In thermochemical nanolithography, an atomic force microscope (AFM) tip is heated and run over a thin polymer film, inducing a chemical reaction on its surface. This alters the reactivity of the film, and transforms it from a hydrophobic to a hydrophilic substance that can stick to other molecules.
Write speeds of millimetres per second have so far been achieved, and the researchers say that centimetres per second should be possible. “The technique is immensely scalable,” says University of Illinois mechanical engineer William King, whose group designed the AFM tips. “It would be possible to have this working on many thousands of tips within a year, and with 10 million parallel tips within three years.”
There are a multitude of potential applications for thermochemical nanolithography, but study lead author Robert Szoszkiewicz focuses on microfluidics. “This is a significant step towards miniaturisation and compartmentalising various chemical reactions at a small scale,” he says. “Apart from the potential cost decrease, the microchannels are a step towards mimicking the complicated chemical environment within cells, and generating extremely light and versatile chemical sensors which could be used in pharmaceutical devices, as well as in outer space.”
“I was particularly impressed by the spatial resolution,” says Nicholas Spencer, a materials scientist at the Swiss Federal Institute of Technology in Zürich. “While we do not usually think of thermal approaches as compatible with high resolution, if they are actually initiating a reaction then they can capitalise on the exponential increase of reaction rate with temperature. The potential for nanofluidics is clear.”
A patent has been applied for, and the researchers are looking for a commercial partner eager to turn their proof-of-concept into a working nanofabrication process.
Further reading: High-Speed, Sub-15 nm Feature Size Thermochemical Nanolithography, Szoszkiewicz et al., Nano Lett. 7, 1064 (2007).
Article first published in Nanomaterials News.