Mechanisms of SiC porous anodic etching in the dilute solution of hydrofluoric acid in either ethylene glycol or water
DOI:
https://doi.org/10.51453/2354-1431/2016/132Keywords:
porous SiC; anodic etching; anodic oxidation; HF; Ethylene glycol.Abstract
In this paper, we present the experimental results to indicate the anodic etching mechanism directly SiC in the dilute hydrofluoric (HF) solution. A porous layer has been created in amorphous SiC (aSiC) thin films by constantcurrent anodization in a dilute solution of hydrofluoric acid in either ethylene glycol (HF/EG) or water (HF/H2O). The results showed that the dependence of the morphology of the porous aSiC layer on the anodic current density in the two cases is different from each other. The follow-up study showed that the cause of this difference lies in the almost absence of water in the dilute HF/EG solution. Due to scarcity of water in the electrolyte, at all current densities aSiC reacted directly with HF of the electrolyte, creating a compound between Si and HF which is dissolved into the solution and free carbon. Then a portion of the carbon was oxidized to carbon oxide by water, which is contained in the HF and evaporated away, while anốther part was left on the etched surface, forming a carbon-rich surface. Meanwhile, in the dilute HF/H2O solution, with the increase of the anodic current density, the aSiC anodic etching through the direct reaction of aSiC with HF has gradually been replaced by the etching through the oxidation, which has taken place by the reaction of aSiC with water of the electrolyte.
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