Characterization of single wall carbon nanotubes filled with silver and with chromium compounds

doi:10.1016/j.cplett.2003.11.061

Chemical Physics Letters

Volume 383, Issues 5–6, 15 January 2004, Pages 475-480

https://doi.org/10.1016/j.cplett.2003.11.061 Get rights and content

Abstract

The chemical treatment of single wall carbon nanotube (SWNT) samples leads to a modification of their vibrational and electronic properties. We here report the alteration of the Fermi level of SWNTs chemically modified with Ag and CrO₃ as observed in the resonance Raman spectra of both metallic and semiconducting SWNTs. Our results indicate that while Ag behaves as an electron donor, CrO₃ behaves as an electron acceptor for SWNTs.

Introduction

Prior studies show that the capillarity properties of carbon nanotubes (CNTs) allow the filling of their hollow-cores with chemical species in solution, including proteins [1], ruthenium [2], gold and silver monocrystals [3], metal halides and oxides [4]. Some of these materials were extensively characterized by transmission electron microscopy techniques [4], [5]. Biological and materials science systems where different species (such as metals, metal oxides, proteins, enzymes, etc.) are inserted into carbon nanotubes may find practical application. Moreover, the modification of the electronic properties of the host carbon nanotubes by the introduction of molecules, on one hand, and the modification of the properties of the encapsulated species, on the other hand, are both interesting topics [6], [7].

It has also been reported that single wall carbon nanotubes (SWNTs) could be successfully filled with chromium oxide at room temperature in open air [8]. This material was characterized by X-ray energy dispersive spectroscopy (X-EDS) and electron energy loss spectroscopy (EELS), and it was found that the filling compound is CrO₃. The interest in this kind of study is justified by the potential applications of these nano-products in batteries or in the oxidation of primary alcohols, as suggested by studies made with the analogous graphite intercalation compounds (graphite intercalated with CrO₃) [9].

In this work we report on the characterization of oxidized SWNTs in bundles treated with AgNO₃ and CrO₃ (hereafter called SWNT/Ag and SWNT/CrO₃). Our goal is to study the modification of the nanotube properties as a consequence of the introduction of the foreign material into the nanotube cores or into the interstitial channels of the SWNT lattice, using resonance Raman spectroscopy, which is highly sensitive to the electronic properties of nanotubes. In addition, spectra at different temperatures obtained by increasing the incident laser power on the sample are reported. These results on the modification of the electronic properties of SWNTs by chemical doping are also compared to recently reported modifications observed by electrochemical doping [10].

Section snippets

Experimental

The SWNTs used in this work were produced by the electric arc discharge method, using a catalyst with a 1:1 Ni:Co atomic ratio, and the SWNTs had a diameter distribution of $d_{t} =1.25 ± 0.20$ nm as determined by the Pimenta method [11], [12].

Carbon nanotubes were filled with crystalline silver according to a method similar to the one described by Chu et al. [13]. SWNTs were opened by oxidation in HCl aqueous solution, and the opened tubes were then stirred for 24 h in a concentrated AgNO₃ aqueous

Results and discussion

Since resonance Raman spectroscopy is sensitive to both the electronic structure and the vibrational spectra of carbon nanotubes, the technique can be used to probe the modification of their electronic and vibrational properties caused by the introduction of a different chemical species into the cores of the nanotubes or the interstitial channels of the SWNT lattice [14]. Significant changes can be observed in the Raman spectra of the SWNTs, as shown in Fig. 1, as a result of the silver

Conclusions

SWNTs modified with Ag and CrO₃ were characterized by resonance Raman spectroscopy. A significant charge transfer-induced perturbation to the electronic structure of the SWNTs was observed as a result of chemical interaction.

The characterization of the intercalated SWNTs is consistent with a reduction of the nanotubes (increase in the electron carrier density) for the case of SWNT/Ag and an oxidation of the nanotubes (decrease in electron carrier density) for the case of SWNT/CrO₃ as a result

Acknowledgements

P.C. gratefully acknowledges FAPESP for the grant of a fellowship (02/08596-5). A.P. Santos acknowledges financial support from the Brazilian agency CNPq. This work was partially supported by CNPq and FAPESP. We also acknowledge the NSF/CNPq joint collaboration program (Grant No. NSF INT 00-00408 and CNPq Grant No. 910120/99-4). The MIT authors acknowledge support from NSF grant DMR 01-16042. We thank Prof. C.A. Luengo and his group for the donation of the SWNTs sample used in this work.

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Characterization of single wall carbon nanotubes filled with silver and with chromium compounds

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgements

J. Electroanal. Chem.

Chem. Phys. Lett.

Chem. Phys. Lett.

Chem. Phys. Lett.

Chem. Phys. Lett.

Chem. Comm.

Chem. Comm.

Science

Acc. Chem. Res.

Nature

Nature