Dissertations / Theses on the topic 'Optical Properties - Nanocomposites'

The photoluminescent properties of silicon quantum dots embedded in a stabilizing polymer matrix are relevant to a number of potential applications of these unique nanomaterials such as drug delivery, temperature sensing, and photovoltaics. Aspects of how these photoluminescent properties change with respect to variations in such parameters as excitation intensity, polymer interactions, particle size and particle polydispersity are investigated here. Improving the photostability and understanding the nature of how this is achieved will be critical for realizing the potential of silicon quantum dots in a number of applications. Improvements in photoluminescent stability related to fluorescence intermittency, radiative lifetime, emitted intensity, and wavelength shifts are shown to be due to decreased exposure to oxygen, increased particle packing, decreased temperature, and increased monodispersity of the quantum dots.

Main aim of this work was the fabrication and characterization of polymeric TiO2 hybrid nanocomposites. When dispersed at the nanoscale level, TiO2 can tune the optical properties of the polymeric matrix, such as the UV absorption and the increase of refractive index, preserving the transparency in the visible and the flexibility of the polymer. TiO2 nanopaticles were modified on the surface with different molecules; they were then dispersed in MMA and polymerized in bulk, in order to obtain optically transparent TiO2/Poly-methylmethacrylate (PMMA) sheets. The application of these objects was in the solid-state lighting field, where the nanoparticles play the role of light diffusers according to Rayleigh Scattering. Films based on poly 2-ethyl-2-oxazoline (PEOX) and TiO2 nanoparticles with concentrations up to 44 % in weight were also prepared by casting from water solutions. Nanocomposites films remained highly transparent in the visible, and absorbed UV radiation up to the proximity of the visible range. The refractive indices of the films raised from about 1.52 to 1.65 with increasing of TiO2 concentration. The good optical properties and the solubility in water of these materials could allow their application in the paint and coating industry, and in the field of conservation of cultural heritage as consolidants or varnishes of paintings.

Clusters are aggregates composed of a countable number of atoms or molecules, starting with the dimer and reaching, with a vaguely defined upper bound of several hundred thousand atoms, into that interesting size range. Clusters have properties that are different from both atoms and bulk materials as in these small aggregates the surface-to-volume ratio is very large and hence the surface atoms, play a dominant role compared to the bulk ones. By assembling preformed clusters, one can build nanostructured materials. These can be divided in two main categories: cluster assembled films and nanocomposites. In the former case nanoparticles are deposited on a substrate in the latter they are incorporated in a matrix, a polymer for instance. Nanostructured materials offer exciting pathway for the construction of macroscopic materials with designer-specified optical, electrical, and catalytic properties which reflect the ones of their building blocks. The object of this thesis is the study of the optical and electrical properties of metal-polymer nanocomposites (MPNs) in response to mechanical deformation. Reflectance of MPNs is also exploited to develop reflective and bendable diffracting gratings which can be adapted to concave surfaces in order to add focusing power to the diffracting one. A further study regards the evolution of the electrical resistance during the growing of the nanostructured materials on different substrates. Then, the electrical properties of the systems in response to a voltage applied are explored, to find if peculiar phenomena such as resistance switching could occur. Recipes to fabricate robust and reproducible devices which exhibit controllable resistance switching were developed, both for cluster-assembled thin films and MPNs; in this latter case the possibility of controlling the switching activity with mechanical bending is demonstrated as well.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Nanocompósitos são materiais que combinam duas (ou mais) fases sólidas, uma das quais deve possuir dimensões nanométricas, que pode reunir em um único material várias propriedades melhoradas para uma dada aplicação e, portanto, podem permitir a coexistência de propriedades tradicionalmente antagônicas como, transparência e condutividade. O presente trabalho teve como objetivo a obtenção de um nanocompósito polimérico transparente e condutor de polimetilmetacrilato – PMMA com nanofitas do sistema Indium Tin Oxide – ITO. Para isto primeiramente estudou-se a influência da temperatura na síntese das nanoestruturas de ITO e depois de obtida a temperatura de síntese que proporcionou o crescimento de nanofitas de ITO com maior condutividade e maior transparência no espectro visível, estudou-se a influência da inserção destas nanofitas nas propriedades ópticas e elétricas de filmes nanocompósitos de PMMA. Como as nanofitas obtidas são emaranhadas, para a obtenção do nanocompósito foi realizada uma separação prévia das mesmas utilizando duas dispersões distintas: sendo a primeira em um ultrasom convencional e a segunda em uma ponta ultrasônica. Depois de dispersas, as nanofitas foram misturadas ao PMMA comercial dissolvido em concentrações mássicas de 1%, 2%, 5% e 10% de nanofitas. As soluções foram então depositadas sobre substrato de vidro e, depois de secos, os filmes foram destacados. As caracterizações ópticas mostraram que a transmitância no espectro visível dos filmes diminui em função do aumento da quantidade de nanofitas no compósito. Neste estudo, as caracterizações elétricas mostraram que ocorreu percolação das nanofitas no polímero após a inserção de 5% em massa de nanofitas. As imagens de MET para os filmes corroboraram os resultados previstos pelas caracterizações elétricas. Os filmes...
Nanocomposites are materials which have two or more solid phases, and one of these phases should be in nano-sized scale range. These materials can have several properties increased for special application and it is possible to obtain composites with traditionally antagonistic combinations of properties, such as transparence in the visible range of light and good conductivity. The main goal of this work is obtain a transparent and conductive polymer-based nanocomposite using polymethylmethacrylate – PMMA and ITO (Indium Tin Oxide) nanobelts. To reach this goal it was first studied the influence of temperature on the synthesis of nanostructured ITO. Once the temperature of synthesis was optimized to ensure the growth of ITO nanobelts with both good conductivity and good transparency in the visible spectrum, we studied the influence of ITO nanobelts on the electrical and optical properties of nanocomposites of PMMA. Because the synthesized nanobelts are entangled each other, to obtain the composite it was realized a separation of them using two different ways; first using a conventional ultrasound and after an ultrasonic tip. Then, nanobelts were mixed with commercial PMMA dissolved in THF 10% in mass concentrations of 1%, 2%, 5% and 10%. So, the solution was deposited over a glass substrate by casting. The results showed that films transmittance in visible range decreases by increasing the amount of nanobelts. The electrical characterization showed that percolation occurred after 5%wt of filler. TEM images of composites corroborate the results provided by the electrical measures. The films prepared using both dispersions had the same transmittance in the visible spectrum, despite of the films obtained by dispersing the nanobelts in ultrasonic tip had a lower electrical resistance. Thus it can be concluded that the dispersion by ultrasonic... (Summary complete electronic access click below)

