Diamond-like carbon (DLC)
Results for diamond-like carbon films with the thickness from 58 to 98 nm are shown in Figure 1. The films were deposited on silicon wafers by means of the pulsed laser deposition (PLD). The substrate temperature was varied to study the thermal effects of the deposition process on the stability of the diamond-like carbon films. The laser-acoustic method indicates the varying film quality by different slopes of curves in Figure 3. Considering the relation H > E/10 between hardness H and Young’s modulus E empirically found for diamond-like carbon films [1] reveals that super-hard DLC films were deposited at temperatures lower than 216°C by the PLD-technique. For substrate temperatures higher than 230°C, the film modulus drastically reduces.
Figure 1: Laser-acoustic results for diamond-like carbon films deposited at different substrate temperature
Figure 2 presents the behavior of the DLC-film modulus with increasing deposition temperature for three different deposition technologies: pulsed laser deposition (PLD), mass-selected ion beam (MSIB) and laser-arc. It is obvious that there is a transition temperature for the DLC-films indicating the transition of the film structure from the sp³-rich DLC (E > 700 GPa) to the sp²-bonded graphite (E < 100 GPa). A high transition temperature accompanying with high hardness (H > E/10) and thermal stability can be achieved with deposition techniques of high plasma energy and low deposition rate, whereas techniques with higher deposition rate such as laser-arc may prompt one to accept a reduced transition temperature. It was shown for these films that the mechanical properties indicated by the Young’s modulus correlate with the fraction of sp³-bonds in the film which was proved by ellipsometry and electron energy loss spectroscopy [2].
Figure 2: Young’s modulus E depending on deposition temperature for diamond-like carbon films deposited with PLD (pulsed laser deposition), MSIB (mass-selected ion beam) and laser-arc.
[1] B . Schultrich, K . Kailer, P. Rödhammer, D. Schneider, H.J. Scheibe, Proceedings of the 14th International Plansee Seminar, Eds. G. Kneringer, R. Rödhammer and P. Wilhartitz, Plansee AG, Reutte (1997), Vol. 3, p. 210
[2] D. Schneider, C. F. Meyer, H. Mai, B. Schöneich, H. Ziegele, H. J. Scheibe, and Y. Lifshitz: Diamond and Related Materials 7(1998)973
[2] D. Schneider, C. F. Meyer, H. Mai, B. Schöneich, H. Ziegele, H. J. Scheibe, and Y. Lifshitz: Diamond and Related Materials 7(1998)973