15 results on '"Jiang, Jin-Wu"'
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2. Effect of intrinsic structural defects on mechanical properties of single layer MoS2
- Author
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Mahata, Avik, Jiang, Jin-Wu, Mahapatra, D. Roy, and Rabczuk, Timon
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- 2019
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3. Machine learning-based design of porous graphene with low thermal conductivity.
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Wan, Jing, Jiang, Jin-Wu, and Park, Harold S.
- Subjects
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THERMAL conductivity , *GRAPHENE , *LATTICE dynamics , *WAVE packets , *PHONONS , *MACHINE learning - Abstract
The thermal conductivity of two-dimensional materials like graphene can efficiently be tuned by introducing holes, in which the density and distribution of the holes are the key parameters. Furthermore, the distribution of holes can induce a variation as high as 74% in the thermal conductivity for porous graphene with a given density of holes. Therefore, an existing challenge is to find the optimal distribution of holes that can minimize or maximize the thermal conductivity of porous graphene as the design space expands dramatically with increasing hole density. We therefore apply an inverse design methodology based on machine learning to reveal the relationship between hole distribution and thermal conductivity reduction in monolayer graphene. The methodology reveals that holes that are randomly distributed transverse to the direction of heat flow, but that exhibit some periodicity along the direction of heat flow, represent the optimal distribution to minimizing the thermal conductivity for porous graphene. Lattice dynamics calculations and wave packet simulations reveal that this spatial distribution effectively causes localization of the phonon modes in porous graphene, which reduces the thermal conductivity. Overall, this work demonstrates the power of machine learning-based design approaches to efficiently obtain new physical insights for scientific problems of interest. Image 1 [ABSTRACT FROM AUTHOR]
- Published
- 2020
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4. A universal law for the pattern evolution of fullerene-based sandwiches.
- Author
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Xue, Yixuan, Jiang, Jin-Wu, and Park, Harold S.
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FULLERENES , *SANDWICH construction (Materials) , *MOLECULAR dynamics , *FULLERENE polymers , *THERMAL conductivity , *CHARGE transfer - Abstract
Fullerene-based sandwiches have excellent controllable physical properties such as cross-plane thermal conductivity and charge transfer, which provide new possibilities for advancing the field of thermoelectricity. Because the pattern of the fullerene cluster impacts the physical properties of the sandwiches, it is important to understand the mechanisms for their structural transformations. In the present work, we find that the graphene/fullerene/graphene sandwich structure transforms among three configurations in an ideal environment, depending on the fullerene to graphene area ratio. Molecular dynamics simulations show that there are two critical values for the area ratio. The fullerene pattern transforms from circular to rectangular at the first critical area ratio of 1 π. The critical value of 1 π is successfully derived by comparing the geometrical perimeter of the circular and rectangular shapes for the fullerene cluster without any physical parameters. At the second critical area ratio, the graphene layers surrounding the fullerene cluster become separated due to the competition between the bending energy and the cohesive energy. The vacuum space is predicted to be 34 Å based on the analytic model. These findings provide fundamental insights into the mechanisms driving structural transformation of fullerene-based sandwiches, which will enable the selection of appropriate structures and materials to guide the design of future electronic and energy storage applications. [Display omitted] • The stable fullerene-based sandwich structure evolves among three typical configurations, which are governed by two critical ratios for the area ratio. • The fullerene pattern transforms from circular to rectangular at the first critical area ratio of 1 π. • At the second critical area ratio, the graphene layers surrounding the fullerene cluster are separated by the fullerenes. • It is demonstrated that the analytic models are universal and are applicable to other sandwich structures such as the MoS 2 /fullerene/MoS 2 structure. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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5. The bubble effect on the thermal expansion coefficient of few-layer MoS2.
