Jige Chen

Anisotropy Enhancement of Thermal Energy Transport in Supported Black Phosphorene.

Thermal anisotropy along the basal plane of materials possesses both theoretical importance and application value in thermal transport and thermoelectricity. Though common two-dimensional materials may exhibit in-plane thermal anisotropy when suspended, thermal anisotropy would often disappear when supported on a substrate. In this Letter, we find a strong anisotropy enhancement of thermal energy transport in supported black phosphorene. The chiral preference of energy transport in the zigzag rather than the armchair direction is greatly enhanced by coupling to the substrate, up to a factor of approximately 2-fold compared to the suspended one. The enhancement originates from its puckered lattice structure, where the nonplanar armchair energy transport relies on the out-of-plane corrugation and thus would be hindered by the flexural suppression due to the substrate, while the planar zigzag energy transport is not. As a result, thermal conductivity of supported black phosphorene shows a consistent anisotropy enhancement under different temperatures and substrate coupling strengths.

Anisotropic Dielectric Relaxation of the Water Confined in Nanotubes for Terahertz Spectroscopy Studied by Molecular Dynamics Simulations

The dynamics and structure of the hydrogen-bond network in confined water are of importance in understanding biological and chemical processes. Recently, terahertz (THz) time domain spectroscopy was widely applied for studying the kinetics of molecules and the hydrogen-bond network in water. However, the characteristics of the THz spectroscopy varying with respect to the confinement and the mechanism underlying the variation are still unclear. Here, on the basis of molecular dynamics simulations, the relationship between the anisotropic dielectric relaxation and the structure of the water confined in a carbon nanotube (CNT) was investigated. The results show that there are two preferred hydrogen-bond orientations of the confined water in the nanotube: (1) parallel to the CNT axis and (2) perpendicular to the CNT axis, which are clearly different. Moreover, the response of the orientations to the increment of the CNT diameters is opposite, leading to the opposite variations of the dielectric relaxation times along the two directions. The anisotropy in the relaxation time can be presented by the anisotropic dielectric permittivity which is able to be observed through THz spectroscopy. The anormal behaviors above are attributed to the special structure of the water close to the nanotube wall due to the confinement and hydrophobicity of CNT. These studies contribute an important step in understanding the THz experiments of water in nanoscales, and designing a chamber for specific chemical and biological reactions by controlling the diameters and materials of the nanotube.

Effect of water molecules on nanoscale wetting behaviour of molecular ethanol on hydroxylated SiO2 substrate

Abstract The wettability property of silica (SiO2) substrate by the ethanol molecules may play important roles in nanomedicine and nanomaterials fabrication. In this paper, by molecular dynamics (MD) simulations, we show that ethanol molecules can form an ordered monolayer on hydroxylated β-cristobalite SiO2 (1 1 1) substrate, therefore an ethanol droplet can form on this ordered monolayer. We found that water molecules could affect the formation of ethanol monolayer on SiO2 surface when the amount of water molecules is large, thus regulates the wetting transformation of ethanol molecules. The absorbed water molecules would disrupt the ordered ethanol monolayer and the ethanol molecules could not form the droplet.

Kinetic behavior of subsonic solitary wave in graphene nanoribbon

In this paper we investigate the kinetic behavior of subsonic solitary waves in graphene nanoribbons by means of molecular dynamics simulations. Unlike generating the supersonic solitary waves by a strong excitation, we generate three types of subsonic solitary waves by absorbing the thermal fluctuations in the armchair and zigzag graphene nanoribbons. They are localized in longitudinal, transverse, or coupled in both velocity directions with propagation speeds lower than the sound speeds. Their typical width is about 20-80 nm, which is much longer than the width of the supersonic solitary wave. More interestingly, they correspond to energy cavities rather than energy summits in the energy distribution due to the deformation in the density distribution. The observation of subsonic solitary waves with energy cavities implies the numerical evidence of dark solitary waves in graphene. Furthermore, the collisions between two solitary waves are investigated. The nonlinear phase shift only occurs during the collision of two solitary waves localized in the same velocity direction. We hope our results shed light on understanding the particular nonlinear properties of graphene.

Efficient selection methods for black phosphorene nanoribbons

Black phosphorene (BP) has shown anisotropic, electronic, mechanical, and thermal properties for various promising applications in recent years. To take full advantage of this unique anisotropy in its further functional design and application, it is of paramount importance to separate BP with well-defined chirality quickly and precisely. In this paper, we propose three efficient methods to separate BP ribbons with different chiralities by utilizing their strong chirality-dependent bending stiffness. Our results show that the bending stiffness in the zigzag direction is 4 times larger than that in the armchair direction. The mechanical anisotropy and bending-binding competition are used to realize chirality-dependent design. To fold, wrap or scroll the BP nanoribbons, it is necessary to overcome the bending stiffness by applying the binding energy between the BP nanoribbons and the contact surfaces. Due to the mechanical anisotropy, the BP nanoribbons could easily be folded, wrapped and scrolled along the armchair direction rather than the zigzag direction. Therefore, we introduce this characteristic in our chirality separation designs as, the self-folding model to fold up the armchair BP nanoribbons by nanoparticles, the suspension-bridge sieve model to pull down the armchair BP nanoribbons, and the nanorod-roller model to scroll up the armchair nanoribbons. Our separation methods in this research can be extended to other 2D materials with anisotropic mechanical properties. We hope our findings would offer a novel route for the manufacturing of BP-based electronic devices and self-assembly of nano-devices.