Exploration of Ultrafast Carrier Dynamics In Polymer Semiconductors Using Terahertz Spectroscopy

共轭聚合物中的载流子动力学在亚皮秒的时间尺度上通常是未知的。太赫兹(THz)光谱学的最新发展为研究这一时间域中的载流子输运打开了一扇新的窗口。到目前为止，这项技术主要应用于“传统”半导体。在本项目中，我们将利用这一强大的实验探头来研究各种共轭聚合物中的载流子动力学。这项探索性研究的目标集中在选定的几个目前悬而未决的问题上。我们会进行三项研究。首先，我们将研究当载流子处于扩展态时，在发生显著的载流子捕获和复合之前，光激发后的电荷传输。其次，我们将通过研究PPV及其各种衍生物中的输运来研究链间耦合的强度如何改变载流子的输运。第三，我们将研究高偏压下聚乙炔中的孤子动力学。在这种情况下，理论上预测孤子速度将达到平台期，这一预测尚未得到证实。传输测量是基于电磁辐射的基本过程，通常是在太赫兹范围内，由感应的瞬变光电流发射。监测太赫兹信号的时间演化提供了关于0.1到10ps时间范围内的瞬时光电导性的信息。这项研究采用了最先进的实验技术。研究生和博士后研究员将参与这项研究，从而获得当代凝聚态物理和材料科学前沿领域的最新知识和技能。%随着半导体聚合物被发现为发光二极管(LED)和激光器的有前途的材料，全球范围内出现了一项积极的研究努力，以追求实现基于共轭聚合物的“塑料”激光器、LED和快速光电探测器设备的目标。这个项目是关于准一维聚合物半导体在光激发后迅速发光过程的几个悬而未决的问题的研究。这些过程发生在超快时间尺度上，实验超快光谱学的新发展使它们的研究成为可能。该项目致力于使用这些新技术来定量研究各种聚合物材料光激发后超快发光过程的本质。这项研究将在学生和博士后研究助理的帮助下进行，他们将因此获得当代凝聚态物理和材料科学前沿领域的技能和知识。***

0070285MosesThe carrier dynamics in conjugated polymers in the sub-picosecond time scale are generally unknown. Recent developments in terahertz (THz) spectroscopy have opened a new window to the carrier transport in this time regime. This technique has so far been applied mostly to "conventional" semiconductors. In this project advantage will be taken of this powerful experimental probe in using it to study the carrier dynamics in various conjugated polymers. The goals of this exploratory research are focused on a selected few currently open questions. Three studies will be undertaken. Firstly, the charge transport promptly following photoexcitations will be studied while the carriers occupy extended states, and before significant carrier trapping and recombination can occur. Secondly, a study will be performed on how the strength of the inter-chain coupling modifies the carrier transport by exploring the transport in PPV and its various derivatives, and thirdly, the soliton dynamics in polyacetylene at high bias fields will be studied. In this case the soliton velocity is predicted theoretically to reach a plateau, a prediction that has yet not been verified. The transport measurement is based on the fundamental process of electromagnetic radiation, typically in the THz range, emitted by the induced transient photocurrent. Monitoring the time-evolution of the THz signal provides information regarding the transient photoconductivity in the 0.1 to 10 ps time scale. This research employs state-of-the-art experimental techniques. Graduate students and post doctoral research associates will participate in this research and thereby acquire up-to-date- knowledge and skills in a forefront area of contemporary condensed matter physics and materials science.%%% Following the discovery of semiconductor polymers as promising materials for light emitting diodes (LEDs) and lasers, an active research effort has emerged worldwide in pursuit of the goal of realizing "plastic" lasers, LEDs, and fast photo-detector devices based on conjugated polymers. This project is concerned with the investigation of several unsolved questions concerning the nature of the light emission process in quasi-one dimensional polymer semiconductors promptly following photoexcitation. These processes occur at ultrafast time scales and their studies are now made possible by new developments in experimental ultrafast spectroscopy. This project is concerned with using these new techniques in the quantitative study of the nature of the processes that underlie the ultrafast emission of light following photoexcitation of various polymer materials. This research will be conducted with the assistance of students and post doctoral research associates who will thereby acquire skills and knowledge in a contemporary forefront area of condensed matter physics and materials science. ***