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R10.3.1

Metal incorporation into nanoporous carbon S. J. Henley1, N. E. P. Woolger1, J. D. Carey1, S. R. P. Silva1, G. M. Fuge2 and M. N. R. Ashfold2 1 Advanced Technology Institute, School of Electronics and Physical Sciences, University of Surrey, Guildford, GU2 7XH, U.K. 2 School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K. ABSTRACT Nanoporous carbon films were deposited by 248 nm pulsed laser ablation of a graphite target in different background pressures of argon (PAr). The morphology changed from smooth, high-density amorphous carbon films at PAr = 20 mTorr to ultra-low density nanoporous material at PAr = 380 mTorr. Subsequently, the nanostructural, chemical and electrical properties of metal containing nanoporous carbon samples were investigated by ablating graphite targets containing known contents of Ni and Co. We demonstrate how the ablation plume dynamics affect both the nanostructure of the material and the incorporation of metal atoms. The suitability of these functionalised ultra-low density materials for gas sensing applications is discussed. INTRODUCTION The presence of ambient gas can have a dramatic effect on the expansion dynamics of laser-ablated plasmas [1]. Nanosecond pulsed laser ablation (PLA) of graphite results in the deposition of quite different carbonaceous structures depending on the pressure of ambient gas in the chamber [2, 3]. PLA of graphite in vacuum is typically used to produce smooth, hard, high-density amorphous carbon (a-C) films with high sp3 bonded C content (up to 90%)[4, 5]. The introduction of a low pressure of inert gas into the growth chamber reduces the kinetic energy of the growth species due to the increased collision frequency. At higher pressures plume confinement, and plume heating occurs, which leads to enhanced excitation/ionisation at the plume front. Compared with growth in vacuum, these conditions have been shown to yield lower density nanoporous carbon (NPC) films [3, 6], which can exhibit a range of useful properties including low thresholds for electron emission [7] and high porosities [3] suggesting gas sensor applications [8]. Recent work on high repetition rate laser ablation of carbon in background pressures of argon has shown that these conditions can deposit carbon nanofoam [9]. However, porous carbon samples have been found typically to have very high resistivities [8, 9] of the order of 107–109 Ωcm, limiting their usefulness in electronic devices applications. One possible technique for improving the conductivity of these films is by incorporating metal atoms during the growth. The doping of a-C thin films by incorporation of metals has been attempted and it was found that the mechanical, tribological, and electrical properties are all strongly influenced by the metal content in the films [10, 11]. For example, electrical conductivity could be increased many orders of magnitude by varying the metal content [11–13]. In this paper we investigate the incorporation of metal into the NPC films deposited by PLA of graphite. We examine the