Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Idaho, 2005. / Also available online in PDF format. Abstract. "July 2005." Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.

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Graphene is a single atomic sheet of graphite that exhibits a diverse range of unique properties. The electrons in intrinsic graphene behave like relativistic Dirac fermions; graphene has a record high Young's modulus but extremely low bending rigidity; and suspended graphene exhibits very high thermal conductivity. These properties are made more intriguing because with a thickness of only a single atomic layer, graphene is both especially affected by its environment and readily manipulated. In this dissertation the interaction between graphene and its environment as well as the exciting new physics realized by manipulating graphene's lattice are investigated. Lattice manipulations in the form of strain cause alterations in graphene's electrical dispersion mathematically analogous to the vector potential associated with a magnetic field. We complete the standard description of the strain-induced vector potential by explicitly including the lattice deformations and find new, leading order terms. Additionally, a strain engineered device with large, localized, plasmonically enhanced pseudomagnetic fields is proposed to couple light to pseudomagnetic fields. Accurate strain engineering requires a complete understanding of the interactions between a two dimensional material and its environment, particularly the adhesion and friction between graphene and its supporting substrate. We measure the load dependent sliding friction between mono-, bi-, and trilayer graphene and the commonly used silicon dioxide substrate by analyzing Raman spectra of circular, graphene sealed microchambers under variable external pressure. We find that the sliding friction for trilayer graphene behaves normally, scaling with the applied load, whereas the friction for monolayer and bilayer graphene is anomalous, scaling with the inverse of the strain in the graphene. Both strain and graphene's environment are expected to affect the quadratically dispersed out of plane acoustic phonon. Although this phonon is believed to provide the majority of graphene's very high thermal conductivity, its contributions have never been isolated. By measuring strain and pressure dependent thermal conductivity, we gain insight into the mechanism of graphene's thermal transport.

>Magister Scientiae - MSc / One-dimensional silicon nanowires (SiNWs) are promising building blocks for solar cells as they provide a controlled, vectorial transport route for photo-generated charge carriers in the device as well as providing anti-reflection for incoming light. Two major approaches are followed to synthesise SiNWs, namely the bottom-up approach during vapour-liquid-solid mechanism which employs chemical vapour deposition techniques. The other method is the top-down approach via metal assisted chemical etching (MaCE). MaCE provides a simple, inexpensive and repeatable process that yields radially and vertically aligned SiNWs in which the structure is easily controlled by changing the etching time or chemical concentrations. During MaCE synthesis, a crystalline silicon (c-Si) substrate covered with metal nanoparticles (catalyst) is etched in a diluted hydrofluoric acid solution containing oxidising agents. Since the first report on SiNWs synthesised via MaCE, various publications have described the growth during the MaCE process. However lingering questions around the role of the catalyst during formation, dispersion and the eventual diameter of the nanowires remain. In addition, very little information pertaining to the changes in crystallinity and atomic bonding properties of the nanowires post synthesis is known. As such, this study investigates the evolution of vertical SiNWs from deposited silver nanoparticles by means of in-depth electron microscopy analyses. Changes in crystallinity during synthesis of the nanowires are probed using x-ray diffraction (XRD) and transmission electron microscopy (TEM). Deviations in the optical properties are quantified using optical reflectivity measurements by employing ultraviolet-visible (UV-Vis) spectroscopy, whereas the bonding configurations of the nanowires are probed by Raman and Fourier transforms infrared spectroscopy. Diameters of 50 – 200 nm vertical SiNWs were obtained from scanning electron micrographs and nanowires lengths linearly increased with etching time duration from about 130 nm after 30 seconds to over 15 μm after 80 minutes. No diameter modulations along nanowires axial direction and rough nanowires apexes were observed for nanowires obtained at longer etching times. These SiNWs remained crystalline as their bulk single crystalline Si wafers but had a thin amorphous layer on the surface, findings confirmed by TEM, XRD and Raman analysis. Nanowires were found to be partially passivated with oxygen with small traces of hydrogen termination, confirmed with infrared absorption studies. Finally, low optical reflection of less than 10% over visible range compared to an average of 30% for bulk Si were measured depicting an antireflective ability required in silicon solar cells.

