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

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

聚焦电子束诱导SiOx纳米线表面碳沉积的分形生长

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

Simulation on Localized Surface Plasmon Resonance Behaviors of Nanosized PMMA/Ag Core-Shell Structure

应用米氏理论,对银膜包覆PMMA纳米核壳结构的局域表面等离激元共振行为进行了模拟计算,研究了颗粒尺寸、核壳比等参数对纳米核壳结构局域表面等离激元共振消光光谱的影响;同时将其与实心银纳米球的局域表面等离激元共振光谱行为进行了比较。结果表明,相对于实心银纳米球,银膜包覆PMMA纳米核壳结构的共振峰位更加红移,且共振峰的宽度更窄。这些性能上的提高,是由于纳米PMMA介质核的存在减弱了电子云振荡过程中的滞后效应,利于化学生物传感器方面的应用。Localized surface plasmon resonance(LSPR) spectrum behaviors of PMMA/Ag core-shell nanoparticles are extensively and systematically simulated by a calculation method based on Mie theory.Through the simulation calculation,the dependence of the LSPR behaviors of the core-shell nanoparticle on nanoparticle size,ratio of the radius of PMMA core to the thickness of Ag shell,and some other factors is studied.Furthermore,LSPR behaviors of Ag nanoparticles are simulated as well for comparison.The simulation results show that the nanosized PMMA dielectric core can weaken the retardation effects in the process of free electron resonance in the Ag nanoshell.Thus,compared with the LSPR of Ag nanoparticles,the position of the LSPR peak of the PMMA/Ag core-shell nanoparticles has an even more obvious red shift and the width of the LSPR becomes even narrower.Such simulation results indicate that the core-shell nanoparticles would have more advantages over Ag nanoparticles for potential applications of future chemical and biological nanosensors.国家科技计划国际科技合作与交流专项(2008DFA51230);国家973计划(2007CB936603);国家自然科学基金(11074207;50861007)资助课

CVD制备SiO_x纳米线的各个生长阶段的直接实验证据

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SiO_x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SiO_x纳米线VLS催化生长机制的理解的突破

PMMA纳米球的制备及其银膜包覆技术. Preparation of polymethyl methacrylate(PMMA) nanosphere and technique of coating Ag layer

In this paper, we reported a two-step technique for fabrication of PMMA/Ag nano coreshell structure with well-established processing parameters and an ease control. Firstly, we fabricated the monodisperse PMMA nanospheres with a diameter of about 170 nm by emulsifier-free emulsion polymerization. Then, we modified the PMMA nanospheres surface with (3-methacryloxypropyl) trimethoxysilane(MATS) and (3-mercaptopropyl) trimethoxysilane(MPTMS), resulting in a uniform sulfhydryl (SH)-group modified outlayer and Ag nanoparticles further grew on the modified surface of PMMA nanospheres with an effective interaction between sulfhydryl(SH) groups and Ag+. In doing so, finally we synthesized PMMA/Ag core-shell composited nanoparticles. The structure of the synthesized sample was investigated by scanning electron microscopy (SEM), transmission electron microscopy(TEM) and UV-Vis extinction spectra. The results indicate that the well-dispersed PPMA/Ag core-shell nanoparticles with uniform particle size distribution were successfully fabricated using this improved technique

Preparation of Polymethyl Methacrylate(PMMA) Nanosphere and Technique of Coating Ag Layer

【中文摘要】采用无皂乳液聚合法制备了单分散、直径为170mm左右的聚甲基丙烯甲酯（PMMA)纳米球，然后利用3-甲基丙烯酰氧基丙基三甲氧基硅烷（MATS)和3-巯丙基三甲氧基硅烷（MPTMS)对PMMA纳米球进行表面改性，在其表面包覆一层均匀的巯基，通过巯基与银离子之间的相互作用，使银在PMMA纳米球表面成核长大，从而合成PMMA/Ag纳米球壳粒子。通过扫描电子显微镜、投射电子显微镜和紫外-可见吸收光谱测试技术对产物性能进行了表征，研究结果表明，制备的PMMA/Ag纳米球壳粒子的分散性好、包覆均匀。 【Abstract】In this paper, we reported a two-step technique for fabrication of PMMA/Ag nano coreshell structure with well-established processing parameters and an ease control. Firstly, we fabricated the monodisperse PMMA nanospheres with a diameter of about 170 nm by emulsifier-free emulsion polymerization. Then, we modified the PMMA nanospheres surface with (3-methacryloxypropyl) trimethoxysilane(MATS) and (3-mercaptopropyl) trimethoxysilane(MPTMS), resulting in a uniform sulfhydryl (SH)-group modified outlayer and Ag nanoparticles further grew on the modified surface of PMMA nanospheres with an effective interaction between sulfhydryl(SH) groups and Ag+. In doing so, finally we synthesized PMMA/Ag core-shell composited nanoparticles. The structure of the synthesized sample was investigated by scanning electron microscopy (SEM), transmission electron microscopy(TEM) and UV-Vis extinction spectra. The results indicate that the well-dispersed PPMA/Ag core-shell nanoparticles with uniform particle size distribution were successfully fabricated using this improved technique

准噶尔盆地南缘草本层碳通量及土壤呼吸的变化特征/Variation characteristics of herb layer carbon flux and soil respiration in southern edge of Jungggar basin,Northwest China[J]

利用LI-840以及LI-8100土壤呼吸测量仪,对准噶尔盆地南缘草本层片碳通量以及沙丘不同部位的土壤呼吸速率进行了测量,探讨了草本层片碳通量季节动态以及日过程的变化特征,沙丘不同部位土壤呼吸速率的年变化特征以及环境因子对草本层片碳通量以及土壤呼吸速率的影响.结果表明:草本层片碳通量不仅在日尺度上呈现单峰的变化趋势,在季节尺度上也呈现相同的变化趋势.生长旺盛季草本层碳通量日过程变化幅度较大,草本层片净碳交换(NEE)从-2.5～0.02 μmol·m-2·s-1,草本层总生产力(GEP)则从-4.4～-1.1 μmol· m-2 ·s-1,而9月份以后则基本维持在0附近.通过分析碳通量与环境因子的关系,草本层片碳通量与土壤温度呈正相关关系,草本层土壤呼吸(ER)与光合有效辐射呈正相关关系,而草本层GEP与光合有效辐射则呈负相关关系.沙丘不同部位(沙丘顶部、中部、底部)土壤呼吸速率年动态变化为双峰型,且不同坡位之间土壤呼吸速率差异显著