Obtenção e caracterização de materiais dopados SiO2-CdSe a partir de sonogeis de silica

AUTOR(ES)
DATA DE PUBLICAÇÃO

1994

RESUMO

The sol-gel process has proved to be extremely interesting in the production of new materiaIs. This is clearly indicated by the great number of publications in this area in the last decade. The possibility of obtaining monolithic solid materials and also powders, films and fibers from a liquid mixture of components at room temperature via aggregation and polymerization reactions is particularly interesting. The easy way in which chemical composition can be modified allows the preparation of composite materiais with specific optical, electronic, chemicalor mechanical properties designed for special applications in modern tecnology. In particular, materiaIs consisting in a vitreous matrix with embedded nanocrystals of semiconductor compounds are known to present non-linear optical properties wich makes them very important in strategic technological applications, such as communications and data processing. In this work we present the results of the preparation of materials consisting of semiconducting nanoparticles embedded in a silica gel matrix. The host matrices were prepared by hydrolysis of tretaethylortosilicate (TEOS) with the addition of cadmium nitrate. Two different additives were used as a drying control agent (DCCA) : formamide and N-Ndimethylformamide. The preparation process included the use of pre-determined doses of high power ultrasound. The matrices were characterized by thermal analyses (TGA and DTA), gas adsorption techniques (BET), mercury picnometry, scanning electron microscopy (SEM) and small angle X ray scattering (SAXS). The impregnation of the dry "sonogels" using a KSeCN solution under vacuum, led to the formation of CdSe nanocrystals and improved the mechanical properties of the matrix. Typically red, transparent xerogels were obtained and characterized by optical absorption spectroscopy, transmission electron microscopy (TEM), and SAXS. The results of this study lead to propose a structural model for these materials, consisting of a porous matrix containing CdSe nanocrystals with a bimodal size distribution that depends on the selenium content in the solution used for the liquid diffusion. The shift in the optical absorption band towards higher energies (blue shift) revcals the quantum confinement in the nanosized particles of cadmium selenide

ASSUNTO(S)

silica-gel supercondutividade

ACESSO AO ARTIGO

Documentos Relacionados