published_or_final_version / Physics / Master / Master of Philosophy

This work has centered on the interface dipoles arising at heterojunctions between metals, semiconductor nanoparticles, self-assembled monolayers, and organic semiconductor materials. Alkanethiol self-assembled monolayers, CdSe nanocrystals, and the organic semiconductors zinc phthalocyanine (ZnPc) and Buckminster fullerene (C60) were the basis of these investigations. UV photoemission spectroscopy has proven to be an invaluable tool to observe the vacuum level shifts for these analyses while using XPS to corroborate surface structure. With a full evaluation of these surfaces, the shifts in the vacuum level, valence ionizations, and core ionizations, the impact of these interfaces, as well as their influence on the subsequent deposition of organic semiconductor layers is established.Alkanethiols possessing varying dipole moments were examined on gold and silver substrates. The viability of these alkanethiols was demonstrated to predictively adjust the work function of these metals as a function of their intrinsic dipole moments projected to surface normal, and established differences between Ag--S and Au--S bonds. The capability of the SAMs to modify the work function of gold provided an opportunity for mixed monolayers of the alkanethiols to produce a precise range of work functions by minimal adjustments of solution concentration, which were examined with a simple point dipole model.Photoemission spectroscopy offers a thorough analysis of CdSe nanoparticle films. Despite a plethora of research on these nanocrystals, there still is controversy on the magnitude of the shift in the valence band with diameter. In our research we found the majority of the valence band shift could be attributed to the interface dipole, ignored previously. Meanwhile, the valence band tethered films was obscured by the sulfur of the thiol tether.Finally, organic semiconductor layers deposited on SAMs on gold exhibited various interface dipole effects at these heterojunctions. Charge transfer states of ZnPc did not favor energy level alignment on the SAM/Au substrates used; C60 demonstrated vacuum level shifts on C15 and C12ph alkanethiol monolayers consistent with the interface charge transfer (ICT) model. These results provide credibility to models recently demonstrated in the literature for other passivated metal surfaces, and include the viability of SAMs in these discussions.

The emerging field of nanotechnology, which spans diverse areas such as nanoelectronics, medicine, chemical and pharmaceutical industries, biotechnology and computation, focuses on the development of devices whose improved performance is based on the utilization of self-assembled nanoscale components exhibiting unique properties owing to their miniaturized dimensions. The first phase in the conception of such multifunctional devices based on integrated technologies requires the study of basic principles behind the functional mechanism of nanoscale components, which could originate from individual nanoobjects or result as a collective behaviour of miniaturized unit structures. The comprehensive studies presented in this thesis encompass the mechanical, dynamical and photophysical aspects of three nanoscale systems. A newly developed europium sulfide nanocrystalline material is introduced. Advances in synthetic methods allowed for shape control of surface-functionalized EuS nanocrystals and the fabrication of multifunctional EuS-CdSe hybrid particles, whose unique structural and optical properties hold promise as useful attributes of integrated materials in developing technologies. A comprehensive study based on a new class of multifunctional nanomaterials, derived from the basic unit of barcoded metal nanorods is presented. Their chemical composition affords them the ability to undergo autonomous motion in the presence of a suitable fuel. The nature of their chemically powered self-propulsion locomotion was investigated, and plausible mechanisms for various motility modes were presented. Furthermore functionalization of striped metallic nanorods has been realized through the incorporation of chemically controlled flexible hinges displaying bendable properties. The structural aspect of the light harvesting machinery of a photosynthetic cryptophyte alga, Rhodomonas CS24, and the mobility of the antenna protein, PE545, in vivo were investigated. Information obtained through a combination of steady-state and time-resolved spectroscopy in conjunction with quantum chemical calculations aided in the elucidation of the dynamics and the mechanism of light harvesting in the multichromophoric phycobiliprotein phycocyanin PC645 in vitro. Investigation of the light-harvesting efficiency and optimization of energy transfer with respect to the structural organization of light-harvesting chromophores on the nanoscale, can provide us with fundamental information necessary for the development of synthetic light-harvesting devices capable of mimicking the efficiency of the natural system.

