Second harmonic generation of nonpoled polyurea thin film prepared via vapor deposition polymerization method

Abstract This study reports the second-order nonlinear optical properties of polyurea thin film synthesized from 4,4′-diphenyl methane diisocyanate and 2,7-diaminofluorene via a vapor deposition polymerization. The second harmonic generation (SHG) effect was observed in the as-deposited polyurea thin film on a SiO 2 substrate, even without conventional poling. The SHG operation remained stable at temperatures up to 140 °C. The SHG signal was resolved as functions of fundamental light wavelength, the incidence angle of the fundamental light and the rotation angle around the surface normal of the sample. The electronic and structural properties of the polyurea were also studied using quantum chemical calculations based on a density functional theory, revealing molecular orientation and electronic features that trigger the second-order nonlinear susceptibility of this material.