BEZERRA NETO, João Rufino. Abordagem ab inito do aledronato molecular e três de seus cristais. 2014. 120 f. Dissertação (Mestrado em química)- Universidade Federal do Ceará, Fortaleza-CE, 2014. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-10-11T15:22:27Z No. of bitstreams: 1 2014_dis_jrbezerraneto.pdf: 12998956 bytes, checksum: e466987d7e35404faec036345189962b (MD5) / Approved for entry into archive by Jairo Viana (jairo@ufc.br) on 2016-10-11T23:50:01Z (GMT) No. of bitstreams: 1 2014_dis_jrbezerraneto.pdf: 12998956 bytes, checksum: e466987d7e35404faec036345189962b (MD5) / Made available in DSpace on 2016-10-11T23:50:01Z (GMT). No. of bitstreams: 1 2014_dis_jrbezerraneto.pdf: 12998956 bytes, checksum: e466987d7e35404faec036345189962b (MD5) Previous issue date: 2014 / Well know therapies for the treatment of osteoporosis, syndrome characterized by increased bone fragility and fracture consist primarily of drugs which prevent bone losses, such as bisphosphonates. Among them, alendronate (PO3)-(OH)-C-((CH2)3 NH3)-(PO3) is one of the chosen treatments in the clinic, IC50 = 50 nM. In this work a study of the molecular alendronate and three of its crystals (sodium alendronate trihydrate and anhydrous and calcium alendronate ) is performed in the scope of Density Functional Theory (DFT). In the first case, the focus is the lowest energy conformations of the molecular alendronate in vacuum, in an aqueous medium in accordance with the model of polarization continuum (PCM), and interacting with three molecules of water of a sodium atom based on the characteristics structural relevadas diffraction X-ray crystal alendrontao sodium trihydrate; their vibrational infrared and Raman spectra are calculated to explain in detail the abundant signatures of the phosphate group in the frequency range 400-1400 cm −1 with the assignments of the most important vibrational modes. In the case of crystals, their structural, electronic and optical properties are obtained in the generalized gradient approximation taking into account the description of the term correlation and exchange Tchatschenko (GGA+TS ); Hirshfeld population analysis in which verified is presented alendronate is that the three crystals is in zwitterionic state. From the calculation of the band structure was obtained GAPs with very close values for the three crystals, however, with the density of states and characteristic for each crystal. The effective masses, dielectric function and theoretical optical absorptions for all crystals are presented. / Terapias estabelecidas para o tratamento da osteosporose, síndrome caracterizada por aumento na fragilidade óssea e fraturas, consistem primariamente de drogas que previnem a perda óssea, como os bisfosfonatos. Entre eles, o alendronato (PO3)-(OH)-C-((CH2)3 NH3)-(PO3) é um dos tratamentos escolhidos na clínica, pois possui o IC50=50 nM. Neste trabalho é realizado um estudo do alendronato molecular e de três de seus cristais (alendronato de sódio trihidratado e anidro, e alendronato de cálcio) utilizando da Teoria do Funcional da Densidade (DFT). No primeiro caso, o foco são os confôrmeros de menor energia do alendronato molecular no vácuo, em meio aquoso de acordo com o modelo contínuo polarizável (PCM), e interagindo com três moléculas de água e um átomo de sódio de acordo com as características estruturais reveladas por difração de raios-X do cristal do alendrontao de sódio trihidratado; seus espectros vibracionais no infravermelho e Raman são calculados para explicar com detalhes as abundantes assinaturas do grupo fosfato no intervalo de frequência 400-1400 cm−1, com as atribuições dos modos vibracionais mais importantes. No caso dos cristais, são obtidas suas propriedades estruturais, eletrônicas e ópticas na aproximação da gradiente generalizado levando-se em conta a descrição do termo de correlação e troca de Tchatschenko (GGA+TS); é apresentada a análise populacional de Hirshfeld na qual verificou-se que o alendronato nos três cristais encontra-se no estado zwitterionico. A partir do cálculo de estrutura de banda, foi obtido GAPs com valores muito próximos para os três cristais, porém, com densidade de estados bem característica para cada cristal. São apresentadas as massas efetivas, função dielétrica e absorções ópticas teóricas para todos os cristais.

