Cross section STEM analysis (Figure ) shows that an approximately 400 nm thick film is deposited on the Ag coated areas of the SiO2 (resistivity ρAg,bulk = 1.59 x 10 -8 Ωm) (Figure ), while no film can be seen on the bare SiO2 (resistivity ρSilica = 5 x 10 11 -10 14 Ωm) (Figure . 1b). The deposited Fe film is relatively rough, with height variations of 100 nm and porous, which is more prevalent near the Ag layer. Compositional mapping by STEM-EDS (inserts in Figure and), reveals that the film deposited on Ag coated is Fe rich. Further analysis of the EDS data shows that the film also has a high O content (composition FeO1.3) with trace amounts of Ti and C. The presence of Ti is most likely due to sputtering of the titanium hollow cathode and the presence of C is in part due to contamination during preparation and analysis.