorescence lifetime measurements and Stern-Volmer analysis revealed that both static and dynamic quenching processes are dominant at low and high concentrations of Fe3+ ions respectively. The developed CDs were successfully applied to track the dynamic generation of endogenous Fe3+ in living cells under stress induced conditions.

Self-assembly of nanomaterials over macroscopic dimensions and development of novel nano-electromechanical systems (NEMS) hold great promise for numerous nanotech applications. However, it has always been a great challenge to find a general route for controlled self-assembly of nanomaterials and generating electromechanical response at the nanoscale level. This work indicates that self-organized anisotropic nematic liquid crystals (LC) can be exploited for nanotemplating purposes to pattern carbon nanotubes (CNTs) and Quantum dots (QDs) over a macroscopic dimension. The pattern formed by the CNTs or QDs can be controlled by applying external electric and magnetic fields, developing novel nano-electromechanical and nano-magnetomechanical systems. Self-organizing nematic liquid crystals (LC) impart their orientational order onto dispersed carbon nanotubes (CNTs) and obtain CNT-self-assembly on a macroscopic dimension. The nanotubes-long axis, being coupled to the nematic director, enables orientational manipulation via the LC nematic reorientation. Electric field induced director rotation of a nematic LC+CNT system is of potential interest due to its possible application as a nano-electromechanical system. Electric field and temperature dependence of dielectric properties of an LC+CNT composite system have been investigated to understand the principles governing CNT-assembly mediated by the LC. In the LC+CNT nematic phase, the dielectric relaxation on removing the applied field follows a single exponential decay, exhibiting a faster decay response than the pure LC above a threshold field. Due to a strong LC-CNT anchoring energy and structural symmetry matching, CNT long axis follows the director field, possessing enhanced dielectric anisotropy of the LC media. This strong anchoring energy stabilizes local pseudo-nematic domains, resulting in nonzero dielectric anisotropy in the isotropic LC phase. These anisotropic domains respond to external electric fields and show intrinsic frequency response. The presence of these domains makes the isotropic phase electric field-responsive, giving rise to a large dielectric hysteresis effect. These polarized domains maintain local directors, and do not relax back to the original state on switching the field off, showing non-volatile electromechanical memory effect. Assembling quantum dots (QDs) into nanoscale configurations over macroscopic dimensions is an important goal to realizing their electro-optical potential. In this work, we present a detailed study of a pentylcyanobiphenyl liquid crystal (LC) and a CdS QD colloidal dispersion by probing the dielectric property  and relaxation as a function of an applied ac-electric field Eac. In principle, dispersing QDs in a nematic LC medium can direct the dots to align in nearly one-dimensional chain-like structures along the nematic director and these assemblies of QDs can be directed by external electric fields. In a uniform planar aligned cell, the Fréedericksz switching of the LC+QDs appears as a two-step process with the same initial switching field as the bulk but with the final value larger than that for an aligned bulk LC. The relaxation of  immediately following the removal of Eac follows a single-exponential decay to its original value that is slower than the bulk but becomes progressively faster with increasing Eac, eventually saturating. These results suggest that the arrangement of the QDs is mediated by the LC.

FREIRE, Rafael Melo. Magnetic nanoparticles and carbon quantum dots: interdisciplinary nanoparticles for sensing and/or education. 182 f. 2016. Tese (Doutorado em Química)-Universidade Federal do Ceará, Fortaleza, 2016.
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In this work, a sensing strategy for detection and identification of proteins with magnetic nanoparticles (MNPs) and carbon quantum dots (CQDs) was developed. In this sense, mixed ferrites of general formula M0.5Zn0.5Fe2O4 (M=Mn or Ni) were first investigated. Therefore, the hydro/solvothermal synthesis of these magnetic nanoparticles was performed under different conditions (solvent, reaction time and base concentration). Based on the magnetic properties of the two MNPs investigated, the mixed ferrite of formula Mn0.5Zn0.5Fe2O4 (MnZn) synthesized using water showed the greatest potential for sensing. Since among all synthesized MNPs, this sample displayed the highest saturation magnetization value ( M S  50 emu/g), lower crystallite size around 12 nm and superparamagnetic behavior. Once the first part of the doctoral thesis was concluded, the next step was to find a fluorescence probe. In this regard, it was performed the synthesis, as well as the application of branched poliethylenimine-functionalized carbon quantum dots (CQDs.BPEI). These new carbon-based nanoparticles were found to be protein-responsive. Since CQDs.BPEI were able to detect eight different proteins (four metallic and four non-metallic) even using concentrations in the range of 5 – 40 nM. Fluorescence titrations performed at 298 and 310 K displayed the fluorescence quenching through collisional mechanism. Therefore, it was also possible to conclude that the fluorescence quench comes from the amino acid residues on the surface of the proteins. To further check the potential of the CQDs.BPEI, it was developed a “nose” based methodology to identify proteins. Using materials as cheap as Cu2+ and ethylenediaminetetraacetic acid, the chemical “nose” approach was able to discriminate six different proteins at 40 nM concentration in phosphate buffered saline (PBS, pH 7.4). The identification accuracy of the random unknown set was 90% with all misclassification occurring for albumin proteins (e.g., Bovine Serum Albumin and Human Serum Albumin). The displayed results evidence the great potential of CQDs.BPEI as a protein-responsive probe to detect and identify proteins. Taken together, MnZn and CQDs.BPEI were capable to build up a powerful protein sensing approach. In addition, realizing the great potential of CQDs in the educational field, it was also developed and successfully applied (for more than 70 students from biotechnology, pharmacy, engineers and geology courses) a lab experiment to demonstrate lightrelated quantum phenomena.
Neste trabalho, uma estratégia para detecção e identificação de proteínas incluindo nanopartículas magnéticas (MNPs) e pontos quânticos de carbono (CQDs) foi desenvolvida. Assim, ferritas mistas de fórmula M0.5Zn0.5Fe2O4 (M=Mn or Ni) foram inicialmente investigadas. Neste sentido, suas sínteses foram feitas utilizando diferentes condições (solvente, tempo reacional e concentração de base). Logo, baseado nas propriedades magnéticas das MNPs sintetizadas, escolheu-se a Mn0.5Zn0.5Fe2O4 (MnZn) sintetizada em água por mostrar grande potencial, uma vez que essa amostra apresentou alto valor de magnetização de saturação ( M S  50 emu/g) em comparação com outras ferritas de composição semelhante, baixo tamanho de cristalito por volta de 12 nm e comportamento superparamagnético. Com a primeira parte do trabalho concluída, a próxima etapa foi encontrar uma sonda fluorescente. Assim, realizou-se a síntese dos CQDs funcionalizados com grupamentos amina (CQDs.BPEI). Quando testada contra 8 diferentes proteínas (4 metálicas e 4 não-metálicas), apresentou variação da emissão para concentrações na faixa de 5 – 40 nM. Titulações fluorescentes também foram realizadas e observou-se que a supressão da fluorescência ocorre via mecanismo colisional a partir de resíduos aminoácidos na superfície da proteína. Para adicionalmente checar o potencial dos CQDs.BPEI, foi desenvolvida abordagem para identificar proteínas utilizando materiais Cu2+ e o ácido etilenodiamino tetraacético. No total, a estratégia desenvolvida foi capaz de identificar corretamente 6 diferentes proteínas a 40 nM. A precisão da identificação encontrada foi 90% para as amostras desconhecidas. Contudo, vale ressaltar que os 10% de engano foram apenas entre BSA e HSA, duas proteínas albumínicas muito similares. Os resultados obtidos nessa parte do trabalho evidenciam o alto potencial de CQDs.BPEI para detecção e identificação de proteínas. Observando os resultados do trabalho como um todo, pode-se afirmar que MnZn e CQDs.BPEI são capazes de compor excelente abordagem para detecção e identificação de proteínas. Adicionalmente, foi explorada a utilidade dos CQDs para o campo educacional. Dessa forma, foi também desenvolvido e aplicado (mais de 70 estudantes de graduação oriundos dos cursos de biotecnologia, farmácia, engenharias e geologia) um experimento de laboratório para demonstrar fenômenos quânticos relacionados com a luz.

The overall research theme of this dissertation was the study of nanoparticle/polymer composites. Two types of nanoparticles were utilized: Single-Walled Carbon Nanotubes and quantum dots. Chapter 1 of this thesis comprises an extensive literature review on Carbon Nanotubes, which presents theoretical aspects relevant to the structure and properties of CNTs, methods of purifying and solubilizing CNTs in aqueous and organic solvents and selected applications. This literature review is followed by the study and comparison of the optical limiting performances of different Single-Walled Carbon Nanotubes/conjugated polymer dispersions (Chapter 2). The results obtained are discussed in terms of dispersion of the SWNTs in the polymer solutions and resulting SWNT bundle diameters. Chapter 3 presents the spontaneous assembly of dendrimer patterns induced by SWNTs. Finally, chapter 4 presents a new method for fabricating quantum dot/polymer composites, which uses the extraction of positively charged quantum dot into a hydrophobic liquid. The resulting solution is used as a compatible polymerization medium for poly(methylmethacrylate ) networks enabling the formation of transparent and fluorescent composites.
Ph. D.

>Magister Scientiae - MSc
Currently, non-renewable sources are mostly used to meet the ever-growing demand for energy. However, these sources are not sustainable. In addition to these energy sources being not sustainable, they are bad for the environment although the energy supply sectors highly depend on them. To address such issues the use of renewable energy sources has been proven to be beneficial for the supply of energy for the global population and its energy needs. Advantageous over non-renewable sources, renewable energy plays a crucial role in minimizing the use of fossil fuel and reduces greenhouse gases. Minimizing use of fossil fuels and greenhouse gases is important, because it helps in the fight against climate change. The use of renewable energy sources can also lead to less air pollution and improved air quality. Although solar energy is the most abundant source of renewable energy that can be converted into electrical energy using various techniques, there are some limitations. Among these techniques are photovoltaic cells which are challenged by low efficiencies and high costs of material fabrication. Hence, current research and innovations are sought towards the reduction of costs and increasing the efficiency of the renewable energy conversion devices.

