Effects of corona charging on nonlinear optical property and morphology of VOPc thin film prepared on polyimide substrate by molecular beam epitaxy

One important factor for a nonlinear optical thin film having high second and third nonlinear optical susceptibilities is a high packing density. Vanadyl-phthalocyanine (VOPc) thin films were prepared on non-charged and corona-charged polyimide substrates by the molecular beam epitaxy (MBE). The Vis/UV spectrum of Sample 1on a non-charged substrate had a maximum absorption peak at 835 nm. According to Griffiths et al., the VOPc thin film has a maximum absorption peak at 830 nm, after prepared on a glass at room temperature and heated at 325°C for 2 hours. He called the morphology of Phase III. The maximum absorption peak of Sample 1 shifted longer by 5 nm than that reported by Griffiths. This means that the packing density of Sample 1 is higher than that of the VOPc thin film reported by Griffiths. A maximum absorption peak in Q band region of Sample 4 on a corona charged substrate appeared at 845 nm, which is longer by 10 nm than that of Sample 1. This suggests that a strong interaction between VOPc molecule and electric charge on polyimide substrate makes a high molecular packing of Sample 4. The third harmonic (TH) generations of Samples 1 and 4 were measured by Maker fringe with P polarized laser light. The peak value of TH intensity of Sample 4 was larger by 2 times than that of Sample 1. This means that the nonlinear optical property of VOPc thin film is improved by corona charging