Growth and Properties of Carbon Nitride Thin Films
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Z. JOHN ZHANG, PEIDONG YANG AND CHARLES M.LIEBER Division of Applied Sciences and Department of Chemistry Harvard University, Cambridge, MA 02138
ABSTRACT
Recent research on carbon nitride thin films grown using pulsed laser deposition combined with atomic beam techniques is reviewed. The composition, growth mechanism and phases of these films have been systematically investigated. The nitrogen composition was found to increase to a limiting value of 50% as the fluence was decreased for laser ablation at both 532 nm and 248 nm wavelengths. Time of flight mass spectroscopy investigations of the ablation products have shown that the fluence variations affect primarily the yield of the carbon reactant. These experiments demonstrate that the overall film growth rate determines the average nitrogen composition, and furthermore, suggest that a key step in the growth mechanism involves a surface reaction between carbon and nitrogen. Infrared spectroscopy has been used to assess the phases present in the carbon nitride thin films as a function of
the overall nitrogen content. These measurements have shown that a cyanogen-like impurity occurs in films with nitrogen compositions greater than 30%. Studies of thermal annealing have shown, however, that this impurity phase can be eliminated to yield a single phase C2N material. In addition, systematic studies of the electrical resistivity and thermal conductivity of the carbon nitride films are discussed. I. INTRODUCTION Carbon nitride materials represent an exciting challenge to both fundamental and applied research [1]. Basic research is needed to develop new preparative methods for combining rationally carbon and nitrogen into solid materials and to elucidate the structures and physical properties of these new materials. In addition, applications of carbon nitride solids are being actively pursued since simple bonding arguments and more rigorous theoretical calculations suggest that these materials should have attractive properties, such as extreme hardness and thermal conductivity. 271
Mat. Res. Soc. Symp. Proc. Vol. 388 ©1995 Materials Research Society
Early theoretical investigations of carbon nitride solids focused on a hypothetical binary carbon-nitrogen compound, P-C3N4, that has the P-Si3N4 structure [2]. The results from this theoretical work suggested that 3-C3N4 should have a reasonably large cohesive energy and thus should be metastable. More recent theoretical studies have also investigated the stability and properties of C3N4 compounds that have structures distinct from that of the P-Si3N4 structure [3]. Significantly, these latter studies have found that carbon nitride C3N4 materials having either defect zinc-blende or rhombohedral graphite-like structures should have stabilities comparable to or greater than P-C3N4. Because there is also no reason to assume that carbon nitride must have a C3N4 stoichiometry, there is many metastable C-N phases that must be carefully considered in experimental studies of this new class of materials. Experimental approache
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