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

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，对钛酸锶和铌酸钽这两种技术上重要的材料的结构、电学和弹性/声学特性进行全面研究，重点研究当大块（日常使用中常见的大尺寸）材料逐渐变薄到接近原子尺度的层时，它们的特性是如何变化的。当以原子薄层的形式在微观体积中生长时，这些材料表现出独特而新颖的特性。该项目增强了新一代新型纳米机电设备的知识库，这些设备可以集成在未来电子产品的微芯片上，包括射频和光信号处理电路，对民用和国防部门的许多技术都很有用。此次合作将两所主要本科院校的教师和学生聚集在一起，在材料物理学的前沿进行实验和理论研究。通过研究与教育的整合，所提出的努力对两所院校的本科物理学生和应用物理硕士研究生的教育体验产生了积极的影响。他是陶森大学的学生。学生需要参与计划、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结果并在科学期刊上发表。这种与研究相结合的教育经历是培养具有全球竞争力的科学、技术、工程和数学（STEM）劳动力的关键。技术描述。本项目通过结合超声脉冲回波探测声子，以及介电光谱和拉曼光谱，研究钙钛矿中自发和电场诱导的相变。实验研究辅以理论探究，利用第一性原理密度泛函理论计算和基于蒙特卡罗的声子输运模拟。研究开始于仔细扩展铁电性铌酸钽钾单晶模型到对电性钛酸锶单晶。模型，然后进一步开发的降维系统，包括钛酸锶薄膜和微桥装置。用于实验的薄膜样品是通过脉冲激光沉积生长的，该沉积允许仔细操纵广泛的参数，这些参数可用于控制薄膜的应变状态，化学计量和缺陷结构。利用x射线衍射监测薄膜的结构质量，同时利用扫描电镜和原子力显微镜对薄膜的形貌和缺陷结构进行了研究。阳离子的化学计量是用电子能量色散光谱测定的。通过选择引起双轴拉伸或压缩应力的衬底，探讨了与晶格失配应变相关的降维效应。薄膜中的声学测量是使用特殊设计的表面声波装置进行的。为了排除衬底的影响，采用了独立薄膜微桥。这一研究结果为探索相变现象开辟了新的途径。系统地研究薄膜中的铁电性对于在机电、电光和声光器件中的技术应用具有重要意义。

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.