report
9.13.3 Short description

A number of anti-counterfeiting technologies are being developed to counter theft of brand and intellectual property. This section will observe the technology developments addressing the increasing problems. Nanotechnology methods such as holographic features, laser surface authentication, physically unclonable functions, magnetic fingerprints, nanobarcodes, surface enhanced Raman scattering have been mentioned. Nanomaterials such as carbon nanotubes, quantum dots, organic nanofibres are being developed for anti-counterfeiting applications. The development of nanostructure, nanoscale features and nanoscale clusters to enhance the security of supply chains.

Holographic features - Holographic patterns provide security features both overt and covert to bank notes and credit cards. Application of holography has also been suggested for art. Nanozeolites have been used in photopolymerisable recording material for security application [330]. The addition of inorganic additives has improved the properties of holographic polymers that can be used for new photonic applications. The working principle of holographic recording is the photo-induced modulation of the refractive index. This results from the variation in material composition and density from photopolymerisation of nanocomposite and diffusion of components from exposure to interference patterns. Experimental research has demonstrated nanocomposites consisting of acrylate polymers and organically capped inorganic nanoparticles as a medium for holography. Nanoparticles of SiO₂ ,TiO₂ and ZrO₂ were used in the study.  Phololuminiscent nanoparticles of non-oxide semiconductors cadmium sulphide and zinc selnide were also used.  The research had investigated the preparation, properties, holographic performance, and the polymer-nanoparticle structure. The nanoparticles of SiO₂  were observed to be the most effective in producing low scattering and highly selective holograms [331].

Experimental research has demonstrated the possibility of using luminescent nanoparticles in
photopolymerisable composites for holographic security technology. Lanthanum phosphate, with an average size of 7nm, doped with cerium and terbium has been used as nanoparticles. Two dimensional gratings have been recorded in the nanocomposite. Photoluminescence of these nanoparticles within homogenous polymer film has been measured under ultraviolet light excitation. The advantage of the luminescent nanoparticles is that they provide an additional level of security for the hologram [332]. Experimental synthesis of fluorescent ZrO2:Eu3+ nanoparticles have been reported in the literature. These spherical nanoparticles 4nm in size can be easily dissolved in organic solvent and can be used to produce holographic gratings [333]. Progress in holographic imaging has demonstrated a 164nm resolution using a table top extreme ultraviolet laser. The experimental research was demonstrated on a photo resist of PMMA 120 nm thick, the image of which was digitised using an AFM. The results demonstrated an improvement by a factor of two in the lateral resolution [334].

Laser surface authentication - In laser surface authentication a laser is used to examine the map of the surface roughness of an object using diffused scattering of a focused laser. The obtained code is thereafter stored in a database that can be accessed at a later date. The code of surface roughness is similar to iris scans and fingerprints, the probability of two codes matching was demonstrated to be 10^-72 for paper and 10^-20 for matt finished plastic cards and coated cardboard paper [335]. The advantages of the Laser Surface Authentication technique is that surface roughness of a surface cannot be replicated therefore a high level of security is offered to
products, as compared to holograms and watermarks. Other advantages offered by the technique are robustness against wear and tear, low cost of hardware, 100% accuracy, highly unique features, covertness of the feature, speed at which scanning takes place on a production line, and the overall low cost due to absence of chips. One of the main disadvantages is that it cannot be used on transparent and reflecting surfaces, and the acceptable alignment limit is 1mm [336].

Physically unclonable function (PUF) – The anti-counterfeiting technology is being developed at Philips Research for applications in optical devices, integrated circuits and S-RAM devices. PUF comprises of two components, a physical protection layer and a cryptic layer. The physical layer has a unique fingerprint, similar to LSA, and serves to protect the digital signature. Due to the physical and cryptic layer, the solution is tamper resistant as verification of both layers is essential. The fingerprint is printed on the surface of the packaging or the product which can be then verified. The benefits offered by the technology are its tamper resistant nature, covertness of
the feature, ease with which it can be evaluated and non-reproducibility. The PUF could potentially be embedded in RFID tags with digital signatures, thereby making the features physically unclonable. S-RAM PUFs are also being developed by Philips [338].

