Correlated high resolution transmission electron microscopy and X-ray photoelectron spectroscopy studies of structured CNx (0 < x < 0.25) thin solid films

Structured carbon nitride (CNx), thin solid films, also known as fullerene-like, consist of, upon nitrogen substitution, bent and cross-linked graphene planes. They were synthesized by unbalanced reactive magnetron sputtering and analyzed by high-resolution transmission electron microscopy (HRTEM) in combination with X-ray photoelectron spectroscopy (XPS). The microstructure evolution in terms of plane alignment, extension and cross-linking can be controlled by adjusting the synthesis conditions, such as growth temperature, N-2 fraction in the discharge gas and ion energy. HRTEM on plan-view samples was used to examine the structural changes depending on growth temperature and N-2 fraction. The problem of projection artifacts for imaging the structural features was partially overcome by selected area electron diffraction analysis, where it is shown that diffraction corresponding to 3.5 Angstrom is associated with the formation of structured CNx. The incorporation of N is crucial for the evolution of heavily bent and frequently cross-linked basal planes, since it triggers pentagon formation and cross-linking at much lower energies compared to pure carbon films. Therefore, the two spectral features in the nitrogen Is core electron spectra as examined by XPS were correlated to the microstructure evolution. (C) 2004 Elsevier Ltd. All rights reserved.