MRI: Development of an Ultrafast Photoluminescence and Transient Absorption Microscope in Ultrahigh Vacuum for Studying Electronic Properties of 2-Dimensional Materials

控制硅等半导体的生长和掺杂的能力使电子材料的发展在数字时代给现代社会带来了革命性的变化。二维材料，如过渡金属二卤化物，是一类新的电子材料，有可能开启类似规模的新技术进步。近年来，二维材料的生长取得了重大进展。然而，仍然需要开发能够控制二维材料的电子性质的掺杂和加工化学。该项目开发的仪器结合了超快光致发光和瞬时吸收显微镜来表征二维材料的电子性质，以及控制掺杂化学的超高真空系统。它极大地扩展了NSF材料创新平台用户的研究基础设施，通过使用多种表征方法在样品中的相同位置进行相关测量，从而专注于二维材料。该仪器服务于宾夕法尼亚州立大学和更广泛的国家二维材料社区的研究人员的用户基础。使用该仪器的研究生和博士后学者通过促进研讨会和相关培训模块获得重要的专业发展经验，这些培训模块通过宾夕法尼亚州立大学材料研究所和原子薄壁多功能涂料中心提供和宣传，该中心是一个产学合作研究中心。超高真空系统中超快光致发光和瞬时吸收显微镜的发展使人们能够在成像平台上以超快的时间分辨率探测发射态和非发射态。它还可以控制样品环境和掺杂化学，以表征二维材料的电子和传输特性。这些能力是至关重要的，因为二维材料是具有电子性质的单层或少数层结构，受到表面相互作用的强烈影响。此外，二维材料中涉及电荷转移和输运的许多电子态都是弱发射或非发射的，具有扩散性质和寿命，这敏感地依赖于材料的外延排列和生长。该仪器的超快显微能力与超高真空样品转移系统和附加的制备室相结合，使激子和载流子的动力学和输运能够在空间和时间上进行分辨，并与它们的生长和掺杂化学相关联。可以使用扫描探针和电子显微镜测量和光电子发射研究来研究样品相同区域的电子和传输特性，以完成表征和制定指导二维材料和设备开发的设计规则。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。

The ability to control the growth and doping of semiconductors such as silicon enabled the development of electronic materials that revolutionized modern society in the digital age. Two-dimensional materials such as transition metal dichalcogenides are a new class of electronic materials that have the potential to open new technological advances on a similar scale. Major advances in the growth of two-dimensional materials have occurred in recent years. However, there remains a fundamental need to develop doping and processing chemistries that enable the control of the electronic properties of two-dimensional materials. The instrument developed in this project combines an ultrafast photoluminescence and transient absorption microscope, to characterize the electronic properties of two-dimensional materials, with an ultrahigh vacuum system that controls doping chemistries. It significantly expands the research infrastructure for users of the NSF Materials Innovation Platform focused on two-dimensional materials by enabling correlative measurements at the same locations in the samples using multiple characterization methods. The instrument serves a user-base of researchers both at Pennsylvania State University and in the broader national two-dimensional materials community. Graduate students and post-doctoral scholars using the instrument gain important professional development experience by facilitating workshops and associated training modules that are offered and advertised through the Materials Research Institute at Pennsylvania State University and the Center for Atomically Thin Multifunctional Coatings, which is an Industry-University Cooperative Research Center. The development of the ultrafast photoluminescence and transient absorption microscope in an ultrahigh vacuum system opens the ability to probe both emissive and non-emissive states with ultrafast time resolution in an imaging platform. It also enables the control of the sample environment and doping chemistry for characterization of the electronic and transport properties of two-dimensional materials. These capabilities are critical because two-dimensional materials are single- or few layer-structures with electronic properties that are strongly influenced by surface interactions. Furthermore, many of the electronic states involved in charge transfer and transport in two-dimensional materials are weakly- or non-emissive with diffusion properties and lifetimes that depend sensitively on the epitaxial alignment and growth of the materials. The ultrafast microscopy capability of the instrument combined with an ultrahigh vacuum sample transfer system and attached preparation chamber enables the dynamics and transport of excitons and charge carriers to be spatially and temporally resolved and correlated with their growth and doping chemistries. The electronic and transport properties of the same regions of the samples can be investigated using scanned probe and electron microscopy measurements and photoemission studies for complete characterization and development of design rules that will guide the development of two-dimensional materials and devices.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.