Orientador: Marcelo Ornaghi Orlandi
Banca: Walter Katsumi Sakamoto
Banca: Emerson Rodrigues de Camargo
Resumo: Nanocompósitos são materiais que combinam duas (ou mais) fases sólidas, uma das quais deve possuir dimensões nanométricas, que pode reunir em um único material várias propriedades melhoradas para uma dada aplicação e, portanto, podem permitir a coexistência de propriedades tradicionalmente antagônicas como, transparência e condutividade. O presente trabalho teve como objetivo a obtenção de um nanocompósito polimérico transparente e condutor de polimetilmetacrilato - PMMA com nanofitas do sistema Indium Tin Oxide - ITO. Para isto primeiramente estudou-se a influência da temperatura na síntese das nanoestruturas de ITO e depois de obtida a temperatura de síntese que proporcionou o crescimento de nanofitas de ITO com maior condutividade e maior transparência no espectro visível, estudou-se a influência da inserção destas nanofitas nas propriedades ópticas e elétricas de filmes nanocompósitos de PMMA. Como as nanofitas obtidas são emaranhadas, para a obtenção do nanocompósito foi realizada uma separação prévia das mesmas utilizando duas dispersões distintas: sendo a primeira em um ultrasom convencional e a segunda em uma ponta ultrasônica. Depois de dispersas, as nanofitas foram misturadas ao PMMA comercial dissolvido em concentrações mássicas de 1%, 2%, 5% e 10% de nanofitas. As soluções foram então depositadas sobre substrato de vidro e, depois de secos, os filmes foram destacados. As caracterizações ópticas mostraram que a transmitância no espectro visível dos filmes diminui em função do aumento da quantidade de nanofitas no compósito. Neste estudo, as caracterizações elétricas mostraram que ocorreu percolação das nanofitas no polímero após a inserção de 5% em massa de nanofitas. As imagens de MET para os filmes corroboraram os resultados previstos pelas caracterizações elétricas. Os filmes... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Nanocomposites are materials which have two or more solid phases, and one of these phases should be in nano-sized scale range. These materials can have several properties increased for special application and it is possible to obtain composites with traditionally antagonistic combinations of properties, such as transparence in the visible range of light and good conductivity. The main goal of this work is obtain a transparent and conductive polymer-based nanocomposite using polymethylmethacrylate - PMMA and ITO (Indium Tin Oxide) nanobelts. To reach this goal it was first studied the influence of temperature on the synthesis of nanostructured ITO. Once the temperature of synthesis was optimized to ensure the growth of ITO nanobelts with both good conductivity and good transparency in the visible spectrum, we studied the influence of ITO nanobelts on the electrical and optical properties of nanocomposites of PMMA. Because the synthesized nanobelts are entangled each other, to obtain the composite it was realized a separation of them using two different ways; first using a conventional ultrasound and after an ultrasonic tip. Then, nanobelts were mixed with commercial PMMA dissolved in THF 10% in mass concentrations of 1%, 2%, 5% and 10%. So, the solution was deposited over a glass substrate by casting. The results showed that films transmittance in visible range decreases by increasing the amount of nanobelts. The electrical characterization showed that percolation occurred after 5%wt of filler. TEM images of composites corroborate the results provided by the electrical measures. The films prepared using both dispersions had the same transmittance in the visible spectrum, despite of the films obtained by dispersing the nanobelts in ultrasonic tip had a lower electrical resistance. Thus it can be concluded that the dispersion by ultrasonic... (Summary complete electronic access click below)
Mestre

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.
Title from PDF t.p. (viewed Feb. 3, 2010). Additional advisors: Derrick R. Dean, Sergey B. Mirov, Sergey Vyazovkin, Mary Ellen Zvanut. Includes bibliographical references (p. 122-145).

Les matériaux composites peuvent présenter des propriétés qu'aucun des composants individuels ne présente. En outre, à l'échelle du nanomètre les nanocomposites peuvent présenter de nouvelles propriétés par rapport à l'état massif ou à des macrocomposites des mêmes composants en raison d’effets de confinement et d’effets quantiques liés à la taille. Les nanocomposites semi-conducteur/métal sont très intéressants en raison de leurs uniques propriétés catalytiques et opto-électroniques et la possibilité de les ajuster facilement. Ce travail de thèse étudie les interactions spécifiques et les propriétés physiques qui se manifestent dans les films minces de ZnO et nanocomposites ZnO-Au synthétisés par pulvérisation magnétron réactive continue. Premièrement, il est observé qu’il est possible d'ajuster les propriétés microstructurales et optiques des couches de ZnO en réglant les paramètres expérimentaux. La croissance épitaxiale de ZnO sur saphir a été réalisée pour la première fois dans des conditions riches en oxygène sans assistance thermique. En outre, une étude des propriétés optiques met en évidence la relation étroite entre les propriétés optiques et de la chimie des défauts dans les couches minces de ZnO. Un modèle a été proposé pour expliquer la grande dispersion des valeurs de gap rencontrées dans la littérature. Deuxièmement, il a été possible de révéler l'influence profonde de l'incorporation de l'or dans la matrice de ZnO sur des propriétés importantes dans des films nanocomposites. En outre, la présence de défauts donneurs (accepteurs) au sein de la matrice ZnO se permet de réduire (oxyder) les nanoparticules d’or. Ce travail de recherche contribue à une meilleure compréhension des nanocomposites semi-conducteurs/métal et révèle le rôle important de l'état de la matrice semi-conductrice et de la surface des particules pour les propriétés finales du matériau
Composite materials can exhibit properties that none of the individual components show. Moreover, composites at the nanoscale can present new properties compared to the bulk state or to macro-composites due to confinement and quantum size effects. The semiconductor/metal nanocomposites are highly interesting due to their unique catalytic and optoelectronic properties and the possibility to tune them easily. This PhD work gives insight into the specific interactions and resulting physical properties occurring in ZnO and ZnO-Au nanocomposite films grown by reactive DC magnetron sputtering. The results can be summarized in two points: First, it was possible to tune the microstructural and optical properties of ZnO. Epitaxial growth of ZnO onto sapphire was achieved for the first time in O2-rich conditions without thermal assistance. Also, a study of the optical properties highlights the close relationship between the bandgap energy (E_g ) and the defect chemistry in ZnO films. A model was proposed to explain the large scatter of the E_g values reported in the literature. Second, the deep influence of the incorporation of gold into the ZnO matrix on important material properties was revealed. Moreover, the presence of donor (acceptor) defects in the matrix is found to give rise to the reduction (oxidation) of the Au nanoparticles. This research work contributes to a better understanding of semiconductor/metal nanocomposites revealing the key role of the state of the semiconductor matrix