- Author
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Qu, Zhao-Xia and Jiang, Jin-Wu
- Subjects
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THERMAL expansion , *IDEAL gases , *NONLINEAR theories , *EQUATIONS of state , *THERMAL stability , *BUBBLES - Abstract
The thermal expansion coefficient of van der Waals layered structures plays an important role in governing the thermal stability of high-performance electronic devices. Meanwhile, bubbles are frequently observed in the van der Waals layered structures due to the weak inter-layer interaction and the extremely small bending stiffness of the layered structure, but the effect of bubbles on the thermal expansion coefficient for layered structures remains unclear. We derive an analytic formula for the bubble effect on the length variation of the MoS 2 layer. In the analytic derivation, the MoS 2 layer is described by three mechanics models, including the elastic membrane theory, the nonlinear plate theory, and the linear plate theory. The gas inside the bubble is described by two types of state equations, including the ideal gas law and the generalized van der Waals equation. It is found that the nonlinear plate theory with the generalized van der Waals equation gives the most accurate description for the bubble effect, since MoS 2 has a moderate bending stiffness. The analytic formula shows that the bubble can cause strong thermal contraction for few-layer MoS 2 with increasing temperature. The analytic predictions are verified by comprehensive molecular dynamic simulations for few-layer MoS 2 with different layer numbers and different gas molecule numbers. These results shall be valuable for understanding the thermal stability of functional devices based on the van der Waals layered structure. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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6. Twin graphene: A novel two-dimensional semiconducting carbon allotrope.
- Author
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Jiang, Jin-Wu, Leng, Jiantao, Li, Jianxin, Guo, Zhengrong, Chang, Tienchong, Guo, Xingming, and Zhang, Tongyi
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MOLECULAR dynamics , *GRAPHENE , *BAND gaps , *ALLOTROPY , *SEMICONDUCTORS , *TRANSISTORS - Abstract
Graphene has been expected to revolutionize the electronics, but suffered from its zero bandgap that will lead to an unacceptable leakage current in graphene-based transistors. Although a bandgap engineered graphene structure may have a bandgap, such bandgap is sensitively dependent on the geometry of the structure. Finding new two-dimensional (2D) semiconducting carbon allotropes is therefore extremely important for the new emerging all-carbon electronics. Based on first principles calculations, here we predict a new 2D semiconducting carbon allotrope, referred to as twin graphene. The allotrope has an intrinsic direct bandgap, very close to that of silicon and tunable by in-plane strain, indicating its great potential in nanoelectronics. The stability of twin graphene is carefully verified by both the first principles calculations and the molecular dynamics simulations. We determine also the mechanical properties of twin graphene, including the in-plane stiffness, Poisson’s ratio, shear stiffness and bending stiffness. Its excellent electronic and mechanical properties suggest that twin graphene may have a significant impact on many disciplines and fields related to nanotechnology. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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7. The effects of free edge interaction-induced knotting on the buckling of monolayer graphene.
- Author
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Zhang, Hao-Yu, Jiang, Jin-Wu, Chang, Tienchong, Guo, Xingming, and Park, Harold S.
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GRAPHENE , *KNOTS & splices , *MONOMOLECULAR films , *EDGES (Geometry) , *MECHANICAL buckling - Abstract
Edge effects play an important role for many properties of graphene. While most works have focused on the effects from isolated free edges, we present a novel knotting phenomenon induced by the interactions between a pair of free edges in graphene, and investigate its effect on the buckling of monolayer graphene. Upon compression, the buckling of graphene starts gradually in the form of two buckling waves from the warped edges. The collision of these two buckling waves results in the creation of a knot structure in graphene. The knot structure enables the buckled graphene to exhibit two unique post-buckling characteristics. First, it induces a five-fold increase in graphene’s mechanical stiffness during the buckling process. Second, the knotted structure enables graphene to exhibit a mechanically stable post-buckling regime over a large (3%) compressive strain regime, which is significantly larger than the critical buckling strain of about 0.5%. The combination of these two effects enables graphene to exhibit an unexpected post-buckling stability that has previously not been reported. We predict that numerical simulations or experiments should observe two distinct stress strain relations for the buckling of identical graphene samples, due to the characteristic randomness in the formation process of the knot structure. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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8. Strain engineering for thermal conductivity of single-walled carbon nanotube forests.
