NIRT: Strain-Enhanced Nanoscale Ferroelectrics

非技术描述：多年来，分子束外延（MBE）已被用于逐原子地构建分层半导体纳米结构，以研究和提高我们对半导体物理的理解并创建新器件。 这些设备（包括激光二极管、高性能晶体管和磁场传感器）具有先进的医疗保健、国家安全、通信、娱乐和运输功能，从而显著改善了所有美国人的生活质量。 最近的研究进展表明，这种相同的原子-原子合成技术可用于构建氧化物的纳米结构，包括铁电体，具有可比的纳米级分层控制。 由于铁电材料表现出各种各样的电学、光学和机电性质，因此它们广泛用于医疗保健（例如，医学超声），国防（例如，夜视和声纳系统），以及通信（例如，用于蜂窝电话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开辟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。 未来的科学家在一个高度跨学科的研究环境中，在一个技术上具有重要意义的国家领域的重要性将在该计划内进行培训和教育。 来自宾夕法尼亚州立大学、威斯康星州大学、密歇根大学和罗格斯大学的教授将在夏季在参与该研究团队的每个校区举办实践研讨会，让K-12学生感受科学的刺激。技术目标是了解电，磁，以及应变纳米铁电体和多铁性材料的光学响应。将采取综合的理论和实验努力。 具体而言，“第一原理有效哈密顿”的基础上晶格Wannier函数和朗道-金兹伯格型唯象方法的方法将被用来识别铁电和多铁性材料和异质结构，其中大的性能增强，预计与应变。 薄膜将通过MBE和激光MBE生长，通过聚焦离子束形成图案，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的组合进行表征，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薄半导体层的输运性质。 在该项目中，它将用于增强铁电体的性能。 铁电体对应变非常敏感，并且薄铁电体材料相对于它们的本体对应物的明显优势在于它们可以被应变得远远超过它们的本体对应物将破裂的地方。 对于纳米铁电体，巨大的应变变得容易获得。 这一特点结合在原子水平上精确集成和设计氧化物的能力，提供了一种手段来研究、开发和利用氧化物的性质，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.