SARAIVA, Gilberto Dantas. Espectroscopia Raman ressonante em nanotubos de carbono funcionalizados. 2008. 145 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2008. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-04T19:13:31Z No. of bitstreams: 1 2008_tese_gdsaraiva.pdf: 6765379 bytes, checksum: ded06cc237d77dabfc5886e3ed738be4 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-07T14:32:02Z (GMT) No. of bitstreams: 1 2008_tese_gdsaraiva.pdf: 6765379 bytes, checksum: ded06cc237d77dabfc5886e3ed738be4 (MD5) / Made available in DSpace on 2015-05-07T14:32:02Z (GMT). No. of bitstreams: 1 2008_tese_gdsaraiva.pdf: 6765379 bytes, checksum: ded06cc237d77dabfc5886e3ed738be4 (MD5) Previous issue date: 2008 / In this Thesis we report a study of the synthesis and functionalization of carbon nanotubes. Regarding the synthesis, we produced carbon nanotubes samples using the chemical vapor deposition method. Both single-wall and multi-wall carbon nanotubes were produced. The basic difference between these two growth results was the catalyst employed. We also have changed the exposure time of catalyst particle to the hydrogen gas to find out the optimal parameters for growing the nanotubes. The obtained samples were characterized by resonance Raman spectroscopy and thermal analysis. The obtained samples show higher thermal stability compared with some commercially available samples. Regarding functionalization of the tubes we studied three different systems. Firstly, we investigated the effect of Si+ and C+ ions bombardment on the structural and electronic properties of highly pure double wall carbon nanotubes (DWNTs). The implantation was performed at room temperature with high fluencies of ions varying from 1 to 100 x( 10 13 ions/cm2) and the Raman spectroscopy was the main technique employed for studying the ion implantation-induced changes in the nanotubes. The effects of the Si+ implantation is stronger than that of C+ and this is attributed to the larger ionic radius of Si. The D to G band intensity ratio was used for probing the ion concentration for which the system looses its sp2 character leading to a highly disordered system with a high concentration of sp3 bonds. We observed that as the ion implantation dosage increases, the D-band intensity increases and the radial breathing modes (RBM) of the semiconducting (outer) and metallic (outer) tube disappear first, before from the inner tubes. At higher ion-implantation dosage, the carbon nanotubes are completely deformed and the Raman spectrum is typical of highly disordered graphite. Secondly, we investigated the effects of H2SO4 doping on DWNTs and SWNTs where the diameter of SWNTs are in the same range as the inner tube of the DWNTs. The comparison of these two systems allow to further improve the knowledge of doping effects on the constituents of DWNTs as well as to establish differences between the exohedral doping of SWNTs and DWNTs bundles. Upon doping with H2SO4 the Breit-Wigner-Fano lineshape of metallic tubes in the SWNTs samples decreases and the G band frequencies increase thus indicating that an electronic charge transfer is occurring from the nanotubes to the dopant molecule. The effect on the DWNTs is opposite to that of SWNTs thus evidencing that the inner and outer shell interaction seems to affect the inner tube electronic transitions more than those of the outer tubes. Thirdly, we report a detailed characterization of a novel carbon nanotube-based system that is a coaxial nanocable made of carbon as core and selenium as shell. Carbon nanotube bundles are wrapped up within a trigonal selenium shell. We have demonstrated that the Butyl-lithium compound plays an important role in promoting the interaction between the carbon nanotubes and the selenium shells and thus enables the preparation of these nanocable structures. The Raman spectra of the SWNTs in the residue and the Se-CNT nanocables suggests that this