High-Field Terahertz Driven Photocarrier Dynamics in Nanomaterials

摘要本课题的目的是研究半导体材料中电子在短脉冲大能量电磁波下的运动。更好地了解这种相互作用的基础科学，可以制造出高速运行的电子和光子设备。自然产生的电磁波充满了日常生活的空间，因此了解半导体中的电子在暴露于高能电磁波时的反应是很重要的。该研究小组将利用极短的大能量电磁脉冲，研究碳纳米管、石墨烯、二氧化钒等纳米尺度材料中电子的运动。这个项目的结果可能会发现新的知识，对于开发量子信息处理设备和下一代高速电子和光子设备至关重要。该项目还将教育和培训研究生和本科生，为他们提供深厚的知识，为他们在高科技行业就业做好准备。该项目的夏季推广活动包括为波特兰社区学院系统的高中生和少数民族学生提供光学演示和研究经验。技术摘要纳米材料在太赫兹（THz）波段的场电子动力学是一个未知的课题，然而考虑到纳米结构的场控制在高速电子学和量子信息处理等领域的潜在应用，其重要性再怎么强调也不为过。该项目旨在了解在强太赫兹脉冲驱动下纳米材料中的超快光载流子动力学，其中太赫兹场足以使材料的电子能带结构发生实质性变化。研究小组研究了在强太赫兹脉冲和飞秒激光激励下，强相关材料二氧化钒的超快绝缘体到金属的转变，并描述了高度非平衡状态下相关电子的动力学特征。它还研究了低维材料（如碳纳米管、石墨烯和二硫化钼）在极端条件下的高场光载流子动力学的微观机制，在极端条件下，太赫兹场强到足以诱导带到带隧穿。时间分辨光学和太赫兹光谱学被用于以亚皮秒分辨率观察和相干控制许多电子的极端非平衡动力学，同时利用太赫兹等离子体器件中的场增强和亚波长限制。该研究项目为超高速电子学和光子学（如场效应晶体管、光调制器、无线互连和频率转换器）的潜在应用奠定了基础。本研究获得的基本认识和实验方法，对于研究固体中的非调和声子动力学、超导体的非微扰动力学和分子中的非线性振动等各种材料系统中的高场光-物质相互作用具有重要的参考价值。太赫兹等离子体器件的场增强和亚波长聚焦可以应用于成像和传感领域。参与研究项目的学生将获得深厚的基础科学知识和技术技能，并使用最先进的光电仪器进行实验。该项目包括本科生研究人员撰写他们的毕业论文或参加REU活动，并支持启发年轻人思想的外展活动。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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 goal of this project is to study the movement of electrons in semiconductor materials when exposed to electromagnetic waves with short pulses but large energy. Better knowledge of the fundamental science of this interaction could lead to making electronic and photonic devices that operate at high-speed. Naturally occurring electromagnetic waves fill up space of everyday life, so it is important to understand how electrons in semiconductors react when exposed to high-energy electromagnetic waves. This research team will employ extremely short electromagnetic pulses with large energy to investigate the movement of electrons in materials with nanometer-scale dimensions such as carbon nanotubes, graphene and vanadium dioxide. The outcome of this project could uncover new knowledge crucial for developing devices for quantum information processing and for the next generation high-speed electronic and photonic devices. This project will also educate and train graduate and undergraduate students, giving them profound knowledge that will prepare them for employment in high-tech industries. The summer outreach activities in the project include optics demonstrations and research experience for high school students and minority students in the Portland Community College system. Technical AbstractHigh-field electron dynamics in nanomaterials in the terahertz (THz) regime is an uncharted subject, yet the importance of field-control of nanostructures cannot be emphasized enough considering its potential application to high-speed electronics and quantum information processing among other areas. This project aims to understand ultrafast photocarrier dynamics in nanomaterials driven by intense terahertz pulses, where the terahertz field is strong enough to make substantial changes in the electronic band structure of the material. The research team investigates ultrafast insulator-to-metal transition in a strongly correlated material, vanadium dioxide, driven by strong THz pulses and femtosecond laser excitations, and characterize the dynamics of correlated electrons in highly non-equilibrium states. It also studies the microscopic mechanisms underlying the high-field photocarrier dynamics in low-dimensional materials, such as carbon nanotubes, graphene and molybdenum disulfide, under extreme conditions where the THz field is strong enough to induce band-to-band tunneling. Time-resolved optical and THz spectroscopy is employed to observe and to coherently control the extreme non-equilibrium dynamics of many electrons with sub-picosecond resolution, while exploiting the field enhancement and subwavelength confinement in THz plasmonic devices. This research project lays the groundwork for the potential applications to ultrahigh-speed electronics and photonics such as field-effect transistors, optical modulators, wireless interconnects, and frequency converters. The fundamental understandings and experimental methods obtained from this research is valuable information for studying high-field light-matter interactions in various material systems such as anharmonic phonon dynamics in solids, nonperturbative dynamics of superconductors, and nonlinear vibrations in molecules. The field enhancement and subwavelength focusing in terahertz plasmonic devices can be applied to imaging and sensing applications. The students working on the research project will gain profound knowledge about the fundamental science and technical skills to conduct experiments using state-of-the-art optoelectronic instruments. The project involves undergraduate researchers working on their senior thesis or participating in REU activities and support outreach activities inspiring young minds.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.