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Evaluation of molecular orientation of Cu phthalocyanine thin film on rubbing-processed glass substrates


One series of next-generation semiconductor thin-film materials that has received a lot of attention recently is organic semiconductors. These materials have promising features, such as low cost, ease of manufacturing and physical properties that are induced by the overall structure determined from the molecular orientation and packing.


In this study, the molecular orientation of a thin film of copper phthalocyanine (CuPc) on a glass substrate subjected to surface rubbing, is studied using in-plane and out-of-plane X-ray diffraction on Rigaku's SmartLab multipurpose diffractometer. CuPc is of interest due to its optical conductivity and electroluminescence properties.

Out-of-plane measurement
Out-of-plane measurement (diffraction by lattice surfaces parallel to the sample surface)
In-plane measurement
In-plane measurement (diffraction by lattice surfaces perpendicular to the sample surface)


In the out-of-plane measurement, only the CuPc (h00) reflection is observed as a diffraction peak, revealing that the thin film of the a-axis oriented CuPc phase is created on the surface. Moreover, in the in-plane measurement, in which the profiles are different between the parallel direction and the perpendicular direction, anisotropy of orientation consisting of the b-axis normal direction perpendicular to rubbing direction and the c-axis normal direction parallel to rubbing direction is confirmed.

The figure below shows the relationship between these directions as a schematic diagram of the orientation of the CuPc molecules for the rubbing direction of the substrate.

Rubbing direction
Schematic diagram of the orientation of the CuPc molecules

The in-plane and out-of-plane measurements presented here were performed in a relatively short time, on the order of half an hour.

Sample provided by Takezawa and Ishikawa laboratories, Department of Organic and Polymeric Materials, Academic School of Engineering, Tokyo Institute of Technology.