One of the most promising processes for the formation of complex surface morphology is electrochemical anodic etching, which is used to obtain nanostructured silicon-based materials. During the process, the system of pores forms, and the material becomes heterophase, including nanocrystalline and amorphous Si, SiOx, and various functional groups that were adsorbed by the surface. Different effects and the variety of functions based on them are caused by different hierarchical levels of pores as shown by scanning electron microscopy (SEM).
The nucleation of paramagnetic centers (PMCs) on the sample surface and the formation of substance clusters from them proceeds from the initial stage of the pore formation process. While applying of an external voltage, the uniform etching of silicon and the accumulation of ions starts.
Making the surface morphology more complex by depositing thin layers of zinc oxide on porous silicon by spray pyrolysis, it was obtained a uniform distribution of ZnO nanocrystals over the surface of the sample.
The transition to the crystalline phase is associated with the formation of particles with stable bonds. With a gradual change in the power of ultrahigh-frequency radiation in the spectrum of electron paramagnetic resonance (EPR), PMCs of various structures were identified and the formation of ZnO nanocrystals based on them was shown.
According to SEM images, after deposition of ZnO layers on PorSi, the surface of the sample become more fine porous and the porosity is more homogeneous by size. The coating is localized at the pore boundaries, thus forming particles with dangling bonds.
Thus, a hierarchical surface structure, including macro and mesopores, was formed by the method of electrochemical etching. The formation of nanocrystalline structures was confirmed by the EPR method and the mechanism involving particles with uncompensated charge was proposed.