Mestrado em Ciência e Engenharia de Materiais
O principal objectivo desta dissertação foi estudar novas perspectivas na preparação de nanocompósitos de matriz polimérica, através da síntese e caracterização de nanomateriais do tipo SiO2/ polímero e CdS/ polímero. O primeiro capítulo consiste numa revisão bibliográfica, com destaque para os principais tópicos discutidos ao longo da tese. São efectuadas algumas considerações sobre a utilização de nanopartículas inorgânicas como cargas, e sobre os aspectos mais relevantes da aplicação de polímeros como matrizes. São ainda descritas, algumas estratégias utilizadas para compatibilizar estes componentes. A revisão é concluída com uma breve descrição das metodologias aplicadas na preparação de nanocompósitos de matriz polimérica. No segundo capítulo apresenta-se a síntese e caracterização das cargas inorgânicas. Seguindo métodos descritos na literatura, foram preparadas nanopartículas de SiO2, esféricas e sob a forma de fibras ocas, nanocristais de CdS e compósitos inorgânicos do tipo SiO2@CdS. Estes últimos, foram sujeitos a um tratamento superficial orgânico com TOPO e ainda com SiO2. Para os materiais tratados com TOPO verificou-se uma melhoria das suas propriedades ópticas, nomeadamente ao nível da fotoluminescência à temperatura ambiente. No terceiro e quarto capítulos, são apresentados os nanocompósitos do tipo SiO2/ polímero, que foram sintetizados por polimerização in situ de matrizes semicristalinas (poliamidas e poliuretanos), e amorfas (poli(estireno)). A sua caracterização foi efectuada por espectroscopia de IV, SEM, TEM, TGA e DSC. Os nanocompósitos de matriz semicristalina foram preparados por polimerização por etapas. No caso das poliamidas, foi investigada a influência das cargas de SiO2 com diferentes morfologias e tratamentos de superfície, no processos de fusão e cristalização da matriz. Os materiais de matriz amorfa foram preparados por polimerização radicalar em emulsão e dispersão. Neste caso o estudo incidiu sobre a morfologia das partículas dos nanocompósitos, nas possíveis condições experimentais que a determinam e na influência destas sobre as propriedades térmicas do nanocompósito. Por fim descreve-se no quinto capítulo a síntese e caracterização dos nanocompósitos do tipo CdS/ polímero. Estes materiais foram preparados por polimerização radicalar em solução, na presença de nanocristais de CdS, e compósitos inorgânicos do tipo SiO2@CdS. A inserção das cargas na matriz promoveu as suas propriedades de fotoluminescência à temperatura ambiente. Foram ainda avaliadas as propriedades térmicas de algumas amostras representativas. Neste trabalho foram preparados uma série de novos nanocompósitos de matriz polimérica, que fazem antever futuras aplicações tecnológicas. Foram ainda estabelecidos novos caminhos para a compreensão dos mecanismos de formação de materiais híbridos, e das interacções que ocorrem ao nível das interfaces de natureza orgânica/ inorgânica.
The aim of this thesis was to study new methods for the preparation of polymer based nanocomposites, through the synthesis and characterisation of SiO2/polymer and CdS/ polymer nanomaterials. The first chapter consists in an introduction to the aim topics that are discussed in the thesis as well as a literature review. Some considerations are made regarding the use of inorganic nanoparticles as fillers, and to the methods used to modify the inorganic materials surface in order to make them more compatible with the organic nature of polymeric matrices. In this introduction some relevant aspects of the use of polymers as matrices are reported, and a brief review of the polymerisation methods to be used in the nanocomposites preparation is given. The second chapter is devoted to the preparation and characterisation of the fillers. Following methods previously described on the literature, SiO2 nanoparticles with spherical and hollow fibres morphologies, CdS nanocristalites and SiO2@CdS inorganic composites were prepared. The last were organically treated with TOPO and also with SiO2. It was concluded that the TOPO capping results in improved room temperature photoluminescence properties. In the third and fourth chapters, the synthesis and characterisation of SiO2/ polymer nanocomposites is discussed. Using several in situ polymerisation techniques semi-crystalline (polyurethanes and polyamides) and amorphous (poly(styrene)) matrices were prepared. The materials were characterised by FTIR spectroscopy, TEM and SEM, TGA and DSC analysis. The semicrystalline polymeric matrix nanocomposites were prepared by steppolymerisation. In the case of the polyamide based nanocomposites the influence of the SIO2 nanoparticles on the melting and crystallization behaviour of the matrices is discussed. As regards the amorphous matrix nanocomposites these were prepared by radical emulsion and dispersion polymerisation. The morphology of the nanocomposite particles is discussed in light of changes in experimental conditions, and its possible influence on thermal properties. Finally, the chapter five is concerned with CdS/ polymer nanocomposites prepared by in situ polymerisation in the presence of CdS nanocrystals, and SiO2@CdS inorganic composites. TOPO capping results in higher affinity of the fillers to the matrix, and its insertion on the matrices promotes their optical properties, namely room temperature photoluminescence. The thermal properties of some representative samples were also studied. In this work a wide range of novel polymer based nanocomposites were prepared. This study showed that nanomaterials have unique properties that can anticipate potential technologic applications. Furthermore, new routes have been opened to the understanding of the mechanisms of nanocomposites formation, as well as the nature of interactions between organic/ inorganic interfaces.

Liquid crystals (LCs) are an interesting class of materials that are attracting significant attention due to their ever-growing applications in a wide variety of fields such as liquid crystal display (LCD) technology, materials science and bioscience. In recent years, along with the developments of materials at the nanoscale, doping LCs with nanoparticles (NPs) has emerged as a very promising approach for improving LC properties. Nanoparticle additives can introduce novel effects on optical and electro-optical properties of nematic liquid crystals (N-LCs), such as altered molecular alignment, faster response time and increased efficiency. This thesis studies the impacts that the inclusion of metallic NPs made of gold or semiconductor CdSe quantum dots (QDs), have on optical and electro-optical properties of N-LCs. Using polarized optical microscopy and detailed capacitance and transmittance measurements of nematic mixtures in electro-optic test cells, characteristics such as optical texture, phase transition temperatures, switching voltages and dielectric anisotropy are investigated in pure as well as doped samples. Surface ligands in NPs and their chemical functionalization play an important role in the LC-NP interactions, largely by determining the dispersibility of NPs and stability of the nanocomposites. One important objective of this thesis is to investigate and prepare a series of gold nanoparticles (Au NPs) with specially formulated robust coatings that maximizes solubility and stability in LC medium. Silanization of NPs is developed as a method to overcome the stability challenge. The functionalization of silanized NPs with aliphatic ligands or liquid crystalline molecules, provides chemically and thermally stable NPs with hydrophobic and structurally compatible surfaces required for dispersion in N-LCs. After complete characterization the synthesized particles are used to make the new nematic nanocomposites. By analysis of the structure-property relationships governing LC-nanomaterial composites and by comparison of new results and data from previous studies on other types of NPs, this thesis will further reveal the mechanism of the interrelations between host LC molecules and NP, considering the role of variables such as core composition, size and surface chemistry of NPs (e.g. siloxane shell, aliphatic ligand vs. liquid crystalline ligand) in achieving stable LC composites with desired optical and electro-optical properties.

Today’s electronic society relies on the functionality of electrical contacts. To achieve good contact properties, surface coatings are normally applied. Such coatings should ideally fulfill a combination of different properties, like high electrical conductivity, high corrosion resistance, high wear resistance and low cost. A common coating strategy is to use noble metals since these do not form insulating surface oxides. However, such coatings are expensive, have poor wear resistance and they are often applied by electroplating, which poses environmental and human health hazards. In this thesis, nanocomposite carbide-based coatings were studied and the aim was to evaluate if they could exhibit properties that were suitable for electrical contacts. Coatings in the Cr-C, Cr-C-Ag and Nb-C systems were deposited by magnetron sputtering using research-based equipment as well as industrial-based equipment designed for high-volume production. To achieve the aim, the microstructure and composition of the coatings were characterized, whereas mechanical, tribological, electrical, electrochemical and optical properties were evaluated. A method to optically measure the amount of carbon was developed. In the Cr-C system, a variety of deposition conditions were explored and amorphous carbide/amorphous carbon (a-C) nanocomposite coatings could be obtained at substrate temperatures up to 500 °C. The amount of a-C was highly dependent on the total carbon content. By co-sputtering with Ag, coatings comprising an amorphous carbide/carbon matrix, with embedded Ag nanoclusters, were obtained. Large numbers of Ag nanoparticles were also found on the surfaces. In the Nb-C system, nanocrystalline carbide/a-C coatings could be deposited. It was found that the nanocomposite coatings formed very thin passive films, consisting of both oxide and a-C. The Cr-C coatings exhibited low hardness and low-friction properties. In electrochemical experiments, the Cr-C coatings exhibited high oxidation resistance. For the Cr-C-Ag coatings, the Ag nanoparticles oxidized at much lower potentials than bulk Ag. Overall, electrical contact resistances for optimized samples were close to noble metal references at low contact load. Thus, the studied coatings were found to have properties that make them suitable for electrical contact applications.

Metal-polymer nanocomposite materials were found to have highly tunable opti- cal properties. Density functional theory-based calculations were employed to study trends in Ag/polyvinylidene fluoride nanocomposite optical properties. The frequency- dependent imaginary part of the dielectric constant was calculated from dipolar inter- band transitions. The metallic inclusion introduced both occupied and unoccupied states into the large polymer band gap. Thus, higher inclusion volume fractions generally led to stronger composite optical response. Spectra from monodisperse sys- tems correlated well with nanoparticle quantum confinement models. A polydisperse system exhibited optical properties that correlated best with interparticle distances along the field direction. Nanodisk and nanorod-shaped inclusions had tunable re- sponse from field polarization, aspect ratio, crystallographic projections, and nanorod end-cap morphology.
Graduate
0495

碩士
南臺科技大學
機械工程系
107
Massive production of graphene is synthesized by a low-cost electro-chemically exfoliated approach and then incorporated with γ-alumina for developing a novel composite ink, graphene/γ-alumina ink. It is coated onto single-side of the glass by spraying with an adiabatic closed system as the thermal and optical barriers for the energy efficient glass of the business buildings. The coating thickness of graphene/γ-alumina layer is around 2~3μm detected by scanning electron microscope. The temperature in an adiabatic closed system and the temperatures of the glass are measured with a heat source by lamp radiation. The temperature difference between inside and outside of the closed adiabatic system can achieve around 20ºC after thermal radiation test for 15 hours. 0.1wt% of graphene in NMP (N-Methyl-2-pyrrolidone) incorporated with 1wt% of γ-alumina in NMP has the optimal effect of good transmittance and heat flux reduction. The transmittance is adjustable from 5.57% ~ 81% at 550 nm wavelength, depending on the composition and content of graphene and γ-alumina. Electro-chemically exfoliated graphene (ECG) and γ-alumina are also good absorbents for UV absorbance. According to the relationship between transmittance and temperature difference through the thermal radiation experiment, the temperature difference between the inside and outside of the coating in the adiabatic closed system gradually decrease with 1wt% of γ-alumina incorporated with different concentrations of 0.03wt%, 0.1wt%, 0.3wt% of electro-chemically exfoliated graphene and the temperature difference is approaching to a constant with transmittance decrease.