Title of thesis: Polymeric stabilizers maintaining the saturation solubility of itraconazole nanocrystals after dissolution process Author: Jana Kubačková Department: Pharmaceutical Technology Supervisor: PharmDr. Ondřej Holas, Ph.D. Specialized supervisor: Assoc. Prof. Leena Peltonen, Ph.D. The increase of bioavailability of poorly water soluble drugs is still an issue. One of the techniques improving aqueous drug substance solubility, and consequently enhancing bioavailability, is formation of nanoparticles. However, the bioavailability is determined by the concentration of the dissolved drug achieved at the time of absorption. This fact emphasizes the importance of the maintenance of the high solubility until the absorption area is reached. Sufficiently stabilised nanocrystalline drugs offer a solution to this problem. In this thesis, the solid nanoparticle formations of an antifungal agent itraconazole (ITZ) are presented. Wet milling was employed to create the nanosuspension stabilised by binary mixture of stabilisers or by a single stabiliser. An aggregation inhibitor Poloxamer 407 (F127) in the combination with a polymeric precipitation inhibitor hydroxypropyl methylcellulose (HPMC) or polyvinyl pyrrolidone (PVP) at different ratios, or a single precipitation inhibitor, were utilised. The...

The aim of this thesis is a study of NV centres in crystalline and nanocrystalline diamond by laser spectroscopy methods. In the theoretical part we discuss the laser spectroscopy methods, the studied material - diamond and the NV colour centres. In the experimental part we discuss the influence of nanoparticle size on luminescence spectra. We measure the luminescence of samples at room and also at low temperatures depending on the intensity and wavelength of the excitation. We study the photo-conversion of negatively charged state of NV centres to the neutral in detail. We make the time resolved measurements of the luminescence on streak camera for characterization the dynamical properties of the studied samples. The result is the comparison of lifetimes of the states in NV centres in selected samples.

Submitted in fulfillment of the academic requirements of the degree of Master of Applied Sciences in Chemistry, Durban University of Technology, Chemistry Department, Durban, South Africa, 2016. / Cellulose is a sustainable, abundant biopolymer derived from a variety of living species such as plants, animals, bacteria and some amoebas. An attractive source of cellulose for industrial uses is agricultural waste, as this use does not jeopardize food supplies and improves the local rural economy. Sugarcane bagasse (SCB) is one of the main biomass wastes from sugar production and represents 30–40 wt % of sugar production waste. In 2008, South Africa produced on average 22 million tons of sugar cane each season from 14 sugar mill supply areas which resulted in 7,9 million tons of “waste” bagasse. In this study cellulose nanocrystals were prepared from soda pulped sugarcane bagasse by acid hydrolysis followed by separation using centrifugation, ultrasonication and dialysis. Transmission Electron Microscopy (TEM) images showed nanocrystals of approximately 300 nm in length and 20 nm in width. Thermogravimetric Analysis and Differential Thermogravimetry (TGA and DTG) profiles of FD CNC, MCC and Pulped bagasse all had characteristic onset and decomposition temperatures indicating a change in the structure after chemical treatments. Particle size distribution measurements corroborated with the TEM and FE - SEM results and showed that the majority of the nanocrystals were in the 100 – 300 nm range. Attenuated Total Reflectance – Fourier Transform Infra Red (ATR - FTIR) analysis showed functional group changes as the amorphous regions of the polymer were removed revealing the ordered crystalline portions. These were further confirmed by an increase in the Lateral Orientation Index (LOI) of the samples as the nanocrystals were isolated. X - Ray Diffraction (XRD) Crystallinity Index (CrI) calculations showed a steady increase in the crystallinity of the materials from pulped bagasse to MCC to FD CNC. / M