Magnetic fingerprinting - Magnetic fingerprints are being developed and commercialised by Singular ID as tags for products for which illegal counterfeits are being produced. The unique fingerprints are created by distributing micro to nanoscale magnets in a non-magnetic matrix material. The specific process used to synthesize magnetic nanoparticles depends on the application and specification of the tag. Porous materials such as aluminium oxide can be used as the matrix material and nickel based magnetic material are deposited through the pore structure. The electroplating process used creates a random pattern and a unique magnetic signature [339].  The unique signatures are read using GMR head scanner to obtain information which is stored into a database. The magnetic material can be embedded in materials such as metal, plastics and glass. The covert security features provide additional security to products in the pharmaceutical, medical, engineering component, and bank cards. The tags are being produced for anti-counterfeiting and brand security for automotive, fashion and pharmaceutical markets [340].

Nano barcodes- Three dimensional nanoscale data encryption key, similar to barcodes has been proposed in a filed patent. It consists of three dimensional polymer patterns in tens of nanometres, of poly (methylmethacrylate) on silicon substrates as tri-dimensional barcodes. Cross-linking the polymer using ultraviolet light provides a high durability material. Nano-imprint lithography is used to generate the pattern on the surface. A number of dimensional coding arrangements have been suggested - two dimension, two and a half dimension, three dimensions, three and a half dimension and four dimensional code. A high resolution charged coupled device camera fitted with an infrared filter is used to detect the reflection from silicon surface using a laser in the infra-red range. The advantage that nanometre scale features provide are the difficultly of being identified and even more difficult to duplicate such features. The application of these features can be with banknotes, security papers, art, jewellery and gem stones [341].

NanobarcodesTM particle system is being developed and commercialised by Oxonica. These barcodes consist of striped submicron scale metallic rods. The barcodes use the difference in reflectivity of gold, silver and platinum. These codes are read through an optical microscope using proprietary software. A combination of one thousand metallic rods can be used to generate a trillion unique codes. These barcodes can be applied in distinct surfaces such as those present  in inks, adhesives, laminates, paper, packaging, and films. They also find application in textiles, thread and glass [342].

Surface enhanced Raman scattering tags - The unique spectra generated by Raman scattering of substances can be utilised as an identification tool. SERS tags developed by Nanoplex technologies use the principles of Raman scattering for identification purposes. The SERS tag consists of metal nanoparticles, SERS reporter and, eventually, a coating material like silica. Gold and silver nanoparticles are mainly used in SERS tags. These find applications in bank notes, paper, packing, clothing and pills. The advantages offered by the technique difficultly in reproducing due to infinite combinations, covert security feature, non-toxic, and multifunctionality. One of the main disadvantages of the technique is the weak signal from the tag that can be improved using surface enhancement by adjusting the type of substrate [342].  

Quantum dots as barcodes for identification - A method for identifying and locating products using quantum dots has been patented. Quantum dots fluoresce and produce characteristic emission based on their composition and size. In the patented method quantum dots of one or more particle size distribution are utilised as barcodes. The intensity of the emission at a fixed wavelength can be varied to produce a binary or higher coding scheme. Quantum dots of semiconductors for group II-VI, III-V, and IV are suitable for the identification application. Semiconductor materials such as ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, GaN, GaP, GaAs, GaSb, InP, InAs, InSb, AlS, AlP, AlSb, PbS, PbSe, Ge and Si were considered to be suitable for application as quantum dots. The security tag can be used for consumer items such precious jewellery, vehicles, and confidential paper [343].

Organic nanofibers - Organic nanofibers have been suggested for application in banknotes. Gas phase synthesis of functionalised organic nanofibres from organic precursors has been mentioned in a filed patent. These organic nanofibres have been reported to have novel optical properties such as pre-determined fluorescence under UV excitation [344] Gain and lasing of self assembled nanofibres have been studied experimentally, which was shown to be dependent on the structure of the fibres [345].

Nanostructures - Anti-counterfeiting patterns have been produced for banknotes by depositing adapted multilayered nanostructures. These structures produce different effects when interacting with light such as change of luminosity and change of color which are used in security applications in bank notes and credit cards. Experimental studies were conducted on concave or convex structures of insect wings to study the effect [346].

Nanoclusters - Nanoclusters are assemblies of atoms or molecules that are covalently or non-covalently bonded with largest overall dimension in the nanoscale [347]. They have novel physical and chemical properties, which can be used for security applications. Clusters of metals deposited on a substrate at a nanometric distance (5-500nm), from a wave reflecting layer can act as a nanoresonator. Sensors and devices are based on surface enhancement of light absorption. This technique forms the basis of producing thin film for anti-counterfeiting applications, which is based on characteristic colours and special optical effects. This has formed the basis of commercial products through Brandsealing which uses the patented cluster technology to produce optical coding. These spectroscopic properties of the optical code are authenticated using a reader. This technology has been considered by the authors to enhance the security feature of threads in bank notes and much better than holograms for authentication of new currency [348].

