AVS 60th International Symposium and Exhibition
    Thin Film Friday Sessions
       Session TF+EM+NS+SS-FrM

Paper TF+EM+NS+SS-FrM9
Sandwiched Antibacterial Layers Topped by Thin Polymeric Coatings and Deposited in Thin Capillaries

Friday, November 1, 2013, 11:00 am, Room 104 A

Session: Thin Film: Growth and Characterization III
Presenter: G.F. Franz, Munich University of Applied Scienes, Germany
Authors: G.F. Franz, Munich University of Applied Scienes, Germany
F.S. Schamberger, Munich University of Applied Scienes, Germany
Correspondent: Click to Email
Bottom-down strategies for nanostructures require tailoring techniques for very thin layers. One of the film-building polymers which cannot be deposited with ALD is poly-p-xylylene, commonly known as polyparylene, which has evolved to generate universally employable layers with unique properties. As known from growth theory, very thin layers below 100 nm in thickness are necessarily porous which reduces the property of preventing diffusion. This feature, however, is required to control the process of dissolution from metallic silver to silver ions of a layer lying beneath. The silver layer is used as a long-term depot for the generation of silver ions which exhibit an antibacterial conduct. The silver ions break through the cell walls of the bacteria, causing them to die.

To deposit very thin layers of polyparylene, the conventional Gorham method has been improved. We present a completely new method to control the growth of these very thin layers with defined porosity for which exact knowledge of vapor pressure and evaporation rate is required [1]. To tailor this long-term property above the death-causing threshold, the porosity (i. e. hole density) is:

(i) quantitatively determined with a digital evaluation procedure of the micrographs gained with AFM as function of the parameters of deposition.

and (ii) has been correlated with the breakdown voltage and the capacitance which can both easily applied to the samples (electro impedance spectroscopy, EIS).

This makes the hole density a quantitative measure to rate the degree of permeability for silver ions. Applying ICP-OES, the concentration of silver ions in the adjacent liquid around the silver spots is measured. This concentration depends on the thickness of the films of polyparylene. With standard biological procedures, this is correlated to the lethal impact on bacteria. Whereas layer growth upon open surfaces is controlled by the density of reactive particles (surface polymerization), the density becomes locally dependent for coating of narrow holes which occurs as a diffusive process with losses due to deposition. In a series of experiments, the growth behavior in thin, narrow pipes with an aspect ratio between 10 and 30 has been obtained, and a theoretical model is presented which reflects the crossover of these two transport mechanisms as function of chamber pressure and temperature.

[1] G. Franz et al., German patent disclosure DE 2012 014 915.8