AVS 61st International Symposium & Exhibition
    Thin Film Friday Sessions
       Session TF+AS-FrM

Paper TF+AS-FrM9
Polarization-dependent X-ray Absorption Fine Structure Analysis of TES Pentacene Thin Films

Friday, November 14, 2014, 11:00 am, Room 307

Session: Thin Film Characterization
Presenter: Beatrix Pollakowski, Physikalisch-Technische Bundesanstalt (PTB), Germany
Authors: B. Pollakowski, Physikalisch-Technische Bundesanstalt (PTB), Germany
J. Wade, Imperial College London, UK
JS. Kim, Imperial College London, UK
F.A. Castro, National Physical Laboratory (NPL), UK
J. Lubeck, Physikalisch-Technische Bundesanstalt (PTB), Germany
R. Unterumsberger, Physikalisch-Technische Bundesanstalt (PTB), Germany
A. Zoladek-Lemanczyk, National Physical Laboratory, UK
B. Beckhoff, Physikalisch-Technische Bundesanstalt (PTB), Germany
Correspondent: Click to Email
Research in organic electronics shall open up alleys for many of its promising applications, including promising applications, including: light emitting diodes, photovoltaics, transistors, biosensors and photonic devices. Despite of the diversity of device functionalities, all these applications are based on thin films of organic materials and in each case their performance is critically dependent upon the precise arrangement and packing structure of the organic molecules in thin films. Our research focuses on this fundamental issue, seeking to better understand the relationships between device performance and thin film morphology of organic semiconductors on the molecular scale [1,2].

A set of 6,13-Bis((triethylsilyl)ethynyl)pentacene (TES-PEN) samples has been prepared on a silicon substrate by using a well controlled printing technique.[2] Different substrate shift speeds were used to modify the layer thickness and the crystallinity.

All X-ray based measurements were carried out at the plane grating monochromator PGM beamline for undulator radiation in the laboratory of the Physikalisch-Technische Bundesanstalt PTB at BESSY II, providing tunable radiation of both high photon flux and high spectral purity in the soft x-ray range [3]. Different kinds of X-ray spectrometry (XRS) analyses were employed to determine the chemical binding state, elemental distribution depending on the depth, and lateral mass deposition.

To analyze the chemical binding state of the molecules, the method Near-Edge X-ray

Absorption Fine Structure spectroscopy (NEXAFS) in fluorescence mode has been employed. Varying the angle of incidence in the fluorescence mode the information depth can be tuned to a pre-selectable depth of interest. In addition, the mean penetration depth at large angles of incidence is high enough to analyze even thicker layers of up to a few hundreds of nanometers as is often the case for complex organic materials. For an analysis of the molecular orientation, the angle between the electric field vector and predominant direction of the molecules has to be varied.

Initial measurement sequences exhibit the potential of this X-ray spectrometry method to significantly contribute to the quantitative analysis of organic materials in thin films. In particular, polarization dependent NEXAFS offers a clear discrimination capability for the orientation of the molecules.

[1] S. Wood, J.S. Kim, D.T. James, W.C. Tsoi, C.E. Murphy, and J. S. Kim, J. Chem. Phys. 139, 2013, 064901

[2] D.T. James, J. M. Frost, J. Wade, J. Nelson, J. S. Kim, ACS Nano 7(9), 2013, 7983.

[3] J. Lubeck, B. Beckhoff, R. Fliegauf, I. Holfelder, P. Hönicke, M. Müller, B. Pollakowski, F. Reinhardt, J.