Effect of ion treatment on metal-polymer interface formation – from atomic
sticking to macroscopic adhesion
V. Zaporojtchenko, J. Zekonyte , and F. Faupel
Chair for Multicomponent Materials, Institute for Materials Science, Faculty of Engineering,
Christian-Albrechts University Kiel, Kaiserstr. 2, 24143 Kiel, Germany, ff@tf.uni-kiel.de
Since a long time ion treatment with low energy ions is applied to improve metal adhesion to
polymers. Technological approaches range from ion-beam modification in high vacuum to
atmospheric plasmas. It is well known that the ion-polymer interaction gives rise to various
processes in the polymer near-surface layer such as etching or ablation, cross-linking or
branching, as well as modification of the surface chemical structure and physicochemical
properties, i.e. of the reactivity, bonding characteristics, surface energy, hydrophobicity, glass
transition, and conductivity.
Nevertheless, many open questions remain concerning the details, which are both of
fundamental interest and technological importance. A striking example is the behavior of PS
vs. PMS. Both polymers are quite similar in terms of chemistry. However, while Cu
adhesion to PS can be improved by orders of magnitude, the same ion treatment has no effect
on adhesion to PMS,. Other open questions concern the understanding of overtreatment and
its relation to the polymer properties as well as the formation of the so-called weak boundary
layer.
To address these questions we used low energy ion beams of well defined energy, which are
very good tools for controlled polymer surface modification. The changes in the polymer near
surface region were analyzed by combining well established surface analytical tools such as
X-ray photoelectron spectroscopy with new methods recently developed by our group. These
include direct measurement of atomic sticking of metal atoms on polymers [1,2] and a new
technique to measure the degree of ion induced surface cross-linking [4] via changes in the
surface glass transition temperature [3].
The results clearly show that the maximum macroscopic adhesion is reached at ion fluences
that are about two orders of magnitude below the saturation fluence for atomic sticking. This
implies that the number of bonding sites only plays a minor role in metal adhesion on
polymers. We present a quantitative layer model of ion modification which also explains the
formation of the week boundary layer and relates the adhesion enhancement to the
competition of chain scission and cross-linking.
[1] A. Thran, M. Kiene, V. Zaporojtchenko, and F. Faupel, Phys. Rev. Lett. 82, 1903 (1999).
[2] V. Zaporojtchenko, K. Behnke, T. Strunskus, F. Faupel, Surf. Interf. Anal., 30, 439 (2000).
[3] V. Zaporojtchenko, T. Strunskus, J. Erichsen, and F. Faupel, Macromolecules 34, 1125 (2001).
[4] V. Zaporojtchenko, J. Zekonyte, S. Wille, U. Schürmann, and F. Faupel, NIMB 236, 95 (2005).