【作者】 韦逢艳；

【导师】 王万录； 胡陈果；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2006， 硕士

【摘要】 碳纳米管是极具应用潜能的新型材料,但关于它电导率的计算到目前为止都没有令人信服的说法,成为碳纳米管研究中的瓶颈。本论文通过对比分析,选择出最优化模型,对碳纳米管膜的电导率进行了计算,并做了相关的实验研究进行验证。文章还研究了应变及掺杂对碳纳米管膜电导率的影响,并用前面的计算结果进行分析,发现理论和实验吻合得很好。本文首先系统的介绍了碳纳米管的结构,在此基础上,分析了几种计算碳纳米管电导常用的原理和模型。经过总结前人的实验和模型,提出计算碳纳米管膜电导率的最佳模型——异质丝状模型。然后从活化隧道理论出发,采用三角形势垒计算传输几率,最后得出碳纳米管电阻率和电导率的表达式,并计算了电阻温度系数TCR;测定了不同管径的碳纳米管膜电阻和温度的关系。实验发现,单壁碳纳米管膜的电阻随温度的增高而降低,表现出金属电导的行为;而多壁碳纳米管膜的电阻随着温度先大幅下降之后上升,转变温度T*介于338K到358K之间,比前人得结果要高得多。对此结果做出了解释。实验还发现,碳纳米管膜的电阻温度系数TCR和管径成反比,和文中理论计算的结果符合得很好。本文首次研究了不同管径的碳纳米管膜的压阻效应及基于此效应的加速度灵敏性,发现碳纳米管膜电阻相对变化率和形变基本呈线性关系,且多壁管膜的管径越小,电阻相对变化率就越明显,而单壁纳米管膜的电阻随形变只有微小的变化;在800微应变之上,压阻因子随着多壁碳纳米管管径的增大而减小。还发现在比较低的应变下(低于0.7×10-6),碳纳米管膜的加速度和应变呈现出比较好的线性关系;高于此值时,线性关系降低,但加速度的变化明显增快。文中对这些现象都做了解释,论证了碳纳米管膜作为加速度传感器的潜能。本文还实现了对碳纳米管电极的电化学掺杂,给出了掺杂前后的循环伏安曲线;之后系统的比较了不同方法做成的碳纳米管膜的水掺杂效应。并就掺杂对碳纳米管电导的影响做了深入而细致的讨论。更多还原

【Abstract】 Carbon Nanotubes(CNTs) are advanced materials with many potential applications. However, there is no effective and convictive method to calculate their conductance till now, which prevented its development seriously. In this paper, an optimal model was chosen to calculate CNT films’conductance after contrasting and analyzing large numbers of literature. Related experiments had been done to demonstrate the model. Stress and doped effect of CNT films were also been studied. We analyzed the data, finding good match between the calculation and experiments.Firstly, according to analyzing some regular principles and models to calculate CNTs’conductance after introducing their structures, the most optimal model-- Heterogeneous Fibrillar Model has been proposed to compute CNT films’conductance, and the formulas of resistivity and conductance for CNT films have been obtained on the base of Neugebauer-Webb Theory and triangle barrier model. the TCRs have been calculated by using these formulas. Then we measured the resistance of CNT films with different diameters under different temperature. It is found that the resistance of single-walled carbon nanotube (SWNT) film increases with increasing of temperature, indicating metal behavior, while the resistance of multi-walled carbon nanotube (MWNT) films exhibite a crossover from decreasing to increasing resistance with temperature increasing, the cross temperature ranged from 338K to 358 K, much higher than the former results. It is also showed that the TCR of MWNT films had an inverse proportion to their diameters, being consistent with our computation result.Furthermore, this paper firstly exams piezoresistive effect of CNT films with different diameters and their acceleration sensing based on piezoresistive effect. The experimental results indicate that the fractional increase in resistance increases linearly versus the increase of strain; In the case of MWNT film, the slope increases with the decrease of diameters; for SWNT film, the resistance just has very slight change when the strain vary; Piezoresistive sensitivity reduces with the accretion of the diameters for MWNT films up to 800 micro strain. The experimental results also show that centripetal acceleration of MWNT films exhibites a well linear behavior with strain under low strain (beneath 0.7×10-6). But up to 0.7×10-6, the linear behavior is weaken while the acceleration having a sharp increase of the slope. All the results above were explained, and the potential application of MWNT films for acceleration sensor is demonstrated.更多还原