Synthesis and characterisation of silicon nanocrystals (Si NCs) materials are carried out. We investigated the morphological and structural Si NCs embedded in the silicon nitride (SiN x ) matrix. The study has been carried out on thin films thermally annealed at high temperature by rapid thermal annealing after deposition at 380°C by plasma-enhanced chemical vapour deposition. Our study evidenced the existence of an Si NCs embedded on the SiN x matrix. This has been proven by Raman spectra and high-resolution transmission electron microscopy (HR-TEM). A sharp peak at a frequency of 515 cm −1 ascribed to the transverse optical (TO) mode becomes broader and makes a symmetric shoulder on the higher frequency side with an increase in the annealing temperature. HR-TEM analyses have demonstrated that Si NCs having a mean radius ranging between 3 and 5 nm. This confirms the a-SiN phase transition to the c-SiN phase by the formation of silicon NCs.
Optical properties of silicon-based coatings are investigated in which the refractive index n is varied gradually (SiON with continuously changing x and y) or in discrete steps (Si02/SiN13 multilayers). The films are prepared at room temperature in a dual-mode microwave/radiofrequency (MW/RF) plasma in which the substrates are placed on an RF powered substrate holder, while simultaneously exposed to a MW discharge. The films' composition is controlled by the working gas mixture using SiH, NH3 and N20, and their microstructure, such as packing density and interface roughness, is controlled independently by varying the energy and the flux of bombarding ions. The deposition process is monitored in-situ by optical emission spectroscopy (OES) measurements which are related to the compositional depth profiles provided by elastic recoil detection (ERD) analysis. The optical evaluations are based on spectrophotometric measurements. A scalar model is used to elucidate the effect of the interfacial structure on the specular and the diffuse transmission and reflection data. Calculated n values for the graded layers are correlated with the compositional depth profiles. The films are considered for applications such as antireflective coatings for solar cells, rugate filters and integrated optical devices.
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