Thesis advisor: Chia-Kuang F. Tsung / Thesis advisor: Dunwei Wang / In order to understand the lattice strain effect and its relationship to size, shape, composition, and catalytic performance, novel well-defined nanocrystal archetypes were designed and synthesized by taking advantage of wet chemical, seed-mediated (mild) reduction routes developed by our lab. First, the current synthesis challenges are addressed in creating smaller monometallic shape-controlled metal nanocrystals, and novel cuboctopods via a hybrid nanoparticle stabilizer. A look at the relationship between lattice strain and morphology is then shown in a single-component system, where still new features have been observed for the first time by the traditional technique of powder x-ray diffraction. Synthesis methods for differently strained Pd surfaces are described and catalysis by these surfaces is discussed. Finally, studies of the synthesis, characterization, electrocatalytic activity, and restructuring of novel and more sophisticated strained architectures are presented: core-island-shell nanocrystals, phase-segregated nanoboxes, island nanoframeworks, and core-sandwich-shell nanoparticles. Lattice strain and composition effects were studied in carbon monoxide, small alcohol, and formic acid electrocatalytic oxidations as well as in oxygen reduction, the latter of which, governs the commercial viability of automotive fuel cells, a sustainable energy and zero-emission technology. Here it is demonstrated how a tunable thickness of Ni sandwich layers can be used to improve catalytic performance by increasing lattice strain on the Pt surface. The sandwich archetype offers a new platform for the investigation of lattice strain and could be a promising, industrially relevant, catalyst design concept, to help address the need for a more sustainable energy future. The results help paint a new picture of catalysis by metal nanocrystals; one which brings lattice strain to the forefront of the discussion, as an important parameter for further study and for use in developing higher-performing catalysts. / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Torsten Fiebig / Thesis advisor: Mary Roberts / Understanding the electronic nature of DNA is profound and has been attempted for decades. Photoexcitation of DNA with UV light deposits electronic energy in the base stack and prepares highly reactive excited states. These states are precursors for photoinduced damage reactions which can lead to mutations and ultimately to cell death. While many DNA photo products have been isolated and characterized, the primary events immediately after photon absorption are not yet understood. Recent studies with ultrafast lasers have revealed that the majority of excess energy gained by DNA with light absorbance is dissipated on the femtosecond and picosecond time scales. In this study double-stranded oligonucleotides with different base sequences, content and lengths were systematically examined using femtosecond pump-probe spectroscopy. The results indicate that excitations in DNA are delocalized over more than two bases and the extent of the delocalization depends strongly on the structure of the investigated systems. Exciton delocalization domains in the longer duplexes are larger than in the shorter ones. Also, single-stranded oligonucleotides show smaller extent of exciton delocalization than duplexes with the same length. In addition to the fundamental studies on DNA photophysics, the properties and the structure of new molecular beacons based on thiazole orange dimers were studied. A full account of the optical and structural properties of the dimers in different base environments and orientations is presented here. Currently, the development of efficient ways to utilizing solar energy is at the forefront of the scientific community due to the ever rising demand for energy. Both, colloidal semiconductor nanocrystals and single-walled carbon nanotubes are potential alternatives to conventional inorganic and organic materials in photovoltaic devices Thorough understanding of the charge transfer and related photophysical phenomena in these systems will answer the question whether these nanomaterials can be applied in future generations of solar cells. The photoinduced electron transfer in donor-acceptor CdSe/CdTe heterostructured nanorods, in which CdTe is grown on top of CdSe in a single rod structure, was studied. The electron transfer between the two nanocrystals occurs on the subpicosecond time scale, competing with the ultrafast relaxation mechanisms in the quantum confined nanocrystals. Furthermore, investigations on how quantum confinement influences the phonon wavepackets in semiconductor nanocrystals were carried out. Quantum beats corresponding to longitudinal optical phonon modes were observed in the femtosecond pump-probe spectra of colloidal CdTe nanocrystals. Size-dependent experiments revealed that the optical phonon frequencies and the exciton-phonon coupling strength do not depend on the crystal's size. Only the wavepacket dephasing time was influenced