Controlling the resistivity of multi-walled carbon nanotube networks by copper encapsulation

doi:10.1016/j.matlet.2011.06.113

Materials Letters

Volume 65, Issues 19–20, October 2011, Pages 3187-3190

https://doi.org/10.1016/j.matlet.2011.06.113 Get rights and content

Abstract

The resistivity of multi-walled carbon nanotube networks can be changed by filling Cu into the nanotubes as well as by preparing the nanotube networks with various densities. The resistivity can be controlled to be lower than the c-axis resistivity of graphite, and has a low temperature coefficient of −1.12 × 10⁻⁵/K over the temperature range of 20–500 K. Filling Cu into the nanotubes decreases the intra-tube resistivity, but the temperature coefficient of the resistivity is governed by the inter-tube resistivity of the nanotube network.

Highlights

► We studied the effects of Cu filling on the resistivity of carbon nanotube networks. ► Cu was filled into the multi-walled nanotubes by laser ablation. ► The resistivity can be controlled to be lower than c-axis resistivity of graphite. ► Filling Cu into the nanotubes decreases the intra-tube resistivity. ► The inter-tube resistivity of the networks governs its temperature coefficient.

Introduction

Carbon nanotubes (CNTs) are being used extensively for electronic applications such as in optoelectronic devices, transistors, touch-screens, flexible microelectronics, and chemical sensors [1]. In such applications, the CNTs are used in forms such as single tubes, bundles, random networks, and composites with polymers, metals, or ceramics. When CNTs are used in a device, foreign atoms will adsorb onto their internal and external surfaces, and this leads to degradation of their electronic properties of the device if the CNTs are single-walled carbon nanotubes (SWCNTs). For this reason, multi-walled carbon nanotubes (MWCNTs) are more suitable for the device applications than SWCNTs because the inner graphene walls of MWCNTs can remain unreacted and the essential electronic structures can be retained.

SWCNT films are attractive replacements for transparent conductors such as tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO) in optoelectronic devices [2]. However, their room-temperature conductivity decreases by about four orders of magnitude as thickness decreases from 100 to 1 nm [3]. The resistance of the SWCNT films is dominated by the resistance of the intertube junctions formed from the crossed semiconducting SWCNTs. On the other hand, the electrical and optical properties of MWCNT films related to their thickness are still not studied in detail. Moreover, it is highly possible to achieve low resistivity MWCNT films with reduced monolayer density by filling high-conducting metals into the MWCNTs resulting in a high transparency of MWCNT network as well.

It is reported that the conductance of an individual MWCNT is lower than that of a SWCNT because the conductance is only formed at the outermost wall of the MWCNT and also, the interaction of the tube walls decreases the conductance. But recent results reveal a substantial contribution of conduction from the second wall after carrier's tunnel from the outermost wall [4]. A perfect electrical contact with an MWCNT can be achieved by preparing the contact electrodes during the tube growth and this technique has shown that the conductivity of MWCNT can be several hundred times higher than that of SWCNT [5]. From the above results, new application fields based on MWCNT networks can be developed by controlling the contact properties of the MWCNTs with metals as well as by filling metals into the nanotubes.

In this study, we have prepared copper-filled MWCNT networks at various Cu concentrations, and the resistivity of the network prepared with various densities is measured as a function of temperature. Carrier transport mechanisms in the various networks are also discussed.

Section snippets

Experimental procedure

Laser vaporization of a carbon target containing Cu was carried out in an argon gas atmosphere at a pressure of 0.5 MPa. A continuous wave Nd:YAG laser was used to vaporize the Cu/carbon target at room temperature. The Cu-filled MWCNT (Cu@MWCNT) powders obtained were characterized by field emission scanning electron microscope (FE-SEM; JEOL JSM-7000), transmission electron microscope (TEM; HITACHI H-9000NAR), and X-ray diffraction (XRD; JEOL JDX-3500K). The compositions of C and Cu in the

Results and discussion

The SEM image of a typical Cu@MWCNT pellet is shown in Fig. 1(a). The nanotubes with uniform diameter and high aspect-ratio, which constitute a random network, can be seen. From the SEM image, it is suggested that the resistance of the network will be determined by the total resistance of the inter- and intra-tubes as the filling of copper changes only the resistance of the intra-tube.

Fig. 1(b) is a TEM image of the network showing filled and hollow tubes with an average diameter of about 20 nm

Conclusion

In summary, the Cu@MWCNT network was prepared and its resistivity was measured as a function of temperature and density of the network. The resistivity can be lower than the c-axis resistivity of graphite and has a smaller and constant temperature coefficient over the temperature range from 20 to 500 K. The resistivity decreases with increasing the Cu amount encapsulated into the tubes as well as the density of the network.

Acknowledgments

This work was partially supported by project No. 15-B01, Program of Research for the Promotion of Technological Seeds, Japan Science and Technology Agency. The work was also partially supported by Grant-in-Aid for Exploratory Research No: 23651115, Japan Society for the Promotion of Science (JSPS).