selenium-carbon interaction is stronger for semiconducting nanotubes than for metallic nanotubes. The chemistry of Selenium would allow the synthesis of carbon nanotubes decorated with other functional Se-based structures, such as CdSe, ZnSe, among others. / Esta tese consiste no estudo do processo de síntese e funcionalização de nanotubos de carbono. A síntese dos nanotubos de carbono foi realizada usando a técnica de deposição química a partir da fase vapor (CVD). Foram sintetizados Nanotubos de parede simples (SWNTs) e múltipas (MWNTs) . A diferença básica das metodologias usadas para preparar as amostras foi o uso de diferentes catalisadores expostos ao gás hidrogênio por diferentes intervalos de tempo. As amostras obtidas foram caracterizadas por espectroscopia Raman ressonante e análise térmica. Os resultados de análise térmica mostraram que as amostras sintetizadas apresentam uma excelente estabilidade térmica, quando comparada com algumas amostras disponíveis no mercado. Foram estudados três diferentes sistemas em relação ao processo de funcionalização de nanotubos de carbono. No primeiro sistema, investigamos o efeito da irradiação de íons de silício (Si+) e carbono (C+) nas propriedades eletrônicas e estruturais dos nanotubos de parede dupla (DWNTs). A implantação foi realizada à temperatura ambiente com concentrações de íons que variam de 1 a 100 x (1013 íons/cm2); e a espectroscopia Raman ressonante foi a principal técnica utilizada para estudar os efeitos da implantação. Os efeitos da implantação dos íons de Si+ na estrutura dos nanotubos são mais fortes do que os íons de C+ o que é atríbuido ao maior raio iônico do Si+. A razão das intensidades das bandas D e G foi usada para investigar a concentração de íons para a qual o sistema perde a característica sp2, deixando o sistema muito desordenado e com grande concentrações de ligações sp3. Observamos que o aumento da dosagem de íons aumenta a intensidade da banda D e os modos radiais de respiração dos nanotubos semicondutores (tubo externo) e metálicos (tubo externos) desaparecem primeiramente do que os tubos internos. Para altas dosagens de implantação de íons de silício ou carbono observamos que os nanotubos são completamente deformados e os espectros Raman apresentam aspectos de grafite altamente desordenados. No segundo sistema estudado, investigamos os efeitos da dopagem da molécula de H2SO4 nos SWNTs e DWNTs com distribuição de diâmetros dos SWNTs similar aos tubos internos dos DWNTs. A comparação destes dois sistemas permitiu ter um maior conhecimento dos efeitos da molécula H2SO4 nos sistemas DWNTs como também estabelecer diferenças entre a dopagem por intercalação nos feixes de SWNTs e DWNTs. A dopagem com H2SO4 torna o perfil Breit-Wigner-Fano (BWF) dos nanotubos metálicos nos sistemas SWNTs menos acentuado e a freqüência da banda G aumenta indicando que uma transferência de carga ocorre dos nanotubos para as moléculas de H2SO4. O efeito nos DWNTs é o oposto ao que foi evidenciado para os SWNTs, mostrando que a interação entre os tubos internos e externos no sistema DWNTs parece afetar mais fortemente as transições eletrônicas dos tubos internos do que as transições dos tubos externos. No terceiro sistema estudado, caracterizamos de maneira detalhada um novo sistema híbrido baseado em nanotubos de carbono que consiste de um cabo coaxial com carbono no interior e uma casca de selênio como tubo exterior. Demonstramos que o composto Butil-Lítio promove a interação entre os nanotubos de carbono e a casca de selênio levando a formação destes nanocabos. O espectro Raman dos SWNTs da amostra resíduo e selênio-nanotubos sugere que os nanocabos de selênio carbono interagem mais fortemente com os nanotubos semicondutores do que com os nanotubos metálicos. Estimamos que a química do selênio permitirá sintetizar nanocabos de selênio-carbono decorados com outros compostos funcionais tais como CdSe, ZnSe entre outros.

