RAMAN-SCATTERING FROM ION-IMPLANTED DIAMOND, GRAPHITE, AND POLYMERS

Raman scattering studies were carried out to investigate the effects o f ion implantation on the structure of diamond, graphite, and polymers . Carbon phases produced by chemical vapor deposition (CVD diamond) an d rf discharge (diamondlike carbon or DLC) were also analyzed. Two typ es of amorphous carbon phases were distinguished with relevance to har dness. In general, amorphous carbon phases produced by electron beam e vaporation and sputtering are soft (hardness much less than 1 GPa), wh ile DLC and some ion-beam-modified polymers are much harder. In all ca ses, the characteristic Raman bands of the starting material were lost upon ion implantation, and for the lowest fluences the one-phonon ban ds near 1360 cm-1 (D line) and 1580 cm-1 (G line) of disordered polycr ystalline graphite appeared. With increasing fluence these bands coale sced into a broad, asymmetric peak with the D line shifting to higher wave number and the G line shifting to lower wave number. This trend w as clearly distinguishable from the finite crystallite size effect see n in graphite, where, in addition to the appearance of the D line, the G line shifts to higher wave number with decreasing crystallite sizes . Raman scattering could not distinguish between soft and hard amorpho us carbon. There was also no indication that the hardness of DLC films and ion-beam-modified polymers was due to diamondlike sp3 bonds. Inst ead, hardness in these materials is related to the three-dimensional i nterconnectivity of chemical bonds. Experimental results suggest that the amorphous carbons examined in this study are composed of random ne tworks of distorted sp, sp2, and Sp3 bonded atoms, sometimes in a hydr ogenated state. The hard carbons such as DLC films and ion beam modifi ed polymers have long-range chemical connectivity while the soft carbo ns such as damaged graphite, and carbon films prepared by sputter depo sition lack such connectivity.