Plasma Diagnostics During Pulsed Laser Deposition of Diamond-Like Carbon Using Single Crystal Graphite and Amorphous Car
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JAPAN ** NSF Center for Advanced Materials and Smart Structures, Dept. of Materials Science and
Engineering, North Carolina State University, Raleigh, NC 27695-7916 *** Dept. of Nuclear Engineering, North Carolina State University, Raleigh, NC 27695-7909 Abstract Optical emission study of ablation plasma plumes from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been investigated. The C I emission intensity increases with laser energy density (EL) increase, while the C 2 emission changes drastically with EL for both ablated plasma plumes. The C 2/C emission intensity ratio for the a-C plume decreases with EL increase, while the CJC ratio for the SCG plume decreases with EL increase up to 3.0 J/cm2, then increases slightly with further El. increase- Nanohardness of the DLC films decreases with the C 2/C ratio increase. It is suggested that the C 2 molecule in the plasma plume does not play an important role in producing high quality DLC films, and that the C 2/C ratio is a good parameter to monitor the PLD process. I. Introduction Pulsed laser deposition (PLD) has attracted much attention for the synthesis of thin films of carbon-related materials, such as diamond-like carbon (DLC) 1-9, high fullerene carbon molecules of C60, C70 and C8 4, carbon nanotubes, and carbon nitride. In order to prepare these films by PLD, amorphous carbon (a-C) target is widely used. Single crystal graphite (SCG) has strong in-plane bonds and very weak bonds between planes. If the fraction of a graphite sheet is ejected from the target, the carbon fullerenes and nanotubes may be formed to minimize energy. It is speculated that SCG has a high potential to produce carbon enriched with fullerenes and nanotubes using PLD To our knowledge, however, there is no investigation to synthesize these carbon-related materials by PLD using SCG target. The dynamic behavior of species in the laser plasma plume affects the film characteristics. Although several investigations, such as optical emission spectroscopy (OES) 1-3, electrostatic probe method 46, mass spectroscopy, and laser-induced fluorescence spectroscopy have been employed to understand the process, the mechanism of the PLD process has not yet been understood in detail, even in the DLC deposition. Therefore, the comparative study of the PLD using the SCG and the a-C targets should be important from the point of view of the characteristics of deposited films, the dynamics of the laser ablated plume, and the correlation between film properties and plasma characteristics. We have systematically investigated the DLC films preparation using KrF excimer PLD using the SCG and the a-C targets. The properties of laser-ablated plasma plume have been diagnosed
255 Mat. Res. Soc. Symp. Proc. Vol. 593 © 2000 Materials Research Society
using OES I 2 and electrostatic probe measurement 4, 5. The deposited DLC films have been characterized using Raman spectroscopy and nanohardness
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