Structural investigation of copper phthalocyanine thin films using X-ray diffraction, Raman scattering and optical absorption measurements

Structural properties of copper phthalocyanine (CuPc) powder and its thin films coated on glass plate are investigated using X-ray diffraction, Raman scattering and optical absorption techniques. These experiments are carried out at room temperature on CuPc powder and as-coated, 320 degreesC and 520 degreesC annealed, CuPc thin films. From the X-ray diffraction (XRD), we find that the CuPc powder exists in monoclinic phase, alpha-coated film is in orthorhombic a-phase and the film annealed at 320 degreesC exists in monoclinic beta-phase with different lattice parameters as compared to those of the powder phase. The XRD peaks in 520 degreesC annealed film do not show the presence of CuPc but indicate the presence of copper oxide (CuO) nanoclusters of approximately 15 nm size. The optical Raman phonon frequencies of CuPc powder, as-coated and 320 degreesC annealed CuPc films show a slight shift in the intramolecular high frequency modes. Whereas, their low frequency Raman spectra from intermolecular modes are characteristically different indicating different phases. The different characteristic behavior of the optical absorption spectra of the as-coated and 320 degreesC annealed CuPc films corroborate the structural changes in the annealed film.