Coherent optical phonon spectroscopy studies of femtosecond-laser modified Sb2Te3 films

Li, Yuwei W; Stoica, Vladimir; Endicott, Lynn; Wang, Guoyu; Uher, Ctirad; Clarke, Roy

doi:10.1063/1.3499742

Cited by 31 publications

(23 citation statements)

References 28 publications

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“…Changes in the phonon spectrum of Sb 2 Te 3 films after laser irradiation have been reported recently. 15 In that case, an additional A 1g -mode related to Te ͑3.6 THz͒ developed, which the authors attributed to Te segregation, which cannot account for the mode observed in our study. Assigning it to the weak mode observed in hcp-GST would not make sense either, since hcp-GST has never been obtained by laser irradiation.…”

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confidence: 53%

Coherent optical phonons in different phases of Ge2Sb2Te5 upon strong laser excitation

Hernández-Rueda

Savoia

Gawełda

et al. 2011

Applied Physics Letters

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The transient reflectivity response of phase-change Ge 2 Sb 2 Te 5 films to intense femtosecond laser pulses is studied by ultrafast coherent phonon spectroscopy. The three different phases ͑amorphous, fcc-, and hcp-crystalline͒, as well as laser-crystallized films, are investigated, featuring different photoexcited carrier and coherent optical phonon dynamics. At least two main phonon frequencies are identified for each phase/material and their evolution for increasing pump fluences is investigated for the fcc-crystalline phase and the laser-crystallized material, revealing strong differences. We find evidence that a considerable fraction of amorphous phase remains in the laser-crystallized material, which features a different phonon frequency, not related to other phases. These results are important for emerging strategies aimed at driving ultrafast phase transitions via coherent phonon excitation for applications in data storage.

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confidence: 53%

Coherent optical phonons in different phases of Ge2Sb2Te5 upon strong laser excitation

Hernández-Rueda

Savoia

Gawełda

et al. 2011

Applied Physics Letters

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“…In previous studies of amorphous and polycrystalline Ge 2 Sb 2 Te 5 films, a 3.4 THz mode observed in the R signal was assigned A 1g character5678. However, Merlin's theory (described in Supplementary Information S4) predicts that the A and E modes should be observed only within the R signal, with no dependence on pump or probe polarization, while being absent from the AR signal.…”

Section: Discussionmentioning

confidence: 96%

“…Knowledge and understanding of the phonon spectrum can provide a fingerprint of the crystallographic structure while large amplitude phonons may appear as a precursor to the phase transition itself. Although several studies of coherent optical phonon (COP) dynamics have been performed upon both amorphous and polycrystalline Ge 2 Sb 2 Te 5 56789, no such study has been conducted on a Ge 2 Sb 2 Te 5 single crystal. Therefore the growth of epitaxial Ge 2 Sb 2 Te 5 films upon GaSb(001) substrates10 by molecular beam epitaxy provides an opportunity to explore the character of the phonon spectrum of Ge 2 Sb 2 Te 5 .…”

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confidence: 99%

Observation of T2-like coherent optical phonons in epitaxial Ge2Sb2Te5/GaSb(001) films

Shalini

Liu

Al-Jarah

et al. 2013

Sci Rep

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The phonon spectrum of Ge2Sb2Te5 is a signature of its crystallographic structure and underlies the phase transition process used in memory applications. Epitaxial materials allow coherent optical phonons to be studied in femtosecond anisotropic reflectance measurements. A dominant phonon mode with frequency of 3.4 THz has been observed in epitaxial Ge2Sb2Te5 grown on GaSb(001). The dependence of signal strength upon pump and probe polarization is described by a theory of transient stimulated Raman scattering that accounts for the symmetry of the crystallographic structure through use of the Raman tensor. The 3.4 THz mode has the character of the 3 dimensional T2 mode expected for the Oh point group, confirming that the underlying crystallographic structure is cubic. New modes are observed in both Ge2Sb2Te5 and GaSb after application of large pump fluences, and are interpreted as 1 and 2 dimensional modes associated with segregation of Sb.

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“…9,10 Coherent phonon spectroscopy (CPS) has recently been applied to GST materials of alloy 11 and superlatticed films, 12 and the related Sb 2 Te 3 films. 13 In their study, the observed local phonon modes in the amorphous GST films were found to be strongly damped modes, with its relaxation time of less than a few picoseconds due to the scattering by lattice defects. 11,12 The CPS on GST compounds, however, have not yet been applied to investigate thermal properties, although Wang et al have recently proposed to use CPS as a powerful method to estimate lattice thermal conductivity.…”

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confidence: 99%

Thermal conductivity of GeTe/Sb2Te3 superlattices measured by coherent phonon spectroscopy

Hase

Tominaga

2011

Applied Physics Letters

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We report on evaluation of lattice thermal conductivity of GeTe/Sb 2 Te 3 superlattice (SL) by using femtosecond coherent phonon spectroscopy at various lattice temperatures. The time-resolved transient reflectivity obtained in amorphous and crystalline GeTe/Sb 2 Te 3 SL films exhibits the coherent A 1 optical modes at terahertz (THz) frequencies with picoseconds dephasing time. Based on the Debye theory, we calculate the lattice thermal conductivity, including scattering by grain boundary and point defect, umklapp process, and phonon resonant scattering. The results indicate that the thermal conductivity in amorphous SL is less temperature dependent, being attributed to dominant phonon-defect scattering.

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Coherent optical phonon spectroscopy studies of femtosecond-laser modified Sb2Te3 films

Cited by 31 publications

References 28 publications

Coherent optical phonons in different phases of Ge2Sb2Te5 upon strong laser excitation

Coherent optical phonons in different phases of Ge2Sb2Te5 upon strong laser excitation

Observation of T2-like coherent optical phonons in epitaxial Ge2Sb2Te5/GaSb(001) films

Thermal conductivity of GeTe/Sb2Te3 superlattices measured by coherent phonon spectroscopy

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