French materials scientists using laser-generated micromolding that are impossible to reproduce — they can be used as unique labels for protection against counterfeiting, and to believe it can be a simple optical microscope. The article in which the authors tell you how to get random patterns of chalcogenides Germany, published in the journal Advanced Materials.
It is impossible to get two absolutely identical subject — there are always errors and accidents on a small scale. In mass production it is rather a harm, as the items are obtained slightly different, but you can create a unique label physically uncloneable system. They have two properties that allow you to use them to uniquely identify. Such a system cannot be reproduced in practice, and its modeling is very costly, which makes it protected (more on physically uncloneable functions can be read in this material).
In nature we know of many manifestations uncloneable functions: for example, fingerprints and iris and the cornea. Wrinkle from fingerprints better than anyone suitable for the role of combating counterfeiting, as reading information requires only an optical microscope. Such wrinkles are already made from double-layered structures (metal on the surface of flexible polymer), or through laser melting layer covered with a tough layer of oxide.
Paloma Martinez (Paloma Martinez) with colleagues from the University of Bordeaux has developed a new method of generation of unique systems through the formation of wrinkles from the melting of the chalcogenide (sulfur, selenium, tellurium) Germany. To generate wrinkles, the scientists shone the laser on the sample, consisting of oriented silicon substrate, a layer of telluride of germanium with a thickness of 500 nanometers and a layer of silicon nitride.
For melting, the scientists chose the intensity of flow 21, 25 and 30 millijoules per square centimeter. At a lower flow was not melting telluride Germany, and thus the formation of wrinkles. Scientists noticed that after melting and hardening of a material changes its refractive index, the telluride of germanium from the amorphous material is not secretariatmolsa, but the phases before and after the laser processing differ in their amorphous structure. The layer of silicon nitride is left intact. The researchers assessed the stability of the structure wrinkles for recrystallization: for alloy of germanium, antimony and selenium at 90 degrees Celsius wrinkles may persist for up to ten years.