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Master's Dissertation
DOI
10.11606/D.88.2007.tde-09042008-144931
Document
Author
Full name
Hilton Barbosa de Aguiar
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2007
Supervisor
Committee
Miranda, Paulo Barbeitas (President)
Corio, Paola
Rodrigues Filho, Ubirajara Pereira
Title in Portuguese
Alguns aspectos acerca da adsorção de alcanotióis e bases nitrogenadas em ouro via espectroscopia não linear e microscopia de tunelamento de elétrons
Keywords in Portuguese
Adsorção
Alcanotiol
Au
derivados de uracil
Eletroquimica
Espectroscopia vibracional de geração de fotons por soma de frequências
Microscopia de tunelamento de elétrons
Abstract in Portuguese
Estudos de interface têm presenciado um recente crescimento devido as novas propriedades físico-químicas, que puderam ser explorados com o advento de técnicas com resolução ao nível molecular/atômico. Dessas técnicas, dois ramos que merecem destaque são as Microscopias de Varredura por Ponta de Prova e Espectroscopias Óticas. Neste trabalho fazemos uso de algumas destas técnicas (o Microscópio de Tunelamento de Elétrons e Espectroscopia Vibracional por Geração de Soma de Freqüências) para estudar a adsorção de moléculas alifáticas e aromáticas em Au. Dois casos são abordados: como a rugosidade do substrato influencia no mecanismo de automontagem de monocamadas de alcanotióis e a automontagem de derivados de uracil em interfaces eletroquímicas. No primeiro caso, mostra-se que a quantidade de defeitos moleculares na monocamada adsorvida e extremamente sensível a rugosidade do substrato utilizado. Unem-se os resultados das técnicas acima aos resultados de sondas eletroquímica para se chegar a um modelo. Também e estudado a dependência das etapas de fisisorção e quimisorção em função da concentração da solução de alcanotiól. Para o segundo caso, um derivado halogenado do uracil (5-fluorouracil), mostra-se como a substituição química na base nitrogenada leva a diferentes mecanismos de formação de monocamadas na interface eletroquímica. Imagens de Microscopia de Tunelamento de Elétrons com resolução atômica e molecular mostram que em densidade de cargas negativas as moléculas estão fisisorvidas, porém não formam estruturas periódicas em contraste com uracil e timina, entretanto em densidades de cargas positivas formam estruturas periódicas quimisorvidas, assim como uracil e timina. E discutido como são diferentes os mecanismos de interação intermolecular: no caso dos alcanotiois preponderando às interações de van der Waals e no caso dos derivados de uracil pelas ligações via pontes de hidrogênio são dominantes.
Title in English
Some aspects concerning the adsorption of alkanethiols and uracil derivates on Au via nonlinear spectroscopy and scanning tunneling microscopy
Keywords in English
Adsortion
Alkanethiol
Au
Electrochemistry
Microscopy (STM)
Scanning tunneling
Uracil derivates
Vibration sum frequency generation spectroscopy (VSFG)
Abstract in English
Interface science has experienced a new rebirth since the development of new probes with atomic/molecular resolution, giving new insights about the physical-chemical properties, which differ substantially from the bulk. Among these techniques, two branches deserve special attention: the Scanning Probe Microscopies and Optical Spectroscopy. In this work, two derivatives of theses techniques (the Scanning Tunnelling Microscopy and Vibrational Spectroscopy by Sum-Frequency Generation) are combined giving new insights about the molecular adsorption onto Au. Two examples are focused: how roughness plays a key role in the structure of self-assembled alkanethiol monolayer and the uracil derivatives self-assembling at electrochemical interfaces. For the former, it has been shown that the amount of defects on the adsorbed monolayer is highly sensitive to substrate roughness. Combining the results of each technique with a well-known electrochemical probe, a physical model is proposed. The physisorbed and chemisorbed states are studied as a function of alkanethiol solution concentration as well. For the later case, the chemical substitution of uracil leads to drastically different results for the physisorbed phase (negative charge densities), compared to uracil and thymine. In the chemisorbed phase (positive charge densities) imaging with molecular resolution is achieved showing a quasi-hexagonal structure, similar to the structure of thymine and uracil. It is discussed what are the main driving forces for the self-assembling mechanism: van der Waal interactions for the alkanethiols and hydrogen bonding for uracil derivatives.
 
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HiltonAguiar_M.pdf (3.75 Mbytes)
Publishing Date
2008-04-10
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • de Aguiar, H. B., et al. Adsorption Behavior of 5-Fluorouracil on Au(111): An In Situ STM Study [doi:10.1021/jp100890a]. Journal of physical chemistry. C [online], 2010, vol. 114, p. 6663-6670.
  • BERGAMASKI, Kleber, et al. Characterization of alkanethiol self-assembled monolayer by SFG vibrational spectroscopy. In 2nd International symposium on advanced materials and nanostructures, São Carlos, SP, 2007. Book of Abstracts, 2nd International symposium on advanced materials and nanostructures., 2007. Resumo.
  • BERGAMASKI, Kleber, et al. Characterization of an alkanethiol self-assembled monolayer via sum-frequency vibrational spectroscopy. In V Encontro da SBPMat, Florianópolis, SC, 2006. Livro de resumos doV Encontro da SBPMat. : SBPMat, 2006. Resumo.
  • GOMES, J. F., et al. New information about adsorbed intermediates of the electrooxidation of ethanol on Pt as probed by SFG spectroscopy. In Annual 58th meeting of the international society of electrochemistry, Banff, 2007. Book of abstracts of the Annual 58th meeting of the international society of electrochemistry. : International society of electrochemistry, 2007. Resumo.
  • SILVA, Heurison da Sousa e, et al. Sum-frequency vibrational spectroscopy of self-assembled ultrathin organic layers. In The 7th Pacific Rim Conference on Lasers and Electro-optics, Seoul, 2007. Final program of the 7th Pacific Rim Conference on Lasers and Electro-optics.Seoul, Coréia do Sul, 2007. Resumo.
  • UEHARA, Thiers Massami, et al. Characterization of an alkanethiol self-assembled monolayervia sum-frequency vibrational spectroscopy. In VII Encontro da SBPMat, Guarujá, 2008. CD de resumos do VII Encontro da SBPMat., 2008. Resumo.
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