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Organic thin films with non-centrosymmetric ordering of dipoles are very attractive as waveguides for nonlinear optic and electro-optic applications. [1,2] High electric field poling or self-assembly has been widely used to align dipolar molecules perpendicular to the film surface. [2] However, only a few examples of in-plane alignment of dipolar molecules have been described, including epitaxy on a lattice-matched organic substrate surface, [3,4] in-plane poling, [5] and Langmuir±Blodgett film deposition. [6,7] Based on a new type of nonlinear optical material, we have demonstrated, to our knowledge for the first time, that the dipolar molecules in an organic thin film can be in-situ aligned in any desired direction within the film plane by organic molecular beam deposition (OMBD) at oblique incidence. [8] This one-component, relatively fast (5 nm min ±1 ), OMBD based, and easily controlled thin film growth technique provides a new tool for the production of organic thin films with an in-plane directional order for second-order nonlinear optics (NLO) and electro-optics.Growth of organic thin films by OMBD (Fig. 1A) in ultrahigh vacuum (UHV) has many advantages over solution-based techniques, [9,10] such as greatly reduced contamination in the UHV environment, in-situ growth monitoring, high density of chromophores, and reasonably high growth rate. In addition, mask-defined microstructures such as strip waveguides, and integrated hetero-layer structures, like light emitting diode (LED) devices, [8,11] can be fabricated by OMBD. Despite these advantages, OMBD is still much less developed as compared to solution-based techniques for the preparation of second-order NLO films. The main obstacle lies within the materials.

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