Thermal Inkjet Printing of Quantum Dot Inks for

Thermal Inkjet Printing of Quantum Dot Inks for Overt and Covert Security Printing James 1 Technology 1 Stasiak , Tom 1 Etheridge , Steve 2 Simske , Tim 1 Strecker , and Garry 1 Hinch Development Operations, Hewlett-Packard Company, Corvallis, Oregon; 2 Print Production Automation Laboratory, Hewlett-Packard Company, Fort Collins, Colorado Relevant Quantum Dot Properties Motivation • Ink formulations consisting emissive nanoparticles (quantum dots) can be developed and engineered to be optically active (emission and absorption) at precise wavelengths. • Water-based colloidal suspensions of quantum dot “inks” can provide new security printing applications using thermal ink jet printing methods Components of a water-based TIJ ink formulation (First step: modifying off-the-shelf ink jet inks for QD’s) Architecture of a typical-core shell (e. g Cd. Se/Zn. S) quantum dot Water: major formulation component – all other components must be water-stable Semiconducting nanoparticles have unique optical and electronic properties determined by the quantum mechanics of reduced dimensional (confined) systems. Co-solvent/humectant: control boiling point/evaporation of ink solvent (vehicle); promotes nozzle health • Mixtures of QD-based inks can be developed to provide rich and complex optical spectra enabling the printing of: • overt and covert anti-counterfeiting patterns • marks with increased information “payloads” Colorant: dyes or pigments (dissolved or suspended in ink vehicle) = Colloidal suspension of quantum dots Fixative/penetrant: modify interaction of ink with substrate (control migration of ink through substrate via wicking) 5 – 10 nm e. g. Cd. Se e. g. Zn. S Surfactant: modifies surface tension of ink, critical to surface wetting properties and proper jetting performance of ink Resins: used to improve image permanence – potential issues with nozzle plugging Biocide/fungicide: provide capability for long–term ink storage e. g. tri-n-octylphosphine oxide Thermal Inkjet (TIJ) Drop Relevant Quantum Dot Properties Ejection Engineering Emission Intensity by Multi-Pass Printing Eliminated from TIJ Buffer: provide stability for other ink components (primarily colorants) ink formulation Ink formulation and quantum dot stability …the art of adding dots to solvent Dot Diameter • Fluorescence spectra obtained on Photon Technologies QM-4/2006 spectrofluorimeter • Emission intensity proportional to amount of material printed (negligible selfabsorption) • Amount of material controlled with number of print passes (1 X-5 X for these samples) • Experiment demonstrates basis for creating information within security mark based on emission amplitude (also demonstrated at other emission wavelengths) Varying Emission Wavelength: Overt and Covert Marks Emission spectrum from printed barcode Fluorescence Addition of quantum dots to ink formulation ~400 nm Wavelength (nm) …however for many inks, there is minimal degradation resulting from the ejection event Why? -A very small ink film participates in the nucleation (<50 nm) event. Less than ~ 1% of the droplet is exposed to high temperatures. nozzle Control of quantum dot size provides tunable fluorescent emission The absorption and emission peaks are precisely determined by the QD diameter. Peaks are typically sharp and well separated providing a unique “signature”. Security Printing Overview Classification of security marks • Overt – Observable without device: naked eye, feel, smell – Limited personnel training required Brand identification • Covert – Often not perceptible to untrained or Investigation/Lead Generation with naked eye alone – Machine identifiable or readable Product • Forensic Authentication – Laboratory required for checking resistor Ink reservoir The TIJ Ink “Laundry List”: A (surprisingly) large number of inks can be engineered through surface tension, viscosity, DHvap, chamber geometry, etc. Recent work by Hewlett-Packard and other groups have shown that many other materials are and usable: • 1 -part 2 -part UV curable • PEDOT, PANI (conductive polymers) • Silver and gold nanoparticle suspensions • Quantum dots • Carbon nanotubes, nanowires, … • Ethanol, Methanol, IPA • OLED precursor solution • Toluene, gasoline • Acetonitrile, Chloroform, HEMA • Zinc Tin