¹³C NMR spectroscopy of amorphous hydrogenated carbon and amorphous hydrogenated carbon nitride grown at various substrate temperatures

S.-H. Lin, J. BraddockWilking and B. J. Feldman

Department of Chemistry and Physics and the Center for Molecular Electronics

University of Missouri-St. Louis, St. Louis, MO 63121 USA

Abstract

We report the ¹³C NMR spectra of amorphous hydrogenated carbon (a-C:H) and amorphous hydrogenated carbon nitride (a-C:N:H) grown at various substrate temperatures. The a-C:H spectra were deconvoluted into a contribution from hydrogen bonded carbon and one from non-hydrogen bonded carbon. This successful deconvolution supports the idea that a-C:H is inhomogeneous and consists of hydrogen-rich and hydrogen-poor regions. As the substrate temperature is increased, a-C:H films have less hydrogen by having less hydrogen-rich regions -- not less hydrogen in the hydrogen-rich regions.

The ¹³C NMR spectra of a-C:N:H also provide strong evidence of an inhomogeneous material. The spectra consist of both sharp lines from ordered regions and broad lines from amorphous regions. The sharp lines at 138 ppm and 172 ppm are due to nitrogen-containing aromatic rings terminated by amino groups. The sharp line at 80 ppm is possibly due to b phase C₃N₄ nanocrystals. The broad line at 50 ppm due to sp³ bound carbon narrows with increasing substrate temperature due to a decrease in hydrogen-rich regions.

Corresponding author: Bernard J. Feldman, Department of Physics, University of Missouri, St. Louis, MO 63121, USA. E-mail: C4840@jinx.umsl.edu FAX: 314-516-6801 TEL: 314-516-5019.

There are two significant points in my presentation. First, these results demonstrate the power of NMR to uncover atomic structure of amorphous materials. Second, these results provide strong evidence that these two amorphous materials are inhomogeneous and suggest the reason why they are inhomogeneous. This in turn suggests that many other amorphous materials are inhomogeneous for the same reason.

Keywords: Nuclear magnetic resonance, amorphous hydrogenated carbon, amorphous hydrogenated carbon nitride, inhomogeneous materials.