Anisotropic nanofriction on MoS2 with different thicknesses

Cao, Xing’an; Xi, Gan; Lang, Haojie; Yu, Kang Yang Trevor; Ding, Shuyang; Peng, Yitian; Yi, Wangmin

doi:10.1016/j.triboint.2019.02.010

Cited by 47 publications

(36 citation statements)

References 41 publications

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“…No experiments performed on scan areas smaller than 1.5 µm × 1.5 µm featured twofold anisotropy, while the largest scan area on which higher-symmetry anisotropy was recorded was 50 nm × 50 nm. Anisotropy ratios (the ratio between the highest and lowest friction values recorded in a~360°cycle) for the experiments were 2.0 ± 0.4, in the range of previously reported values for graphene and MoS 2 16,20 .…”

Section: Friction Anisotropy On Mossupporting

confidence: 80%

“…Considering that the direction dependence, i.e., anisotropy, of friction can be potentially an important design parameter for 2Dmaterial-based solid lubrication in small-scale mechanical systems, we performed FFM measurements to probe friction anisotropy on MoS 2 flakes exfoliated onto SiO 2 . Our work was additionally motivated by previous reports of friction anisotropy on 2D materials including graphene and MoS 2 , where twofold and sixfold symmetries have been reported [16][17][18][19] , as well as irregular anisotropic behavior 20 . While twofold anisotropic behavior was tentatively explained by the presence of ripples 16,17 or stripes formed by molecular adsorbates 18 , sixfold anisotropy was ascribed to the hexagonal symmetry of the atomic structure of the involved materials 19 .…”

Section: Friction Anisotropy On Mosmentioning

confidence: 95%

“…Despite this seemingly widespread idea-together with a competing theory based on the presence of linearly aligned stripes formed by environmental adsorbates 18 -, the connection to friction anisotropy remains controversial, as the ripples are not directly observed during the experiments. Moreover, the literature also includes friction anisotropy studies that deviate from twofold symmetry 19,20 .…”

Section: Introductionmentioning

confidence: 99%

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Direct imaging, three-dimensional interaction spectroscopy, and friction anisotropy of atomic-scale ripples on MoS2

et al. 2020

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Theory predicts that two-dimensional (2D) materials may only exist in the presence of out-of-plane deformations on atomic length scales, frequently referred to as ripples. While such ripples can be detected via electron microscopy, their direct observation via surface-based techniques and characterization in terms of interaction forces and energies remain limited, preventing an unambiguous study of their effect on mechanical characteristics, including but not limited to friction anisotropy. Here, we employ high-resolution atomic force microscopy to demonstrate the presence of atomic-scale ripples on supported samples of few-layer molybdenum disulfide (MoS 2). Three-dimensional force/energy spectroscopy is utilized to study the effect of ripples on the interaction landscape. Friction force microscopy reveals multiple symmetries for friction anisotropy, explained by studying rippled sample areas as a function of scan size. Our experiments contribute to the continuing development of a rigorous understanding of the nanoscale mechanics of 2D materials.

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Section: Friction Anisotropy On Mossupporting

confidence: 80%

Section: Friction Anisotropy On Mosmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Direct imaging, three-dimensional interaction spectroscopy, and friction anisotropy of atomic-scale ripples on MoS2

et al. 2020

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“…The anisotropy of friction on MoS2 is another topic that has been investigated via AFM on 2D samples. Specifically, Cao et al determined, by means of consecutive friction measurements performed on MoS2 flakes gradually rotated with respect to the scanning direction during AFM experiments, that the friction forces on MoS2 exhibit anisotropic behavior with a periodicity of 180 o [91]. This observation is surprising at first glance, as a periodicity of 60 0 would have been expected based on crystal symmetry.…”

