不同温度硅纳米薄膜在表面重构下杨氏模量的分子动力学研究

采用分子动力学方法计算了100K到800K之间（001）面硅纳米薄膜（1nm,2nm厚）[110]与[1—10]两个方向上的杨氏模量。2×1表面重构形成了dimmer键,使[110]方向杨氏模量大于[1—10]方向杨氏模量。纳米薄膜的杨氏模量随着温度升高而下降。热膨胀导致了温度效应。当尺度到达纳米尺度,表面重构和温度效应更加明显。     

硅薄膜导热系数微尺度效应的临界尺寸

基于灰介质假设及拟合的色散关系,采用蒙特卡洛方法对微纳米硅薄膜内的声子热输运特性进行了模拟.将3μm厚的硅薄膜导热系数的计算结果与文献结果进行了对比,二者吻合较好.分析了厚度对薄膜内温度场及导热系数的影响.结果表明,当厚度小于某一尺度时,薄膜导热系数会随着厚度的减小而降低,呈现尺度效应;薄膜内温度场也不再是线性分布,而是在边界处呈现阶跃特性,且随着厚度减小,温度阶跃增大.基于该方法求得了100~400 K温度区间内,硅薄膜法向导热系数出现明显尺度效应的临界尺寸.计算发现,随着温度的升高,临界尺寸变化范围很大,平均温度为100 K时,临界尺寸约为50μm,平均温度为400 K时,临界尺寸约为2.5μm,前后相差了一个数量级.     

单晶硅纳米梁杨氏模量的弯曲测试

为研究纳米梁的力学特性,采用SOI晶圆制备了硅双端固支梁纳米梁,利用典型的原子力显微镜（AFM）弯曲测试方法测试了硅纳米梁〈100〉晶向的杨氏模量.AFM悬臂探针定位在纳米梁的中点处向下移动,纳米梁受到挤压发生弹性形变,形变过程存在一个最大形变点,在该点后,纳米梁被挤压在SOI硅片底层硅上.最大形变前的测试数据用于计算力-位移曲线斜率,最大形变后的测试数据用于计算探针的灵敏度,其实验值分别为0.792N/m和81.83nm/V.最终得到的杨氏模量为104GPa,该值小于体硅的杨氏模量,表面应力和缺陷可能是导致实验值偏小的原因.     

纳米发电机首次实现纳米尺度机械能转换

来自美国亚特兰大的最新消息，佐治亚理工学院（Georgia Institute of Technology）校董事讲座教授和工学院杰出讲座教授、中国国家纳米科学中心海外主任王中林教授等成功地在纳米尺度下将机械能转换成电能，在世界上首次研制成功纳米发电机，开启了纳米科学和技术的新篇章。     

金在纳米尺度下“性情大变”

在正常尺度下，金是出了名的“极不活泼的”金属之一，不易被氧化，也不易被腐蚀。但美国科学家最新研究发现，金在纳米尺度下会“性情大变”，一切似乎都变得皆有可能（论文发表在最近的《物理评论通讯》杂志上）。     

纳米尺度铁电畴的扫描力显微镜成像研究进展

扫描力显微镜(SFM)作为一种新型的超分辨率近场扫描探针显微仪器正日益受到各学科领域的高度重视.在铁电材料领域,SFM是开展纳米尺度铁电畴结构成像、纳米尺度畴结构控制及纳米尺度微区的铁电性、介电性、压电性等特性研究的潜在的强有力的研究工具.本文就纳米尺度铁电畴的扫描力显微镜的成像原理的研究进展作一综述.     

环氧树脂/二氧化硅纳米尺度杂化材料的制备

本文通过溶胶-凝胶过程制备了环氧树脂/二氧化硅的杂化材料,材料宏观上皆为透明的块状固体,扫描电镜观察发现无机粒子达到了纳米级的分散.并对材料的热性能和力学性能进行了研究.     

纳米纤维组织工程支架及其纳米效应研究进展

综述了纳米纤维组织工程支架的最新研究进展,评述了其制备技术、特点及其存在的纳米效应.指出天然细胞外基质为三维纳米纤维结构,其纤维连续,直径为纳米级,包含比例确定的纳米与微米空间,且与细胞存在纳米水平的相互作用;然而,目前的人工纤维支架,其纤维直径多为微米或数百纳米,或者缺乏纳米空间.采用生物纳米技术获得的细菌纤维素纳米纤维,其直径小于10 nm,自身呈三维网状结构,富含纳米空间,是构建新一代纳米组织工程支架的理想材料.     

碳基纳米填料填充聚丙烯纳米复合材料的制备与流变特性

采用熔融共混法分别制备了多壁碳纳米管(MWCNT)、炭黑(CB)、石墨微片(GNP)填充聚丙烯(PP)纳米复合材料。采用毛细管流变仪和旋转流变仪对所制备的复合材料的黏度尺度效应和动态流变特性进行了实验研究。研究发现,填充材料的形态和含量都会对黏度的尺度效应和粘弹性产生影响。各填充体系的剪切黏度都会随着粒子质量分数的增加而增大,不同直径口模下的剪切黏度偏差值有逐渐减小的趋势,炭黑填充体系具有明显的黏度尺度效应。填充体系的储能模量和损耗模量均随着粒子质量分数的增加而增大。     

纳米硅的光致发光机制

10多年来,人们对纳米硅的制备方法、微结构特征以及发光机制等方面进行了深入的研究和探讨.重点对不同制备条件及后期处理条件下的纳米硅的发光机制做了评述和总结,并对目前研究状况中存在的问题及发展前景进行了分析.     

