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Master's Dissertation
DOI
10.11606/D.43.2001.tde-02082013-141746
Document
Author
Full name
Doris Maribel Escriba Villanueva
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2001
Supervisor
Committee
Santos, Marina Amelia Pinto Viegas da Silveira (President)
Coelho, Antonio Carlos Vieira
Muramatsu, Mikiya
Title in Portuguese
O método de decoração com ouro aplicado ao estudo da superfície de cristais inorgânicos
Keywords in Portuguese
Argilominerais.
Decoração com Ouro
Filme Fino
Microscopia Eletrônica
Superfície Microtopográfica
Abstract in Portuguese
O método de decoração metálica com ouro, desenvolvido por Bassett, em 1958, é de muito interesse no estudo de cristais por microscopia eletrônica de transmissão. Desde aquela época, o método vem sendo aplicado ao estudo de vários fenômenos físicos relacionados à nucleação e epitaxia de filmes finos, bem como em estudos de crescimento e evaporação de cristais. Neste trabalho o método de réplica de decoração foi utilizado para investigar a microtopografia superficial de cristais inorgânicos, de interesse tecnológico e industrial. Nos vários experimentos de decoração, obtivemos adsorção bem localizada dos núcleos de ouro, ao longo de orientações definidas. Nos argilominerais caulinita e diquita, foram marcadas figuras poligonais que seguem os contemos pseudo-hexagonais da própria partícula cristalina. Nos cristais iônicos usados, brometo de potássio e cloreto de sódio, observaram-se degraus monoatômicos em formas variadas, inclusive em espirais originadas por discordâncias em parafuso. Outros sítios da superfície com diferentes energias de adsorção puderam ser identificados em todas as amostras estudadas, através desta metodologia. Nos cristais de calcita não logramos obter figuras de decoração bem definidas, mas sim áreas alternadas com ouro condensado e áreas de interdição, causadas provavelmente pela hidratação natural do mineral. Defeitos pontuais como vacâncias, ilhas ou depressões monoatômicas foram reconhecidos nas figuras de decoração, assim como degraus lineares causados por clivagem.
Title in English
The method of gold decoration applied to the study of the surface of inorganic crystals
Keywords in English
Clay minerals.
Decorating with Gold
Electron Microscopy
Surface Microtopographic
Thin Film
Abstract in English
The gold decoration method originally developed by Bassett in 1958, still is of great interest for unraveling microtopographic details of crystal surfaces in the transmission electron microscope. It is of interest also for studies relating to nucleation and epitaxial growth of thin films, as well as in the study of crystal growth and evaporation itself. The present study was intended to investigate the surface morphologies and defects of some selected inorganic crystals, having technological applications. Ali the different samples prepared by this replica method, presented a clear localization of the gold clusters, along very specific sites. The clay minerais kaolinite and dickite exhibited polygonal figures with a pseudo hexagonal arrangement, parallel to the crystal's edges. Growth steps having two different spacings were seen to interlace at 120°. Bromine and sodium halides have monoatomic steps aligned along linear or curved paths; these gold decorated steps could be followed for ample extents in the replicas; among them, other less usual patterns of gold decorated imperfections forming loops, waves and circles were located. The only exception was represented by calcite, in which the decoration was at random. Despite this, some images of deep steps caused by cleavage of the crystals could be clearly recognized. Control images obtained by scanning electron microscopy of cleaved crystals and direct transmission electron microscopy of clay mineral particles, were helpful in the interpretation of the results.
 
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Publishing Date
2013-08-02
 
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