CdSe quantum dots (QDs) doped glasses have been widely investigated for optical filters, LED color converter and other optical emitters. Unlike CdSe QDs in solution, it is difficult to passivate the surface defects of CdSe QDs in glass matrix, which strongly suppress its intrinsic emission. In this study, surface passivation of CdSe quantum dots (QDs) by Cd1−xZnxSe shell in silicate glass was reported. An increase in the Se/Cd ratio can lead to the partial passivation of the surface states and appearance of the intrinsic emission of CdSe QDs. Optimizing the heat-treatment condition promotes the incorporation of Zn into CdSe QDs and results in the quenching of the defect emission. Formation of CdSe/Cd1−xZnxSe core/graded shell QDs is evidenced by the experimental results of TEM and Raman spectroscopy. Realization of the surface passivation and intrinsic emission of II-VI QDs may facilitate the wide applications of QDs doped all inorganic amorphous materials.
Crystallization
kinetics of phase change materials (PCMs) at high
temperatures is of key importance for the extreme speed of data writing
and erasing. In this work, the crystallization behavior of one of
the typical PCMs, GeTe, has been studied using ultrafast differential
scanning calorimetry (DSC) at high heating rates up to 4 × 104 K s–1. A strong non-Arrhenius temperature-dependent
viscosity has been observed. We considered two viscosity models for
estimating the crystal growth kinetics coefficient (U
kin). The results showed that the MYEGA model was more
suitable to describe the temperature-dependent viscosity and the crystal
growth kinetics for supercooled liquid GeTe. The glass transition
temperature (T
g) and fragility m were estimated to be 432.1 K and 130.7, respectively.
The temperature-dependent crystal growth rates, which were extrapolated
by the MYEGA model, were in line with the experimental results that
were measured by in situ transmission electron microscopy at a given
temperature. The crystal growth rate reached a maximum of 3.5 m s–1 at 790 K. These results based on ultrafast DSC with
the MYEGA model offer a revelation for crystallization kinetics of
supercooled liquid GeTe.
ZnSb films have higher crystallization temperature (~257 °C), larger crystalline activation energy (~5.63 eV), better 10 year-data-retention (~201 °C) and lower melting temperature (~500 °C).
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