Damage-Free Low Temperature Pulsed Laser Printing of Gold Nanoinks On Polymers

Schematic of nanoink printing and curing system

Bipolar voltage waveform applied to piezoelectric actuator

Configuration of jet head and aluminum heating block. The nozzle to substrate distance was 1.2mm and in addition to Tj and Ts, the temperature at the aluminum heating block and the fluid temperature at the reservoir were measured to use as boundary conditions for numerical simulations. This configuration was used for numerical simulations.

(a) Variation of droplet velocity at 1mm from the nozzle in response to changing voltage amplitude and temperature of jetting head and substrate. Gap distance between the substrate and nozzle is 1.2mm. Ts and Tj represent the temperature of the substrate and the jetting head. When only Ts is changed, Tj is set to 37°C. However, Tj increases to 41°C when Ts⩾107°C. Note that the nozzle temperature (Tn) is approximately equal to Tj when Ts=Tj, and that Tn is higher than Tj when Ts>Tj due to heat conduction from the substrate. Images (b), (c), (d) are obtained by multiple 2μs exposures with a 98μs delay when Ts=107°C and Tj=41°C.

Variation of droplet velocity at 1mm from the nozzle changing dwell time, td [(B) in Fig. 2]. Ts changes and Tj is set to 37°C. Inset picture corresponds to the case for Ts=107°C and Vamp=13V and similar satellite droplet was observed at the dwell time of 30μs at different substrate temperatures and voltages.

Numerical result when Ts=147°C and Tj=37°C. (a) Velocity profile with stream lines. (b) temperature profile.

Estimated nozzle temperature (Tn) from experiment and numerical simulation due to substrate heating at Tj=37°C.

Morphology of printed and cured nanoink on polyimide film. The same voltage waveform in Fig. 2 was used with Vamp=14V. Before AFM (atomic force microscopy) scans, all lines were cured at 200°C to evaporate toluene solvent. (a) Shows the morphology of a single droplet deposition obtained at Ts=25°C. In (b–d), the translation speed and jetting frequency were 2mm∕s and 30Hz, respectively. Therefore, the distance between the droplet centers is 67μm. Ts for (b), (c), and (d) was 25, 50, and 90°C, respectively.

(a) rms (root mean square) roughness and resistance per length of printed lines cured at different temperatures. (b) Cross-sectional profiles of printed lines cured at different temperatures.

Pulsed laser cured printed line at different scanning gaps, dgap. The same voltage waveform in Fig. 2 was used and Vamp=15V. Nanoink was printed on a polyimide film at room temperature and cured by a substrate heating at 200°C. During laser curing, the film was heated at 200°C using the vacuum chuck in Fig. 1. Laser power, beam waist (1∕e2), frequency and translation speed are 0.85W, 30μm, 100Hz, and 0.5mm∕s, respectively. (a) RL versus scanning gap of laser beam. Inset pictures are reflection images corresponding to cases circled with a dotted line. (b) AFM image before pulsed laser irradiation. (c) AFM image after pulsed laser irradiation at tpulse=10μs and dgap=40μm. (d) AFM image after pulsed laser irradiation at tpulse=20μs and dgap=10μm. rms roughness is 2.7nm.

Pulsed laser cured printed line at different laser pulse durations. Printed lines in Fig. 1 were used. During laser curing, the polyimide film was heated at 200°C using the vacuum chuck in Fig. 1. Laser power, beam waist (1∕e2), frequency, translation speed and scanning gap are 0.85W, 30μm, 100Hz, 0.5mm∕s, and 10μm, respectively. Inset pictures in (a) are reflection images corresponding to cases circled with dotted line. (b) and (c) are AFM images of the areas circled with a white line in (a).

Transient temperature profiles in depth with 40μs heating time