Optical Property, Charge Carrier Relaxation and Charge Transfer Properties in Chemically-Synthesized Layered TiS2 Nanodiscs with Controlled Lateral and Transverse Dimensions

非技术描述：本研究项目研究了一类新的二维纳米材料的性质，即层状过渡金属二硫族化合物，其中在体相中未观察到的独特的电子、光学和输运性质可以通过纳米尺度的控制来获得。该研究团队由材料的光谱表征和计算机模拟专家组成，他们合作了解物理和化学结构的变化如何调节材料性能。本研究结果对这些纳米材料潜在的光电应用具有重要价值。该项目的首席研究员还与一个工业合作伙伴合作，开发了一个仪器仪表培训计划，重点是信号测量和处理，面向多学科的本科生和研究生。这一努力缩小了当前课程中这些主题与许多科学和工程学科所需的仪器技术之间的差距。技术描述：本项目采用溶液中化学合成的二硫化钛纳米片作为模型体系。在化学合成中，纳米片的厚度可以控制，从几个原子层到十多个原子层不等，纳米片的直径可以从几十纳米到几百纳米不等，在两个垂直的方向上提供了显著的尺寸控制范围。利用这些纳米材料，重点研究了以下具体任务：(1)了解二硫化钛纳米片的光学跃迁能和层间声子如何受到纳米片厚度和直径的变化以及载流子的光激发的影响；(2)了解载流子弛豫和电荷转移的速率和途径与尺寸变化和界面结构的关系。时间分辨泵浦-探针光谱和电子显微镜是阐明结构-性能关系的主要实验工具。利用密度泛函理论计算了不同维度纳米片的电子和振动结构，提供了这种层状材料系统结构依赖的材料特性的原子图像。

Non-technical Description: This research project investigates the properties of a new class of 2-dimensional nanomaterials, i.e., layered transition metal dichalcogenides, where unique electronic, optical and transport properties not observed in the bulk phase can be harvested through the control of the dimensions in nanoscale. The research team, consisting of experts in the spectroscopic characterization and computer simulation of the materials, collaborates to gain an understanding on how the variations of the physical and chemical structures can tune the material properties. The outcome of this research will be valuable to the potential optoelectronic applications of these nanomaterials. The principal investigator of this project also develops, in collaboration with an industrial partner, a training program on instrumentation, focusing on signal measurement and processing, for both undergraduate and graduate students in multiple disciplines. This effort narrows the gap between current curriculum on such topics and the instrumentation skills required in many science and engineering disciplines.Technical Description: The project utilizes chemically synthesized titanium disulfide nanodiscs in solution as a model system. The nanodisc thickness can be controlled in chemical synthesis, varying from a few to more than ten atomic layers, and the nanodisc diameter can be varied from tens to hundreds of nanometers, providing a significant range of dimensional control in two perpendicular directions. Using these nanomaterials, the research focuses on the following specific tasks: (i) understanding how the optical transition energy and interlayer phonon of titanium disulfide nanodiscs are influenced by the variations of both the nanodisc thickness and diameter and by the photoexcitation of the charge carriers; and (ii) understanding the rates and pathways of the charge carrier relaxation and charge transfer correlated with the dimensional variation and the interfacial structure. Time-resolved pump-probe spectroscopy and electron microscopy are the main experimental tools to elucidate the structure-property relationship. The calculation of the electronic and vibrational structures of the nanodiscs of different dimensions, employing density functional theory, provides an atomistic picture of the structurally dependent material properties of this layered material system.