X-RAY REFLECTIVITY AND AFM STUDY OF THIN LAYERS OF COPPER PHTHALOCYANINE

P. Poloucek¹, V. Holý¹, F. Lopour² A. Fejfar³

¹Laboratory of Thin Films and Nanostructures, Faculty of Science, Masaryk University, Kotlárská 2, 611 37 Brno, Czech Republic,
²Institute of Physical Engineering, Technical University, Technická 2, 616 69, Czech Republic,
³Institute of Physics, Czech Academy of Science, Cukrovarnická 10, 162 00 Praha, Czech Republic.

Keywords: copper phthalocyanine, x-ray reflection, atomic force microscopy

Thin layers of phthalocyanine with various metal atoms are very promising because of their prospective applications in optoelectronics. In this study we report on the structure of copper phthalocyanine (CuPc) layers with nonstoichiometric concentration of Cu atoms. The layers several hundreds nm thick have been prepared by vapor deposition on Si substrates using separate phthalocyanine and Cu evaporation cells. The structure of the layers has been investigated by means of x-ray diffraction , x-ray reflection under grazing angles and atomic force microscopy (AFM).

From the diffraction studies it follows that the layers with stoichiometric Cu concentration are polycrystalline without any significant texture. Excess Cu atoms destroy the crystalline struc-ture and the layers become amorphous.

Under grazing angles of incidence, we have measured both the specularly and the diffusely reflected x-ray intensity. From the distribution of the diffusely scattered intensity in reciprocal space we have concluded that the most of the scattered intensity stems from volume inhomogeneities in the layer, most likely clusters of Cu atoms. We have simulated the distribution of the scattered intensity in reciprocal space using the DWBA approach and we have determined the size, the concentration as well as the electron density of these clusters.

In order to distinguish x-ray scattering by the volume inhomogeneities from that caused by surface roughness we have studied in detail the surface morphology by means of AFM. It has been found that the root-mean-square roughness of the surface decreases slightly with increasing Cu concentration; thus, the surface profile reflects mainly the crystallographic structure of the layers and it is nearly not influenced by the Cu clusters. The Fourier analysis of the surface profile yielded the correlation length of the interface, this compares well to the mean size of the crystallites.