Optical Characterization of Polydiacetylene Langmuir Blodgett Film on Silicon Substrates
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OPTICAL CHARACTERIZATION OF POLYDIACETYLENE LANGMUIR-BLODGETT FILM ON SILICON SUBSTRATES. P. MILLER, A.K.M. RAHMAN, S.V. BROUDE and S. TRIPATHY University of Lowell, Departments of Physics and Chemistry Lowell, MA, 01854. ABSTRACT A bilayer of a surfactive polydiacetylene (15-8 PDA) has technique on a smooth been deposited by Langmuir-Blodgett Silicon substrate using a commercial Lauda film balance [1]. The morphology of the deposited film has been studied by cross-polarized optical micr3scopy, and laser light scattering microscopy. Usual crystalline domains with size ranging from 5 to 50 gm can be seen between cross polarizers. Nonuniformities and voids in the film are observed by imaging the scattered light from a visible laser beam incident at grazing angle onto the film. Raman scattering study on these bilayers have been carried out to investigate their vibronic structure. Information about vibronic levels from PDA has been used to define the extent of disorder and crystalline phase of the bilayer. INTRODUCTION Polydiacetylene is a promising material for nonlinear optical applications because of its large third order susceptibility. In addition, the molecule can be engineered to improve its nonlinear properties by attaching appropriate side groups onto the monomer [2]. To be suitable for optical applications, the material has to have also good linear optical the Any micron-range defects produced during properties. processing of the polymer will give rise to scattering centers. There is a strong interest in studying the morphology of these materials and in developing fast, reliable and nondestructive techniques to control and monitor their optical quality and uniformity. Using Langmuir-Blodgett (LB) technique, polydiacetylene may be produced as ultra thin multilayers with polycrystalline structure [1]. This versatile technique produces, films with thickness and chemical nature controlable down to a single molecular layer. However, unavoidable structural defects remain obstacles for technological applications of these LB films [3]. Cross-polarized optical microscopy, laser light scattering microscopy and Raman scattering were used to investigate ultrathin LB films of the 15-8 polydiacetylene. Each of these characterization technique is discused as a potential inspection tool for this particular material. PREPARATION OF THE FILMS Monolayer films of 15-8 diacetylene monomer were prepared at the air-water interface using LB technique. The subphase contained a solution of CoCl 2 of concentration 2.5x10 M in water. The water used was double distilled and Millipore Milli-Q purification system. A constant Mat. Res. Soc. Symp. Proc. Vol. 173. @1990 Materials Research Society
purified by temperature
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bath was used to control the subphase temperature. The diacetylene monomer was dissolved in HPLC grade chloroform to a 1-2mM concentration. The monomer solution was spre
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