The Characterization of Copper-Doped Carbon Aerogels by Transport Properties Measurements
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The Characterization of Copper-Doped Carbon Aerogels by Transport Properties Measurements R.W. Fu1,2), N. Yoshizawa1,3), Y. Hanzawa4), K.Kaneko4), A. P. Santos1), M. S. Dresselhaus1), G. Dresselhaus1), J. Satcher5) and T. Baumann5) 1 Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA, USA 2 PCFM Laboratory, Zhongshan University, Guangzhou, 510275 China 3 National Institute of Advanced Industrial Science and Technology, Onogawa, Tsukuba, Japan 4 Department of Chemistry, Faculty of Science, Chiba University, Chiba, Japan 5 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, USA ABSTRACT Copper-doped carbon aerogels, which were prepared by sol-gel polymerization of a mixture of resorcinol, formaldehyde and copper ions, followed by supercritical drying with liquid CO2 and carbonization at different temperatures under a N2 atmosphere, were characterized by magnetic susceptibility and temperature-dependent conductivity measurements. The experimental results show that the magnetic susceptibilities (χ) of all the copper-doped carbon aerogels are larger than that of the blank carbon aerogel. The temperature-dependent magnetic susceptibilities of the copper-doped carbon aerogels are well fit to a Curie function in the low temperature region (below 45 K). According to the Curie constant obtained, the spin concentration (N) of the copper-doped carbon aerogels was calculated and the results show that the spin concentration of doped samples increases at first with an increase in the copper concentration used in doping, and then drops from the maximum in N and χ when the copper concentration is further increased above 0.1 wt%. Magnetic susceptibility results suggest that copper-doped carbon aerogels carbonized at 800 ºC are more disordered than those carbonized at 1000 ºC. The conductivity of these copper-doped carbon aerogels is apparently higher than that of the blank carbon aerogel, especially at low temperature (T < 45 K). The temperaturedependent resistivities of both the copper-doped and the blank carbon aerogels follow a linear functional form log ρ(T) ~ (1/T) 1/2 with two distinct regions below and above 45 K, indicating that the conduction of both the copper-doped and the blank carbon aerogels obey a tunneling and/or a hopping mechanism. INTRODUCTION Carbon aerogels (CA) are a class of cluster-assembled porous materials, which have been of interest for both science and applications [1-9]. Their unique microstructure consists primarily of a network of covalently interconnected carbon nanoclusters (grains) (3-25nm), which defines an open substructure of mesopores (2-50 nm). Inside the carbon particles is a network of intertwined graphitic filaments of width ~ 25 Å. A few micropores have also been found to exist inside the grains. This structure leads to extremely high surface areas (600-800 m2/g) and to an intrinsic disorder of the system, with a large fraction of dangling bonds and defect states on the surface and inside the grains [4]. Besides that, carbon aerogels combine the
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