Materials World Network: Science of Polar Homo- and Heterointerfaces

北卡罗莱纳州立大学、柏林工业大学（TUB）和德国柏林莱布尼茨研究所（Leibniz-Institut f<e:1> r kristallzchtung， IKZ）之间的一项重点国际研究合作，探索了外延界面的基础科学，该界面定义了氮化氮化和氮化氧化物系统中电极化的不连续。目的是了解调节界面电子特性的结构、化学和电子特征。这项工作是基于一个假设，即垂直和横向的异极界面可以制备出接近“半导体级”质量的界面，他们的研究将为界面物理和光学/电子功能的基础进步带来令人兴奋的机会。国际团队的每个成员都带来了独特的前沿技术能力，共同使这项研究成为可能。锡塔尔集团（NC State）带来了一种金属有机化学气相沉积技术，可以在横向和纵向上控制氮化半导体薄膜的极性；Maria小组（NC State）开发了一种表面活性剂辅助分子束外延技术，首次可以在GaN表面上以二维生长模式制备立方氧化物，并显著降低缺陷浓度；Hoffmann组（TUB）带来了极性材料和异质结构的光学表征；Albrecht小组（IKZ）带来了亚-Å空间分辨率和亚ev能量分辨率的像差校正透射电子显微镜表征。该研究改进了合成技术，使混合薄膜结构能够无缝地融合氧化物和氮化物，并且具有迄今为止无法实现的材料质量。通过将合成和表征相结合，研究人员能够识别和理解能够实现、干扰或增强异极界面耦合的结构和化学特征。实现对异极性界面性质关系的理解将推动混合系统的研究，从而导致新的物理，新的功能，一组扩展的低维光电器件，以及以新的方式利用铁电体的非线性介电响应的智能结构的途径。通过这种合作，来自NCSU， TUB和IKZ的学生和教师可以在技术领域获得指导专家和世界一流的实验室设施，这是国内机构所缺乏的。美国和德国学生在项目第三年参加为期6个月的研究生休假，以确保丰富的国际经验。在他们的头两年，美国学生被鼓励用两个学期的德语来获得基本的沟通技巧。德国参与者的工作得到德国研究基金会（DFG）的支持。

A focused international research collaboration linking North Carolina State University, the Technical University Berlin (TUB) and the Leibniz-Institut für Kristallzüchtung (IKZ) in Berlin, Germany, explores the fundamental science of epitaxial interfaces that define a discontinuity in electrical polarization in nitride-nitride and nitride-oxide systems. The aim is to understand the structural, chemical, and electronic features that regulate the interfacial electronic properties. The effort is based on a hypothesis that vertical and lateral heteropolar interfaces that approach 'semiconductor-grade' quality can be prepared, and that their study will lead to exciting opportunities for fundamental advances in interface physics and optic/electronic functionality. Each member of the international team brings a unique and leading edge technical capability that collectively enables this research. The Sitar group (NC State) brings a metalorganic chemical vapor deposition technology that can control polarity in thin films of nitride semiconductors both laterally and vertically; the Maria group (NC State) developed a surfactant-assisted molecular beam epitaxy technique that can for the first time prepare cubic oxides on GaN surfaces with a 2-D growth mode and dramatically reduced defect concentrations; the Hoffmann group (TUB) brings in optical characterization of polar materials and heterostructures; and the Albrecht group (IKZ) brings aberration-corrected transmission electron microscopy characterization with sub-Å spatial resolution and sub-eV energy resolution. The research refines synthesis techniques that enable hybrid thin film structures that seamlessly merge oxides and nitrides with heretofore unachievable material quality. By combining synthesis and characterization the investigators are able to identify and understand the structural and chemical features that enable, interfere, or enhance heteropolar interface coupling.Achieving an understanding of heteropolar interface-property relationships will propel research in hybrid systems that lead to new physics, new functionality, an expanded set of low dimension optoelectronic devices, and a pathway to smart structures that utilize in a new way the non-linear dielectric response of ferroelectrics. Through this collaboration, students and faculty from NCSU, TUB, and IKZ have access to mentoring expertise and world-class laboratory facilities in technical areas that are absent from the home institutions. U.S. and German students participate in a 6-month graduate sabbatical in program year three to ensure substantive international experience. During their first two years, U.S. students are encouraged take two semesters of German to acquire basic communication skills. The work of the German participants is supported by the German Research Foundation (DFG).