Next Generation Phase Change Memory Materials: Nanostructure, Electronic Properties and Thermal Transformations

技术方面：本项目对相变记忆材料进行基础性研究，包括掺杂二元和探索硫系薄膜三元组成。目的是详细了解这些材料的相变机制和以下性质：非晶相的纳米级结构；相变时的热释放；掺杂部位、可能的电激活和掺杂剂的结构效应；态的价带密度的组成依赖性以及由合金成分、合成条件（包括掺杂）和沉积后的热或光学处理引起的修饰。扫描透射电子显微镜，结合统计数据处理，将用于表征热历史和成分对纳米级结构秩序的影响。主要目标包括确定由激光激发或熔体淬火引起的变化，以及检查与写/擦除周期相关的结构变化。纳米量热法将用于研究每个相的热容。态的价带密度，包括带尾和隙中的态，与晶体结构的关系，以及开关机制，将通过电导率及其温度依赖性的测量来探测；带隙吸收边缘的光谱学；以及x射线和紫外线光发射。泵浦探测激光诱导的相变和反射率的原位测量将作为时间的函数进行。在转化过程中研究的现象包括部分结晶的薄膜样品中的晶体的原子力显微镜和使用电子背散射衍射的晶体的结晶性和方向性。非技术：用于高级数据存储应用的硫系材料的未来发展需要掌握成分，结构，热转变和电子性能之间的关系。本项目以基础材料研究为重点，将对相变存储材料的纳米级结构、热性能、电子性能和相变动力学等方面产生深刻的科学认识，促进基于相变材料的光存储器和非易失性存储器的快速发展。该项目将资助两名研究生。一至两名本科生将完成本项目的部分内容，作为其毕业论文。为了扩大代表性不足群体的参与，将通过伊利诺伊大学厄巴纳香槟分校的SURGE（工程领域代表性不足群体的支持）和WISE（科学和工程领域的女性）项目来确定合格的学生。

Technical: This project is to conduct fundamental study of phase change memory materials, including doped binary and exploratory ternary compositions of chalcogenide thin films. The objective is to achieve a detailed understanding of the phase-changing mechanism and the following properties of these materials: the nanoscale structure of the amorphous phase; thermal heat release during phase transitions; incorporation site, possible electrical activation, and structural effects of dopants; composition dependence of the valence band density of states; and the modifications resulting from alloy composition, conditions of synthesis including doping, and post-deposition thermal or optical processing. Scanning transmission electron microscopy, coupled with statistical data processing, will be used to characterize the effect of thermal history and composition on nanoscale structural order. Key objectives include determination of change induced by laser priming or melt-quenching and examination of structural changes associated with write/erase cycles. Nanocalorimetry will be used to study the heat capacity of each phase. Valence band density of states, including band tails and states in the gap, relationships to crystal structure, and switching mechanism, will be probed by measurements of the electrical conductivity and its temperature dependence; optical spectroscopy of the band gap absorption edge; and X-ray and UV photoemission. Pump-probe laser-induced phase transformations and in-situ measurements of the reflectivity will be carried out as a function of time. Phenomena to be studied during the transformations include atomic force microscopy of crystallites in a partially crystallized thin film sample and crystallinity and directionality of the crystallites using electron backscattered diffraction.Non-technical: Future development of chalcogenide materials for advanced data storage applications requires mastery of the relationship between composition, structure, thermal transformation, and electronic properties. This project, focusing on the fundamental materials research, will generate a deep scientific understanding of the nanoscale structure, thermal properties, electronic properties, and kinetics of the phase transformation of the phase change memory materials, enabling rapid development of optical memory and non-volatile memory based on phase change materials. The project will support two graduate students. One or two undergraduates will carry out portions of this project as their senior theses. To broaden the participation of underrepresented groups, qualified students will be identified through the SURGE (Support of Under-represented Groups in Engineering) and WISE (Women in Science and Engineering) programs at the University of Illinois - Urbana Champaign.