Discovering Novel Properties in Few-Layer MXenes Using Analytical, In-Situ Scanning Transmission Electron Microscopy

非技术描述：被称为MXenes的材料是不断增长的二维结构家族的一部分，由于其广泛的性质而吸引了巨大的研究兴趣。这些层状过渡金属碳化物和氮化物的化学式为：Mn+1XnTx(n=1-3)，其中M是过渡金属，X是碳或氮，Tx是O、OH、F、Cl或其他表面基团，它们键合到二维MXene层的过渡金属上。这个项目的重点是在原子尺度上理解MXenes的光学性质，包括它们在可见光和近红外区域的可调等离子激元共振，这可用于纳米光子学或等离子激元。PI的假设是，不同的官能团Tx不仅控制二维Mxene层的层到层间距，而且还提供了调节Mxene层之间的相互作用以及每层中自由电荷密度的能力。具有单一表面端接的Ti3C2和Ti2C基MXenes将被用来研究原子、电子和等离子体结构的高分辨电子显微镜和光谱。伊利诺伊大学芝加哥分校(UIC)将利用独特的仪器在广泛的温度范围内以前所未有的空间和能量分辨率研究这些材料。该项目的研究活动围绕着UIC理工科本科生和研究生的实践研究和学习经验展开，UIC是一家为西班牙裔研究机构提供服务的机构。招聘和培训的重点是下一代研究人员，特别是通过与蒙特雷理工大学、拉丁@S参加科学促进网络和DuSable学者方案的学生交换方案，吸引来自代表性不足群体和少数群体的学生。本科生参与积极的研究项目是通过伊利诺伊大学芝加哥分校的PI本科生研究杂志培养的。该项目的毕业生将为学术界、国家实验室或行业，包括半导体公司做出贡献。技术描述：本研究项目的目标是利用原子分辨率扫描电子显微镜(STEM)成像、常规和单色电子能量损失谱(EELS)结合原位冷却到液氮温度，对Ti3C2Tx和Ti2CTx MXenes的纳米光子和等离子体性质进行原子尺度的了解，并使用单一的、控制良好的物种进行功能化处理。显示莫尔晶格效应的扭曲双层MXenes将被研究杂化等离子激子或激子的出现，以及其他新出现的、潜在的强关联现象。基于机器学习的多维数据立方体中的自主异常检测，将研究结构缺陷之间的相关性及其对等离子体和光子性质的影响。这项研究项目将包括两个任务，i)MXenes的原子分辨率分析和ii)开发卷积神经网络来识别原子分辨率STEM图像中的晶体缺陷，并识别低损耗或价态EELs中的相关变化。这两项任务的洞察力将被结合在一起，从而产生测量和控制单官能化MXen的光学或电学甚至可能是磁性的能力。通过对本科生和研究生进行最先进的原位扫描透射电子显微镜和最先进的ML方法的培训，将研究和教育相结合是该项目的一个组成部分。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。

NON-TECHNICAL DESCRIPTION: Materials known as MXenes are part of a growing family of two-dimensional structures that have attracted significant research interests due to their wide range of properties. These layered transition metal carbides and nitrides have the chemical formula of Mn+1XnTx (n=1-3), where M is a transition metal, X is either carbon or nitrogen, and Tx is either O, OH, F, Cl, or other surface groups that are bonded to the transition metal of the two-dimensional MXene layer. This project focuses on developing an atomic-scale understanding of the optical properties of MXenes, including their tunable plasmon resonances in the visible and near-infrared regime, which can be used for applications in nano-photonics or plasmonics. It is the PI’s hypothesis that different functional groups, Tx, control not only the layer-to-layer spacings of the two-dimensional MXene layers, but also provide the ability to tune the interactions between MXene layers as well as the density of free charges in each layer. Ti3C2 and Ti2C-based MXenes with a single type of surface termination will be used to study the atomic, electronic and plasmonic structures high-resolution electron microscopy and spectroscopy. Access to unique instrumentation at University of Illinois - Chicago (UIC) will be leveraged to study these materials over a wide range of temperatures and with unprecedented spatial and energy resolution. The project’s research activities center around hands-on research and learning experiences for science and engineering undergraduate and graduate students at the UIC, a Research-1 Hispanic-serving institution. Recruitment and training focuses on the next generation of researchers, in particular involving students from underrepresented groups and minorities through a student exchange program with Tecnologico de Monterrey, Latin@s Gaining Access to Networks for Advancement in Science and the DuSable Scholars programs. The participation of undergraduate students in active research projects is fostered through the PI’s Journal of Undergraduate Research at the University of Illinois - Chicago. Graduates of this program will contribute to academia, National Laboratories or industry, including semiconductor companies.TECHNICAL DESCRIPTION: The objectives of this research project are to develop an atomic-scale understanding of the nano-photonic and plasmonic properties of Ti3C2Tx and Ti2CTx MXenes, functionalized with a single, well-controlled species, using atomic-resolution scanning transmission electron microscopy (STEM) imaging, conventional and monochromated electron energy loss spectroscopy (EELS) combined with in-situ cooling to liquid nitrogen temperatures. Twisted bi-layer MXenes exhibiting Moiré lattice effects will be studied for the emergence of hybridized plasmons or excitons, as well as other emerging, potentially strongly correlated phenomena. Using autonomous anomaly detection in multi-dimensional data cubes via machine learning (ML), the correlation between structural defects and their impact on the plasmonic and photonic properties will be studied. This research project will consist of two tasks, i) atomic-resolution analysis of MXenes and ii) development of convolutional neural networks to identify crystal defects in atomic-resolution STEM images and identify the correlated changes in the low-loss or valence EELS. The insights from both tasks will be combined, yielding the ability to measure and control the optical or electronic, and possibly even magnetic properties of single-functionalized MXenes. The integration of research and education through the training of undergraduate and graduate students in state-of-the-art in-situ scanning transmission electron microscopy and state-of-the-art ML approaches is an integral feature of this project.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.