Optical and Structural Properties of Si Nanocrystals in SiO2 Films

Abstract

Optical and structural properties of Si nanocrystals (Si-nc) in silica films are described. For the SiOx (x < 2) films annealed above 1000 °C, the Raman signal of Si-nc and the absorption coefficient are proportional to the amount of elemental Si detected by X-ray photoelectron spectroscopy. A good agreement is found between the measured refractive index and the value estimated by using the effective-medium approximation. The extinction coefficient of elemental Si is found to be between the values of crystalline and amorphous Si. Thermal annealing increases the degree of Si crystallization; however, the crystallization and the Si–SiO2 phase separation are not complete after annealing at 1200 °C. The 1.5-eV PL quantum yield increases as the amount of elemental Si decreases; thus, this PL is probably not directly from Si-nc responsible for absorption and detected by Raman spectroscopy. Continuous-wave laser light can produce very high temperatures in the free-standing films, which changes their structural and optical properties. For relatively large laser spots, the center of the laser-annealed area is very transparent and consists of amorphous SiO2. Large Si-nc (up to ~300 nm in diameter) are observed in the ring around the central region. These Si-nc lead to high absorption and they are typically under compressive stress, which is connected with their formation from the liquid phase. By using strongly focused laser beams, the structural changes in the free-standing films can be made in submicron areas.

Correlation of size and oxygen bonding at the interface of Si nanocrystal in Si–SiO2 nanocomposite: A Raman mapping study

“…This further supports the interpretation that LW phonons originate from surface/interface of smaller Si NCs, whereas, HW phonons originate from core of larger Si NCs. Similar experimental observations have been reported by Nikitin et al They observed that the wavenumbers in the Raman spectra of smaller (10–20 Å) and larger (>40 Å) Si NCs lie in the ranges 490–500 and 518–519 cm −1 , respectively, which further supports our interpretation.…”

“…We wish to emphasize that the results obtained from theoretical calculations of Raman spectra clearly elucidate dominant contribution of Si atoms located at the surface. This further [67] They observed that the wavenumbers in the Raman spectra of smaller (10-20 Å) and larger (>40 Å) Si NCs lie in the ranges 490-500 and 518-519 cm À1 , respectively, which further supports our interpretation. On the other hand, the calculated wavenumber of a strong peak in the Raman spectra of hydrogen terminated cluster is much lower (~499 cm À1 ) than the corresponding wavenumber in oxygen terminated cluster.…”

New functional material: spark plasma sintered Si/SiO2 nanoparticles – fabrication and properties

“…An ensemble of nanostructured silicon particles embedded into an SiO 2 host has been the subject of intensive research over the last two decades. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The main motivation for research in this eld is the fabrication of silicon-based light emitters, which utilize the reduced dimension connement effect to overcome indirect bandgap limitations for radiative recombination in Si. 2,11,12,15 It is also worth citing some other applications of Si nanoparticles, such as photovoltaic cells, 14,21,22 batteries, 23,24 etc.…”

Surface-Enhanced Raman Scattering of Silicon Nanocrystals in a Silica Film

“…The position and the width of the Raman band of Si-nc provide a valuable information on their sizes, stress, and temperature13141516. A known problem of conventional Raman spectroscopy is a small cross-section of this process.…”