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。     

基于量子修正的石墨烯纳米带热导率分子动力学表征方法

本文提出了基于量子修正的非平衡态分子动力学模型,可用于石墨烯纳米带热导率的表征.利用该模型对不同温度下,不同手性及宽度的石墨烯纳米带热导率进行了研究,结果发现:相较于经典分子动力学模型给出的热导率随温度升高而单调下降的结论,在低于Debye温度的情况下,量子修正模型的计算结果出现了反常现象.本文研究还发现,石墨烯纳米带的热导率呈现出明显的边缘效应及尺度效应:锯齿型石墨烯纳米带的热导率明显高于扶手椅型石墨烯纳米带;全温段的热导率及热导率在低温段随温度变化的斜率均随宽度的增加而增大.最后,文章用Boltzmann声子散射理论对低温段的温度效应及尺度效应进行了阐释,其理论分析结果说明文章所建模型适合在全温段范围内对不同宽度和不同手性的热导率进行精确计算,可为石墨烯纳米带在传热散热领域的应用提供理论计算和分析依据.     

介孔尺度及结构对混合硝酸盐热输运特性的影响

米用分子动力学方法模拟介孔尺度和结构对混合硝酸盐热输运特性的影啊.便用Material Studio软件分别建立不同尺度、两种结构的混合硝酸盐模型以及达到共晶状态的不同比例的NaNO₃-KNO₃模型,通过对模型进行运算并整理计算结果,对纳米尺度下混合硝酸盐热输运特性的微观机理进行分析.结果表明:太阳盐的相变温度随着纳米孔尺度的增大呈现先增加后减小的趋势,最终与宏观尺度下的熔点一致;阳离子的比例对混合硝酸盐的相变温度有很大的影响,且纳米线结构也会改变硝酸盐的相变温度.硝酸盐的体热膨胀系数随着介孔尺度的增大而减小,随着NaNO₃含量的增加而增大,随着介孔结构的改变而改变.离子之间的相互作用的增强会使导热率增大,但对定压比热容没有太大影响.     

掺杂单晶硅纳米薄膜杨氏模量的多尺度理论模型

硅纳米材料物理性能的研究对其在半导体技术中的应用是十分重要的. 而掺杂有利于改善硅纳米材料的物理特性, 提高应用价值, 所以本文基于半连续体模型运用Keating形变势, 通过模型计算, 研究了不同位置及不同掺杂浓度的单晶硅纳米薄膜[100]方向的杨氏模量, 分析了掺杂浓度及掺杂位置不同时硅膜杨氏模量与膜厚关系, 结果表明, 与纯硅膜杨氏模量相比, 不同位置的掺杂对硅膜杨氏模量的影响并不明显, 不同浓度的掺杂对硅膜杨氏模量的影响较小. 而随着硅膜厚度的不断增加, 掺杂硅膜杨氏模量与纯硅膜杨氏模量的变化趋势一致, 特别是较小尺寸时的硅膜杨氏模量变化较大. 说明影响硅膜杨氏模量的主要因素是硅膜厚度. 该计算结果对研究硅纳米材料的其他力学特性有一定的参考价值, 也为进一步研究掺杂对纳米硅材料力学性能的影响提供一种全新思路.     

利用Keating模型计算Si(1-χ)Geχ及非晶硅的拉曼频移

利用Keating模型计算了Si(1-χ)Geχ合金中Si-Si,Ge-Ge和Si-Ge三种振动模态的拉曼频移,计算分别获得Ge浓度为0.1,0.5和0.9时,Si-Ge的振动拉曼频移分别为402.75,413.39和388.15 cm-1,这些结果与文献的实验结果符合,证明了Keating模型建立的关于原子振动模型是有效的,并可以利用拉伸压缩和相邻原子键之间弹性系数变化获得处于应变状态的拉曼光谱频率.利用Keating模型首次计算得到了非晶硅材料的单声子散射峰为477.029 cm-1,与文献实验结果480.0 cm-1相近,说明了非晶硅中原子的总体效果与晶体硅相比处于拉伸状态.     

