Determining the metallicity and semiconductivity of a multi-walled carbon nanotube (MWCNT) bundle plays a particularly vital role in its interconnection with the metal electrode of an integrated circuit. In this paper, an effective method is proposed to determine the electrical transport properties of an MWCNT bundle using a current–voltage characteristic curve during its electrical breakdown. We established the reliable electrical nanoscale contact between the MWCNT bundle and metal electrode using a robotic manipulation system under scanning electron microscope (SEM) vacuum conditions. The experimental results show that the current–voltage curve appears as saw-tooth-like current changes including up and down steps, which signify the conductance and breakdown of carbon shells in the MWCNT bundle, respectively. Additionally, the power law nonlinear behavior of the current–voltage curve indicates that the MWCNT bundle is semiconducting. The molecular dynamics simulation explains that the electron transport between the inner carbon shells, between the outermost carbon shells and gold metal electrode and between the outermost carbons shells of two adjacent individual three-walled carbon nanotubes (TWCNTs) is through their radial deformation. Density functional theory (DFT) calculations elucidate the electron transport mechanism between the gold surface and double-wall carbon nanotube (DWCNT) and between the inner and outermost carbon shells of DWCNT using the charge density difference, electrostatic potential and partial density of states.

Carbon nanotubes (CNTs) have excellent electrical properties. However, it is challenging to demonstrate these properties in actual electrochemical measurements fully. Previous research has improved the electrical properties of CNTs through welding experiments. But the mechanism of the conductivity enhancement is still unclear. The welding process lacks adequate mechanistic studies and theoretical models. This article presents a theoretical model of a CNT circuit with staggered electrodes, which considers the effect of twist angle on a CNT bundle. A welding model of the CNT bundle circuit is also developed based on the structural changes of CNTs after welding and characterized by the resistance ratio of the CNT circuit pre- and post-welding. The welding model is analyzed to explore how the quantity, diameter, and length of CNTs in the bundle affect the welding effect. An electrical measurement system for CNTs was established to validate the welding model using a nanomanipulation system compatible with a scanning electron microscope. Then, a constant voltage and long-duration electric welding experiment was performed, which showed that the conductivity was enhanced about 1.5–4 times after welding. The results also demonstrated that longer and fewer CNTs in the bundle could improve the electrical conductivity by the welding process more significantly. These findings were consistent with the trend of the welding model. This article establishes a welding theoretical model of the CNT bundle with staggered electrodes, which effectively accounts for the electrical conductivity enhancement during CNT welding and will help more fully express excellent performance in carbon-based nanoelectronic devices, nanoelectromechanical systems, and electrocatalysts in its manufacturing stage.

The interfacial contact configuration and contact intensity between carbon nanotube and metal surface play an important role in the electrical performance of carbon nanotube field effect transistors and nanoscale carbon nanotube robotic manipulation. In this paper, we investigate numerically the contact configuration and the contact intensity between multiwall carbon nanotube with open ends or capped ends and various metal surfaces in carbon nanotube field effect transistor assembly by the molecular dynamics simulation. The simulation results show that the change in the position and shape of multiwall carbon nanotube on the metal surface are mainly due to the decrease of van der Waals energy reduction: the decrement of van der Waals energy is converted into the internal energy and kinetic energy of carbon nanotubes. Moreover, the binding energy between multiwall carbon nanotube and metal surface is negative, which indicates that multiwall carbon nanotube adheres to the metal surface. In addition, the contact intensity of multiwall carbon nanotube in horizontally contacting metal surface is influenced by initial distance, contact length and metal materials. The final equilibrium distance is around ~0.3 nm when the initial distance is less than ~1 nm. And the contact intensity increases with the augment of contact length between carbon nanotube and metal. The contact intensity between platinum and carbon nanotube is larger than that between tungsten and aluminum, therefore, platinum-coated probe is generally utilized for picking carbon nanotube up. The contact intensity of the carbon nanotubes with the open ends and closed ends in the vertical contact with the metal surface are both lower than those in the horizontal contact. The interfacial contact configuration of carbon nanotube and metal materials mainly include the displacement and geometric deformation of carbon nanotube. The displacement and geometric deformation of multiwall carbon nanotube with open ends on the metal surface finally result in its radial nanoscale ribbon structure. But the closed-end three-wall carbon nanotube has the small axial geometric deformation through comparing the concentration profiles between the initial carbon nanotube and the collapsed carbon nanotube. In a carbon nanotube field effect transistor, the collapsed multiwall carbon nanotube forms the ribbon structure like a single wall carbon nanotube. And the distance between carbon nanotube walls and between the outermost carbon nanotube wall and the metal electrode are both about ~0.34 nm. The atomic scale spacing ensures that electrons tunnel from the metal to the outermost carbon nanotube wall and migrate radially between the inner carbon nanotube walls.

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In this paper, a length-controllable picking-up method of carbon nanotubes (CNTs) is proposed and the electrical performance data utilized for the conductivity analysis of CNT are also obtained. The micro-nano-operation system inside scanning electron microscope (SEM) is composed of 4 manipulation units each with 3 degrees of freedom, which is driven by piezoelectric ceramics and flexure hinges. In this micro manipulation system, an atomic force microscope (AFM) probe is used as the end effector to adjust the spatial pose of the CNT based on van der Waals force and two tungsten needles are used to cut the CNT from the target length and to measure the <i>I-V</i> characteristic data simultaneously. At first, the AFM probe is moved in the <i>z</i> direction to approach to the CNT until the end of the CNT is adsorbed onto the surface of the AFM probe. And then the AFM probe moves alternately in the <i>x</i> and <i>z</i> direction in order to stretch the CNT into a horizontal straight line, only in this way can the length of the CNT be measured accurately and can the cutting position be determined. Two tungsten needles cleaned by using hydrofluoric acid to remove the oxide layer are controlled to contact both sides of the cutting position on CNT and connected to the TECK 2280S power supply through the electric cabinet to apply a gradually increasing DC voltage, and the current in the circuit is measured and recorded by the TECK DMM7510 until the current abruptly changes to zero which indicates that the CNT between the tungsten needles has been cut off. The stress of the CNT in contact with the tungsten needles and the AFM probe are analyzed. The modeling of van der Waals force between AFM probe and CNT which can influence the pick-up length error caused by the deformation of CNT under the force of tungsten needles is completed. It is found that the contact length of them and the pick-up length error decrease while the van der Waals force between the AFM probe and CNT increases. The circuit models for contact between the tungsten needles and three operating objects, such as semiconducting CNT, metallic CNT and CNT bundle, are also established. In addition, the <i>I-V</i> characteristic equations of circuit model which can be used to fit the <i>I-V</i> data are derived separately. The CNT pick-up experiment is carried out and the results demonstrate that the proposed picking method can control the length of CNT effectively, but the conductivity of CNT can also be judged by fitting the <i>I-V</i> obtained experiment data through the derived <i>I-V</i> characteristic equations.