Continuous Nanoparticle Assembly by a Modulated Photo-Induced Microbubble for Fabrication of Micrometric Conductive Patterns

The laser-induced microbubble technique (LIMBT) has recently been developed for micro-patterning of various materials. In this method, a laser beam is focused on a dispersion of nanoparticles leading to the formation of a microbubble due to laser heating. Convection currents around the microbubble carry nanoparticles so that they become pinned to the bubble/substrate interface. The major limitation of this technique is that for most materials, a noncontinuous deposition is formed. We show that continuous patterns can be formed by preventing the microbubble from being pinned to the deposited material. This is done by modulating the laser so that the construction and destruction of the microbubble are controlled. When the method is applied to a dispersion of Ag nanoparticles, continuous electrically conductive lines are formed. Furthermore, the line width is narrower than that achieved by the standard nonmodulated LIMBT. This approach can be applied to the direct-write fabrication of micron-size conductive patterns in electronic devices without the use of photolithography.

Self-Reducing Copper Precursor Inks and Photonic Additive Yield Conductive Patterns under Intense Pulsed Light

Printing conducting copper interconnections on plastic substrates is of growing interest in the field of printed electronics. Photonic curing of copper inks with intense pulsed light (IPL) is a promising process as it is very fast and thus can be incorporated in roll-to-roll production. We report on using IPL for obtaining conductive patterns from inks composed of submicron particles of copper formate, a copper precursor that has a self-reduction property. Decomposition of copper formate can be performed by IPL and is affected both by the mode of energy application and the properties of the printed precursor layer. The energy application mode was controlled by altering three pulse parameters: duration, intensity, and repetitions at 1 Hz. As the decomposition results from energy transfer via light absorption, carbon nanotubes (CNTs) were added to the ink to increase the absorbance. We show that there is a strict set of IPL parameters necessary to obtain conductive copper patterns. Finally, we show that by adding as little as 0.5 wt % single-wall CNTs to the ink the absorptance was enhanced by about 50% and the threshold energy required to obtain a conductive pattern decreased by ∼25%. These results have major implications for tailoring inks intended for IPL processing.