The work presented in this thesis deals with two important low dimensional nanostructures: carbon nanotubes (CNTs) and quantum dots (QDs). In the part of the work related to CNTs a novel method for growing CNTs without the need of metal catalyst is presented. The as produced CNTs were grown by means of chemical vapour deposition on Si-Ge islands and on Ge dots grown with the Stransky — Krastanow method on top of silicon substrates. Through rigorous characterisation products of the method were identified as single wall carbon nanotubes (SWCNTs) with diameters of 1.6 and 2.1 nm. Acquired Raman spectra showed very low intensity or none D — band while the G’ band was of high intensity indicating that the as produced CNTs may be of high quality. A by-product of this method is amorphous fibres which can be easily eliminated when exposed to HF vapour. As this method does not employ metal particles it is fully compatible with the front end silicon processing and therefore opens up the prospect of merging carbon nanotubes with silicon technology. Furthermore CNTs were utilised as probes for atomic force microscopy (AFM). For the fabrication of the CNT probes two methods were applied successfully: the surface growth method and the pick up method. The latter was found to be substantially more efficient than the former and although not proper for mass production it is ideal for laboratory use as it can potentially generate thousands of CNT probes. The as fabricated CNT probes, had diameters in the range of 4 to 7 nm. Using CNT probes the surface of a mesoporous material with pore diameter of 7 to 12 nm and repeated distance of 15 to 18 nm was imaged, proving the high resolution that can be achieved with such probes and that AFM can be applied successfully to mesoporous materials. The latter has the potential to considerably expand the knowledge and the control of such materials to the nanoscale. In the part of the work related to QDs a time resolved two colour pump photoluminescence (PL) technique was applied, with the aim to probe the coherent properties of the excitonic ground state of a single Stransky-Krastanow InGaAs QD. The method comprises of two pulses of different energy; a delayed blue pulse that pumps the GaAs barrier and an infrared (IR) pulse that pumps the excitonic ground state of the QD. The PL of the 1st excitonic excited state of the QD is used in order to probe the occupancy of the ground state. The detection is carried out at zero laser background and thus having a considerably higher signal to noise ratio than other pump and probe methods. A PL intensity variation and a red shift in the energy of the I excitonic excited state were observed, with both effects being dependant upon the intensity of the JR pulse but independent of the time delay and its energy. Further investigations showed that the IR excitation causes all PL and absorption lines of the QD to red shift, induces broadening of the absorption lines and increases the background absorption. Comparison with temperature dependent PL measurements showed that although heating might contribute to the above effects it cannot be the sole reason for their occurrence. Because of the above effects the time resolved two colour pump method cannot be applied as such for probing the coherence of QD ground excitonic state and needs to be modified further.

Cancer therapies are often limited by bulk and cellular barriers to transport. Nanoparticle or chemotherapeutic compound intracellular transport has implications in understanding therapeutic effect and toxicity. The scope of this thesis was to study the intracellular transport of carbon nanohorns and to improve the efficacy of various chemotherapeutic agents through increased intracellular transport. In the first study, fluorescent probes (quantum dots) were conjugated to carbon nanohorns to facilitate the optical visualization of the nanohorns. These hybrid particles were characterized with transmission electron microscopy, electron dispersive spectroscopy and UV-VIS/FL spectroscopy. Their cellular uptake kinetics, uptake efficiencies, and intracellular distribution were determined in three malignant cell lines (breast – MDA-MB-231, bladder – AY-27, and brain – U87-MG) using flow cytometry and confocal microscopy. Intracellular distribution did not vary greatly between cell lines; however, the uptake kinetics and efficiencies were highly dependent on cell morphology. In the second study, the efficacy of various chemotherapeutic agents (i.e., doxorubicin, cisplatin, and carboplatin) was evaluated in AY-27 rat bladder transitional cell carcinoma cells. In the future, severe hyperthermia and chemothermotherapy (chemotherapy + hyperthermia) will also be evaluated. Doxorubicin and cisplatin compounds were more toxic compared to carboplatin. Hyperthermia has previously shown to increase the cellular uptake of chemotherapeutic agents; therefore, chemothermotherapy is expected to have synergistic effects on cell death. This work can then be translated to carbon nanohorn-based laser heating to generate thermal energy in a local region for delivery of high concentrations of chemotherapeutic agents. Although these two concepts are small pieces of the overall scope of nanoparticle-based therapies, they are fundamental to the advancement of such therapies.
Master of Science

Fluorescent carbon dots (C-dots) are well known for their low cell-cytotoxicity, biocompatibility, low preparation cost, excitation dependent photoluminescence, and excellent photostability. Typically, raw C-dots have low quantum efficiency and thus researchers have been utilizing biocompatible polymers such as polyethylene glycol (PEG) as a passivation agent in order to increase fluorescence signal. In this work, we report fluorescent self-passivated carbon nanodots (CNDs) synthesized from PEG by using it as a carbon source as well as a passivating agent. Importantly, the addition of graphene quantum dots (GQDs) during the synthesis of self-passivated CNDs can tune photoluminescence property. The results of bioimaging and cytotoxicity test of self-passivated CNDs hold promises for biomedicine applications.

Ce travail de thèse est centré autour de deux aspects des technologies quantiques: le calcul quantique et la mesure quantique. Il s'appuie sur la boîte à outils de la lumière micro-onde, développé en électrodynamique quantique, pour sonder des circuits mésoscopiques. Ces circuits, fabriqués ici à base de nanotubes de carbone, peuvent être conçus comme des bits quantiques ou comme des systèmes modèles de la matière condensée, et cette thèse explore les deux aspects. La réalisation d'une interface spin-photon cohérente illustre le premier. L'expérience repose sur l'utilisation de contacts ferro-magnétiques pour induire un couplage spin-orbit artificiel dans une double boîte quantique. Ce couplage hybride les degrés de liberté de charge et de spin de l'électron. En incluant ce circuit dans une cavité micro-onde, dont le champ électrique peut être couplé à la charge, nous réalisons une interface spin-photon. Un second projet est centré sur l'utilisation de boîtes quantiques comme systèmes modèles. Ce projet consiste à coupler, via une cavité micro-onde, un qubit supraconducteur, qui servira de sonde peu invasive, et une boîte quantique unique. Un tel circuit peut exhiber différent comportement dont l'effet Kondo, qui est un effet à N-corps. Dans ce travail, nous présentons à la fois une étude théorique, et des travaux expérimentaux. Finalement, un travail en collaboration, sur une proposition théorique pour détecter le caractère auto-adjoint des fermions de Majorana en utilisant une cavité micro-onde, est présenté
This thesis work is centered around two key aspects of quantum technologies: quantum information processing and quantum sensing. It builds up onto the microwave light toolbox, developed in circuit quantum electrodynamics, to investigate the properties of mesosocopic circuits. Those circuits, made out here of carbon nanotubes, can be designed to act as quantum bits of information or as condensed matter model system and this thesis explore both aspects. The realization of a coherent spin-photon interface illustrates the first one. The experiment relies on ferromagnetic contacts to engineer an artificial spin-orbit coupling in a double quantum dot. This coupling hybridizes the spin and the charge degree of freedom of the electron in this circuit. By embedding this circuit into a microwave cavity, whose electrical field can be coupled to the charge, we realize an artificial spin-photon interface. A second project, started during this thesis, focuses on using quantum dot circuits as model systems. This project consists in coupling, via a microwave cavity, a superconducting qubit, that will serve as a delicate probe, and single quantum dot circuit. Such a circuit can display several behaviors including the Kondo effect which is intrinsically a many-body effect. In this work, we present both a theoretical study of some possible outcomes of this experiment, and experimental developments. Finally, a theoretical proposition to detect the self-adjoint character of Majorana fermions using a microwave cavity, is presented

Cette thèse décrit les résultats expérimentaux obtenus au cours de mesures de transport électronique à basse température dans des nanogaps fabriqués par électromigration de nanofils d'or. Bien que ce type de structure soit fréquemment utilisé dans le domaine de l'électronique à molécule unique, le détail des mécanismes de transport dans les nanogaps reste encore méconnu. Nos expériences ont permis de mettre en évidence l'existence de fluctuations de conductance dus à des interférences quantiques entre trajectoires électroniques. De telles fluctuations de conductance n'ont jamais été observées dans ces structures et leur étude renseigne sur la physique du transport électronique dans les nanogaps. Nous présentons également l'étude des propriétés de transport électronique à basse température de boîtes quantiques de taille nanométrique fabriquées par une méthode originale d'électromigration sur nanotube de carbone. A l'instar des transistors à molécule unique, ces dispositifs permettent d'atteindre des régimes Kondo exotiques dont la phénoménologie est différente de l'effet Kondo de spin 1 /2 usuel. Nous présentons notamment des mesures de transport dans le régime d'effet Kondo dit à deux étapes où deux spins sont écrantés successivement par les électrons de conduction. Cet effet n'a été que marginalement observé dans la littérature et ses propriétés, notamment dans des conditions hors-équilibre, restent méconnues aussi bien théoriquement qu'expérimentalement. Ces travaux montrent que la conductance de notre dispositif dans le régime d'effet Kondo à deux étapes suit une loi d'échelle universelle, et conserve ses propriétés d'universalité dans une situation hors-équilibre
This thesis describes the experimental investigation of the low-temperature electronic transport in electromigrated gold nanogaps. Although frequently used in single-molecule electronics, the microscopic mechanisms responsible for the electronic transport in metallic nanogaps are not well understood. The present work evidences the existence of conductance fluctuations due to interferences between electronic trajectories. Such fluctuations have never been observed in nanogaps and can be used to get a better understanding of the electronic transport mechanisms at play in these nanometric structures. We also present the study of the transport properties of nanoscale quantum dots fabricated by an original method of electromigration on top of carbon nanotubes. Just like single-molecule transistors, these devices allow the observation of exotic Kondo regimes which properties are different from the standard spin-1/2 Kondo effect. In particular we present electronic transport measurements in the two-stage Kondo regime, where two spins are successively screened by the surrounding Fermi seas. This regime has rarely been observed experimentally and its properties, especially in an out-of-equilibrium situation, remain unknown. This work shows that the conductance in the the two-stage Kondo regime follows a universal scaling law even in an out-of-equilibrium situation

>Magister Scientiae - MSc
Nanotechnology is a rapidly growing field of research. Due to major innovations brought about by developments in nanotech, several consumer products are currently available containing nanomaterials. The increase of nanomaterial production and use is accompanied by the increased potential of human, plant and animal exposure to these nanomaterials. As a relatively new nanomaterial, carbon quantum dots (CQDs) are being extensively used and researched due to its unique properties. Although many studies have assessed the toxic potential of CQDs, and found them to exhibit low toxicity, there is lack of work assessing the effects on the immune system. In the present study, RAW 264.7 murine macrophages were used as model to assess the immunomodulatory potential of CQDs. RAW cells exposed to varying concentrations of CQDs (0-500μg/ml), showed that CQDs caused a reduction at cell viability. In the absence of a mitogen CQDs, induced an inflammatory response by stimulating the release of various cytokines and chemokines such as, TNFα, MIP-1α, MIP-1β, MIP-2, IP-10, G-CSF, GM-CSF, and JE.