- Author
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Jiang, Jin-Wu
- Subjects
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SINGLE walled carbon nanotubes , *THERMAL conductivity , *MOLECULAR dynamics , *COMPRESSION loads , *MECHANICAL buckling , *VAN der Waals forces , *GROUP velocity - Abstract
We perform classical molecular dynamics simulations to investigate the mechanical compression effect on the thermal conductivity of the single-walled carbon nanotube (SWCNT) forest, in which SWCNTs are closely aligned and parallel with each other. We find that the thermal conductivity can be linearly enhanced by increasing compression before the buckling of SWCNT forests, but the thermal conductivity decreases quickly with further increasing compression after the forest is buckled. Our phonon mode analysis reveals that, before buckling, the smoothness of the inter-tube interface is maintained during compression, and the inter-tube van der Waals interaction is strengthened by the compression. Consequently, the twisting-like mode (good heat carrier) is well preserved and its group velocity is increased by increasing compression, resulting in the enhancement of the thermal conductivity. The buckling phenomenon changes the circular cross section of the SWCNT into ellipse, which causes effective roughness at the inter-tube interface for the twisting motion. As a result, in ellipse SWCNTs, the radial breathing mode (poor heat carrier) becomes the most favorable motion instead of the twisting-like mode and the group velocity of the twisting-like mode drops considerably, both of which lead to the quick decrease of the thermal conductivity with further increasing compression after buckling. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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9. Coarse-grained potentials of single-walled carbon nanotubes.
- Author
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Zhao, Junhua, Jiang, Jin-Wu, Wang, Lifeng, Guo, Wanlin, and Rabczuk, Timon
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SINGLE walled carbon nanotubes , *POTENTIAL theory (Mathematics) , *TORSION , *VAN der Waals forces , *MOLECULAR dynamics , *DEFORMATIONS (Mechanics) , *COMPUTATIONAL mechanics - Abstract
We develop the coarse-grained (CG) potentials of single-walled carbon nanotubes (SWCNTs) in CNT bundles and buckypaper for the study of the static and dynamic behaviors. The explicit expressions of the CG stretching, bending and torsion potentials for the nanotubes are obtained by the stick-spiral and the beam models, respectively. The non-bonded CG potentials between two different CG beads are derived from analytical results based on the cohesive energy between two parallel and crossing SWCNTs from the van der Waals interactions. We show that the CG model is applicable to large deformations of complex CNT systems by combining the bonded potentials with non-bonded potentials. Checking against full atom molecular dynamics calculations and our analytical results shows that the present CG potentials have high accuracy. The established CG potentials are used to study the mechanical properties of the CNT bundles and buckypaper efficiently at minor computational cost, which shows great potential for the design of micro- and nanomechanical devices and systems. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
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10. A theoretical analysis of cohesive energy between carbon nanotubes, graphene and substrates
- Author
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Zhao, Junhua, Jiang, Jin-Wu, Jia, Yue, Guo, Wanlin, and Rabczuk, Timon
- Subjects
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CARBON nanotubes , *GRAPHENE , *SUBSTRATES (Materials science) , *COHESION , *SOLUTION (Chemistry) , *MOLECULAR dynamics , *NANOELECTROMECHANICAL systems - Abstract
