Nanoscale Crystalline to Amorphous Phase Transition Studies in Nanowires: Controlled Synthesis, Characterization, Memory Switching Devices and Size-Dependent Properties

技术：本项目研究在亚光刻长度尺度上自组装锗锑碲纳米线（NW）材料的可逆晶体到非晶相变现象。该方法的重点是合成和表征复杂的、定义良好的Ge-Sb-Te NWs，并控制其组成和尺寸，以研究基本的相开关特性，以及原型存储元件的组装。该方法的组成部分包括：1)发展脉冲激光沉积（PLD）生长技术，以精确控制NW的化学成分和直径，合成复杂的三元Ge-Sb-Te NWs。2)利用电子显微镜（SEM， TEM）表征了NWs的结构和化学成分。3)电场诱导相开关行为的研究及其与化学成分和粒径的关系。纳米粒子尺寸对热力学参数的影响及其对相变机理的影响研究。4)原位透射电镜分析了Ge-Sb-Te NWs的结构变化与外加电流脉冲的关系。NWs非晶化和再结晶机理的尺寸和化学成分依赖性研究。5)基于上述实验获得的见解，制作新型NW存储器件。非技术性：项目涉及电子/光子材料科学领域的基础研究问题，具有较高的技术相关性。研究和教育活动将通过本科生参与研究项目，将新的研究成果纳入教学模块，并培训来自费城地区的高中和大学教师，学生来自少数民族和代表性不足的地区。

Technical: This project addresses reversible crystalline to amorphous phase transition phenomena in self assembled Ge-Sb-Te nanowire (NW) materials at sub-lithographic length scales. The approach focuses on synthesis and characterization of complex, well defined Ge-Sb-Te NWs with control over composition and dimension for investigating fundamental phase switching properties, and assembly of prototype memory elements. Components of the approach include: 1) Development of pulsed laser deposition (PLD) growth technique to synthesize complex ternary Ge-Sb-Te NWs with precise control over NW chemical composition and diameters. 2) Characterization of structural and chemical composition of NWs with electron microscopy (SEM, TEM). 3) Investigation of electric field induced phase switching behavior and its dependence on chemical composition and size (diameter) of NWs. Study of the influence of size on thermodynamic parameters and its affect on phase transition mechanism in NWs. 4) Insitu TEM analysis of structural transformations in Ge-Sb-Te NWs as a function of applied current pulses. Size and chemical composition dependent study of amorphization and recrystallization mechanism in NWs. 5) Fabrication of novel NW memory devices based on insights obtained from the experiments described above. Non-technical: The project addresses basic research issues in a topical area of electronic/photonic materials science with high technological relevance. Research and educational activities will be integrated by the involvement of undergraduates in the research program, incorporating new research results in a teaching module, and training high school and college teachers from the Philadelphia district with student population from minority and underrepresented sections.