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, wh en slid against a 52100 steel ball under dry conditions, have exhibite d low coefficient of friction (similar to 0.12). Films with different purities can be produced by sublimation at different substrate tempera tures. In this paper, effects of purity of fullerene films and ion imp lantation of the films with Ar ions on the friction and wear propertie s of sublimed fullerene films are reported. C-60-rich films (called he re films with high purity) exhibit low macroscale friction. An increas ed amount of C-70 and impurities in the fullerene film determined usin g Raman and Fourier transform infrared (FTIR), increases its coefficie nt 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 formatio n of a tenacious transfer film of C-60 molecules on the mating 52100 s teel ball surface. Based on scanning tunneling microscopy (STM), trans mission 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 1 0(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 wea r life; higher doses disintegrated the C-60 molecules. Based on STM, T EM, 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 smoothe ning of the fullerene film surface probably by compacting clusters, bu t 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 a morphous carbon. Nanoindentation studies show that ion implantation wi th a dose of 1 x 10(16) Ar+ cm(-2) resulted in an increase in the hard ness 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.