Tunable Photochemical Method to Grow Silver Dendrites Under Ambient Conditions
The global value of counterfeit goods has risen above half a trillion dollars in the past few years. In addition to the direct economic losses, counterfeit materials, parts and assemblies typically provide inferior performance and poor reliability, which can cause security issues, e.g. for national defense. There is an increasing demand for high-trust, high-reliability tagging methodologies in which only the genuine articles would carry unclonable “trust elements” during manufacture in a legitimate facility. Current physical tagging technologies include holograms, coded tags, DNA signature, mechanical deformation, and nanostructures. Such techniques usually possess several disadvantages, including difficulties in fabrication, lack of structural stability/reliability, and complicated readout procedures.
Fractal structures, specifically synthetic dendritic silver nano-particles (AgNPs), are promising candidates for physical identifiers. Entropic growth of AgNPs will determine the positions and dimensions of minutiae (e.g., bifurcations) in a stochastic manner, resulting in a vast number of unique morphologies. These AgNPs can be applied to an item and decoded to yield a large exclusive integer which in turn would be mapped to the same item in a secure database. However, those benefits will only be realized if dendritic AgNPs can be made efficiently and read using simple methods. Dendritic AgNPs have been prepared using organic reducing agents, ultrasonically assisted templated synthesis, direct replacement reactions, ultraviolet irradiation photoreduction, plating, γ-irradiation route, magnetic field assisted growth, and pulsed sonoelectrochemical methods. Despite their success, the above methods usually require a long preparation time up to three days or precisely controlled environmental conditions, which are not conducive to mass manufacturing outside labs. In addition, the morphology of AgNPs obtained by those methods can lack diversity.
Researchers at Arizona State University have developed a one-pot photochemical synthetic method to produce dendritic silver nano-particles (AgNPs) for physical taggants. This method can readily generate large quantities of dendritic AgNPs in 20 minutes under UV illumination and ambient conditions. The size and shape of the particles can be easily tuned by varying illumination time and the concentration of a polymeric ligand. Unique dendritic structures obtained by this method possess distinctive morphological characteristics, but all are essentially intricate branching structures that possess a singular set of minutiae that may be used to tag and secure items. The as-formed dendrites possess great complexity and uniqueness. The total number of possible patterns formed in a 50 μm x 50 μm area is on the order of 10^75, making dendrites almost impossible to clone. As the AgNP sizes reach 10-100 μm, the structural information may be quickly read and analyzed by optical microscopy, which is promising for anti-counterfeiting labeling applications. Compared to current physical tagging technologies, this invention reduces the fabrication time by at least an order of magnitude, and does not require special equipment to maintain certain environmental conditions.
• Silver dendrite physical identifiers
• Item tagging and tracking
• Item authenticity verification
Benefits and Advantages
• Rapid reaction takes less than 20 minutes, while competing methods can take hours to days
• Simple reaction conditions require only UV illumination under ambient conditions
• Allows tunability of the size and morphology of the dendrites across a very wide range