Development of a Wide-Field Transient Absorption Microscope for Applications to Two-Dimensional Perovskite Quantum Wells

在化学系化学测量和成像计划以及物理系原子、分子和光学实验物理计划(AMO-E)的支持下，北卡罗来纳大学教堂山分校的莫兰教授正在开发一种能够成像钙钛矿晶体中电子运动的显微镜。这项工作的动机是由钙钛矿展示的太阳能收集潜力。该项目中的目标钙钛矿晶体具有二维(2D)形状，其中晶体的表面具有毫米级尺寸。这种2D钙钛矿在可见光范围内吸收光线，并相对耐湿，这是利用太阳能所需的。莫兰教授和他的团队计划同时监测晶体表面的多个位置，以获得晶体中电子运动的统计信息。这些实验的信息可以用来指导材料合成，以制造更好的太阳能转换装置。参与这个项目的研究生和本科生精通化学、计算机编程、机械加工、电子学和光学，因为研究小组正在建造他们自己的大部分设备。此外，莫兰教授和他的学生与北卡罗来纳大学校园内的莫尔黑德天文馆合作，指导初中生和高中生演示光学和太阳能电池原理的实验室练习。北卡罗来纳大学教堂山分校的莫兰教授正在开发一种基于衍射光学的瞬时吸收显微镜，能够成像二维(2D)钙钛矿型量子井中的电子扩散。目标量子阱因其在潮湿条件下的稳定性和大的激子结合能而引起了人们的关注。此外，研究小组还在研究由多层量子阱组成的层状系统，其中带隙随着薄膜高度的增加而减小。因此，在这些层状钙钛矿中，电子激发从薄膜的底部漏斗到薄膜的顶部。本研究中使用的衍射光学显微镜在一次实验中获得了样品表面41个位置的瞬时吸收数据。使用一对阵列探测器(例如，对应于能量施主和受主量子井的波长)以两个探测波长同时检测信号。在对剥离晶体的研究中，测量了激子在多个激发波长下的扩散系数，以建立载流子扩散系数和激发能量之间的定量关系。通过分析样品上41个不同点的动力学，得到了扩散速率的统计分布。从这些实验中获得的信息可以用于指导材料合成和器件工程。研究生和本科生精通计算机编程、机械加工、电子学和光学，因为研究小组正在建造他们自己的大多数设备。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry and the Atomic, Molecular, and Optical Experimental Physics Program (AMO-E) in the Division of Physics, Professor Moran at the University of North Carolina, Chapel Hill, is developing a microscope capable of imaging electron movement in perovskite crystals. This work is motivated by the potential for solar energy harvesting demonstrated by perovksites. The perovskite crystals targeted in this project have two-dimensional (2D) shapes where the faces of the crystals have millimeter-scale dimensions. Such 2D perovskites absorb light in the visible range and are relatively resistant to humidity, which is desirable for harnessing solar energy. Professor Moran and his team plan to simultaneously monitor multiple places on the crystal surface to get statistical information on electron movement in the crystals. The information from these experiments can be used to guide material synthesis to make better solar energy conversion devices. Graduate and undergraduate students involved in this project become proficient in chemistry, computer programming, machining, electronics, and optics as the research group is building most of their own equipment. In addition, Professor Moran and his students supervise laboratory exercises that illustrate the principles of optics and solar cells for middle and high-school students in collaboration with the Morehead Planetarium on the UNC campus.Professor Moran at the University of North Carolina, Chapel Hill is developing a diffractive optic-based transient absorption microscope capable of imaging electron diffusion in two-dimensional (2D) perovskite quantum wells. The quantum wells targeted have garnered attention for their stabilities under humid conditions and large exciton binding energies. In addition, the research team is investigating layered systems that consist of "stacks" of quantum wells in which the band gap decreases with respect to height in the film. Thus, electronic excitations are funneled from the bottom to the top of the film in these layered perovskites. The diffractive optic-based microscope employed in this research acquires transient absorption data at 41 locations on the sample surface in a single experiment. Signals are simultaneously detected at two probe wavelengths using a pair of array detectors (e.g., wavelengths corresponding to energy donor and acceptor quantum wells). In studies of exfoliated crystals, diffusivities of excitons are being measured at a number of excitation wavelengths to establish a quantitative relationship between the carrier diffusivity and excitation energy. Statistical distributions of diffusion rates are generated by analyzing the dynamics at 41 different spots on the sample. The information derived from these experiments can be used to guide materials synthesis and device engineering. Graduate and undergraduate students becoming proficient in computer programming, machining, electronics, and optics as the research group is building most of their own equipment.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.