Ultra-thin polymer films with distinct mechanical and chemical properties are developed as a coating for polymer based storage media. The ultra-thin films were deposited via plasma-polymerisation from the monomers such as hexamethyldisiloxane or norbornene. The variation of the reaction conditions, e.g. plasma power, reaction time, pulse modes and additional gases allow adjusting mechanical and interface properties like hardness or hydrophilicity. In particular, our focus is to optimize the ultra-thin films for the use as a protection layer for storage media as used for thermomechancial probe based storage. We found that film thicknesses < 10 nm can be fabricated and used as suitable wear resistant protection layers for polystyrene. These hyper thin films still allow thermomechancial read and write operations. These studies were performed for the EU consortium ProTeM and in close cooperation with IBM.

In general, the protective layer needs to comply with several demanding specifications: The root mean square roughness must be < 1 nm per µm² to preserve the smoothness of the surface which directly determines the signal to noise ratio for data storage applications. The layer should not dewet and should not delaminate, while being flexible and not brittle. Cracks would reduce the lifetime of the protection layer significantly. Furthermore the thickness of the protection layer should be as thin as possible in order to allow thermomechanical indentations at low temperatures and forces (Figure d), without sacrificing its mechanical stability. Increasing the protection layer thickness (Figure e) is associated with an increase in temperature or force required to indent into the polymer layer to the same depth (Figure f). In addition, the lateral size of the indents become larger thus increasing the minimum possible distance between two indents. Further increasing the protection layer thickness (Figure g) would exceed the maximum applied loads that can be used for thermomechancial writing experiments (Figure h). Finally, the protection layer should be hydrophobic in order to reduce the amount of water that is adsorbed to the surface at ambient conditions. Adsorbed water on the surface would lead to increased tip wear and should therefore be avoided.

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