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类型 基础研究 预答辩日期 2018-01-12
开始(开题)日期 2016-09-12 论文结束日期 2017-11-27
地点 田家炳楼南楼205 论文选题来源 国家自然科学基金项目     论文字数 5.4 (万字)
题目 二维材料表面功能化与设计的多尺度模拟
主题词 二维材料,表面功能化,分子自组装,面外铁电,多尺度模拟
摘要 自石墨被剥离成石墨烯后,原子厚度的二维材料便成为了一个新兴学科并且在许多领域展示出了光明的应用前景。尽管二维材料有着诱人的前景,然而在其走向实际应用的过程中却遇到了一些严峻问题,例如黑磷的环境不稳定性、二硫化钼的表面惰性以及二维面外铁电材料的稀有性等等。这些问题制约着它们进一步的应用,但同时也给研究者们带来了新的挑战与机遇。由于二维材料具有较大表面比,因此合理的表面功能化与设计被公认是克服二维材料所存在问题并提升二维材料在诸多实际应用中性能的重要策略。本论文通过使用多尺度模拟,从如下两方面出发探究了二维材料的表面功能化与设计:1)理解通过表面自组装来实现类石墨烯材料功能化的内在机制;2)提供一些合理的表面功能化与设计方案来解决二维材料所面临的一些严峻问题。本论文的主要研究内容包括以下几个方面: 1)分子在石墨烯上自组装内在机制的理论研究。分子在石墨烯上的自组装已经成为实现石墨烯功能化的一个有效方法,然而自组装的动态机制仍然不清楚。在这里通过运用分子动力学模拟,我们成功可视化了有机分子在石墨烯表面从无序到有序的过程。在此基础上,我们发现从无序到有序的内在驱动力是分子与分子间的相互的作用。更具体地说,对于非极性体系而言分子与分子间的范德华相互作用起着决定性作用,而对于极性体系而言分子与分子间的范德华和库伦相互作用都是决定性因素。分子与石墨烯的相互作用则决定分子在石墨烯上的取向(包括面内和面外取向)。我们还发现分子间氢键在自组装过程中起到了非常积极的作用,包括扩大成核区间、提升稳态到亚稳态临界温度以及提升成核速度。另外,我们也很好地解释了实验上观测到的分子在石墨烯表面自限外延生长的现象,分子层间相互作用的能量梯度是自限外延生长的本质原因。 2)利用表面自组装有机薄膜提升黑磷环境稳定性。由于具有高载流子迁移率以及可调控带隙等优越性质,黑磷在近几年已经吸引了人们的广泛注意。然而由于氧气以及水的共同作用,黑磷在环境中将会被快速腐蚀掉,这一严重问题极大制约了黑磷的实际应用。在这个工作中,通过使用多尺度理论模拟,我们证实有机分子在黑磷上形成的自组装有机薄膜能够有效保护黑磷。我们以PTCDA分子为例(一种具有强自组装能力的有机分子)证实,在黑磷上的PTCDA分子之间能够依靠强的氢键进行自组装结合,同时PTCDA分子与黑磷没有发生化学反应。两者之间通过弱相互作用进行结合,并且PTCDA分子不会破坏黑磷原有的电子结构。然后,我们表明PTCDA薄膜厚度达到约2纳米便能够起到使黑磷与外界氧气和水隔绝的作用,进而起到保护黑磷的效果。 3)通过表面自组装提升二硫化钼表面析氢活性。发展廉价的电解水催化剂是未来实现可持续能源供应的关键一步。二硫化钼作为一个潜在的廉价电化学析氢反应催化剂已经吸引了大量的研究兴趣。然而二硫化钼的析氢位点仅仅位于边界,它大面积的表面则是惰性的。在这个工作中,我们证实有机分子在二硫化钼表面的自组装可以作为一种简单、有效且无破坏性的方法来开发二硫化钼惰性的表面。首先,有机分子能够不破坏二硫化钼自身稳定性和结构。其次,有机分子的引入可以明显增加体系的催化活性位点,并且有机分子在二硫化钼表面可以具有很好的水稳定性。值得一提的是,通过简单的液相沉积技术便能够很好地实现有机分子在二硫化钼表面的自组装。此外,我们证实表面自组装还可以被用来制备双功能电催化剂。 (4)表面空缺诱导三碘化铬的铁磁增强与面外铁电。原子厚度的具有面外极化的二维铁电材料在当前是迫切需求的,源于它的稀有性以及其在数据存储和纳米电子器件中的重要作用。作为实验上证实的最薄铁磁材料,单层三碘化铬为二维材料在纳米级自旋电子器件中的应用打开了新的大门。通过系统的第一性原理计算,我们发现碘原子空缺会在三碘化铬中诱导出面外铁电,并且碘原子空缺还会略微增强三碘化铬的铁磁性。因此,带有碘空缺的三碘化铬是一个内禀铁磁和面外铁电共存的多铁材料。通过卤原子空缺来诱导面外铁电的策略也适用于许多其它过渡金属三卤族化合物。
英文题目 MULTISCALE SIMULATIONS ON SURFACE FUNCTIONALIZATION AND DESIGN OF TWO-DIMENSIONAL MATERIALS
英文主题词 2D materials, surface functionalization, molecular self-assembly, out-of-plane ferroelectricity, multiscale simulations
英文摘要 Since graphite was exfoliated into graphene, atom-thick two-dimensional (2D) materials have emerged as a new frontier and showed a bright prospect in various fields. Although 2D materials own attractive properties, they suffer from some serious problems for the practical application, such as the ambient instability of black phosphorus (BP), the inert basal plane of MoS2, and the rarity of 2D ferroelectric materials with out-of-plane polarization. Owing to the large ratio surface, rational surface functionalization and design are well known as an important strategy toward removing the existing problems. The motivation of this thesis is to theoretically explore the surface functionalization and design of 2D materials from two aspects: i) understanding the intrinsic mechanisms on the functionalization of graphene-like materials via surface self-assembly; and ii) providing some rational designs for better solutions to some problems 2D materials are