Northwestern University nanoscientist Chad A. Mirkin, who led the study, and his colleagues printed the logos as well as an integrated gold circuit using a new printing technique, called Polymer Pen Lithography (PPL), that can write on three different length scales using only one device. The new printing method could find use in computational tools (the electronics that make up these tools), medical diagnostics (gene chips and arrays of biomolecules) and the pharmaceutical industry (arrays for screening drug candidates), among others.
"While watching the Olympics opening night ceremonies I was delighted to see that printing was highlighted as one of ancient China's four great inventions," said Mirkin, George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences, professor of medicine and professor of materials science and engineering. "We consider Dip-Pen Nanolithography (DPL), which is nanotechnology's version of the quill pen, and now Polymer Pen Lithography to be two of Northwestern's most important inventions." Polymer Pen Lithography uses arrays of tiny pens made of polymers to print over large areas with nanoscopic through macroscopic resolution. By simply changing contact pressure (and the amount the pens deform), as well as the time of delivery, dots of various diameters can be produced. (The pen tips snap back to their original shape when the pressure is removed.)
"We can go, in a sense, from an ultrafine-point Sharpie® to one with a fat tip," said Mirkin, director of Northwestern's International Institute for Nanotechnology. "The tip of each polymer pen starts with nanometer-scale sharpness, but if we press down harder the tip flattens out. This gives us great flexibility in the structures we can produce." In the case of the Olympic logo, the researchers started with its bitmap image and uniformly printed 15,000 replicas onto a gold substrate using an "ink" of the molecule 16-mercaptohexadecanoic acid. (The ink is one molecule thick.) This took less than 40 minutes.
The letters and numbers, "Beijing 2008," were generated from approximately 20,000 dots that were 90 nanometers in diameter. Then, with more force applied to the pens, the stylized human figure and the Olympic rings were made from approximately 4000 dots that were 600 nanometers in diameter.