RUI:Unraveling the Influence of Free Carriers, Phonons and Band Electrons from the Dielectric Function of van der Waals Solids

非技术摘要本项目的重点是研究一类新的材料，称为2D范德沃尔斯固体，它具有有趣的性质，可以用来制造新型电子和光学器件。一种被称为光谱椭偏测量的技术，具有独特的宽光能范围，被用来研究各种2D van der wall固体的特性。从这项研究中获得的知识可以促进各种设备的发展，如发光二极管、晶体管、光伏设备和激光。这项研究工作由文科本科生进行，他们接受材料表征方面的培训，为研究生学习和科学技术职业做准备。为了提高教育目标，一些实验活动被纳入当前课程的课程中。此外，为了培养更广泛的对科学的兴趣，还为高中生开展了几项外展活动。技术摘要通过结合椭圆偏振光谱和反射率测量来覆盖宽光谱范围(即1 meV到6 eV)，该项目探索了2D van der wallers材料，特别是过渡金属二卤化物(TMDCs)的介电功能和复电导率。有了高光谱范围，就可以研究TMDDC的自由载流子、声子和带电子(和激子)的贡献。具体地，讨论了以下问题：(I)能带跃迁的激子效应；(Ii)跃迁随层数的演化；(Iii)控制载流子弛豫时间的机制；(Iv)掺杂对输运性质的影响；(V)电子-声子耦合对TMDCs的意义；以及(Vi)对TMDCs中的圆二向色性进行量化并解释它们的差异。这项研究工作由本科生在文科背景下进行。在目前的课程中，如凝聚态物理、光学和高等实验室，都会加入一些实验活动。本科生接受材料表征、光学和低温方面的培训，为他们在STEM领域的研究生学习或职业生涯做好准备。此外，还开展了一些针对高中生的外展活动，以培养更广泛的对科学的兴趣。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical AbstractThe focus of this project is to investigate a new class of materials called 2D van der Walls solids which have interesting properties that can be exploited for making novel electronic and optical devices. A technique known as spectroscopic ellipsometry with a uniquely wide light energy range is used to study the characteristics of a variety of the 2D van der Walls solids. Knowledge gained from this study could advance the development of various devices, such as light emitting diodes, transistors, photovoltaic devices, and lasers. The research work is performed by undergraduate students in a liberal-arts setting, who receive training in materials characterization, preparing them for graduate studies and careers in science and technology. To enhance educational goals, several experimental activities are incorporated into current courses in the curriculum. Additionally, to foster a wider interest in the sciences, several outreach activities for high school students are conducted. Technical AbstractBy combining spectroscopic ellipsometry and reflectivity measurements to cover a wide-spectral range (i.e. 1 meV to 6 eV), this project explores the dielectric function and the complex conductivity of 2D van der Walls materials, particularly transition metal dichalcogenides (TMDCs). Having access to a high spectral range enables the study of the contributions of free carriers, phonons and band electrons (and excitons) of TMDCs. Specifically, the following issues are addressed: (i) the excitonic effects of band transitions; (ii) evolution of transitions with the number of layers; (iii) the mechanism that governs the carrier relaxation time; (iv) the influence of dopants on the transport properties; (v) the significance of electron-phonon coupling on TMDCs; and (vi) quantifying the circular dichroism in TMDCs and explaining their differences. The research work is performed by undergraduate students in a liberal-arts setting. Several experimental activities are injected into current courses such as Condensed Matter Physics, Optics and Advanced Lab. The undergraduate students receive training in materials characterization, optics, and cryogenics, preparing them for graduate studies or careers in STEM-based fields. Additionally, several outreach activities for high school students are conducted in order to foster a wider interest in the sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.