Raman scattering in cluster-deposited nanogranular silicon films

Abstract

We study nanograin size confinement effects, and the effect of the increase of local temperature on the first-order Raman spectrum in silicon nanogranular films obtained by cluster deposition. The local temperature was monitored by measuring the Stokes/antiStokes peak ratio with the laser power up to ϳ20 kW/cm 2. We find large energy shifts, up to 30 cm Ϫ1 , and broadenings, up to 20 cm Ϫ1 , of the Raman-active mode, which we attribute to both laser heating and confinement effects. The phonon softening and phonon linewidth are calculated using a phenomenological model which takes into account disorder effects through the breakdown of the kϭ0 Raman-scattering selection rule, and also anharmonicity, which is incorporated through the threeand four-phonon decay processes. Very good agreement with experimental data is obtained for calculated spectra with nanograin sizes of about 10 nm, and with an increase in the anisotropy constants with respect to those of bulk silicon.

Hybrid C-nanotubes/Si 3D nanostructures by one-step growth in a dual-plasma reactor

“…Kostantinovic et al [33] rationalized the detected Raman shift, induced by a low temperature increase due to a laser irradiation at low power, also on the base of a poor thermal contact with the substrate.…”

Failure of the empirical OCT law in the Bi 2 Sr 2 CuO 6 + δ compound

“…Temperature and voltage gradients were simultaneously measured using Ttype (25 µm) thermocouples fixed on two gold sputtered contact pads. Detailed thermopower measurements on ceramic samples are published separately [15]. The observed TEP properties are fully reproducible in both thin films and ceramic samples.…”

“…While a nonmonotonous behaviour is observed for the underdoped states (A2-A6), a marked upward curvature is present in the overdoped states (B, A1). A possible scenario where S arises from two different drag and diffusion contributions was discussed previously [4,15,18].…”

“…Within the frame of the drag model [18,4], the positive thermopower values of LSCO could be explained with the anomalously large contribution of drag, arising from the existing excitation of carriers. In the case of Bi-2201 family, the drag contribution is diminished down to zero leaving only negative diffusion contribution in the strongly overdoped region (δ>0.17) [15]. On the other hand, the anomalously negative thermopower in Bi-2201 is possibly related to the underlying electronic structure, giving rise to the non-classical Fermi-liquid diffusion [15,23].…”

Si and SixGe1‐x NWs studied by Raman spectroscopy

“…(3). This is only a first approximation, because one can expect a variation of the anharmonic constants of nanostructures with respect to the anharmonic constants of the bulk material [9].…”