Materials characterization and effect of purity and ion implantation on the friction and wear of sublimed fullerene films

Abstract

In previous studies, sublimed C₆₀-rich fullerene films on silicon, when slid against a 52100 steel ball under dry conditions, have exhibited low coefficient of friction (∼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. C₆₀-rich films (called here films with high purity) exhibit low macroscale friction. An increased amount of C₇₀ 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 C₆₀-rich films on silicon is probably due to the formation of a tenacious transfer film of C₆₀ 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 C₆₀ molecules in a fcc lattice structure. Nanoindenter was used to measure hardness and elastic modulus of the as-deposited films. Ion-implantation with 1 × 10¹⁶ 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 × 10¹⁶ ions cm⁻² gave three times higher friction and poorer wear life; higher doses disintegrated the C₆₀ 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 × 10¹⁶ Ar⁺ cm⁻² resulted in smoothening of the fullerene film surface probably by compacting clusters, but without disintegrating the C₆₀ molecules. However, a high dose of 5 × 10¹⁶ Ar⁺ cm⁻² damaged the C₆₀ molecules, converting it to an amorphous carbon. Nanoindentation studies show that ion implantation with a dose of 1 × 10¹⁶ 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.