The speed at which phase change memory devices can operate depends strongly on the crystallization kinetics of the amorphous phase. To better understand factors that affect the crystallization rate, we have investigated crystallization of GeTe films as a function of their deposition temperatures and deposition rates, using X-ray synchrotron radiation and Raman spectroscopy. As-deposited films were found to be fully amorphous under all conditions, even though films deposited at higher temperatures and lower rates experienced lower effective quench rates. Non-isothermal transformation curves show that the apparent crystallization temperature of GeTe films decreases with increasing deposition temperature and decreasing deposition rate. It was found that this correlates with a decrease in the activation energy for nucleation (calculated using Kissinger's analysis), while the activation energy for crystal growth remained unaffected. From Raman spectroscopy measurements, it was found that increasing the deposition temperature or decreasing the deposition rate, and therefore the effective quench rate, reduces the number of homopolar Te-Te bonds and thereby reduces the barrier to crystal nucleation.
We investigated nanoneedle arrays fabricated on a series of metal-silicon substrates using Ga(+) ion beam patterning. It is shown that the low sputtering rate of the metal is preserved on the tip of each nanoneedle in the form of a gallium alloy nanodot. The generated nanodot was found to greatly alleviate the ion sputtering of the underlying materials. These protective metals are promising materials that act as a shelter for the functional layer, which is vulnerable to ion beam irradiation. In the present work, as an example, we report a bundle of GaAs nanowhiskers that were successfully grown on each gold nanodot protected by an iron-gallium alloy.
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