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Neste trabalho, Carbon Dots (CDs) obtidos a partir de celulose de algod?o e contendo 4,5 mmol.g-1 de grupos funcionais ?cidos, dos quais 63 % exibiam pKas t?picos de ?cidos carbox?licos foram usados na prepara??o de filmes automontados com os biopol?meros quitosana (QT) e col?geno (CL) a fim de verificar a morfologia, espessura e intera??es moleculares entre os componentes. A quitosana usada apresentou um total de 4,2 mmolg-1 de grupos funcionais -NH2, correspondente a um grau de desacetila??o de ~70 %. Por outro lado, o col?geno hidrolisado apresentou diferentes grupos funcionais com acidez de Br?nsted, t?picos da presen?a de diferentes amino?cidos na estrutura. Todos os filmes finos foram preparados com a t?cnica de deposi??o camada por camada (do ingl?s: Layer-by-layer (LbL)) por meio de imers?o do substrato nas diferentes solu??es. Os materiais foram caracterizados por diferentes t?cnicas, incluindo Microscopia de For?a At?mica, Espectroscopia na regi?o do UV-Vis, Espectroscopia de Resson?ncia de Plasma de Superf?cie e Titula??o Calorim?trica. Em todas as condi??es experimentais utilizadas para o crescimento dos filmes, observou-se um crescimento linear da quantidade de material depositado com o n?mero de imers?es realizadas. No entanto, diferentes condi??es das solu??es dos biopol?meros e da suspens?o de Carbon Dots produziram filmes com espessura e morfologia diferentes. Nos filmes de QT/CDs a quantidade de nanopart?culas depositadas por bicamada, com solu??o de quitosana em pH = 3,5, pH = 5 e pH = 3,5 na presen?a de 0,1 mol/L de NaCl, foram, respectivamente, 11 mg.m-2, 16 mg.m-2 e 24 mg.m-2 sendo as espessuras dos filmes, com 20 bicamadas, correspondentes a estas quantidades foram de 60, 150 e 200 nm. Este resultado ? atribu?do ao aumento da flexibilidade das cadeias polim?ricas dos biopol?meros, as quais est?o menos carregadas. Dessa forma, as cadeias podem apresentar conforma??es mais adequadas para recobrir eficientemente a estrutura das nanopart?culas quase esf?ricas. Al?m disso, o aumento da for?a i?nica da solu??o de Carbon Dots tamb?m contribui para o aumento de material depositado devido ? forma??o de aglomerados sob estas condi??es. Nos filmes de CL/CDs, a quantidade de nanopart?culas depositadas, com solu??o de col?geno em pH = 3,16, pH = 5 e pH = 3,16 na presen?a de 0,1 mol/L de NaCl, foram 2,3 mg.m-2, 6,46 mg.m-2 e 6,41 mg.m-2, respectivamente. No entanto, a energia de intera??o, obtida por calorimetria isot?rmica, ? maior em pH baixo. Em geral, a quantidade de material depositado nos filmes de col?geno ? bem inferior ?s observadas para os filmes de QT/CDs e, consequentemente, filmes com espessuras entre 40 e 50 nm. Al?m disso, n?o foi observada varia??o significativa entre as massas depositadas nestes filmes com o aumento do pH e for?a i?nica. Estes resultados podem estar relacionados ? menor ?carga parcial positiva? sobre as cadeias da prote?na em rela??o a quitosana, observada pelos potenciais zeta nestas condi??es. Por fim, os resultados aqui apresentados sugerem que as estruturas dos filmes, isto ?, morfologia e espessura, podem ser facilmente controladas e reproduzidas manipulando-se as condi??es das solu??es dos biopol?meros, al?m do tradicional n?mero de imers?es. Em adi??o, o estudo pode contribuir para o desenvolvimento de uma nova classe de dispositivos de alto desempenho, como sensores e superf?cies fotoativas.
Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Qu?mica, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017.
In the present work, Carbon Dots (CDs), obtained from cotton cellulose and containing 4.5 mmol g-1 of acid functional groups, of which 63% exhibited typical pKa?s compared to carboxylic acids, were used in the preparation of self-assembled films with the biopolymers Chitosan (QT) and Collagen (CL) in order to verify the morphology, thickness and molecular interactions among the components. The chitosan used in this work had a total of 4.2 mmol g-1 of functional groups ?NH2, corresponding to a deacetylation degree of ~70%. On the other hand, the hydrolyzed collagen showed different functional groups with Br?nsted acidity typical to the presence of different amino acids in the structure. All the thin films were prepared using the Layer-by-layer method (LbL) by immersing the substrate in different solutions. The materials were characterized by several techniques, such as Atomic Force Microscopy, UV-Vis Spectroscopy, Surface Plasmon Resonance and Calorimetric Titration. It was observed, in all experimental conditions for the growth of the films, a linear increase in the amount of deposited material with the number of immersions performed. However, different conditions of the biopolymer solutions produced films with different thickness and morphology. In the films QT/CDs the amount of nanoparticles deposited per bilayer, with the chitosan solution at pH = 3.5, pH = 5 and pH = 3.5 with the presence of 0.1 mol L-1 of NaCl, were, respectively, 11 mg m-2, 16 mg m-2 and 24 mg m-2 with the thickness of the film, at 20 bilayers, at 60, 150 and 200 nm. This result is associated to the increase in the flexibility of the polymeric chains of the biopolymers, which are less charged. Thus, the chains can present conformations that are proper to cover more efficiently the structure of the almost spherical nanoparticles. Furthermore, the increase of the ionic strength of the Carbon Dots solution also contributes to the increase of the material deposited due to the formation of agglomerates in these conditions. In the films CL/CDs, the amount of nanoparticles deposited, with the collagen solution at pH = 3.16, pH = 5 and pH3.16 in the presence of 0.1 mol L-1 of NaCl, were 2.3 mg m-2, 6.46 mg m-2 and 6.41 mg m-2, respectively. However, the interaction energy, obtained by isothermal calorimetry, is higher in low pH. In general, the amount of material deposited on the collagen films is much lower than that observed for the QT/CDs films and, consequently, films thickness are 40 and 50 nm. Besides that, it was not observed any significant variation between the masses deposited in these films with the increase of the pH and the ionic strength. These results may be associated to the lower ?partial positive charge? on the protein chains in relation to the chitosan, observed by the zeta potentials in these conditions. The presented results suggest that the structures of the films, i.e. morphology and thickness, can be easily controlled and reproduced manipulating the conditions of the biopolymer solutions and the number of immersions. Additionally, the study may contribute to the development of a new class of high performance devices, such as sensors and photoactive surfaces.

Cette thèse est consacrée au transport quantique à travers une impureté Kondo, formée dans une boîte quantique réalisée dans un nanotube de carbone. L’effet Kondo est ainsi sondé à travers deux situations : en compétition avec l’effet Josephson induit dans le nanotube par des contacts supraconducteurs et à travers son émission haute fréquence. Dans une première série d’expériences, nous avons introduit un nanotube dans un SQUID, afin de mesurer la relation entre son supercourant et la différence de phase supraconductrice à ses bornes. Nous avons mesuré cette relation lorsque les corrélations Kondo et supraconductrices sont du même ordre de grandeur et montré que l’état du système, singulet ou doublet (correspondant respectivement à une jonction 0 ou π) peut alors être contrôlé par la phase supraconductrice. Nous avons également montré que, si un deuxième niveau d’énergie participe au transport des paires de Cooper, la transition 0-π n’est plus une transition du premier ordre comme c’est le cas quand un seul niveau est impliqué. Dans la deuxième partie de la thèse, le nanotube de carbone est couplé, aux fréquences déterminées par un résonateur, à une jonction tunnel supraconductrice servant de détecteur on-chip de bruit haute fréquence. Ceci nous a permis de mesurer le bruit en émission de la boîte quantique dans le régime Kondo avec des couplages aux réservoirs plus ou moins symétriques. Nos mesures posent le problème de l’asymétrie spatiale du bruit mesuré et semblent montrer que, plus le couplage aux réservoirs est symétrique, plus la résonance Kondo est affaiblie dans une situation hors équilibre. Enfin, ce dispositif a été utilisé afin de mesurer l’émission Josephson AC d’un nanotube avec des électrodes supraconductrices, afin de voir ce que devient la compétition entre l’effet Kondo et la supraconductivité à haute fréquence. Ces mesures révèlent une diminution de l’émission Josephson alors que l’on a un maximum de supercourant
This thesis is dedicated to quantum transport through a Kondo impurity, formed in a carbon nanotube quantum dot. We probe the Kondo effect in two situations: in competition with the Josephson effect induced in the nanotube by superconducting contacts and through its high frequency emission. In a first experiment, we have introduced a nanotube in a SQUID in order to measure its supercurrent as a function of the superconducting phase across it. We have measured this quantity in the regime where the Kondo and superconducting correlations are of the same order of magnitude and shown that the ground state of the system, singlet or doublet (corresponding respectively to 0 and π junctions), is then controlled by the superconducting phase. We have also demonstrated that, if a second energy level participates in the transport of Cooper pairs, the 0-π transition is not anymore a first order one as it is the case when only one level is involved. In the second part of the thesis, the carbon nanotube is coupled, at some frequencies determined by a resonator, to a tunnel superconducting junction which is used as an on-chip high-frequency noise detector. This enables the measurement of the emission noise of the quantum dot in the Kondo regime, with reservoirs coupled either symmetrically or not to the dot. Our measurements raise the problem of the spatial asymmetry of the measured noise and seem to show that, the more symmetric is the coupling of the reservoirs to the dot, the more the Kondo resonance is weaken in an out-of-equilibrium situation. Finally, this setup has been used in order to measure the AC Josephson emission of a nanotube contacted with superconducting electrodes, in order to extend our investigation of the competition between the Kondo effect and superconductivity at high frequency. These measurements reveal a decrease of the Josephson emission observed together with a maximum of supercurrent