体声波力传感器灵敏度的微分-综合分析法

为了分析基于应力/应变效应的体声波(BAW)力传感器的敏感机理、准确计算其灵敏度,提出了一种用于BAW力传感器灵敏度分析的微分-综合分析法。该方法借鉴了微积分的原理,在Mason等效电路模型中将一个完整的BAW谐振器替换为多个谐振器微元的并联,从而将谐振器有源区面积A上应力/应变场的有限元计算结果与压电薄膜材料的力学特性、谐振器微元的电声学特性关联起来;最后,在射频电路仿真软件中进行等效电路的综合,得到整个BAW谐振器在应力/应变场作用下的阻抗特性曲线及其串/并联谐振频率。当BAW谐振器微元的划分足够细密时,获得的灵敏度分析结果将足够精确。为了论证该方法的原理,给出了一个直观的校核案例。以一个嵌入式FBAR结构的四梁BAW加速度计表头为例,介绍了该方法用于BAW力传感器灵敏度分析的详细过程。虽然案例中只讨论了一种应力/应变型BAW力传感器的单一力敏机理,但该方法具有普适性。并且,当谐振器微元小到接近其压电材料晶格的尺度时,就能与压电薄膜的力-声-电特性的第一性原理计算结果关联起来,实现从微观材料特性到介观器件物理的多尺度计算。     

体声波力传感器灵敏度的微分-综合分析法

为了分析基于应力/应变效应的体声波(BAW)力传感器的敏感机理、准确计算其灵敏度,提出了一种用于BAW力传感器灵敏度分析的微分-综合分析法。该方法借鉴了微积分的原理,在Mason等效电路模型中将一个完整的BAW谐振器替换为多个谐振器微元的并联,从而将谐振器有源区面积A上应力/应变场的有限元计算结果与压电薄膜材料的力学特性、谐振器微元的电声学特性关联起来;最后,在射频电路仿真软件中进行等效电路的综合,得到整个BAW谐振器在应力/应变场作用下的阻抗特性曲线及其串/并联谐振频率。当BAW谐振器微元的划分足够细密时,获得的灵敏度分析结果将足够精确。为了论证该方法的原理,给出了一个直观的校核案例。以一个嵌入式FBAR结构的四梁BAW加速度计表头为例,介绍了该方法用于BAW力传感器灵敏度分析的详细过程。虽然案例中只讨论了一种应力/应变型BAW力传感器的单一力敏机理,但该方法具有普适性。并且,当谐振器微元小到接近其压电材料晶格的尺度时,就能与压电薄膜的力-声-电特性的第一性原理计算结果关联起来,实现从微观材料特性到介观器件物理的多尺度计算。     

金、银纳米结构中的非局域吸收特性

采用时域有限差分方法（FDTD）研究金、银纳米结构的非局域吸收。对金属材料的Drude-Lorentz模型进行离散差分,详细推导各项迭代系数。研究一维、二维、三维金、银纳米结构的吸收特性。讨论一维分层纳米薄膜吸收率与材料的关系。结果表明：非局域分层介质板仍然符合等效介质理论。在一维、二维情况下,金、银纳米结构的非局域吸收峰只与纳米尺度相关而与材料无关。三维纳米结构的非局域吸收特性不仅与纳米尺度相关还与材料特性相关。三维纳米结构尺度更小,非局域效应表现也更为明显,吸收峰的蓝移也更大。因此,三维纳米颗粒有望在纳米材料以及纳米器件的研究中发挥更大的作用。     

海洋湍流外尺度对高斯光束传输特性的影响

针对功率谱反演法模拟的海洋湍流相位屏中缺乏外尺度对光学特性影响的模型,基于Nikishov海洋湍流功率谱模型,提出一种指数型外尺度的Nikishov谱的修正模型,并通过功率谱的收敛性质及标准化光谱对该模型进行验证。相比于已有的包含外尺度参量的功率谱模型,该修正谱形式较为简单,便于分离变量,可在后续的研究中基于波动光学理论借助超几何函数对光学参量理论公式进行推导。基于该功率谱修正模型建立复合海水信道湍流相位屏仿真模型,针对功率谱反演法生成的相位屏存在低频信息不足的缺陷采用低频次谐波进行补偿,通过光线追踪的蒙特卡洛统计方法分析了湍流外尺度对高斯光束光学特性以及信号时域扩展特性的影响。波动理论数值计算与基于相位屏的仿真结果一致表明：在弱湍流条件下,海洋湍流外尺度对准直高斯光束光束扩展、质心漂移特性的影响较大,对光强闪烁的影响较小;海洋湍流外尺度对时域展宽影响较小,湍流影响下的信号时域扩展与传输距离近似呈现二次函数关系。     

