Vibration analysis of nano-structure multilayered graphene sheets using modified strain gradient theory

In this paper, for the first time, the modified strain gradient theory is used as a new size-dependent Kirchhoff micro-plate model to study the effect of interlayer van der Waals (vdW) force for the vibration analysis of multilayered graphene sheets (MLGSs). The model contains three material length scale parameters, which may effectively capture the size effect. The model can also degenerate into the modified couple stress plate model or the classical plate model, if two or all of the material length scale parameters are taken to be zero. After obtaining the governing equations based on modified strain gradient theory via principle of minimum potential energy, as only infinitesimal vibration is considered, the net pressure due to the vdW interaction is assumed to be linearly proportional to the deflection between two layers. To solve the governing equation subjected to the boundary conditions, the Fourier series is assumed for w=w(x, y). To show the accuracy of the formulations, present results in specific cases are compared with available results in literature and a good agreement can be seen. The results indicate that the present model can predict prominent natural frequency with the reduction of structural size, especially when the plate thickness is on the same order of the material length scale parameter.     

考虑范德华力的微型活齿传动系统应力分析

提出了一种微型集成活齿传动系统,介绍了其工作原理,推导了微尺度下任一活齿在不同啮合位置的静力学方程,利用范德华势函数对活齿所受的范德华力进行求解,研究了考虑范德华力时啮合活齿所受波发生器、活齿架、中心轮三者作用力的变化规律;运用Hertz理论,对活齿与波发生器、活齿架、中心轮的接触应力进行了理论推导,并研究了微结构不同几何参数对活齿所受作用力及接触应力规律的影响。     

Low‐Dimensional Topological Crystalline Insulators

Topological crystalline insulators (TCIs) are recently discovered topological phase with robust surface states residing on high‐symmetry crystal surfaces. Different from conventional topological insulators (TIs), protection of surface states on TCIs comes from point‐group symmetry instead of time‐reversal symmetry in TIs. The distinct properties of TCIs make them promising candidates for the use in novel spintronics, low‐dissipation quantum computation, tunable pressure sensor, mid‐infrared detector, and thermoelectric conversion. However, similar to the situation in TIs, the surface states are always suppressed by bulk carriers, impeding the exploitation of topology‐induced quantum phenomenon. One effective way to solve this problem is to grow low‐dimensional TCIs which possess large surface‐to‐volume ratio, and thus profoundly increase the carrier contribution from topological surface states. Indeed, through persistent effort, researchers have obtained unique quantum transport phenomenon, originating from topological surface states, based on controllable growth of low‐dimensional TCIs. This article gives a comprehensive review on the recent progress of controllable synthesis and topological surface transport of low‐dimensional TCIs. The possible future direction about low‐dimensional TCIs is also briefly discussed at the end of this paper.     

多壁碳纳米管横向扰动波传播的研究

将N层碳纳米管模拟成N层连续弹性壳模型，研究横向扰动波在单个多壁碳纳米管中轴向传播问题。研究表明，当扰动频率低于多壁碳纳米管的临界频率时，振动模态是同轴的；如果扰动频率至少高于多壁碳纳米管的一个临界频率时，振动模态是非同轴的，并以不同的波速传播，或低或高于单壁连续弹性壳模型的波速。因此，多壁碳纳米管的THz高频波存在着复杂现象，振动基本是不同轴的。特别是当多壁碳纳米管THz高频波以不同的速度传播时，传播速度不仅依赖于频率，而且依赖于非同轴的振动模态。     

Multibit Optoelectronic Memory in Top‐Floating‐Gated van der Waals Heterostructures

Nonvolatile memories based on van der Waals heterostructures have been proved to be promising candidates for next‐generation data storage devices. However, little attention has been focused on the structure with separated floating and control gates (the floating gates and control gates distribute at the different side of the channels), which were recently predicted to be capable of further improving device performance. Here, nonvolatile multibit optoelectronic memories are demonstrated using MoS₂, hexagonal boron nitride (h‐BN), and graphene in a top‐floating‐gated structure. With separated top graphene floating gate, the devices show a large memory window (≈95 V) via sweeping gate voltage from 80 to ?80 V, a high on/off ratio (≈10⁶) with an ultralow dark current (≈10^?14 A), as well as excellent retention characteristic (≈10⁴ s) and cyclic endurance. In addition, these devices can also be erased by a laser illumination with broadband spectrum after being electrically programmed. For the multilevel storage property, 7/6 stages controlled by different electrical operations, and 13/6/3 stages by different laser pulse illuminations are gained. The obtained results show a promising performance for nonvolatile optoelectronic memory using a top‐floating‐gated structure.     

Integrating spin-based technologies with atomically controlled van der Waals interfaces

As the feature sizes of electronic devices continue to shrink, new technologies—in particular spintronics and derived interfacial architectures—become increasingly pivotal. In this context, two-dimensional van der Waals materials and their interfaces are particularly attractive, relying on their ultimate atomic thicknesses and exceptional spin-related properties. This review provides a critical evaluation on the state-of-the-art of van der Waals interfaces and projected technological applications in spintronics, highlights major challenges and a viable solution—an all-in-situ growth and characterization strategy, and finally identifies several emerging spin-based technologies that might significantly benefit from the versatile van der Waals interfaces enabled by the strategy.     

Effects of combination modes of favorable growth unit of Al（OH）3 crystals precipitating on Van der Waals and chemical bond force

The dipole moment, total energy, atomic charge, orbital population and orbital energy of four representative combination models of the favorable growth unit Al6（OH）18 （H2O）6 of Al（OH）3 crystals precipitating are calculated by ab initio at RHF/STO-3G, RHF/3-21G, RHF/6-31G levels and DFT at RB3LYP/STO-3G, RB3LYP/ 3-21G, RB3LYP/6-31G levels with Dipole ＆ Sphere solvent model. The effect of various combination models on Van der Waals force is analyzed using dipole moment and molecular radius, and that on chemical bond force is analyzed using total energy, orbital population and orbital energy.     

液氨卧罐液体实时连续泄漏建模及分析

基于范德瓦耳斯方程和流体力学理论,考虑液氨卧罐泄漏时罐压和液面面积变化,建立了液氨卧罐液体实时连续泄漏模型.利用模型对某制冷企业液氨卧罐进行数学模拟,并将计算结果与PHAST模拟结果进行对比分析.结果 表明,液面高度h下降幅度先减缓后变大,液体泄漏质量流率Qm和泄漏孔处液体泄漏速率v的下降幅度及泄漏液体质量m的增加幅度...     

One-Pot Exfoliation of Graphite and Synthesis of Nanographene/Dimesitylporphyrin Hybrids

A simple one-pot process to exfoliate graphite and synthesize nanographene-dimesitylporphyrin hybrids has been developed. Despite the bulky mesityl groups, which are expected to hinder the efficient π–π stacking between the porphyrin core and graphene, the liquid-phase exfoliation of graphite is significantly favored by the presence of the porphyrins. Metallation of the porphyrin further enhances this effect. The resulting graphene/porphyrin hybrids were characterized by spectroscopy (UV-visible, fluorescence, and Raman) and microscopy (STEM, scanning transmission electron microscopy).