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，由于其广泛的特性，吸引了重要的研究兴趣。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为过渡金属，X为碳或氮，Tx为O、OH、F、Cl或其他与二维MXene层过渡金属结合的表面基团。该项目的重点是发展对MXenes光学特性的原子尺度理解，包括它们在可见光和近红外波段的可调谐等离子体共振，这可以用于纳米光子学或等离子体学的应用。PI的假设是，不同的官能团Tx不仅控制着二维MXene层之间的层间距，而且还提供了调整MXene层之间相互作用以及每层自由电荷密度的能力。采用单一类型表面末端的Ti3C2和ti2c基MXenes进行原子、电子和等离子体结构的高分辨率电子显微镜和光谱研究。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的科学和工程本科生和研究生的实践研究和学习经验，UIC是一个研究-1西班牙裔服务机构。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学院的学生交流项目、Latin@s获取科学进步网络和可使用学者项目，让代表性不足的群体和少数民族的学生参与其中。通过伊利诺伊大学芝加哥分校的PI本科生研究期刊，促进了本科生参与积极的研究项目。该计划的毕业生将为学术界，国家实验室或工业，包括半导体公司做出贡献。技术描述：本研究项目的目标是发展对Ti3C2Tx和Ti2CTx MXenes的纳米光子和等离子体性质的原子尺度理解，用单一的，良好控制的物种功能化，使用原子分辨率扫描透射电子显微镜（STEM）成像，常规和单铬化电子能量损失光谱（EELS）结合原位冷却到液氮温度。显示莫尔维尔晶格效应的扭曲双层MXenes将被用于研究杂化等离子体或激子的出现，以及其他新出现的，潜在的强相关现象。利用机器学习（ML）在多维数据立方体中进行自主异常检测，研究结构缺陷及其对等离子体和光子特性的影响之间的相关性。本研究项目将包括两项任务，i) MXenes的原子分辨率分析和ii)卷积神经网络的发展，以识别原子分辨率STEM图像中的晶体缺陷，并识别低损耗或价态EELS的相关变化。这两项任务的见解将结合起来，产生测量和控制单功能化MXenes的光学或电子，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机器学习方法的培训，将研究和教育结合起来，这是该项目的一个整体特征。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.