碳烟纳米颗粒在电阻加热碳微管表面的自组装
Self-Assembly of Soot Nanoparticles on the Surface of Resistively Heated Carbon Microtubes in Near-Hexagonal Arrays of Micropyramids
摘要：
在石墨化中空丝的表面上形成由烟灰纳米颗粒组成的几微米高和宽的微金字塔的几乎规则的六边形阵列，所述石墨化中空丝在含有痕量氧（~300 p. p.m.）的Ar气氛中被连续加热至~1800 $^\circ$ C-2400 $^\circ$ C。在较高的温度（T>2300 $^\circ$ C，大约）下，烟灰颗粒主要由多壳碳纳米洋葱表示。金字塔的高度和宽度强烈地依赖于电阻加热的温度，从T=1800 $^\circ$ C时的5- 10 mkm减小到2300-2400 $^\circ$ C时的1 mkm。准六边形阵列的微金字塔被组织在微管表面上的凸起的“火山口”中，其随着热处理的时间而生长。金字塔总是垂直指向陨石坑的表面，除了陨石坑之间的边界，那里的法线方向没有很好的定义。金字塔很软，很容易被触摸破坏，但可以通过在无氧气氛中加热来硬化。只在微管的外表面上观察到金字塔，而不在其内表面上观察到金字塔。这表明，热泳力所产生的强烈的温度梯度附近的管的外表面可能是微金字塔的形成的原因。烟炱纳米颗粒由于电子发射而产生的静电荷也可能与这种现象有关。微金字塔可以作为场发射点源，如使用安装在扫描电子显微镜中的微纳米探测站所证明的。
英文摘要：
Almost regular hexagonal arrays of a few micrometers tall and wide micropyramids consisting of soot nano-particles are formed on the surface of graphitized hollow filaments, which are resistively heated to ~1800$^\circ$C-2400$^\circ$C in an Ar atmosphere containing trace amounts of oxygen (~300 p.p.m.). At the higher temperatures (T>2300$^\circ$C, approximately) the soot particles are represented mainly by multi-shell carbon nano-onions. The height and the width of the pyramids is strongly dependent on the temperature of the resistive heating, diminishing from 5-10mkm at T=1800$^\circ$C to 1mkm at 2300-2400$^\circ$C. Quasi-hexagonal arrays of the micropyramids are organized in the convex ``craters'' on the surface of the microtubes, which grow with the time of the thermal treatment. The pyramids are pointing always normally to the surface of the craters, except at the boundaries between the craters, where the normal direction is not well defined. The pyramids are soft and can be easy destroyed by touching them, but can be hardened by heating them in the oxygen-free atmosphere. The pyramids are observed only on the exterior surface of the microtubes, but not on their inner surface. This suggests that the thermophoretic force generated by a strong temperature gradient near the external surface of the tubes may be the cause of the micropyramids formation. Electrostatic charging of the soot nanoparticles due to thermionic emission may also be relevant to this phenomenon. The micropyramids can function as field emission point sources, as demonstrated with the use of a micro-nanoprobing station, mounted in a scanning electron microscope.
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