Thesis (Ph.D.)--Murdoch University, 2008. / Thesis submitted to the Faculty of Minerals and Energy. Includes bibliographical references (leaves 238-246)

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 79-81). Also available on the World Wide Web.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed October 13, 2009). PDF text: 261 p. : ill. (some col.) ; 5 Mb. UMI publication number: AAT 3359063. Includes bibliographical references. Also available in microfilm and microfiche formats.

In this thesis study, the surface/interface plasmon excitations in different Si nanostructures were revealed through the EELS study in TEM/STEM. In the case of the planar boundary such as the wedge-like specimen, the spatially resolved EELS results disclose the dependence of the intensity and the position of the interface plasmon peak on the sample thickness. In the case of the Si-core/ SiO2-shell nanoparticles, we found that the SP/IP peak will firstly red-shifts with the increase of the SiO2 shell thickness and eventually levels off . As the aspect ratio of the Si nanoparticles increases, (from spherical particle to nanorod and nanowire), the SP/IP will split into two branches: transverse and longitudinal modes. We also found the intensity ratio of the transverse/longitudinal mode excitations depends on the diameter of the Si core size in the nanostructures. In the one-dimensional interacting Si nanoparticle chains, the Si nanoparticles were embedded in the SiO 2 shell, the splitting of the SP excitation into transverse and longitudinal modes was also observed. As the inter-particle distance reduces to several nanometers, the coupling of the IP excitation between the adjacent particles becomes significant, and results in the local field enhancement in-between the two particles. This is directly visualized using EFTEM imaging in TEM/STEM. / Surface/interface plasmons (SP/IP) are the plasmons confined at specific boundaries, describing the surface/interface charge density oscillation. They are generated when the scattered electromagnetic wave with its scattering vector component parallel to the boundary propagates along the surface/interface. Study of surface plasmon resonance in noble metals such as gold and silver nanoparticles have started decades ago, and recent interests are focused on the plasmonic properties of individual nanoparticles, as enabled by the size/shape control in the nanostructure growth and advances made in the characterization methodologies. Besides the noble metals, semiconductor such as silicon also attracts much attention for its plasmonic behavior. The surface/interface plasmon resonance frequency of Si-based nanostructures occurs at relatively higher energies (compared to Au and Ag), making it a perfect system to be studied using electron energy loss spectroscopy (EELS) based techniques. When performed in a scanning transmission electron microscope (STEM), such a technique enjoys excellent spatial resolution, and can map the local plasmonic properties of individual nanostructures. / The plasmon excitation depends sensitively on not only the material dielectric properties but also the geometrical configurations of the material. In the present thesis work, silicon-based nanostructures with planar, spherical, and cylindrical boundaries were investigated using both experimental and theoretical approaches, with focus on the plasmon oscillation originating from the Si/SiO 2 interface. The specimens employed include silicon/silica thin films, Si-core/SiO2-shell nanoparticles with different aspect ratios and spherical-shaped nanoparticle chains, as well as Si-core/SiO2-shell nanocables. / Wang, Xiaojing = 低維硅納米結構表界面等離激元之研究 / 王笑靜. / Adviser: Li Quan. / Source: Dissertation Abstracts International, Volume: 73-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 118-122). / 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, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Wang, Xiaojing = Di wei gui na mi jie gou biao jie mian deng li ji yuan zhi yan jiu / Wang Xiaojing.

Molecular fluorophores and semiconductor quantum dots (QDs) have been used as cellular imaging agents for biomedical research, but each class has challenges associated with their use, including poor photostability or toxicity. Silicon is a semiconductor material that is inexpensive and relatively environmental benign in comparison to heavy metal-containing quantum dots. Thus, red-emitting silicon nanoparticles (Si NPs) are desirable to prepare for cellular imaging application to be used in place of more toxic QDs. However, Si NPs currently suffer poorly understood photoinstability, and furthermore, the origin of the PL remains under debate. This dissertation first describes the use of diatomaceous earth as a new precursor for the synthesis of photoluminescent Si NPs. Second, the stabilization of red PL from Si NPs in aqueous solution via micellar encapsulation is reported. Thirdly, red to blue PL conversion of decane-terminated Si NPs in alcohol dispersions is described and the origins (i.e., color centers) of the emission events were studied with a comprehensive characterization suite including FT-IR, UV-vis, photoluminescence excitation, and time-resolved photoluminescence spectroscopies in order to determine size or chemical changes underlying the PL color change. In this study, the red and blue PL was determined to result from intrinsic and surface states, respectively. Lastly, we determined that the blue emission band assigned to a surface state can be introduced by base addition in originally red-emitting silicon nanoparticles, and that red PL can be restored by subsequent acid addition. This experimentally demonstrates blue PL is surface state related and can overcome the intrinsic state related excitonic recombination pathway in red PL event. Based on all the data collected and analyzed, we present a simple energy level diagram detailing the multiple origins of Si NP PL, which are related to both size and surface chemistry.

With recent development of nanoscience and nanotechnology, a great amount of efforts have been devoted to nanomedicine development. Among various nanomaterials, silica nanoparticle (NP) is generally accepted as non-toxic, and can provide a versatile platform for drug loading. In addition, the surface of the silica NP is hydrophilic, being favorable for cellular uptake. Therefore, it is considered as one of the most promising candidates to serve as carriers for drugs. / The present thesis mainly focuses on the design of silica based nanocarrier-drug systems, aiming at achieving safe nanocarrier excretion from the biological system and enhanced drug efficacy, which two are considered as most important issues in nanomedicine development. / To address the safe carrier excretion issue, we have developed a special type of self-decomposable SiO₂-drug composite NPs. By creating a radial concentration gradient of drug in the NP, the drug release occurred simultaneously with the silica carrier decomposition. Such unique characteristic was different from the conventional dense SiO₂-drug NP, in which drug was uniformly distributed and can hardly escape the carrier. We found that the controllable release of the drug was primarily determined by diffusion, which was caused by the radial drug concentration gradient in the NP. Escape of the drug molecules then triggered the silica carrier decomposition, which started from the center of the NP and eventually led to its complete fragmentation. The small size of the final carrier fragments enabled their easy excretion via renal systems. / Apart from the feature of safe carrier excretion, we also found the controlled release of drugs contribute significantly to the drug efficacy enhancement. By loading an anticancer drug doxorubicin (Dox) to the decomposable SiO₂-methylene blue (MB) NPs, we achieved a self-decomposable SiO₂(MB)-Dox nanomedicine. The gradual escape of drug molecules from NPs and their enabled cytosolic release by optical switch, led to not only high but also stable drug concentration in cytosol within a sustained period. This resulted in enhanced drug efficacy, which is especially manifested in multidrug resistant (MDR) cancer cells, due to the fact that the NP-carrier drug can efficiently bypass the efflux mechanisms and increase drug availability. Together with its feature of spontaneous carrier decomposition and safe excretion, this type of nanomedicine’s high drug efficacy highlights its potential for low dose anticancer drug treatment and reduced adverse effect to biological system, holding great promise for clinical translation. / The enhanced drug efficacy by employing the self-decomposable silica nanocarrier is also demonstrated in photodynamic therapy (PDT). The loose and fragmentable features of the self-decomposable SiO₂-photosensitizer (PS) NPs promoted the out-diffusion of the generated ROS, which resulted in a higher efficacy than that of dense SiO₂-PS NPs. On the other hand, we also explored another nanocarrier configuration of Au nanorods decorated SiO₂ NP, with PS drug embedded into dense SiO₂ matrix. A different mechanism of drug efficacy enhancement was presented as the Au’s surface plasmon resonance enhanced the ROS production. Although the drug efficacy of such SiO₂(PS)-Au NPs was similar to that of self-decomposable SiO₂-PS NPs, their potential for clinical applications was limited without the feature of safe carrier excretion. / In summary, the self-decomposable SiO₂ based NP developed is a most promising system to serve as safe and effective carriers for drugs. Together with the known biocompatibility of silica, the feature of controllable drug release and simultaneous carrier decomposition achieved in the self-decomposable SiO₂-drug NPs make it ideal for a wide range of therapeutic applications. / 隨著近年來納米科學技術的快速發展，致力於納米藥物的研发也越來越多。在眾多納米材料體系中，二氧化硅納米顆粒因其無毒、易載藥、且易於細胞攝入等特性，被認為是最具前景的藥物載體之一。 / 本文主要致力於設計以二氧化硅納米顆粒為載體的納米藥物體系，使之同時具備能夠被生物體安全排泄以降低潛在不良影響，并且能夠加強藥效的特性，而這兩方面被認為正是納米藥物發展中最重要的議題。 / 爲了實現藥物載體安全排泄，我們設計了一種特殊類型可自降解的二氧化硅-藥物複合納米顆粒。通過在納米顆粒中控制形成徑向藥物濃度梯度分佈，我們達到了藥物釋放的同時伴隨二氧化硅載體解體的效果。這一特徵不同於傳統二氧化硅-藥物複合納米顆粒中藥物均勻分佈而難以擴散出載體的情況。我們發現在這種可自降解的二氧化硅-藥物複合納米顆粒中，首先徑向藥物濃度梯度分佈所引起的擴散控制著藥物釋放，而後藥物分子的流失促發二氧化硅載體由內而外的逐步分解，最終全面解體分裂成碎片。這些碎片的小尺度使得它們易於經泌尿系統安全排泄出體外。 / 除此之外，我們發現這種納米載體的可控藥物釋放特性可以大大提高藥效。通過將抗癌藥阿黴素載入自降解二氧化硅-亞甲藍納米顆粒中，我們得到一種可自降解二氧化硅/亞甲藍-阿黴素(SiO₂(MB)-Dox)複合納米顆粒。藥物分子可以逐漸擴散出納米顆粒，並且在光控開關作用下釋放到細胞胞漿中，使之在胞漿中持續保持穩定高濃度。這樣使得藥效得以加強，尤其是在多藥抗藥性腫瘤細胞中作用尤為明顯，這得益於納米載體藥物可以有效避開藥泵機制并提高藥物利用率。除了它的自發載體分解和安全排泄特性，這種納米藥物的高藥效使得它在低藥量治療和減少不良副作用方面的潛力突出，臨床應用前景廣大。 / 可自降解二氧化硅納米載體所帶來的的藥效增強亦顯示在光動力學治療法中。可自降解二氧化硅-光敏劑藥物(SiO₂-PS)複合納米顆粒鬆散易分解的結構特性促使其內部產生的活性氧物質易於擴散出藥物載體，這使得它的藥效高於傳統二氧化硅-光敏劑複合納米顆粒。另一方便，我們設計了一種金修飾的二氧化硅納米顆粒載體。它具有另一種不同的藥效增強機制，即利用金納米顆粒表面等離子體共振效應來增強活性氧物質的產生。雖然藥效與可自降解二氧化硅-光敏劑複合納米顆粒相似，但是它無法安全排泄，限制了其在臨床上的應用。 / 綜上所述，我們發展的可自降解二氧化硅納米顆粒作為一種安全高效的藥物載體顯示出其非常大的應用前景。二氧化硅以其衆所周知的生物相容性，和我們發展的可控藥物釋放及同步載體分解特性，已成為理想的藥物載體并有希望廣泛適用於治療應用。 / Zhang, Silu = 基於無定二氧化硅納米顆粒的安全高效納米藥物的研究 / 張思鷺. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Title from PDF title page (viewed on 12, October, 2016). / Zhang, Silu = Ji yu wu ding er yang hua gui na mi ke li de an quan gao xiao na mi yao wu de yan jiu / Zhang Silu. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs. Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl3-derived (HSiO1.5)n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment. First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface. Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λmax of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample. Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -- 655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of photo-excited Si NPs.

Thesis (Ph. D.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

This dissertation describes the synthesis and characterization of fluorescent semiconductor nanoparticles (NPs) in order to optimize their biomedical utility for imaging and sensing applications. While both direct and indirect bandgap semiconductor NPs have been studied, control over their emission properties vary. Quantum confinement (QC), which primarily controls the emission wavelength of nanosized semiconductors, dictates that as the size of semiconductor NPs decrease, the magnitude of the bandgap increases, resulting in changes in the observed emission wavelength: smaller NPs have a larger bandgap, and thus a bluer emission. However, surface, interfacial, or shell defects can act as non-radiative or radiative recombination sites for excitons formed within the NP; the latter results in emission competition with the bandgap transition, as described Chapters 1 and 2. Because the emission wavelengths of direct bandgap semiconductor NPs correlate with size according to the expectations of QC, and are stable in aqueous environments with high quantum efficiencies (quantum yield, QY), current research focuses on their potential biomedical applications. Chapter 3 describes red-emitting CdSe/ZnS quantum dots (QDs) that exhibit a concentration-dependent decrease in fluorescence intensity in response to the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). A mechanistic study was performed to understand a 5-HT-dependent decrease in QD emission and calibration curves relating QD intensity loss to 5-HT concentration in ensemble and single QD studies were generated. Unfortunately, the known toxicity of CdSe-based QDs has generated interest in more benign semiconductor NPs to replace these QDs in biological applications, while maintaining the same degree of control over the emission color and QY. Bulk indirect bandgap semiconductors, such as Si, have low efficiency inter-band transitions, and Si NPs are known to contain radiative defects that can alter the emission wavelength from QC-based size expectations; these competitive emission pathways must be controlled in order for Si NPs to be successfully used in biological applications. In general, synthetic methods that gives precise control over both the particle size and surface termination are needed in order to produce emission controlled Si NPs. Relative to groups II and VI QDs, synthetic routes to prepare Si NPs are few in numbers, and the size vs. defect emission events are difficult to assign. Not only do these assignments vary amongst reports, but they also vary with particle size, solvent, sample age, and identities of the surface ligands. Si NPs have been prepared through two synthetic routes using the Zintl salt, sodium silicide (NaSi) and ammonium bromide (NH4Br) as precursors. Chapter 4 describes the synthesis performed in the solvent N,N,-dimethylformamide (DMF). This reaction produces blue-emitting Si NPs (5.02 ± 1.21 nm) that bear partial hydride surface termination. However, it was determined that the solvent was able to interact with the Si NP surface, and prevent subsequent functionalization. This observation was used advantageously, and Chapter 5 describes a one-pot Zintl salt metathesis of Si NPs (3.9 + 9.8 nm) performed in a bi-functional (amine or carboxylic acid) solvent ligand, where the observations indicated that the solvent ligands coordinate to the Si NP. The emission maxima of the Si NPs prepared from the Zintl salt metathesis exhibited a dependence on the excitation energy, and is indicative of emission that is influenced by QC, which likely originates from deeply oxide embedded 1-2 nm crystalline cores. The Si NPs prepared from the one-pot Zintl salt metathesis were exposed to metals salt ions of varying reduction potentials to determine the band edges by what will or will not be reduced (Chapter 6). By monitoring the emission intensity of the Si NPs, in addition to the UV-Vis of the metal ions, the band edge of Si NPs may be determined. The value of the band edge may lend insight into the origin of Si NP emission. To utilize fluorescent Si NPs for biological applications, red emission is strongly preferred. Unfortunately, when preparing aqueous Si NPs, red emission usually changes to blue, likely from the oxidation of the Si NP surface. Therefore, the red emission needs to be efficiently protected from surface oxidants. Because both increased chain lengths and steric modalities have been found to protect the emission properties of Si NPs, red-emitting, ester-functionalized Si NPs (5.51+1.35 nm) with varying chain lengths and ester termination moieties were prepared to determine the best method of preserving the observed red emission in the presence of potential alcoholic oxidants. By determining the best was to protect Si NPs emission, the red-emission from Si NPs may be preserved for biological applications.

La découverte de la photoluminescence du silicium sous sa forme nanométrique a ouvert la voie de l’utilisation du silicium dans les composants optoélectroniques. Cependant cette photoluminescence reste trop peu efficace et de nombreuses recherches portent aujourd’hui sur l’amélioration des propriétés optiques du silicium. Ce travail de thèse s’intéresse particulièrement à l’utilisation de plasmons de surface localisés afin d’améliorer les propriétés optiques de nanocristaux de silicium. Grâce au contrôle de tous les paramètres géométriques des nanocristaux de silicium et des nanoparticules métalliques lors de la fabrication des échantillons, il a été possible d’étudier les phénomènes physiques du couplage entre ces deux objets. Une modification de l’émission des nanocristaux de silicium en fonction de la distance, de la taille et de la nature des nanoparticules métalliques a été étudiée. Grâce au développement de différentes techniques de caractérisation optique, il a été possible de montrer que la photoluminescence des nanocristaux de silicium était modifiée à la fois spectralement et spatialement par les plasmons de surface localisés. Ce travail montre que grâce aux plasmons de surface localisés il est possible de grandement améliorer la photoluminescence des nanocristaux de silicium et ainsi il est possible d’imaginer de nouveaux composants optoélectroniques à base de silicium et de plasmons / The discovery of photoluminescence of nanometric silicon paves the way to use silicon in optoelectronic devices. However this photoluminescence remains low and a lot of works aim at improving silicon optical properties. In this dissertation we study localized surface plasmons to improve optical properties of silicon nanocrystals. Thanks to the control of all geometrical parameters of silicon nanocrystals and metallic nanoparticles during the fabrication process, the coupling process between these two objects has been studied. The modification of silicon nanocrystals emission as a function of the distance, the size and the nature of metallic nanoparticles has been investigated. Thanks to the development of experimental optical characterization techniques we showed that silicon nanocrystals photoluminescence is modified both spectrally and spatially by localized surface plasmons. This work shows that it’s possible to enhance silicon’s optical properties and thus to devise optoelectronic devices with silicon and plasmons