  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.