My PhD thesis work is to design, synthesize, and characterize inexpensive and reliable nanocomposites for the photovoltaic (PV) devices. Photovoltaic materials utilized in our studies were synthesized using simple and inexpensive methods. The material properties were tailored and optimized to improve the optical absorption and charge transport properties. The PV cells fabricated with these materials exhibited improved power conversion efficiencies (PCE). The origin of charge generation and charge transfer was studied using different photoactive materials such as CdSe quantum dots (QDs), perylene-3, 4, 9, 10-tetracarboxylic-3, 4, 9, 10-dianhydride (PTCDA), poly(3-hexylthiophene) (P3HT), multiwalled carbon nanotubes (MWCNTs), multilayer graphene (MuLG), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM).

Low-dimensional systems in condensed matter physics exhibit a rich array of correlated electronic phases. One-dimensional systems stand out in this regard. Electrons cannot avoid each other in 1D, enhancing the effects of interactions. The resulting correlations leave distinct spatial imprints on the electronic density that can be imaged with scanning probes. Disorder, however, can destroy these delicate interacting states by breaking up the electron liquid into localized pieces. Thus, to generate fragile interacting quantum states, one requires an extremely clean system in which disorder does not overcome interactions, as well as a high degree of tunability to design potential landscapes. Furthermore, to directly measure the resulting spatial correlations, one requires an exceptionally sensitive scanning probe, but the most sensitive probes presently available are also invasive, perturbing the system and screening electron-electron interactions.
Engineering and Applied Sciences

Unrelenting advances in the field of nanoscience are fostering the progress in diverse research fields, ranging from light-emitting to medicine and diagnostics, from energy conversion to communication technologies. Besides representing the most paradigmatic example of nanoscience, semiconductor quantum dots (QDs) avowedly brought revolutions in many of the research fields mentioned above. Nowadays, some QDs-based devices and applications reported efficiencies almost as good as current state-of-the-art technologies. The founding concept of QDs is the application of quantum confinement effects on excitons, i.e., the main players of optical properties in bulk semiconductors. Among the wealth of ensuing properties, the size- and shape- tunability of the electronic excitations and increased coupling with light field aroused much interest. Also, the colloidal approach endows QDs with high processability and low cost, thereby encouraging their implementation in existing technologies and extending their impact to other fields. Howbeit, despite three decades of investigations, the bottom line has not been reached yet, and researchers are still delving deeper into the photophysics of these nanosystems. Though many of the low hanging fruit of QDs have been harvested, higher-lying ones seem to be even more succulent. This thesis deals with the quest for highly performing nanostructures, as a prerequisite for some high impact optoelectronic applications, e.g., QD-Lasers and QD-Solar Cells. Within this framework, the struggle against fast Auger recombinations and trapping of either hot carriers or cold excitons was addressed mainly by sophisticated core/shell technologies. Thus, the first part of the thesis reports how tuning different shell parameters (e.g., the smoothness of the interface potential, the height of the confining potential, and the interfacial strain) it is possible to exert control on these detrimental recombination processes. Though often disregarded, even the role of organic capping ligand is reconsidered in promoting the outcoupling of QDs excited states and addressing their interaction. Besides the useful and technologically relevant advice gathered within these studies, the primary inheritance of the first part is the comprehensive photophysical scenario, portrayed by a phenomenological model that successfully describes many aspects of the exciton dynamics in QDs. This amount of knowledge was capitalized in the second part of this thesis, dealing with the quest for novel materials, potentially outpacing conventional CdSe-based QDs. Perovskite-based QDs reported promising results, whereas some pitfall in the conventional characterization of carbon-based QDs were discovered. The rationalization of both nature and dynamics of this materials is expected to expedite their development as alternative (and potentially superior) technologies concerning those studied in the first part.
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[EN] In this Doctoral Thesis, it has been studied the photophysical and photochemical properties of new nanomaterials based on carbon as graphene derivatives (GO, rGO, graphene (N,O)-codoped and graphene reconstituted halogenated) and two different types of carbon nanoparticles (C-dots and C-NOR). These materials have been applied in the photocatalytic hydrogen generation, such as gas sensors and bioimaging techniques. In a first stage the material was characterized with different spectroscopic and microscopic techniques, and subsequently was studied the behavior of these materials as semiconductors. Using the techniques of fluorescence spectroscopy and absorbance transition has been proven generation state of charge separation after excitation. The different strategies used in the modification of graphene are aimed at getting systems with higher lifetimes of charge separation to harness the energy absorbed from light. It has been observed that the lifetime and quantum yield of charge separation is greater in rGO than GO. For graphenes (N,O)-codoped, which were prepared by pyrolysis natural chitosan, has shown that there is a direct relationship between the percentage of dopants and the energy of the conduction band and the quantum yield of charge separation state. In the case of reconstituted graphenes halogenated it has been shown the influence of the nature of the halogen in the generation charge separation. The charge separation lifetime obtained in these materials is in the scale of microseconds which is encouraging for possible application in photocatalysis and optoelectronic devices. For this reason we use these materials as photocatalysts for hydrogen generating from a methanol-water mixture and yields were higher for the sample (Cl)G that were seven times higher than the starting GO. Nanoparticles have been prepared using two different carbon methodologies. In one case they have been used zeolites with different pore size as templates, being those of small pore size with a directing agents with large structure, such as ITQ-29 and ITQ-12, were the most suitable for production of photoluminescent carbon dots. Pyrolysis of structure directing agent of these zeolites results in carbon quantum dots with particle sizes between 5 and 12 nm and photoluminescence quantum yield of 0.4 to that were used as photoluminescent oxygen sensors. Another methodology involves the synthesis of carbon nanomaterials from annealing of a mixture of PTCA and PEG under air atmosphere. Nanoobjects are obtained with height of 2.5 nm and with an average size of 40 nm. The morphology of the C-NOR is similar to an onion formed by concentric circles. These nanoparticles can be internalized in the human carcinoma HeLa cells and Hep 3B and they have interesting photoluminescent properties, in the same way as in solution. They showed a remarkable biocompatibility affecting in a very low way to cell viability to short periods of exposure according to the test MTT. In order to address the possible use of this nanoparticles in bioimaging a complete toxicology study was performed in vitro. It was performed feasibility assessments, proliferation, apoptosis studies generation and oxidative stress experiments after continuous and limited exposure, and also varying concentrations. It was observed that both nanoparticles showed no toxicity in the two situations at low and higher concentration, although some toxicity was determined at higher concentrations under continuous exposure. These results support the potential use of nanoparticles C-NOR and C-NOR(Eu) as bioimaging agents.
[ES] En esta Tesis Doctoral se han estudiado las propiedades fotofísicas y fotoquímicas de nuevos nanomateriales basados en carbono como son los derivados de grafeno (GO, rGO, grafenos (N,O) codopados y grafenos reconstituidos halogenados) y dos tipos diferentes de nanopartículas de carbono (C-dots y C-NOR). Estos materiales se han aplicado en la generación fotocatalítica de hidrógeno, como sensores de gases y en técnicas de bioimagen. En una primera etapa se ha caracterizado el material con distintas técnicas espectroscópicas y de microscopia, y a posteriori se ha estudiado el comportamiento de estos materiales como semiconductores. Mediante las técnicas de espectroscopia de fluorescencia y de absorbancia de transición se ha comprobado la generación del estado de separación de cargas tras su excitación. Las distintas estrategias utilizadas en la modificación del grafeno van dirigidas a conseguir sistemas con tiempos de vida del estado de separación de cargas elevados que permitan aprovechar la energía absorbida de la luz. Se ha observado que el tiempo de vida y el rendimiento cuántico de la separación de cargas es mayor en el rGO que en el GO. Para los grafenos (N,O)-codopados, que han sido preparados por pirólisis del quitosano natural, se ha demostrado que existe una relación directa entre el porcentaje de dopantes y la energía de la banda de conducción y el rendimiento cuántico de la separación de cargas. Para el caso de los grafenos reconstituidos halógenados se ha demostrado la influencia de la naturaleza del halógeno en la generación del estado de separación de cargas. El tiempo de vida del estado de separación de cargas obtenido en estos materiales se encuentra en la escala de los microsegundos lo cual resulta esperanzador para su posible aplicación en fotocatálisis y en dispositivos optoelectrónicos. Por este motivo utilizamos estos materiales como fotocatalizadores para la generación de hidrógeno a partir de una mezcla metanol agua y los rendimientos más altos fueron para la muestra (Cl) G que fueron siete veces más elevadas que el GO de partida. Se han preparado nanoparticulas de carbono empleando dos metodologías distintas. En un caso se han utilizado zeolitas de distinto tamaño de poro como plantillas, siendo las de tamaño de poro pequeño con agentes directores de estructura voluminosos, como la ITQ-29 y ITQ-12, las más adecuadas para obtener puntos de carbono fotoluminiscentes. La pirólisis del agente director de estructura de estas zeolitas da lugar a puntos cuánticos de carbono con tamaños de partícula entre 5 y 12 nm y un rendimiento de fotoluminiscencia cuántica de 0.4 que fueron utilizados como sensores de oxígeno fluorescentes. La otra metodología consiste la síntesis de nanomateriales de carbono a partir de un recocido de una mezcla de PTCA y PEG bajo atmosfera de aire. Se obtiene nanoobjetos de 2.5 nm de altura y con un tamaño medio de 40 nm. La morfologia de los C-NOR es de círculos concéntricos similar a una cebolla. Estas nanopartículas pueden internalizarse en las células de carcinoma humano HeLa y Hep 3B y presentan propiedades fotoluminiscentes interesantes, de la misma manera que en disolución. Demostraron una notable biocompatibilidad afectando de manera poco perceptible a la viabilidad celular a cortos periodos de exposición según la prueba MTT. Con el fin de abordar el posible uso de esta nanopartículas en bioimagen y su toxicidad se realizó un estudio toxicológico completo in vitro. Se realizaron evaluaciones de viabilidad, proliferación, estudios de generación de apoptosis y estrés oxidativo tras la exposición limitada o continua variando las concentraciones. Se observó que ambas nanopartículas no mostraron toxicidad en las dos situaciones a baja concentración, aunque cierta toxicidad se ha determinado a concentraciones superiores bajo exposición continua.
[CAT] En aquesta tesi doctoral s'han estudiat les propietats fotofísiques i fotoquímiques de nous nanomaterials basats en carboni com són els derivats de grafè (GO, rGO, grafens (N,O) codopats i grafenos reconstituïts halogenats) i dos tipus diferents de nanopartícules de carboni ( C-dots i C-NOR). Aquests materials s'han aplicat en la generació fotocatalítica d'hidrogen, com a sensors de gasos i en tècniques de bioimatge. En una primera etapa s'ha caracteritzat el material amb diferents tècniques espectroscòpiques i de microscòpia, i a posteriori s'ha estudiat el comportament d'aquests materials com semiconductors. Mitjançant les tècniques d'espectroscòpia de UV-Vis i d'absorbància de transició (T.A.S.) s'ha comprovat la generació de l'estat de separació de càrregues després de la seva excitació. Les diferents estratègies utilitzades en la modificació del grafè van dirigides a aconseguir sistemes amb temps de vida de l'estat de separació de càrregues elevats que permetin aprofitar l'energia absorbida de la llum. S'ha observat que el temps de vida i el rendiment quàntic de la separació de càrregues és més gran en el rGO que al GO. Per als grafenos (N,O)-codopats, que han estat preparats per piròlisi del quitosan natural, s'ha demostrat que existeix una relació directa entre el percentatge de dopants i l'energia de la banda de conducció i el rendiment quàntic de la separació de càrregues. Per al cas dels grafens reconstituïts halogenats s'ha demostrat la influència de la naturalesa de l'halogen en la generació de l'estat de separació de càrregues. El temps de vida de l'estat de separació de càrregues obtingut en aquests materials es troba en l'escala dels microsegons la qual cosa resulta esperançador per a la seva possible aplicació en fotocatàlisi i en dispositius optoelectrònics. Per aquest motiu utilitzares aquests materials com fotocatalitzadors per a la generació de hidrogen a partir de una mescla metanol- aigua y els rendiments mes alts van ser per la mostra (Cl)G que van ser set vegades mes elevades que el GO de partida. S'han preparat nanoparticules de carboni emprant dues metodologies diferents. En un cas s'han utilitzat zeolites de diferent grandària de porus com plantilles, sent les de mida de porus petit amb agents directors d'estructura voluminosos, com la ITQ-29 i ITQ-12, les més adequades per obtenir punts de carboni fotoluminiscents. La piròlisi de l'agent director d'estructura d'aquestes zeolites dóna lloc a punts quàntics de carboni amb mides de partícula entre 5 i 12 nm i un rendiment de fotoluminiscència quàntica de 0.4 que van ser emprats com a sensors d'oxigen fluorescents. L'altra metodologia consisteix en la síntesi de nanomaterials de carbono a partir d'un recuit d'una barreja de PTCA i PEG sota atmosfera d'aire. S'obté nanoobjectes de 2.5 nm d'alçada i amb una longitud mitjana de 40 nm. La morfologia dels C-NOR és de cercles concèntrics similar a una ceba. Aquestes nanopartícules poden internalitzar-se en les cèl·lules de carcinoma humà HeLa i Hep 3B i presenten propietats fotoluminiscents interessants, de la mateixa manera que en dissolució. Van demostrar una notable biocompatibilitat afectant de manera poc perceptible a la viabilitat cel·lular a curts períodes d'exposició segons la prova MTT. Per tal d'abordar el possible ús d'aquesta nanopartícules en bioimatge i la seva toxicitat es va realitzar un estudi toxicològic complet in vitro. Es van realitzar avaluacions de viabilitat, proliferació, estudis de generació d'apoptosi i estrès oxidatiu després de l'exposició limitada o contínua amb diferents concentracions. Es va observar que les dos nanopartícules no van mostrar toxicitat en les dues situacions a baixa concentració, encara que certa toxicitat s'ha determinat a concentracions superiors sota exposició contínua. Aquests resultats donen suport a la possible utilització de nanopartícules C-NOR i C-NOR(Eu) com a agents
García Baldoví, H. (2016). Preparación y propiedades fotofísicas de materiales grafénicos y puntos cuánticos basados en carbono. Aplicaciones en nanotecnología [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68505
TESIS
Premiado

