Selective Deposition of Iron Oxides Thin Layers on Si(100) from Aqueous Solutions

Abstract

o C for 1 h. A solution of OTS in anhydrous hexane (10 mM) was used as an ink and applied to the stamp using a spinner at 3000 rpm for 30 s. The inked stamp was placed in contact with Si and held in place for 30 seconds, yielding OTS thin films with approximately 30 A mass coverage. 10 Fe(NO3)3·9H2O and FeCl3·6H2O were used as starting ma- terials to produce hematite and akaganeite, respectively. The hematite thin films were deposited from a 0.05 M iron nitrate solution. The akaganeite thin film was deposited from 0.05 M iron chloride in 0.1 M acetate buffer solution. The OTS-pat- terned Si substrates were immersed in the solution for 2 h at 75 o C with constant stirring. The final pH range of the iron nitrate and iron chloride-acetate buffer solutions was 1.5 ~ 1.7 and 2.5 ~ 3.0, respectively. The color of the nitrate and chloride solutions was red-brown and light ochre, respectively. Both precipitates and thin films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Figure 1(a) and (c) show SEM images of the precipitates and thin film prepared in Fe(NO3)3 solution. The deposited thin film was densely covered with hematite nanoparticles with spherical shapes with an average size of 20 - 50 nm. XRD of both the powder and film showed three predominant peaks at 33.2, 35.6, 65.4° 2θ, which were assigned to (104), (110) and (214) for the hematite phase.