Atomic-Scale Understanding of Phase-Change Phenomena in Amorphous Chalcogenides

无定形硫族化物相变现象的原子尺度理解

• 批准号: 0906070
• 负责人: Sabyasachi Sen
• 金额: $ 24万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0906070&HistoricalAwards=false
• 关键词: Atomic; Scale; Understanding; Phase; Change

NON-TECHNICAL DESCRIPTION: We live in the Information Age where storage of large amount of information in a small space is of paramount importance. Glassy materials consisting primarily of Ge, Sb, As and Te (chalcogenides) have recently received significant attention due to their extraordinary technological importance in rewritable optical data storage applications in the forms of compact disk (CD), digital versatile disk (DVD) and Blu-ray disk and in electronic memory applications. These chalcogenides have been aptly termed phase-change materials as they show rapid and repeatable switching between crystalline and glassy phases under suitable conditions that forms the basis of writing, reading and storage of data. However, the details of the structure-property relationships in phase-change chalcogenides are not well understood at the atomic level and they often remain controversial and conjectural, especially in the technologically relevant multi-component systems. This lack of knowledge regarding the connection between the microscopic and the macroscopic results in extensive trial and error tests in composition and processing related optimization in this fast-paced industry. We hope to address the fundamental issues associated with the atomic-scale understanding of the key properties of phase-change chalcogenides based on systematic structural and dynamical studies using state-of-the-art experimental and simulation techniques. Such studies will allow the development of physically more accurate models of structure-property relationships and will better guide future technological development of these materials with improved functionality. Scientifically, the proposed work impacts materials science, solid-state chemistry and solid-state physics. The materials studied have actual or potential applications in a wide range of technologies including optical memory devices, telecommunication, remote-sensing and photovoltaics. The interdisciplinary nature of our research transfers knowledge between fields and provides a unique intellectual environment. This project will continue to foster ongoing collaborations with scientists in industry, universities and Argonne National Laboratory (ANL) and to enrich the graduate education and training experience for participating students through scientific dialogue and interactions between the collaborating scientists and students. Students in this research program will learn to investigate problems in the realm of ?basic science? that underlies industrial applications. This program will coordinate with the underrepresented minority-serving and K-12 outreach programs at UC Davis to attract and recruit underrepresented graduate students and to increase the awareness of students in the science and technology of phase-change chalcogenides.TECHNICAL DETAILS: Chalcogenides that primarily belong to the Ge-Sb/As-Te system constitute an important class of materials known as the ?phase-change? materials that display thermally or electrically induced rapid and reversible transformation between crystalline and amorphous phases under suitable conditions. These chalcogenides have recently received remarkable attention due to their extraordinary technological importance in rewritable optical data storage and non-volatile electronic memory applications. From the point of view of direct atomic-scale understanding of the phase-change phenomena, a number of fundamental questions remain unresolved in these systems: What are the structural similarities and differences between the amorphous and crystalline phases and how do they affect the relevant physical properties such as density, optical absorption and electrical conductivity? What are the possible effects of pressure and temperature on the structure of the amorphous phase, i.e. do these external variables select a particular structure from a ?landscape? of possible structures? What are the nature, timescales and length scales of the atomic/molecular dynamics in the glassy and supercooled liquid state and how are they related to entropy generation, macroscopic relaxation and transport processes and crystallization kinetics? Some of these issues are understood only at the macroscopic level within the framework of phenomenological models. The primary focus of the work proposed here is to address these questions at the microscopic/atomic level using a uniquely powerful combination of neutron/X-ray diffraction, Raman spectroscopy, inelastic neutron scattering, 125Te NMR spectroscopy and Reverse Monte Carlo modeling. Specifically, phase-change chalcogenides in Ge-Sb-Te and Ge-As-Te systems will be investigated. Models linking the atomic-scale structure and dynamics with macroscopic physical and thermodynamic properties will be formulated and tested. Such studies will allow the development of physically more accurate models of structure-property relationships and although they are in the realm of basic science, they should have long-term significance in guiding future technological development of phase-change materials with improved functionality. This work includes significant training of graduate students in state-of-the-art spectroscopic, diffraction and simulation techniques. The equipment and expertise at UC Davis and ANL will provide students with a variety of modern research tools and a supportive structure for learning to use them.

