The utilization of high mobility organic semiconductors in spintronics is expected to provide a breakthrough improvement in the device operation. Pentacene is nowadays the material of choice for most OFET investigations and thus is among the main candidates for spintronic applications.

We present here the study of the growth dynamics of pentacene on ferromagnetic oxide surfaces, namely on La_0,7Sr_0,3MnO₃ (LSMO) manganites. This work is additionally stimulated by recent report of magnetoresistance in planar devices with two LSMO electrodes and pentacene spacer[1]. It is important to mention that no magnetoresistance has been detected in similar geometry with cobalt electrodes [2].

Pentacene films in the thickness range of 3-100 nm were thermally evaporated in UHV conditions on LSMO films at several deposition temperatures. A strictly diffusion limited, thermically activated (Arrhenius-type) growth was found. The molecule diffusion was found to have a strongly anisotropic character. Pentacene molecules form very wide and extended flat islands having size of a few microns. These large structures are delimited by quite high steps and show terraced features. The step height was estimated independently via AFM characterizations and NEXAFS studies and constitutes 1.5nm, corresponding to 70° angle between molecule axis and surface plane.

The pentacene growth on LSMO is related to the uncommon properties of the surface [3], which determine the growth mode by acting on the molecules mobility.

[1] T. Ikegami et al. Appl. Phys. Lett. 92. 153304 (2008)

[2] M. Popinciuc, Ph.D. Thesis, University of Groningen (2007)

[3] M. Cavallini et al,. arXiv:cond-mat/0301101v1

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