Plasma, photon, and beam synthesis of diamond films and multilayered structures. Final report for the period July 1996 - December 1998

The DOE has been supporting Professor Chang and his students in the area of plasma and photon synthesis of diamond-like and ceramic films with varying complexity during the past three years. We have made substantial contribution to the field during this period of time. Some of the important questions have been addressed, and they include: a. How does the energy (wavelength) of the laser change the composition and energy distribution of the ablated species? b. How do surface mobility and the intensity of the plasma plume affect crystal nucleation and growth? c. How can one manipulate the system parameters during film growth to achieve special properties for unique applications? In the area of photon synthesis, we have shown that amorphous diamond films can have properties very similar to polycrystalline diamond films and yet they may have wider applications in such areas as coating and electronics. For example, we have shown that these films can be used to protect plastics such as polycarbonate surfaces. During the course of our amorphous diamond films research, we have also identified important parameters which alter the film properties. Higher photon energy and laser power density contribute to higher percentage of carbon ion density and energy in the plasma plume. This in turn proves films with higher percentage of diamond-like sp{sup 3} bonds and thus diamond-like properties of the films. Lower photon energies and collision of the plasma plume with background gas will produce films which are rich in graphitic properties. In the area of oxide film growth, we have found, in general, that better crystalline films can be grown by laser ablation at much lower substrate temperatures than by chemical vapor deposition process. This is due to the fact that in laser ablation the depositing species have more kinetic energies and the whole process involves rapid solidification. By using optical emission spectroscopy, we have learned how to adjust the deposition parameters to control film properties such as grain size and crystal orientations. These control capabilities have allowed us to grow oxide films with unique properties, such as high optical nonlinearity. In addition, we have been able to grow films with special crystalline orientations to serve as templates for chemical vapor deposition processes