Phonon mode study of Si nanocrystals using micro-Raman spectroscopy

Abstract

First-order Raman spectra of hydrogenated nanocrystalline silicon (nc:Si:H) films show unexpected features in their optical vibrational modes for crystallites with sizes ranging from 2 to 6 nm. Two size-dependent spectral regions, one with the stronger intensity peaking at 505–509 cm−1 and another a shoulder-like band between 512 and 517 cm−1, are clearly identified using a detailed line-shape analysis and the strong phonon confinement model. The strong size dependence of the relative integrated intensities of the two bands suggests that the modification of the vibrational spectra can be attributed to an effect induced by the atomic vibrations from the near-surface region of the nanocrystals.

Modified phonon confinement model for size dependent Raman shift and linewidth of silicon nanocrystals

“…Crystallite size (nm) Pennisi data [9] Richter data [10] Xia data [3] Present theory Sirekno data [7] Crystallite size (nm) …”

“…In Fig. 4, BP model [8] Cheng theory [4] Present theory Xia data [3] RWL model [8] Richter data [10] Pennisi data [9] Paillard data [8] Li data [6] Faraci data [12] Sirekno data [7] Peak Shift (cm…”

“…In recent years the finite size effects on the Raman spectrum of a nanocrystal silicon have attracted considerable interest [1,2] due to the role of Si in the current semiconductor industry and potential technological applications [3][4][5] resulting from the optical properties of Si quantum dots. However, most of the efforts are dedicated to interpret the experimental Raman spectra particularly in terms of confinement effect, which in 0D systems are difficult to evidence experimentally by Raman shift in contrast to 2D and 1D nanostructures.…”

“…However, there are some reports on the limitations of the phonon confinement model (PCM) [3,[8][9][10][11][12]. To obtain a good interpretation of the experimental data many other models such as the microscopic force model [4], the bond polarizable model [13][14] and the spatial correlation model [15] have been reported.…”

New explanation of Raman peak redshift in nanoparticles

“…Frequency shifts for silicon particles of different sizes are presented in Ref. [19]. Comparison of the theoretical curves, calculated with formulae (11,12) and the experimental data for the considered materials are presented in Fig.…”