Research ArticlePRINTING TECHNOLOGY

Ultrathin high-resolution flexographic printing using nanoporous stamps

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Science Advances  07 Dec 2016:
Vol. 2, no. 12, e1601660
DOI: 10.1126/sciadv.1601660
  • Fig. 1 Direct printing of ultrathin colloidal ink patterns using microstructured nanoporous stamps.

    Schematics of the printing procedure (A) and the uniform transfer of ink (B) from the nanoporous stamp to the target substrate surface via conformal contact. (C) Scanning electrode microscopy (SEM) images of stamp features comprising an array of squares (side length, 25 μm), along with corresponding optical and atomic force microscopy (AFM) images of the resulting printed Ag ink [particle size, <10 nm; 50 to 60 weight % (wt %) in tetradecane] patterns. (D) Photographs of printed Ag ink patterns on a rigid glass plate and on a flexible polyethylene terephthalate (PET) film. (E) SEM image of the stamp feature (upper left) and optical microscope image of the printed Ag NP ink pattern (lower right) of a flower-like pattern with feature widths varying from 20 to 150 μm. (F) Fluorescence microscope image (wavelength emission, 620 nm) of printed QD ink (CdSe/ZnS, ~5 to 6 nm, 10 wt % dispersed in tetradecane) of a pattern with minimum internal linewidth of 5 μm and hole size of 11 μm.

  • Fig. 2 Fabrication, wetting behavior, and mechanical properties of microstructured nanoporous stamps.

    (A) Schematic of the stamp fabrication process. (B) Optical images of the wetting/dewetting behavior after each step (~10 μl of water droplet). Load-displacement curves obtained using a 1-μm radius conical tip (C) and a flat tip (D), respectively, to measure the surface modulus and the overall elastic modulus in compression.

  • Fig. 3 Control of ink loading and transfer to achieve ultrathin high-resolution flexoprinting.

    (A) Schematic (not to scale) of nanoscopic view of CNT stamp surface after loading with ink and upon contact with target substrate surface. (B) Ratio of contact between CNT surface fibers and target substrate (black solid line; contact model shown in Eqs. 2 and 3) and contact ratio of colloidal ink transferred onto a glass substrate (gray diamonds with error bars; experimental results) versus applied pressure. (C) Magnified SEM image of CNT stamp feature (fabricated as in Fig. 2) having a honeycomb structure with minimum internal linewidth of 3 μm. (D) Schematics and optical microscope images of a CNT stamp feature, after spin coating of ink, after removal of the excess ink by contact against a nonpatterned CNT forest and the resulting printed pattern on a glass substrate after solvent evaporation. (E) AFM images of printed honeycomb pattern of Ag NPs, CdSe/Zn QDs, and WO3 NPs. (F) Cross-sectional profiles and a plot of average thickness versus ink concentration of printed lines (width, 3 μm) for 2.5 wt % (Al-doped ZnO, red; WO3 NPs, blue), 10 wt % (CdSe/Zn QDs, green), and 55 wt % (Ag NPs, orange) inks.

  • Fig. 4 Functional large-area printing of electronic materials.

    (A) Optical images of Ag honeycomb patterns having a minimum linewidth of 3 μm between adjacent holes printed on glass slides, along with fluorescence images of CdSe/ZnS core-shell QDs, printed as large-area honeycomb patterns [fluorescent emission peak, ~ 540 nm (green)] and arrays of half circles having a diameter of 15 μm with spacing of 5 μm (horizontal) and 250 μm (vertical), concentric circles with linewidth and spacing of 5 to 10 μm [fluorescent emission peak, ~620 nm (red)]. SEM images of printed Ag line array (B) (linewidth, 20 μm; pitch, 200 μm) and SEM images showing evolution of printed Ag morphology after sintering (C) at indicated times and temperatures along with corresponding conductivity values (D). (E) Comparison of the sheet resistance and transmission (at wavelength of 550 nm) values of the printed Ag honeycomb (solid red square) to other transparent materials reported in literature, including Cu honeycomb grids with Al-doped ZnO layer (56), Ag nanowires (54), graphene (53), indium tin oxide (ITO) (55), and single-walled carbon nanotubes (SWCNTs) (52).

  • Fig. 5 High-speed printing and process performance metrics.

