Study on Structural Instability of Carbon Nanotube as Induced by In-situ Electron Beam Irradiation in Transmission Electron Microscope

自从碳纳米管被发现以来，它们独特的一维管状结构和奇异的电学和力学性质引起了人们的极大关注。尤其是近年来，碳纳米管应用于纳米器件和纳米技术方面的诱人前景，促使利用电子束对它们的稳定性和相关纳米加工等进行研究成为热点研究领域。目前，利用电镜中电子束研究碳纳米管收缩、切割、焊接、改性及相关结构变化方面已有了一些报道，但是这些工作并没有把电子束辐照下碳纳米管的结构不稳定性作为一个独立课题来进行系统、定量地研究，尤其是人们只得借助现有概念并配合经典的碰撞（knock-on）机制和相关分子动力学模拟来解释和预言，而忽略了对碳纳米管结构不稳定性转变起关键作用的纳米曲率效应和电子束诱导非热激活效应。 为此，...Since carbon nanotube (CNT) was discovered, its unique one-dimensional tube structure and fantastic electrical and mechanical characters have attracted much attention. Especially, in recent years, the study of the instability and the relevant nanoprocessing of CNT through energetic electron beam (e-beam) irradiation for CNT’s potential applications in nanodevice and nanotechnology has became a hot...学位：理学博士院系专业：物理与机电工程学院物理学系_凝聚态物理学号：1812005140302

In situ observation of the instability of double-walled carbon nanotubes under electron beam irradiation

室温下利用高分辨透射电子显微镜原位观察了两端固定和一端固定、另一端自由的双壁碳纳米管在电子束辐照下的结构不稳定性.实验发现,在相同辐照条件下,两端固定的双壁碳纳米管首先径向持续均匀收缩,然后局部颈缩,最后在颈缩处断裂;一端固定、另一端自由的双壁碳纳米管轴向长度持续快速缩小,而径向收缩相对缓慢.我们利用最近提出的表面纳米曲率效应和能量束诱导非热激活效应基础上新发展的碳原子“融蒸“和“扩散“机制,对上述电子束辐照下双壁碳纳米管结构不稳定现象进行了全新、合理的解释.The structural instabilities of double-walled carbon nanotubes in two typical environments were investigated in situ by transmission electron microscopy at room temperature.The double-walled carbon nanotube with two fixed ends shrank uniformly in the radial direction,bent locally and finally broke.The double-walled carbon nanotube with one free capped end and the other fixed to a rope of nanotubes shrank quickly and continually in the axial direction and slowly in the radial direction.All experimental phenomena could be well accounted for by the vaporization and diffusion of carbon atoms driven by the surface nanocurvature effect and electron beam-induced athermal activation,which have been underestimated or neglected in existing theoretical descriptions and simulations.国家自然科学基金(11074207);国家重点基础研究发展计划(2007CB936603);教育部高等学校博士学科点专项科研基金(20100121110023);国家科技计划国际科技合作与交流专项(2008DFA51230)资

Controllable surface modification of nanowires by focused-electron-beam-induced deposition of carbon

作为一种典型的准一维纳米材料,纳米线具有纳米材料所特有的小尺寸效应或纳米曲率效应,经表面修饰的纳米线一般具有不同于普通纳米线的特殊性质.利用实验室发展成熟的透射电子显微镜原位辐照技术,以透射电子显微镜中残留的有机气体分子为前驱体,成功地在纳米线表面可控沉积了非晶碳纳米颗粒和碳纳米棒,以及局域凸起的非晶碳膜并形成局域肿大的同轴结构.实验结果表明,该方法能够方便地通过控制聚焦电子束的束斑尺寸、辐照方式、辐照时间以及辐照位置等参数,在纳米线表面精确可控地沉积各种非晶碳纳米结构,从而实现纳米线的表面可控修饰.对聚焦电子束辐照下基于纳米线的各种碳纳米结构的可能沉积机理作了进一步地探索,并针对透射电子显微镜中如何减少因电子束辐照诱导非晶碳沉积造成的样品污染提出了几点建议.Surface-modified nanowires generally own some additional properties,and thus in this paper,the authors particularly studied the surface modification of nanowires via irradiation of focused electron beam in a Tecnai F-30 field emission transmission electron microscope (TEM).It was observed that controllable deposition of all kinds of amorphous carbon nanostructures,such as carbon particles,carbon rods and carbon films with local bulging,could be got on the surface of nanowires after intentional irradiation.In details,the controllable deposition of carbon nanostructures could be easily and precisely controlled by changing of some irradiation parameters such as beam spot diameter,irradiation manner,irradiation time and irradiation position.The possible deposition mechanisms of carbon nanostructures on the wire surface as induced by irradiation of focused electron beam in TEM were further discussed.In addition,some suggestions were also proposed on reducing of specimen pollution caused by undesired deposition of amorphous carbon materials during the irradiation.国家科技计划国际科技合作与交流专项(编号:2008DFA51230);国家重点基础研究发展计划(编号:2007CB936603);国家自然科学基金(批准号:90401022;60776007);中澳科技合作特别基金(编号:20050222);教育部科技研究重点项目(编号:105099)资

