Micro-scratch test of DLC films on Si substrates prepared by bipolar-type plasma based ion implantation

Diamond-like carbon (DLC) films were prepared on Si substrates using a variety of positively and negatively pulsed voltages (Vp and Vn), by a bipolar-type plasma based ion implantation system, and adhesion strength and toughness of the samples were examined in terms of the higher critical load (Lc2) and the scratch crack propagation resistance (CPRs) by a micro-scratch test. Cross sectional transmission electron microscopy (TEM) and Raman spectroscopy were also carried out to examine the microstructure of the samples. The Lc2 and CPRs were increased by increasing Vp and Vn. TEM observation showed that a graphite-like form, such as turbostratic structure, is increased by increasing Vp and Vn. Raman spectra also indicated that the clustering of aromatic rings is enhanced at high Vp and Vn. From these results, it is suggested that the increase of the graphite-like form at high Vp and Vn should reduce the internal stress. In addition, it may act as a lubricant, resulting in the enhancement of the adhesion strength and the toughness of the films. The ID/IG obtained from Raman spectra measured at the different points of the pre-scratched region, the cracking region and the partial destruction region was varied, and a tentative explanation was made on the basis of a 3 stage model.