研究单壁碳纳米管杨氏模量的一种能量方法

本文利用能量方法研究了单壁碳纳米管(single-walled carbon nanotubes, SWCNT)的杨氏模量.文中,首先采用分子力学理论得出了受轴向载荷作用下单壁碳纳米管的总势能;然后通过总势能与相应薄圆柱壳的应变能比较,推导出了单壁碳纳米管杨氏模量的计算公式.另外,从一系列碳纳米管杨氏模量的计算发现,本文研究结果与现有研究结果比较一致.     

Evaluation of Young''''s Modulus and Residual Stress of NiFe Film by Microbridge Testing

Microbridge testing was used to measure the Young's modulus and residual stress of metallic films. Samples of freestanding NiFe film microbridge were fabricated by microelectromechanical systems. Special ceramic shaft structure was designed to solve the problem of getting the load-deflection curve of NiFe film microbridge by the Nanoindenter XP system with normal Berkovich probe. Theoretical analysis of load-deflection curves of the microbridges was proposed to evaluate the Young's modulus and residual stress of the films simultaneously. The calculated results based on experimental measurements show that the average Young's modulus and residual stress for the electroplated NiFe films are 203.2 GPa and 333.0 MPa, respectively, while the Young's modulus measured by the Nano-hardness method is 209.6±11.8 GPa for the thick NiFe film with silicon substrate.     

小直径环状试样静态杨氏模量测试仪的研制

介绍了微小试样材料弹性模量测试仪的组成概况(硬件及软件)。对测试仪做了标定、校核工作。利用该仪器实测了高温气冷堆包覆燃料颗粒SiC层(直径<1mm)的弹性模量。测试仪精度为:力:0-0.2N,+0.005N 位移:0.60μm,±0.5μm     

Measuring True Young's Modulus of a Cantilevered Nanowire: Effect of Clamping on Resonance Frequency

The effect of clamping on resonance frequency and thus measured Young's modulus of nanowires (NWs) is systematically investigated via a combined experimental and simulation approach. ZnO NWs are used in this work as an example. The resonance tests are performed in situ inside a scanning electron microscope and the NWs are cantilevered on a tungsten probe by electron-beam-induced deposition (EBID) of hydrocarbon. EBID is repeated several times to deposit more hydrocarbons at the same location. The resonance frequency increases with the increasing clamp size until approaching that under the "fixed" boundary condition. The critical clamp size is identified as a function of NW diameter and NW Young's modulus. This work: 1) exemplifies the importance of considering the effect of clamping in measurements of Young's modulus using the resonance method, and 2) demonstrates that the true Young's modulus can be measured if the critical clamp size is reached. Design guidelines on the critical clamp size are provided. Such design guidelines can be extended to other one-dimensional nanostructures such as carbon nanotubes.     

Computational Design of Silicon Suboxides: Chemical and Mechanical Forces on the Atomic Scale

Silicon suboxides play an important role in different industrial applications, particularly in the form of the Si–SiO₂ interface, which is one of the key elements in present day microelectronics and potentially in future nano-electronics as well. This paper focuses on the chemical and mechanical effects related to the existence of different oxidation states of Si atoms in SiO _x systems with various Si:O composition and topology, such as O atoms in Si, the Si–SiO₂ interface, and O vacancies in SiO₂. We compare the stress–strain relation in SiO₂ interfaces with (100), (111) and (110) surfaces, the relative stability of oxygen vacancies at different locations in Si–SiO₂ layers and defects in Si and SiO₂ crystals related to O migration. Our study is based on ab initio computations of molecular and periodic systems with both localized and plane wave basis sets.     

微纳米尺度单晶硅各向异性表面的切削特性

利用纳米压痕仪和原子力显微镜,分别对单晶硅Si(100)、Si(110)、Si(111)三种晶面取向的表面进行微纳米尺度下的切削性能进行了实验研究。实验结果表明:在定载荷下,刻划速度的大小对单晶硅Si(100)、Si(110)晶面取向的切削力、摩擦系数的大小影响较小,但对单晶硅Si(111)晶体取向影响较大;在较低载荷下,单晶硅各晶面取向表面划痕细小,深度较浅且不明显,切削力大小无明显变化规律。随着载荷的逐渐增大,划痕宽度及深度也逐渐增大,切削力也相应增大,但并非呈线性增长。当载荷增大到一定值后,单晶硅各表面发生严重的塑性变形,变形积累一定程度后,沟槽两侧及探针前端形成明显的切屑堆积。     

Effect of Sn on HighPermeability Grain-Oriented Silicon Steel

The effect of Sn on highpermeability grain-oriented silicon steel was studied by PHI-700 Auger electron spectroscopy (AES), JEM-2100 transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) technology. The results show that (1) the magnetic properties could be significantly increased by adding Sn; (2) the primary grain size becomes smaller with the addition of 0.19 wt% Sn and the Goss orientation crystal nucleus become more numerous as well; (3) the grain boundary segregation of Sn is still obvious at 970 °C in hightemperature annealing process; and (4) the average size of precipitates becomes smaller with the addition of 0.19 wt% Sn; meanwhile the dispersion and the inhibitor are also promoted. These conclusions are in agreement with the experimental results.     

分散剂对氮化硅浆料流变性的影响

本文研究了分散剂对氮化硅粉体的胶体特性,流变特性的影响,结果发现,Ｓｉ３Ｎ４（Ｓｔａｒｃｋ）粉料的等电点在ｐＨ＝４．２,粉料的最大Ｚｅｔａ电位在ｐＨ＝１１附近,分散剂的引入将使其等电点位移,其位移量与分散剂的用量有关,最佳分散剂用量在０．８－１．２ｗｔ％之间。该氮化硅浆料属非牛顿的依时性流体。