facing. The main conclusions are summarized as follows: (1) Theoretical investigation on the intrinsic mechanisms of molecular self-assembly on graphene. Molecular self-assembly on graphene has been regarded as an effective method toward achieving the functionalization of graphene in experiment, whereas the dynamic mechanism of the self-assembly remains elusive. Here, we visualize the nanoscale self-assembly of organic molecules on graphene from disorder to order via molecular dynamics (MD) simulation. It is revealed that the assembly toward 2D ordered structures is driven by the molecule-molecule interaction, that is, the van der Waals (vdW) interaction in nonpolar systems and the vdW and Coulomb interactions in polar systems that are the decisive factors for the formation of the 2D ordering. The role of the substrate is mainly governing the array orientation of the adsorbates. Also, we unveil that intermolecular H-bonds can considerably widen the nucleation area, heighten the stability-metastability critical temperature, and promote the nucleation speed. An interesting phenomenon, self-limited growth of organic molecules on graphene, is well explained. It is found that the gradient of interlayer interactions is responsible for the self-limited growth. (2) Passivation of black phosphorus via self-assembled organic monolayers. In recent years, BP has attracted rapidly growing attention for potential applications in electronic devices because of its high carrier mobility and sizable bandgap. However, the fast degradation of BP in ambient conditions, arising from the concurrence of oxygen and water, hinders its practical application severely. Based on multi-scale simulations, an effective passivation approach (self-assembly of organic monolayers on BP via vdW epitaxy) to protect BP from degradation is proposed. We take PTCDA (an organic molecule that has strong self-assembly capacity) as an example. It is found that the self-assembly of on-BP PTCDA molecules depends on H-bond interaction. On-BP PTCDA does not react with BP and their combination is dominated by the intermolecular weak interaction. PTCDA molecules on BP also do not break the original electronic properties of BP. Meanwhile, PTCDA monolayers can well isolate BP from the ambient O2 and H2O molecules when its thickness amounts to about 2 nm. (3) Exploitation of the large-area basal plane of MoS2 through on-surface self-assembly. The development of nonprecious electrochemical catalysts for water splitting is a key step to achieve a sustainable energy supply for the future. Molybdenum disulfide (MoS2) has been extensively studied as a promising low-cost catalyst for hydrogen evolution reaction (HER), whereas HER is only catalyzed at the edge for pristine MoS2, leaving a large area of basal plane useless. Herein, on-surface self-assembly is demonstrated to be an effective, facile, and damage-free method to take full advantage of the large ratio surface of MoS2 for HER. On-surface self-assembly will not break the structure and stability of MoS2 and can increase