共查询到20条相似文献,搜索用时 94 毫秒
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本文采用分子动力学模拟方法研究了在拉伸载荷下,堆垛层错和温度对纳米多晶镁力学性能的影响,在模拟中,采用嵌入原子势描述镁原子之间的相互作用.计算结果表明:在纳米晶粒中引入堆垛层错能明显增强纳米多晶镁的屈服应力,但堆垛层错对纳米多晶镁杨氏模量的影响很小;温度为300.0K时,孪晶在晶粒交界附近形成,孪晶随着拉伸应变的增加而逐渐生长.当拉伸应变达到0.087时,一种基面与X—Y面成大约35°角且内部包含堆垛层错的新晶粒成核并快速增长.也就是说,孪晶和新晶粒的形成和繁殖是含堆垛层错的纳米多晶镁在300.0K温度下的主要变形机理.模拟结果也显示,当温度为10.0K时,位错的成核和滑移是含堆垛层错的纳米多晶镁拉伸变形的主要形式. 相似文献
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Yoshida等人提出的惯性流体模型只能解释脉冲激光烧蚀制备纳米硅晶粒平均尺寸随环境气压的变化规律.在此模型基础上,考虑到烧蚀粒子的初始速度分布(Maxwell分布),得到了纳米硅晶粒尺寸分布的解析表达式,数值模拟结果与Yoshida等人在不同环境氦气压下制备样品的晶粒尺寸分布的实验统计数据基本相符.还利用修正后的模型对不同环境气体种类(氦、氖、氩)中制备的纳米Si晶粒尺寸分布进行了模拟,模拟结果与实验数据相符.结论可为实现纳米硅晶粒尺寸的均匀可控提供理论依据.
关键词:
纳米硅晶粒
脉冲激光烧蚀
惯性流体模型
尺寸分布 相似文献
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采用氧化和析出的方法在氧化硅中凝聚生成锗纳米晶体量子点结构. 其形成的锗晶体团簇没有突出的棱角和支晶结构,锗晶体团簇的轮廓较圆混,故可以用球形量子点模型来模拟实际的锗晶体团簇. 对比了在长时间退火氧化条件下和在短时间退火用激光照射氧化条件下所生成的锗纳米晶体结构的PL光谱和对应的锗纳米晶体团簇的尺寸分布. 短时间退火氧化条件下生成的锗纳米晶体较小(3.28—3.96nm),长时间退火用激光照射氧化条件下所生成的锗纳米晶体较大(3.72—4.98nm);其分布结构显示某些尺寸的锗纳米晶体团簇较稳定,适当的氧化条件可以得到尺寸分布范围较窄的锗纳米晶体团簇. 用量子点受限模型计算了锗纳米晶体团簇的能隙结构,用Monte Carlo方法模拟了PL光谱和对应的锗纳米晶体团簇的尺寸分布,分别与实验结果符合较好.
关键词:
锗晶体团簇
纳米晶体
量子点
激光照射 相似文献
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用湿化学法在水溶液中合成了单分散的、大小尺寸可控的、巯基包裹的胶体CdTe纳米晶体,并利用CdTe纳米晶体和双功能分子poly(diallyldimethylammonium chloride)(PDDA)在Si衬底表面自组织生长了有序的层状纳米晶薄膜,荧光光谱研究了层状纳米晶体之间的共振能量迁移过程.结果表明:层状自组织生长的样品中纳米晶粒的间隔几乎一样,表明它们是有序排列的;而用直接干燥形成的样品中,小尺寸和大尺寸的纳米晶体之间间隔较短,发生荧光共振能量迁移,较小尺寸的纳米晶粒荧光峰(即波长较短处的晶
关键词:
CdTe纳米晶体
量子限制效应
共振能量迁移 相似文献
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采用分子动力学模拟方法研究了硅纳米颗粒在碳纳米管上的生长,并分析了这种复合材料的基本结构.研究表明,由于硅原子和碳纳米管之间的相互作用以及碳纳米管的巨大的表面曲率,硅原子在碳纳米管表面不是形成覆盖碳纳米管的二维薄膜,而是生成具有三维结构的硅纳米颗粒.小纳米颗粒的结构和无基底条件下生成的颗粒结构基本一致.对于大纳米颗粒,不同于无基底条件下形成的球状纳米晶体硅结构,硅纳米颗粒沿管轴方向伸长,其结构为类似于硅晶体的无定形网络结构.
