Elsevier

Scripta Materialia

Volume 44, Issues 8–9, 18 May 2001, Pages 1869-1872
Scripta Materialia

Ambient gas effects on iron oxide particle aggregated films prepared by laser ablation

https://doi.org/10.1016/S1359-6462(01)00735-7Get rights and content

Introduction

Magnetic oxide nanoparticles possess unique superparamagnetism and quantum tunneling of magnetization 1, 2. Fabrication of magnetic iron oxide nanoparticles has been studied because of their advanced applications for magnetic recording, magnetic refrigeration, color imaging, ferrofluids and magnetic resonance imaging enhancement. In addition, iron oxide is a very useful material for gas sensor application. The response of such a sensor is strongly affected by the morphology of the iron oxide film [2] because of the large surface area of the iron oxide particles. Generally, these various functionalities strongly depend on the crystal structure, morphology and stoichiometry of the oxide. Fabrication of the nanostructured materials by laser ablation has the following advantages to manipulate their structural properties: (a) easy control of the preparation process by manipulation of laser parameters such as fluence and wavelength, (b) suppression of particle contamination, and (c) application to many kinds of materials such as metals, intermetallic compounds, simple oxides, complex oxides and polymers. In this work we characterized the iron oxide particle aggregated films deposited by laser ablation using X-ray diffraction (XRD) technique especially focusing on the crystallinity and stoichiometry of the products.

Section snippets

Experiment

A Lambda Physik ArF excimer laser (LPX110i, 193 nm) was used for the ablation. The repetition rate and pulse width of the laser were 10 Hz and 17 ns, respectively. The laser light was focused onto the target through a lens with a laser focal spot size of 4.1 mm2 (for XRD film analysis) and 3.25 mm2 (for film thickness distribution). The pulse energy was varied from 40 to 200 mJ/pulse. Target material was Fe2O3 pellet prepared by the usual ceramics techniques. α-Fe2O3 powder was pressed under

Results and discussion

In order to show the effects of pressure of various background gases and the laser pulse energy on the composition of the ablation product, the R ratio, defined as R = I Fe2O3(311)/IFeO(200), was introduced. This XRD peak intensity ratio of Fe2O3 and FeO measures the relative amount of both phases in the deposited films and is a convenient way of showing the effects of ablation parameters on the product chemistry. Actually, the product of ablation was comprised of two phases, Fe2O3 and FeO, and

Conclusions

The most pronounced change in product chemistry is observed in Ar in the pressure range 13.3–267 Pa. Changing Ar pressure from lower to upper limit of this range varies the product chemistry from being close to stoichiometric to being very far off stoichiometric. Varying oxygen pressure has little effect on the product chemistry. Laser fluence strongly affects the chemistry of the ablation product during deposition in argon whereas the fluence plays a minor role in the compositional changes of

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