A Route Towards Efficient Energy Relaxation from Nanocrystals to Oxide-free Semiconductor Surfaces

摘要技术：基于能量转移的混合纳米结构由具有不同功能的元件明智地设计而成，为光电子器件的应用提供了一个通用的平台。在强吸收元件的光吸收之后，从纳米结构中产生的激子到导电半导体薄膜中的电子-空穴对的非接触电磁能量转移。这种对具有良好控制界面的纳米材料中激发的电磁操纵是迈向下一代功能纳米器件的重要一步，这种器件不依赖于组件之间的电荷转移。本项目主要研究层状混合纳米结构中高吸收纳米晶体量子点和高迁移率硅半导体元件之间的辐射和非辐射能量转移现象的基本原理。第一项工作旨在研究共价接枝在硅表面上的NQD单层的非辐射能量转移。为了促进完全的光吸收，需要制作多层NQD结构，并探索和优化通过纳米晶层之间的非辐射相互作用向硅衬底的能量‘漏斗’扩散。第二个任务是研究纳米晶发射与硅纳米膜中的波导模的辐射耦合。放置在高介电常数材料(如硅)附近，纳米晶体发射在硅层中转换为波导模，最终在那里被吸收，有助于整体能量转移。第三个方向探索了具有长寿命多激子态的新的多壳层NQD用于能量转移的适用性。采用时间分辨光致发光光谱和光电流测量相结合的方法对平面NQD/Si结构的总能量转移效率进行了评估。这项研究的结果将有助于理解混合激子结构中克服与界面态有关的电荷陷阱的能量转移路径。结合建模工具和实现所需功能的指导方针，这些结果可以应用于设计高效光伏结构的实用架构。非技术性：由附着在薄膜上的纳米颗粒组成的纳米结构为现代光子学提供了一个通用的平台，应用于先进的传感、光伏和新型发光光源。该项目的基础研究成果有望极大地影响我们对这些纳米结构中的能量传递现象和操纵的理解，从而产生更高效的光电子器件，给社会带来巨大的好处。参与这项研究的学生能够获得激子和混合纳米材料领域的专业知识。这项研究本质上是跨学科的，使学生能够熟练掌握物理、光子学和材料科学，并发展实验和建模技能。致力于让本科生和预科学生参与进来，促进他们对科学的兴趣。该项目的PI致力于通过开发一门关于可持续能源的光子学应用和与当地行业的互动的课程来加强课程，以传授知识。

Abstract Technical: Energy-transfer-based hybrid nanostructures judiciously engineered from components with separate functionalities offer a versatile platform for optoelectronic device applications. Light absorption in the strongly absorbing component of the hybrid is followed by non-contact electromagnetic energy transfer from the resulting excitons in nanostructures to electron-hole pairs in the conductive semiconductor thin film. This electromagnetic manipulation of excitations in nanoscale materials with well-controlled interfaces is an important step towards the next generation of functional nanodevices, which does not rely on charge transfer between the components. This project focuses on the fundamental principles of radiative and non-radiative energy transfer phenomena between highly absorbing nanocrystal quantum dots (NQDs) and high-mobility Si semiconductor components combined in layered hybrid nanostructures. The first effort aims to study non-radiative energy transfer from monolayers of NQDs covalently grafted on Si surfaces. To facilitate complete light absorption, multilayer NQD structures are to be fabricated and energy 'funneling' diffusion via non-radiative interactions between nanocrystal layers into Si substrate is explored and optimized. The second task focuses on radiative coupling of nanocrystal emission to waveguiding modes in Si nanomembranes. Placed in the vicinity of a high dielectric constant material such as Si, the nanocrystal emission is converted to waveguide modes in the Si layer where it is eventually absorbed, contributing to overall energy transfer. The third direction explores the applicability of new multishell NQDs that possess long-lived multiexitonic states for energy transfer. The overall energy transfer efficiency of planar NQD/Si structures is assessed by employing time-resolved photoluminescence spectroscopy combined with photocurrent measurements. The results of this research will lead to the understanding of energy transfer pathways in hybrid excitonic structures that overcome charge trapping related to interfacial states. Together with modeling tools and guidelines for achieving desired functionalities, these results could be applied to engineer practical architectures for efficient photovoltaic structures.Non-technical: Nanostructures composed on nanoparticles attached to thin silicon films offer a versatile platform for modern photonics with applications in advanced sensing, photovoltaics and novel light emitting sources. The fundamental research results of this project are expected to significantly impact our understanding of energy transfer phenomena and manipulation in these nanostructures leading to more efficient optoelectronic devices of great benefit to society. Students participating in this research are able to acquire expertise in the field of excitonics and hybrid nanomaterials. The research is inherently interdisciplinary in nature, allowing students to gain proficiency in physics, photonics and materials science and to develop both experimental and modeling skills. A strong effort is devoted to involve undergraduate and pre-college students and facilitate their interest in science. The PI of this project is committed to knowledge transfer via enhancing the curriculum by developing a course on Photonics Applications for Sustainable Energy and the interaction with the local industry.