Abstract: Explicit solutions for the cohesive energy between carbon nanotubes, graphene and substrates are obtained through continuum modeling of the van der Waals interaction between them. The dependence of the cohesive energy on their size, spacing and crossing angles is analyzed. Checking against full atom molecular dynamics calculations and available experimental results shows that the continuum solution has high accuracy. The equilibrium distances between the nanotubes, graphene and substrates with minimum cohesive energy are also provided explicitly. The obtained analytical solution should be of great help for understanding the interaction between the nanostructures and substrates, and designing composites and nanoelectromechanical systems. [Copyright &y& Elsevier]
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- 2013
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11. A full spd tight-binding treatment for electronic bands of graphitic tubes
- Author
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Tang, Hui, Jiang, Jin-Wu, Wang, Bing-Shen, and Su, Zhao-Bin
- Subjects
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GRAPHITE , *ELECTRONIC structure , *CARBON nanotubes , *ANISOTROPY , *NANOSTRUCTURES - Abstract
Abstract: A tight-binding (TB) treatment with the inclusion of d orbitals is applied to the electronic structures of graphitic tubes. The results show that the high angular moment bases in TB scheme are necessary to account the severe curvature effect in ultra-thin single wall carbon nanotubes, especially for properly reproducing the band edge overlap behavior in (5, 0) tube, predicted by the existing ab initio calculations. In the large diameter limit, the participation of two symmetry-allowed d bases provides a natural replication to the recent measured electronic dispersions of valence band of graphene when the strong anisotropy due to the two-dimensional planar hexagonal sheet structure is dealt with properly. In addition, the detailed relation between the two sets of quantum numbers of screw symmetry and that of zone folding is formulated in appendix. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
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12. A surface stacking fault energy approach to predicting defect nucleation in surface-dominated nanostructures.
- Author
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Jiang, Jin-Wu, Leach, Austin M., Gall, Ken, Park, Harold S., and Rabczuk, Timon
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STACKING faults (Crystals) , *SURFACE energy , *NUCLEATION , *CRYSTAL defects , *NANOSTRUCTURES , *NANOWIRES , *TWINNING (Crystallography) , *MOLECULAR dynamics - Abstract
Abstract: We present a surface stacking fault (SSF) energy approach to predicting defect nucleation from the surfaces of surface-dominated nanostructure such as FCC metal nanowires. The approach leads to a criterion that predicts the initial yield mechanism via either slip or twinning depending on whether the unstable twinning energy or unstable slip energy is smaller as determined from the resulting SSF energy curve. The approach is validated through a comparison between the SSF energy calculation and low-temperature classical molecular dynamics simulations of copper nanowires with different axial and transverse surface orientations, and cross sectional geometries. We focus on the effects of the geometric cross section by studying the transition from slip to twinning previously predicted in moving from a square to rectangular cross section for nanowires, and also for moving from a rhombic to truncated rhombic cross sectional geometry for nanowires. We also provide the important demonstration that the criterion is able to predict the correct deformation mechanism when full dislocation slip is considered concurrently with partial dislocation slip and twinning. This is done in the context of rhombic 〈110〉 aluminum nanowires which do not show a tensile reorientation due to full dislocation slip. We show that the SSF energy criterion successfully predicts the initial mode of surface-nucleated plasticity at low temperature, while also discussing the effects of strain and temperature on the applicability of the criterion. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
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13. On/off switchable interfacial thermal resistance in graphene/fullerene/graphene heterostructures.
