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

非技术性描述：我们生活在信息时代，在小空间中存储大量信息至关重要。主要由Ge、Sb、As和Te（硫属化物）组成的玻璃材料最近受到了极大的关注，这是由于它们在致密盘（CD）、数字多功能盘（DVD）和蓝光盘形式的光存储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。 这些硫属化物被恰当地称为相变材料，因为它们在形成数据的写入、阅读和存储的基础的适当条件下显示出在结晶相和玻璃相之间的快速且可重复的切换。 然而，相变硫族化合物的结构-性质关系的细节在原子水平上并没有很好地理解，并且它们通常仍然是有争议的和不确定的，特别是在技术相关的多组分系统中。 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组成和加工相关优化方面的广泛试错测试。 我们希望解决的基本问题与原子尺度的理解相变硫属化物的关键属性的基础上系统的结构和动力学研究，使用国家的最先进的实验和模拟技术。 这些研究将允许开发物理上更准确的结构-性能关系模型，并将更好地指导这些具有改进功能的材料的未来技术开发。 科学上，拟议的工作影响材料科学，固态化学和固态物理。 所研究的材料在包括光存储器件、电信、遥感和光电子学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各个领域之间转移知识，并提供独特的知识环境。 该项目将继续促进与工业界、大学和阿贡国家实验室（ANL）科学家的持续合作，并通过合作科学家和学生之间的科学对话和互动，丰富参与学生的研究生教育和培训经验。在这个研究项目的学生将学习调查的领域的问题？基础科学？工业应用的基础。 该计划将与加州大学戴维斯分校代表性不足的少数民族服务和K-12外展计划协调，以吸引和招募代表性不足的研究生，并提高学生对相变硫属化物科学和技术的认识。相变在合适的条件下，在结晶相和非晶相之间显示热或电诱导的快速和可逆转变的材料。 这些硫族化合物由于其在光存储和非易失性电子存储应用中的特殊技术重要性，最近受到了极大的关注。 从直接的原子尺度的相变现象的理解的角度来看，一些基本问题仍然没有解决，在这些系统中：什么是非晶相和结晶相之间的结构相似性和差异，以及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结构的可能影响是什么，即这些外部变量是否从a中选择了特定的结构？风景？可能的结构？玻璃态和过冷液态中原子/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何关系？ 其中一些问题只能在现象学模型的框架内在宏观层面上理解。 这里提出的工作的主要重点是解决这些问题，在微观/原子水平上使用一个独特的强大的组合中子/X-射线衍射，拉曼光谱，非弹性中子散射，125碲NMR光谱和反向蒙特卡罗建模。 具体而言，在Ge-Sb-Te和Ge-As-Te系统中的相变硫属化物将被研究。 将制定和测试连接原子尺度结构和动力学与宏观物理和热力学性质的模型。这些研究将允许开发物理上更精确的结构-性能关系模型，虽然它们属于基础科学领域，但它们在指导具有改进功能的相变材料的未来技术发展方面具有长期意义。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重要培训。 在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化的研究工具和学习使用它们的支持结构。

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.