The sequential infiltration synthesis (SIS) of group 13 indium and gallium oxides (In2O3 and Ga2O3) into polymethyl methacrylate (PMMA) thin films is demonstrated. Examples highlight the an SIS process using trimethylindium (TMIn) and trimethylgallium (TMGa), respectively, with water. In situ Fourier transform infrared (FTIR) spectroscopy reveals that these metal alkyl precursors reversibly associate with the carbonyl groups of PMMA in analogy to trimethylaluminum (TMAl), however with significantly lower affinity. SIS with TMIn and water enables the growth of In2O3 at 80° C., well below the onset temperature of atomic layer deposition (ALD) using these precursors.