- Author
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Xue, Yixuan, Park, Harold S., and Jiang, Jin-Wu
- Subjects
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INTERFACIAL resistance , *FULLERENES , *THERMAL resistance , *SANDWICH construction (Materials) , *GRAPHENE , *STRAINS & stresses (Mechanics) , *HETEROSTRUCTURES - Abstract
• The interfacial thermal resistance shows a switchable, step-like enhancement by varying the number of fullerene, where the magnitude can be enhanced by a factor of two. • The switchable phenomenon can be analyzed using analytic expressions based on the thermal transport theory. • The switchable phenomenon can be realized by applying mechanical strain or by varying the temperature of the sandwich structure. • The temperature range can be increased using mechanical strain, demonstrating the robust environmental sensitivity of the proposed thermal switch structure. [Display omitted] Switchable thermal devices are attracting significant research interest as a basic thermal management component. In this work, taking graphene/fullerene/graphene sandwiches as an example, we demonstrate that the interfacial thermal resistance can show a switchable, step-like change by varying the number of fullerenes in the sandwich structure. Changing the number of fullerenes causes a structural transition between the graphene layers from adhered to separated, resulting in an enhancement of about a factor of two in the interfacial thermal resistance during this on/off switchable phenomenon, which we analyze using analytic expressions based on the thermal transport theory. We further illustrate that the switchable phenomenon can also be realized by applying mechanical strain or by varying the temperature of the sandwich structure. This work demonstrates that the sandwich-liked nanoscale heterostructures can exhibit hysteretic changes in heat transport, and thus have promise for potential applications in switchable thermal devices. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
14. Interfacial thermal conductance in graphene/MoS2 heterostructures.
- Author
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Ding, Zhiwei, Pei, Qing-Xiang, Jiang, Jin-Wu, Huang, Wenxuan, and Zhang, Yong-Wei
- Subjects
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THERMAL analysis , *ELECTRIC admittance , *GRAPHENE , *HETEROSTRUCTURES , *DYNAMIC simulation - Abstract
Using non-equilibrium molecular dynamics simulations, we investigate the thermal transport in van der Waals heterostructures consisting of alternating multilayer graphene and multilayer MoS 2 . It is found that the thermal conductance at graphene/MoS 2 (G/M) interface is much lower than that at graphene/graphene (G/G) and MoS 2 /MoS 2 (M/M) interfaces. This low interfacial thermal conductance is attributed to the low friction at G/M interface, which significantly reduces the contribution of shearing modes to the thermal conductance. It is also found that there is no thermal rectification at the G/M interface as the thermal conductance is independent on the heat flux direction. Moreover, the interfacial thermal conductance can be effectively tuned by cross-plane strain. More specifically, a 5% tensile strain is able to reduce the interfacial thermal conductance by 70%; while a 5% compressive strain is able to increase the thermal conductance by 150%. Unexpectedly, the G/M interfacial thermal conductance is found to increase with increasing the defect density near the interface, which is in strong contrast to the in-plane thermal conductivity. This unexpected increase in thermal conductance can be explained by the enhanced phonon coupling at the G/M interface arising from the enhanced interface friction caused by the defects. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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15. Thermal-fluctuation gradient induced tangential entropic forces in layered two-dimensional materials.
- Author
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Zhu, Fangyan, Leng, Jiantao, Jiang, Jin-Wu, Chang, Tienchong, Zhang, Tongyi, and Gao, Huajian
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TANGENTIAL force , *DOUBLE walled carbon nanotubes , *NANOELECTROMECHANICAL systems , *THERMOPHORESIS , *BORON nitride , *MOLECULAR dynamics , *NANOMECHANICS - Abstract
Recent studies on nanomechanical devices based on low-dimensional nanomaterials have revealed several different types of thermal fluctuation gradient induced tangential entropic forces (TEFs), including expulsion force, edge force, thermophoretic force, nanodurotaxis force, etc. While all these forces originate from thermal fluctuation gradients, they can take different forms for different problems and have been treated case-by-case in the literature. Here, we develop a unified theoretical framework for TEFs in layered low-dimensional materials. In particular, we derive explicit analytical solutions for TEFs in layered two-dimensional materials and validate them with molecular dynamics simulations for various bilayers composed of graphene, graphyne, hexagonal-boron nitride (h -BN), boron-carbon-nitride (BCN), and double walled nanotubes. We present also approximate solutions to TEFs in hetero- or substrate-supported-bilayers based on a solution-guided machine learning (SGML) technique. The developed concept for TEFs is unique to nanomechanical systems and may serve as one of the founding pillars of nanomechanics. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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