This thesis reports the study of single photon sources that emit one infrared wavelength photon at a time, creating cavity quantum electrodynamical effects for applications such as quantum information processing. This work considers two major single photon sources: a) InAs single quantum dots and b) single carbon nanotubes, which both emit in the infrared range. Photonic crystal slabs and photonic crystal waveguides are served as distinctive passive devices with manipulated photonic band-gaps to control the propagating light. A simulation of leaky modes of two-dimensional photonic crystal slabs is introduced to constrain model parameters in the device design. Fullerenes are used as fluorescent material to achieve resonance of a leaky mode with excitation 1492 nm and emission at 1519 nm and to see enhancement of the PL. We include novel characterization techniques and PL measurements to show sharp emission peaks from single quantum dots and successfully couple them to micro-cavities. The strong coupling effect is observed and is amongst the best examples of cavity-dot structures achieved to date. Single-walled carbon nanotubes have shown anti-bunched light emission, thus we systematically study them as another possible candidate of single photon sources. PLE spectra show clear evidence of the existence of excited states, and time evolution measurements reveal the disorder induced diffusion, which separate the tubes into a series of quantum dots. These strongly confined states are concluded as the origin of the possibility that single-walled carbon nanotubes are single photon sources.

Cette thèse utilise les micro-ondes pour étudier des circuits de boîtes quantiques à base de nanotubes de carbone. Dans une première expérience, l'excitation micro-onde est appliquée directement sur une électrode du circuit pour une boîte quantique dans le régime Kondo. Nous réalisons la première caractérisation fréquence-amplitude de la conductance Kondo à biais nul. Des données préliminaires sont en accord avec la prédiction d'universalité. Nous présentons deux autres expériences, où les boîtes quantiques sont insérées dans des résonateurs micro-ondes. Les photons de la cavité sondent la résistance de relaxation de charge et l'émission de photons dans une boîte quantique couplée à des réservoirs normaux et supraconducteurs, en présence de répulsion coulombienne. Nos observations valident une modélisation en termes de réponse linéaire du circuit. Nous présentons aussi la première implémentation d'une lame séparatrice à paires de Cooper en cavité. Le régime de couplage fort est atteint, une première avec des circuits de boîtes quantiques. Nos résultats renforcent l'idée que l'électrodynamique quantique mésoscopique est une boîte à outils fructueuse, aussi bien dans le contexte du domaine du transport quantique que dans celui de l'information quantique
This thesis uses microwaves as probe of carbon nanotube quantum dot circuits. In a first experiment, a microwave excitation is directly applied to a circuit electrode for a quantum dot in the Kondo regime. We provide the first frequency-amplitude characterisation of the Kondo zero-bias conductance. Preliminary data are consistent with predicted universal behaviour. We present two other experiments, where quantum dot circuits are embedded in microwave resonators. Cavity photons probe charge relaxation resistance and photon-emission in a quantum dot coupled to normal and superconducting reservoirs in presence of Coulomb repulsion. Our observations validate a modelling in terms of the circuit linear response. We also present the first implementation of a Cooper pair splitter in cavity. The strong coupling regime is achieved, a premiere with quantum dot circuits. Our findings support the idea, that mesoscopic quantum electrodynamics is a fruitful toolbox in the context of both fields of quantum transport and quantum information science

