​By melting a thin layer of material onto an object, CEA-Leti researchers can produce a micrometric pattern, resulting in a unique non-reproducible artificial fingerprint. This holds excellent potential for creating anti-counterfeiting labels on processors, jewelry, watches, and other valuables. 

• The concept of anti-counterfeiting labels produced by a filler material is not new. Other teams have tried this, using fine polymer or metal layers over the object that requires protection. But the size of ensuing patterns was not satisfactory. They were either nanometric, but only decipherable using a scanning electron microscope. Or they were millimetric, and not discreet enough. 

Our patterns strike just the right balance," explains Pierre Noé of CEA-Leti. Their wrinkles are a few dozen nanometers high and feature micrometric periodicity. They can be read using a simple binocular magnifier, or a smartphone equipped with a lens

Impossible to reproduce, yet easy to recognize

• How are they produced? By melting a thin film (100 nm) of germanium-based amorphous chalcogenide using a laser pulse. It is first covered with a very fine, rigid layer of a dielectric material such as silicon nitride, widely used in the microelectronics industry. Once deposited on the molten chalcogenide film, the dielectric expands, slackens, and forms randomly shaped and oriented wrinkles. The best equipped forger would never be able to duplicate them.
  

• However, these patterns are easy to recognize for authentication purposes. Researchers have verified this using two methods—a cross-correlation procedure and a neural network. In both cases, the observed pattern is compared to a reference image with a high recognition ratio, mostly under real conditions. 
  

• These results, published in Advanced Materials were obtained as part of a PhD thesis at the Bordeaux-based CELIA* laboratory, in collaboration with CEA-Leti. They have already drawn interest from several manufacturers who design products that are targeted by counterfeiting, such as processors, watches, jewelry, or automotive spare parts.