Phonon Scattering in Bi2Te3/Sb2Te3 Superlattice

Ultrafast time-resolved measurements were conducted to investigate scattering mechanism of coherent optical and acoustic phonons in Bi2Te3, Sb2Te3 and Bi2Te3/Sb2Te3 superlattice (SL) films. Strong phonon scatterings in the Bi2Te3/Sb2Te3 SLs are attributed to the interfaces of their hetero-structures. Moreover, decreases of acoustic phonon velocity are observed in SLs, coming from phonon folding and softening. Our results show that both the enhanced interface scattering and the reduced phonon velocity contribute to suppressing the heat transport in SLs.

Download Full-text

Phonon Scattering in Bi2Te3/Sb2Te3 Superlattice

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44012 ◽

2011 ◽

Author(s):

Yaguo Wang ◽

Xianfan Xu ◽

Rama Venkatasubramanian

Keyword(s):

Thermal Conductivity ◽

Thermoelectric Materials ◽

Phonon Scattering ◽

Quantum Confinement Effect ◽

Theoretical Models ◽

Heat Transfer Process ◽

Acoustic Phonons ◽

Time Resolved ◽

Hetero Structure ◽

Phonon Velocity

Thermoelectric materials are characterized with the figure of merit, ZT = S2σT/κ, where T is the temperature, S the Seebeck coefficient, σ the electrical conductivity and κ the thermal conductivity. Many researches have been focused on reducing lattice thermal conductivity through increasing phonon scattering at interfaces. Thin-film superlattices are one of the promising candidates for high ZT thermoelectric materials. Several theoretical models have been used to explain the large ZT in superlattice. One comes from the extra scattering channels at interfaces introduced by the hetero-structure. Another is a result of quantum confinement effect which reduces the phonon group velocity propagating perpendicularly through the superlattice layers through flattening the dispersion curve of acoustic phonons. In this work, ultrafast time-resolved measurements were conducted on Bi2Te3, Sb2Te3 and Bi2Te3/Sb2Te3 superlattice (SL) films to detect coherent acoustic phonons in these materials. Scattering of these phonons is revealed in the Bi2Te3/Sb2Te3 SLs, which comes from the interfaces of the hetero-structure in SL. Also, a decrease of acoustic phonon velocity resulted from folding and flattening of phonons branches is observed. Results show that both interface scattering and the reduced phonon velocity contribute to suppressing the heat transfer process.

Download Full-text

Thermal conductivity in the ferromagnetic metallic phase of monovalent Ag doped manganites

International Journal of Computational Materials Science and Engineering ◽

10.1142/s2047684114500158 ◽

2014 ◽

Vol 03 (03) ◽

pp. 1450015

Author(s):

Dinesh Varshney ◽

E. Khan ◽

Dinesh Choudhary

Keyword(s):

Thermal Conductivity ◽

Relaxation Rate ◽

Acoustic Phonon ◽

Phonon Scattering ◽

Metallic Phase ◽

Charge Carriers ◽

Metallic State ◽

Scattering Mechanism ◽

Doped Manganites ◽

Heat Carriers

The thermal conductivity (κ) behavior in La 0.75 Ag 0.25 MnO 3 manganites is investigated by probing the phonon, carrier and magnon scattering sources. The acoustic phonon contribution to the thermal conductivity (κph) is investigated within the Debye-type relaxation rate approximation. The scattering of phonon from defects, grain boundaries, charge carriers, and phonon are the major sources. La 0.75 Ag 0.25 MnO 3 witnesses the dominant κph and is artifact of strong phonon–impurity and phonon–phonon scattering mechanism in the ferromagnetic metallic state. The carrier contribution to the thermal conductivity (κe) is estimated following the Wiedemann–Franz law. In the metallic phase spin waves (κm) also shows the importance. It is noticed that κm increases with a T2 dependence on the temperature. The behavior of thermal conductivity (κ) in La 0.75 Ag 0.25 MnO 3 is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron, magnon, and phonon contributions.

Download Full-text

Electron Mobility for a SiSi1−xGex Quantum Well: Acoustic Phonon Scattering Mechanism

physica status solidi (b) ◽

10.1002/pssb.2221630111 ◽

1991 ◽

Vol 163 (1) ◽

pp. 125-134 ◽

Cited By ~ 4

Author(s):

J. Tutor ◽

J. A. Bermudez ◽

F. Comas

Keyword(s):

Quantum Well ◽

Electron Mobility ◽

Acoustic Phonon ◽

Phonon Scattering ◽

Scattering Mechanism

Download Full-text

Defect Scattering of Phonons in Phoiopcited GaAs

MRS Proceedings ◽

10.1557/proc-46-447 ◽

1985 ◽

Vol 46 ◽

Author(s):

J.C. Culbertson ◽

P.B. Klein ◽

S.A. Wolf ◽

U. Strom

Keyword(s):

Band Gap ◽

Metastable State ◽

Strong Evidence ◽

Acoustic Phonon ◽

Phonon Scattering ◽

Heat Pulse ◽

Time Resolved ◽

Defect Interaction

AbstractThe time resolved heat pulse generated by above band gap light is studied at 2 K in undoped, semi—insulating GaAs. The phonon lineshape changes with irradiation by 1.1 micron below gap light. The changes in phonon lineshape are reversed by raising the sanple teaperature to 130 K and recooling to 2M. The results provide strong evidence for the change in acoustic phonon scattering when the defect EL2 is transferred to its metastable state. The phonon scattering anisotropies observed for the [100] and [111] directions is indicative of an anisotropic phonon—defect interaction.

Download Full-text

Polar Optical Phonon Instability and Intervalley Transfer in Gallium Nitride

MRS Proceedings ◽

10.1557/proc-512-549 ◽

1998 ◽

Vol 512 ◽

Cited By ~ 2

Author(s):

B. E. Foutz ◽

S. K. O'leary ◽

M. S. Shur ◽

L. F. Eastman ◽

B. L. Gelmont ◽

...

Keyword(s):

Gallium Nitride ◽

Analytical Model ◽

Optical Phonon ◽

Room Temperature ◽

Phonon Scattering ◽

Polar Optical Phonon ◽

Scattering Mechanism ◽

Loss Mechanism ◽

One Dimensional ◽

Optical Phonon Scattering

ABSTRACTWe develop a simple, one-dimensional, analytical model, which describes electron transport in gallium nitride. We focus on the polar optical phonon scattering mechanism, as this is the dominant energy loss mechanism at room temperature. Equating the power gained from the field with that lost through scattering, we demonstrate that beyond a critical electric field, 114 kV/cm at T = 300 K, the power gained from the field exceeds that lost due to polar optical phonon scattering. This polar optical phonon instability leads to a dramatic increase in the electron energy, this being responsible for the onset of intervalley transitions. The predictions of our analytical model are compared with those of Monte Carlo simulations, and are found to be in satisfactory agreement.

Download Full-text