Les circuits électroniques mesurés à des températures cryogéniques permettent d'étudier le comportement quantique des électrons. En particulier, les circuits de boites quantiques sont des systèmes accordables modèles pour l'étude des électrons fortement corrélés, symbolisée par l'effet Kondo. Dans cette thèse, des circuits de boîtes quantiques à base de nanotube de carbone sont intégrés à des cavités micro-onde coplanaires, avec lesquelles l'électrodynamique quantique en cavité (cQED) a atteint un degré de contrôle remarquable de l'interaction lumière-matière. Les photons de la cavité micro-onde sont ici utilisés pour sonder la dynamique de charge dans le circuit de boîtes quantiques. Plus précisément, la cavité micro-onde de grande finesse nous a permis de mesurer la compressibilité du gas d'électrons dans une boîte avec une sensibilité sans précédent. Des mesures simultanées de transport électronique et de la compressibilité montrent que la résonance Kondo observées dans la conductance est transparente aux photons micro-ondes. Cela révèle le gel de la dynamique de charge dans la boîte quantique pour ce mécanisme particulier de transport d'électrons et illustre que la résonance Kondo à N-corps dans la conductance est associée aux corrélations issues des fluctuations de spin d'une charge gelée. Nous étudions aussi dans cette thèse la possible émergence d'une nouvelle quasi-particule, appelée état lié de Majorana, et qui serait sa propre anti-particule. Dans ce but, une grille ferromagnétique a été placée sous le nanotube pour créer un couplage spin-orbit artificiel. L'observation d'états d'Andreev dans un tel dispositif est un premier pas prometteur vers la détection avec une architecture cQED d'états liés de Majorana dans les nanotubes de carbone
On-chip electronic circuits at cryogenic temperature are instrumental to studying the quantum behavior of electrons. In particular, quantum dot circuits represent tunable model systems for the study of strong electronic correlations, epitomized by the Kondo effect. In this thesis, carbon nanotube based-quantum dot circuits are embedded in coplanar microwave cavities, with which circuit quantum electrodynamics (cQED) has reached a high degree of control of the light-matter interaction. Here, microwave cavity photons are used to probe the charge dynamics in the quantum dot circuit. More precisely, the high finesse cavity allows us to measure the compressibility of the electron gas in the dot with an unprecedented sensitivity. Simultaneous measurements of electronic transport and compressibility show that the Kondo resonance observed in the conductance is transparent to microwave photons. This reveals the predicted frozen charge dynamics in the quantum dot for this peculiar electron transport mechanism and illustrates that the many-body Kondo resonance in the conductance is associated to correlations arising from spin fluctuations of a frozen charge. A second quantum phenomenon addressed in this thesis is the possible emergence of a new quasi-particle in condensed matter, called Majorana bound state, which would be its own anti-particle. For that purpose, a ferromagnetic gate has been placed below a nanotube in order to generate a synthetic spin-orbit coupling. The observation of Andreev bound states in such a device is a first promising step towards the detection with a cQED architecture of Majorana bound states in a carbon nanotube

The main goal of this study was to demonstrate the potential of atmospheric pressure cold plasmas to synthesize nanoparticles and surface treatments. Silver nanoparticles and carbon quantum dots were selected for this work. The use of silver nanoparticles in bactericidal applications has been tested. In addition, carbon quantum dots are used to manufacture a low-cost metal ion sensor for the detection of copper in drinking water. The second part of the study investigated the chemical reactions that occur in plasma treated mesoporous tin oxide films. These are used to increase the efficiency of dye sensitized solar cells.

This Master’s thesis deals with isolating carbon nanoparticles from South Moravian lignite using "green" – environmentally friendly methods. This method consists of mechanical-chemical-thermal stressing of lignite using ultrasound, hydrogen peroxide and high temperatures. This work aims to develop recommendations on coal as a source of carbon nanoparticles and based on these recommendations, to design procedures for isolating nanoparticles from South Moravian lignite using environmentally friendly methods. The identified procedures were designed to meet carbon-based particles with an oxidized surface. From the results we can deduct that it is possible to use South Moravian lignite for the preparation of carbon nanoparticles. However, it will be necessary to modify the process further and also to optimize the purification of the obtained particles.

We report on conductance measurements in carbon nanotube based double quantum dots connected to two normal electrodes and a central superconducting finger. By operating our devices as Cooper pair beam splitters, we provide evidence for Crossed Andreev Reflection (CAR). We inject Cooper pairs in the superconducting electrode and measure the differential conductance at both left and right arm. The contacts split the device into two coupled quantum dots. Each of the quantum dots can be tuned by a lateral sidegate. If the two sidegates are tuned such that both quantum dots are at a transmission resonance, a considerable part of the injected Cooper pairs splits into different normal contacts. On the contrary, if only one of the two dots is at resonance, nearly all pairs tunnel to the same normal contact. By comparing different triple points in the double dot stability diagram, we demonstrate the contribution of split Cooper pairs to the total current. In this manner, we are able to extract a splitting efficiency of up to 50% in the resonant case. Carbon Nanotubes ensure ballistic transport and long spin-flip scattering lengths. Due to these properties they are promising candidates to investigate EPR-type correlations in solid state systems.

La thèse intitulée «Design, Synthesis and SupramolecularArchitectures of New Heterocyclic Compounds with PotentialApplications in Material Chemistry and Photovoltaic Conversion” eststructurée en cinq chapitres traitant de nouveaux: a)cyclopenta[c]pyrannes hétérocyclique; b)des propriétés fluorescentes; d) potentiels dispositifs de l'électroniquemoléculaire; d) donneurs moléculaires pour les photovoltaïquesorganiques et e) carbon‘quantum’dots électroluminescents.Le premier chapitre présente une étude des dérivéspseudoazulenique ayant une unité cyclopenta[porte sur leur synthèse, l'analyse structurale et leur comportement dansdes réactions de substitution électrophile pour obtenir des composésayant des propriétés fluorescentes.Le deuxième chapitre présentediastéréoisomères et l'étude de propriétés de fluorescencedérivés d’indenopyrone.Le troisième chapitre décrit la synthèse des nouvellesarchitectures basées sur l’unité cyclopenta[être modifiés structurellement par l'influence d'un stimulus chimiqueou électrochimique afin d'élaborer des potentiels dispositifs del'électronique moléculaire.Dans le quatrième chapitre, la synthèsedes propriétés électroniques des nouvelles molécucellules solaires organiques (OSC) ontLe cinquième et dernier chapitre décrit la passivation desdéfauts de surface des nanoparticules de carbone avec desmolécules organiques ou des polymères pour obtenir desnanoparticules de carbone photoluminescentse surnommé ‘quantum dots
The thesis entitled “Design, Synthesis and SupramolecularArchitectures of New Heterocyclic Compounds with PotentialApplications in Material Chemistry and Photovoltaic Conversion” isstructured into five chapters concerning new: a) heterocycliccyclopenta[c]pyrans; b) indenopyrone derivatives with fluorescentproperties; c) potential devices of molecular electronics; d)donors for organic photovoltaics and e) electroluminescent carbon‘quantum’ dots.The first chapter presents a study of pseudoazulenederivatives having a cyclopenta[c]pyran unit. The survey comprises thesynthesis, structural analysis and reactivity towards electrophilicsubstitution in order to obtain fluorescent compounds.The second chapter deals with the separation odiastereoisomers and the study of fluorescent propertiesindenopyrone derivatives.The third chapter describes the synthesis of newarchitectures based on cyclopenta[c]pyran unit that can be structurallymodified by the influence of a chemical or electrochemical stimulus inorder to work as potential devices in molecular electronics.In the fourth chapter, the synthesis andelectronic properties of new molecular donors for organic solar cellswas described.The fifth and last chapter outlines the passivation of surfacedefects on carbon nanoparticles using small organic molecules orpolymers in order to obtain photoluminescent carbon nanoparticlesdubbed as carbon‘quantum’dots

This thesis is devoted to the optical properties of low-dimensional structures based on such two-dimensional materials as graphene, silicene and phosphorene. We investigate optical properties of a variety of quasi-one dimensional and quasi-zero-dimensional structures, which are promising for future optoelectronics. Primarily we focus on their low-energy optical properties and how these properties are influenced by the structures’ geometry, external fields, intrinsic strain and edge disorder. As a consequence of this endeavor, we find several interesting effects such as correlation between the optical properties of tubes and ribbons whose periodic and ‘hard wall’ boundary conditions are matched and a universal value of matrix element in narrow-gap tubes and ribbons characterizing probability of transitions across the band gap opened up by intrinsic strain originating from the tube’s surface curvature or ribbon’s edge relaxation. The analytical study of the gapped 2D Dirac materials such as silicene and germanene, which have some similarity to the aforementioned quasi-one-dimensional systems in terms of physical description, reveals a valley- and polarization-dependent selection rules. It was also found that absorption coefficient should change in gapped materials with increasing frequency and become a half of its value for gap edge transitions when the spectrum is linear. Our analysis of the electronic properties of flat clusters of silicene and phosphorene relates the emergence and the number of the peculiar edge states localized at zero energy, so-called zero-energy states, which are know to be of topological origin, to the cluster’s structural characteristics such as shape and size. This allows to predict the presence and the number of such states avoiding complicated topological arguments and provides a recipes for design of metallic and dielectric clusters. We show that zero-energy states are optically active and can be efficiently manipulated by external electric field. However, the edge disorder is important to take into account. We present a new fractal-based methodology to study the effects of the edge disorder which can be applied also to modeling of composite materials. These finding should be useful in design of optoelectronic devices such as tunable emitters and detectors in a wide region of electromagnetic spectrum ranging form the mid-infrared and THz to the optical frequencies.

The work developed in this thesis is based on the study of systems for the generation of nanoparticles in liquids by means of pulsed lasers, improving their production and using the generated nanoparticles in applications of great technological relevance such as biomedical imaging or additive manufacturing. For the femtosecond laser production improvement, the novel implementation of a spatio temporal focusing system is proposed which, by varying the temporal pulse duration out-of-focus, suppresses nonlinear effects in the liquid medium and the associated energy losses. For the colloidal size reduction by fragmentation, a continuous flow system is proposed that allows to increase the control over the irradiation parameters while ensuring homogeneous irradiation. Finally, the carbon quantum dots generated are used as fluorescent markers and different metal and oxide nanoparticles are synthesized for their later application as bactericides and in the improvement of materials used in additive manufacturing.
El trabajo desarrollado en esta tesis se basa en el estudio de sistemas de generación de nanopartículas en líquidos mediante láser pulsado, mejorando su producción y empleando los nanomateriales generados en aplicaciones como imagen biomédica o additive manufacturing. Para la mejora en la producción mediante láser de femtosegundo se propone la implementación de un sistema de focalización espacio-temporal que, mediante la variación de la duración temporal de los pulsos fuera de foco, consigue suprimir los efectos no lineales en el medio líquido. Para la mejora en el proceso de reducción del tamaño de coloides, se propone un sistema de flujo continuo que aumenta el control sobre los parámetros de irradiación. Finalmente, los puntos cuánticos de carbono generados se utilizan como marcadores fluorescentes y se sintetizan distintas nanopartículas metálicas y óxidos para su posterior aplicación como bactericidas y en la mejora de materiales utilizados en fabricación aditiva.

