Thermochemical nanolithography uses an atomic force microscope (AFM). Researchers heat a silicon tip and run it over a thin polymer film. The heat from the tip induces a chemical reaction at the surface of the film. This reaction changes the film’s chemical reactivity and transforms it from a hydrophobic substance to a hydrophilic one that can stick to other molecules. The technique is extremely fast and can write at speeds faster than millimeters per second. That’s orders of magnitude faster than the widely used dip-pen nanolithography (DPN), which routinely clocks at a speed of 0.0001 millimeters per second.
Using the new technique, researchers were able to pattern with dimensions down to 12 nanometers in width in a variety of environments. Other techniques typically require the addition of other chemicals to be transferred to the surface or the presence of strong electric fields. TCNL doesn’t have these requirements and can be used in humid environments outside a vacuum. By using an array of AFM tips developed by IBM, TCNL also has the potential to be massively scalable, allowing users to independently draw features with thousands of tips at a time rather than just one.
It’s the heated AFM tips that are one key to the new technique. Designed and fabricated by a group led by William King at the University of Illinois, the tips can reach temperatures hotter than 1,000 degrees Celsius. They can also be repeatedly heated and cooled 1 million times per second.
“The heated tip is the world’s smallest controllable heat source,” said King.
TCNL is also tunable. By varying the amount of heat, the speed and the distance of the tip to the polymer, researchers can introduce topographical changes or modulate the range of chemical changes produced in the material.
“By changing the chemistry of the polymer, we’ve shown that we can selectively attach new substances, like metal ions or dyes to the patterned regions of the film in order to greatly increase the technique’s functionality,” said Seth Marder, professor in Tech’s School of Chemistry and Biochemistry and director of the Center for Organic Photonics and Electronics. Marder’s group developed the thermally switchable polymers used in this study.