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Micropaper and laser pen

Braille notation of 'secret message' encoded onto the sulphur-based, erasable film Credit: Angew. Chem. Int. Ed. 2024 63:e202404902

Flinders University researchers have discovered a light-responsive, inexpensive sulphur-based polymer that can be written upon by low-power, visiblelight lasers – providing a new surface for erasable information storage.

Advances in data storage have been driven by evolution in printable and erasable materials.

Hard drives function by storing data on a disk’s magnetic layer. When you save a file, the information is transformed from human-readable text into binary code (1s and 0s). The read-write heads then create a permanent magnetic field on the disk to store this data. Deleting a file doesn’t erase the data; it merely removes the directory path to it. The binary data remains on the disk until it is overwritten by new data. The disk is printable, but not truly erasable.

Used widely in a variety of devices such as smartphones and USB drives, flash memory has recently emerged as a form of data storage that will eventually take us away from storage involving spinning disks and other moving parts. Rather than using a read/write head to write data to a magnetic layer of material, the data is written to an array of memory cells via electrical charges. The memory can be electrically erased and reprogrammed.

The next level in memory storage will come from the physical encoding of information in polymeric materials that can be modified by lasers. Many polymer films can be modified by direct laser lithography and laser surface ablation to make channels, lines, holes, spikes or other surface architectures with exquisite spatial control on the micro- and nanometre scales. However, these techniques usually require high power and high energy consumption, leading to higher costs to create modifications in these polymers. The challenge is to find a polymer film that is both writable with low-power systems and erasable.

A team of researchers at Flinders University, led by Prof Justin Chalker, have met and overcome this challenge with their discovery of a low-cost, sulphur-based polymer that is unusually sensitive to laser light. As soon as a low-power laser touches the surface, it causes a local response in the polymer such as swelling or the etching of a pit.

The polymer’s interaction with low-power light allows for the creation of surface microstructures. Spearheaded by PhD candidate Abigail Mann, with the support of ANFF-SA Flinders spectroscopist Dr Jason Gascooke, the Flinders team analysed how laser modifies the polymer and how to control the type and size of the modification. Ms Mann showed that the modifications were rapid, with exposure times on the millisecond to second timescales. Controlling the power, wavelength, beam diameter and writing speed enabled the installation of spikes, raised dots, pits, channels and holes on the polymer surface. 

The outcome is a new technology for writing precise patterns on polymeric materials. Another important outcome is that information encoded on their writable polymer can be subsequently erased. 

To illustrate the erasable information storage capability of their sulphur-based films, the team used laser to create a series of raised dots encoding the micro-scale Braille text ‘secret message’ on the polymer surface. The polymer film was then heated in a 160 °C oven until the raised dots were erased. This erasable information-encoding process constitutes a new direction in photoresponsive materials, with benefits in the simplicity of the material synthesis and use of low-power lasers. 

The impact of this sulphur-based, direct write polymer extends far beyond erasable data storage, providing new possibilities for patterning surfaces on biomedical devices and new ways to make micro- and nanoscale devices for electronics, sensors and microfluidics. 

Post-publication Note: Microscopy Australia’s Flinders Microscopy & Microanalysis facility also supported this research. To read their research highlight, go to https://micro.org.au/big-impact/rewritable-polymers-innovation-for-data-storage/

Published 15 October 2024 in ANFF’s 2024 Casebook ‘ANFF NEXT

Posted 28 January 2025