Ki powder

To make an aqueous solution, KI powder (0.002 mol, Sigma-Aldrich, Seoul, Korea) and 10 mL of Au NPs (3 nM, particle size = 20 nm, Sigma-Aldrich, Seoul, Korea) dispersed in H₂O were mixed in 80 mL of deionized water. Subsequently, 20 mL of 30% aqueous SMS (Gelest, Morrisville, PA, USA) was added to the mixed solution. In order to mix the solution properly, the aqueous solution was stirred magnetically at 85 °C on a hot plate. Then, samples were prepared by dropping aqueous solution onto the Si substrate. All samples were cooled down 4 °C or room temperature (RT), or maintained at 70 °C over 24 h until the solution droplets dried. The structural, compositional, and optical properties of the samples were investigated using scanning electron microscopy (SEM, SU-8230, Hitachi, Japan), energy-dispersive X-ray spectrometry (EDX, SU-8230, Hitachi, Japan), X-ray diffraction (XRD, X’pert Pro Powder, PANalytical, Netherlands), transmission electron microscopy (TEM, HD-2300A, Hitachi, Japan), and PL (SpectraPro 500i, Acton, USA). To further investigate the growth mechanism of the a-Si nanotips on the Si substrate, focused ion beam (FIB)-SEM (FB-2100, Hitachi, Japan) and atomic force microscopy (AFM, MOD-1M series, Nanofocus, Richmond, VA, USA) analyses were also performed.