Epitaxial Growth and Doping of Topological Insulator Heterostructures

技术：本项目旨在促进对Bi2X3 （X=Se, Te）拓扑绝缘体及其调制掺杂超晶格的外延生长和掺杂的理解。关键问题是在生长过程中控制杂质掺入与嵌入，目标是选择性地指定所需性质的位置。采用原位扫描隧道显微镜/光谱学研究了表面形貌、原子结构和载流子的台阶散射和磁性杂质，并确定了磁性杂质掺杂、间隙打开和狄拉克锥翘曲对拓扑绝缘体的定义性质的影响。扫描隧道显微镜还用于研究拓扑绝缘子薄膜和异质结构的原位输运性质。通过x射线吸收光谱和磁性圆二色性确定掺杂剂的特定元素的电子和磁性能，通过x射线衍射、拉曼光谱和透射电子显微镜进行结构表征，通过温度和场相关磁化测量和霍尔效应进行磁性和输运性质。通过密度泛函理论计算杂质吸附和掺杂的能量学，电子能带结构的变化，x射线吸收光谱和磁圆二色光谱以及扫描隧道显微镜图像，有助于确定最有希望合成的异质结构及其实验特征。非技术：该项目涉及材料科学主题领域的基础研究问题，具有高技术相关性。通过对成分和掺杂的精确控制，分子束外延促进了与现有半导体器件制造基础设施一致的拓扑绝缘体异质结构的合成，这可能为下一代电子学带来新的范例。研究生在材料生长、表征和建模的跨学科环境中接受培训。pi积极参与正在进行的教师研究经验推广计划，继续将材料科学的前沿研究带给高中生，以影响他们对科学和技术的看法，并激励他们寻求科学和工程方面的大学学位和职业。

Technical: This project aims to advance the understanding of the epitaxial growth and doping of the Bi2X3 (X=Se, Te) topological insulators and their modulation-doped superlattices. The critical issue is to control impurity incorporation vs. intercalation during growth, with the goal to selectively designate the sites for desired properties. In-situ scanning tunneling microscopy/spectroscopy is carried out to study the surface morphology, atomic structure, and carrier scattering by steps and magnetic impurities, and to determine how the defining properties of topological insulators are affected by magnetic impurity doping, gap opening, and warping of the Dirac cone. Scanning tunneling microscopy is also used to investigate the transport properties of topological insulator films and heterostructures in situ. Element-specific electronic and magnetic properties of dopants are determined by x-ray absorption spectroscopy and magnetic circular dichroism, while structural characterization is carried out using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and magnetic and transport properties by temperature- and field-dependent magnetization measurements and Hall effects. The experimental efforts are complemented by density functional theory calculations of the energetics of impurity adsorption and doping, the changes in the electronic band structure, the x-ray absorption spectroscopy and magnetic circular dichroism spectra, and scanning tunneling microscopy images, which helps to identify the most promising heterostructures to be synthesized and their experimental signatures.Nontechnical: The project addresses basic research issues in a topical area of materials science with high technological relevance. With precise control of composition and doping, molecular beam epitaxy facilitates the synthesis of topological insulator heterostructures congruent with existing semiconductor device fabrication infrastructure, which can potentially bring a new paradigm for the next generation electronics. Graduate students are trained in an interdisciplinary environment for materials growth, characterization, and modeling. The PIs' active involvement in an on-going Research Experience for Teachers outreach program continues to bring cutting-edge research on materials sciences to high school students to impact their perception of science and technology, and to inspire them to seek college degrees and careers in science and engineering.