Search

The Kapitza resistance is of fundamental importance for the thermal stability of the interface between the ceramic top coat and the thermal growth oxide layer in the thermal barrier coating structure, which is widely used to protect high-temperature components in current gas turbine engines. The top coat typically consists of the ZrO 2 partially stabilized by 8% Y 2 O 3 (YSZ), and the main component of the thermal growth oxide is α -Al 2 O 3 . In this work, the Kapitza resistance is found to be a small value of 0.69 m 2 · K/GW for the YSZ/ α -Al 2 O 3 interface based on the heat dissipation simulation method. It indicates that the localization of thermal energy is rather weak, which is beneficial for the thermal stability of the YSZ/ α -Al 2 O 3 interface. This Kapitza resistance can be further reduced to 0.50 m 2 · K/GW by a mechanical or thermal compressive strain of 8%. To explore the underlying mechanism for this strain effect, we analyze the phonon vibration and the microscopic deformation in the interface region. It is revealed that the interface becomes denser through the compression-induced twisting of some Al-O Zr and Al-O Al chemical bonds in the interface region, which is responsible for the reduction in the Kapitza resistance. The temperature effect and crystal size effect on the Kapitza resistance of the YSZ/ α -Al 2 O 3 interface are also systematically studied. These findings shall provide valuable information for further understanding of the thermal conductivity and thermal stability of the thermal barrier coating structures. [ABSTRACT FROM AUTHOR]

Zirconia has many important phases with Zr coordination varying from six-fold in the orthorhombic phase to eight-fold in the cubic and tetragonal phases. Development of empirical potentials to describe these zirconia phases is an important but long-standing challenge, and it is a bottleneck for theoretical investigation of large zirconia structures. Here, instead of using the standard core—shell model, we developed a new potential for zirconia by combining the long-range Coulomb interaction and bond-order Tersoff model. The bond-order characteristic of the Tersoff potential enables it to be well suited to describe the zirconia phases with different coordination numbers. In particular, the complex monoclinic phase with two inequivalent oxygen atoms, which is difficult to describe with most existing empirical potentials, is well described by this newly developed potential. This potential provides reasonable predictions of most of the static and dynamic properties of various zirconia phases. Besides its clear physical essence, this potential is at least one order of magnitude faster than core—shell based potentials in molecular dynamics simulation. This is because it does not include an ultralight shell that requires an extremely small time step. We also provide potential scripts for the widely used simulation packages GULP and LAMMPS. [ABSTRACT FROM AUTHOR]

Resistance change under mechanical stimuli arouses mass operational heat, damaging the performance, lifetime, and reliability of stretchable electronic devices, therefore rapid thermal heat dissipating is necessary. Here we report a stretchable strain sensor with outstanding thermal management. Besides a high stretchability and sensitivity testified by human motion monitoring, as well as long-term durability, an enhanced thermal conductivity from the casted thermoplastic polyurethane-boron nitride nanosheets layer helps rapid heat transmission to the environments, while the porous electrospun fibrous thermoplastic polyurethane membrane leads to thermal insulation. A 32% drop of the real time saturated temperature is achieved. For the first time we in-situ investigated the dynamic operational temperature fluctuation of stretchable electronics under repeating stretching-releasing processes. Finally, cytotoxicity test confirms that the nanofillers are tightly restricted in the nanocomposites, making it harmless to human health. All the results prove it an excellent candidate for the next-generation of wearable devices. Though stretchable strain sensors are attractive for next-generation applications due to their high sensitivity, heat generated in these devices limits their reliability. Here, the authors report boron nitride nanosheet-based stretchable strain sensors with enhanced thermal management. [ABSTRACT FROM AUTHOR]

