Morphologies and nonlinear optical characteristics of vanadylphthalocyanine thin films prepared on polycarbonate and KBr substrates

The morphologies and nonlinear optical properties of vanadylphthalocyanine (VOPc) thin films on polymer and KBr substrates remain unclear. This paper investigates the morphologies and nonlinear optical properties of VOPc thin films prepared on polycarbonate (PC) and KBr substrates by UV/Vis spectrum measured with UV/Vis spectroscopy, X-ray diffraction (XRD) and third-order harmonics (TH), as well as second-order harmonics (SH) detected using the Maker fringe method. The UV/Vis spectra of VOPc thin films prepared on a PC substrate with different evaporating source temperatures have a peak at 840 nm in the Q-band region. This indicates that the morphology of the VOPc thin films prepared is Phase II. Moreover, the UV/Vis spectra of each sample do not change with increasing thickness. Therefore, this also suggests that interaction between a VOPc molecule and the surface of a polycarbonate film is strong. The number of VOPc molecules oriented at 60° to a substrate markedly increases with the increase in evaporating source temperature. This indicates that there is an optimum evaporating source temperature for the orientation of VOPc thin films prepared on a PC substrate. In VOPc thin films prepared on a KBr substrate, the phase morphology of VOPc thin films changes from pseudoepitaxy to epitaxy by increasing the annealing time. Moreover, the incident angle dependence of second harmonic (SH) intensity shows a lower convex curve when irradiated with a p-polarized laser light, and the SH intensity is enhanced with the increase of the annealing time. Moreover, the incident angle dependence of third harmonic (TH) intensity shows upper convex curves and the maximum values of TH intensity are enhanced with the increase of the annealing time. These findings indicate that the orientation of VOPc thin films is improved with the increase in annealing time. It is closely related to molecular diffusion during annealing.