极化合成孔径雷达海面成像模拟及分析

海浪极化SAR成像模拟对海面散射的研究有重要的意义.基于海浪谱理论,在考虑大、小尺度海浪影响的基础上,构建了双尺度的随机粗糙海面.根据该海面模型,利用Bragg散射模型,小扰动模型与速度聚束理论,模拟了不同状况下海浪的极化SAR图像.并针对海浪参数对极化图像的影响进行了分析,结果符合成像统计特性,得出了一些有益于海浪信...     

Mechanical properties of silicon nanobeams with an undercut evaluated by combining the dynamic resonance test and finite element analysis

Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications.A numerical experimental method of determining resonant frequencies and Young’s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper.Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process,which inevitably generates the undercut of the nanobeam clamping.In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut,dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L,which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data.By using a least-square fit expression including △L,we finally extract Young’s modulus from the measured resonance frequency versus effective length dependency and find that Young’s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon.This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.     

Influences of surface effects and large deformation on the resonant properties of ultrathin silicon nanocantilevers

The purpose of the present work is to quantify the influences of the discrete nature, the surface effects, and the large deformation on the bending resonant properties of long and ultrathin 〈100〉 silicon nanocantilevers. We accomplish this by using an analytical semi-continuum Keating model within the framework of nonlinear, finite deformation kinematics. The semi-continuum model shows that the elastic behaviors of the silicon nanocantilevers are size-dependent and surface-dependent, which agrees well with the molecular dynamics results. It also indicates that the dominant effect on the fundamental resonant frequency shift of the silicon nanocantilever is adsorption-induced surface stress, followed by the discrete nature and surface reconstruction, whereas surface relaxation has the least effect. In particular, it is found that a large deformation tends to increase the nonlinear fundamental frequency of the silicon nanocantilever, depending not only on its size but also on the surface effects. Finally, the resonant frequency shifts due to the adsorption-induced surface stress predicted by the current model are quantitatively compared with those obtained from the experimental measurement and the other existing approach. It is noticed that the length-to-thickness ratio is the key parameter that correlates the deviations in the resonant frequencies predicted from the current model and the empirical formula.     

Mechanical properties of silicon nanobeams with undercut evaluated by combining dynamic resonance test and finite element analysis

Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young's modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by laser Doppler vibrometer is presented in this paper. Silicon nanobeams test structures are fabricated from silicon-on-insulator wafers by using a standard lithography and anisotropic wet etching release process, which inevitably generates the undercut of the nanobeam clamping. In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut, dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value Δ L, which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data. By using a least-square fit expression including Δ L, we finally extract Young's modulus from the measured resonance frequency versus effective length dependency and find that Young's modulus of silicon nanobeam with 200-nm thickness is close to that of bulk silicon. This result supports that the finite size effect due to surface effect does not play a role in mechanical elastic behaviour of silicon nanobeams with the thickness larger than 200 nm.     

掺杂硅纳米梁谐振频率的理论模型及分子动力学模拟

通过理论计算与模拟,研究分析了P元素替代掺杂单晶硅纳米梁的谐振频率.计算模拟了两端固支单晶硅纳米梁的谐振频率随尺寸、掺杂浓度与温度的变化.通过对计算结果与模拟结果的分析得到:单晶硅纳米梁的谐振频率随着硅纳米梁长度尺寸的增大而减小;硅纳米梁的谐振频率随着掺杂浓度的增大而增大,但变化趋势并不明显;最后考虑了温度效应,发现掺杂硅纳米梁的谐振频率随着温度的增大而减小,但从谐振频率的数值来看,硅梁的谐振频率随温度的变化趋势并不明显,即温度对硅梁谐振频率基本无影响.由此得出结论:掺杂浓度与温度对硅纳米梁谐振频率的影响很小,影响单晶硅纳米梁谐振频率的主要因素是尺寸大小,掺杂单晶硅纳米梁的谐振频率具有尺寸效应.     