关键词:
纳米颗粒
碳纳米管
硅
分子动力学模拟 相似文献
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运用分子动力学方法对纳米晶柱阵列衬底上铝簿膜的外延生长进行了模拟研究.所采用的原子间相互作用势为嵌入原子法(EAM)多体势.模拟结果表明:采用纳米晶柱阵列衬底可以在不形成失配位错的条件下释放其上生长的外延薄膜晶体中的失配应变,有效地抑制其中失配位错的形成,获得高质量的外延薄膜晶体;这种纳米晶柱阵列的几何设计应满足两个基本条件:1) 晶柱的横截面尺寸应大于对应温度下的晶柱热失稳临界尺寸,以克服纳米结构的热失稳,模拟显示700K下铝的热失稳临界尺寸为19nm;2) 晶柱的高度与间距之比应大于076,以保证
关键词:
失配位错
分子动力学
纳米晶柱
铝 相似文献
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A.S. AL-DMOURK.S. MOHAMMAD 《Journal of sound and vibration》2002,253(3):545-569
Principal component analysis is used to simplify the extraction of the natural frequencies and their corresponding orthonormal mode shapes directly from experimental data of unknown flexible structures. A control law is designed using a state-space modal model and is tested on different structures. The results are extremely encouraging and demonstrate successful implementation of the active control strategies. The controller actuator as well as the detection sensor locations are examined throughout the structure length. 相似文献
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差谱技术用于塑料焊接剂的结构鉴定 总被引:1,自引:0,他引:1
本文利用NICOLET20DXB傅里叶变换红外光谱仪的差减光谱(差谱)软件对复杂混合物的光谱成功地进行了二次光谱图的差减,得到了很好的单一组分的红外光谱图,从而鉴定了塑料焊接剂主成分的结构。 相似文献
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本文讨论了在单晶体结构分析中出现的各种类型的对映相位双解情况及其一般形式,给出了能够用统一的方式处理各类对映相位双解的变型分量关系式以及相应的概率公式。本文还讨论了将上述结果实际应用于测定蛋白质晶体结构的有关问题。
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本文用X射线衍射方法研究电沉积Ni-P合金的结构。研究表明:当P含量小于5.4at%时合金为P在Ni中的过饱和固溶体;当P含量大于7.8at%时结构发生明显变化,衍射花样可解释成一些大小为6—8?的密堆小片。它们作平行而无规的相对错动,片间距为2.04?,堆垛成小柱状,柱高随含P量的增高而减小,从含P为7.8%时的124?降到含P为18%时的13?,成为典型的非晶态合金的衍射花样。利用{lll}谱线的强度比,或者用原子径向分布函数的峰形和峰高,估算出原子偏离平衡位置的均方根值为0.17?。由于这些扭曲,使层间距在小于原子直径的情况下仍能实现片与片间相对平行而无规的错动,而且使一个小柱能够直接过渡到另一个取向不同的小柱而无须形成晶界。所以样品是一个连续分布的整体而不是一个微晶的集合体。另外,还测量了{lll}谱线不同衍射级的宽度。发现βlll/β222lll/cosθ222,或许线宽除受垛高因素所制约外,可能还与成份起伏、微应变以及片层间距轻微的不规则性有关。
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本文讨论了非晶态NdxT1-x(T=Fe,Co,Ni)薄膜为滋结构,以及在低温下磁化强度随温度变化的反常特性,在20K附近观测到磁化强度有陡降现象,并且在较大的成份范围内所对应的温度基本不变,我们认为,在这类非晶态合金中,当Nd含量超过一定值后,其磁中性态(通称基态)可能同时是散反铁磁性和散铁磁性的共存态,在20K附近的磁化强度发生陡降,是散反铁磁性←→顺磁性相转变的反映,这两种磁结构共存的临界成份相应约为:Nd-Fe情况x≥0.45;Nd-Co,x≥0.20;Nd-Ni,x≥0.08。
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LOW TEMPERATURE OPTICAL PROPERTIES OF AMORPHOUS OXIDE NANOCLUSTERS IN POLYMETHYL METHACRYLATE MATRIX 下载免费PDF全文
We studied the temperature-dependent steady-state and time-resolved fluorescence properties of very small (1-2 nm) ZnO, CdO, and PbO amorphous nanoclusters prepared in AOT reverse micelles and imbedded in polymethyl methacrylate(PMMA) films. X-ray diffraction and electron diffraction and imaging indicate that these structures are amorphous. These amorphous oxide nanoclusters demonstrate similar structural, electronic, and optical properties. Properties of steady-state fluorescence spectra indicate the unique localization of electronic states due to the amorphous structure. ZnO and CdO show double-band fluorescence structure, which is due to the spin-orbital splitting, similar to Cu2O. Time-resolved fluorescence studies of the nanoclusters in the polymer reveal two lifetime components, as found in solution. The slow component reflects relaxation processes from band-tail states while the fast component may be related to high-lying extended states. The temperature dependence of fast fluorescence component reveals the presence of exciton hopping between anharmonic wells at temperatures higher than 200K. We correlate the barrier height between two wells formed around local atoms with the inter-atomic distance and bond ionicity. 相似文献
