Organic electro-optic single-crystalline thin films grown directly on modified amorphous substrates

Organic single crystals grown directly on substrates with desired orientation of molecules are important for fundamental and applied chemistry([1,2]) and numerous nonlinear optical([3]) and optoelectronic([4]) applications. For integrated photonic applications such as microresonator filters and modulators single crystalline thin films with a thickness in the range of 0.2-10 mu m are required. Such crystalline films can be grown by epitaxial growth methods, for which lattice matching is an important parameter for obtaining high-quality single-crystalline thin films without defects on other materials (or substrates).([6]) 1 Therefore, epitaxial growth is usually limited to lattice-matched crystalline substrates and cannot be simply used on amorphous substrates. Only a few approaches have been reported on the growth of organic crystals on non-crystalline substrates, for example by using graphoepitaxy on amorphous SiO2 substrates,([7]) chemical epitaxy on ordered gold-thiol self-assembled monolayers,([1]) and shear-induced polar interaction on silica (fused quartz).([8]) Moreover, the epitaxial growth based on the lattice matching technique usually combines two very similar materials([9]) and therefore does not allow for a high refractive index contrast needed, for example, for micro-ring resonators and photonic crystal structures.([3,5]) In order to overcome these restrictions we report here on the growth of organic nonlinear optical single-crystalline thin films using surface-specific interactions combined with a capillary method on amorphous glass substrates. The surface of the substrates has been modified with functional groups of chromophores to mimic the crystal surface of a growing crystal.