Fluorinion transfer in silver-assisted chemical etching for silicon nanowires arrays

Uniform silicon nanowires arrays (SiNWAs) were fabricated on unpolished rough silicon wafers through KOH pretreatment followed by silver-assisted chemical etching (SACE). Density functional theory (DFT) calculations were used to investigate the function of silver (Ag) at atomic scale in the etching process. Among three adsorption sites of Ag atom on Si(1 0 0) surface, Ag(T4) above the fourth-layer surface Si atoms could transfer fluorinion (F ^- ) to adjacent Si successfully due to its stronger electrostatic attraction force between Ag(T4) and F ^- , smaller azimuth angle of F-Ag(T4)-Si, shorter bond length of F-Si compared with F-Ag. As F ^- was transferred to adjacent Si by Ag(T4) one by one, the Si got away from the wafer in the form of SiF ₄ when it bonded with enough F ^- while Ag(T4) was still attached onto the Si wafer ready for next transfer. Cyclic voltammetry tests confirmed that Ag can improve the etching rate by transferring F ^- to Si.