非技术描述：我们生活在信息时代，在一个很小的空间中存储大量信息是至关重要的。由于主要由Ge、Sb、As和Te(硫族化合物)组成的玻璃材料在光盘(CD)、数字多功能光盘(DVD)和蓝光盘形式的可重写光学数据存储应用中以及在电子存储器应用中具有非凡的技术重要性，最近受到了极大的关注。这些硫系化合物被恰当地称为相变材料，因为它们在适当的条件下在晶相和玻璃相之间显示出快速和可重复的切换，形成了数据写入、读取和存储的基础。然而，相变硫化物的结构-性质关系的细节在原子水平上还没有得到很好的理解，它们往往仍然存在争议和猜测，特别是在技术上相关的多组分体系中。这种对微观和宏观之间联系的知识的缺乏导致了在这个快节奏的行业中在成分和加工相关优化方面进行广泛的试错测试。我们希望通过使用最先进的实验和模拟技术，在系统的结构和动力学研究的基础上，解决与原子尺度上理解相变硫化物的关键性质相关的基本问题。这样的研究将允许开发物理上更准确的结构-性质关系模型，并将更好地指导这些材料未来的技术开发，提高功能。从科学上讲，这项拟议的工作将影响材料科学、固态化学和固态物理。所研究的材料在包括光存储设备、电信、遥感和光伏在内的广泛技术中具有实际或潜在的应用。我们研究的跨学科性质在不同领域之间传递知识，并提供一个独特的知识环境。该项目将继续促进与工业界、大学和阿贡国家实验室(ANL)的科学家的持续合作，并通过合作的科学家和学生之间的科学对话和互动，丰富参与项目的学生的研究生教育和培训经验。这个研究项目的学生将学习研究基础科学领域的问题。这是工业应用的基础。这项计划将与加州大学戴维斯分校的少数族裔服务和K-12推广计划相协调，以吸引和招收代表不足的研究生，并提高学生对相变硫化物科学和技术的认识。技术细节：主要属于Ge-Sb/As-Te系统的硫化物是一类重要的材料，称为相变？在适当的条件下，在晶相和非晶相之间表现出热或电诱导的快速和可逆转变的材料。由于它们在可重写光学数据存储和非易失性电子存储器应用中的非凡技术重要性，这些硫族化合物最近受到了显著的关注。从原子尺度对相变现象的直接理解的角度来看，这些系统中的一些基本问题仍然没有得到解决：非晶相和晶相之间的结构相似和不同之处是什么，它们如何影响相关的物理性质，如密度、光吸收和电导率？压力和温度对非晶相的结构有什么可能的影响，即这些外部变量是否从景观中选择了特定的结构？可能的结构？玻璃态和过冷液态的原子/分子动力学的性质、时间尺度和长度尺度是什么，它们与熵产生、宏观弛豫和输运过程以及结晶动力学有什么关系？其中一些问题只能在现象学模型框架内的宏观层面上得到理解。这里提出的工作的主要焦点是利用中子/X射线衍射、拉曼光谱、非弹性中子散射、125Te核磁共振光谱和反向蒙特卡罗模拟的独特强大的组合，在微观/原子水平上解决这些问题。具体地说，将研究Ge-Sb-Te和Ge-As-Te系统中的相变硫化物。将制定和测试将原子尺度的结构和动力学与宏观物理和热力学性质联系起来的模型。这类研究将允许开发物理上更准确的结构-性质关系模型，尽管它们属于基础科学领域，但它们应该对指导未来具有改进功能的相变材料的技术开发具有长期意义。这项工作包括对研究生进行最先进的光谱、衍射和模拟技术方面的大量培训。加州大学戴维斯分校和ANL的设备和专业知识将为学生提供各种现代研究工具和学习使用它们的支持性结构。