Scientists from IBM Research and ETH Zurich, arranged gold nanorods to display the STOP Ampelmann, which is 50 μm × 60 μm in size. The arrows indi- cate the traveling direction of the meniscus in the assembly process. The nanorods, which constitute the individual pixels of the image, are placed with single-particle resolution in line- lets measuring 50 nm × 140 nm in size. The assembly yield is larger than 95%. The pixels are separated by 500 nm. The round holes placed next to the linelet array serve as pinning features. b) Dark-field optical microscopy images of the WALK Ampelmann were recorded through a pola- rizer. The pixels change their color from green to red as the polarizer is rotated by 90°. The scale bars are 10 μm. The Ampelmann
is a registered trademark of the Ampelmann GmbH. Published in Advanced Functional Materials, DOI: 10.1002/adfm.201101760 (via IBM Research)
Manipulating objects in the nano-scale is impossible for unaided humans. We simply cannot grasp it, literally. At these dimensions, not even gravity has much influence over particles of this size. Researchers at IBM in Zurich, along with the ETH University in Zurich, realized this and found that intermolecular force, specifically surface tension, was more apt for handling nano-sized objects. This may be the best way to foil counterfeiters.
This team has developed a method that can deposit gold nano rods and arranges them into predetermined positions and orientations. This process uses the surface tension found around the edge of a drop to deposit them onto a premade holder as it the drop is dragged over this stencil. This holder has oblong nano holes whose shape aligns the rods. After this is done, a stamp can be printed using a nano printing process similar to the printing process used in our order of magnitude.
These stamps can be printed into any array, picture or logo. IBM thinks these stamps could be used as a measure against counterfeiting because they can be placed on to any adhesive surface like paper documents, jewelry or other materials. To check if a stamp of nanorods is authentic, it can be viewed through a polarized filter where the color of the light will change depending on its position relative to the alignment of the gold nanorods.
Using a similar process, IBM can arrange nano sizes fluorescent polystyrene spheres that can be red, blue or green and make similar stamps. The mathematical possibilities for these color patterns are so immense they always turn out altogether randomized, and not even IBM could reproduce the same pattern twice, which also makes these stamps attractive for detecting authenticity. IBM calls these unpredictable sequences “physically unclonable functions”.
Apart from preventing counterfeiting, these arrays of aligned gold nano-rods or other materials of interest, could be used in previously unexplored electronic applications. These could also hold potential for the fields of IT, energy conversion and storage or related technology. Anti-counterfeit stamps will be available for consumers in about 5 years. For the record, 2011 brought over 327,000 counterfeit items (est $76.8 billion) caught at customs. Measures like this should help keep that money where it belongs.
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