利用Keating模型计算Si（1-x）Gex及非晶硅的拉曼频移

利用Keating模型计算了Si_（1-x）Ge_x合金中Si—Si,Ge—Ge和Si—Ge三种振动模态的拉曼频移,计算分别获得Ge浓度为01,05和09时,Si—Ge的振动拉曼频移分别为40275,41339和38815 cm^-1,这些结果与文献的实验结果符合,证明了Keating模型建立的关于原子振动模型是有效的,并可以利用拉伸压缩和相邻原子键之间弹性系数变化获得处于应变状态的拉曼光谱频率.利用Kea 关键词： Keating模型 拉曼光谱 （1-x）Ge_x')" href="#">Si_（1-x）Ge_x 非晶硅     

Randomization-and-relaxation model revisited

Abstract

The interatomic potentials of Stillinger-Weber and Tersoff were incorporated into the randomization-and-relaxation model, which was originally developed for modelling amorphous silicon by using the Keating interatomic potential. The inclusion of more recent and more complicated interatomic potentials resulted in a more sophisticated set of bond switching rules which form the basis for the randomization-and-relaxation algorithm. This improved model was then used to model small isolated amorphous zones which are produced by individual heavy ions during ion implantation in silicon. The temperature evolution during zone creation was calculated by using idealized thermal spike model. The structure and stability of these amorphous zones was examined with respect to the energy of incoming ion and with respect to the interatomic potential employed. It was established that significantly lower spike energy is required to create a stable amorphous region than in the simulation where the Keating potential was employed.     

Wave propagation in magneto-electro-elastic nanobeams via two nonlocal beam models

This paper makes the first attempt to investigate the dispersion behavior of waves in magneto-electro-elastic (MEE) nanobeams. The Euler nanobeam model and Timoshenko nanobeam model are developed in the formulation based on the nonlocal theory. By using the Hamilton’s principle, we derive the governing equations which are then solved analytically to obtain the dispersion relations of MEE nanobeams. Results are presented to highlight the influences of the thermo-electro-magnetic loadings and nonlocal parameter on the wave propagation characteristics of MEE nanobeams. It is found that the thermo-electro-magnetic loadings can lead to the occurrence of the cut-off wave number below which the wave can’t propagate in MEE nanobeams.     

Internally consistent verification of mean-field models for aggregation using large-scale molecular dynamics

The underlying atomistic mechanisms that govern vacancy aggregation in crystalline silicon are probed using a parametrically consistent, two-scale approach. The essential ingredient in this framework is a direct, quantitative comparison between the predictions of atomistic and continuum simulations for the transient size distribution of vacancy clusters. The former is carried out with parallel molecular dynamics simulation of a silicon system containing 215?000 atoms and 1000 vacancies. The continuum model is based on a sequence of coupled Master equations and is parametrized based on the same empirical potential used to perform the atomistic aggregation simulation. An excellent representation of the cluster size distribution can be obtained with consistent parameters only if the relevant physical mechanisms are captured correctly. The inclusion of vacancy cluster diffusion and a model to capture the dynamic nature of cluster morphology at high temperature are necessary to reproduce the results of the large-scale atomistic simulation. Finally, the continuum model is used to investigate cluster evolution for longer times, which are relevant for process simulation of defect-optimized silicon substrates for microelectronic device fabrication.     

Improved model of optical phonon confinement in silicon nanocrystals

We develop a model for calculating the Raman scattering spectra from phonons confined in for silicon nanocrystals, which is based on the familiar approach taking into account the uncertainty in the quasi-momentum of phonons localized in the nanocrystals. The model is considerably improved by taking into account dispersion of phonons not only in the magnitude of the quasi-momentum, but also in its direction. A significant refinement of the model is also due to the fact that phonon dispersion is calculated using the widely approved Keating model instead of being approximated by empirical expressions as was done in earlier approaches. The calculations based on this model make it possible to determine the sizes of silicon nanocrystals more precisely from analysis of the experimental Raman spectra.