Raman amplification for trapped radiation in crystalline single Si nanoparticle

Abstract

In a single crystalline Si particle, we observed a huge amplification of the Raman peak at 521 cm−1. With an AFM microscope, coupled with a Micro-Raman spectrometer, we investigate a single Si particle at wavelengths of 532 nm, 633 nm, and 785 nm. As observed by transmission electron microscopy, it has an octahedral shape of 150 nm in size. Thermal effects were detected on the Raman peak when the laser radiation, trapped inside, determines the heating of the particle up to its fusion. In these cases, the Raman peak splits into two components, the first at the crystal position and the other shifted at a lower value. The data permit the identification of the amplification mechanism of the Raman peak as trapped radiation moving forward and backwards into the particle. The thermal effects are attributed to phonon confinement and reduced thermal exchange with the surrounding. The present results are discussed in light of local order, the uncertainty principle, and phonon dispersion curves, and corroborated by shape-dependent simulation of absorption, scattering, and extinction behaviour.