Swiatkowska-Warkocka et al. Nanoscale Research Letters 2011, 6:226 http://www.nanoscalereslett.com/content/6/1/226 Page 3 of 7 Figure 1 FE-SEM and TEM images of iron oxide nanoparticles. Before and after laser irradiation with various fluences. (111) at 36.1 and (200) at 42.0 appears as shoulders of magnetite (222) at 37.1 and (400) at 43.1, respectively in the 66-mJ/pulse cm2 result in Figure 3. Those wustite reflections grew and magnetite ones decreased with the Figure 2 Examination by FE-SEM. Variation of particle size (dotted curve) and relative fraction of Fe3O4 and FeO with fluence (solid line). irradiation fluence increase. Volume fractions of Fe3O4/ FeO, calculated by ratio of highest intensity peaks from XRD data, are summarized in Figure 2. Further information about the iron oxide formation during laser irradiation can be gained by analyzing XPS data. For the sake of simplicity, just the XPS Fe 2p depth profile of sample obtained after irradiation with fluence 177 mJ/pulse cm2 is shown as being representa- tive of the behaviour of all composite particles (Figure 4). All spectra for pre-sputtering and post-sputtering shows peaks positioned around 711 and 724 eV, which are typical core level spectra of Fe3O4 and around 710 and 723 eV, which are characteristic for Fe2+ ions in FeO [20]. These results are qualitatively consistent to the XRD measurements. On the basis of TEM and XPS results, we can suppose that composite particles obtained by pulsed laser irradiation reveal aggregated structures. Morphology and composition of the particles obtained by laser irradiation suggest that Fe3O4 nanoparticles are melted to form a large spherical shape and reduced to form FeO phase. Temperature to melt iron oxide nano- particles definitely induces the decomposition of sur- rounding ethyl acetate and possibly leads to the reduction of magnetite to wustite. Thermodynamic cal- culation was performed to investigate the possible ther- mal decomposition reaction of ethyl acetate and probable reducing reaction of magnetite. Gibbs free energy calcu- lation of possible thermal decomposition reaction sug- gests that ethyl acetate can be thermodynamically decomposed at 1,600°C (the melting point of bulk mag- netite) to methane, ethylene, carbon monoxide or hydro- gen, and that these gases can reduce Fe3O4 to FeO. The magnetite nanoparticles dispersed in ethyl acetate melt and formed spherical hollow particles by laser irra- diation at low fluence. The formation of submicrometer hollow particles at low fluence may be related to the