Paper is becoming a high-tech material according to researchers using it to create electrically conducting structures.
Being a light and foldable raw material, the team at the Max Planck Institute of Colloids and Interfaces in Potsdam-Golm say it is a cost-efficient and simple means of creating targeted conductive structures suitable for use as electronic components in everyday objects.
Their method involves using a conventional inkjet printer to print a catalyst on a sheet of paper and then heating it to convert the printed areas on the paper into conductive graphite.
Though many scientists around the world are successfully developing flexible chips, they have been forced to rely on plastics as the carrier and, in some cases, use polymers and other organic molecules as conductive components, which are sensitive to heat.
“Their processing cannot be integrated into the usual production of electronics, because temperatures in production can reach over 400 degrees Celsius,” says Cristina Giordano, who leads a working group at the Max Planck Institute of Colloids and Interfaces.
Carbon electronics, which Giordano and her colleagues create from paper, can withstand temperatures of around 800 degrees Celsius during production in an oxygen-free environment, and would not have a negative impact on established processes.
And the light and inexpensive material can be processed very easily, even into three-dimensional conductive structures.
The Potsdam-based researchers convert the cellulose of the paper into graphite with iron nitrate serving as the catalyst.
“Using a commercial inkjet printer, we print a solution of the catalyst in a fine pattern on a sheet of paper,” says Stefan Glatzel, who is responsible for bringing electronics to paper in his doctoral thesis.
If the researchers then heat the sheets that were printed with a catalyst to 800 degrees Celsius in a nitrogen atmosphere, the cellulose will continue to release water until all that remains is pure carbon.
Whereas an electrically conducting mixture of regularly structured carbon sheets of graphite and iron carbide forms in the printed areas, the non-printed areas are left behind as carbon without a regular structure, and they are less conductive.
That actual, precisely formed conducting paths are created in this way was demonstrated by the researchers in a simple experiment in which they printed the catalyst on a sheet of paper in the pattern of Minerva, the symbol of the Max Planck Society.
The printed pattern was then converted into graphite and they then used the graphite Minerva as a cathode, which was electrolytically coated with copper. The metal was only deposited on the lines sketched by the printer.
In another experiment, the team in Potsdam demonstrated how three-dimensional, conductive structures can be created using their method. For this experiment, the team folded a sheet of paper into an origami crane. This was then immersed in the catalyst and baked into graphite.
“The three-dimensional form was completely retained, but consisted entirely of conductive carbon after the process,” says Stefan Glatzel. He demonstrated this again by electrolytically coating the origami bird with copper. The entire crane subsequently had a copper sheen.
By reducing the paper strength and subtly controlling the process the team also want to create conducting paths from wonder material graphene.