AFM investigation of selective etching mechanism of nanostructured silica

We have developed the atomic force microscope (AFM) for in situ observation of SiO2 etching in the HF aqueous solution. This work is devoted to the AFM investigation of etching of the SiO2 surface layer modified by high-dose Fe+ ion bombardment. Such samples have a two-phase nanostructure (SiO2 containing buried Fe nanoparticles). Formation and dissociation of nanorelief during etching was observed in situ with AFM. The computer animation of this phenomenon was made with morphing of the experimental AFM images. The additional in situ registration of the optical absorption of Fe nanoparticles during etching, ex situ AFM and ferromagnetic resonance measurements enable us to propose that observed morphology transformation takes place because the etching rate of Fe nanoparticles is much higher than the SiO2 etching rate. This etching mechanism was used for computer simulation of the AFM image transformation during etching of the model samples with buried nanoparticles. Good correlation of simulated and experimental AFM images and the corresponding surface roughness parameters vs. etching time confirms that this structural model and the mechanism of selective etching are correct.