Target density and surface state effects on the compositional changes in iron oxide particle aggregated films prepared by laser ablation

Iron oxide nanoparticle aggregated films were prepared using the excimer laser ablation technique by adopting an off-axis configuration and the gas condensation process. Sintered iron oxide (α-Fe2O3) targets were ablated in oxygen ambient by an ArF excimer laser. The product of ablation comprised Fe2O3 at lower pressure and a mixture of Fe2O3 and FeO at higher pressure by X-ray-diffraction measurements. The maximum ambient oxygen pressure, PS(O2), at which the product composition was still a single Fe2O3 phase was higher for the higher-density target than for its lower-density counterpart. The target surface state affected the product composition only if the pressure was set to the pressure PS(O2) of 40 Pa for a high-density target. When the fluence was high (200 mJ/pulse, 3.3-mm2 spot size), the product composition varied at the initial stage of laser irradiation with the number of laser pulses from a mixture of Fe2O3 and FeO to only Fe2O3 along with the target surface morphological change from a grooved structure to a smooth surface. Product composition was practically independent of the number of pulses by low-fluence laser irradiation even at this particular pressure of 40 Pa.