VIANA NETO, Bartolomeu Cruz. Propriedades estruturais e vibracionais de nanocristais de TiO2 dispersos em matriz vítrea porosa. 2006. 49 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2006. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-11-13T22:08:54Z No. of bitstreams: 1 2006_dis_bcviananeto.pdf: 1287691 bytes, checksum: a818652b8c5c3fe5884464f939ed254d (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-11-13T22:19:20Z (GMT) No. of bitstreams: 1 2006_dis_bcviananeto.pdf: 1287691 bytes, checksum: a818652b8c5c3fe5884464f939ed254d (MD5) / Made available in DSpace on 2014-11-13T22:19:20Z (GMT). No. of bitstreams: 1 2006_dis_bcviananeto.pdf: 1287691 bytes, checksum: a818652b8c5c3fe5884464f939ed254d (MD5) Previous issue date: 2006 / Nanostructured materials are the subject of intense investigation due to their remarkable properties as compared their bulk counterparts. The size-induced phenomena are interesting their own and open unique opportunities not only for using these properties in novel applications but also for improving the current technology. In this scenario integrated chemical systems (ICS) are set apart owing their complexity and the possibility ofcombining diferent nanosystems for getting materials with a designed functionality. For instance, nanocrystal growth in the cavities of a porous host is an attractive ICS because the porous is a restricted environment that can be used as nanoreactors. Besides the such system is very promising for catalysis it also important for studying the size-induced properties of the guest material as well. In this work we report the study of vibrational and structural properties of TiO2 nanocrystals dispersed into a porous vycor glass. We have obtained very small TiO2 nanocrystals in the anatase form. The nanocrystal size is controlled via the mass increment only thus preventing the growth through the coalescence process. The nanocrystal size as monitored through transmission electron microscope and Raman scattering. The Eg lowest frequency mode experiences an upshift and becomes broader as the nanocrystal size decreases. This phenomena is attributed to a size-induced e®ect and we analyzed it based on a phonon con¯nement model. As the nanocrystal size gets smaller the q = 0 selection rule is relaxed and the phonon con¯nement involves large q values contribute to the Raman intensity. The frequency follows the same trend of the phonon dispersion relation for the TiO2 bulk as the nanocrystal size decreases. / Materiais nanoestruturados são objetos de intensa investigação devido as suas notáveis propriedades físicas e químicas e quando comparados em suas formas “bulk". Os fenômenos induzidos pela redução do tamanho são interessantes por si próprio e abrem oportunidades únicas, não somente para o uso dessas propriedades em várias aplicações más também para o aprimoramento da tecnologia corrente. Os sistemas químicos integrados (SQI) são um conjunto à parte com complexidade própria e diferentes possibilidades de combinações de nanosistemas para obtenção de materiais com uma funcionalidade desejada. Por exemplo, o crescimento de nanocristais nas cavidades de um hospedeiro poroso é um SQI atrativo, pois o ambiente dos poros pode ser usado como nanoreatores. Da mesma forma que o sistema pode ser muito promissor para catálise é também importante no estudo das propriedades induzidas pelo tamanho do material hóspede. Neste trabalho, estudamos as propriedades estruturais e vibracionais de nanocristais de TiO2 dispersos dentro dos poros do vidro vycor. Foram estudados nanocristais de TiO2 com tamanhos variando de 3-20 nm na fase anatásio. O tamanho dos nanocristais foi monitorado através de microscopia de transmissão eletrônica e espalhamento Raman. O modo Eg, com freqüência em torno de 144 cm-1, experimenta um deslocamento e alargamento de seu pico com a diminuição do tamanho do nanocristal. Este fenômeno é atribuído ao efeito induzido pelo tamanho e analisamos os resultados experimentais com base no modelo de confinamento de fônons. Quando o tamanho do nanocristal é pequeno, a regra de seleção q ≈ 0 no espalhamento Raman de primeira ordem é relaxada e fônons com grandes valores de q contribuem para a intensidade do pico Raman. A freqüência do pico Raman à medida que o tamanho diminui segue o mesmo comportamento da relação de dispersão de fônons para o TiO2 “bulk".

