MATERIALS CHARACTERIZATION AND EFFECT OF PURITY AND ION-IMPLANTATION ON THE FRICTION AND WEAR OF SUBLIMED FULLERENE FILMS

In previous studies, sublimed C-60-rich fullerene films on silicon, when slid against a 52100 steel ball under dry conditions, have exhibited low coefficient of friction (similar to 0.12). Films with different purities can be produced by sublimation at different substrate temperatures. In this paper, effects of purity of fullerene films and ion implantation of the films with Ar ions on the friction and wear properties of sublimed fullerene films are reported. C-60-rich films (called here films with high purity) exhibit low macroscale friction. An increased amount of C-70 and impurities in the fullerene film determined using Raman and Fourier transform infrared (FTIR), increases its coefficient of friction. Microscale friction measurements using friction force microscopy also exhibited similar trends. Low coefficient of friction of sublimed C-60-rich films on silicon is probably due to the formation of a tenacious transfer film of C-60 molecules on the mating 52100 steel ball surface. Based on scanning tunneling microscopy (STM), transmission electron microscopy (TEM), and high resolution TEM (HRTEM), we found that fullerene films primarily consisted of C-60 molecules in a fee lattice structure. Nanoindenter was used to measure hardness and elastic modulus of the as-deposited films. Ion-implantation with 1 X 10(16) Ar+ cm(-2) reduced macroscale friction down to about 0.10 from 0.12 with an increase in wear life by a factor of 4; however, doses of 5 x 10(16) ions cm(-2) gave three times higher friction and poorer wear life; higher doses disintegrated the C-60 molecules. Based on STM, TEM, Raman, FTIR, and laser desorption Fourier-transform ion cyclotron resonance mass spectrometer (LD/FT/ICR) studies, we found that the ion implantation with a dose of 1 x 10(16) Ar+ cm(-2) resulted in smoothening of the fullerene film surface probably by compacting clusters, but without disintegrating the C-60 molecules. However, a high dose of 5 X 10(16) Ar+ cm(-2) damaged the C-60 molecules, converting it to an amorphous carbon. Nanoindentation studies show that ion implantation with a dose of 1 x 10(16) Ar+ cm(-2) resulted in an increase in the hardness from about 1.2 to 4.0 GPa and in elastic modulus from about 70 to 75 GPa and modified the elastic-plastic deformation behavior.