Kyeongwoo Nam*

* e-mail : peternam2@hotmail.com

Many attractive organic compounds with large optic nonlinearities and high optical damage thresholds have been studies for theoretical molecular designs and experimental reports. From these points of view, a crystal of 2-methyl-4-nitroaniline (MNA) is of special interest of second harmonic generation (SHG). As reported, MNA has 2.5 3 10^-10 m/V of the largest element of SHG tensor and the figure of merit is 2,000 times larger than that of LiNbO₃. Unfortunately, it is impossible to apply the nonlinear coefficient to the phase-matched SHG in the bulk crystal because an MNA bulk crystal has no matching angle for critical phase matching and no matching temperature for right-angle

Phase matching. To study of nonlinear optical (NLO) properties, MNA thin films are grown using an organic molecular beam deposition (OMBD) technique.

Despite the intense interest in the microstructure of MNA over the last decade, a detailed understanding of its structure and variations with preparation conditions remains to be achieved. Preparation-structure-property relation of thin films are often sought: however, in many instances these relations are vague and complex. One reason is that thin film properties generally vary by orders of magnitudes depending upon preparation conditions. This can only occur if a thin vapor-deposited film is not the same as a thin bulk material of normally the same composition. Thin films are, in general, not ideal materials systems in terms of bond distortion, coordination changes, point defects, dislocations, compositional inhomogeneities and impurities, grain boundaries, and disordered low-density void regions. These defects are created by a complex array of internal interfaces and are directly related to the external on top surface interface. Thus, it is expected that any quantitative description of preparation-property relations must first start with a quantitative description of its internal and external morphology.