Direct Printing of Fine Copper Lines by Self-organized Convective Flow

We have developed a technique for the printing of fine copper lines using solutions of a metal organic precursor, copper hexanoate (CuHex). Liquid ribbons 500 μm wide, deposited on a glass substrate either by ink-jetting or capillary writing, are observed to split into two or four finer lines depending on the solution concentration. Surface profiles indicate that the thickness, width and number of lines formed are strongly dependent on the solution viscosity and volume per unit length deposited. From particle tracking analysis and surface profiling, we find that a combination of two key effects contact line pinning and evaporative cooling accrete solute along two boundaries of the flow. The pinning produces an exterior line pair; the evaporative cooling induces Bénard convection cells which accrete material into an interior line pair. These accretion patterns are then annealed to form pure copper lines.