Effect of gases on the temperature dependence of the electric conductivity of CVD multiwalled carbon nanotubes
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RES AND LOW-DIMENSIONAL SYSTEMS
Effect of Gases on the Temperature Dependence of the Electric Conductivity of CVD Multiwalled Carbon Nanotubes T. I. Buryakova, c, *, A. I. Romanenkoa, c, O. B. Anikeevaa, c, V. L. Kuznetsovb, c, A. N. Usol’tsevab, c, and E. N. Tkachevc a Nikolaev
Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090 Russia b Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090 Russia c Novosibirsk State University, Novosibirsk, 630090 Russia *e-mail: [email protected]; [email protected]
Abstract—The influence of various gaseous media on the temperature dependence of the electric conductivity σ of multiwalled carbon nanotubes (MWNTs) synthesized using the method of catalytical chemical vapor deposition (CVD) has been studied. The σ(T) curves were measured in a temperature range from 4.2 to 300 K in helium and its mixtures with air, methane, oxygen, and hydrogen. The introduction of various gaseous components into a helium atmosphere leads to a significant decrease in the conductivity of MWNTs in the interval between the temperatures of condensation and melting of the corresponding gas. Upon a heating–cooling cycle, the conductivity restores on the initial level. It is concluded that a decrease in σ is caused by the adsorption of gases on the surface of nanotubes. PACS numbers: 73.63.Rt DOI: 10.1134/S1063776107070345
1. INTRODUCTION The development of science and technology in the 21st century is related to a considerable extent to the creation of nanomaterials, which possess a number of unique advantageous properties in comparison to massive analogs [1, 2]. The modified properties of nanomaterials are mostly due to the following principal factors: (i) small dimensions of particles and their specific distribution; (ii) special chemical composition of components; (iii) the presence of developed boundaries between particles, heterophase contacts, and free surfaces; and (iv) a specific nature of interactions between particles. It is very important to note that the surface (interfacial) atoms in such materials account for a considerable proportion of the total number of atoms. Therefore, a change in the state of surface atoms as a result of their interaction with the environment not only influences the surface properties, but affects the bulk characteristics of nanostructures as well. Carbon nanotubes (CNTs) are among the most extensively studied nanomaterials [3, 4]. It should be noted that theoretical investigations into the properties of CNTs have been devoted for the most part to objects with a few (one or two) layers. However, the most important practical results have been obtained during the development of novel materials based on multiwalled CNTs (MWNTs) [5–7]. Numerous practical
applications of MWNTs (gas sensors, cold cathodes, field-effect transistors, etc.) are based on their special electrical properties. Naturally, one of the most important issues in the development of new devices based on MW
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