Theoretical study of electromechanical property in a p-type silicon nanoplate for mechanical sensors

Electromechanical property of a p-type single-crystal silicon nanoplate is modelled by a microscopic approach where the hole quantization effect and the spin-orbit coupling effect are taken into account. The visible anisotropic subband structures are calculated by solving self-consistently the stress-dependent 6×6 k.p Schrodinger equation with the Poisson equation. The strong mixing among heavy, light, and split-off holes is quantitatively assessed. The influences of the thickness and the temperature on the piezoresistive coefficient are quantitatively investigated by using the hole concentrations and the effective masses from the complex dispersion structure of the valence band with and without stresses. Our results show that the stress determines the extent to which the band is mixed. The hole quantization effect increases as the thickness decreases, and therefore the valence band is strongly reshaped, resulting in the size-dependent piezoresistivity of the silicon nanoplate. The piezoresistive coefficient increases almost 4 times as the thickness reduces from the bulk to 3 nm, exhibiting a promising application in mechanical sensors.     

Keating改良模型的硅纳米梁动态特性

提出一种用于分析硅纳米梁动态特性的改良型半连续体模型,对比传统的连续体理论,这种新模型使用了Keating势,并考虑了纳米梁在宽厚两个维度的分立特性。依据Sun-Zhang模型思想和能量守恒定律,建立了改良型Keating模型,并进行了双端固支梁的基频计算。在这个过程中,对一些表面效应也进行系统分析。结果表明,该改良模型一方面在纳米尺度下与Material StudioTM软件仿真结果较为符合,另一方面也能在微观尺度下较好的接近连续体模型的计算数据。同时,该模型还反映了基频随纳米梁宽度变化的特性,这也符合一些实际实验。     

Effect of （2 ×1） Surface Reconstruction on Elasticity of a Silicon Nano-Plate

A semi-continuum approach is developed to describe the effect of （2 ×1） surface reconstruction on the elastic modulus of the silicon nano-plate. Young＇s moduli of a （001） silicon nano-plate along the high-symmetry [100] direction are obtained with and without considering （2 × 1） surface reconstruction. The approach predicts that the nano-plate with unreconstructed （001） surface is elastically softer than the bulk while it exhibits the opposite behaviour with （2 × 1） reconstructed surface. On the （001） surface, the （2 × 1） reconstructed surface dominates the plate as the thickness of the plate scaling decreases to several tens of nanometre. Whether the nano-plate is softer or stiffer depends on bond loss, bond saturation and direction of bond alignment, which have major impacts on the mechanics of the nano-plate.     

Keating改良模型的硅纳米梁动态特性（英文）

提出一种用于分析硅纳米梁动态特性的改良型半连续体模型,对比传统的连续体理论,这种新模型使用了Keating势,并考虑了纳米梁在宽厚两个维度的分立特性。依据Sun-Zhang模型思想和能量守恒定律,建立了改良型Keating模型,并进行了双端固支梁的基频计算。在这个过程中,对一些表面效应也进行系统分析。结果表明,该改良模型一方面在纳米尺度下与Material StudioTM软件仿真结果较为符合,另一方面也能在微观尺度下较好的接近连续体模型的计算数据。同时,该模型还反映了基频随纳米梁宽度变化的特性,这也符合一些实际实验。     

土壤/沉积物吸附有机污染物机理研究的进展

有机污染物与土壤、沉积和以及地表水中悬浮物（如腐殖质）之间的相互作用——吸咐与解吸是决定它们环境行为最重要的因素之一。自60年代末期以来,经各国科学院们的共同努力,该项工作取得了一些非常重要的研究成果,本文将对该领域的研究现状进行评述,并对其未来可能的发展方向提出自己的见解。     

径向洛伦兹阵列光束在自由空间的传输特性

推导出有初始相位分布的径向洛伦兹阵列光束在自由空间传输的解析公式,用以研究相干合成光束在自由空间的传输特性。结果表明:在远场,具有不同相位分布的光束光强剖面成为空心形状,具有相同相位分布的光束光强剖面中心为亮斑。合成光束束宽和桶中功率与子光束束腰宽度、径向阵列的初始相位分布和半径有关。对所得结果用数值计算例做了说明。当阵列半径较大和束腰宽度较小时,具有不同相位分布和相同相位的光束束宽随传输距离的变化曲线和桶中功率都趋于一致。