How ultra-thin polymer films can be used for storage technology

Precisely applied mechanical pressure can improve the electronic properties of a widely used polymeric material. This requires the material to be mechanically processed with an accuracy of a few nanometers, writes a team from Martin Luther University Halle-Wittenberg (MLU) in the scientific journal Advanced electronic materials. In their new study, the researchers show how this previously unknown physical effect works and how it could also be used for new storage technologies. The team also managed to draw the coat of arms of the city of Halle as an electrical pattern with a spatial resolution of 50 nanometers in matter.

Polyvinylidene fluoride (PVDF) is a polymer widely used by industry to produce gaskets, membranes and packaging films. It has many practical properties as it is stretchable, biocompatible and rather inexpensive to produce. “PVDF is also a ferroelectric material. This means that it has positive and negative charges that are spatially separated, which can be used for storage technology,” says physics professor Kathrin Dörr from MLU. However, there is a drawback: PVDF is a semi-crystalline material whose structure, unlike crystals, is not completely ordered. “There’s so much mess in the material that some of the properties you’d actually like to enjoy are lost,” says Dörr.

His team accidentally discovered that atomic force microscopy can be used to establish some electrical order in material. This method typically involves scanning a sample of material with a tip of only a few nanometers. A laser is then used to measure and evaluate the vibrations produced. “This allows us to analyze the surface structure of the material at the nano level,” explains Dörr. Atomic force microscopes can also be used to apply pressure to the material sample using the tiny tip. MLU physicists have discovered that this also changes the electrical properties of PVDF. “Pressure elastically compresses the material to a desired point without displacing the molecules that make it up,” says Dörr. The electrical polarization of the material, i.e. its electrical orientation, rotates in the direction of pressure. Thus, the polarization can be controlled and reoriented at the nano level. The electrical domains thus created are extremely stable and were still intact four years after the original experiment.

The effect discovered by the Halle researchers can be controlled with such precision that they were able to use the electric charges to draw in the material a nanoscale version of the city’s coat of arms – probably the smallest in the world. The new process could help enable the use of materials like PVDF in new electrical and storage applications.

The study was funded by the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG).

Source of the story:

Material provided by Martin-Luther-Universität Halle-Wittenberg. Note: Content may be edited for style and length.

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