Oxide, ITO precursors epoxies • Small organic molecules in water • DMSO • Antibodies • Enzymes • Cells and other biological materials • • • Brand identification Product Anticounterfeiting Document Anti-counterfeiting Track and Trace Product Authentication Evidentiary Track and Trace Evidentiary/Forensics • Emission and Adsorption wavelengths determined by size Interrogation Wavelength = 254 nm (UV) Ink vehicle solvents 1, 2 -HD: 1, 2 hexanediol DGBE: dipropylene glycol butyl ether Experimental Printing Test Beds and Printing Details Electronic Materials Printer for fine “tuning”ink formulation Original Package: Security marks include static content, include branding, regulatory compliance, recall sell, point of sale, track and trace • Resolved spectral features can provide increased information “payload” density • inorganic nanoparticles offer potential for increased stability vs. organic fluorophores • Ink stability is highly dependent on co-solvent used in ink vehicle • There is a limit on using solution viscosity to stabilize nanoparticle dispersion (high viscosity can lead to poor jetting) • Solvent initially chosen for jettability (HEP) provides limited solution stability for red-emitting QD’s • Other solvents show possibility for improved solution stability (2 -P, 1, 2 -HD) • 2 -D barcode printed with two QD “colors” • Relative peak areas depend on sample position (spot sampled is larger than barcode pixels) • Sharp, well-resolved peaks allow precise specification of emission wavelength and amplitude to generate covert “signature” Increasing information “Payload” of QD inks • Ink formulation contains two different sizes of Cd. Se/Zn. S quantum dots • Relative peak intensity dependent on concentration of quantum dot sizes in ink • Line widths sufficiently narrow to allow data encoding • Composition of ink can be continuously varied to create dynamic information content Varying the “information content” of the ink by incorporating QD’s with different diameters Challenges and Path Forward QD Ink Development Challenges • Sharp, well separated emission and adsorption peaks • Mixtures of QD’s enable highly complex spectra QD stability in ink vehicles studied by measuring solution fluorescence 2 -P: 2 -pyrrolidinone Why QD-inks enable new security printing methods: • Visible and “invisible” emission enabling overt, covert and forensic applications Which can lead to particle aggregation, surface reaction, and loss of sizedependent properties (e. g. , fluorescence) HEP: 1 -(2 hydroxyethyl)-2 pyrrolindinone Security and Forensics Printing Applications High Temp Region <0. 05 µm Barcode printed with QDcontaining ink shown under UV (254 nm) illumination ~650 nm The fluorescence spectra of quantum dots as a function of dot diameter at a fixed excitation wavelength Major caveat: For TIJ, all inks are required to boil… QD synthesis, stability provided by incorporation of “ligand” cap Photo by Xiaohu Gao But “ligands” can easily be displaced from surface by solvent, other formulation components Security Marks Added to Packaging: Unique ID, mass serialization, steganography, QA/inspection marks, 1 and 2 dimensional barcodes, microtext , and covert (invisible in optical spectrum)security ink marking based on emissive quantum dots? Experimental QD Ink printing using a standard desktop ink jet printer/print. Paper head platen • Ink = Water + humectant + surfactant resolution • Print System = HP 95 cartridge. Cartridge in Desk. Jet Encoder 6540 TIJ printer= 1 mm X, Y axis accuracy = +/- 5 mm • Quantum Dots = blue- and red-emitting Cd. Se: Zn. S with TOPO X, Y axis repeatability = +/- 1 mm ligand • Media = Low-fluorescence office paper Quantum Dots 1. Elimination of heavy metals (HP’s commitment to the environment forbids introduction of any product containing Cd, Pb, or Hg) 2. Longer life 3. Broader color selection 4. More robust “ligand” sphere 5. Price 6. Improved optical properties 7. …. Water-based Inks 1. Improved ink stability 2. Greater solvent flexibility 3. Longer shelf live 4. … Functional Inkjet Inks – enabling the printing-ofthings MIT Cabot i. Ti & NIST Inorganic TFT Sirringhaus, et al. L = 5 mm Organic TFT (PIJ) OLED (TIJ) PZT actuators (TIJ) Metals (PIJ) HP HP Nanowires (TIJ) HP HP Quantum dots (TIJ) Clemson U. CNT’s on paper (TIJ) Printed neurons (TIJ)