Cette thèse décrit des expériences sur la synthèse de nanotubes de carbone (CNT) mono-paroi, leur intégration dans des dispositifs ultra-propres, ainsi que l'étude de leurs propriétés électroniques par des mesures de transport à très basse température. La première partie de ce travail décrit l'optimisation des paramètres de synthèse par déposition chimique en phase vapeur (CVD) tels que les précurseurs de carbone, les flux de gaz, la température, ou le catalyseur pour la croissance de CNT de très bonne qualité. Parmis tous ces paramètres, la composition du catalyseur joue un rôle decisif pour permettre une croissance sélective en mono-paroi ansi qu'une distribution de faible diamètre. Dans la deuxième partie nous développons la nanofabrication de boites quantiques ultra-propres à base de CNT ainsi que les mesures de transport de ces échantillons à basse température (40 mK). Le spectre de la première couche électronique du nanotube est mesuré par spectroscopie de cotunneling inélastique sous champ magnétique, montrant alors un fort couplage spin-orbite négatif, dans ce système. Nous montrons que la séquence de remplissage d'électrons dans notre cas (ΔSO < 0) est différente de celle que l'on obtiendrait en régime Kondo SU (4) (ΔSO = 0). En effet, un effet Kondo purement orbital est observé pour N =2e à champ magnétique fini. Dans la dernière partie de cette thèse, nous décrivons la mise en œuvre expérimentale d'un évaporateur thermique à aimants à molécule unique (SMM) pour la fabrication future de dispositifs hybrides CNT-SMM ultra-propres
This thesis describes experiments on the synthesis of single wall carbon nanotubes (SWNTs), fabrication of ultra-clean CNT devices, and study of electronic properties of CNTs with transport measurements. The first part of this work describes the optimization of the synthesis parameters (by chemical vapor deposition - CVD) such as carbon precursor, gas flows, temperature, catalyst for the growth of high quality SWNTs. In all these parameters, the catalyst composition plays a very important role on the high selective growth of SWNTs with a narrow diameter distribution. The second part deals with the nanofabrication of ultra-clean CNT devices and the low temperature (40 mK) transport measurements of these CNT quantum dots. The level spectra of the electrons in the first shell are investigated using inelastic cotunneling spectroscopy in an axial magnetic field, which shows a strong negative spin-orbit coupling of electron. We find that the sequence of electron shell filling in our case (ΔSO < 0) is different from which would be obtained in the pure SU(4) Kondo regime (ΔSO = 0). Indeed, a pure orbital Kondo effect is observed in N=2e at a finite magnetic field. In the last part of this thesis, we describe the experimental implementation of the thermal evaporation of single-molecule magnet (SMM) for the future fabrication of ultra-clean CNT-SMM hybrid devices

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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
In this work, a novel fluorescence method using flow-batch analysis for the determination of copper in edible oil, employing carbon quantum dots (CDs) was developed. The in-line single-phase extraction of iron consisted of the addition of a mixture of isopropyl alcohol/chloroform (70:30, v/v) to dissolve the oil samples. Moreover, an eco-friendly, simple, and low-cost hydrothermal method was developed for preparation of water-soluble fluorescent carbon quantum dots using pineapple juice as carbon precursors. The fluorescence properties of CDs were examined by fluorescent detection of Cu(II) in oil. Their photoluminescence can be significantly quenched by simply using the buffer solution PBS of pH 4.0. This mechanism was presumably explained by the interactions between the surface groups of CDs with metal ions studied. Concerning the flow-batch analysis a new mixing chamber was developed in polytetrafluoroethylene provided with quartz windows in order to allow the excitation and fluorescence detection online. For this, an LED UV was used as the excitation source and a portable spectrofluorometer as detector. The limits of detection and relative standard deviation were estimated as 2.9 μg L−1 and < 2.5 % (n=3). The analysis of interfering was successful for the major ions present in solution, revealing significant percentage interference (≤ 5 %).The precision of the method was evaluated by recovery test (96 to 106 %). The robustness of the method was evaluated by intra- and inter- day comparison of the results obtained and using the reference method with detection by atomic absorption graphite furnace at a 95% level of statistical confidence. Finally, the system showed quite satisfactory analytical frequency (60 h–1) and considerably reducing the consumption of chemicals. Thus, it is demonstrated appreciably the viability of new fluorescent method, thus allowing the development of new analytical strategies employing potentially useful carbon quantum dots and flow-batch analyzer.
Neste trabalho foi desenvolvido um novo método automático em fluxo-batelada baseado em pontos quânticos de carbono (PQCs) para determinação fluorescente de cobre(II) em óleos comestíveis. O método analítico proposto apresenta como estratégia de pré-tratamento da amostra a disponibilização on-line do cobre por meio de extração em fase única utilizando uma mistura de solventes álcool isopropílico/clorofórmio na proporção 70:30 (v/v). Para a preparação dos PQCs, foi empregado o tratamento hidrotérmico, simples e de baixo custo, do suco de abacaxi, como bioprecursor. Foi constatado que a fluorescência dos PQCs pode ser significativamente reduzida na presença do Cu(II) simplesmente utilizando um tampão PBS pH 4,0. O mecanismo de extinção da fluorescência pode ser atribuído as interações entre os grupos presentes na superfície dos PQCs com os íons Cu(II). Concernente ao sistema automático fluxo-batelada uma nova câmara de mistura foi construída em politetrafluoretileno, provida de três janelas de quartzo, com o objetivo de permitir a excitação e aquisição dos espectros de fluorescência on-line. Para isso, foi utilizado um LED-ultravioleta como fonte de excitação e um espectrofluorímetro portátil como detector. Os limites de detecção e os desvios padrão relativo foram estimados como sendo 2,9 μg L–1 e < 2,5 % (n = 3), respectivamente. A análise de íons interferentes foi realizada com êxito para os principais íons metálicos presentes na matriz da amostra, não revelando interferência percentual significativa (≤ 5 %). A exatidão do método foi avaliada através do teste de recuperação (96 a 106 %). A robustez do método foi avaliada por comparação intra e inter-dia dos resultados obtidos e empregando o método de referência com detecção por absorção atômica em forno de grafite, a um nível de 95% de confiança estatística. Por fim, o sistema apresentou frequência analítica bastante satisfatória (60 h–1) com uma redução considerável do consumo de produtos químicos. Desta forma, é evidenciado de modo apreciável a viabilidade do novo método fluorescente, permitindo, dessa maneira, o desenvolvimento de novas estratégias analíticas potencialmente úteis baseadas em nanopartículas de carbono e automação em sistemas fluxo-batelada.

