Influence of dielectric substrate modification and deposition temperature on structure and morphology of CuPc thin films: X-ray reflectivity and angle dependent NEXAFS study

The performances of organic thin film transistor devices are significantly linked with the structural properties at organic semiconductor/dielectric interface. The changes in internal structure, molecular ordering and morphology of 20 nm thick CuPc thin films have been investigated by modifying surface of the dielectric substrate with various organic buffer layers at different deposition temperatures. CuPc films are prepared on bare and modified SiO2 substrates at three deposition temperatures. Dielectric surface modification and deposition temperature modify the CuPc /dielectric interfaces accordingly and growth of subsequent CuPc layer. The internal structure, ordering and morphology of CuPc film strongly depends on the behavior of the dielectric layers at various temperatures as well as the diffusion of CuPc molecules. The XRR results reveal that the thickness and ordering of periodic part of CuPc film is varied with dielectric substrate modification as well as deposition temperature. The periodicity of CuPc molecules in the film is always obtained in its α-form. In addition, the angle dependent NEXAFS data determine the angle of CuPc molecular orientation in the range 64° to 71° in the range of 40° to 120 °C deposition temperature, independent of surface modification. The results pave the way for the design and realization of CuPc based thin film transistor devices.