References (10)

R.J. Bandaru Prabhakar
Nanosci Nanotech
(2007)
Z.C. Wu et al.
Science
(2004)
E. Bekyarova et al.
J Am Chem Soc
(2005)
B. Bourlon et al.
Phys Rev Lett
(2004)
H.J. Li et al.
Phys Rev Lett
(2005)

There are more references available in the full text version of this article.

Cited by (6)

Preparation of carbon nanotubes with high filling rate of copper nanoparticles
2022, Microporous and Mesoporous Materials
Citation Excerpt :
In particular, Cu-filled CNTs have shown a potential application prospect in the field of novel composites and functional devices because Cu is an excellent conductor of electricity and heat and has weak interaction with carbon. Studies have shown [9,10,19] that the conductive cross section of CNTs can be increased due to Cu filling, thus reducing gas scattering and the resistivity of CNTs and forming a device similar to nano-thermistors. In the present study, a wet chemical method is adopted to prepare Cu-filled multi-walled CNTs (in the following sections, CNTs are referred to as multi-wall CNTs unless otherwise specified).
Performance of carbon nanotubes (CNTs) can be adjusted by filling their cavities with guest materials. In this study, Cu nanoparticles are filled into CNTs via wet chemical method. To improve the filling efficiency, oxygen-containing functional groups (OCFGs) are introduced onto the tube walls of CNTs by acid treatment. The defects and pore size distribution on CNTs are detected and quantified by N₂ adsorption-desorption experiment, Raman spectra, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Morphologies of CNTs before and after filling treatment are observed by transmission electron microscope (TEM). The filling rate is characterized by inductively coupled plasma emission spectrometer (ICP) and thermal gravimetric analysis (TGA). The results indicate that the OCFGs can not only improve the hydrophilicity of CNTs, but also greatly affect the filling rate of CNTs. The filling rate of CNTs acid-treated for 24 h (1.99 wt% tested by TGA) is significantly lower than that of acid-treated for 8 h (12.11 wt% tested by TGA), which can be ascribed to the fact that excessive OCFGs could hinder Cu²⁺ ions from entering the cavity of CNTs. The obtained results can provide a new perspective for the application of CNTs in composite preparation and related fields.
Enhancement of mechanical properties and conductivity in carbon nanotubes (CNTs)/Cu matrix composite by surface and intratube decoration of CNTs
2021, Materials Science and Engineering: A
Citation Excerpt :
As a good electrical conductor, Cu has a low binding energy with carbon, and numerous interesting practical applications can be expected by filling Cu into CNTs [14]. Studies have indicated that the intra-tube resistivity of CNTs can be decreased by filling Cu into the hollow tubes of CNTs, thus improving the conductivity of CNT networks [15]. Wet chemistry is one of the methods to fill Cu into the prepared CNTs with easy operation procedure [14].
Strength and ductility are often a paradox in carbon nanotubes (CNTs) reinforced Cu matrix composite, as well as strength and electrical conductivity. Interface and characteristics of CNTs are critical factors in determining the mechanical properties and conductivity of Cu matrix composites. In the present study, a novel tactic by surface and intratube decoration of CNTs is adopted to break the above mentioned dilemmas. By decorating the surface of CNTs with CuO nanoparticles and taking advantage of the good wettability between CuO and Cu matrix, uniform dispersion of CNTs is realized through ball milling. In the final composite, CuO nanoparticles on the surface of CNTs are reduced to Cu. High density interfacial dislocations and interfacial disordered areas are formed between Cu matrix and CNTs, thus forming a strong interfacial bonding. By decorating the inner walls of CNTs with Cu nanoparticles, the interfacial shear stress between Cu matrix and CNTs is improved due to the extrusion effect of Cu nanoparticles on the inner walls. Moreover, the Cu filled inside the tubes can also reduce the intra-tube resistivity of CNTs by increasing their conducting cross-section. Consequently, the Cu matrix composite with simultaneous improvement of strength (272 MPa), ductility (14.3%) and conductivity (93.6% IACS) is achieved in our present study. This tactic provides a new idea to deal with the strength-ductility and strength-conductivity dilemmas in CNTs reinforced metal matrix composites.
Nanopackaging: Nanotechnologies and electronics packaging
2018, Nanopackaging: Nanotechnologies and Electronics Packaging, Second Edition
A review of properties influencing the conductivity of CNT/Cu composites and their applications in wearable/flexible electronics
2017, Journal of Materials Chemistry C
Research progress of electrical properties for carbon nanotubes reinforced metal matrix composites
2016, Fuhe Cailiao Xuebao/Acta Materiae Compositae Sinica
Copper Encapsulation of Multi-Walled Carbon Nanotubes
2013, Encapsulation Nanotechnologies

View full text