【作者】 孙敏；

【导师】 高义华；

【作者基本信息】 华中科技大学 ， 凝聚态物理， 2011， 博士

【摘要】 Ga辅助生长的一维纳米结构材料具有特别的物理和机械特性,在微纳技术领域有许多重要而潜在的应用。其中,镓催化生长的硅纳米结构可以实现元器件之间的链接,与其他器件匹配较好,为组装高集成、智能化的器件提供了新途经；利用镓填充纳米管研制的纳米温度计和纳米开关也为微纳电机器件的设计描绘了新的应用前景。在此基础上,本文围绕Ga辅助生长一维纳米结构的光、电、热效应及其应用开展工作,现将原创性和创新性的主要结果总结如下：(1)设计了一种可控的大面积制备硅多级枝状结构的单步合成方法,可以研制出多种Si基多级枝状纳米结构。创新性的利用镓的催化作用,制备出大面积整齐的硅的多级枝状纳米结构阵列。进一步对多级枝状纳米结构的生长机理给予了合理的解释。(2)与单晶硅的一阶光学-声子谱相比,多级枝状纳米结构、较大的多级枝状纳米结构和多级枝状纳米线三种结构的拉曼峰均有一定的蓝移,且相应的半高宽有-定的展宽。光致发光测试显示,三种结构的发射峰均出现在550nm处,与已报道的硅纳米结构的光致发光性能相比,也有相应的蓝移。我们将此现象归结为纳米结构的量子尺寸效应或缺陷(如堆垛层错)引起的。(3)硅多级枝状结构阵列拥有优越的场发射和电输运性能。优越的场发射性能显示其具有较低的开启电场(3.16 V/μm)和较高的场增强因子(1252)。电输运测试结果显示硅的纳米枝状结构有较小的电阻。通过改变枝状结构与电极的接触,真空退火较大程度地减小了其电阻的50%。然而,热氧化直接导致硅的枝状结构的表面形成了一层氧化层,其电阻增加了近2倍。然而真空退火和热氧化使电流-电压特性变得更加线性对称,电输运的稳定性明显提高。(4)在原位透射电镜的电子束辐照下,利用制备的镓填充二氧化硅纳米管的异形异标度的异质结构,首次发现镓液体在二氧化硅纳米管异质结构中的快速膨胀现象。这是一一种山内部巨大压强引起的电液压膨胀效应。此内部巨大压强来至于电子束轰击镓液体产生带正电的镓离子,造成镓离子之间的库伦排斥力,驱使它们向表面移动而引起膨胀。基于镓液体膨胀和经典静电理论,计算出正电荷引起的内部压强Pin值。以上所述的电液压膨胀效应为微纳液压驱动系统提供了新的应用机制。(5)在改变实验方法制备出大面积镓填充碳纳米管的基础上,我们为镓填充碳纳米管在纳米领域的应用提供了新途径。利用STM-TEM测试设备,将该结构放在不同的电场中,电驱动力的作用使得镓在碳纳米管中做不同模式的运动。其一,在单电极的电场中,镓在电场力的驱动下做周期性的弹性运动,可以将其看做电场驱动下的“纳米弹簧”。用新的弹性运动模式对该机理进行了合理的解析。其二,在双电极高电流密度的电场中,高电流密度驱动镓的迁移速度由1.328fgs-1变化到10.345fgs-1,远大于已报道的实验结果。这里我们定义镓填充的碳纳米管为双电极作用下的“高速质量传输机”。(6)首次发现,在高电流密度的驱动下,镓与碳纳米管发生分离,在电场驱动力的作用下镓快速移动,质量输运速度逐渐变快,然而,碳纳米管两端的电输运性能变化较小。在低电流密度下,镓沿着碳纳米管移动缓慢,导致碳纳米管两端的电输运性能变化较大,这种镓填充的碳纳米管可以作为电驱动的“纳米滑动变阻器”或者“纳米开关”应用。.在已有纳米温度计工作的基础上,我们研制出灵敏度高、测温范围广、性能稳定的新一代纳米温度计,它们各自具有特殊的性能：(a)镓填充氧化镁纳米管温度计具有四方开口的结构,测温范围广,灵敏度高达6.13nm/℃,是目前报道的灵敏度最高的纳米温度计之一。(b)首次研制的镓填充二氧化硅纳米管温度计不仅测温范围广、灵敏度高,而且稳定性好、抗氧化性能强,具有优化的几何结构,易于实现大面积制备。(c)通过改进实验方法,制备出产率大、灵敏度高的镓填充碳纳米管的温度计。以上三种纳米温度计的研制即从源头上解决了纳米温度计的高产率生长问题,又提高了纳米温度计的关键性能,如灵敏度、测温范围、稳定性和抗氧化性等诸多问题,为纳米温度计的实用化提供了坚实的基础。更多还原

