Hard Amorphous Carbon Films Deposited by ArF Pulse Laser Ablation of Graphite at Room Temperature
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HARD AMORPHOUS CARBON FILMS DEPOSITED BY ArF PULSE LASER ABLATION OF GRAPHITE AT ROOM TEMPERATURE Fulin Xiong and R. P. H. Chang Department of Materials Science and Engineering, and Materials Research Center Northwestern University, 2145 Sheridan Road, Evanston, IL 60208
ABSTRACT Hard amorphous carbon films have been deposited by ArF pulsed laser ablation of graphite at room temperature, with the laser power density of 5x108 W/cm 2. The films prepared in the high vacuum environment possess remarkable diamond-like properties with a hardness up to 38 GPa and an optical energy band gap of 2.4 eV. The properties of the films doped with nitrogen vary with the nitrogen content, but improve interface adhesion, resulting in the extension of the film thickness limit to a greater range. The results suggest that the properties of the laser ablation deposited diamond-like carbon films depend not only on the laser power density, but also strongly on the laser wavelength or photon energy. INTRODUCTION While a great effort has been made to grow diamond through the metastable synthesis process at low temperatures and low pressures, deposition of amorphous diamond-like carbon (a-DLC) films has also 1 been attracting a great attention. DLC films encompass a wide variety of forms including amorphous carbon (a-C), amorphous hydrocarbon (a-C:H) and ion beam carbon (i-C). They have many remarkable properties close or similar to those of diamond and give these films high potential in many important practical t2 applications, ranging from tribological coating, optical IR coating, to microelectronics ' . In particular, the smooth surface morphology and homogeneity of DLC films make them more useful than polycrystalline diamond films prepared by chemical vapor deposition. For many applications where crystalline diamond is not essential, DLC films will suffice. With improved properties and better controlled deposition processes, the expanded use of these films can certainly be anticipated. Among the various methods for preparing DLC films, such as ion beam deposition, plasma deposition, sputtering, and chemical vapor deposition, pulsed laser 10 ablation (PLA) has been shown to be one of most attractive techniques.3" This technique has several merits, including the simplicity of implementation and operation, high energetic power for deposition of materials with a high melting point, ready incorporation to ultrahigh vacuum systems and low temperature processes, and easy control of film microstructures. In general, the properties of a-C films prepared by PLA range from soft and graphitic to hard and diamond-like, depending on the deposition parameters, such as the laser power density and wavelength, as well as background gas conditions. Several types of lasers have been used in the deposition of DLC films, 79 including KrF (248 nm) and XeCI (308 nm) excimer lasers,36 Nd:YAG (1064 and 532 nm) lasers, " CO 2 CW 1 2 2 10 laser, and pulsed ruby laser (683 nm).1 The power density ranges from 108 W/cm to 1011 W/cm . In this paper, we report the resu
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