碩士
元智大學
化學工程與材料科學學系
96
To prepare the diffuser film with high haze and transmittance, the diffuser particle and nanoparticle are blended with PMMA solution and spin coated onto the glass substrate. The formulation of diffuser film for the optimum optical properties is studied in this research using experimental Taguchi method. Usually, the required haze and transmittance for the diffuser film are about 85%. Though the higher transmittance is preferred, but the haze decreases with increasing transmittance. The target to achieve in this study is to enhance the transmittance of diffuser film and to keep the haze. The various particle sizes of nanoparticles are prepared with hydrophobic surface modification by microwave-assisted emulsion polymerization. The optical properties of spin coated film are measured along with microscopic morphology of particle distribution in the diffuser film. The results reveal that the obtained diffuser film possesses optimum optical properties of 87% haze and 90% transmittance.

博士
國立中山大學
材料與光電科學學系研究所
106
This study is mainly focused on the optical properties of Al-based thin film metallic glasses (TFMGs) and thin film metallic glasses nanocomposite (TFMGCs). The mechanical properties and the antimicrobial activities were also examined. Finally, these films are applied as the high optical reflective films with outstanding antimicrobial and antifungal responses in the newly developed UV-LED exposure system. The elements of Al-based TFMGs and TFMGCs used in this study include aluminum (Al), nickel (Ni), and yttrium (Y). The magnetron co-sputtering is adopted to fabricate the films on silicon or glass substrate. In this research, various Al-Ni-Y films are firstly synthesized with different compositions and under different process conditions, in order to reach the optimum process and high optical reflectivity performance. Next, the antimicrobial and antifungal responses of such films are explored and rated. In order to determine the antimicrobial activities, the P. aeruginosa, E. coli and S. aureus were selected. Finally, the films with both high reflectivity and antimicrobial/antifungal properties are applied in the novel ultraviolet UV-LED exposure system. In comparison with commercial pure Al and Ag thin film coatings for high optical reflection applications, the current Al-based TFMGs and TFMGCs are demonstrated to possess a better combination of mechanical and optical properties.

Ferroelectric materials are widely used in capacitors, actuators, non-volatile memory, electro-optic materials for data storage applications and thermistors. In recent years ferroelectrics with narrow bandgap offer tremendous scope for applications in the field of photocatalysis and photovoltaics because of their efficient ferroelectric polarization-driven carrier separation which in principle can lead to better photocatalytic activity compared to conventional semiconducting oxides. However, the efficiency reported so far for conventional ferroelectrics is still too low to be considered for practical application due to wide band gap (>3 eV) of these materials. The invention of visible light absorbing semiconducting ferroelectric oxide (1-x)KNbO3-x(BaNi12Nb12O3−δ) (KBNNO) by Grinberg et al. augmented global research activity in the area of semiconducting ferroelectric. However, the synthesis of KBNNO by solid state route, require high calcination temperature (850oC) and sintering at further higher temperature (1100oC). Due to this prolonged heat treatment at high temperature, potassium volatizes which results in non-stoichiometry may have an adverse effect on densification, dielectric and optical properties. Very few reports are available on the effect of dopants on structural, electrical and optical properties. Hence, a systematic study of the effect of suitable dopant atoms in such oxide perovskite would throw light on the structure-band gap microstructure-electronic property relationship in these materials which is one of the objectives of the present work. In addition to band gap of a photocatalyst, particle size and particle morphology also have an important role on the photocatalytic activity of oxide semiconductor. Furthermore, it will be interesting to study the synthesis of KBNNO at significant lower temperature compared to solid state method. There are no reports available on the detailed study of photocatalytic mechanism in KBNNO. Coupling of narrowband gap oxide semiconductors with conventional ferroelectrics, photocatalytic efficiency can be enhanced further by preventing the charge carriers from rapid recombination and increase in visible light activity. However, there are no reports available on the formation of heterojunction composite with KBNNO. The purpose of this proposed work is focused on the preparation of KNbO3, KNb1- x/2Ni x/2O3-δ (KNNO), [KNbO3]1-x[BaNb1/2Ni1/2]xO3-δ (KBNNO) (x = 0.05, 0.1, 0.15 and 0.2) visible light absorbing ferroelectric perovskite through solid state method and characterization of their structural, dielectric, ferroelectric, electrical, optical and photocatalytic properties. XRD and Raman spectroscopy confirm the orthorhombic structure in synthesized ceramics. Ni substitution in KNbO3 showed appearance of absorption peaks in visible region. Furthermore, a shifting in absorption edge to higher wavelength was observed for Ba, Ni co-doped KNbO3. Raman spectroscopy shows weakening of long range polar order with increase in Ba-Ni doping (x>0.1). FESEM micrographs show the drastic reduction in grain size in KBNNO ceramics. Ni doping shifted the Curie temperature slightly towards the room temperature and in Ba, Ni co-doped samples, a broad hump can be observed around phase transition. From Impedance spectroscopy, the decrease in conductivity of Ba, Ni modified KNbO3 compared to Ni-doped KNbO3 may be due to the reduction of oxygen vacancies created by acceptor doping (Ni+2) in KNbO3 which in turn led to better photocatalytic activity for KBNNO ceramics. Raman, P-E hysteresis, PL, Impedance spectroscopy indicate optimum dopant concentration that is necessary to get visible absorption with retention of ferroelectricity and better photocatalytic activity in KBNNO. These results are useful in the understanding of phase evolution, bandgap tunability, electrical conductivity and photocatalysis in KNbO3 and show the potential of such materials in photocatalysis and photovoltaic application. In order to reduce the phase formation temperature and to prepare nano structured KBNNO ceramics, solution combustion method was explored. (1-x)KNbO3-x(BaNi12Nb12O3−δ) (x = 0, 0.05, 0.1, 0.15 and 0.2) ceramics were successfully synthesized at low temperature using citrate-nitrate solution combustion method at 600oC. The fuel-to-oxidizer ratio (Φe) (0.6–1.0) has significant effect on the combustion process and phase evolution. TEM micrograph of KBNNO 0.1 shows that the particles are in nano meter range and the average particle size is around 17 nm. Raman and P-E loop indicate polar structure and photoluminescence spectroscopy displays the lowest electron-hole recombination, in KBNNO 0.1 and this may be the reason for the best photocatalytic activity. The rate constant of KBNNO 0.1 for RhB degradation is 3.17 times and 1.4 times higher than KNbO3 and P25 (commercial TiO2 based photocatalyst), respectively under similar visible light illumination. The mechanism behind photocatalytic activity and photo-stability have also been studied for the best composition. In order to further reduce the phase formation temperature and to make oriented nanostructure (nanorods/nano wires), hydrothermal method was explored. Phase pure KBNNO 0.1 were successfully synthesized via hydrothermal method at 200oC. In hydrothermal synthesis of KBNNO 0.1, the effect of KOH concentration (1M-18M) and the effect of reaction time (30min-12h) on phase evolution and powder morphology were investigated. We found that to get complete phase purity atleast 10M KOH concentration and 12h soaking time were required. The Powder morphology varies from spherical to irregular shape, to rod like nature, to cube shape when KOH concentration of the starting solution in the range of 4-6M, 8-12M and 14-18M, respectively. However, its photocatalytic properties are poorer compared to combustion derived samples and comparable to that of solid state samples. To further enhance the photocatalytic property of KBNNO 0.1, nanostructured ferroelectric/conventional semiconductor heterostructure (KBNNO-Ag2O and KBNNO-Bi2O3) has been explored. In context, a series of KBNNO-Ag2O/Bi2O3 composites with varying weight ratios (75:25, 50:50 and 25:75) by a simple precipitation technique/solid state method. Preparation method and processing temperature have significant effect on phase stability and interface formation for KBNNO-Ag2O/Bi2O3 composites. UV-Vis spectroscopy shows that the synthesized composites exhibited higher visible light absorption and PL spectroscopy indicates reduced recombination time of charge carriers than the parent materials. Photocatalytic studies shows that KBNNO:Ag2O (50:50) composite sample can completely mineralize the dye within 25 min. However, the best composition for KBNNO:Bi2O3 (25:75) can completely mineralize RhB in 45 min. Radical trapping experiment shows that O2− , h+ and .OH are the major reactive species helping in mineralization of RhB in KBNNO:Bi2O3 system and h+ and O2− are the major reactive species in KBNNO:Ag2O (50:50) system. The significant absorption in visible region and reduced recombination time of charge carriers in the composite than the parent materials were responsible for excellent photocatalytic properties. The mechanism for degradation was also studied in detail. Moreover, a reasonable degradation of 95% (on an average) was observed after 5 cycles, suggesting a good photocatalytic stability of the composites. Ag nanoparticle dispersed orthorhombic KBNNO are synthesized by photoreduction method. The photoreactivity of Ag/KBNNO nanocomposites as a function of Ag content (0.5-4 wt%) is studied toward aqueous rhodamine B degradation under visible light. The photocatalytic degradation of RhB under visible light irradiation indicates that 3wt% Ag-KBNNO has the highest rate of degradation (0.056 min-1) and can completely mineralize RhB in 60 min. However, the rate constant and degradation time is much lower than the best composition of KBNNO/Ag2O (50:50) which are 0.113 min-1 and 25 min respectively. In Ag-KBNNO, radical trapping experiments show that O2− and .OH are the major reactive species involved in photodegradation of RhB.

