Analysis of fluorocarbon plasma-treated diamond powders by solid-state fluorine-19 nuclear magnetic resonance

Abstract

In this work, solid-state [sup 19]F NMR has been used to characterize fluorine on diamond powder surfaces after CF[sub 4] and 98% CF[sub 4]2% O[sub 2] radio-frequency plasma treatment. The fluorine surface coverage of the pure CF[sub 4] treated powder was 7.1 [times] 10[sup 14] F/cm[sup 2] while the other plasma yielded a much lower coverage, 7.4 [times] 10[sup 13] F/cm[sup 2]. In both cases, only CF[sub x] (x = 1-3) functionalities were observed with the majority species being carbon monofluoride. Only 5-10% of the fluorine was bonded as CF[sub 3]. With high-speed magic-angle spinning, isotropic chemical shifts were resolved and assigned relative to CFCl[sub 3] as follows: CF, 148 [+-] 1 ppm; CF[sub 2], 106 [+-] 2 and 123 ppm; CF[sub 3], 78 [+-] 1 ppm. The peak at 123 ppm was only observed in the CF[sub 4]O[sub 2] plasma-treated sample and is speculated to be the result of atomic fluorine etching of diamond. Multiple-quantum NMR indicates that fluorine coverage is not uniform. Some fluorine is relatively dispersed on the order of approximately 5 Angstroms while the remaining fluorine occurs in aggregates of greater than 40 nuclei. This is consistent with preferential deposition of reaction occurring at and aroundmore » surface defects. 51 refs., 10 figs., 5 tabs.« less