Synthesis and Characterization of Two-Dimensional Mn+1Xn Layers Derived from the MAX Phases

非技术总结：与传统的三维材料相比，原子薄的二维（2D）材料具有独特的性能。石墨烯是碳的单原子层，是这些新兴的二维材料中最引人注目和研究最多的。然而，石墨烯仅限于一种元素——碳。最近，一种新的二维早期过渡金属（如钛、钒、铌等）碳化物和碳氮化物（称为MXene）被报道。与石墨烯相比，这些二维材料提供了多种化学成分，它们可以存在于不同数量的原子层中。MXenes可能具有广泛的潜在应用，从复合材料增强剂到工业催化剂，再到能量存储和电子设备。然而，在确定最佳应用之前，必须开发这些材料的基本物理特性，并建立合成-结构-性能关系。实验和理论相结合的工作将用于了解MXenes化合物的表面化学，结构和性质。这项工作可能会导致电池在几分钟内充电数千次循环或强大的超级电容器，可用于非常高功率的能量存储应用，如汽车的再生断路器。技术细节：最近，一个新的二维早期过渡金属（如钛、钒、铌等）碳化物和碳氮化物（所谓的MXene）家族被发现。后者提供了多种化学成分，因为多个原子可以共存于二维薄片中。此外，MXenes存在于3、5或7个原子层中。合成的MXene表面被OH， O和/或f功能化，理论计算预测MXene可以是导体或半导体，这取决于它们的表面化学性质。MXenes可能具有广泛的潜在应用，从复合材料增强剂到工业催化剂，再到能量存储和电子设备。由于这类固体是相当新的，这些材料的基础科学必须得到发展，它们的合成-结构-性能关系需要建立。该项目的目的是：(i)在不同的衬底上分离单个MXene层，（ii）确定这些层是否像石墨烯一样具有吸引人的电子特性，从而可以用作晶体管，（iii）测量这些薄膜的电学和光学特性，作为表面末端和MXene化学的函数，（iv）将2D薄片分散在各种溶剂中，包括水，并形成稳定的悬浮液，(v)利用各种光谱技术研究MXene表面，并将其与理论第一性原理计算相关联，以充分了解表面化学及其对性能的影响；（vi）研究MXene表面如何被化学官能化，并了解这种官能化对上述性能的影响；（vii）自旋涂覆MXene薄膜，并测量其光学和输运性能。这项工作为学生提供了令人兴奋的研究机会-本科生将接受最先进设备的培训，研究生将努力获得博士学位。

NON-TECHNICAL SUMMARY: Atomically thin two-dimensional (2D) materials have unique properties compared to their conventional three-dimensional counterparts. Graphene, which is a single atomic layer of carbon, is the most illustrious and studied of these newly emerging 2D materials. Graphene, however, is limited to just one element - carbon. Recently, a new family of 2D early transition metal (e.g. titanium, vanadium, niobium, etc.) carbides and carbonitrides (so called MXene) was reported. These 2D materials offer a large variety of chemical compositions compared to graphene and they can exist in different numbers of atomic layers. MXenes may have a wide range of potential applications, ranging from composite reinforcements, to industrial catalysts, to energy storage and electronic devices. Before the best application can be identified, however, the fundamental physics of these materials must be developed and the synthesis-structure-property relationships must be established. Combined experimental and theoretical work will be used to understand the surface chemistry, structure and properties of MXenes compounds. This work could result in batteries that charge in minutes for thousands of cycles or robust supercapacitors that can be used for very high power energy storage applications such as regenerative breaking in cars. TECHNICAL DETAILS: Recently, a new family of 2D early transition metal (e.g. titanium, vanadium, niobium, etc.) carbides and carbonitrides (so called MXene) was discovered. The latter offer a large variety of chemical compositions, as multiple atoms can co-exist in the 2D sheets. Furthermore MXenes exist in 3, 5 or 7 atomic layers. The as-synthesized MXene surfaces are functionalized with OH, O, and/or F. Theoretical calculations predict that the MXenes can be either conductors or semiconductors depending on their surface chemistry. MXenes may have a wide range of potential applications, ranging from composite reinforcements, to industrial catalysts, to energy storage and electronic devices. Since this class of solids is quite new, the fundamental basic science of these materials must be developed and their synthesis-structure-property relationships need to be established. The aims of this project are: (i) isolate single MXene layers on different substrates, (ii) determine whether these layers have attractive electronic properties like graphene and could thus be used as transistors, (iii) measure the electrical and optical characteristics of these films, as a function of surface terminations and MXene chemistry, (iv) disperse the 2D sheets in various solvents, including water, and form stable suspensions, (v) use various spectroscopy techniques to investigate MXene surfaces and correlate them to theoretical first principles calculations to fully understand the surface chemistry and its effect on properties, (vi) investigate how MXene surfaces can be chemically functionalized and understand the effects of such functionalization on the aforementioned properties, and (vii) spin-coat MXene thin films and measure their optical and transport properties. This work offers exciting research opportunities for students - undergraduate students will be trained on state of the art equipment and graduate students will work towards their doctorates.