Fractal growth of deposited carbon on the unirradiated surface of SiO_x nanowires induced by focused electron beam

电子束诱导沉积技术已被证实可以实现各种材料的分形生长,但是目前尚未发现聚焦电子束辐照下低维纳米结构表面未受辐照位置的分形生长现象,造成了聚焦电子束诱导分形生长机理研究的空白与片面性.以透射电子显微镜中残留的有机气体分子为前驱体,室温下利用高能聚焦电子束辐照,研究了一维非晶SIOX纳米线表面未受辐照位置碳沉积的分形生长.利用高分辨透射电子显微镜对SIOX纳米线表面非晶碳的沉积过程进行原位观察,发现了SIOX纳米线表面未受辐照位置非晶碳的不均匀沉积及分形生长,并捕捉到了碳沉积分形生长过程的细节.同时对聚焦电子束诱导SIOX纳米线表面未受辐照位置非晶碳的不均匀沉积及分形生长机理进行了深入的探索.It has been proven that electron beam induced deposition technique can lead to fractal growth of some materials,while there is no report on the fractal growth on the unirradiated surface of low dimensional nanostructures as induced by focused electron beam irradiation.In this paper,the fractal growth on the unirradiated surface of amorphous SiOx nanowire was designedly investigated via focused electron beam irradiation at room temperature,and the deposition details of amorphous carbon on the surface of SiOx nanowire was in-situ observed by a high resolution transmission electron microscope.It was found that a series of intriguing phenomena such as nonuniform deposition and fractal growth of amorphous carbon occured on the unirradiated surface of SiOx nanowire.More importantly,details of the fractal growth process of deposited carbon were also in-situ observed.Furthermore,the nonuniform deposition and fractal growth mechanisms of amorphous carbon occurred on the unirradiated surface of SiOx nanowire under focused electron beam irradiation were proposed and discussed.国家科技计划国际科技合作与交流专项(2008DFA51230);国家重点基础研究发展计划(2007CB936603);国家自然科学基金(90401022;60776007);中澳科技合作特别基金(20050222);教育部科技研究重点项目(105099)资

Structural instabilities of single-walled carbon nanotubes under electron beam irradiation

利用透射电镜(TEM)原位观察了一端固定一端自由和两端固定的单壁碳纳米管(SWNT(s))在电子束辐照下的结构不稳定性。研究发现,一端固定一端自由的SWNT优先轴向和径向收缩后颈缩,最后形成一个个碳笼紧密相连的收缩结构("碳笼-碳笼"结构);两端固定的SWNT仅径向收缩后颈缩,最后形成许多碳笼相连的类似结构。此外,后者在电子束辐照下断开后又会重新粘合起来,表现出很强的表面塑性流变或湿润效应。这些电子束辐照诱导SWNTs非热激活结构不稳定性现象可以用我们最近提出的表面纳米曲率效应和能量束超快诱导软模和点阵失稳进行全新、全面、正确的解释。Structural instabilities of single-walled carbon nanotubes(SWNTs) of two typical settings,which are respectively fixed at only one end and at both ends,were investigated under electron beam irradiation by our developed in-situ transmission electron microscopy observation technique.It was observed that the tube fixed only at one end preferentially shrunk in axis direction first,then shrunk and necked in diameter,and finally formed a carbon cagelike strand structure at the tube free end whereas the tube fixed at both ends merely shrunk and necked in diameter with the similar formation of carbon cage-like strand structure.It is especially intriguing that the necked carbon cage-like strand structure in the latter case was able to re-fuse after breaking and thus demonstrated a strong wetting ability and an amazing athermal plastic flow on the surface of the SWNT fixed at both ends under the electron beam irradiation at room temperature.The above athermal structural instabilities of SWNTs as induced by electron beam irradiation can be well accounted for by the completely new concepts of the surface nanocurvature and ultrafast energetic beam-induced soft mode and lattice instability as we recently proposed.国家自然科学基金资助项目(No.90401022No.90406024);; 国家教育部科技重点资助项目(No.105099);; 中澳科技合作特别基金资助项目(No.20050222);; 福建省科技项目(No.2005HZ1019);; 厦门市科技局资助项目(No.3502Z20055010

