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Temperature dependence of the crystal growth rate of Ge_xSb_(1-x) phase-change alloys using laser irradiated crystallization measurements

Damme, T.van (2014) Temperature dependence of the crystal growth rate of Ge_xSb_(1-x) phase-change alloys using laser irradiated crystallization measurements. Master's Thesis / Essay, Physics.

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To obtain a proper understanding of the crystallization nature of GexSb1-x alloys, with compositions x = 6, 7, 8, 9, 10, depending on the temperature, the crystal growth rate has to be measured over a large range of temperatures. Previously isothermal measurement as well as measurements with a low intensity laser spot have been performed. By focusing a laser beam a smaller, more intense laser spot of 250 μm by 110 μm was obtained. With this laser spot it was possible to measure in higher temperature regimes than previously possible. It is found that the laser spot only locally heats the sample and thus only locally crystallizes the sample. To determine the temperature at the locally measured area a calibration has been made with the lowest germanium content composition studied here, Ge6Sb94. By assuming Arrhenius behavior for Ge6Sb94 up to the high temperature regime, it is possible to measure the heat added by the laser. This calibration is then used to determine the local temperature during measurements of the higher germanium content composition. As expected deviation from the Arrhenius behavior is observed. To complete our understanding of the different compositions over the whole temperature range, the viscosity is calculated from the measured growth rates. Using the VFT model and more recently proposed Mauro model it is possible to obtain a relation of the viscosity over the complete temperature range from glass transition temperature, Tg to the melting temperature, Tm. Converting back to the crystal growth rate, maximum possible growth rates up to ~10 m/s are found. Also the fragility and the glass transition temperature of the different compositions is calculated. For the fragility values between m = 46-68 (Mauro) and m = 60-109 (VFT) and for the glass temperatures values of Tg = 324-430 (Mauro) and Tg = 331-443 (VFT) are found. Following a side track incorporating the use of gold nanoparticles to increase the local temperature during a laser measurement, gold nanoparticles were deposited on the surface of a Ge8Sb92 sample. Although no major improvements in crystal growth were found, there are strong indications that the nanoparticles do in fact increase the crystal growth rate.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Physics
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:01
Last Modified: 15 Feb 2018 08:01

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