NIRT: Strain-Enhanced Nanoscale Ferroelectrics

非技术描述：多年来，分子束外延（MBE）已被用于构建层状半导体纳米结构的原子，以研究和提高我们对半导体物理的理解，并创造新的器件。这些设备（包括激光二极管、高性能晶体管和磁场传感器）促进了医疗保健、国家安全、通信、娱乐和交通——显著提高了所有美国人的生活质量。最近的研究进展表明，同样的原子-原子合成技术可以用于构建氧化物的纳米结构，包括铁电体，具有相当的纳米级分层控制。由于铁电材料表现出各种各样的电学、光学和机电特性，它们被广泛应用于医疗保健（例如，医用超声）、国防（例如，夜视和声纳系统）和通信（例如，用于手机和计算机的微型电容器）。在原子层水平上定制铁电材料的分层并使其应变的能力为显着提高其性能提供了令人兴奋的可能性。通过这项研究获得的更好的理解将应用于改进的光学和声学设备的开发。未来的科学家将在一个高度跨学科的研究环境中，在一个具有国家重要性的重要技术领域进行培训和教育。来自宾夕法尼亚州立大学、威斯康星大学、密歇根大学和罗格斯大学的教授们将于夏季在参与该研究团队的每个校园举办实践研讨会，让K-12学生接触到科学的刺激。技术细节：技术目标是了解应变纳米级铁电体和多铁电体的电、磁和光学响应的基础科学。将采取理论和实验相结合的努力。具体来说，基于晶格万尼尔函数和朗道-金兹堡型现象学方法的“第一性原理有效哈密顿”方法将用于识别铁电和多铁材料和异质结构，这些材料和异质结构的性能随着应变的增加而大幅增强。薄膜将通过MBE和激光MBE生长，通过聚焦离子束进行图形化，并使用x射线衍射、分析和透射电子显微镜、拉曼光谱、二次谐波产生和铁电测量相结合的方法进行表征，所有这些都是温度的函数。在许多半导体器件结构中利用应变来改善半导体薄层的输运特性。在这个项目中，它将用于提高铁电体的性能。铁电体对应变非常敏感，薄铁电材料相对于块状材料的一个明显优势是，它们的应变可能远远超出块状材料的裂纹范围。对于纳米级铁电体，可以获得巨大的应变。这一特性与在原子水平上精确集成和设计氧化物的能力相结合，为研究、开发和利用氧化物的性质提供了一种手段，这些氧化物可用于光学调制器、二维光子带隙结构和与声子激光器的长期实现相关的声子限制压电结构。

NON-TECHNICAL DESCRIPTION: For many years molecular beam epitaxy (MBE) has been used to build layered semiconductor nanostructures atom-by-atom to investigate and improve our understanding of semiconductor physics and create new devices. These devices (which include laser diodes, high-performance transistors, and magnetic field sensors) have advanced healthcare, national security, communications, entertainment, and transportation-resulting in significant improvements in the quality of life for all Americans. Recent progress in research has demonstrated that this same atom-by-atom synthesis technique can be used to build nanostructures of oxides, including ferroelectrics, with comparable nanometer-scale layering control. Since ferroelectric materials exhibit a wide variety of electrical, optical, and electromechanical properties, they are extensively used in healthcare (e.g., medical ultrasound), national defense (e.g., night vision and sonar systems), and communications (e.g., miniature capacitors for cell phones and computers). The ability to customize the layering of ferroelectric materials at the atomic-layer level and strain them opens exciting possibilities to dramatically enhance their properties. The improved understanding gained via this research will be applied to the development of improved optical and acoustic devices. Future scientists in a highly interdisciplinary research environment in a technologically significant area of national importance will be trained and educated within this program. Professors from Pennsylvania State University, University of Wisconsin, University of Michigan and Rutgers University will run hands-on workshops during the summers at each of the campuses involved in this research team to expose K-12 students to the thrill of science.TECHNICAL DETAILS: The technical objective is to understand the fundamental science underlying the electric, magnetic, and optical responses of strained nanoscale ferroelectrics and multiferroics. An integrated theoretical and experimental effort will be taken. Specifically, "first-principles effective Hamiltonian" approaches based on lattice Wannier functions and Landau-Ginzburg type phenomenological methods will be used to identify ferroelectric and multiferroic materials and heterostructures in which large enhancements in properties are expected with strain. Films will be grown by MBE and laser-MBE, patterned by focused ion beams, and characterized using a combination of x ray diffraction, analytical and transmission electron microscopy, Raman spectroscopy, second harmonic generation, and ferroelectric measurements, all as a function of temperature. Strain is utilized in many semiconductor device structures to improve the transport properties of thin semiconductor layers. Within this project, it will be used to enhance the properties of ferroelectrics. Ferroelectrics are very sensitive to strain and a distinct advantage of thin ferroelectric materials over their bulk counterparts is that they may be strained well beyond where their bulk counterparts would crack. For nanoscale ferroelectrics, huge strains become accessible. This feature combined with the ability to precisely integrate and engineer oxides at the atomic level provides a means to investigate, develop, and exploit the properties of oxides for optical modulators, two-dimensional photonic bandgap structures, and phonon-confining piezoelectric structures relevant to the long-term realization of a phonon laser.