二维过渡金属硫族材料原子尺度的缺陷结构与物性关联研究

         二维过渡金属硫族化合物（transition metal dichalcogenides, TMDs）作为近年来热门的一类二维材料，由于其众多的结构多型体和丰富的物理性质，不仅为探索奇异的物理现象提供了理想的平台，也为下一代高集成电学、光学器件的研发奠定了坚实的材料基础。在原子尺度上理解二维材料的构效关系，是深入理解其理化性质，推动器件研发的关键，另外还能够指导材料设计，通过结构调控实现材料物性转变或者性能提升。比如，基于对缺陷的结构和浓度调控，能够实现对二维材料载流子浓度、光学带隙、偶极矩等的连续调节。本文中，我们利用自上而下的电子束、离子束调控和自下而上的化学生长，在二维TMDs中创造了几种不同类型和浓度的新奇缺陷结构。借助球差校正的低电压扫描透射电子显微镜（low voltage scanning transmission electron microscopy, LVSTEM）、冷冻透射电子显微镜（cryogenic transmission electron microscopy, Cryo-TEM），电子能量损失谱等工具精确解析了这些缺陷结构的存在形式、成分结构与动态演变过程。使用原子力显微镜（Atomic Force Microscope, AFM）和电学输运测量，并结合第一性原理计算和分子动力学模拟，揭示它们与电学输运和力学断裂行为等物性的关联性。论文的主要研究内容如下：

        （1）使用电子束辐照在单层WSe₂中引入分散的Se₂垂直双空位，进一步通过调控扫描电子束的剂量和辐照方式，激发Se₂双空位缺陷产生动态演变，逐渐演化成为高密度的十元、十二元、十四元和十六元孔缺陷网络。对比其他单层三棱柱构型的TMDs材料，同样的实验条件，单层WS₂, MoSe₂和MoS₂只能产生S原子或者Se原子不足的线缺陷。结合原子尺度的结构演变追踪和密度泛函理论计算发现，潜在的原子尺度演变优先形成降低体系总能量的缺陷结构，从缺陷形成能的角度解释了电子束辐照下不同缺陷形成的物理机制。

        （2）使用氦离子和镓离子束刻蚀技术，在单层MoS₂中选择性地产生了S和MoS_n点缺陷，基于AFM的纳米压痕测试显示，这两者都降低了单层材料的刚性，但增强了其断裂韧性。通过LVSTEM监测材料断裂前后的原子结构发现，不同类型的点缺陷导致单层MoS₂出现不同的断裂行为，产生有区别的裂纹原子结构。基于实验条件的分子动力学模拟，揭示了S和MoS_n点缺陷在断裂过程中的关键作用。断裂韧性增强的起源，可以归结于点缺陷引起的裂纹偏转和分叉提高了断裂能量释放率，并且裂纹与点缺陷的融合会形成宽化的裂纹尖端，进一步钝化裂纹的扩展。

        （3）通过化学气相沉积（chemical vapor deposition, CVD）方法，在单双层MoS₂中引入高浓度替位掺杂的钒（V）原子。电学输运测量发现，掺V的单层和双层MoS₂器件分别表现出双极性和重p型场效应特性，而原始的单层和双层MoS₂器件显示出类似的n型电学输运行为。此外，相比于原始的单层、双层和掺杂后的单层MoS₂器件，掺杂双层MoS₂器件的电导率显著增强。为了研究导电性增强的起源，我们使用LVSTEM在原子尺度上精确测绘单双层V掺杂MoS₂的原子结构，确立单双层样品中V原子替位掺杂的浓度和排布规律。结合第一性原理计算，揭示了掺杂双层样品导电性的惊人提升，源于掺杂V原子激活了相邻层之间的S-3p_z轨道，形成层间杂化相关的导电网络。

        （4）使用最先进的像差校正Cryo-TEM结合直接探测电子计数相机，我们在远低于电荷密度波（charge density wave, CDW）超晶格损伤阈值（3000 e^- Å^-2）的条件下，研究了1T-TaS₂公度的CDW超结构在面内和面外的排布。这种大卫星图案状的超结构可以被视作一种特殊的面内缺陷，最近研究发现它们的堆叠构型与轨道序交织，对体结构物性具有不可分割的影响，但是目前人们对CDW的三维堆叠结构知之甚少。本论文中我们通过分析受调制Ta原子的相位强度变化，并提取CDW相关的相位信号，从而透视出1T-TaS₂体结构中CDW的堆叠情况。最终揭示了三维CDW形成于三种垂直CDW堆叠构型的局部混合，呈现出多畴交织共存的状态。

[1] NOVOSELOV K S, GEIM A K, MOROZOV S V, et al. Electric field effect in atomically thin carbon films[J]. Science, 2004, 306: 666-669.
[2] GEIM A K. Graphene: Status and Prospects[J]. Science, 2009, 324: 1530-1534.
[3] ZHANG Y, TAN Y W, STORMER H L, et al. Experimental observation of the quantum Hall effect and Berry’s phase in graphene[J]. Nature, 2005, 438: 201-204.
[4] NOVOSELOV K S, GEIM A K, MOROZOV S V, et al. Two-dimensional gas of massless Dirac fermions in graphene[J]. Nature, 2005, 438: 197-200.
[5] HAN W Q, WU L, ZHU Y, et al. Structure of chemically derived mono- and few-atomic-layer boron nitride sheets[J]. Applied Physics Letters, 2008, 93: 1-4.
[6] NAG A, RAIDONGIA K, HEMBRAM K P S S, et al. Graphene analogues of BN: Novel synthesis and properties[J]. ACS Nano, 2010, 4: 1539-1544.
[7] JIN C, LIN F, SUENAGA K, et al. Fabrication of a freestanding boron nitride single layer and Its defect assignments[J]. Physical Review Letters, 2009, 102: 3-6.
[8] MEYER J C, CHUVILIN A, ALGARA-SILLER G, et al. Selective sputtering and atomic resolution imaging of atomically thin boron nitride membranes[J]. Nano Letters, 2009, 9: 2683-2689.
[9] MA W, LU J, WAN B, et al. Piezoelectricity in multilayer black phosphorus for piezotronics and nanogenerators[J]. Advanced Materials, 2020, 32: 1-9.
[10] CHEN C, LU X, DENG B, et al. Widely tunable mid-infrared light emission in thin-film black phosphorus[J]. Science Advances, 2020, 6: 1-8.
[11] ZHAO S, WANG E, ÜZER E A, et al. Anisotropic moiré optical transitions in twisted monolayer/bilayer phosphorene heterostructures[J]. Nature Communications, 2021, 12: 3947.
[12] LIU Z, SUN Y, CAO H, et al. Unzipping of black phosphorus to form zigzag-phosphorene nanobelts[J]. Nature Communications, 2020, 11: 1-10.
[13] RADISAVLJEVIC B, RADENOVIC A, BRIVIO J, et al. Single-layer MoS2 transistors[J]. Nature Nanotechnology, 2011, 6: 147-150.
[14] YIN Z, LI H, LI H, et al. Single-layer MoS2 phototransistors[J]. ACS Nano, 2012, 6: 74-80.
[15] YE G, GONG Y, LIN J, et al. Defects engineered monolayer MoS2 for improved hydrogen evolution reaction[J]. Nano Letters, 2016, 16: 1097-1103.
[16] ZHAO W, GHORANNEVIS Z, CHU L, et al. Evolution of electronic structure in atomically thin sheets of WS2 and WSe2[J]. ACS Nano, 2013, 7: 791-797.
[17] LIU W, KANG J, SARKAR D, et al. Role of metal contacts in designing high-performance monolayer n-type WSe2 field effect transistors[J]. Nano Letters, 2013, 13: 1983-1990.
[18] GENG D, YANG H Y. Recent advances in growth of novel 2D materials: beyond graphene and transition metal dichalcogenides[J]. Advanced Materials, 2018: 1800865.
[19] VOIRY D, MOHITE A, CHHOWALLA M. Phase engineering of transition metal dichalcogenides[J]. Chemical Society Reviews, 2015, 44: 2702-2712.
[20] MIRÕ P, GHORBANI-ASL M, HEINE T. Two dimensional materials beyond MoS2: Noble-transition-metal dichalcogenides[J]. Angewandte Chemie - International Edition, 2014, 53: 3015-3018.
[21] JARIWALA D, SANGWAN V K, LAUHON L J, et al. Emerging device applications for semiconducting two-dimensional transition metal dichalcogenides[J]. ACS Nano, 2014, 8: 1102-1120.
[22] CHHOWALLA M, JENA D, ZHANG H. Two-dimensional semiconductors for transistors[J]. Nature Reviews Materials, 2016, 1: 16052.
[23] JEONG Y, PARK J H, AHN J, et al. 2D MoSe2 Transistor with polymer-brush/channel interface[J]. Advanced Materials Interfaces, 2018, 5: 1800812.
[24] LIN Y chang, KOMSA H pekka, YEH C hui, et al. Single-layer ReS2 : Two-dimensional semiconductor with tunable in-plane anisotropy[J]. ACS Nano, 2015, 9: 11249-11257.
[25] LIU F, ZHENG S, HE X, et al. Highly sensitive detection of polarized light using anisotropic 2D ReS2[J]. Advanced Functional Materials, 2016, 26: 1169-1177.
[26] ZHANG E, JIN Y, YUAN X, et al. ReS2-based field-effect transistors and photodetectors[J]. Advanced Functional Materials, 2015, 25: 4076-4082.
[27] AIVAZIAN G, GONG Z, JONES A M, et al. Magnetic control of valley pseudospin in monolayer WSe2[J]. Nature Physics, 2015, 11: 148-152.
[28] ZHOU J, SHI J, ZENG Q, et al. InSe monolayer: synthesis, structure and ultra-high second-harmonic generation[J]. 2D Materials, 2018, 5: 025019.
[29] BHANDAVAT R, DAVID L, SINGH G. Synthesis of surface-functionalized WS2 nanosheets and performance as Li-ion battery anodes[J]. The Journal of Physical Chemistry Letters, 2012, 3: 1523-1530.
[30] CHANG K, CHEN W. L-Cysteine-assisted synthesis of layered MoS2/graphene composites with excellent electrochemical performances for Lithium ion batteries[J]. ACS Nano, 2011, 5: 4720-4728.
[31] HEIRANIAN M, FARIMANI A B, ALURU N R. Water desalination with a single-layer MoS2 nanopore[J]. Nature Communications, 2015, 6: 1-6.
[32] YANG Y, YANG X, LIANG L, et al. Large-area graphene-nanomesh/carbon-nanotube hybrid membranes for ionic and molecular nanofiltration[J]. Science, 2019, 364: 1057-1062.
[33] LI W, YANG Y, WEBER J K, et al. Tunable, strain-controlled nanoporous MoS2 filter for water desalination[J]. ACS Nano, 2016, 10: 1829-1835.
[34] GUPTA A, RAWAL T B, NEAL C J, et al. Molybdenum disulfide for ultra-low detection of free radicals: electrochemical response and molecular modeling[J]. 2D Materials, 2017, 4: 025077.
[35] PRASAI D, TUBERQUIA J C, HARL R R, et al. Graphene: corrosion-inhibiting coating[J]. ACS Nano, 2012, 6: 1102-1108.
[36] YANG J, WANG Y, LAGOS M J, et al. Single atomic vacancy catalysis[J]. ACS Nano, 2019, 13: 9958-9964.
[37] WEI Q, PENG X. Superior mechanical flexibility of phosphorene and few-layer black phosphorus[J]. Applied Physics Letters, 2014, 104: 251915.
[38] LU J M, ZHELIUK O, LEERMAKERS I, et al. Evidence for two-dimensional Ising superconductivity in gated MoS2[J]. Science, 2015, 350: 1353-1357.
[39] XI X, ZHAO L, WANG Z, et al. Strongly enhanced charge-density-wave order in monolayer NbSe2[J]. Nature Nanotechnology, 2015, 10: 765-769.
[40] KVASHNIN Y, VANGENNEP D, MITO M, et al. Coexistence of superconductivity and charge density waves in tantalum disulfide: experiment and theory[J]. Physical Review Letters, 2020, 125: 1-6.
[41] SOLUYANOV A A, GRESCH D, WANG Z, et al. Type-II Weyl semimetals[J]. Nature, 2015, 527: 495-498.
[42] ZHOU W, ZOU X, NAJMAEI S, et al. Intrinsic structural defects in monolayer molybdenum disulfide[J]. Nano Letters, 2013, 13: 2615-2622.
[43] RHODES D, CHAE S H, RIBEIRO-PALAU R, et al. Disorder in van der Waals heterostructures of 2D materials[J]. Nature Materials, 2019, 18: 541-549.
[44] MANZELI S, OVCHINNIKOV D, PASQUIER D, et al. 2D transition metal dichalcogenides[J]. Nature Reviews Materials, 2017, 2: 17033.
[45] MULLER D A, KOURKOUTIS L F, MURFITT M, et al. Atomic-scale chemical imaging of composition and bonding by aberration-corrected microscopy[J]. Science, 2008, 319: 1073-1076.
[46] NELLIST P D, CHISHOLM M F, DELLBY N, et al. Direct sub-angstrom imaging of a crystal lattice[J]. Science, 2004, 305: 1741-1741.
[47] BATSON P E, DELLBY N, KRIVANEK O L. Sub-ångstrom resolution using aberration corrected electron optics[J]. Nature, 2002, 418: 617-620.
[48] LIU X, HERSAM M C. Interface characterization and control of 2D materials and heterostructures[J]. Advanced Materials, 2018, 30: 1801586.
[49] HONG J, JIN C, YUAN J, et al. Atomic defects in two-dimensional materials: from single-atom spectroscopy to functionalities in opto-/electronics, nanomagnetism, and catalysis[J]. Advanced Materials, 2017, 29: 1606434.
[50] MENDES R G, PANG J, BACHMATIUK A, et al. Electron-driven in situ transmission electron microscopy of 2D transition metal dichalcogenides and their 2D heterostructures[J]. ACS Nano, 2019, 13: 978-995.
[51] DYCK O, ZIATDINOV M, LINGERFELT D B, et al. Atom-by-atom fabrication with electron beams[J]. Nature Reviews Materials, 2019, 4: 497-507.
[52] WILLIAMS D B, CARTER C B. The Transmission electron microscope[M]. Boston, MA: Springer US, 1996: 3-17.
[53] Corrected Electron Optical Systems, Inc. Residual aberrations of hexapole-type Cs-correctors[EB/OL].
[2021]. https://www.ceos-gmbh.de/de/produkte/residualsCEXCOR.[M].
[54] STEPHEN J. PENNYCOOK, PETER D. NELLIST. Scanning transmission electron microscopy: Vol. 21[M]. New York, NY: Springer New York, 2011.
[55] HARTEL P, ROSE H, DINGES C. Conditions and reasons for incoherent imaging in STEM[J]. Ultramicroscopy, 1996, 63: 93-114.
[56] CHEN Q, DWYER C, SHENG G, et al. Imaging beam-sensitive materials by electron microscopy[J]. Advanced Materials, 2020, 32: 1-42.
[57] KRETSCHMER S, LEHNERT T, KAISER U, et al. Formation of defects in two-dimensional MoS2 in the transmission electron microscope at electron energies below the knock-on threshold: the role of electronic excitations[J]. Nano Letters, 2020, 20: 2865-2870.
[58] KOMSA H P, KOTAKOSKI J, KURASCH S, et al. Two-dimensional transition metal dichalcogenides under electron irradiation: defect production and doping[J]. Physical Review Letters, 2012, 109: 035503.
[59] SUENAGA K, IIZUMI Y, OKAZAKI T. Single atom spectroscopy with reduced delocalization effect using a 30 kV-STEM[J]. The European Physical Journal Applied Physics, 2011, 54: 33508.
[60] BANHART F. Irradiation effects in carbon nanostructures[J]. Reports on Progress in Physics, 1999, 62: 1181-1221.
[61] ERNI R, ROSSELL M D, KISIELOWSKI C, et al. Atomic-resolution imaging with a sub-50-pm electron probe[J]. Physical Review Letters, 2009, 102: 1-4.
[62] LINCK M, HARTEL P, UHLEMANN S, et al. Chromatic aberration correction for atomic resolution TEM imaging from 20 to 80 kV[J]. Physical Review Letters, 2016, 117: 1-5.
[63] EGERTON R F. Choice of operating voltage for a transmission electron microscope[J]. Ultramicroscopy, 2014, 145: 85-93.
[64] LIN Z, CARVALHO B R, KAHN E, et al. Defect engineering of two-dimensional transition metal dichalcogenides[J]. 2D Materials, 2016, 3: 022002.
[65] LEE Y H, ZHANG X Q, ZHANG W, et al. Synthesis of large-area MoS2 atomic layers with chemical vapor deposition[J]. Advanced Materials, 2012, 24: 2320-2325.
[66] LIU K K, ZHANG W, LEE Y H, et al. Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates[J]. Nano Letters, 2012, 12: 1538-1544.
[67] LUO Y, ZHANG S, PAN H, et al. Unsaturated single atoms on monolayer transition metal dichalcogenides for ultrafast hydrogen evolution[J]. ACS Nano, 2020, 14: 767-776.
[68] ZHOU J, LIN J, SIMS H, et al. Synthesis of Co‐Doped MoS2 monolayers with enhanced valley splitting[J]. Advanced Materials, 2020, 32: 1906536.
[69] RAMASUBRAMANIAM A, NAVEH D. Mn-doped monolayer MoS2: An atomically thin dilute magnetic semiconductor[J]. Physical Review B, 2013, 87: 195201.
[70] MISHRA R, ZHOU W, PENNYCOOK S J, et al. Long-range ferromagnetic ordering in manganese-doped two-dimensional dichalcogenides[J]. Physical Review B, 2013, 88: 144409.
[71] CHENG Y C, ZHU Z Y, MI W B, et al. Prediction of two-dimensional diluted magnetic semiconductors: Doped monolayer MoS2[J]. Physical Review B, 2013, 87: 100401.
[72] YUN S J, DUONG D L, HA D M, et al. Ferromagnetic order at room temperature in monolayer WSe2 semiconductor via Vanadium dopant[J]. Advanced Science, 2020, 7: 1-6.
[73] YU P, LIN J, SUN L, et al. Metal-semiconductor phase-transition in WSe2(1-x)Te2x monolayer[J]. Advanced Materials, 2017, 29: 1603991.
[74] SUSARLA S, HACHTEL J A, YANG X, et al. Thermally induced 2D alloy-heterostructure transformation in quaternary alloys[J]. Advanced Materials, 2018, 30: 1-6.
[75] RASOOL H I, OPHUS C, ZHANG Z, et al. Conserved atomic bonding sequences and strain organization of graphene grain boundaries[J]. Nano Letters, 2014, 14: 7057-7063.
[76] LIN J, PANTELIDES S T, ZHOU W. Vacancy-induced formation and growth of inversion domains in transition-metal dichalcogenide monolayer[J]. ACS Nano, 2015, 9: 5189-5197.
[77] KOMSA H P, KURASCH S, LEHTINEN O, et al. From point to extended defects in two-dimensional MoS2: Evolution of atomic structure under electron irradiation[J]. Physical Review B, 2013, 88: 035301.
[78] HAN Y, HU T, LI R, et al. Stabilities and electronic properties of monolayer MoS2 with one or two sulfur line vacancy defects[J]. Physical Chemistry Chemical Physics, 2015, 17: 3813-3819.
[79] KIM K, LEE Z, REGAN W, et al. Grain boundary mapping in polycrystalline graphene[J]. ACS Nano, 2011, 5: 2142-2146.
[80] ZOU X, LIU Y, YAKOBSON B I. Predicting dislocations and grain boundaries in two-dimensional metal-disulfides from the first principles[J]. Nano Letters, 2013, 13: 253-258.
[81] GONG Y, LIN J, WANG X, et al. Vertical and in-plane heterostructures from WS2/MoS2 monolayers[J]. Nature Materials, 2014, 13: 1135-1142.
[82] ZAN R, RAMASSE Q M, JALIL R, et al. Control of radiation damage in MoS2 by graphene encapsulation[J]. ACS Nano, 2013, 7: 10167-10174.
[83] LIN J, CRETU O, ZHOU W, et al. Flexible metallic nanowires with self-adaptive contacts to semiconducting transition-metal dichalcogenide monolayers[J]. Nature Nanotechnology, 2014, 9: 436-442.
[84] KLEIN J, LORKE M, FLORIAN M, et al. Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation[J]. Nature Communications, 2019, 10: 2755.
[85] THIRURAMAN J P, MASIH DAS P, DRNDIĆ M. Irradiation of transition metal dichalcogenides using a focused ion beam: controlled single-atom defect creation[J]. Advanced Functional Materials, 2019, 29: 1-9.
[86] LIN J, FANG W, ZHOU W, et al. AC/AB stacking boundaries in bilayer graphene[J]. Nano Letters, 2013, 13: 3262-3268.
[87] LIU X, XU T, WU X, et al. Top-down fabrication of sub-nanometre semiconducting nanoribbons derived from molybdenum disulfide sheets[J]. Nature Communications, 2013, 4: 1-6.
[88] BREHM J A, LIN J, ZHOU J, et al. Electron-beam-induced synthesis of hexagonal 1H -MoSe2 from square β-FeSe decorated with Mo adatoms[J]. Nano Letters, 2018, 18: 2016-2020.
[89] MITTERREITER E, SCHULER B, SCHULER B, et al. Atomistic positioning of defects in Helium ion treated single-layer MoS2[J]. Nano Letters, 2020, 20: 4437-4444.
[90] FUJISAWA K, CARVALHO B R, ZHANG T, et al. Quantification and healing of defects in atomically thin Molybdenum disulfide: Beyond the controlled creation of atomic defects[J]. ACS Nano, 2021, 15: 9658-9669.
[91] ZHANG X, LIAO Q, KANG Z, et al. Hidden vacancy benefit in monolayer 2D semiconductors[J]. Advanced Materials, 2021, 33: 2007051.
[92] MANZANARES-NEGRO Y, LÓPEZ-POLÍN G, FUJISAWA K, et al. Confined crack propagation in MoS2 monolayers by creating atomic vacancies[J]. ACS Nano, 2021, 15: 1210-1216.
[93] LUNDSTROM M. Moore’s Law Forever?[J]. Science, 2003, 299: 210-211.
[94] DESAI S B, MADHVAPATHY S R, SACHID A B, et al. MoS2 transistors with 1-nanometer gate lengths[J]. Science, 2016, 354: 99-102.
[95] LI M Y, SU S K, WONG H S P, et al. How 2D semiconductors could extend Moore’s law[J]. Nature, 2019, 567: 169-170.
[96] PENG Q, DE S. Outstanding mechanical properties of monolayer MoS2 and its application in elastic energy storage[J]. Physical Chemistry Chemical Physics, 2013, 15: 19427-19437.
[97] JUNG G S, WANG S, QIN Z, et al. Interlocking friction governs the mechanical fracture of bilayer MoS2[J]. ACS Nano, 2018, 12: 3600-3608.
[98] WANG S, QIN Z, JUNG G S, et al. Atomically sharp crack tips in monolayer MoS2 and their enhanced toughness by vacancy defects[J]. ACS Nano, 2016, 10: 9831-9839.
[99] QIU H, XU T, WANG Z, et al. Hopping transport through defect-induced localized states in molybdenum disulphide[J]. Nature Communications, 2013, 4: 2642.
[100] KOMSA H P, KRASHENINNIKOV A V. Native defects in bulk and monolayer MoS2 from first principles[J]. Physical Review B - Condensed Matter and Materials Physics, 2015, 91: 125304.
[101] SINGH A, SINGH A K. Origin of n -type conductivity of monolayer MoS2[J]. Physical Review B, 2019, 99: 121201.
[102] ZHANG S, WANG C G, LI M Y, et al. Defect structure of localized excitons in a WSe2 monolayer[J]. Physical Review Letters, 2017, 119: 1-6.
[103] MITTERREITER E, SCHULER B, MICEVIC A, et al. The role of chalcogen vacancies for atomic defect emission in MoS2[J]. Nature Communications, 2021, 12: 3822.
[104] KRASHENINNIKOV A V., BANHART F. Engineering of nanostructured carbon materials with electron or ion beams[J]. Nature Materials, 2007: 723-733.
[105] LEHNERT T, GHORBANI-ASL M, KÖSTER J, et al. Electron-Beam-Driven structure evolution of single-layer MoTe2 for quantum devices[J]. ACS Applied Nano Materials, 2019, 2: 3262-3270.
[106] LEHTINEN O, KOMSA H P, PULKIN A, et al. Atomic scale microstructure and properties of se-deficient two-dimensional MoSe2[J]. ACS Nano, 2015, 9: 3274-3283.
[107] WANG S, LEE G Do, LEE S, et al. Detailed atomic reconstruction of extended line defects in monolayer MoS2[J]. ACS Nano, 2016, 10: 5419-5430.
[108] LEITER R, LI Y, KAISER U. In-situ formation and evolution of atomic defects in monolayer WSe2 under electron irradiation[J]. Nanotechnology, 2020, 31: 8.
[109] REIFSNYDER HICKEY D, YILMAZ D E, CHUBAROV M, et al. Formation of metal vacancy arrays in coalesced WS2 monolayer films[J]. 2D Materials, 2021, 8: 011003.
[110] LIN J, ZHANG Y, ZHOU W, et al. Structural flexibility and alloying in ultrathin transition-metal chalcogenide nanowires[J]. ACS Nano, 2016, 10: 2782-2790.
[111] LIN Y C, BJÖRKMAN T, KOMSA H P, et al. Three-fold rotational defects in two-dimensional transition metal dichalcogenides[J]. Nature Communications, 2015, 6: 1-6.
[112] RYU G H, FRANCE-LANORD A, WEN Y, et al. Atomic structure and dynamics of self-limiting sub-nanometer pores in monolayer WS2[J]. ACS Nano, 2018, 12: 11638-11647.
[113] WANG S, LI H, SAWADA H, et al. Atomic structure and formation mechanism of sub-nanometer pores in 2D monolayer MoS2[J]. Nanoscale, 2017, 9: 6417-6426.
[114] YOSHIMURA A, LAMPARSKI M, KHARCHE N, et al. First-principles simulation of local response in transition metal dichalcogenides under electron irradiation[J]. Nanoscale, 2018, 10: 2388-2397.
[115] YANG D, FAN X, ZHANG F, et al. Electronic and magnetic properties of defected monolayer WSe2 with vacancies[J]. Nanoscale Research Letters, 2019, 14: 192.
[116] IBERI V, LIANG L, IEVLEV A V, et al. Nanoforging single layer MoSe2 through defect engineering with focused Helium ion beams[J]. Scientific Reports, 2016, 6: 1-9.
[117] KLEIN J, KUC A, NOLINDER A, et al. Robust valley polarization of helium ion modified atomically thin MoS2[J]. 2D Materials, 2017, 5: 011007.
[118] THIRURAMAN J P, FUJISAWA K, DANDA G, et al. Angstrom-size defect creation and ionic transport through pores in single-layer MoS2[J]. Nano Letters, 2018, 18: 1651-1659.
[119] ZHOU J, LIN J, HUANG X, et al. A library of atomically thin metal chalcogenides[J]. Nature, 2018, 556: 355-359.
[120] KRESSE G, FURTHMÜLLER J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set[J]. Physical Review B, 1996, 54: 11169-11186.
[121] BLÖCHL P E. Projector augmented-wave method[J]. Physical Review B, 1994, 50: 17953-17979.
[122] PERDEW J P, BURKE K, ERNZERHOF M. Generalized gradient approximation made simple[J]. Physical Review Letters, 1996, 77: 3865-3868.
[123] GRIMME S, ANTONY J, EHRLICH S, et al. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu[J]. Journal of Chemical Physics, 2010, 132.
[124] RYU G H, FRANCE-LANORD A, WEN Y, et al. Atomic structure and dynamics of self-limiting sub-nanometer pores in monolayer WS2[J]. ACS Nano, 2018, 12: 11638-11647.
[125] SHIN D, WANG G, HAN M, et al. Preferential hole defect formation in monolayer WSe2 by electron-beam irradiation[J]. Physical Review Materials, 2021, 5: 044002.
[126] GHORBANI-ASL M, KRETSCHMER S, SPEAROT D E, et al. Two-dimensional MoS2 under ion irradiation: from controlled defect production to electronic structure engineering[J]. 2D Materials, 2017, 4: 025078.
[127] LI L, QIN Z, RIES L, et al. Role of sulfur vacancies and undercoordinated Mo regions in MoS2 nanosheets toward the evolution of hydrogen[J]. ACS Nano, 2019, 13: 6824-6834.
[128] JOSWIG J ole, LORENZ T, WENDUMU T B, et al. Optics, mechanics, and energetics of two-dimensional MoS2 nanostructures from a theoretical perspective[J]. Accounts of Chemical Research, 2015, 48: 48-55.
[129] BERTOLAZZI S, BRIVIO J, KIS A. Stretching and breaking of ultrathin MoS2[J]. ACS Nano, 2011, 5: 9703-9709.
[130] LY T H, ZHAO J, CICHOCKA M O, et al. Dynamical observations on the crack tip zone and stress corrosion of two-dimensional MoS2[J]. Nature Communications, 2017, 8: 14116.
[131] JUNG G S, WANG S, QIN Z, et al. Anisotropic fracture dynamics due to local lattice distortions[J]. ACS Nano, 2019, 13: 5693-5702.
[132] LIANG T, PHILLPOT S R, SINNOTT S B. Parametrization of a reactive many-body potential for Mo-S systems[J]. Physical Review B, 2009, 79: 245110.
[133] LIANG T, PHILLPOT S R, SINNOTT S B. Erratum: Parametrization of a reactive many-body potential for Mo-S systems [Phys. Rev. B 79, 245110 (2009)][J]. Physical Review B, 2012, 85: 199903.
[134] https://research.matse.psu.edu/sinnott/software[EB].
[135] CHEN W, KHAN U, FENG S, et al. High-fidelity transfer of 2D Bi2O2Se and its mechanical properties[J]. Advanced Functional Materials, 2020, 30: 1-8.
[136] LEE C, WEI X, KYSAR J W, et al. Measurement of the elastic properties and intrinsic strength of monolayer graphene[J]. Science, 2008, 321: 385-388.
[137] LIU K, YAN Q, CHEN M, et al. Elastic properties of chemical-vapor-deposited monolayer MoS2, WS2, and their bilayer heterostructures[J]. Nano Letters, 2014, 14: 5097-5103.
[138] RITCHIE R O. Mechanism of fatigue-crack propagation in ductile and brittle materials[J]. International Journal of Fracture, 1998, 100: 55-83.
[139] NATTERER F D, YANG K, PAUL W, et al. Reading and writing single-atom magnets[J]. Nature, 2017, 543: 226-228.
[140] GAMBARDELLA P, RUSPONI S, VERONESE M, et al. Giant magnetic anisotropy of single Cobalt atoms and nanoparticles[J]. Science, 2003, 300: 1130-1133.
[141] YANG K, PAUL W, NATTERER F D, et al. Tuning the exchange bias on a single atom from 1 mT to 10 T[J]. Physical Review Letters, 2019, 122: 227203.
[142] QIN Z, SONG X, WANG J, et al. Development of flexible paper substrate sensor based on 2D WS2 with S defects for room-temperature NH3 gas sensing[J]. Applied Surface Science, 2022, 573: 151535.
[143] CHOI W, KIM J, LEE E, et al. Asymmetric 2D MoS2 for scalable and high-performance piezoelectric sensors[J]. ACS Applied Materials & Interfaces, 2021, 13: 13596-13603.
[144] COCHRANE K A, LEE J H, KASTL C, et al. Spin-dependent vibronic response of a carbon radical ion in two-dimensional WS2[J]. Nature Communications, 2021, 12: 1-10.
[145] TSAI J Y, PAN J, LIN H, et al. Antisite defect qubits in monolayer transition metal dichalcogenides[J]. Nature Communications, 2022, 13: 492.
[146] CHEN Y, XI J, DUMCENCO D O, et al. Tunable band gap photoluminescence from atomically thin transition-metal dichalcogenide alloys[J]. ACS Nano, 2013, 7: 4610-4616.
[147] KANG J, TONGAY S, LI J, et al. Monolayer semiconducting transition metal dichalcogenide alloys: Stability and band bowing[J]. Journal of Applied Physics, 2013, 113: 143703.
[148] KIM S, MYEONG G, SHIN W, et al. Thickness-controlled black phosphorus tunnel field-effect transistor for low-power switches[J]. Nature Nanotechnology, 2020, 15: 203-206.
[149] HUANG B, CLARK G, NAVARRO-MORATALLA E, et al. Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit[J]. Nature, 2017, 546: 270-273.
[150] WU F, LOVORN T, TUTUC E, et al. Topological insulators in twisted transition metal dichalcogenide homobilayers[J]. Physical Review Letters, 2019, 122: 086402.
[151] QUAN J, LINHART L, LIN M L, et al. Phonon renormalization in reconstructed MoS2 moiré superlattices[J]. Nature Materials, 2021, 20: 1100-1105.
[152] NAIK M H, JAIN M. Ultraflatbands and shear solitons in Moiré patterns of twisted bilayer Transition metal dichalcogenides[J]. Physical Review Letters, 2018, 121: 266401.
[153] CASTELLANOS-GOMEZ A, VAN DER ZANT H S J, STEELE G A. Folded MoS2 layers with reduced interlayer coupling[J]. Nano Research, 2014, 7: 572-578.