Section: Mechanisms Of Low Friction and Wearmentioning

confidence: 99%

Solid Lubrication with MoS2: A Review

et al. 2019

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Molybdenum disulfide (MoS2) is one of the most broadly utilized solid lubricants with a wide range of applications, including but not limited to those in the aerospace/space industry. Here we present a focused review of solid lubrication with MoS2 by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence. An effort is made to cover the main theoretical and experimental studies that constitute milestones in our scientific understanding. The review also includes an extensive overview of the structure and tribological properties of doped MoS2, followed by a discussion of potential future research directions.MoS2 belongs to the family of layered two-dimensional transitional metal dichalcogenides (TMDs). Like graphite and hexagonal boron nitride, its crystal structure consists of covalently bonded sheets, which form stacks that are held together only by weak Van der Waals interactions [16]. It occurs naturally as the mineral molybdenite, an important Mo ore. Due to the strong bonding inplane and weak bonding out-of-plane, mechanical and other properties are highly anisotropic [17], and the stacks can be easily sheared. Single-layer or few-layer (i.e. 2D) MoS2 (analogous to graphene) can be produced and studied individually [18].MoS2 has several different possible structures (polytypes), depending on the bonding within the sheets and the stacks of the sheets. While graphite has a single plane of atoms per sheet, in MoS2 each sheet consists a plane of Mo atoms sandwiched between two planes of S atoms. The single-sheet structure can feature trigonal prismatic coordination around Mo, which is the semiconducting 1H ("hexagonal") structure, or octahedral bonding, which is the metallic 1T ("trigonal") phase. 1H and the ideal 1T each have 3 atoms (MoS2) per unit cell ( Figure 1); however, theoretical calculations with density-functional theory (DFT)[19] and X-ray diffraction (XRD) experiments [20] have shown that in fact 1T is unstable with respect to distortions. The most commonly reported structure is a 3× 3 distortion that triples the unit cell, known as the 1T′ phase [21].Each single-sheet structure can be stacked into a crystal where the next sheet is exactly above the preceding one (AA stacking), producing the 1H, 1T, and 1T′ polytypes. The naturally occurring polytypes in molybdenite, however, are only based on the 1H sheet, and show more complicated stacking [9]. The more common is the 2H structure with 2 sheets per cell in AB stacking, where an S atom in one layer is above an Mo atom in the layer below [22,23]. The less common 3R ("rhombohedral") structure has 3 sheets per cell with ABC stacking [22,24]. These structures are shown in Figure 1. Mo-S bond lengths are around 2.4 Å for all polytypes [25]. DFT calculations show only very small energy differences between the 2H and 3R phases [25]. This insensitivity to stacking, and the low surface energy for 2H-MoS2 of 47 mJ/m 2 =...

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“…2D materials present extremely strong covalent bond interactions in molecular layer, while there is only a relatively weak van der Waals force in the interlayer. The special layered structure endows them with excellent mechanical performance [2][3][4][5][6] and tribological performance [7][8][9][10][11][12]. The discovery and preparation of 2D materials, as represented by graphene and molybdenum disulfide (MoS 2 ), provides new directions for the development and improvement of the solid lubricant materials.…”

Section: Introductionmentioning

confidence: 99%

Effect of Compressive Prestrain on the Anti-Pressure and Anti-Wear Performance of Monolayer MoS2: A Molecular Dynamics Study

et al. 2020

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The effects of in-plane prestrain on the anti-pressure and anti-wear performance of monolayer MoS2 have been investigated by molecular dynamics simulation. The results show that monolayer MoS2 observably improves the load bearing capacity of Pt substrate. The friction reduction effect depends on the deformation degree of monolayer MoS2. The anti-pressure performance of monolayer MoS2 and Pt substrate is enhanced by around 55.02% when compressive prestrain increases by 4.03% and the anti-wear performance is notably improved as well. The improved capacities for resisting the in-plane tensile and out-of-plane compressive deformation are responsible for the outstanding lubrication mechanism of monolayer MoS2. This study provides guidelines for optimizing the anti-pressure and anti-wear performance of MoS2 and other two-dimension materials which are subjected to the in-plane prestrain.

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Anisotropic nanofriction on MoS2 with different thicknesses

Cited by 47 publications

References 41 publications

Direct imaging, three-dimensional interaction spectroscopy, and friction anisotropy of atomic-scale ripples on MoS2

Direct imaging, three-dimensional interaction spectroscopy, and friction anisotropy of atomic-scale ripples on MoS2

Solid Lubrication with MoS2: A Review

Effect of Compressive Prestrain on the Anti-Pressure and Anti-Wear Performance of Monolayer MoS2: A Molecular Dynamics Study

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