Esta tese consiste no estudo do processo de sÃntese e funcionalizaÃÃo de nanotubos de carbono. A sÃntese dos nanotubos de carbono foi realizada usando a tÃcnica de deposiÃÃo quÃmica a partir da fase vapor (CVD). Foram sintetizados Nanotubos de parede simples (SWNTs) e mÃltipas (MWNTs) . A diferenÃa bÃsica das metodologias usadas para preparar as amostras foi o uso de diferentes catalisadores expostos ao gÃs hidrogÃnio por diferentes intervalos de tempo. As amostras obtidas foram caracterizadas por espectroscopia Raman ressonante e anÃlise tÃrmica. Os resultados de anÃlise tÃrmica mostraram que as amostras sintetizadas apresentam uma excelente estabilidade tÃrmica, quando comparada com algumas amostras disponÃveis no mercado. Foram estudados trÃs diferentes sistemas em relaÃÃo ao processo de funcionalizaÃÃo de nanotubos de carbono. No primeiro sistema, investigamos o efeito da irradiaÃÃo de Ãons de silÃcio (Si+) e carbono (C+) nas propriedades eletrÃnicas e estruturais dos nanotubos de parede dupla (DWNTs). A implantaÃÃo foi realizada à temperatura ambiente com concentraÃÃes de Ãons que variam de 1 a 100 x (1013 Ãons/cm2); e a espectroscopia Raman ressonante foi a principal tÃcnica utilizada para estudar os efeitos da implantaÃÃo. Os efeitos da implantaÃÃo dos Ãons de Si+ na estrutura dos nanotubos sÃo mais fortes do que os Ãons de C+ o que à atrÃbuido ao maior raio iÃnico do Si+. A razÃo das intensidades das bandas D e G foi usada para investigar a concentraÃÃo de Ãons para a qual o sistema perde a caracterÃstica sp2, deixando o sistema muito desordenado e com grande concentraÃÃes de ligaÃÃes sp3. Observamos que o aumento da dosagem de Ãons aumenta a intensidade da banda D e os modos radiais de respiraÃÃo dos nanotubos semicondutores (tubo externo) e metÃlicos (tubo externos) desaparecem primeiramente do que os tubos internos. Para altas dosagens de implantaÃÃo de Ãons de silÃcio ou carbono observamos que os nanotubos sÃo completamente deformados e os espectros Raman apresentam aspectos de grafite altamente desordenados. No segundo sistema estudado, investigamos os efeitos da dopagem da molÃcula de H2SO4 nos SWNTs e DWNTs com distribuiÃÃo de diÃmetros dos SWNTs similar aos tubos internos dos DWNTs. A comparaÃÃo destes dois sistemas permitiu ter um maior conhecimento dos efeitos da molÃcula H2SO4 nos sistemas DWNTs como tambÃm estabelecer diferenÃas entre a dopagem por intercalaÃÃo nos feixes de SWNTs e DWNTs. A dopagem com H2SO4 torna o perfil Breit-Wigner-Fano (BWF) dos nanotubos metÃlicos nos sistemas SWNTs menos acentuado e a freqÃÃncia da banda G aumenta indicando que uma transferÃncia de carga ocorre dos nanotubos para as molÃculas de H2SO4. O efeito nos DWNTs à o oposto ao que foi evidenciado para os SWNTs, mostrando que a interaÃÃo entre os tubos internos e externos no sistema DWNTs parece afetar mais fortemente as transiÃÃes eletrÃnicas dos tubos internos do que as transiÃÃes dos tubos externos. No terceiro sistema estudado, caracterizamos de maneira detalhada um novo sistema hÃbrido baseado em nanotubos de carbono que consiste de um cabo coaxial com carbono no interior e uma casca de selÃnio como tubo exterior. Demonstramos que o composto Butil-LÃtio promove a interaÃÃo entre os nanotubos de carbono e a casca de selÃnio levando a formaÃÃo destes nanocabos. O espectro Raman dos SWNTs da amostra resÃduo e selÃnio-nanotubos sugere que os nanocabos de selÃnio carbono interagem mais fortemente com os nanotubos semicondutores do que com os nanotubos metÃlicos. Estimamos que a quÃmica do selÃnio permitirà sintetizar nanocabos de selÃnio-carbono decorados com outros compostos funcionais tais como CdSe, ZnSe entre outros. / In this Thesis we report a study of the synthesis and functionalization of carbon nanotubes. Regarding the synthesis, we produced carbon nanotubes samples using the chemical vapor deposition method. Both single-wall and multi-wall carbon nanotubes were produced. The basic difference between these two growth results was the catalyst employed. We also have changed the exposure time of catalyst particle to the hydrogen gas to find out the optimal parameters for growing the nanotubes. The obtained samples were characterized by resonance Raman spectroscopy and thermal analysis. The obtained samples show higher thermal stability compared with some commercially available samples. Regarding functionalization of the tubes we studied three different systems. Firstly, we investigated the effect of Si+ and C+ ions bombardment on the structural and electronic properties of highly pure double wall carbon nanotubes (DWNTs). The implantation was performed at room temperature with high fluencies of ions varying from 1 to 