    (A) Custom-built desktop P2R printing system with a CNT stamp attached on a flat flexure and a PET film attached to a roller with a diameter of 5 cm. (B) Optical microscope image of Ag honeycomb pattern with minimum internal linewidth of 3 μm printed on a PET substrate at a printing speed of 0.2 m/s using the P2R system. (C) Comparison of speed and resolution of conventional printing technologies for electronically functional materials. Conventional processes include flexography, gravure, screen, and inkjet (824). Soft lithography includes μCP and nTP (25, 26, 5759, 6770); Nozzle-based high-resolution printing methods include direct writing and EHD printing (27, 6264). Tip-based methods include DPN and polymer pen lithography (PPN) (28, 29, 60, 61). (D) Comparison of volume per unit length, lateral feature size, and thickness of ink that transfers to the substrate by single print (by mechanical contact or drop) in conventional printing technologies (824), compared to nanoporous flexographic printing, as shown in this paper.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/12/e1601660/DC1

    fig. S1. SEM images of the cross section of a CNT microstructure after infiltration of silver NP ink and dried at ambient conditions for 3 days.

    fig. S2. SEM images (30° tilted view) of a square pattern of Fe (1 nm)/Al2O3 (10 nm) catalyst film and CVD-grown vertically aligned CNT on the same catalyst pattern.

    fig. S3. SEM and AFM images of the top surface of a CNT forest microstructure (as-grown).

    fig. S4. SEM images of the top surface of a circular (diameter, 100 μm) CNT microstructure at each fabrication stage.

    fig. S5. Comparison of a square micropattern at each stage of stamp fabrication and the printed Ag pattern from this stamp feature.

    fig. S6. Comparison between as-grown and pPFDA-coated CNT micropillars.

    fig. S7. Optical image of a silver NP ink droplet on an array of CNT pillars (diameter, 100 μm) coated with pPFDA before the second plasma treatment (Fig. 2).

    fig. S8. Schematics and optical microscope images.

    fig. S9. AFM images and schematics (not to scale) of lines printed using stamp.

    fig. S10. Transmission spectrum of printed Ag honeycomb pattern on a glass plate.

    fig. S11. Uniaxial stress-strain curves and SEM images of the base regions CNT microstructures.

    fig. S12. Optical microscope images of a nanoporous honeycomb stamp microstructure before and after multiple prints of the Ag ink.

    video S1. Wetting/dewetting tests on plasma-etched CNT micropillars.

    video S2. Wetting/dewetting tests on plasma-treated pPFDA-CNT micropillars.

    video S3. Wetting/dewetting tests on pPFDA-CNT micropillars.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. SEM images of the cross section of a CNT microstructure after infiltration of silver NP ink and dried at ambient conditions for 3 days.
    • fig. S2. SEM images (30° tilted view) of a square pattern of Fe (1 nm)/Al2O3 (10 nm) catalyst film and CVD-grown vertically aligned CNT on the same catalyst pattern.
    • fig. S3. SEM and AFM images of the top surface of a CNT forest microstructure (as-grown).
    • fig. S4. SEM images of the top surface of a circular (diameter, 100 μm) CNT microstructure at each fabrication stage.
    • fig. S5. Comparison of a square micropattern at each stage of stamp fabrication and the printed Ag pattern from this stamp feature.
    • fig. S6. Comparison between as-grown and pPFDA-coated CNT micropillars.
    • fig. S7. Optical image of a silver NP ink droplet on an array of CNT pillars (diameter, 100 μm) coated with pPFDA before the second plasma treatment (Fig. 2).
    • fig. S8. Schematics and optical microscope images.
    • fig. S9. AFM images and schematics (not to scale) of lines printed using stamp.
    • fig. S10. Transmission spectrum of printed Ag honeycomb pattern on a glass plate.
    • fig. S11. Uniaxial stress-strain curves and SEM images of the base regions CNT microstructures.
    • fig. S12. Optical microscope images of a nanoporous honeycomb stamp microstructure before and after multiple prints of the Ag ink.
    • Legend for videos S1 to S3

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    Other Supplementary Material for this manuscript includes the following:

    • video S1 (.mov format). Wetting/dewetting tests on plasma-etched CNT micropillars.
    • video S2 (.mov format). Wetting/dewetting tests on plasma-treated pPFDA-CNT micropillars.
    • video S3 (.mov format). Wetting/dewetting tests on pPFDA-CNT micropillars.

    Files in this Data Supplement: