Northwestern University (NU) researchers have used a new printing technique, called Polymer Pen Lithography (PPL), to print 15,000 Beijing Olympic logos on one square centimeter. Besides this 'marketing' approach, the PPL technique is very innovative. It can write on three different length scales -- nanometer, micrometer and millimeter -- using only one device. This new printing method could soon be used for more serious applications. Some of them include '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).' But read more...
You can see on the left one of these tiny Beijing Olympic logos. (Credit: NU, via Wired News, link to a larger version) The NU news releas adds that "each Olympic logo is so small -- 70 micrometers long and 60 micrometers wide -- that 2,500 of them would fit on a grain of rice."
This research project has been led by Chad Mirkin, Professor of Chemistry, Professor of Medicine, Professor of Materials Science and Engineering, and Director of the International Institute for Nanotechnology at Northwestern University. I'm amazed. How can this scientist fill all these roles? And I have an additional question: is he paid for all these positions or does he have a single contract with Northwestern University? Please send me your comments if you know more about Mirkin's situation.
Of course, Mirkin wasn't alone to work on this project. Fengwei Huo, Zijian Zheng, Gengfeng Zheng, Louise Giam and Hua Zhang, all members of his research group were part of this effort. The company that Mirkin created, NanoInk, was also involved.
Here is a description of what is PPL. "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.)"
Apparently, the technique is ready to use because it only took two hours to the researchers to design this microscopic Beijing Olympic logo. "In the case of the Olympic logo, the researchers started with a bitmap image of the logo and uniformly printed 15,000 replicas onto a gold substrate using an 'ink' of the molecule 16-mercaptohexadecanoic acid. (The ink is a mere one molecule thick.) This took less than 40 minutes. The logo is so small that 2,500 of them would fit on a single grain of rice. 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 4,000 dots that were 600 nanometers in diameter."
In "Drawing Circuits with Nano Pens," Technology Review provides more technical details about the PPL technique. It "uses arrays of pyramid-shaped polymer pens whose tips are dipped in solutions of chemicals that may feature almost any molecule, including proteins and acids; the pens are then traced over a surface by a mechanical arm to create millions of structures in parallel. The width of the lines drawn by each pen can be carefully controlled by varying the force exerted on the flexible pen tips. Because Mirkin's pens trace out designs programmed by computer software, they can quickly switch between complicated designs, making possible the creation of complex patterns whose features are very close together."
Here is an additional precision given by Technology Review. "Polymer-pen lithography is an improvement over dip-pen lithography, a technique that Mirkin has been developing since 1999. Dip-pen lithography uses arrays of sharp, stiff cantilevered probes -- the same ones used for atomic force microscopy. Mirkin created a company, NanoInk, to commercialize the technology. But, he acknowledges, 'its ultimate utility has been limited by problems with throughput, cost, and complexity.' The size of its molecular strokes has been restricted to a relatively narrow range, the cantilevers are prone to breaking, and the number of structures that can be made in parallel is limited."
Now Mirkin expects that this new PPL technique "will make the dip-pen technology 'accessible to a large number of people.'" Now I have a question for you: do you really dream about getting access to dip-pen technology?
Anyway, this research work will soon be published in Science, but is already available online under the title "Polymer Pen Lithography." Here is the abstract. "We report a low-cost, high-throughput scanning probe lithography method that uses a soft elastomeric tip array, rather than tips mounted on individual cantilevers, to deliver inks to a surface in a "direct write" manner. Polymer pen lithography merges the feature size control of dip-pen nanolithography with the large-area capability of contact printing. Because ink delivery is time and force dependent, features on the nanometer, micrometer, and macroscopic length scales can be formed with the same tip array. Arrays with as many as about 11 million pyramid-shaped pens can be brought into contact with substrates and readily leveled optically to ensure uniform pattern development."
Sources: Northwestern University news release, August 14, 2008; Katherine Bourzac, Technology Review, August 14, 2008,and various websites
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