by the diameter of the particles which was correlated with the hole relaxation to the exciton band edge. Electron donor-acceptor constructs, based on single-walled carbon nanotubes (SWNT), can be attained by noncovalent functionalization of the nanotubes with pyrene derivatives. However, charge transfer does not take place in the simplest pyrene-SWNT constructs. For the first time the pure SWNT-pyrene construct was isolated and investigated. Our results revealed that the optical properties of pyrene are drastically altered due to strong electronic interactions with the SWNT surface. In other words, aromatic molecules lose their electronic (and chemical) signature when non-covalently attached to carbon nanotubes. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

A simple bottom-up-based synthetic strategy named a solvothermal technique is introduced as the primary synthetic approach and its crystal growth mechanism is scrutinized. N-type cobalt-doped ZnO-based DMS nanocrystals are employed as a model system, and characterized by a broad spectrum of advanced microscopic and spectroscopic techniques. It is found that the self-orientation growth mechanism, imperfect oriented attachment, is intimately correlated with the high-temperature ferromagnetism via defects. The influence of processing on the magnetic properties, such as compositional variations, reaction conditions, and post-growth treatment, is also studied. In this way, an in-depth understanding of processing-structure-property interrelationships and origins of magnetism in DMS nanocrystals are obtained in light of the theoretical framework of a spin-split impurity band model. In addition, a nanoscale spinodal decomposition phase model is also briefly discussed. / Following the similar synthetic route, copper- and manganese-doped ZnO nanocrystals have been synthesized and characterized. They both show high-temperature ferromagnetism in line with the aforementioned theoretical model(s). Moreover, they display interesting exchange biasing phenomena at low temperatures, revealing the complexity of magnetic phases therein. / Spintronics (spin transport electr onics), in which both spin and charge of carriers are utilized for information processing, is believed to challenge the current microelectronics and to become the next-generation electronics. Nanostructured spintronic materials and their synthetic methodologies are of paramount importance for manufacturing future nanoscale spintronic devices. This thesis aims at studying synthesis, characterization, and magnetism of transition-metal-doped zinc oxide (ZnO) nanocrystals---a diluted magnetic semiconductor (DMS)---for potential applications in future nano-spintronics. / The crystal growth strategy demonstrated in this work not only provides a more convenient approach to directly tailor magnetic properties of advanced multifunctional spintronic materials on a nanometer scale but also contributes to a deeper insight into the microscopic origin of magnetism in wide-band-gap oxide DMSs. / Wang, Xuefeng. / "August 2007." / Adviser: J. B. Xu. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1230. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

A tuberculose (TB) ainda se apresenta como desafio para a Saúde Pública, a nível global. Essa doença negligenciada (DN) tem como tratamento de primeira escolha a rifampicina. Esse fármaco pertence à classe II, segundo o Sistema de Classificação Biofarmacêutica (SCB), apresentando baixa solubilidade em água. Tal característica constitui desafio no desenvolvimento de formas farmacêuticas eficazes e seguras. O uso de nanotecnologia tem se destacado como alternativa promissora para melhorar a solubilidade aquosa de fármacos. Nesse sentido, o presente trabalho teve como objetivo a preparação e a caracterização físico-química de nanocristais de rifampicina. A preparação dos nanocristais foi realizada empregando método de moagem de alta energia, homogeneização a alta pressão e moagem via úmida em escala reduzida. Os resultados referentes ao método de moagem de alta energia (MAE) demostraram formação de nanocristais, mas em quantidade reduzida seguida da formação de agregados (F1-M, F2-M e F3-M). A homogeneização a alta pressão (HAP) permitiu a formação de nanocristais (F1-H e F2-H). A formulação F1-H contendo o poloxâmero 188 não apresentou estabilidade após 24 horas da preparação. A F2-H obteve diâmetro hidrodinâmico médio (DHM) de 412,60 ± 4,12 nm, índice de polidispersividade igual a 0,12 ± 0,02 e potencial zeta igual a -9,94 ± 0,19 mV. A elevada concentração requerida do agente estabilizante para essa