Yarema Olesya, Perevedentsev Aleksandr, Ovuka Vladimir, Baade Paul, Volk Sebastian, Wood Vanessa, Yarema Maksym
Materials and Device Engineering Group, Department of Information Technology and Electrical Engineering, ETH Zurich, Gloriastrasse 35, CH-8092 Zurich, Switzerland.
Polymer Technology, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, CH-8093 Zurich, Switzerland.
Chem Mater. 2018 Sep 11;30(17):6134-6143. doi: 10.1021/acs.chemmater.8b02702. Epub 2018 Aug 20.
Phase-change memory materials refer to a class of materials that can exist in amorphous and crystalline phases with distinctly different electrical or optical properties, as well as exhibit outstanding crystallization kinetics and optimal phase transition temperatures. This paper focuses on the potential of colloids as phase-change memory materials. We report a novel synthesis for amorphous GeTe nanoparticles based on an amide-promoted approach that enables accurate size control of GeTe nanoparticles between 4 and 9 nm, narrow size distributions down to 9-10%, and synthesis upscaling to reach multigram chemical yields per batch. We then quantify the crystallization phase transition for GeTe nanoparticles, employing high-temperature X-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. We show that GeTe nanoparticles crystallize at higher temperatures than the bulk GeTe material and that crystallization temperature increases with decreasing size. We can explain this size-dependence using the entropy of crystallization model and classical nucleation theory. The size-dependences quantified here highlight possible benefits of nanoparticles for phase-change memory applications.
相变存储材料是指一类能够以具有明显不同电学或光学性质的非晶相和晶相存在，并且具有出色的结晶动力学和最佳相变温度的材料。本文重点关注胶体作为相变存储材料的潜力。我们报道了一种基于酰胺促进法的非晶态GeTe纳米颗粒的新型合成方法，该方法能够精确控制GeTe纳米颗粒的尺寸在4到9纳米之间，尺寸分布窄至9-10%，并且能够扩大合成规模以达到每批数克的化学产率。然后，我们采用高温X射线衍射、差示扫描量热法和透射电子显微镜对GeTe纳米颗粒的结晶相变进行了量化。我们表明，GeTe纳米颗粒比块状GeTe材料在更高的温度下结晶，并且结晶温度随着尺寸的减小而升高。我们可以使用结晶熵模型和经典成核理论来解释这种尺寸依赖性。这里量化的尺寸依赖性突出了纳米颗粒在相变存储应用中的潜在优势。