100 x( 10 13 ions/cm2) and the Raman spectroscopy was the main technique employed for studying the ion implantation-induced changes in the nanotubes. The effects of the Si+ implantation is stronger than that of C+ and this is attributed to the larger ionic radius of Si. The D to G band intensity ratio was used for probing the ion concentration for which the system looses its sp2 character leading to a highly disordered system with a high concentration of sp3 bonds. We observed that as the ion implantation dosage increases, the D-band intensity increases and the radial breathing modes (RBM) of the semiconducting (outer) and metallic (outer) tube disappear first, before from the inner tubes. At higher ion-implantation dosage, the carbon nanotubes are completely deformed and the Raman spectrum is typical of highly disordered graphite. Secondly, we investigated the effects of H2SO4 doping on DWNTs and SWNTs where the diameter of SWNTs are in the same range as the inner tube of the DWNTs. The comparison of these two systems allow to further improve the knowledge of doping effects on the constituents of DWNTs as well as to establish differences between the exohedral doping of SWNTs and DWNTs bundles. Upon doping with H2SO4 the Breit-Wigner-Fano lineshape of metallic tubes in the SWNTs samples decreases and the G band frequencies increase thus indicating that an electronic charge transfer is occurring from the nanotubes to the dopant molecule. The effect on the DWNTs is opposite to that of SWNTs thus evidencing that the inner and outer shell interaction seems to affect the inner tube electronic transitions more than those of the outer tubes. Thirdly, we report a detailed characterization of a novel carbon nanotube-based system that is a coaxial nanocable made of carbon as core and selenium as shell. Carbon nanotube bundles are wrapped up within a trigonal selenium shell. We have demonstrated that the Butyl-lithium compound plays an important role in promoting the interaction between the carbon nanotubes and the selenium shells and thus enables the preparation of these nanocable structures. The Raman spectra of the SWNTs in the residue and the Se-CNT nanocables suggests that this selenium-carbon interaction is stronger for semiconducting nanotubes than for metallic nanotubes. The chemistry of Selenium would allow the synthesis of carbon nanotubes decorated with other functional Se-based structures, such as CdSe, ZnSe, among others.

No description available.

In this thesis, experimental studies are reported of ultrafast dynamics and third order optical nonlinear coefficients of carbon nanotubes, and time resolved coherent phonon dynamics of semiconductors and rare earth titanates. The thesis is divided into three parts. The first part presents (i) general introduction to theoretical background on nonlinear optical susceptibility and time resolved studies, and systems studied (chapter 1) and (ii) experimental techniques (chapter 2). The second part of the thesis deals with the measurements of third order nonlinear susceptibilities and ultrafast dynamics of single and double walled carbon nanotubes (chapter 3). The third part contains coherent phonon dynamics in semiconductors, Te (chapter 4), Bi2Te3 (chapter 5), and ZnTe (chapter 6) and spin-frustrated rare earth titanate insulators (chapter 7). Chapter 1: This chapter is a general introduction to the thesis. The chapter is divided into two parts: (i) light-matter interaction, and (ii) systems studied. Under light-matter interaction, we describe the required theoretical and conceptual background of nonlinear optical susceptibilities and time resolved carrier and phonon dynamics. In the next part, a brief summary of details of the systems studied, that include carbon nanotubes (single and double walled), semiconductors (Te, Bi2Te3 and ZnTe) and insulating spin-frustrated rare earth titanates (Gd2Ti2O7, Dy2Ti2O7 and Tb2Ti2O7), are presented. Chapter 2: Details of the ultrafast laser systems (femtosecond oscillator and amplifier), pulse width measurements and ultrafast experimental pump-probe and z-scan techniques, used in this thesis are given in this chapter. Chapter 3: Here the experimental results on the measurements of third order optical nonlinearity and ultrafast dynamics of single and double walled carbon nanotubes are presented. The chapter starts with a general overview of optical switching followed by known ultrafast dynamics and nonlinear studies on carbon nanotubes. In the next section, our theoretical modelling of nonlinear absorption and refraction in the limit of saturable absorption is described. The final two sections depict our results on single and double walled carbon