Charge and Surface Effects on Exciton and Hot Carrier Relaxation in Colloidal Quantum Dots

非技术摘要：在过去的二十年里，半导体纳米结构使光学技术发生了革命性的变化，在通信和消费电子领域产生了广泛的影响。更小的、可溶的、可能定义更好或更复杂的纳米结构的化学合成有望将其影响扩大到医学成像、显示器和太阳能。这些技术正被几家风险投资公司积极开发。然而，较低的设备效率和有限的使用寿命可能会成为阻碍表演的因素。它们最终由这些微小结构中电子能量的耗散机制来定义。特别是，很明显，强烈的电荷斥力和极端的表面接近导致了非常快的能量损失，其机制尚不清楚。了解微观效率损失的一般机制在纳米技术中具有广泛的重要性。这是这个面向物理和化学博士生的基础材料科学项目的主题。学生将接受在这些材料的研究中使用的几种研究技术的培训，这些技术将在各种产品中发挥重要作用。技术摘要：该项目专注于胶体半导体量子点以及电荷和表面如何影响其带间和带内能量弛豫。前者与发光二极管或太阳能电池的发展有关，而后者可能导致红外应用。该项目量化了过量电荷对稳定性、光激发、荧光和弛豫的影响。实验是在带电的系综和单点上进行的。缓慢的带内弛豫将在设计纳米结构以及红外应用方面打开新的机会，到目前为止，它似乎受到表面的强烈影响。材料的合成侧重于表面控制和核/壳，而表征则涉及时间分辨光学光谱。该项目支持两名化学和物理交界处的博士生的研究。它还为一名暑期本科生提供了科学的环境，而荧光材料经常用于课堂演示。研究生将接受在这些材料的研究中使用的广泛研究技术的培训，这些材料将在各种产品中发挥重要作用。

Non-technical abstract:Over the last twenty years, semiconductor nanostructures have revolutionized optical technology with wide impact in communication and consumer electronics. Chemical synthesis of smaller, soluble, possibly better defined or more complex nanostructures promises to expand the impact to medical imaging, displays and solar energy. These Technologies are aggressively pursued by several venture firms. However, poor device efficiency and limited lifetimes may turn out to be show- stoppers. They are ultimately defined by the mechanisms of dissipation of the electronic energy in these tiny structures. In particular, it is becoming clear that the strong charge repulsion and the extreme surface proximity lead to very fast energy loss by yet unclear mechanisms. Understanding the generic mechanisms of the microscopic efficiency loss will be of broad importance in nanotechnology. This is the topic of this basic materials science project with physics and chemistry PhD students. The students will receive training in several research technique used in the study of these materials which will play important role in various products.Technical abstract:The project focuses on colloidal semiconductor quantum dots and how charge and surface affect their interband and intraband energy relaxation. The former is relevant to light-emitting diode or solar cell developments, while the latter may lead to infrared applications. The project quantifies how excess charge affects the stability, photo-excitation, fluorescence and relaxation. Experiments are performed on charged ensemble as well as single dots. Slow intraband relaxation would open new opportunities in engineering the nanostructure as well as in infrared applications and to date it appears to be strongly affected by the surface. The materials synthesis focuses on surface control and core/shells while the characterization involves time-resolved optical spectroscopy. The project supports the research of two PhD students at the interface of Chemistry and Physics. It also provides the scientific environment for one summer undergraduate, while the fluorescent materials are regularly used in classroom demonstration. Graduate students will receive training in broad spectrum of research technique used in the study of these materials which will play importnat role in various products.