Quantum State Resolved Charge Dynamics in Nanoscale Heterostructures at Low Temperatures

“该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该计划将扩展威斯康星州大学开发的相干多维光谱（CMDS）方法，用于半导体纳米结构中的相干电子输运。这些方法将通过在我们未来的太阳能收集器的复杂纳米结构中创建多个量子相干态来解决相干传输的单个量子态。新方法将定义相干电子转移中涉及的量子态，隔离特定的相干路径，缩小宽光谱特征，减少光谱拥塞，解决高阶过程，访问定义多激子的能量和退相速率的零量子相干性和双量子相干性，定义电荷转移产生的状态之间的相关性，隔离和测量相干和非相干动力学，并为纳米结构中的各个材料创建光谱特征。样品包括量子点，量子线，超支化树结构，核壳结构，纳米线异质结，和量子线上的二氧化钛。 该计划有九个目标：1）使用多个状态创建光谱特征; 2）探索多激子状态的光谱和动力学; 3）探测在纳米结构中引导电子的势能面; 4）识别电荷倍增的机制; 5）扩展纳米结构材料的范围; 6）创建跨纳米结构异质结的多量子相干; 7）多激子的探针供体-受体耦合; 8）定义跨异质结的量子态排列; 9）使用跨异质结的电荷转移来收获由电荷倍增产生的多激子。该项目将为合成包含相干电子传输的新纳米结构提供见解和测量工具。相干电子传输是制造在将太阳能转化为电能或化学能时具有最小能量损失的材料的基础。它将为纳米结构中的量子态和动力学提供更深入的基本见解，并指导开发更好材料的努力。该项目将使用五种方法向更广泛的科学界传播我们的发现- 1）多维光谱学国际会议; 2）教程网站; 3）非线性光谱学和CMDS的完整在线课程; 4）教程论文和书籍章节; 5）会议和大学演讲; 6）与纳米结构发展研究小组和教师和学生的颜色在斯佩尔曼学院的合作。太阳能是世界上最有可能的全球解决方案？长期能源需求。太阳能可以直接转化为电能，也可以催化转化为燃料，储存能量供以后使用。收集太阳能的最有前途的方法之一是使用纳米结构，其吸收光以产生电子和空穴，在电子和空穴重新结合之前将其分离，并将电力输送到动力设备或在催化化学反应中使用电子和空穴来制造燃料。为了获得最高的太阳能转换效率，重要的是减少所有释放能量的因素。相干电子转移没有能量损失。它最常发生在非常低温度的超导体中，但它也可以发生在室温下的纳米结构中，因为距离很短，量子效应很重要。这个项目？的目标是开发所需的见解和工具，以创建一个新的家庭复杂的纳米结构，纳入相干电子传输。电荷倍增是一种很有前途的提高转换效率的方法，因为它使用了太阳光谱中的所有颜色，并且没有能量浪费。本计画将发展新的飞秒雷射方法，可直接观察相干电子转移与电荷倍增，并具有量子态解析度。这些方法将把威斯康星州大学的发现扩展到太阳能领域。直接观察相干电子转移和电荷倍增的能力将指导合成材料化学家？努力设计优化传输和太阳能收集效率的材料。该项目将涉及与洛斯阿拉莫斯国家实验室的太阳能研究人员、威斯康星州大学的合成材料化学家和表面化学家以及斯佩尔曼学院的有色人种教师和学生的合作。它还将建立一个指导网站、在线课程材料和专业会议，以便向公众推广和传播这些新发现。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."TECHNICAL SUMMARY This program will extend the coherent multidimensional spectroscopy (CMDS) methods developed at the University of Wisconsin to coherent electron transport in semiconducting nanostructures. The methods will resolve the individual quantum states of coherent transport by creating multiple quantum coherences of states throughout the complex nanostructures of our future solar collectors. The new methods will define the quantum states involved in coherent electron transfer, isolate specific coherence pathways, narrow broad spectral features, reduce spectral congestion, resolve higher order processes, access the zero quantum coherences and double quantum coherences that define the energies and dephasing rates of multiexcitons, define the correlations between states created by charge transfer, isolate and measure the coherent and incoherent dynamics, and create spectroscopic signatures for the individual materials in a nanostructure. The samples include quantum dots, quantum wires, hyperbranched tree structures, core-shell structures, nanowire heterojunctions, and quantum wires on TiO2. This program has nine goals- 1) creating spectroscopic signatures using multiple states; 2) exploring the spectra and dynamics of multiexcitonic states; 3) probe the potential energy surface that guides electrons in a nanostructure; 4) identify the mechanism of charge multiplication; 5) expand the range of nanostructured materials; 6) create multiple quantum coherences across a nanostructured heterojunction; 7) probe donor-acceptor coupling of multiexcitons; 8) define the quantum state alignment across heterojunctions; 9) use charge transfer across heterojunctions to harvest the multiexcitons created by charge multiplication. The project will provide the insights and measurement tools for the synthesis of new nanostructures that incorporate coherent electron transport. Coherent electron transport is fundamental to making materials that have minimal energy loss in changing solar energy into electrical or chemical energy. It will provide deeper fundamental insights to the quantum states and dynamics in nanostructures and guide efforts to develop better materials. The project will use five methods to disseminate our discoveries to the broader scientific community- 1) the International Conference on Multidimensional Spectroscopy; 2) a tutorial web site; 3) a complete on-line course in nonlinear spectroscopy and CMDS; 4) tutorial papers and book chapters; 5) conference and university presentations; 6) collaboration with nanostructure development research groups and faculty and students of color at Spelman College. NON-TECHNICAL SUMMARY Solar energy is the most likely global solution to the world?s long-range energy needs. Solar energy can be either directly converted to electricity or catalytically converted into fuels that store the energy for later use. One of the most promising methods for harvesting solar energy is using nanostructures which absorb the light to create electrons and holes, separate the electrons and holes before they recombine, and either deliver the electricity to power equipment or use the electrons and holes in catalytic chemical reactions to create fuels. In order to have the highest solar energy conversion efficiencies, it is important to reduce all the factors that loose energy. Coherent electron transfer has no energy loss. It occurs most commonly in superconductors at very low temperatures but it can also occur in nanostructures at room temperature because the distances are short and quantum effects are important. This project?s goal is to develop the insights and tools required to create a new family of complex nanostructures that incorporate coherent electron transport. Charge multiplication is a promising approach to raising conversion efficiency because it uses all the colors in the solar spectrum and no energy is wasted. This project will develop new femtosecond laser methods that can directly observe the coherent electron transfer and charge multiplication with quantum state resolution. The methods will extend discoveries made at the University of Wisconsin to the field of solar energy. The ability to directly see coherent electron transfer and charge multiplication will guide synthetic materials chemists? efforts to design materials that optimize the transfer and solar energy collection efficiency. This project will involve collaborative work with solar energy researchers at Los Alamos National Laboratories, synthetic materials chemists and surface chemists at the University of Wisconsin, and faculty and students of color at Spelman College. It will also develop a tutorial web site, on-line course materials, and professional conferences for outreach and dissemination of these new discoveries to the general public.