碩士
中原大學
化學研究所
94
In this study, we applied the natural clay mineral, Montmorillonite, which aspect ratio is about 100 ~ 150 with the thickness of approximately 1 nm. The interaction between the gallery of clay is ionic bonds, which construct the layer stacking together to form a micrometer particle. The modified agent, 2-undecyl-1H-imidazole-1-propiononitrile, C11Z-CN, which is a carbon long chain with the cycloalkenes, was intercalated into the clay layers and increased the compatibility of the interface between the clay and liquid crystal. The properties were characterized by XRD, FT-IR, TGA, DSC and POM. In this work, we reported a new type of organic–inorganic hybrid nanocomposite, comprised by the nematic liquid-crystal and nanoscale montmorillonite. The electro-optical effects were discussed such as the voltage- transmittance, voltage-capacitance and time-transmittance curves, which explain the charge-retention effect under the application of dc bias voltage in antiparallel-aligned cells. Polymer dispersed liquid crystal (PDLC) doped with clay, which were fabricated by photo-polymerization with liquid crystal and monomers under UV-curing, characterized by different curing power and frequency under ac bias voltage for the electro-optical properties. We also studied on the holography of PDLC doped with clay. There are two coherent Ar+ laser interfering on the sample to form the interference field of the spatially periodic distribution. The effects of the incident writing angles, light intensity of incident laser beams and doped the small amount of clay on the diffraction efficiencies and morphology were investigated.

碩士
國立臺灣科技大學
材料科學與工程系
106
Nanomaterials have numerous commercial and technological applications in chemical, biomedical, optoelectronics, electronics and space industries. Once nanomaterials are released into the environment via manufacturing, use or disposal, their transport is the critical parameter in assessing their exposure and impact on the public health and the ecosystem, therefore understanding the fate of nanomaterials in the environment is critical. This research goal aims at developing nanomaterials derived from natural resources, both reinforcement and matrix are biobased and biodegradable. Cellulose nanofibers from wood, plants and agricultural by-products is an abundant renewable resources. The fabrication of cellulose based-nanocomposite film without affecting the optical, mechanical and thermal properties of cellulose triacetate (CTA), one of the most widely used polymers, and cellulose nanofiber (CNF), which represent the world’s most abundant bio-based nanofiller, is investigated. In this study, using recycled the polarizers industrial CTA film waste – recycled triacetate cellulose (rTAC), the conventional waste disposal could be improved for the environmental issues. Furthermore, the reinforcement from the raw material, which was the extraction of nanofibers consisted of sudachi residue (lemon peel) after juice extraction. Cellulose nanofiber suspension was solvent-exchanged with acetone-methanol by series of centrifuging and re-dispersing steps. After that, using the solution casting method including the mixture of rTAC film and nanofibers that was prepared by stirring in combination with ball milling technique to achieve full dispersed solution, was coated on the glass to obtain a thin film. And for comparative purposes, industrial cellulose nanofiber (OJI-CNF) in its pristine form, is also reported. The structure of nanofibers and the dispersion effect of both CNFs in TAC were observed by scanning electron micrograph (SEM) and transmission electron microscopy (TEM). The optical, mechanical and thermal properties of the nanocomposite films were characterized experimentally. The results showed that by varying nanofiber contents (1~7wt%), the haze was slightly increased while the transmittance was not be affected compared to that of rTAC film (92.7%). On the other hand, OJI-CNF showed a lower transparency significantly when increasing nanofiber contents, compared to lemon peel-CNF, indicated that the poor dispersion due to the aggregates of OJI-CNF in solution. It was found that the addition of CNFs increased the tensile stress by 60%; the tensile strain by 150% and the yield stress by 50%. The dynamic mechanical properties (creep behavior) results were also positive; the creep compliance improved for all nanocomposites compared to rTAC film. These both nanofibers contributed to a significant reduction in the thermal expansion properties of rTAC film while maintaining their ease of bending.

The design of efficient and stable solar selective coatings for Concentrating Solar Power (CSP) central receivers requires a comprehensive knowledge about the incorporated materials. In this work solar selective coatings were grown by filtered cathodic vacuum arc (FCVA) deposition. The complete stacks consist of an infrared reflection layer, an absorber layer of C:ZrC nanocomposites and an antireflection layer. The Carbon-transition metal nanocomposites were studied as absorber materials because they show appropriate optical properties, i.e. high absorption in the solar region and low thermal emittance. Furthermore metal carbides are thermally and mechanically stabile in air at high temperatures. In order to optimize the absorber layer, the metal content was controlled by adjusting the pulse ratio between the two arc sources. The elemental composition of the absorber layers was determined by Ion Beam Analysis. X-Ray diffraction (XRD) measurements show the formation of metal carbides when the metal content is high enough. The optical properties of the deposited coatings were characterized by spectroscopic ellipsometry (SE). The reflectance spectra of the complete selective coating were simulated with the optical software CODE. Bruggeman effective medium approximation (EMA) was employed to average the dielectric functions of the two components which compose the nanocomposite in the absorber layer. Good agreement was found between simulated and measured reflectance spectra of the solar selective multilayer.

