【作者】 张琪；

【导师】 焦丽颖；

【作者基本信息】 清华大学 ， 化学， 2019， 博士

【摘要】 二维过渡金属硫族化合物（Transistion Metal Chalcogenides,TMCs）具有超薄的平面结构、丰富的元素组成和性质,为未来集成电路的构建提供了可选择的新材料。二维材料作为结构基元经过面内拼接或层层堆叠形成异质/相结构,此类结构蕴含着新奇的物理现象,可用于构筑新功能器件,为解决二维器件加工和实用化所面临的问题提供新思路。然而,二维异质/相结构的构筑与器件研究还面临诸多挑战,主要包括:如何在原子尺度上通过化学手段精确控制不同组分的排布,二维异质/相结构的组成、堆垛方式对电学输运性质有哪些有影响,如何通过设计制备异质/相材料来优化器件性能、实现二维晶体电子器件的无损加工与集成等。针对这一领域的关键科学问题,本论文以建立二维晶体异质/相结构的化学构筑方法为突破口,重点关注二维异质/相结构的组成、结构与其能带结构及性质的关联,在此基础上研究基于二维异质/相结构的器件制备与性能优化,提出了器件制备新策略并实现了二维晶体电子器件的初步集成。本论文包括以下三个部分:1.二维MoS₂/WS₂异质结构的控制合成与性质研究:针对生长过程中由于熵效应驱动易形成合金的挑战,发展了以WO_3-x/MoO_3-x核壳结构纳米线为前驱体制备MoS₂/WS₂异质结构的合成策略;系统地研究了二维MoS₂/WS₂异质结的结构、组成及性质间的关系;基于MoS₂/WS₂层间异质结的场效应晶体管性能优于单一组分,展示了异质结材料体系用于制备高性能器件的潜力。2.二维1T’/2H MoTe₂异相结构的图案化制备与性质研究:针对热力学亚稳定相的合成难点,发展了以MoO_2.0-2.5和MoO₃为前驱体通过控制缺陷密度来实现2H-MoTe₂和1T’-MoTe₂薄膜原位生长的方法;利用光刻技术图案化前驱体实现了1T’/2H MoTe₂异相结构的图案化生长,为集成电路的构建提供了图案化的金属性和半导体性的超薄单元,展示了异相结构用于构筑全二维器件的可行性。3.全二维器件的制备与集成方法研究:针对目前二维器件加工过程存在的材料损伤、接触不良及器件集成等问题,提出了材料合成与器件集成一体化的器件制备新策略,即通过一步化学反应完成沟道、接触、互连各部分材料的图案化制备,实现了二维器件的无损加工与集成;以MoTe₂为核心材料制备了一系列高性能的原型器件:场效应晶体管、反相器、频率可调制的射频晶体管阵列、超短栅极晶体管、互连的多层器件和柔性器件等,展示了此策略用于构建未来集成电路的前景。更多还原

【Abstract】 Two-dimensional（2D）transition metal chalcogenides（TMCs）atomic crystals have emerged as promising building blocks for creating functional architectures and devices due to their diverse compositions and unique properties.2D heterostructures and hetero-phase structures composed of TMCs exhibit new physical phenomena and unique electrical properties,and therefore,have great potential for the applications in future nanoelectronics and optoelectronics.However,the studies on 2D heterostrccutres are still at the infant stage and there exist many challenges in electronic-grade 2D heteromaterials processing,such as precisely controlled synthesis of the heteromaterials at atomic scale,the structure-property relationship,the nondestructive construction of high-performance device and integrated circuits and so on.Here,we explored chemical methods for synthesizing 2D heterostructures and hetero-phase structures based on TMCs by the rational design of precursors.We investigated the relationship between composition,structure and properties in these 2D heterostructures and hetero-phase structures and explored possible approaches for tuning the band structure of these materials.We characterized the electrical properties of these 2D heterostructures and hetero-phase structures for fabricating high performance field effect devices.We proposed a nondestructive approach for constructing 2D electronic devices in which the 2D electronic components in the active layer are chemically synthesized and integrated simultaneously in a single step.The main contents are as the following three parts:1.Controlled synthesis and properties of 2D MoS₂/WS₂ heterostructuresThe major challenge in the growth of MoS₂/WS₂ heterostructures is the sequential supply of Moand W to avoid the formation of the alloys.To address this,we developd a novel approach for synthesizing MoS₂/WS₂ heterostructures via chemical vapor deposition（CVD）by using core-shell WO_3-x/MoO_3-xnanowires as growth precursor,which naturally ensures the sequential growth of MoS₂ and WS₂.We investigated the relationship between composition,structure and properties in these 2D heterostructures via various high-precision characterizations and measurements.The obtained heterostructures exhibited high crystallinity,strong interlayer interaction,and high mobility,suggesting their promising applications in nanoelectronics.2.Controlled patterned synthesis of 2D 1T’/2H MoTe₂hetero-phase structuresWe proposed a new method for preparing 2H/1T’MoTe₂ hetero-phase structures via CVD by tuning the defects densities in the productions.As the thin film precursors for the phase-selective growth of MoTe₂ can be patterned into desired architectures via standard lithographic processes,we achieved the simultaneous growth of 2H and 1T’MoTe₂ into predesigned patterns.The interface of the two phases was connected seamlessly with atomically sharp boundaries,suggesting that the two phases were connected via covalent bonds.The hetero-phase structures can potentially serve as semiconducting channels and metallic electrodes and interconnects to create functional devices.3.Construction and integration of all 2D devicesWe presented a nondestructive approach for constructing 2D electronic devices in which the 2D electronic components in the active layer are chemically synthesized and integrated simultaneously in a single step and each component is connected via covalent bonds instead of physical interfaces.As a proof of the concept,we synthesized FETs and arrays of logic devices with high performance through the phase-patterned growth of ultrathin atomic layers.We also explored the construction of FETs with ultrashort gate length,multilayered FETs with vertical interconnections and flexible devices with our approach.This approach makes the design and optimization of electronic devices based on 2D materials much more flexible and preserves the intrinsic performance of the materials to the largest extent and therefore,provides a new route for constructing nanoelectronic circuits.更多还原