Polymerization in nanocrystalline diamond films by oxygen incorporation

Structure and resistivity of nanocrystalline diamond films deposited using microwave Ar-rich/O₂/CH₄ plasmas have been examined as a function of the O₂/CH₄ ratio from 0 to 0.53. Addition of O₂ to Ar-rich/CH₄ plasmas likely reduced the density of C₂ radicals due to loss reactions of O atoms with CH₄ and CH_x radicals. The Raman peak of diamond at 1332 cm^-1 was overlapped by the D peak of sp²-bonded, disordered carbon and its intensity was a little enhanced by the O₂ addition, while the average size of sp²-bonded carbon clusters in nondiamond phases was increased. Oxygen was incorporated into the films in forms of C-O bonds, which bridged the carbon clusters themselves, and formed polymer-like, large-unit structures. The resistivity of the films was drastically increased from the order of 10^-4 up to 10⁴ Ω · m with a small O₂ addition (1.2 vol.-% in total pressure), providing novel sensor and storage applications based on oxygen incorporation and desorption. A figure is presented. Decomposition of a Raman spectrum showing the diamond, D and G modes of amorphous carbon, and trans-polyacetylene peaks. The insert represents a typical SEM image showing a film surface.