The successful discovery and isolation of graphene in 2004, and the subsequent synthesis of layered semiconductors and heterostructures beyond graphene have led to the exploding field of two-dimensional (2D) materials that explore their growth, new atomic-scale physics, and potential device applications. This review aims to provide an overview of theoretical, computational, and machine learning methods and tools at multiple length and time scales, and discuss how they can be utilized to assist/guide the design and synthesis of 2D materials beyond graphene. We focus on three methods at different length and time scales as follows: (i) nanoscale atomistic simulations including density functional theory (DFT) calculations and molecular dynamics simulations employing empirical and reactive interatomic potentials; (ii) mesoscale methods such as phase-field method; and (iii) macroscale continuum approaches by coupling thermal and chemical transport equations. We discuss how machine learning can be combined with computation and experiments to understand the correlations between structures and properties of 2D materials, and to guide the discovery of new 2D materials. We will also provide an outlook for the applications of computational approaches to 2D materials synthesis and growth in general. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are performed to investigate the misfit strain-induced buckling of the transition-metal dichalcogenide (TMD) lateral heterostructures, denoted by the seamless epitaxial growth of different TMDs along the in-plane direction. The Stillinger-Weber potential is utilized to describe both the interaction for each TMD and the coupling between different TMDs, i.e., MX2 (with M=Mo, W and X=S, Se, Te). It is found that the misfit strain can induce strong buckling of the freestanding TMD lateral heterostructures of large area, resulting from the TMDs' atomic-thick nature. The buckling phenomenon occurs in a variety of TMD lateral heterostructures of different compositions and in various patterns. Our findings raise a fundamental mechanical challenge for the structural stability of the freestanding TMD lateral heterostructures. [ABSTRACT FROM AUTHOR]

The single-layer black phosphorus is characterized by its puckered configuration that possesses the hinge-like behavior, which leads to the highly anisotropic in-plane Poisson's ratios and the negative out-of-plane Poisson's ratio. We demonstrate that the hinge-like mechanism can be described by the angle–angle cross interaction, which, combined with the bond stretching and angle bending interactions, is able to provide a good description for the mechanical properties of single-layer black phosphorus. We also propose a nonlinear angle–angle cross interaction, which follows the form of Stillinger–Weber potential and can be advantageous for molecular dynamics simulations of single-layer black phosphorus under large deformation. [ABSTRACT FROM AUTHOR]

Graphene and MoS are two well-known quasi two-dimensional materials. This review presents a comparative survey of the complementary lattice dynamical and mechanical properties of graphene and MoS, which facilitates the study of graphene/MoS heterostructures. These hybrid heterostructures are expected to mitigate the negative properties of each individual constituent and have attracted intense academic and industrial research interest. [ABSTRACT FROM AUTHOR]

Stimulated by the success of graphene and diamond, a variety of carbon allotropes have been discovered in recent years in either two-dimensional or three-dimensional configurations. Although these emerging carbon allotropes share some common features, they have certain different and novel mechanical or physical properties. In this review, we present a comparative survey of some of the major properties of fifteen newly discovered carbon allotropes. By comparing their structural topology, we propose a general route for designing most carbon allotropes from two mother structures, namely, graphene and diamond. Furthermore, we discuss several future prospects as well as current challenges in designing new carbon allotropes. [ABSTRACT FROM AUTHOR]

While most existing theoretical studies on the borophene are based on first-principles calculations, the present work presents molecular dynamics simulations for the lattice dynamical and mechanical properties in borophene. The obtained mechanical quantities are in good agreement with previous first-principles calculations. The key ingredients for these molecular dynamics simulations are the two efficient empirical potentials developed in the present work for the interaction of borophene with low-energy triangular structure. The first one is the valence force field model, which is developed with the assistance of the phonon dispersion of borophene. The valence force field model is a linear potential, so it is rather efficient for the calculation of linear quantities in borophene. The second one is the Stillinger-Weber potential, whose parameters are derived based on the valence force field model. The Stillinger-Weber potential is applicable in molecular dynamics simulations of nonlinear physical or mechanical quantities in borophene. [ABSTRACT FROM AUTHOR]

We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. [ABSTRACT FROM AUTHOR]

The Euler buckling theory states that the buckling critical strain is an inverse quadratic function of the length for a thin plate in the static compression process. However, the suitability of this theory in the dynamical process is unclear, so we perform molecular dynamics simulations to examine the applicability of the Euler buckling theory for the fast compression of the single-layer MoS2. We find that the Euler buckling theory is not applicable in such dynamical process, as the buckling critical strain becomes a length-independent constant in the buckled system with many ripples. However, the Euler buckling theory can be resumed in the dynamical process after restricting the theory to an individual ripple in the buckled structure. [ABSTRACT FROM AUTHOR]

The Euler buckling theory states that the buckling critical strain is an inverse quadratic function of the length for a thin plate in the static compression process. However, the suitability of this theory in the dynamical process is unclear, so we perform molecular dynamics simulations to examine the applicability of the Euler buckling theory for the fast compression of the single-layer MoS2. We find that the Euler buckling theory is not applicable in such dynamical process, as the buckling critical strain becomes a length-independent constant in the buckled system with many ripples. However, the Euler buckling theory can be resumed in the dynamical process after restricting the theory to an individual ripple in the buckled structure. [ABSTRACT FROM AUTHOR]