Vadim Bromberg

High-resolution inkjet printing of electrically conducting lines of silver nanoparticles by edge-enhanced twin-line deposition

We report a process for inkjet printing electrically continuous micron-wide lines of silver nanoparticles by exploiting edge-enhanced evaporation commonly associated with the coffee-stain effect. In situ and real-time flow observation confirmed preferential nanoparticle deposition at the contact line of printed rivulets. The resulting twin-pair of parallel continuous lines showed characteristic width (2–8 μm), height (100–300 nm), and pair spacing (100–600 μm) that depended on substrate and printing conditions in a theoretically predictable way. Thermally sintered lines were used to form rectilinear grids showing ∼5 Ω/◻ effective sheet resistance. The robustness of the deposition process was investigated, and line pathologies were found to depend on substrate surface wettability.

Electroless Copper Plating of Inkjet-Printed Polydopamine Nanoparticles: a Facile Method to Fabricate Highly Conductive Patterns at Near Room Temperature

Aqueous dispersions of artificially synthesized, mussel-inspired poly(dopamine) nanoparticles were inkjet printed on flexible polyethylene terephthalate (PET) substrates. Narrow line patterns (4 μm in width) of poly(dopamine) resulted due to evaporatively driven transport (coffee ring effect). The printed patterns were metallized via a site-selective Cu electroless plating process at a controlled temperature (30 °C) for varied bath times. The lowest electrical resistivity value of the plated Cu lines was about 6 times greater than the bulk resistivity of Cu. This process presents an industrially viable way to fabricate Cu conductive fine patterns for flexible electronics at low temperature, low cost, and without need of sophisticated equipment.

Highly conductive lines by plasma-induced conversion of inkjet-printed silver nitrate traces

We report a rapid process of argon plasma conversion of inkjet printed lines of silver nitrate to yield final electrical resistivities comparable to that of bulk silver. The plasma processing produces a layer of silver with electrical and thickness properties dependent on plasma power and process time. Final line morphology is shown to be determined by the evaporatively driven process of silver nitrate crystallization during printing. This technique holds significant potential for rapid and low-cost additive fabrication of metallization patterns for electronic circuits.

Transport processes associated with inkjet printing of colloidal drops for printable electronics fabrication

This paper presents an experimental investigation of deposition dynamics of inkjet-printed colloidal drops on glass and PET substrates. Using fluorescent particles and confocal microscopy, the evaporatively-driven and thermal Marangoni flows inside a colloidal drop, as well as the particle self-assembly and deposition on the substrate are directly observed. In addition, Ar plasma treatment is used to modify the substrate surfaces. Wetting properties (i.e., advancing /receding contact angle and contact angle hysteresis) of colloidal drops on different substrates, substrate surface roughness, and final particle deposition morphologies are characterized using goniometer, AFM, and SEM. A correlation between the substrate surface roughness, static receding contact angle, contact line pinning/de-wetting, and final particle deposition morphology is explored. This study seeks to provide design guidelines for substrate surfaces that will improve the resolution and edge definition of printable electronics fabrication.

AN EXAMINATION OF FLOW REGIMES ASSOCIATED WITH INKJET - PRINTED COLLOIDAL DROPS

An experimental study of the evaporation dynamics for an inkjet-printed drop on a solid substrate has been attempted. Using fluorescent spherical colloids, the internal flow of an evaporating drop has been observed directly. During the initial stages of the process, a novel inward radial flow carries the particles as a single group towards the center of the drop. Once the particles have converged near the center, a significantly slower outward radial flow proceeds. These flow regimes are qualitatively analyzed and their relationship to a possible thermal Marangoni flow is discussed.Copyright

Studies on the Effects of Particle Size and Substrate Surface Properties on the Deposition Dynamics of Inkjet-Printed Colloidal Drops for Printable Photovoltaics Fabrication

Using fluorescence microscopy, the inkjet deposition dynamics of monodispersed polystyrene particles in the size range of 0.02 to 1.1 μm have been studied on glass, Ar plasma cleaned glass, and PDMS coated glass substrates. The results show that the substrate properties play an important role in determining the final dried patterns formed by the colloidal particles. Our observations also reveal that particle size and contact angle formed by the solvent in the dispersion determine how close to the contact line the particles can be deposited. It is found that smaller particles can move closer to the deposited contact line than particles with bigger sizes. This study can serve as a realistic experimental model system for a number of fundamental queries on how the final deposition microstructure depends on the ink formulation and substrate properties. The knowledge obtained here can be explored further to optimize process parameters for the fabrication of hybrid solar cells with improved morphology and device properties.Copyright