VIANA NETO, Bartolomeu Cruz. Propriedades estruturais e vibracionais de nanotubos e nanofitas de titanato. 2009. 67 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2009. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-11-13T22:32:43Z No. of bitstreams: 1 2009_tese_bcviananeto.pdf: 2854187 bytes, checksum: 4f6bd432814c19af95dec1be0d243db2 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-11-14T17:50:54Z (GMT) No. of bitstreams: 1 2009_tese_bcviananeto.pdf: 2854187 bytes, checksum: 4f6bd432814c19af95dec1be0d243db2 (MD5) / Made available in DSpace on 2014-11-14T17:50:54Z (GMT). No. of bitstreams: 1 2009_tese_bcviananeto.pdf: 2854187 bytes, checksum: 4f6bd432814c19af95dec1be0d243db2 (MD5) Previous issue date: 2009 / This work reports a study on the structural, morphological and vibrational properties of titanate nanotubes and nanoribbons obtained from hydrothermal treatment of TiO$_2$ in aqueous NaOH solutions. The physical properties of these as-synthesized and heat-treated nanostructures are discussed in comparison with their bulk (Na$_2$Ti$_3$O$_7$ and Na$_2$Ti$_6$O$_{13}$) counterparts. The results obtained from transmission electron microscopy, scanning electron microscopy, atomic emission spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, infrared and Raman spectroscopies allowed us to conclude that the layers of both as-synthesized titanates nanotubes and nanoribbons are isostructural to the Na$_2$Ti$_3$O$_7$ lamellar compound. In the titanate nanotubes the chemical bonds are deformed because of the curvature of walls while in the titanates nanoribbons the layers present structural disorder by size effects. The thermal behavior of titanate nanoribbons is similar to those reported in literature for titanate nanotubes, where structural and morphological changes with increases of temperature are observed and indicated that the nanoribbons, at high temperatures, change to bulk with a phase mixing of Na$_2$Ti$_3$O$_7$ and Na$_2$Ti$_6$O$_{13}$. This is similar to what happens with the bulk Na$_2$Ti$_3$O$_7$ when thermally treated. Thus, we conclude that the chemical composition of both the titanate nanotubes and the titanate nanoribbons is the same, Na$_{2-x}$H$_x$Ti$_3$O$_7$.nH$_2$O (0$leq$x$leq$2). Also, we suggest that Raman spectroscopy can be used for an easy and quick identification of both morphology and structure changes of the nanosized titanates. Furthermore, in this work we report the synthesis, characterization and application of Ce ion-exchanged titanate nanotubes. The physicochemical properties of these nanotubes are discussed in comparison with their pure titanate nanotube counterparts. The transmission electron microscope images showed that the Ce ion-exchanged titanate nanotubes have the same morphology of the pristine nanotubes and their external walls are decorated with cerium oxide nanoparticles. The mechanism of nanoparticle formation is based on the precipitation of Ce ion at the nanotube surface. We observed a shift of the absorption band edge towards the visible region that is attributed to the effects of Ce$^{4+}$ addition (intercalation) and/or the presence of CeO$_2$ nanoparticles decorating the nanotubes surfaces. A red shift of vibrational modes associated with metal ion - oxygen interaction was observed and identified as being due to the effect of Ce addition to the lattice as well as the anchoring of CeO$_2$ nanoparticles to the nanotube wall. We show that this hybrid system is promising for applications in photocatalysis using the blue region of the electromagnetic spectrum and this was demonstrated for photodegradation of reactive blue 19 textile dye using visible light ilumination. / Este trabalho relata o estudo das propriedades estruturais, morfológicas e vibracionais dos nanotubos e das nanofitas de titanato obtidos a partir do tratamento hidrotérmico de TiO2 em solução aquosa de NaOH. As propriedades físicas destas nanoestruturas, como preparadas e tratadas termicamente, são discutidas e comparadas com seus similares sólidos estendidos (Na2Ti3O7 e Na2Ti6O13). Os resultados obtidos por microscopia eletrônica de transmissão, microscopia eletrônica de varredura, espectroscopia de emissão atômica, espectroscopia de energia dispersiva de raios-X, difração de raios-X, espectroscopia de absorção no infravermelho com transformada de Fourier e espectroscopia Raman permitem concluir que as camadas (paredes ou lamelas) de nanotubos e nanofitas de titanato, como preparados, são isoestrutural ao composto lamelar Na2Ti3O7. Nos nanotubos de titanato as ligações químicas são deformadas por causa da curvatura das paredes, enquanto nas nanofitas de titanato as camadas apresentam apenas a desordem estrutural causada pelo efeito do tamanho. O comportamento térmico das nanofitas de titanato é similar ao relatado na literatura para os nanotubos de titanatos, onde mudanças estruturais e morfológicas, com o aumento da temperatura, são observadas e indicam que as nanofitas quando submetidas a altas temperaturas mudam sua morfologia para grandes bastões (sólido estendido) com uma mistura das fases Na2Ti3O7 e Na2Ti6O13. Este resultado é similar ao comportamento do Na2Ti3O7, sólido estendido, quando tratado termicamente. Concluímos que os nanotubos e as nanofitas de titanato têm a mesma composição química Na{2-x}HxTi3O7.nH2O(0·x·2).