Raman study of laser-induced heating effects in free-standing silicon nanocrystals

Abstract

This paper demonstrates that free-standing silicon nanocrystals (Si NCs) have significantly different thermal conductivity properties compared to Si NCs embedded in a host matrix. The temperatures of Si NCs under laser illumination have been determined by measuring the ratio of the Anti-Stokes to Stokes intensities of the first order Si-Si transverse optical (TO) phonon mode. It is found that large free-standing Si NCs are easily heated up to ∼953 K by the laser light. The laser heating effects are reversible to a large extent, however the nature of the free-standing Si NCs is slightly modified after intensive illumination. The free-standing Si NCs can even be easily melted when exposed to a well-focused laser beam. Under these conditions, the blackbody radiation of the heated Si NCs starts to compete with the detected Raman signals. A simplified model of the heating effects is proposed to study the size dependence of the heated free-standing Si NCs with increasing laser power. It is concluded that the huge red-shift of the Si-Si TO mode observed under intensive laser illumination originates from laser-induced heating effects. In contrast, under similar illumination conditions Si NCs embedded in matrixes are hardly heated due to better thermal conductivity.

Heterogeneous reduction of carbon dioxide by hydride-terminated silicon nanocrystals

“…Porous Si nanoparticles have been used for photothermal therapy33. For Si nanocrystals, laser light could induce intense local heating34, and the photothermal effect of ncSi increases with irradiation energy, consistent with a combination of thermalization of hot carriers under irradiation greater in energy than the bandgap (ultraviolet/visible light) and defect-mediated heating processes (induced by both ultraviolet/visible light and infrared light)35. A preliminary Raman study also shows that laser light could significantly heat up Si nanocrystals embedded in SiO x matrix (Supplementary Fig.…”

Molecular hydrogen‐induced nucleation of hydrogenated silicon nanocrystals at low temperature

“…In the last few years, light generation and amplification in silicon were pursued through the use of nanocrystals (NCs), taking advantage of their reduced size (less than 10 nm), to reduce refection of incident light in the hope of increasing the conversion efficiency of solar cells . These NCs can either be free standing or embedded in a host matrix such as a‐Si:H, the result of which is usually called polymorphous silicon . In this case, the optical properties of the films will depend mainly on the amorphous matrix, while the electronic transport will be governed by the size and density of the NCs, which improve carrier mobility and insure stability of the films against radiation…”

Silicon monoxide – a convenient precursor for large scale synthesis of near infrared emitting monodisperse silicon nanocrystals

“…12 Such ncSi were also demonstrated to exhibit a more effective photothermal effect than the visible-emitting analogues, which enhances the potential application of an effective photothermal therapy in conjunction with photoluminescence (PL) imaging. 13,14 Unfortunately, production of near infrared emit- 1200°C for 1 h followed by annealing at 1100°C for another 10 h resulted in ncSi with a PL peak maximum at 955 nm. The maximum percentage mass yield of ncSi by this method was 10% after liberation from the silicon oxide matrix, 15 which is considerable since the mass percent composition of Si in the precursor before heating is only slightly above 50%, and there is additional loss of SiH 4 co-generated during heating.…”