Ultrasonication Assisted Production of Silicon Nanoparticles from Nanowires

Abstract

With the rapid development of nanoscience and engineering, silicon nanoparticles (SiNPs) have attracted great attention in the fields of medicine, energy, and optoelectronic engineering due to their remarkable physical and chemical properties. SiNPs offer active surface state for functionalization, size-dependent multicolor light emission, stability against photobleaching, and biocompatibility. Most fabrication methods such as chemical vapor deposition or laser pyrolysis require specialized equipment and harsh chemicals for producing SiNPs. Sonochemical synthesis of SiNPs has advantages such as mild reaction environments and fewer reagent requirements. In this work, a simple method to produce SiNPs by combining the chemistry of two-step metal-assisted chemical etching (MACE) using HF/H2O2 and ultrasonication is demonstrated (Fig. 1). MACE is recognized as a unique process for producing silicon nanowires (SiNWs) (Fig. 1a). Arrays of SiNWs were dislodged from the substrate (Fig. 1c), with their original morphology almost intact and were converted into nanoparticles by fragmentizing using ultrasonication. With a yield strength of 2x106 g/cm2, a SiNW of 100nm diameter can be broken from the substrate with a 1.53mg force. Thus, a standard ultrasonicator with 80W power (40kHz) commonly available in the laboratory is sufficient for this process. In order to study the effect of ultrasonication time on the fragmentation of nanowires at a constant power, the samples were sonicated in IPA and the particles were characterized using SEM and spectrometer. The average number of nanowires dislodged from the substrate increased with time and reached its optimum level at approximately one hour of sonication (Fig. 1b). Fragmentation by longer sonication time, beyond 50mins makes the nanowires shorter to form nanoparticles as small as 50nm (Fig. 1d). These particles can be further reduced in size by controlled chemical etching, if required. The possibility of reusing the silicon wafer after each etching and ultrasonication has been investigated by means of gravimetric analysis of SiNWs fabricated on a 4cmx4cm Si substrate. The efficiency of SiNW production was estimated to be 17%. Further studies on the effect of sonication time and power on the efficiency of SiNW production will be reported. The starting wafer could be reused again to minimize cost, which will be a great advantage for mass production of SiNWs and SiNPs. Figure 1