【Abstract】 Ga-assisted growth one-dimensional nanostructures, with many excellent physical and mechanical characteristics, have many potential application in the micro-nano technology. Ga-catalytic silicon nanostructures can be connect and match with other devices under the good performance, which opens a new field for the high-integrated intelligent devices. Meanwhile, nanothermometer and nanoswitch of Ga-filled nanotubes provide a new technology for the development of mechanical and electrical devices. Based on the above, we have studied the optical, electrical, thermal properties and new applications for the gallium-assisted growth one-dimensional nanostructures, and performed a series of innovative results, which as follows.(1) A simple one-step, controllable and large-area fabrication technique of silicon based multi-level branched nanostructures have been rationally designed. Using the gallium catalytic activity innovatively, ordered arrays of silicon multi-branch nanostructures were synthesized. We gave more analysis about the growth mechanism of multi-level branched nanostructures.(2) In comparing with the first-order optical phonon peak of crystalline silicon, the room-temperature Raman frequency of branched nanostructures, big branched nanostructures and branched nanowires are blue-shifted and its full width at half maximum broadens. The typical room-temperature PL spectra showed, for the three samples, a moderately strong photoluminescence emission was at 550 nm. Compared with the previous studies, three emission bands have blue-shifted, which may be the effect of quantum confinement and/or the defects, such as stacking faults.(3) The ordered arrays of crystallized silicon multi-branch nanostructure on the field electron emission and electric transport properties is excellent. A decent field electron emission with relatively low turn-on field of 3.16 V/μm and high field-enhancement factor of 1252 was received for the silicon nanobranches. In addition, electrical transport measurements revealed a small electrical resistance. In contrast, by improving silicon nanobranches - electrode contact, vacuum annealing dramatically reduced electrical resistance approachly 2-fold, while thermal oxidation resulted in much high resistance due to amorphous oxide coating of silicon nanobranches, both of current versus voltage curves become more linear and symmetrical, the transport stability is obviously improved.(4) Heteroshape-heteroscale structure made of silica-shelled Ga microball-nanotube is rationally fabricated. Undergoing in situ electron-beam irradiation, an abnormal Ga liquid expansion in the nanotube was firstly observed. The expansion was due to an electric-hydraulic expansion effect via a huge inner pressure, which was induced by the repelling Coulomb force of positively charged Ga ions on the surface of Ga liquid. Under the theories of Ga expansion and classical electrostatics, the Ga-ions induced huge pressure is calculated. The electric-hydraulic expansion (EHE) effect can provide new insight for application in the family of micro-nano-electric-hydraulic devices.(5) Based on the large-area fabrication of Ga-filled carbon nanotubes, we provide new ideas of the application fields for Ga-filled carbon nanotubes. By using a "Nanofactory Instruments" scanning tunneling microscope (STM)-TEM joint instrument, under the different electric field, The Gallium performed the different patterns of movement, which was elaborated innovatively. In a single-electrode electric filed, we first find out gallium in the nanotube performs periodic elastic movement, which can be called "electric field - driven nanospring". The relevant theoretical explanation has been addressed by the elastic movement model. Moreover, in a double-electrode electric filed, the high current density makes the gallium migrate at the changing transport froml.328 fg s-1 to 10.345 fg s-1, where Ga-filled carbon nanotube can be considered as "electric field-driven high-speed mass conveyor".(6) In the driving of the high current density, the separation between the gallium and the nanotube was caused, and resulting in Ga fastly moving to the anode, but the slight variation of the nanotube resistance. In contrast, gallium mass transport in the low current density influences significantly the electrical transport property of the nanotube. Our results are potential to Ga-filled carbon nanotube as "electric field - driven rheostats or nanoswitches". (7) Basis on the research of nanothermometer, the new nanothermometer with the high sensitivity, wide measuring-temperature range and steady performance has been designed, each have special performances. (a) Ga-filled MgO nanotubes is the cubic-opening nanotubes with wide measuring-temperature range and high sensitivity up to 6.13nm/℃, which is one of the highest sensitivity in the reported nanothermometer. (b) Ga-filled SiO2 nanotubes not only have the wide measuring-temperature range and high sensitivity, but also good antioxidant and structural geometrical optimization, can be fabricated with large area. (c) By changing the experimental methods, we prepared the nanothermometer of Ga-filled carbon nanotubes with the high output and sensitivity. The development of these three nanothermometers resolved two main matter, one is the high-output fabrication, the other is the modified key performance, such as the problem of sensitivity, measuring-temperature range and steady performance, it provides the most striking evidences for the practice of nanothermometers.更多还原