碩士
國立臺灣大學
物理研究所
97
In this thesis we report the study of optical properties of SnO2 nanowires, photonic crystal formed by Tb(OH)3/SiO2 core/shell nanospheres and SnO2-Tb(OH)3/SiO2 nanocomposites. Photoluminescence (PL), Cathodoluminescence (CL), Raman scattering have been performed. Some peculiar results have been obtained from our studies, which are very useful for the understanding as well as applications of these materials. Based on our newly developed nanocomposites consisting of SnO2 nanowires and photonic crystals based on Tb(OH)3/SiO2 core/shell nanoparticles,1-2 we will show that the light confined inside the photonic crystals due to the formation of stop band can be directed along SnO2 nanowires and gets into air. SnO2 nanowires now serve as a waveguide.3 Because most of the emission arising from Tb ions is directed along SnO2 nanowires, the output emission intensity can be greatly enhanced. This behavior is similar to the design of water fountain in our daily life, in which the water confined under ground is directed to the earth surface through a water pipe. In this thesis, we will show the giant enhancement of the CL emission intensity for the SnO2-Tb(OH)3/SiO2 nanocomposite compared to the pure Tb(OH)3/SiO2 photonic crystal. It is found that lasing behavior can be easily achieved using the nanocomposite consisting of SnO2 nanowires and photonic crystals (PCs) based on Tb(OH)3/SiO2 core/shell nanospheres. Due to the fact that the light output from SnO2 nanowires can be greatly enhanced, it therefore establishes an excellent environment for the observation of stimulated emission. The novel composites developed here should be very useful for the creation of new lasing devices.

Nanoparticles have garnered much attention in pharmaceutical and biomedical fields because their small size and high surface area facilitate drug absorption, improve access to cells and organs, and enhance optical imaging. However, delivery of nanoparticles to the body is not always feasible or effective. Here, nanoparticle assemblies (flocs or clusters) for pulmonary drug delivery and biomedical imaging in cells are shown to facilitate delivery, interactions with cells, and manipulation of optical properties of inorganic/organic nanocomposites. The formation of aggregates by physical techniques and their mechanisms are described in detail. For pulmonary delivery, particles with aerodynamic diameters between 1-5 [mu]m deposit efficiently in the deep lungs. However, crystalline, non-porous, poorly water soluble drugs of this size require long dissolution times, limiting absorption by the body. Therefore, drug dissolution must be “decoupled” from deposition to improve absorption. To address this challenge, drug nanoparticles were dispersed within 4-[mu]m water droplets when administered via nebulization or as micron-sized flocs using a pressurized metered dose inhaler (pMDI). Upon deposition in aqueous media, the aerosolized nanoparticle assemblies dissociated into constituent nanoparticles, raising the available surface area for dissolution and increasing dissolution rates, relative to solid particles. Poorly water soluble drug nanoparticles were prepared using a controlled precipitation (CP) or thin film freezing (TFF) process, in which stable nanoparticles (30-300 nm in diameter) with high potencies (>90 wt% drug) were produced by rapidly nucleating drug solutions in the presence of strongly adsorbing polymers or by freezing, respectively. Amorphous, nanoparticles prepared by CP produced stable aqueous dispersions with high fine particle fractions (FPF) of 77% and total emitted doses (TED) of 1.5 mg/min upon nebulization. CP and TFF also produced anisotropic particles (aspect ratios >5), which formed stable suspensions in a hydrofluoroalkane propellant. Inefficient packing of anisotropic particles formed loose, open flocs that stacked upon each other to prevent settling. Upon pMDI actuation, atomized propellant droplets shear apart and template portions of the floc to yield porous particles with high FPFs (49-64%) and TEDs (2.4 mg/actuation). The controlled assembly of gold nanoparticles into clusters is also of great interest for biomedical imaging and therapy because clusters exhibit improved near infrared absorbance (where blood and tissue are most transparent), relative to single spherical particles, and can biodegrade into clearable particles. Gold nanoparticles (5 nm) were assembled into clusters between 30 to 100 nm in diameter with high gold loadings, resulting in strong NIR absorbance. The assembly was kinetically controlled with weakly adsorbing polymers by manipulating electrostatic, van der Waals, steric, and depletion forces. Furthermore, clusters assembled with a biodegradable polymer deaggregated back into primary particles in physiological media and within cells. This kinetic assembly platform is applicable to a wide variety of fields that require high metal loadings and small particle sizes.
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Optical metamaterials have triggered extensive studies driven by their fascinating electromagnetic properties that are not observed in natural materials. Aside from the extraordinary progress, challenges remain in scalable processing and material performance which limit the adoption of metamaterial towards practical applications. The goal of this dissertation is to design and fabricate nanocomposite thin films by combining nitrides with a tunable secondary phase to realize controllable multi-functionalities towards potential device applications. Transition metal nitrides are selected for this study due to the inherit material durability and low-loss plasmonic properties that offer stable two-phase hybridization for potential high temperature optical applications. Using a pulsed laser deposition technique, the nitride-metal nanocomposites are self-assembled into various geometries including pillar-in-matrix, embedded nanoinclusions or complex multilayers, that possess large surface coverage, high epitaxial quality, and sharp phase boundary. The nanostructures can be further engineered upon precise control of growth parameters.

This dissertation is composed of a general review of related background and experimental approaches, followed by four chapters of detailed research chapters. The first two research chapters involve hybrid metal (Au, Ag) - titanium nitride (TiN) nanocomposite thin films where the metal phase is self-assembled into sub-20 nm nanopillars and further tailored in terms of packing density and tilting angles. The tuning of plasmonic resonance and dielectric constant have been achieved by changing the concentration of Au nanopillars, or the tuning of optical anisotropy and angular selectivity by changing the tilting angle of Ag nanopillars. Towards applications, the protruded Au nanopillars are demonstrated to be highly functional for chemical bonding detection or surface enhanced sensing, whereas the embedded Ag nanopillars exhibit enhanced thermal and mechanical stabilities that are promising for high temperature plasmonic applications. In the last two chapters, dissimilar materials candidates beyond plasmonics have been incorporated to extend the electromagnetic properties, include coupling metal nanoinclusions into a wide bandgap semiconducting aluminum nitride matrix, as well as inserting a dielectric spacer between the hybrid plasmonic claddings for geometrical tuning and electric field enhancement. As a summary, these studies present approaches in addressing material and fabrication challenges in the field of plasmonic metamaterials from fundamental materials perspective. As demonstrated in the following chapters, these hybrid plasmonic nanocomposites provide multiple advantages towards tunable optical or biomedical sensing, high temperature plasmonics, controllable metadevices or nanophotonic chips.

博士
中原大學
化學研究所
100
The morphology and the electro-optical properties of polymer-dispersed liquid crystals (PDLC) were performed in this study. These consist of nematic liquid crystal (LC) E7 filled with different types of inorganic nanoparticles in norland optical adhesive (NOA65) polymer matrices. The PDLC film is prepared by the photopolymerization-induced phase separation (PIPS) method using UV light irradiation at 635 nm. Natural clay CL42, CL120, CL88, and titanium dioxides UV-100 are used as nanofillers in the PDLC film through application filed. Wide angle X-ray diffraction (XRD) is used to learn the dispersion of the inorganic nanoparticles in the PDLC and improved the crystalline of E7 in the mixture. The morphology of LC droplets in the hybridization PDLC film was larger and more uniform than an undoping comparison by loading of increased with the diagram of scanning electron microscope (SEM). The clay is existed in the LC droplets and polymer by the transmission electron microscopy (TEM) and temperature dependence WAXD. It has been observed that the appropriate doping of 3 wt% of CL120 in PDLC can effectively reduce the driving (threshold) voltage and improve the optical properties. The threshold voltage, driving voltage, τon, and contrast rate are improved 45.4% (from 64.92 Vrms to 35.45 Vrms), 25.0% (from 9.43 Vrms to 7.07 Vrms), 34.6% (from 4.56 ms to 2.98 ms), and 182.2% (from 4.05 to 11.43), respectively. In the other hand, a montmorillonite CL120 was studied via pentamerous oligo-aniline (POA), which was protonated with a sulfuric acid to emeraldine salts (ES) form, intercalating to form a functional conductive organo-layered material. The characteristics of modified clay—POA/CL120 identified exhaustive by XRD for the d-spacing of the montmorillonite layer, Fourier transform infrared (FTIR) for the oligoaniline and montmorillonite function group, and high-resolution thermogravimetric analyzer (TGA) for the theoretical intercalation capacity of the modified agent in the clay. Therefore, it successfully intercalated the POA into the montmorillonite by ionic exchange reaction and controlled the type dispersion of the modified clay with commanding the pKa of a protonated solution. PDLC composites were prepared from the modified clay loading in the matrix. There is no denying that improves in the electro–optical properties of PDLCs, which hybridization of POA-1/CL120 at 1wt% used in this work, lowers driving voltage by almost 70% ( from 64.92 Vrms to 19.29 Vrms), increases transmission of contrast ratio by 500% (from 4.05 to 21.39), rapid polarizes the LC directors at 25 Vrms by 0.7 ms, and approaching to the undoped PDLC of view angle at 200 Vrms in manner that depends on applied field.

