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TT: Fachverband Tiefe Temperaturen

TT 51: Quantum Wires: Optical Properties (organized by HL)

TT 51.3: Vortrag

Dienstag, 1. April 2014, 15:00–15:15, POT 112

Phonons in PbSe nanostructures — •Efterpi Kalesaki and Ludger Wirtz — Physics and Materials Science Research unit, University of Luxembourg, Luxembourg

The prospect of efficient utilization of lead chalcogenides in optoelectronic, photovoltaic and thermoelectric devices has brought PbSe into the spotlight of scientific research. Bulk PbSe exhibits a plethora of intriguing characteristics, in terms of structural, electronic and vibrational properties, which have been the subject of intense investigation. In particular, the phonon dispersion displays a near-Kohn anomaly of the LO mode at Γ [1]. However, attempts to understand the vibrational properties of corresponding nanostructures are limited.

We present results of ab-initio calculations on the phonon dispersions of <001> - oriented PbSe slabs of various thicknesses. The latter are correlated with the phonon modes of bulk PbSe via the quantum confinement model [2]. Quantum confinement and strain effects are identified as parameters critically affecting the lattice dynamics of PbSe nanostructures. In contrast to most nanocrystalline materials, where the Raman active phonon modes shift down in frequency, a blueshift of the longitudinal optical mode with decreasing layer thickness is recorded for PbSe nanostructures, validating recent experimental results of Raman spectra for lead selenide nanocrystals [2]. Softening of the TO mode in the slabs is an indication of near-ferroelectric behaviour in PbSe nanostructures.

[1] O. Kilian et al., Phys. Rev. B 80, 245208 (2009)

[2] J. Habinshuti et al., Phys. Rev. B 88, 115313 (2013)