In-situ thermal stability analysis of amorphous carbon films with different sp³ content

A synchronized system integrating Raman spectroscopy and depth-sensing techniques was applied to analyze the microstructure, mechanical properties and surface roughness of amorphous carbon (a-C) films in-situ. This integrated system equipped with a high-temperature chamber coupled with feedback control made it possible to study the temperature effects on the mechanical properties and the microstructure of the films. A series of a-C films with different sp³ content were deposited on Si substrates using a filtered cathodic arc vacuum (FCVA) deposition system. Our study confirms previous results that the thermal stability of the a-C films depends on their sp³ content. The results also show that the structural change is accompanied by a significant increase in the surface roughness. This synchronized characterization technique demonstrates that the film hardness decreases with temperature even before any chemical changes detected using Raman spectroscopy. Moreover, the surface of the films is more sensitive to the temperature compared to the bulk as evidenced by the surface roughness characterization, showing that the surface roughness starts to rise at temperatures lower than for the onset of structural transition in the bulk. Nanoscratch and nanowear tests further support the conclusion that the surface sensitivity to temperature is greater than for the bulk.