Laser Printing of Silver and Silver Oxide

We show that direct laser writing (DLW) in aqueous silver nitrate with a 1030 nm femtosecond (fs) laser results in deposition of a mixture of silver oxide and silver, in contrast to the pure silver deposition previously reported with 780 nm fs DLW. However, adding photoinitiator prevents silver oxide formation in a concentration-dependent manner. As a result, the resistivity of the material can also be controlled by photoinitiator concentration with resistivity being reduced from approximately 9e-3 $\Omega m$ to 3e-7 $\Omega m$. Silver oxide peaks dominate the X-ray diffraction spectra when no photoinitiator is present, while the peaks disappear with photoinitiator concentrations above 0.05wt%. While femtosecond pulses are needed to initiate deposition, a continues-wave laser when well overlapped with the previously written material and supplying enough average power can lead to further printing, suggesting thermal deposition can also occur where the photoinitiator molecule also acts as a general reducing agent that prevents oxide formation. We also compare the surface quality of printed lines for different photoinitiator concentrations and laser printing conditions. A THz polarizer and metamaterial are printed as a demonstration of silver oxide printing.