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Y.-B. YANGY.-S. WU 《Journal of sound and vibration》2002,258(1):65-94
The dynamic stability of trains moving over bridges shaken by earthquakes is studied. Unlike the seismic analysis of structures containing a single subsystem, the seismic analysis of a bridge sustaining a passing train requires not only information on acceleration, but also on velocity and displacement of the ground motion. Four typical earthquakes, including the 1999 Chi-Chi Earthquake, were adopted as the input excitations, each of which was normalized to have a moderate intensity. The results indicate that a train initially resting on the bridge can stay safely under the ground motions considered, if the bridge and track structures do not exhibit inelastic deformations during the earthquake. The type of the vertical component of ground motions can affect significantly the stability of the train-rail- bridge system. As a preliminary attempt, safety, possible instability and instability regions were established in a three-phase plot for the train running over the bridge for each of the earthquakes considered, from which the maximum allowable speed for the train to run safely under the specified ground acceleration can be obtained. 相似文献
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用固态反应法制备了YBa2Cu3-xFexOy(x=0—0.5)一系列样品,反应在空气中进行.运用正电子湮没技术、扫描电子显微镜和X射线衍射进行了研究,并测定了氧含量.正电子湮没结果发现,x=0.12时短寿命分量τ1和长寿命分量τ2都存在一异常变化.X射线衍射和扫描电子显微镜研究分别表明,材料在x=0.12—0.15区间内发生正交四方相变,晶粒尺寸突然由小变大.通过对上述实验结果的分析可以得到,在该类材料中,正电子对结构相变十分敏感;另外,当Fe掺杂量增大到一定程度时,Fe原子由随机分布变为成簇分布
关键词:
Fe掺杂YBCO
高温超导电性
正电子湮没
结构相变 相似文献
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《Journal of Macromolecular Science: Physics》2013,52(6):1079-1096
Thin films of nylon-6 (N6), nylon-6,6 (N66), and their blends (N6/N66 = 70/30, 50/50, and 30/70) were prepared by casting from solution (1.0 wt%) in formic acid under ambient conditions. The dried films were melted at 260°C or 280°C and then isothermally crystallized at 200°C. Morphological observations and selected-area electron diffraction (SAED) by transmission electron microscopy (TEM) of the resulting films revealed the following results: All specimen films (N6/N66 = 100/0, 70/30, 50/50, 30/70, and 0/100) had fibrillar entities that were undoubtedly crystalline judging from SAED and dark-field (DF) imaging. Some of the fibrillar entities were constituents of a spherulite or a sheaflike structure (namely, an immature spherulite). To delete the “memory” of the structures of the N66 component that were formed in as-cast films, the films have to be melted at 280°C. As to isothermal crystallization of the blends at 200°C after melting at 280°C, it is postulated that the N66 component first starts to crystallize, and then the N6 one starts to crystallize afterward. 相似文献