[154] CI P, CHEN Y, KANG J, et al. Quantifying van der waals interactions in layered transition metal dichalcogenides from pressure-enhanced valence band splitting[J]. Nano Letters, 2017, 17: 4982-4988.
[155] KRISHNAMOORTHY A, DINH M A, YILDIZ B. Hydrogen weakens interlayer bonding in layered transition metal sulfide Fe1+xS[J]. Journal of Materials Chemistry A, 2017, 5: 5030-5035.
[156] ZUNGER A, WEI S H, FERREIRA L G, et al. Special quasirandom structures[J]. Physical Review Letters, 1990, 65: 353-356.
[157] SOLER J M, ARTACHO E, GALE J D, et al. The SIESTA method for ab initio order-N materials simulation[J]. Journal of Physics: Condensed Matter, 2002, 14: 2745-2779.
[158] VYDROV O A, VAN VOORHIS T. Nonlocal van der Waals density functional: The simpler the better[J]. The Journal of Chemical Physics, 2010, 133: 244103.
[159] ZHANG Q, ZHANG L Y, JIN C H, et al. CalAtom: A software for quantitatively analysing atomic columns in a transmission electron microscope image[J]. Ultramicroscopy, 2019, 202: 114-120.
[160] PISONI R, DAVATZ T, WATANABE K, et al. Absence of interlayer tunnel coupling of K-Valley electrons in bilayer MoS2[J]. Physical Review Letters, 2019, 123: 117702.
[161] CHU L, YUDHISTIRA I, SCHMIDT H, et al. Phase coherent transport in bilayer and trilayer MoS2[J]. Physical Review B, 2019, 100: 125410.
[162] XU Y, YAN X T. Thermodynamics and kinetics of chemical vapour deposition[M]. 2010: 129-164.
[163] GAO J J, SI J G, LUO X, et al. Superconducting and topological properties in centrosymmetric PbTaS2 single crystals[J]. The Journal of Physical Chemistry C, 2020, 124: 6349-6355.
[164] KOGAR A, DE LA PENA G A, LEE S, et al. Observation of a charge density wave incommensuration near the superconducting dome in CuxTiSe2[J]. Physical Review Letters, 2017, 118: 027002.
[165] LIU N, LI Y, LI P, et al. Intertwining of multiphase charge density waves in In-intercalated TaSe2[J]. Physical Review B, 2021, 104: 235410.
[166] GRÜNER G. The dynamics of charge-density waves[J]. Reviews of Modern Physics, 1988, 60: 1129-1181.
[167] CASTRO NETO A H. Charge density wave, superconductivity, and anomalous metallic behavior in 2D transition metal dichalcogenides[J]. Physical Review Letters, 2001, 86: 4382-4385.
[168] CHEN C W, CHOE J, MOROSAN E. Charge density waves in strongly correlated electron systems[J]. Reports on Progress in Physics, 2016, 79: 084505.
[169] CHANG J, BLACKBURN E, HOLMES A T, et al. Direct observation of competition between superconductivity and charge density wave order in YBa2Cu3O6.67[J]. Nature Physics, 2012, 8: 871-876.
[170] LUO H, XIE W, TAO J, et al. Polytypism, polymorphism, and superconductivity in TaSe2−xTex[J]. Proceedings of the National Academy of Sciences, 2015, 112: E1174-E1180.
[171] LAW K T, LEE P A. 1T-TaS2 as a quantum spin liquid[J]. Proceedings of the National Academy of Sciences of the United States of America, 2017, 114: 6996-7000.
[172] YU Y, YANG F, LU X F, et al. Gate-tunable phase transitions in thin flakes of 1T-TaS2[J]. Nature Nanotechnology, 2015, 10: 270-276.
[173] YOSHIDA M, SUZUKI R, ZHANG Y, et al. Memristive phase switching in two-dimensional 1T-TaS2 crystals[J]. Science Advances, 2015, 1: 1-7.
[174] RITSCHEL T, TRINCKAUF J, GARBARINO G, et al. Pressure dependence of the charge density wave in 1T-TaS2 and its relation to superconductivity[J]. Physical Review B, 2013, 87: 125135.
[175] SIPOS B, KUSMARTSEVA A F, AKRAP A, et al. From Mott state to superconductivity in 1T-TaS2[J]. Nature Materials, 2008, 7: 960-965.
[176] LIU Y, SHAO D F, LI L J, et al. Nature of charge density waves and superconductivity in 1T−TaSe2−xTex[J]. Physical Review B, 2016, 94: 045131.
[177] QIAO S, LI X, WANG N, et al. Mottness collapse in 1T-TaS2-XSeX transition metal dichalcogenide: An interplay between localized and itinerant orbitals[J]. Physical Review X, 2017, 7: 041054.
[178] ZHU X Y, WANG S, JIA Z Y, et al. Realization of a metallic state in 1T-TaS2 with persisting long-range oder of a carge dnsity wve[J]. Physical Review Letters, 2019, 123: 206405.
[179] LEE D, JIN K H, LIU F, et al. Tunable Mott Dirac and Kagome bands engineered on 1T -TaS2[J]. Nano Letters, 2022, 22: 7902-7909.
[180] PERFETTI L, LOUKAKOS P A, LISOWSKI M, et al. Femtosecond dynamics of electronic states in the Mott insulator 1T-TaS2 by time resolved photoelectron spectroscopy[J]. New Journal of Physics, 2008, 10: 053019.
[181] PERFETTI L, LOUKAKOS P A, LISOWSKI M, et al. Time evolution of the electronic structure of 1T−TaS2 through the insulator-metal transition[J]. Physical Review Letters, 2006, 97: 067402.