Nano-coloured materials in combination with active and sensory color-changing nano-features and interactive properties are one of the promising concepts of Attophotonic's nanotechnology applications. By using multiple reactive nano-layers and nano-structured surfaces the Attophotonics® Biosciences GmbH creates a wide range of colours using resonant nanoclusters. The layers are designed to specifically reflect some spectral sub-fraction whereas other electromagnetic waves are absorbed efficiently. Based on the particular nanostructure the surfaces shines and even sparkles in a well defined colour-pattern. The innovative products are manifold reaching from novel smart surface materials for design to films, foils, pigmented inks and printed labels visually indicating the identity, quality and status of packed products [349].

Diffractive nanostructures - Diffractive structures are useful for application in anti-counterfeiting and brand protection. Structures of parallel lines with spacing of over 100nm are made up of material with high refraction index surrounded with low refraction index material. In order to enhance the color effect, a layer of chromophores and fluorophors materials such as quantum dots and metallic nanoparticles have been mentioned. The device is to be used in form of transferable labels and tags for banknotes, credit cards, passports and brand protection applications. These have been mentioned to be better than optical variable devices, optical variable ink, diffractive optical image wave device [350]. Diffractive optics based devices enabled by nanomaterials have been reported in a filed patent for application in authentication and security. A number of materials such as epoxy, acrylate, polycarbonate, UV-curable sol-gel material, silicon oxide, carbide, diamond, carbon, carbon derivative, magnesium fluoride, ZnO, ZnS, and/or titanium oxide have been indicated for use in the diffractive layer. Nanoparticles with a high refractive index have been used in polymer matrix. For the mirror layer, metallic nanoparticles have been suggested for use within metallic alloys. The application of the diffractive optic device has been suggested for banknotes, credit cards, passports and for brand protection [351].

Inexpensive and an easy to manufacture security packaging material and paper based on micro-nanostructure have been reported in a filed patent. The packaging carries the micro-nanostructures act as diffractive optical elements. The micro-nanostructures are embossed on to the surface. A laser beam diffracted from the structures is used to detect the security feature. The application of this method has been suggested for consumer applications such as electronics goods and medicine [352]. Experimental research has been shown to demonstrate layer by layer self assembly of gold nanoparticles on cellulosic fibres, wood and bacterial cellulose as substrate. Gold nanoparticles of 15-100nm in size could be modified by silica shells to enhance optical properties of the nanocomposite. The development will have applications in the security paper synthesis [353].

Verify First Technologies have filed a patent for security documents, have described two security features on a printable substrate, one that is on the substrate and the other partially or completely embedded in the first feature. The first security feature has nanostructures for trapping printing matter for latent copy-void warning message. The second security feature is also nanostructured configured for forming pixel pattern on digital document reproduction. Thermochromic ink is partially arranged in the pattern of the first nanostructure. This technology is expected to act as security features for bank cheques, stocks and bond certificates [354]. A prior art by the same organisation has demonstrated nanopatterns with different nanostructures such as polygons, circles, ovals, crosses, and alphanumeric characters [355].

Confocal type laser profile microscope, have been demonstrated in measuring the thickness of films posted on passports [356]. Spectral information based on color of an object captured on to a database has been described in a filed patent. The spatial analysis software along with the apparatus is used to compare unique patterns [357].

Others Nanomaterials - Nanosized titanium dioxide and zinc oxide have been demonstrated as ultraviolet blockers by the Canadian Bank note company, in enhancing security features of documents such as birth-certificates, driver's license, travel documents and bank notes. The patent describes the method of producing a transparent window on a security document, including a transparent ultraviolet blockers, and printing an invisible ultraviolet fluorescent ink. The authentication of the document is done using ultraviolet wavelengths of light [358].

Single walled and multiwalled carbon nanotubes have been demonstrated in a security mark comprising of multiple layers. The identification information is contained with the patterned layers composed of conductive material. The conductive layer is made from carbon nanotubes with diameter in the range of 0.5 nm - 15nm. Antimony Tin-Oxide has been alloyed with carbon nanotubes to produce conductive layers. The conductive layer is patterned to form resistors by printing with conductive ink.  The code in the conductive layer is read by a reader which identifies an object, based on its conductivity. The application has been envisaged in prevention of counterfeiting of products and security cards [359].