Functional oxide-based thin films have attracted much attention owing to their broad applications in modern society. The multifunction tuning in oxide thin films is critical for obtaining enhanced properties. In this dissertation, four new nanocomposite thin film systems with highly textured growth have been fabricated by pulsed laser deposition technique. The functionalities including ferromagnetism, ferroelectricity, multiferroism, magnetoelectric coupling, low-field magnetoresistance, transmittance, optical bandgap and dielectric constants have been demonstrated. Besides, the tunability of the functionalities have been studied via different approaches.

First, varies deposition frequencies have been used in vertically aligned nanocomposite BaTiO₃:YMnO₃ (BTO:YMO) and BaTiO₃:La_0.7Sr_0.3Mn₃ (BTO:LSMO) thin films. In both systems, the strain coupling effect between the phases are affected by the density of grain boundaries. Increasing deposition frequency generates thinner columns in BTO:YMO thin films, which enhances the anisotropic ferromagnetic response in the thin films. In contrast, the columns in BTO:LSMO thin films become discontinuous as the deposition frequency increases, leading to the diminished anisotropic ferromagnetic response. Coupling with the ferroelectricity in BTO, the room temperature multiferroic properties have been obtained in these two systems.

Second, the impact of the film composition has been demonstrated in La_0.7Ca_0.3MnO₃ (LCMO):CeO₂ thin film system, which has an insulating CeO₂ in ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the CeO₂ increases, enhanced low-field magnetoresistance and increased metal-to-insulator transition temperature are observed. The thin films also show enhanced anisotropic ferromagnetic response comparing with the pure LCMO film.

Third, the transition metal element in Bi₃MoM_TO₉ (M_T, transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin films have a multilayered structure with M_T-rich pillar-like domains embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and optical properties have been demonstrated. By the element variation, the optical bandgaps, dielectric constants as well as anisotropic ferromagnetic properties have been achieved.

The studies in this dissertation demonstrate several examples of tuning the multifunctionalities in oxide-based nanocomposite thin films. These enhanced properties can broaden the applications of functional oxides for advanced nanoscale devices.

碩士
國立中興大學
化學系
87
ABSTRACT Part I. Microstructural and Morphological Characteristics of PS-SiO2 Nanocomposites A series of organic-inorganic hybrid materials have been prepared by copolymerizing styrene and alkoxysilane-methacrylate via sol-gel process. The alkoxysilane-containing copolymer precursors were synthesized by free-radical copolymerization of styrene with an alkoxysilane-containing monomer, methacrylic acid 3-(trimethoxysilyl)propyl ester (MAMSE), at several feeds. The copolymer precursors were then hydrolyzed and condensed to generate PS-SiO2 hybrid sol-gel materials. The hybrid copolymers possess excellent optical transparency and a nanoscale microphase separation. The copolymer precursors and their hybrid copolymers were characterized by FTIR spectra, 1H-NMR spectra, DSC, and TGA thermograms. Chemical structural effect on the morphology and thermal properties was investigated with SEM, mapping photographs, and high-resolution solid state 13C- and 29Si-NMR spectra. It is found that compatibility between copolymer and silica mainly contributes from incorporating the polymer with silica covalently. Moreover, MAMSE could be hydrolyzed to methacrylic acid and ester-interchanged to silyl methacrylate during heat treatment. This also enhances compatibility between copolymer and silica. Thermal properties of PS-SiO2 hybrid copolymers are improved as silica content increase. However, the presence of silyl ester groups, which were formed during heat treatment, would reduce thermal stability of the hybrid copolymers. Part II. Synthesis and Optical Properties in the Sol-Gel Matrix Bearing an Azobenzene Chromophores. A series of NLO chromophores with several types of spacers have been synthesized. The chromophores were incorporated with melamine-based polymers by sol-gel process to form soluble prepolymers. Excellent optical transparency and large second-order nonlinearities of up to 28 pm/V have been determined afer poling and curing process. Morphological and temporal characteristics were investigated by SEM photograph, relaxation dynamic and temporal relaxation behaviors. Moreover, the relaxation data have been fitted with KWW equation and Arrhenius equation. In morphological characteristics, It is found that compatibility between chromophores and melamine-based polymers can be enhanced by covalently incorporating the polymer with chromophore by a flexible spacer. In the study, no macroscopic phase separation could be observed even the chromophore content of HHAN/melamine system of up to 30 %. In relaxation dynamic, slow relaxation behavior observed at the temperature at or above effective relaxation temperature, T0, mainly contribute from restraint of the sol-gel network in the poled melamine-based NLO polymers. Alternately, high effective relaxation temperature, T0 = 83 ℃, of the HA1 polymer is dominated from an anchor effect cased by directly covalent bonding rigid chromophore into melamine system. In temporal relaxation behaviors, temperature of thermal aging process has a great effect on the relaxation behaviors. A slow variation of the SHG signal relaxation behavior can be observed at temperature below T0. This relaxation behavior depends on degree of cross-linking density. In the ASH polymer system, a more stable temporal stability was found, which mainly contributes from a more condensed network. In the systems, the relaxation data can be fitted by the Kohlrausch-Williams-Watts (KWW) stretched equation. A high characteristic relaxation time, τ = 9000 min, at room temperature and activation energy, Ea =100 KJ/mole, below effective relaxation temperature was found in the ASH polymer.

碩士
國立清華大學
光電工程研究所
101
Deoxyribonucleic acid (DNA) is an important molecule carrying genetic information in organisms. Due to several features of DNA molecule, such as self-assembly and molecular recognition capabilities, DNA has found broad applications in nanotechnology. Recently, DNA biopolymer has also been reported to exhibit unique optical and electrical properties. Many optoelectronic devices have been implemented using DNA biopolymer with enhanced efficiency. In this study, we used a photochemical method to fabricate DNA-silver nanoparticles nanocomposite and investigated its nonlinear optical properties. A Z scan technique with nanosecond laser pulses at 532 nm was employed to obtain two-photon absorption coefficient. The value of DNA nanocomposite is larger than the value of DNA biomaterials.The results show that the nonlinear properties of DNA nanocomposite can be enhanced due to the surface plasmon resonance effect of silver nanoparticles. And the application in optical limiting was also studied and discussed