[182] THORNE R E. Charge Density Wave Conductors[J]. Physics Today, 1996, 49: 42-47.
[183] ISHIGURO T, SATO H. Electron microscopy of phase transformations in 1T-TaS2[J]. Physical Review B, 1991, 44: 2046-2060.
[184] LEE S H, GOH J S, CHO D. Origin of the insulating phase and first-order metal-insulator transition in 1T-TaS2[J]. Physical Review Letters, 2019, 122: 1-6.
[185] FAZEKAS P, TOSATTI E. Charge carrier localization in pure and doped 1T-TaS2[J]. Physica B+C, 1980, 99: 183-187.
[186] CHO D, CHEON S, KIM K S, et al. Nanoscale manipulation of the Mott insulating state coupled to charge order in 1T-TaS2[J]. Nature Communications, 2016, 7: 10453.
[187] CHO D, GYE G, LEE J, et al. Correlated electronic states at domain walls of a Mott-charge-density-wave insulator 1T-TaS2[J]. Nature Communications, 2017, 8: 1-6.
[188] MA L, YE C, YU Y, et al. A metallic mosaic phase and the origin of Mott-insulating state in 1T-TaS2[J]. Nature Communications, 2016, 7: 1-8.
[189] RITSCHEL T, BERGER H, GECK J. Stacking-driven gap formation in layered 1T-TaS2[J]. Physical Review B, 2018, 98: 1-8.
[190] STAHL Q, KUSCH M, HEINSCH F, et al. Collapse of layer dimerization in the photo-induced hidden state of 1T-TaS2[J]. Nature Communications, 2020, 11: 1-7.
[191] BUTLER C J, YOSHIDA M, HANAGURI T, et al. Mottness versus unit-cell doubling as the driver of the insulating state in 1T-TaS2[J]. Nature Communications, 2020, 11: 7-12.
[192] RITSCHEL T, TRINCKAUF J, KOEPERNIK K, et al. Orbital textures and charge density waves in transition metal dichalcogenides[J]. Nature Physics, 2015, 11: 328-331.
[193] YU X L, LIU D Y, QUAN Y M, et al. Electronic correlation effects and orbital density wave in the layered compound 1T-TaS2[J]. Physical Review B, 2017, 96: 1-12.
[194] SCRUBY C B, WILLIAMS P M, PARRY G S. The role of charge density waves in structural transformations of 1T TaS2[J]. Philosophical Magazine, 1975, 31: 255-274.
[195] CLERC F, BATTAGLIA C, BOVET M, et al. Lattice-distortion-enhanced electron-phonon coupling and Fermi surface nesting in 1T−TaS2[J]. Physical Review B, 2006, 74: 155114.
[196] SATO H, ARITA M, UTSUMI Y, et al. Conduction-band electronic structure of 1T-TaS2 revealed by angle-resolved inverse-photoemission spectroscopy[J]. Physical Review B, 2014, 89: 155137.
[197] PETERSEN J C, KAISER S, DEAN N, et al. Clocking the melting transition of charge and lattice order in 1T-TaS2 with ultrafast extreme-ultraviolet angle-resolved photoemission spectroscopy[J]. Physical Review Letters, 2011, 107: 177402.
[198] ANG R, TANAKA Y, IEKI E, et al. Real-space coexistence of the melted Mott state and superconductivity in Fe-substituted 1T-TaS2[J]. Physical Review Letters, 2012, 109: 176403.
[199] WANG Y D, YAO W L, XIN Z M, et al. Band insulator to Mott insulator transition in 1T-TaS2[J]. Nature Communications, 2020, 11: 1-7.
[200] WANG Z, WANG Z, FENG Y P, et al. Probing the origin of chiral charge density waves in the two-dimensional limits[J]. Nano Letters, 2022, 22: 7615-7620.
[201] SHEN S, SHAO B, WEN C, et al. Single-water-dipole-layer-driven reversible charge order transition in 1T -TaS2[J]. Nano Letters, 2020, 20: 8854-8860.
[202] BAGGARI I El, SAVITZKY B H, ADMASU A S, et al. Nature and evolution of incommensurate charge order in manganites visualized with cryogenic scanning transmission electron microscopy[J]. Proceedings of the National Academy of Sciences of the United States of America, 2018, 115: 1445-1450.
[203] HOVDEN R, TSEN A W, LIU P, et al. Atomic lattice disorder in charge-density-wave phases of exfoliated dichalcogenides (1T-TaS2)[J]. Proceedings of the National Academy of Sciences of the United States of America, 2016, 113: 11420-11424.
[204] YUAN P J, WU K P, CHEN S W, et al. ToTEM: A software for fast TEM image simulation[J]. Journal of Microscopy, 2022, 287: 93-104.
[205] WEN C, GAO J, XIE Y, et al. Roles of the narrow electronic band near the Fermi level in 1T-TaS2-related layered materials[J]. Physical Review Letters, 2021, 126: 256402.
[206] WAN W, HOVMÖLLER S, ZOU X. Structure projection reconstruction from through-focus series of high-resolution transmission electron microscopy images[J]. Ultramicroscopy, 2012, 115: 50-60.
[207] SONG X, LIU L, CHEN Y, et al. Atomic-scale visualization of chiral charge density wave superlattices and their reversible switching[J]. Nature Communications, 2022, 13: 1843.
[208] DANZ T, DOMRÖSE T, ROPERS C. Ultrafast nanoimaging of the order parameter in a structural phase transition[J]. Science, 2021, 371: 371-374.
[209] PARDINI L, LÖFFLER S, BIDDAU G, et al. Mapping atomic rrbitals with the transmission electron microscope: Images of defective graphene predicted from first-principles theory[J]. Physical Review Letters, 2016, 117: 036801.