Investigation of the structure, elemental and phase compositions of Fe$_3$O$_4$–SiO$_2$ composite layers by scanning electron microscopy, X-ray spectroscopy, and thermal nitrogen desorption methods

The composite layers formed by drying a Fe$_3$O$_4$–SiO$_2$-based colloidal solution were studied. The colloidal solution was obtained by the precipitation of Fe$_3$O$_4$ in the presence of highly dispersed silicon dioxide synthesized by the sol-gel method from a tetraethoxysilane alcohol solution. The microstructure and composition of the layers were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, thermal nitrogen desorption, and Raman spectroscopy. The emphasis was placed on the study of phase transitions in iron oxides under laser radiation. It was found that the tetraethoxysilane content has a substantial influence on the ratio of iron oxide and silicon dioxide in the layer, the specific surface area of SiO$_2$ powders, the threshold laser radiation power necessary to induce the Fe$_3$O$_4$ $\alpha$-Fe$_2$O$_3$ phase transformation, and on the position of the maximum of the absorption band corresponding to the $A_{1g}$ vibrations in $\alpha$-Fe$_2$O$_3$.