Laser induced local and periodic phase transformations in iron oxide thin films obtained by chemical vapour deposition

doi:10.1016/j.apsusc.2005.01.088

Applied Surface Science

Volume 247, Issues 1–4, 15 July 2005, Pages 513-517

https://doi.org/10.1016/j.apsusc.2005.01.088 Get rights and content

Abstract

Iron oxide films have been deposited on Si(100) substrates by chemical vapour deposition (CVD) of iron(III) tert-butoxide ([Fe(O^tBu)₃]₂) in the temperature range 350–450 °C. The precursor flux and substrate temperature were varied to control the phase composition, average grain size and film thickness. The nature of substrate and deposition temperature markedly influence the morphology and iron-oxygen stoichiometry in the CVD deposits. Phase transformations in iron oxide films were achieved through precise local and periodic heating of the films by interfering laser beams. The interaction of iron oxide films with short laser pulses (Nd:YAG, 355 nm) induced partial transformation of hematite (α-Fe₂O₃) to magnetite (Fe₃O₄) or magnetite to wüstite (Fe_1−xO), respectively. The phase characterization and morphology of the hematite and magnetite films were investigated before and after laser irradiation by X-ray diffractometry, high resolution scanning electron microscopy and white light interferometry.

Introduction

Iron oxide thin films are currently being investigated for several applications due to their catalytic, sensing, optical and magnetic properties [1], [2], [3]. For instance, hematite (α-Fe₂O₃) films are receiving attention for their use as humidity sensors [4]. Furthermore, hematite has been shown to possess photocatalytic properties as demonstrated for the degradation of phenol under visible light illumination [5]. Nanostructured films of different iron oxides have been obtained by a number of techniques such as pulsed laser deposition, sputtering, sol–gel, spray pyrolysis and chemical vapour deposition [6], [7], [8], [9], [10], [11], [12]. Although deposition of thin films is state-of-the-art, the methods for fabricating patterned nanostructures are currently being explored. Geometrically perfect patterning (long range order) can be obtained by applying interference of coherent laser beams [13], [14].

The nanoscaled oxides of iron, nickel, and cobalt are of great interest due to their magnetic properties [15], [16], [17]. In this context, processing of iron oxide films to produce patterns of non-magnetic and magnetic domains is important. The purpose of this work was to investigate ex situ patterning of magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) films prepared by metal-organic chemical vapour deposition. Considering the thermally labile nature of iron oxides and the facile inter-conversion of hematite (α-Fe₂O₃) to magnetite (Fe₃O₄) and magnetite to wüstite (Fe_1−xO), we were interested in studying laser induced phase transformations in iron oxide films.

Section snippets

Experimental

The [Fe(O^tBu)₃]₂ precursor was synthesized by the reaction between anhydrous FeCl₃ and three equivalents of sodium tert-butoxide (NaO^tBu), as described elsewhere [18]. Iron oxide films were deposited on Si(100) substrates in a low pressure horizontal cold-wall CVD system [11], [12]. The substrates were heated inductively using a graphite susceptor. The precursor flux was guided to the hot (350–450 °C) substrate by applying reduced pressure (0.1–1 Pa). The precursor reservoir was maintained at 80

Thin film deposition

Iron oxide films were deposited in the temperature range from 350 to 450 °C on Si(100) substrates. The films deposited at 350 °C contain mainly magnetite, however a small amount of hematite phase is observed, which might be due to surface oxidation of the nano-sized magnetite film. Nevertheless, pure magnetite phase was obtained in the temperature range of 400–450 °C. The thickness of magnetite films deposited at 450 °C was 1.5–2 μm with the growth rate of 25 nm/min on Si(100) [12]. The formation of

Conclusion

Thin films of iron oxides have been deposited on silicon substrates by chemical vapour deposition of an iron alkoxide [Fe(O^tBu)₃]₂. Whereas a selective synthesis of iron oxide films is difficult due to the narrow processing window of iron oxides, the pre-formed Fe single bond O bonds and clean decomposition profile of the molecular source provides an easy regulation of CVD parameters. The combination of phase-selective CVD and laser interference irradiation for magnetic oxides suggests an effective pathway

Acknowledgments

This study was partially supported by a NATO-CLG Grant (No. 979756). Authors are thankful to the Saarland state and central government for providing the financial assistance. SM acknowledges Prof. M. Veith and Prof. H. Schmidt for providing the necessary infrastructure facilities. Thanks are due to the German Science Foundation (DFG) for supporting this work in the frame of the priority programme on nanomaterials – Sonderforschungsbereich 277 – operating at the Saarland University,

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Laser induced local and periodic phase transformations in iron oxide thin films obtained by chemical vapour deposition

Abstract

Introduction

Section snippets

Experimental

Thin film deposition

Conclusion

Acknowledgments

Sens. Actuators B

Thin Solid Films

Thin Solid Films

Appl. Surf. Sci.

Thin Solid Films

Chem. Eng. News

J. Appl. Phys.

J. Am. Ceram. Soc.

J. Appl. Phys.

IEEE Trans. Magn.

J. Appl. Phys.

J. Mater. Res.