RUI: Collaborative Research: Acoustic Study of Lattice Dynamics and Elastic Properties in Perovskite Dielectrics and Ferroelectrics

RUI：合作研究：钙钛矿电介质和铁电体中晶格动力学和弹性特性的声学研究

• 批准号: 1709282
• 负责人: Oleksiy Svitelskiy
• 金额: $ 20.35万
• 依托单位: Gordon College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-01 至 2021-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1709282&HistoricalAwards=false
• 关键词: RUI; Collaborative; Research; Acoustic; Study

Non-technical Summary: Research teams at Gordon College and Towson University are collaborating in this project to carry out a comprehensive study of structural, electrical and elastic/acoustic properties of two technologically important materials, Strontium Titanate and Potassium Tantalum Niobate, with a focus on how their properties change when bulk (large size scales common in everyday uses) material is progressively thinned to layers approaching atomic scale sizes. These materials demonstrate unique and novel properties when grown in microscopic volumes in the form of atomically thin layers. The project enhances the knowledge base for a new generation of novel nano-electromechanical devices that can be integrated on microchips in future electronics, including radiofrequency and optical signal processing circuits useful for numerous technologies serving both civil and defense sectors. This collaboration brings together faculty and students in two predominantly undergraduate institutions to engage in experimental and theoretical research at the frontiers of materials physics. Through the integration of research and education, the proposed effort positively impacts the educational experience of undergraduate physics students at both institutions and graduate students in the Applied Physics Master?s program at Towson University. Students are expected to participate in the planning, developing equipment and theoretical models, performing measurements and computer simulations, presenting results of their work at scientific conferences and publishing in scientific journals. Such educational experiences integrated with research are key to developing a globally competent science, technology, engineering and mathematics (STEM) work force.Technical description. This project investigates spontaneous and electric-field induced phase transitions in perovskites by using a combination of ultrasound pulse-echo probing of acoustic phonons, along with dielectric and Raman spectroscopies. The experimental studies are complemented by theoretical inquiry using first principle density functional theory calculations and Monte Carlo-based simulations of phonon transport. Investigations begin by carefully extending models for single crystals of ferroelectric potassium tantalum niobate to para-electric strontium titanate single crystals. Models are then further developed for reduced-dimensional systems, including strontium titanate films and microbridge devices. The thin film samples for the experiments are grown by pulsed laser deposition which allows for the careful manipulation of a wide range of parameters that can be used to control the films strain state, stoichiometry and defect structure. The structural quality of the films is monitored using X-ray diffraction, while the films morphology and defect structure studies are performed by scanning electron microscopy and atomic force microscopy. The cation stoichiometry is determined using electron energy dispersive spectroscopy. The reduced dimensionality effects are explored in connection with lattice mismatch strain, which is engineered by choosing substrates that cause bi-axial tensile or compressive stresses. Acoustic measurements in the films are performed using specially designed surface acoustic wave devices. In order to exclude the influence of substrate, microbridges of free standing thin films are employed. The results of this research open up new approaches to exploring phase transition phenomena. Systematic investigation of ferroelectricity in thin films is of significance for technological applications in electro-mechanical, electro-optical and acousto-optical devices.

非技术总结：戈登学院和陶森大学的研究团队正在合作开展该项目，对两种技术上重要的材料，钛酸锶和铌酸钾钽的结构，电气和弹性/声学特性进行全面研究，重点是当散装（日常使用中常见的大尺寸尺度）材料逐渐变薄到接近原子尺度尺寸的层时，它们的特性如何变化。这些材料在以原子级薄层的形式在微观体积中生长时表现出独特和新颖的特性。该项目增强了新一代新型纳米机电设备的知识基础，这些设备可以集成在未来电子产品的微芯片上，包括可用于民用和国防部门的众多技术的射频和光学信号处理电路。这种合作汇集了教师和学生在两个主要的本科院校在材料物理学的前沿从事实验和理论研究。通过研究和教育的整合，建议的努力积极影响本科物理学生在两个机构和研究生的教育经验，在应用物理硕士？在陶森大学的项目。预计学生将参与规划，开发设备和理论模型，进行测量和计算机模拟，在科学会议上展示他们的工作成果，并在科学期刊上发表。这种与研究相结合的教育经验是培养一支具有全球竞争力的科学、技术、工程和数学（STEM）工作队伍的关键。本计画利用超音波脉冲回波探测声子，沿着介电及拉曼光谱，研究钙钛矿中的自发及电场诱导相变。实验研究的补充，使用第一原理密度泛函理论计算和基于Monte Carlo的模拟声子输运的理论探讨。研究开始时，仔细地将铁电钽酸钾单晶的模型扩展到顺电钛酸锶单晶。模型，然后进一步开发的降维系统，包括钛酸锶薄膜和微桥器件。用于实验的薄膜样品通过脉冲激光沉积生长，其允许仔细操纵可用于控制膜的应变状态、化学计量和缺陷结构的宽范围的参数。的薄膜的结构质量进行监测，使用X射线衍射，而薄膜的形貌和缺陷结构的研究进行扫描电子显微镜和原子力显微镜。使用电子能量色散光谱法测定阳离子化学计量。降低维数的影响进行了探讨与晶格失配应变，这是工程通过选择基板，造成双轴拉伸或压缩应力。使用专门设计的表面声波装置进行膜中的声学测量。为了排除基底的影响，采用了自支撑薄膜的微桥。这一研究结果为探索相变现象开辟了新的途径。薄膜铁电性的系统研究对于机电、电光和声光器件的技术应用具有重要意义。