THERMAL-STABILITY OF PULSED-LASER DEPOSITED DIAMOND-LIKE CARBON-FILMS

Pulsed laser deposited diamond-like cabron (PLD DLC) films were prepared with the visible 532 nm Nd:YAG pulsed laser beam of power density Phi from 2.7 x 10(9) to 2.0 x 10(10) W cm(-2), below the Nagel criterion (5 x 10(10) W cm(-2) for 1064 nm Nd:YAG laser). The temperature dependence of the electrical conductivity, sigma(T), the imaginary part of the refractive index, k, and the surface morphology of the films were studied as functions of Phi and post-annealing temperature T-a. Particulates appear on the surface of all samples, with their size increasing with increasing Phi. For Phi between 2.7 x 10(9) and 5.9 x 10(9) W cm(-2), the room temperature electrical conductivity sigma(R) and k decrease from 1.28 x 10(-4) to 3.37 x 10(-5) Omega(-1) cm(-1), and from 0.2 to 0.18, respectively. These results indicate that higher Phi increases the diamond-like content in the films. For Phi from 5.9 x 10(9) to 2.0 x 10(10) W cm(-2), sigma(R) and k increase to reach 3.69 x 10(-4) Omega(-1) cm(-1) and 0.22, respectively. In this power density range the surface graphitic particulates dominate the film properties. Higher Phi generates larger graphite particulates and degrades the film quality, thus leading to increases in sigma(R) and k. The as-deposited samples were annealed at temperatures T-a between 100 and 900 degrees C. In this temperature range, sigma(R) increases by a factor of 10(6), while k rises from about 0.2 to 0.5, indicating that a diamond-like-to-graphitic transition has occurred. The degradation process was observable at T-a as low as 100 degrees C, and became significant for higher T-a. Finally, the films reach a graphitic state when T-a greater than or equal to 750 degrees C. Since the surface density and size of the particulates are not influenced significantly by annealing, we suggest that the variation of the films properties arises from changes in the matrix in which the graphitic particulates are embedded.