Laser-Induced Forward Transfer (LIFT) of aluminum was performed using an Nd:YAG laser operating at 1064 nm, with a 7 ns pulsewidth. Aluminum films of 1 micron thickness on glass “donor” substrates were irradiated at the interface between the film and substrate. LIFT was used to transfer aluminum from the donor substrate to a glass “acceptor” substrate in either contact or non-contact mode. In contact mode the acceptor substrate and thin film were in direct contact, while in non-contact mode they were separated by a 15 micron gap. Laser pulses were focused to a spot diameter of approximately 12 microns.
In both contact and non-contact modes, fluences slightly above the melting threshold resulted in the transfer of single aluminum droplets to the acceptor substrate. Due to fluctuations in laser fluence, droplet sizes varied between 1 and 4 microns. Above a certain value of laser fluence, single droplets were no longer possible and the size of the transferred aluminum deposit approached the size of the laser beam diameter. SEM images of the original donor aluminum film after laser irradiation indicate a re-solidified melt pool with a raised bump at the center, possibly the point of ejection of the transferred droplets. To the knowledge of the authors, this study is the first to report microdroplets transferred by LIFT using nanosecond laser pulses. The only experimental results in the literature to obtain LIFT of features smaller than the laser spot utilized ultrafast laser pulses.
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