Naslov
Modification of Fluorinated SWNTs with Aminosilane Molecules

Autori
Macan, Jelena ; Valentini, Luca ; Armentano, Ilaria ; Mengoni, Francesco ; Kenny, Jose Maria

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
V Convegno Nazionale sulla Scienza e Tecnologia dei Materiali, Atti / Marongiu, Giaime - Cagliari : Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, 2005

Skup
V Convegno Nazionale sulla Scienza e Tecnologia dei Materiali

Mjesto i datum
Geremeas, Italija; Maracalagonis, Italija, 26.09.2005. - 29.09.2005

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
none

Sažetak
Single-walled carbon nanotubes (SWNTs), in addition to their chemical and thermal stability and extremely high strength and elasticity, exhibit either metallic or semiconducting electric properties. However, in order to apply those interesting and unique properties SWNTs have to be incorporated into more complex assemblies, which often entails chemical functionalization of the SWNTs to enable them to form covalent bonds with other components. A common approach for functionalization of SWNTs is the use of sidewall reactions, which opens up a wide range of chemistry that can be performed on the sidewalls of carbon nanotubes. Previously we have demonstrated feasibility of fluorine sidewall functionalization of SWNTs by means of CF_4 plasma treatment at room temperature, and consequent reaction of these fluorinated SWNTs (F-SWNTs) with amines. In this work an aminosilane, 3’ -(aminopropyl)tri-ethoxysilane (APTES, NH_2(CH_2)_3Si(OEt)_3), was used to modify F-SWNTs, and the electrical properties of obtained films were studied. The F-SWNTs (3 wt%) were dispersed in APTES by sonication for 1 h at room temperature. Transmission electron microscopy images showed that, whereas the pristine SWNTs were nearly molecularly clean, the F-SWNTs that reacted with APTES had a thin amorphous coating irreversibly anchored onto them. This finding was supported by attenuated total reflectance infrared spectroscopy (ATR-IR) and thermogravimetric analysis (TGA). The ATR-IR spectrum of the APTES-functionalized F-SWNTs shows the presence N-H bond, with the change to the band of primary amine of APTES after the reaction with F-SWNTs. The formation of the C-N bond as a result of the condensation reaction of APTES with F-SWNTs was also seen, and it can be inferred that the primary amine of APTES directly reacts with the fluorine of F-SWNTs, resulting in the formation of C-N bond between the nanotubes and the alkoxy-silane molecules. The pyrolysis of APTES and APTES modified F-SWNTs in nitrogen atmosphere was monitored by TGA. The pure APTES evaporated completely in one step at 190°C, while the TGA curve for APTES-modified F-SWNTs showed three distinct weight losses. The first occurred at 60°C and is ascribed to evaporation of HF formed by the reaction of F-SWNTs with amine, while the following two steps at temperatures over 400°C are most likely due to degradation of organic chain of APTES, firmly bound to F-SWNTs and thus prevented from evaporating. In case when pristine SWNTs were sonicated with APTES, no change from pure APTES was seen either by IR or TGA, further confirming the our supposition. The presence of an electric field can greatly enhance the assembly of APTES-modified SWNTs on a solid surface, as was clearly shown in the atomic force microscopy images of long nanotubes oriented in the direction of the field. It also aided “ unroping” of F-SWNTs dispersed in APTES compared with pristine SWNTs, as shown by scannine electron microscopy. Before the exposure to dc electric field the I-V characteristics of APTES-modified SWNT film was symmetrical, while after the exposure the device exhibited a pronounced rectifying behaviour similar to a conventional pn junction. This showed that the electron-donating amine groups on nanotubes act as chemical gating by reducing the hole-carriers in p-type SWNTs and therefore decreasing the conductance of the samples. The electron donation only reduces the p-type characteristics of nanotubes and leads to the formation of p/p(-) rectifying junctions. The modulated chemical gating approach presented here is straightforward and can reliably yield intratube junctions exhibiting excellent rectifying characteristics.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemijsko inženjerstvo

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