nanotubes. These studies indicate that double walled carbon nanotubes are best candidates for ultrafast optical switching. Chapter 4: This chapter presents temperature and pump fluence dependent femtosecond time resolved reflectivity measurements on tellurium. The chapter starts with an overview of previous pump-probe reflectivity studies at room temperature on tellurium followed by our results. A totally symmetric A1 coherent phonon at 3.6 THz responsible for the oscillations in the reflectivity data is observed to be strongly positively chirped (i.e, phonon time period decreases at longer pump-probe delay times) with increasing photoexcited carrier density, more so at lower temperatures. We show for the first time that the temperature dependence of the coherent phonon frequency is anomalous (i.e, increasing with increasing temperature) at high photoexcited carrier density due to electron-phonon interaction. At the highest photoexcited carrier densities of ~ 1.4 x 1021cm-3 and the sample temperature of 3K, the lattice displacement of the coherent phonon mode is estimated to be as high as ~ 0.24 Å. Numerical simulations based on coupled effects of optical absorption and carrier diffusion reveal that the diffusion of carriers dominates the non-oscillatory electronic part of the time-resolved reflectivity. Finally, using the pump-probe experiments at low carrier density of 6 x 1018 cm-3, we separate the phonon anharmonicity to obtain the electron-phonon coupling contribution to the phonon frequency and linewidth. Chapter 5: This chapter begins with a introduction of previous ultrafast studies at room temperature on Bi2Te3 and then presents our results on the temperature dependent high pump fluence time resolved reflectivity measurements on Bi2Te3. The time resolved reflectivity data shows two coherently generated totally symmetric A1g modes at 1.85 THz and 3.6 THz at 296K which blue shift to 1.9 THz and 4.02 THz, respectively at 3K. At high photoexcited carrier density of ~ 1.7 x 1021cm-3, the phonon mode at 4.02 THz is two orders of magnitude higher positively chirped than the lower frequency mode at 1.9 THz. The chirp parameter, β is shown to vary inversely with temperature. The time evolution of these modes is studied using continuous wavelet transform of the time-resolved reflectivity data. The analysis shows that the build up time for the two coherent phonons is different. Chapter 6: This chapter starts with a general introduction on various as pects of ZnTe to be used in generation and detection of THz followed by our results on influence of carriers and sample temperature on coherent phonon and polariton generation in ZnTe. Combination of femtosecond Kerr, two photon absorption and impulsive stimulated Raman scattering experiments have been carried out to investigate the effect of pulse energy and crystal temperature on the generation of coherent polaritons and phonons in < 110 > cut ZnTe single crystals of three different resistivities. We demonstrate that the effect of two-photon induced free carriers on the creation of both the polaritons and phonons is largest at 4K where the free carrier lifetime is enhanced. Further, the temperature dependant impulsive stimulated Raman scattering on high and low purity ZnTe crystals allows us to unambiguously assign the phonon mode at 3.5 THz to the longitudinal acoustic mode at X-point in the Brillouin zone, LA(X) in contrast to the assignment as two-phonon process in earlier studies. Chapter 7: This chapter starts with an introduction on previous Raman studies on the pyrochlore systems accompanied by our results on the generation of coherent optical phonons in spin frustrated pyrochlore single crystals Dy2Ti2O7, Gd2Ti2O7 and Tb2Ti2O7 and their behavior as a function of sample temperature from 296K to 4K. At 4K, two coherent phonons are observed at 5.3 THz (5.0 THz) and ~ 9.3 THz (9.4 THz) for Dy2Ti2O7 (Gd2Ti2O7) whereas three coherent phonons are generated at ~ 4.8 THz, 8.6 THz and 9.6 THz for Tb2Ti2O7. In the case of spin-ice Dy2Ti2O7, a clear discontinuity is observed in the linewidths of both the coherent phonons as well as in the phase of low energy coherent phonon mode, indicating a subtle structural change as also suggested by Raman studies. In comparison, such changes are not seen in the coherent phonons of Gd2Ti2O7, and Tb2Ti2O7. Another important observation is the phase difference of ‘π’ between the modes in all the samples, thus suggesting that the driving forces behind the generation of these modes are different in nature unlike a purely impulsive or displacive mechanism. Chapter 8: This chapter summarizes our results reported in this thesis and gives future directions.