Temperature Dependence of the Thermal Properties of Optical Memory Materials

Kuwahara, Masashi; Сузукі, Осаму; Yamakawa, Yuzo; Taketoshi, Naoyuki; Yagi, Takashi; Fons, Paul; Fukaya, Toshio; Tominaga, Junji; Baba, Toshihide

doi:10.1143/jjap.46.3909

Cited by 42 publications

(44 citation statements)

References 11 publications

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“…See the text for an explanation of the choices of the linear expansion coefficient and optical penetration depth. Table I [17]. For each time step δt, the Takagi-Taupin dynamical x-ray scattering equations are solved to determine the change in diffracted intensity.…”

Section: B Experimental Resultsmentioning

confidence: 99%

Picosecond strain dynamics inGe2Sb2Te5monitored by time-resolved x-ray diffraction

et al. 2014

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Coherent phonons (CPs) generated by laser pulses on the femtosecond scale have been proposed as a means to achieve ultrafast, nonthermal switching in phase-change materials such as Ge 2 Sb 2 Te 5 (GST). Here we use ultrafast optical pump pulses to induce coherent acoustic phonons and stroboscopically measure the corresponding lattice distortions in GST using 100-ps x-ray pulses from the European Synchrotron Radiation Facility (ESRF) storage ring. A linear-chain model provides a good description of the observed changes in the diffraction signal; however, the magnitudes of the measured shifts are too large to be explained by thermal effects alone, implying the presence of excited-state effects in addition to temperature-driven expansion. The information on the movement of atoms during the excitation process can lead to greater insight into the possibilities of using CP-induced phase transitions in GST.

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Section: B Experimental Resultsmentioning

confidence: 99%

Picosecond strain dynamics inGe2Sb2Te5monitored by time-resolved x-ray diffraction

et al. 2014

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“…The reflectivity R has been directly measured by a spectrophotometer, whereas the absorption coefficient α has been calculated taking into account multiple reflections at the various interfaces of the multilayer stack on the basis of the refractive indices reported in refs 46, 47, 48. The specific heat, the density and the thermal conductivity of the different materials, as function of temperature, have been extracted from refs 43, 49, 50, 51. The melting process has been described taking into account the heat of fusion52.…”

Section: Methodsmentioning

confidence: 99%

Measurement of crystal growth velocity in a melt-quenched phase-change material

et al. 2013

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Phase-change materials are the basis for next-generation memory devices and reconfigurable electronics, but fundamental understanding of the unconventional kinetics of their phase transitions has been hindered by challenges in the experimental quantification. Here we obtain deeper understanding based on the temperature dependence of the crystal growth velocity of the phase-change material AgInSbTe, as derived from laser-based time-resolved reflectivity measurements. We observe a strict Arrhenius behaviour for the growth velocity over eight orders of magnitude (from ~10 nm s−1 to ~1 m s−1). This can be attributed to the formation of a glass at elevated temperatures because of rapid quenching of the melt. Further, the temperature dependence of the viscosity is derived, which reveals that the supercooled liquid phase must have an extremely high fragility (>100). Finally, the new experimental evidence leads to an interpretation, which comprehensively explains existing data from various different experiments reported in literature.

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“…where x ¼ hx=k B T, C V is the lattice specific heat, v the sound velocity, H D the Debye temperature, 21 k B the Boltzmann constant, x the phonon frequency, and s c the acoustic phonon relaxation time, whose inverse (relaxation rate) can be given by contributions from various scattering mechanisms 14,19 :…”

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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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Temperature Dependence of the Thermal Properties of Optical Memory Materials

Cited by 42 publications

References 11 publications

Picosecond strain dynamics inGe2Sb2Te5monitored by time-resolved x-ray diffraction

Picosecond strain dynamics inGe2Sb2Te5monitored by time-resolved x-ray diffraction

Measurement of crystal growth velocity in a melt-quenched phase-change material

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

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