Modification of fluorinated single-walled carbon nanotubes with aminosilane molecules
Introduction
Single-walled carbon nanotubes (SWCNTs) have emerged as materials that potentially may find their way into myriad applications [1], [2], [3], [4]. They exhibit either metallic or semiconducting properties and, at the same time, chemical and thermal stability and extremely high strength and elasticity [5], [6]. Moreover, combining these features with these outstanding properties is expected to reshape the development of functional devices. However, many of these interesting and unique properties can only be realized once the SWCNTs are integrated into more complex assemblies [7], [8].
Two of the key challenges that are in the way of realizing multifunctional nanostructures based on carbon nanotubes are securing a reliable control over their surface chemistry (i.e., through either covalent or non-covalent modification) and achieving monodispersity in terms of length, diameter, and helicity [9], [10], [11]. The ultimate goal is the ability to control the arrangement and interactions of nanoscale objects by functional interfacing. In this regard, a strategy for SWCNT functionalization involved the use of sidewall reactions such as fluorination with elemental fluorine [12], [13].
This covalent functionalization strategy allowed a wide range of chemistry to control the properties of these nanoscale materials. In a previous work, we proposed a method for fluorine sidewall functionalization of SWCNTs with CF4 plasma treatment at room temperature. We also demonstrated the practical use of plasma fluorination to achieve sidewall amino-functionalized nanotubes [14].
In the present work, we suggest the possibility of using amino-functionalized fluorinated SWCNT to make possible a “mix and match” approach towards classes of hybrid materials consisting of carbon nanotubes and alkoxy-silane molecules. We also suggest the possibility of tuning the electrical properties by combining the electric field in the assembling processing.
Section snippets
Experimental details
The single-walled nanotubes were obtained from Bucky USA Inc. and consisted of ≈90 vol% carbon-like SWCNT of 50 nm–1 μm in length and 0.8–2 nm in diameter. Noticeable amount of SWCNT bundles of 50 nm in diameter was found (Fig. 1). Fluorinated SWCNTs (F-SWCNTs) were obtained by the plasma-assisted decomposition of CF4 employing a 13.56 MHz radiofrequency plasma source as previously reported [14]. A commercially available grade of 3′-(aminopropyl)tri-ethoxysilane (APTES, NH2(CH2)3Si(OEt)3, 99%),
Results and discussion
The TEM allowed direct imaging of sidewall modification in the SWCNTs. Fig. 2 shows the TEM images of F-SWCNTs and APTES modified F-SWCNTs placed on a carbon-coated copper grid. The pristine F-SWCNTs (Fig. 2(a)) are nearly clean as well as supported by the height analysis along a backbone of a bundle (inset of Fig. 2(a)). In this regard, it should be mentioned that decomposition of fluorine containing species employing a 13.56 MHz radiofrequency plasma source [15], [16] led to the formation of
Conclusions
In summary, our results demonstrate that the sidewall fluorination of SWCNTs by plasma treatment enhances the reactivity of fluoronanotubes with alkoxy-silane molecules. TEM, IR and TGA results demonstrate how the fluorine termination on the SWCNT sidewall promotes a link between the SWCNTs and 3′-(aminopropyl)tri-ethoxysilane molecules through amine bonds. Under an electric field, the APTES modified F-SWCNTs have been assembled into ordered rectifying diode. These results demonstrate the
Acknowledgments
We thank Prof. Saverio Russo, Dr. Laura Ricco and Dr. Jenny Alongi (Dipartimento di Chimica e Chimica Industriale University of Genova) for access to scanning and transmission electron microscopy as well as technical support.
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