Polymer-Metal Interfaces

Prof. Dr. Peter Müller-Buschbaum

Vacuum deposited metal clusters and thin films play an important role in various fields of technology. Of particular interest are metalized polymers, which are widespread used for decoration purposes, as diffusion barrier in food packaging or as dielectric layers in microelectronics. Within recent years a new application for metalized polymer films has emerged in the fast developing field of organic electronics. Here, a thin metal film is used to apply electrical contact to the active layer of the electronic device. Numerous types of organic transistors (OFET), organic light emitting diodes (OLED) and organic solar cells have already been realized.

Regardless of the polymer and metal used, an important concern in metal coatings are the interactions occurring at the metal-polymer interface, since characteristics like film adhesion and electrical contact properties are strongly influenced by the interface structure. Related to this is the question for the growth kinetics of the metal film on the polymer surface and how the polymer influences the metal film morphology in the initial growth stage. Due to their non-wetting behavior, vapor-deposited metals grow on most oxide and organic surfaces in the form of 3D islands rather than in a monolayer-by-monolayer mode. A number of parameters are involved in the growth process, such as electronic structures and surface free energies of the two materials, surface morphology, polymer chain mobility and experimental deposition conditions, determining size, shape, atomic structure of the metal clusters and the respective temporal correlations. In turn, film morphology influences the characteristics of the interface and consequently the response of the whole system. In the initial stage of film growth, metal atoms can diffuse easily into the polymer and form embedded clusters, presupposed the deposition temperature is close to or above the glass transition temperature of the polymer. Interdiffusion at the interface is in favor to a high adhesion strength, on the contrary penetrating metal atoms may alter the electronic properties at the interface and therefore make it difficult to control the properties of an electronic device.

We perform in-situ investigations of this complex processes to follow growth on the nano-scale.