Tunable morphological evolution of in situ gold catalysts mediated silicon nanoneedles

Achieving tunable growth of high quality Silicon (Si) nanoneedles (NNs) is challenging. We report the optimized morphology of in situ gold (Au) catalysts assisted SiNNs grown via very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The vapor-liquid-solid (VLS) mechanism mediated morphological evolution is tuned using hydrogen (H2) and silane (SiH4) gas flow. Au-coated Si(100) substrates are treated using H2 plasma to create in situ Au nanoparticles (NPs) with high catalytic activity. FESEM images manifested the existence of mono-dispersed Au NPs and high yield of SiNNs having diameter ranging from 80 to 140 nm and lengths up to 2.31±0.3 µm. Furthermore, these NNs gradually became thinner to form sharp tips of diameter as small as 4 nm. XRD pattern confirmed the diamond (cubic) crystalline phases of SiNNs. HRTEM images revealed the occurrence of Au NPs at the crystalline SiNNs tips. Raman spectrum of as-grown SiNNs exhibited the TO phonon mode accompanied by a red-shift (~23.59 cm−1). Synthesized SiNNs displayed extremely low reflectance (~8%) at short wavelengths (λ<700 nm), indicating excellent antireflection properties. Our controllable and optimized growth method may constitute a basis to achieve high quality SiNN arrays, which are beneficial for various applications.