Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics

Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the vicinity of the transverse and longitudinal optical mode frequencies. The significant frequency dependence enables valuable applications such as a tunable terahertz radiation source. The polariton dispersion relations of technologically important dielectric and ferroelectric crystals were reviewed in the broad terahertz range using terahertz time-domain spectroscopy, far-infrared spectroscopy, and Raman scattering spectroscopy.

On determination of properties of ultrathin and very thin silicon oxide layers by FTIR and X - ray reflectivity

ABSTRACTWe analyze properties of ultra-thin SiO2 + very thin SiOx double layer structure formed on high-doped n-type Si (100) wafers using FTIR, X-ray reflectivity and AFM methods. The observed absorption band around 1230 cm−1 is attributed to the longitudinal optical mode of SiOx precipitates incorporated in silicon matrix. In particular, the corresponding peak positions indicate that there are precipitates of SiOx with x >1.8. The absorption band around 1070 cm−1 is attributed to the Si–O–Si stretching bond. This position is characteristic for stoichiometric SiO2. From the results it can be concluded that differently shaped particles co-exist in the samples. This assumption is supported by the oxide density measurements performed by FTIR and X-ray reflectivity. We determined density of oxide layers, roughness of corresponding interfaces, and surface roughness by the X-ray reflectivity. The obtained values were compared with those determined by FTIR and AFM. Additionally, we present the results of multifractal analysis on a complete set of six samples.

Mechanisms of Raman Scattering in doped Indium Nitride

ABSTRACTHighly n-doped InN layers are investigated by means of Raman scattering: a strong mode is evidenced near the frequency of the A1(LO) phonon, despite the high conductivity of the films. This observation is interpreted assuming the breakdown of the wave-vector conservation leading to the decoupling of the plasmon from the phonon. The lineshape of the longitudinal optical mode is simulated using the Lindhard-Mermin dielectric function for various light scattering processes: we found that the charge density fluctuation mechanism is dominant, at least in the visible excitation range.

Experimental detection of collective modes In a polar liquid: application to the case of the solvated electron in H2O and NH3

We present experimental data that confirm the predicted existence of a collective mode in a liquid corresponding to the longitudinal optical mode in an ionic crystal. The experimental investigation was carried out in nitromethane, and the results bear out all the calculated properties of this collective mode: the dipolar plasmon. The calculated frequency of the dipolar plasmon, as well as the dielectric constant at high and low frequencies, are then used to calculate without adjustable parameters the polaron coupling constant of the solvated electron in NH3 and H2O. A comparison of the calculated and measured properties of the solvated electron indicates that in either case a polaron-like continuum theory can at most account for only a fraction of the energy of the observed optical absorption.