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Conference: Bucharest University Faculty of Physics 2002 Meeting

Section: Electricity and Biophysics: Honorary Session Dedicated to Professors: Victor Gheorghe (Head of the Dept. 1972-1984) and Grigore Turcu

Title:

High Purity Organic Crystalline Aromatic Derivatives for Electrical and Optical Applications

Authors:

Anca Stanculescu, LauraTugulea* Florin Stanculescu*, Marcela Socol

Affiliation:

National Institute for Material Physics, Bucharest

* Faculty of Physics, University of Bucharest

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Keywords:

Abstract:

Organic materials, known as potential candidates for non-linear optical applications, present a growing interest as materials for electronic and electro-optic devices processing. The great variety of chemical compositions and crystalline packing structures, offers a large field for study, from the point of view of electrical and optical properties, of the bulk and thin film organic solid state. This paper presents some investigations on the intrinsec properties of different aromatic compounds, as benzil, meta-dinitrobenzene, naphthalene, 1,3-dihydroxybenzene and 8-hydroxy-quinoline, using UV-VIS transmission measurements performed on bulk and/or thin film samples. Organic aromatic derivatives crystals have been grown from the melt, using a Bridgman-Stockbarger method, with a special ampoule configuration to initiate and control the crystal growth process, and an adequate thermal regime (a steep gradient at the growth interface between 5 and 30 oC and a slow moving speed of the interface between 0.7 and 2.5 mm/h). We have used as charge materials the above mentioned compounds obtained after different purification stages. Zone melting refining process was used to remove the main impurities: benzofurazan-1-oxid for meta-dinitrobenzene, methyl and thionaphthalene for naphthalene and benzoin for benzil. We have also made a comparative study on the purity of these organic compounds using X-Ray Diffraction and IR Absorption Spectroscopy (for organic impurities detection) and Inductively Coupled Plasma Optical Emission Spectroscopy (for metallic impurities detection). A general qualitative information on the major component purity was given by thermogravimetric analysis coupled with differential thermal analysis. We have studied the light absorption process near the fundamental absorption edge and underlined the dominant semiconductor character of the organic compounds investigated.