Optical properties of potassium acid phthalate
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Optical properties of potassium acid phthalate Davide Comoretto Dipartimento di Chimca e Chimica Industriale, Universit`a degli Studi di Genova, via Dodecaneso 31, I-16146, Genova, Italy
Laura Rossi INFM, Dipartimento di Fisica “A. Volta,” Universit`a degli Studi di Pavia, via Bassi 6, I-27100 Pavia, Italy
Alessandro Borghesi INFM, Dipartimento di Fisica, Universit´a degli Studi di Modena, via Campi 213ya, I-41100 Modena, Italy (Received 23 February 1995; accepted 12 June 1996)
Potassium acid phthalate (KAP) crystals are promising as substrates for the growth of highly oriented films of conjugated polymers with exceedingly high and fast nonlinear optical response. We report the KAP optical properties (real and imaginary parts of the refractive index n˜ n 1 ik) in the near infrared and visible range deduced by ellipsometric measurements and direct inversion of transmittance and near-normal incidence absolute reflectance measurements. In the infrared region n was also deduced by the interference fringes.
I. INTRODUCTION
Potassium acid phthalate (KAP), whose chemical formula is K(C6 H4 COOH ? COO), is a well-known organic salt used in the production of crystal analyzers for long-wave x-ray spectrometers.1,2 KAP is also known for its piezoelectric, pyroelectric, and elastic properties3,4 as well as for its nonlinear optical properties.3–6 Moreover, KAP and other phthalates are used in the preparation of buffer solutions.7 Recently, KAP crystals have assumed an important role in the epitaxial growth of oriented poly [1, 6-bis(Ncarbazolyl)-2, 4-hexadiyne] (polyDCH),8 a conjugated polymer which shows a very large (x s3d 1027 esu) and fast (0.8 ps) nonlinear optical susceptibility.9 The importance of KAP is related to its uniqueness as a substrate which allows the growth of oriented polyDCH. Usually the substrates used for the deposition of organic thin films are chosen for their optical transparency in the spectral region of interest. In this case, KAP crystals play an active role in the growth process. The orientation of the DCH molecules is driven by the molecular insertion of the carbazolyl side group between the KAP phenyl rings. The molecular matching is stabilized through p interactions between the phenyl groups of the monomer and those of the KAP substrate.8 In a second step, the sample is polymerized by heating. The oriented structure of the monomer is preserved in the polymerization process which does not affect the substrate. In the hope of developing photonics devices based on these highly oriented polymeric thin films grown on KAP, a complete optical characterization of the substrate is essential. 1262
http://journals.cambridge.org
J. Mater. Res., Vol. 12, No. 5, May 1997
Downloaded: 13 Sep 2014
The vibrational properties of KAP were investigated by transmission10 and Raman11 measurements. Few data on the optical response and on n˜ for the KAP crystals are available3 in the spectral region of interest in technological applications (from the near infrare
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