The optical behaviour of both gold and silver nanoparticles has been studied in both experimental and theoretical aspects. In the theoretical part of our thesis, to contribute to a better understanding of particles of various shapes and configurations, the versatile Discrete Dipole Approximation (DDA) has been employed to simulate in depth the absorption spectra of single isolated oriented nanoparticles of different symmetry (nanocube, nanobar and nanoellipsoid). The effect of the plasmonic coupling and the size of spherical particles assemblies on their optical response have also been addressed. It was shown that the plasmonic coupling in the interacting particles in close proximity configuration disturbs the homogenous distribution of surface charges and results in splitting the plasmonic band into two bands. The excitations of two different bands (longitudinal and transverse bands) have been also observed in the absorption spectra of many fold symmetry particles. The diversity of the polarization factors along different symmetry axis was established as the main key for observing several bands. Thus the importance of particle shape and the different interesting possibilities offered by this single factor has been well demonstrated in the DDA calculations performed while our treatment of ensembles of nanospheres showed in detail the effect of interacting particles on the overall optical properties of actual samples. In the experimental part of this thesis, a first part is devoted to the study of the influence of dielectric host material on the optical properties of gold nanoparticles. For this purpose, gold, -poly(methyl methacrylate) (PMMA) and -gelatin nanocomposite materials have been prepared by an in-situ method. Two reduction methods (photochemical and chemical) were used to reduce the gold salt in the presence of the polymer matrix. Firstly, annealed and non annealed samples were prepared by different photochemical methods (UV-, thermal-, and MW-irradiation). Gold-poly(methyl methacrylate) nanocomposites were prepared by irradiating spin-coated films containing the polymer and the gold precursor dissolved in acetone. The reduction of gold ions resulted in the formation of gold that nucleated and grew within the polymer films. It was shown that, depending on the energy source, gold nanoparticles with different shapes could be formed. The nanocomposites prepared through the photochemical methods, showed a low sensitivity toward the environment. However, by annealing the samples at temperatures well above the glass transition temperature of the polymer, the response to dielectric environment appeared to be enhanced significantly. The increased sensitivity of the annealed sample (increase the surface particle density) was accounted for by the increased mobility of both polymer chains and gold nanoparticles in the rubbery state of the material and the presence of the monomer. The results showed that, by using adequate post-synthesis heat treatments, gold-polymer nanocomposites could be used as plasmonic sensing platforms. Secondly, gold–gelatin bionanocomposite films were prepared by the reduction of gold ions by sodium borohydride in an aqueous solution. It was shown that both the solution and the films on glass substrates contained entrapped hydrogen micro- and nanobubbles with diameters in the range of 200 nm–3 μm. The composite films having micro- and nanobubble inclusions have been found to be very stable. The optical properties of gold nanoparticles in the presence of gelatin and hydrogen nanobubbles were measured and simulated by using the discrete dipole approximation (DDA) method. The calculated localized surface plasmon resonance band was found in agreement with the experimental band position only when the presence of hydrogen bubbles around the gold nanoparticles was taken into account. The different morphological features engendered by the presence of the bubbles in the film (gelatin receptacles for the nanoparticles, gelatin hemispheres raised by the bubbles under the surface, cavities on the surface of the film, etc) are potential candidates for many applications.

This work describes the synthesis pathways to the development of optically and thermally responsive nanovalves with fast response times in nanoporous membranes. As an approach, we developed synthesis pathways to couple a thermally responsive polymer with metallic nanoparticles and build a nanocomposite that synergizes the capability of metallic nanoparticles to convert light into heat, and the fast thermal response exhibited by the polymeric material. In addition, we developed a technique to immobilize the synthesized nanocomposite to the surface of nanoporous membranes, which allowed building valves with light and heat triggering responses. This dissertation describes two syntheses pathways developed to produce optically and thermally responsive nanocomposites by coupling metallic nanoparticles, gold and silver, with a thermally responsive polymer, p-N-isopropyl acrylamide (PNIPAM). The coupling is achieved by using PNIPAM as a capping and nucleating agent in the in situ redox reaction of a silver salt with sodium borohydride, and using PNIPAM as a capping and stabilizing agent in the redox reaction of a gold salt with ascorbic acid. The size and shape of the nanoparticles were controlled and the synthesized nanocomposites exhibit “cocoon-like” structures due to the PNIPAM surrounding the metal nanoparticles, giving the capability to aggregate and resolubilize, through many thermal (shown for gold and silver nanocomposites) and optical (shown by exposing to 532 nm wavelength low-power lasers) cycles. The steady state and dynamic heat conduction of the heat generated from the particles was modeled and the results agreed with the observed optical switching at our experimental conditions. Finally, a method to incorporate nanocomposites into nanoporous membranes (NPM) was developed. It involved prior immobilization of PNIPAM through plasma-induced grafting, followed by a reduction in situ of a metallic salt. The composite NPMs showed thermal responses and through simulation of heat conduction within the pores using the model developed in this work we were able to conclude that the synthesized composite membranes will exhibit optical switching when exposed to focused low power lasers. The nanovalves developed in this work have potential applications as optothermally responsive valves for the spatio-temporal delivery of bioactive agents, cell array, and advanced cell culture systems.
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碩士
國立交通大學
材料科學與工程系所
97
This work prepares the nanocomposite thin films containing GaN quantum dots (QDs) in Si3N4 and SiOxNy dielectric matrices by using the target-attached sputtering method. Transmission electron microscopy （TEM） revealed the presence of GaN QDs in the both types of thin-film systems. Although the dot density increases with the number of the target-attached pellets, the dot size is independent of that. Electron spectroscopy for chemical analysis（ESCA）and photoluminescence（PL） analyses indicated that the SiO2 matrix may react with N2 injected during sputtering and generate the SiOxNy. It generates a distinct bonding configuration on GaN QDs surface and induces a stronger surface polarization in GaN QDs-SiOxNy system in comparison with the GaN QDs-Si3N4 system. This, in turn, suppresses the yellow-green transition relating to VGa on GaN QDs. Meanwhile, a specific optical transitions, which improves the defect luminescent intensity due to the diminishing of near-band-edge signals, when the volume ratio of GaN QDs to matrix is about 1:1 in both systems. Although present data are insufficient to correlate the optical transition in complete manner, the results above indeed illustrate that the dielectric matrix type has an important effect on the optical properties of nanocomposite thin films.

博士
國立交通大學
材料科學與工程系所
96
This thesis prepares the nanocomposite thin films containing ZnO quantum dots (QDs) in SiO2 and SiOxNy dielectric matrices by using the target-attached sputtering method. The optical and electrical properties of nanocomposite thin films as well as the effects of dielectric types on the characteristics of ZnO QDs are also investigated. Experiemental results indicate that such a simple physical deposition (PVD) method can effectively grow the ZnO QDs inside the dielectric material within good control on dot sizes and distribution. Via the analyses including microstructure, optical, and electrical properties in conjunction with theoretical modeling and calculation, the interactions of dielectric matrices on ZnO QD surface and the effects of dielectric types on optical ane electrical properties of ZnO QDs are explored. Transmission electron microscopy (TEM) analysis revealed similar microstructure in both nanocomposite films and the ZnO QDs produced by target-attached sputtering method are crystalline rather then amorphous. In ZnO QDs-SiOxNy system, the incorporation of N atoms generates a distinct bonding configuration on ZnO dot surface and induces a stronger surface polarization in comparison with ZnO QDs-SiO2 system. This suppresses the defect chemical reactions relating to oxygen ions on ZnO dot and further affects the transmittance, refractive index and photoluminance properties of nanocomposite films. We also calculated the width of depletion region and dielectric confinement energy for the nanocomposite films and, in corelated with experimental data, the results evidenced the dielectric matrix type indeed affects the optical properties of ZnO QDs. We also built up a multi-shell two-electron system model to calculate the electron ground-state energy of a semiconductor QDs-dielectric matrix system. The calculated results enabled us to clarify the occurrence of quantum confinement and dielectric confinement effects in the ZnO QDs-SiO2 films. In the dc and ac conductivity measurements of ZnO QDs-SiO2 and ZnO QDs-SiOxNy systems, the complex-plane analysis revealed that the ZnO QD content on affects the conduction properties of nanocomposite films. Furthermore, the two nanocomposite systems exhibited different response powers and sensitivities to the frequency dispersion relationship. Though both systems exhibited poor capacitance properties and a new design of sample structure and further investigations are required, the results above cleary demonstrated the feasibility to manipulate the electrical properties of ZnO QDs via the modification of dielectric matrix type.