Inorganically filled carbon nanotubes: Synthesis and properties

Abstract

Since the discovery of carbon nanotubes (CNTs) in 1991, widespread research has been carried out to understand their useful physical and electronic properties and also to explore their use in devices. CNTs have many unique properties such as tunable electrical resistance, mechanical robustness, and high thermal conductivity, which when combined with other inorganic materials such as phosphors or superconductors could lead to heterostructures with diverse functionality. We have been able to obtain mass production of such materials wherein CNTs form core-shell heterostructures with metals, semiconductors, insulators, and even metal-semiconductor heterojunctions. The emerging strategy employs a high-temperature chemical vapor deposition (CVD) technique and high heating rates. Interestingly, due to their high temperature stability, CNTs can act as a nanoreactor for production of exotic materials inside it. In this article, we take ZnS-filled CNTs as an example to explain our synthesis strategy. We explore the optical behavior of these complex materials, analyzing both their luminescence and degradation upon exposure to an electron beam. In addition, the mechanical response of filled CNTs has been evaluated individually inside a transmission electron microscope fitted with an atomic force microscopy-transmission electron microscopy (AFM-TEM) sample holder. Many applications can be envisioned for these nanostructures ranging from nanothermometers to photo-protective storage and delivery devices.gle graphitic sheet rolled up into a cylinder with lengths of micrometers and diameters up to 100 nm [2]. In practice, CNTs can be broadly classified in two classes based on their number of walls, i.e., single-and multi-walled CNTs. Several strategies have been developed for their synthesis, such as laser ablation, arc discharge, and chemical vapor deposition (CVD) techniques [1]. Depending on the way the graphene has been assembled, single-walled CNTs can be either metallic or semiconducting. Because of their exotic properties, CNTs have emerged as an attractive candidate in diverse technological applications, such as in polymer composites, sensors, and several others [3].An interesting aspect of the CNTs is their inner cavity, which can be filled with another material in order to create novel heterostructured nanomaterials [4]. In fact, the cavity may act as a template for other elongated structures. These will have extremely large interface areas, which may well induce unusual properties in the ensemble [5]. Moreover, the CNTs could be used as a storage medium for airor moisture-sensitive materials. Led by such motivations, the prospect to fill their inner cavities with different materials such as fullerenes, metals, alloys, fluids, and biomolecules has been extensively investigated [5][6][7]. The filling procedure is based on two methods, (a) wet chemical methods, where chemicals dissolved in solvent are used as precursors and (b) physical methods, where tip-open CNTs are infiltrated with molten materials [5]. However, a maj...

Multi-component oxide nanosystems by Chemical Vapor Deposition and related routes: challenges and perspectives

“…25,[46][47][48][49][50][51][52][53][54] In addition, increasing attention has been devoted to the combination of oxides and carbon-based nanomaterials, especially involving carbon nanotubes (CNTs), that display attractive properties in terms of chemical and mechanical stability, adsorption capacity, electrical conductivity and nano-size effects. 9,[55][56][57][58][59][60][61][62][63][64] Such features pave the way to the use of the resulting carbon/oxide composites in various fields, including wear-resistant materials, electronic/magnetic nanodevices, supercapacitors, photocatalysts and gas sensors. 7,9,24,28,[58][59][60][61][62][63][65][66][67] In all the above cases, the development of composite systems with an intimate contact between the constituents is a key issue to exploit a unique chemical reactivity and obtain unprecedented and improved performances.…”

“…9,[55][56][57][58][59][60][61][62][63][64] Such features pave the way to the use of the resulting carbon/oxide composites in various fields, including wear-resistant materials, electronic/magnetic nanodevices, supercapacitors, photocatalysts and gas sensors. 7,9,24,28,[58][59][60][61][62][63][65][66][67] In all the above cases, the development of composite systems with an intimate contact between the constituents is a key issue to exploit a unique chemical reactivity and obtain unprecedented and improved performances. 9,10,15,27 The assembly of multi-component nanomaterials with controlled morphology, from nanopowders to supported 1D materials and hierarchical nanostructures, 1,5,23,27,56,[68][69][70][71][72][73][74] requires the development of versatile and efficient fabrication procedures, which have a crucial influence on the ultimate system behaviour.…”

“…The main advantages offered by CVD are high flexibility, high growth rate, good control of the reaction environment, excellent conformal step coverage and adaptability to large scale processing. 63,[74][75][76][77][78][79][80] The unique tailoring of nanomaterial morphology, enabled by a careful control of operational parameters under non-equilibrium conditions, has been exploited for the fabrication of various systems, from inorganic oxides to carbonbased systems, in the form of nanopowders, coatings, nanocrystals, nanorods (NRs) and nanotubes (NTs). 7,8,56,57,63,74,[78][79][80][81][82][83][84][85][86][87][88] Beyond the great interest devoted to CVD precursor design and synthesis, [89][90][91][92][93] intensive efforts have led to the development of a large variety of CVD processes, related to different precursor delivery and operational/activation modes.…”

“…63,[74][75][76][77][78][79][80] The unique tailoring of nanomaterial morphology, enabled by a careful control of operational parameters under non-equilibrium conditions, has been exploited for the fabrication of various systems, from inorganic oxides to carbonbased systems, in the form of nanopowders, coatings, nanocrystals, nanorods (NRs) and nanotubes (NTs). 7,8,56,57,63,74,[78][79][80][81][82][83][84][85][86][87][88] Beyond the great interest devoted to CVD precursor design and synthesis, [89][90][91][92][93] intensive efforts have led to the development of a large variety of CVD processes, related to different precursor delivery and operational/activation modes. These involve atmospheric or low pressure-CVD (AP-CVD or LP-CVD), [78][79][80]94 fluidized-bed CVD, liquid injection-CVD (LI-CVD), 75,76 aerosol assisted-CVD (AA-CVD) 95 and plasma enhanced-CVD (PE-CVD).…”

“…Emphasis is given to innovative approaches to multi-component nanomaterials, with regard to current trends and future directions. Although many excellent works/reviews focused on different kinds of inorganic and hybrid multi-component systems have been published up to date, [9][10][11]15,18,27,37,63,64,73,74,[78][79][80]94,[99][100][101] no similar literature survey on oxide-based nanocomposite systems obtained by CVDrelated methods has been attempted so far.…”