the active sites on surface. On-MoS2 self-assembled monolayers own good water stability and can be obtained through a simple liquid-deposition method. Moreover, on-surface self-assembly provides potential application for bifunctional electrocatalysts. (4) Halogen vacancy-induced enhanced ferromagnetism and out-of-plane ferroelectricity in monolayer chromium triiodide. Atom-thick 2D ferroelectric materials with out-of-plane polarization are now urgently needed for their rarity and important roles in data storage and nanoelectronic devices. Monolayer chromium triiodide (CrI3), as the thinnest ferromagnetic material demonstrated in experiment, opens up new opportunities for the application of 2D materials in spintronic nanodevices. Herein, we identify that I vacancy not only induces out-of-plane ferroelectricity in monolayer CrI3 but also enhances the ferromagnetism of CrI3, using density functional theory calculations. The co-existence of intrinsic ferromagnetism and out-of-plane ferroelectricity makes monolayer CrI3 with I vacancies a desirable atom-thick 2D multiferroic material. The strategy to achieve 2D ferroelectricity via halogen vacancy also applies to many other metal trihalide materials.
学术讨论
主办单位时间地点报告人报告主题
物理学院 2017-11-01 田家炳楼南203室 赵英鹤 Ferromagnetism, Antiferromagnetism, Half-Metal in Metal Trihalide Nanowires
物理学院 2017-05-24 田家炳楼南203室 赵英鹤 Room-Temperature Antiferromagnetism in Two-Dimensional MgMnGe with Tunable, Large Magnetoresistance
物理学院 2017-04-13 田家炳楼南203室 赵英鹤 Computational High-Throughput Screening
物理学院 2017-03-31 田家炳楼南203室 赵英鹤 Molecular Self-Assembly on MoS2: a Promising Strategy to Activate the Inert Basal Plane of MoS2
物理学院 2016-10-12 田家炳楼南203室 赵英鹤 Two-Dimensional Self-Assembled Organic Monolayer: a Promising Strategy toward Hydrogen Evolution
物理学院 2017-11-08 田家炳楼南203室 胡培君 What Can We Learn from DFT Calculations in Heterogeneous Catalysis
物理学院 2017-11-01 田家炳楼南205室 吴梦昊 二维铁电/多铁的第一性原理设计
物理学院 2017-09-25 田家炳楼南203室 Ping Yang Interfacial interactions between nanoclusters and surface ligands
     
学术会议
会议名称时间地点本人报告本人报告题目
东南大学物理学院第三届研究生学术论坛 2017.10.11-2017.10.11 东南大学物理学院 Molecular Self-Assembly on Two-Dimensional Atomic Crystals
International Conference on Advances in functional Materials 2017.08.14-2016.08.17 University of California, Los Angeles, USA Molecular Self-Assembly on Two-Dimensional Atomic Crystals
The 15th International Congress of Quantum Chemistry Satellite Meeting 2015.06.14-2015.06.17 中国科学技术大学 The growth mechanism of two-dimensional molecular crystals on van der Waals substrates
     
代表作
论文名称
Molecular Self-Assembly on Two-Dimensional Atomic Crystals: Insights from Molecular Dynamics Simulat
Passivation of Black Phosphorus via Self-Assembled Organic Monolayers by van der Waals Epitaxy
How To Obtain High-Quality and High-Stability Interfacial Organic Layer: Insights from the PTCDA Sel
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
马晶 正高 教授 博导 南京大学
宋凤麒 正高 教授 博导 南京大学
阚二军 正高 教授 博导 南京理工大学
孙立涛 正高 教授 博导 东南大学
杨永宏 正高 教授 博导 东南大学
陈乾 副高 硕导 东南大学 秘书
      
答辩秘书信息
姓名职称工作单位备注
陈乾 副高 高工 东南大学