The PhD project has been performed in the Surfaces and Catalysts group active in the Department of Chemical Sciences, within the frame of the grant “A rational approach to the optimization of efficient electrocatalysts for the next generation Fuel Cells”, funded by CARIPARO foundation. The project has been focused on the preparation and characterization of new carbon-based materials for applications in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), also known as oxygen-hydrogen FCs. The preparation of the materials has been performed using different techniques, depending on the type of the target material and on the possible applications that these materials can offer. With reference to the studied model systems (Highly Oriented Pyrolytic Graphite (HOPG) and Glassy Carbon (GC)), the introduction of doping heteroatoms has been performed by ion implantation, while the study of new chemical functionalities has been allowed by the use of Wet Chemistry techniques, in particular derived from the electrochemical synthesis. The deposition of thin films or nanoparticles (metal or oxides of transition metals) on the ion-modified materials has been carried out in-situ by using advanced techniques under Ultra High Vacuum conditions (UHV), such as Physical Vapor Deposition (PVD). Within the study of the model systems, PVD was chosen because of its ability to provide an atomic scale control of the metal deposition. In a second time, conventional deposition techniques such as chemical or electrochemical reduction of suitable metal precursors have been performed, in a synergistic combination between Surface Science and Electrochemistry-derived techniques. The characterization of these materials has been performed using the facilities of the Surface Science group, such as the X-ray and Ultraviolet Photoelectron Spectroscopy (XPS - UPS), Scanning Tunneling and Atomic Force Microscopy (STM - AFM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Low Energy Electron Diffraction (LEED). To get a deeper insight in the chemistry/structure/properties of the prepared systems, synchrotron light-based techniques such as HR-XPS, NEXAFS, ARPES, ResPES and PEEM have been extensively used. The study of the electro-catalytic activity has been performed using conventional Electrochemistry techniques, in particular Cyclic and Linear Sweep Voltammetry (CV - LSV), as well as electro-dynamic techniques such as Rotating Disk Electrode (RDE). Finally, in order to support the experimental data or to bring their understanding at a deeper level, simulations using Density Functional Theory (DFT) have been performed in collaboration with the group coordinated by Prof. Cristiana Di Valentin (University of Milano Bicocca). During the course of the doctorate, several collaborations have been pursued with other research groups operating in the Department of Chemical Sciences or abroad, such as the "Interfaces and Energy Conversion E19" research unit, Technical University of Munich (TUM, Germany), coordinated by Profs. O. Schneider and J. Kunze-Liebhäuser.
Il progetto di dottorato nasce all’interno del gruppo di ricerca di Superfici e Catalizzatori operante nel dipartimento di Scienze Chimiche, nell’ambito della borsa a titolo vincolato “Un approccio razionale alla ottimizzazione di elettrocatalizzatori efficienti per le celle a combustibile di nuova generazione”, finanziata da fondazione CARIPARO. Le tematica è stata focalizzata sulla preparazione e caratterizzazione di nuovi materiali a base di carbonio utilizzabili per applicazioni in celle a combustibile di tipo PEMFCs (Polymer Electrolyte Membrane Fuel Cells) ad ossigeno-idrogeno. La preparazione dei materiali è avvenuta facendo uso di differenti tecniche, in relazione al tipo di materiale oggetto di studio ed alle applicazioni che tali materiali possono offrire. Con riferimento allo studio dei sistemi modello (grafite pirolitica altamente orientata, HOPG, e carbonio vetroso, GC), il drogaggio degli stessi mediante l’introduzione di eteroatomi (in particolare azoto) è avvenuto ricorrendo alla tecnica dell’impiantazione ionica, mentre lo studio di nuove funzionalità chimiche è stato permesso dall’utilizzo di tecniche di Wet Chemistry, in particolare mutuate dalla sintesi elettrochimica. La deposizione di film sottili o di nanoparticelle (metalliche o a base di ossidi di metalli di transizione) su tali materiali modificati è stata effettuata facendo uso di tecniche avanzate come la deposizione fisica da fase vapore (PVD) in condizioni controllate di Ultra Alto Vuoto (UHV), in grado di offrire un controllo su scala atomica della deposizione di tali film. Sono state utilizzate anche tecniche di deposizione tradizionali quali la riduzione chimica o elettrochimica di opportuni precursori metallici: l‘utilizzazione di una siffatta combinazione sinergica tra tali differenti tecniche di preparazione ha permesso di ottenere materiali caratterizzati da strutture e proprietà peculiari. La caratterizzazione di tali materiali è svolta utilizzando le facilities del gruppo di Scienza delle Superfici, come la spettroscopia di fotoelettroni (XPS) o della banda di valenza (UPS), la microscopia ad effetto tunnel o a forza atomica (STM - AFM), la microscopia elettronica e la dispersione energetica dei raggi X indotta dagli elettroni (SEM-EDX), la diffrazione di elettroni lenti (LEED). Allo scopo di caratterizzare maggiormente in dettaglio la struttura e le proprietà chimiche dei materiali preparati sono state usate estensivamente le tecniche di indagine offerte dalla luce di sincrotrone (HR-XPS, NEXAFS, ARPES, ResPES, PEEM), mentre lo studio della reattività catalitica si basa su tecniche derivate dall’analisi elettrochimica, in particolare la voltammetria ciclica ed a scansione lineare del potenziale applicato, nonchè tecniche elettro-dinamiche come la voltammetria su elettrodo rotante. Infine, allo scopo di supportare i dati sperimentali o portare la comprensione delle proprietà dei materiali ad un livello più profondo, simulazioni mediante teoria del funzionale densità (DFT) sono state adottate per un approccio critico allo studio dei materiali preparati (in collaborazione con il gruppo coordinato dalla prof. Cristiana Di Valentin, Università di Milano Bicocca). Durante il corso del dottorato, diverse collaborazioni sono state perseguite con gruppi interni al Dipartimento di Scienze Chimiche o anche Esteri, come l’unità di ricerca “Interfaces and Energy Conversion E19”, dell’università tecnica di Monaco di Baviera (TUM, Technische Universität München, Germania), coordinata dai proff. O. Schneider e J. Kunze-Liebhäuser.

Cardiovascular diseases (CVD) with escalating death rates pose one of the greatest threats to global health and well-being. Thus, developing effective interventions to combat CVD are of critical importance. 3D printing fabrication of engineered cardiovascular constructs with complex, hierarchical structures is capable of producing personalized structures. The current material science advancement has drawn a great interest to the researchers towards incorporation of biodegradable materials for the implantable 3D printed scaffolds. The aim of this research work is to design, synthesis, and evaluation of carbon quantum dot-polymer nanocomposites using 3D-printing technology for cardiovascular tissue engineering applications. Freeform (without any support), vascular-scale, small diameter (2 mm) tubular scaffolds were fabricated using 3D printing based on fused deposition modelling (FDM) with nanocomposites of bioresorbable polylactic acid (PLA) and carbon quantum dots (CQDs). The PLA-CQD stents demonstrated excellent processability, hydrophilicity, tensile strength, compressive strength, radial stability and cell proliferation relative to pure PLA scaffolds. The results show that the addition of CQDs enhances scaffolds properties significantly, such as, stent hydrophilicity by about 25%, tensile strength by 24%, compressive strength by 66% and cell proliferation by 50% compared to PLA alone. The results show that the combination of 3D printing with PLA-CQD nanocomposites could be a viable method to produce bioresorbable nanocomposites for cardiovasculatures with non-invasive imaging for monitoring cell growth. Furthermore, biological experiments need to be conducted to justify for incorporation of CQDs into polymer nanocomposites in cardiovascular tissue engineering applications.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Biológicas, Programa de Pós-Graduação em Biologia Animal, 2016.
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O melanoma é um tipo de câncer de pele que tem origem nos melanócitos. Apesar de somente 0,96% dos novos casos de câncer no Brasil para 2016 serem de melanoma, ele é extremamente agressivo, sendo que possui alto potencial metastático o que leva muitos pacientes aóbito. Uma forma de evitar essa alta mortalidade é a realização de um diagnóstico precoce. Estudos propõem a utilização de substâncias ou partículas fluorescentes para identificar focos de câncer, e entre essas partículas carbon dotstem apresentado um grande potencial de marcação de células cancerosas por apresentarem fluorescência. Tendo em vista essa propriedade de carbon dots, este estudo teve o objetivo de realizar a caracterização fotofísicaeavaliar a toxicidade in vitroe in vivode carbondotsrecobertos com boronato (C-DotB) em camundongos com ou sem melanoma. C-DotB apresentaram absorbância na faixa do ultravioleta (abaixo de 400 nm) e quando excitadas a 360 nm apresentaram pico de emissão em 460 nm. Os testes de toxicidade in vitroforam realizados com as linhagens celulares NIH/3T3 (fibroblasto murino) e B16F10 (melanoma murino). Somente a exposição a 0,1 mg/mL de C-DotB ocasionou morte celular significativa de 60 e 70% de fibroblastos e melanoma, respectivamente. Nos experimentos in vivoforam utilizados 66 camundongos C57BL/6. Nas avaliações do peso corporal, da ração consumida e da ingestão de água por animais sem tumor e com a aplicação de C-DotB não mostraram diferenças significativas quando comparados com animais que não receberam o nanomaterial, em um períodode 30 dias. Os exames hematológicosrealizados após 2 e 30 dias da aplicação de C-DotB, mostraram que C-DotB causouum leve aumento na quantidade de células do sistema imunedos animais que receberam C-DotB na concentração de 0,31 mg/mL e que foram monitorados por 30 dias. Os exames bioquímicos mostraram que só ocorreu aumento significativona fosfatase alcalina dos animais que receberam C-DotB na concentração de 0,16 mg/mL e monitorados por 30 dias, o qual pode estar relacionado com algum problema ósseo. As imagens obtidas das lâminas coradas com hematoxilina e eosina mostraram modificações em alguns órgãos, principalmente no pulmão onde é possível ver focos de fibrose e alvéolos coalescidos. No fígado foram encontrados focos de necrose e de inflamação. A única alteração encontrada no baço foi hiperplasia da polpa branca. Tanto no cérebro quanto nos rins não foram encontradas anormalidades. Nos tumores foi possível observado necrose e focos inflamatórios. Para observara deposição de C-DotB nos tecidos analisados, as lâminas histológicas foram analisadas em microscopia de fluorescência. Contudo, não foi possível observar nenhuma fluorescência de C-DotB, provavelmente por não ter mais partícula no animal no momento da coleta do órgão (2 e 30 dias). Com base nesses dados, C-DotB pode ser utilizado na biomedicina por ser biocompatível, possuir baixa toxicidade e ser eliminado rapidamente pelo organismo. _______________________________________________________________________________ ABSTRACT
Melanoma it is a skin cancer, which has its origins in melanocytes. Even though melanoma represents only 0.96% of new cancer cases for 2016 in Brazil, it is extremely aggressive, and because it has a high metastatic potential, it leads many patients to death. One way to avoid this high mortality is achieving an early diagnosis. Studies suggests use substances or fluorescent particles to identify cancer foci. Within these particles, carbon dots has shown a great potential for targeting cancer cells because of its fluorescence. Owing to this propriety of carbon dots, this study has the purpose to perform photophysical characterization, evaluates in vitrotoxicity and biodistribution of carbon dotscovered with boronate (C-DotB) in mices with or without melanoma. C-DotB has absorbance at ultraviolet range (above 400 nm) and emission at 460 nm when excited at 360 nm. In vitro toxicity assays were done with cell lines NIH/3T3 (murine fibroblast) and B16F10 (murine melanoma). Only exposure of 0.1 mg/mL of C-DotB resulted in significant cell death of 40 and 30% of fibroblast and melanoma. For in vivoexperiments, it was used 66 female mice C57BL/6. Body weight, food and water intake evaluations by tumor free mice and that has been applied C-DotB, did not shown significant differences with mice that did not received nanomaterial by a period of 30 days. Hematologic exams shown that C-DotB induce a slight increase in white blood cellsfor animals that received C-DotB (0.31 mg/mL) and monitored for 30 days. Biochemistry assays shown slight increaseonly in alkaline phosphatase of animals that received C-DotB (0.16 mg/mL) and monitored for 30 days, which can be correlated with bone disturbance. Images obtained from histological slices stained by hematoxylin and eosin shown alterations in some organs, mainly in lungs where it is possibly to see fibrosis focus and coalesced alveoli. Inflammatory and necrosis foci could be found at liver. The only alteration found in spleen was whit pulp hyperplasia. There were no abnormalitiesin both brain and kidney. Necrosis and inflammatory focus where found at tumors slices. To confirm C-DotB deposition at the analyzed tissues, histological slices were analyzed by fluorescence microscopy. However, it was not possibly to observe C-DotB fluorescence, probably because there were no more particles in the animals at the time of organ collected (2 and 30 days). Based on this data, C-DotB can be used in biomedicine to be biocompatible, have low toxicity and be cleared rapidly by the body.