formulação foi fator limitante para o seu desenvolvimento. A moagem via úmida em escala reduzida permitiu a formação de nanocristais de rifampicina F1-MU e F2-MU, com DHM igual a 340,20 ± 5,44 nm e 364,2 ± 4,50 nm, respectivamente, e distribuição de tamanho uniforme. A avaliação do DHM, do IP e do PZ, por período de três meses, revelou a estabilidade dessas formulações. Essas formulações foram obtidas por meio de planejamento de experimentos por superfície de resposta tendo como variáreis a concentração de rifampicina, a concentração do agente estabilizante e a quantidade de esferas de zircônia. As medidas de distribuição de tamanho médio das partículas e a morfologia foram realizadas utilizando difração a laser (LD) e microscopia eletrônica de transmissão (MET), respectivamente. Adicionalmente, as avaliações empregando calorimetria exploratória diferencial (DSC) e difração de raio X (DRX) revelaram que não houve mudança na estrutura cristalina do polimorfo II de rifampicina e nem interação entre o fármaco e os excipientes. O presente trabalho permitiu a obtenção de de nanocristais de rifampicina estáveis e com solubilidade maior de até 1,92 vezes (F1-MU) e 1,66 vezes (F2-MU), em água, quando comparada à rifampicina matéria-prima. Os perfis de dissolução das formulações F1-MU e F2-MU demonstraram dissolução de 95% de rifampicina em aproximadamente 5 minutos. Esse resultado é significativamente superior àquele observado para o produto FURP-rifampicina suspensão oral 20 mg/mL que apresentou dissolução de 23,2% nesse mesmo intervalo de tempo. A avaliação da atividade antimicrobiana das nanosuspensões foi confirmada frente à rifampicina padrão por meio da determinação da sua concentração mínima inibitória. / Tuberculosis (TB) still presents a challenge for public health globally. This Neglected Tropical Disease (NTDs) has as the treatment of choice rifampicin. This drug belongs to the class II, according to Biopharmaceutics Classification System (BCS), with low water solubility. This characteristic is a challenge in the development of safe and effective dosage forms. The nanotechnology has emerged as a promising alternative to improve the aqueous solubility of drugs. Accordingly, the present work aimed to the preparation and physicochemical characterization of nanocrystals of rifampicin. The preparation of the nanocrystals was performed using high-energy ball milling method, high-pressure homogenization and wet grinding process on a small scale. The results of the high-energy ball milling method demonstrated formation of nanocrystals, but in small amounts followed by the formation of aggregates (F1-M, F2-M and F3-M). The high pressure homogenization (HPH) allowed the formation of nanocrystals (F1-H and F2-H). F1-M formulation containing Poloxamer 188 did not show stability after 24 hours preparation. F2-H obtained mean hydrodynamic diameter (DHM) of 412.60 ± 4.12 nm, polydispersity index of 0.12 ± 0.02 and zeta potential of -9.94 ± 0.19 mV. The high concentration of stabilizing agent required for this formulation was a limiting factor for the development. The wet grinding process on a small scale allowed the formation of rifampicin nanocrystal F1-MU and F2-MU with DHM of 340,20 ± 5,44 nm e 364,2 ± 4,50, respectively, and size distribution uniform. The evaluation of DHM, IP and PZ, for three months, showed stability of these formulations. These formulations were obtained by design of experiments using response surface having as variables the concentration of rifampicin, the concentration of the stabilizing agent and the amount of zirconia beads. The mean size distribution measurements of particles and morphology were performed using laser diffraction (LD) and transmission electron microscopy (TEM), respectively. Additionally, the evaluations using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) revealed that there was no change in the crystalline structure of polymorph II of rifampicin and no interaction between the drug and excipients. This study allowed obtaining stable rifampicin nanocrystals and greater solubility of up to 1.92 times (F1-MU) and 1.66 times (F2-MU) in water compared to rifampicin feedstock. The dissolution profiles of F1-MU and F2-MU formulations showed 95% dissolution of rifampicin in approximately 5 minutes. This result is significantly higher than that observed for the rifampicin-FURP oral suspension product 20 mg / ml that had Dissolving 23.2% over the same time interval. The evaluation of the antimicrobial activity of nanosuspensions was confirmed against the standard rifampicin by determining its minimum inhibitory concentration.