Structure and composition of interfaces between 2D materials and dielectric substrates

二维(2D)材料丰富而激动人心的电子和机械性能激发了后硅纳米电子学的新想法。其中一些影响最深远的问题涉及到在现代场效应晶体管(FET)中用2D材料取代硅的可能性，以及在下一代存储器和神经形态计算芯片中的应用。这些应用的成功依赖于解决与2D材料与栅电介质或金属电极之间的界面缺陷相关的材料问题。例如，记忆器件的三明治结构通常由绝缘有源层(如过渡金属氧化物(TMOS))、2D材料(石墨烯、MoS_2)和顶/底金属电极组成。该项目将利用硬X射线光电子能谱(HAXPES)将此类界面的理论模型与其性质的实验研究结合起来。对MoS_2和WSe_2等二维材料与SiO_2、HfO_2和CaF_2绝缘层的界面进行了理论模拟，分析了这些系统的实验HAXPES谱，并研究了界面上点缺陷的性质。在钻石和其他设施进行的HAXPES测量将帮助我们阐明沉积和吸附对界面化学成分的影响。使用原子模拟和密度泛函理论计算的理论计算应该使我们能够识别界面缺陷以及界面附近的氧化物缺陷，并将它们与与FET和氧化物电阻开关机制有关的可靠性问题联系起来。

The rich and exciting electronic and mechanical properties of two-dimensional (2D) materials have inspired novel ideas for post-silicon nanoelectronics. Some of the most far-reaching of them concern the possible substitution of Si with 2D materials in modern field-effect transistors (FETs) and applications in next-generation memory and neuromorphic computing chips. Success of these applications relies on solving the materials problems related to defects at interfaces between 2D materials and gate dielectrics or metal electrodes. For example, the sandwich structure of memristive devices is usually composed of an insulating active layer (e.g., transition metal oxides (TMOs)), 2D material (graphene, MoS2) and top/bottom metal electrodes. This project will combine theoretical modelling of such interfaces with experimental investigations of their properties using hard x-ray photoelectron spectroscopy (HAXPES). Theoretical simulations of interfaces of 2D materials, such as MoS2 and WSe2, with SiO2, HfO2 and CaF2 insulating layers will be used to analyse the experimental HAXPES spectra of these systems and study the properties of point defects at interfaces. HAXPES measurements at DIAMOND and other facilities will help us to elucidate the effects of deposition and adsorbates on the chemical composition of interfaces. Theoretical calculations using both atomistic simulations and density functional theory calculations should allow us to identify interface defects as well as oxide defects near interfaces and relate them to reliability issues pertaining to FETs and mechanisms of resistive switching of oxides.