Direct experimental evidence for detailed growth of SiO_x nanowire during CVD

在纳米线的制备中,气-液-固(VlS)生长机制得到了人们的广泛认可,但该机制的很多细节还停留在模型阶段.依托实验室自行设计的一台生长条件高度可控的高温化学气相沉积(CVd)系统,采用较为简便的方法,直接在SI片衬底上制备出了SIOX纳米线.通过严格控制实验参数,用离位观测捕捉到了纳米线的催化、形核和长大的一系列过程及其相关细节,并发现纳米线从细到粗的气-液-固(VlS)生长机制.讨论了气-液-固(VlS)机制中气态SI原子的来源以及纳米线的催化、形核和长大过程中的纳米曲率效应和“纳米熟化“现象,取得了对SIOX纳米线VlS催化生长机制的理解的突破.Among the mechanisms for nanowire growths, the vapor-liquid-solid (VLS) mechanism is the most widely accepted.Nevertheless, the growth process and relevant details for the VLS mechanism are not yet fully understood for the complicated nano processes involved.In the present article, with a precise control of temperature, gas flow, pressure, and reaction periods in a home- built high-temperature chemical vapor deposition (CVD) system, detailed processes of catalyzing, nucleation, and growth of the SiOx nanowires and a stepwise non uniformity in diameter of nano- wire were successfully traced.With analysis of these experimental results via nanocurvature and nano ripening effects, a further understanding of the vapor-liquid-solid mechanism, especially the mechanism for formation of the stepwise non uniformity in diameter of nanowires, was achieved for the first time.国家科技计划国际科技合作与交流专项(编号:2008DFA51230);国家重点基础研究发展计划(编号:2007CB936603);国家自然科学基金(批准号:60776007、90401022);中澳科技合作特别基金(编号:20050222);教育部科技重点项目(编号:105099)资

Selective amorphization and novel coaxial structure formation of a single crystal Si nanowire induced by focused electron beam irradiation

使用改进的原位透射电镜观察技术研究了室温下单晶SI纳米线在聚焦电子束辐照下的结构不稳定性。实验发现辐照区域内单晶SI纳米线外层会优先非晶化且局部径向膨胀,并随辐照剂量增加进一步形成新型3层包裹同轴结构等一系列有趣的变化。传统knOCk-On机制和电子束热效应并不能完全解释上述实验现象,然而利用最近提出的纳米曲率效应和电子束非热激活效应则能得到较好的解释。Structural instability of a single crystal Si nanowire at room temperature under focused electron beam irradiation was investigated by our developed in-situ transmission electron microscopy observation technique.It was observed that a series of intriguing changes such as preferential amorphization at the surface of Si nanowire,local bulging in the radial direction and formation of a novel three layers-packaged coaxial structure of Si nanowire with the increasing of electron doses during the irradiation.The possible mechanism for such phenomena was proposed and further discussed by completely new concepts of nanocurvature effect and energetic beaminduced athermal activation effect,while the current knock-on mechanism and electron beam heating effect seemed inadequate to explain these processes.国家自然科学基金资助项目(11074207); 国家重点基础研究发展计划(973计划)资助项目(2007CB936603); 教育部高等学校博士学科点专项科研基金资助项目(20100121110023); 国家科技计划国际科技合作与交流专项资助项目(2008DFA51230

Research on automatic generation algorithm of 3D printing support structure based on FDM technology

基于FDM技术的3D打印原理是靠加热的喷头挤出熔融的热丝层层堆积而成的。因此对于存在悬臂结构的模型,支撑结构的存在十分必要。为满足模型中形状复杂多变的待支撑区域,提出一种可以适用于复杂形状的树状支撑结构的生成算法。提出的算法基于STL文件模型,根据待支撑区域的特征提取出模型待支撑区域,然后在待支撑区域内由上而下依次建立树干从而生成树状支撑结构。提出的算法明显减少了支撑结构所用材料,提高了打印效率,并且便于模型和支撑结构的分离。</p

Formation and evolution of Cu nanostructures on the surface of nanosized Cu films under high vacuum annealing

Conference Name:2011 International Conference on Energy, Environment and Sustainable Development, ICEESD 2011. Conference Address: Shanghai, China. Time:October 21, 2011 - October 23, 2011.Nanosized Cu films were prepared by direct current (dc) magnetron sputtering method at room temperature. The as-deposited Cu films were subsequently annealed under high vacuum annealing for different time. It was observed that with the annealing various types of Cu nanostructures formed on the surface of films. It was also observed that the appropriate range of film thickness for such formation was from 20 nm to 40 nm. During the annealing, three types of nanoparticles and considerable number of even tiny crystallites forming on the film surface were crucial for the formation. Furthermore, the detailed formation and evolution were studied and two possible mechanisms, i.e., surface nanocurvature effect and thermal activation effect, were proposed for a full explanation. 漏 (2012) Trans Tech Publications, Switzerland

聚焦电子束诱导碳沉积实现纳米线表面可控修饰

作为一种典型的准一维纳米材料,纳米线具有纳米材料所特有的小尺寸效应或纳米曲率效应,经表面修饰的纳米线一般具有不同于普通纳米线的特殊性质.利用实验室发展成熟的透射电子显微镜原位辐照技术,以透射电子显微镜中残留的有机气体分子为前驱体,成功地在纳米线表面可控沉积了非晶碳纳米颗粒和碳纳米棒,以及局域凸起的非晶碳膜并形成局域肿大的同轴结构.实验结果表明,该方法能够方便地通过控制聚焦电子束的束斑尺寸,辐照方式,辐照时间以及辐照位置等参数,在纳米线表面精确可控地沉积各种非晶碳纳米结构,从而实现纳米线的表面可控修饰.对聚焦电子束辐照下基于纳米线的各种碳纳米结构的可能沉积机理作了进一步地探索,并针对透射电子显微镜中如何减少因电子束辐照诱导非晶碳沉积造成的样品污染提出了几点建