Pulsed laser deposition of amorphous diamond-like carbon films with ArF (193 nm) excimer laser
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We have deposited hydrogen-free diamond-like amorphous carbon films by ArF (193 nm) pulsed laser ablation of graphite. The deposition process is performed with a laser power density of only 5 X 108 W/cm 2 at room temperature without any auxiliary energy source incorporation. The resulting films possess remarkable physical, optical, and mechanical properties that are close to those of diamond and distinct from the graphite target used. The films have a mechanical hardness up to 38 GPa, an optical energy band gap of 2.6 eV, and excellent thermal stability. Analysis of electron energy loss spectroscopy reveals the domination of diamond-type tetrahedral bonding structure in the films with the sp3 bond fraction over 95%. Compared with other reported results of pulsed-laser-deposited diamond-like carbon films, our experimental results confirm that the laser wavelength or photon energy plays a crucial role in controlling the properties of the pulsed-laser-deposited diamond-like carbon films.
I. INTRODUCTION While much effort has been spent on growing diamond through the metastable synthesis processes at low temperatures and low pressures, deposition of amorphous diamond-like carbon (DLC) films has also been attracting a great deal of attention.1"3 Even though the terminology of DLC is rather imprecise, DLC films may include many amorphous forms of carbon with or without hydrogen. They have many properties close or similar to those of diamond and are distinct from those of graphite. In particular, the smooth surface morphology and homogeneity of DLC films make them more useful than polycrystalline diamond films in many applications.2'3 Among the various methods for preparing DLC films, such as ion beam deposition, sputtering, plasma-assisted chemical vapor deposition, and cathodic arc, pulsed laser deposition has been shown to be one of the most attractive techniques.3"10 It can produce films without hydrogen and with a high degree of diamond-like properties. These films are composed of noncrystalline tetrahedral carbon networks. Hence, films of this kind have been referred to amorphous (or amorphic) diamond in many reported works.4'10 Several types of laser have been used for the deposition of DLC films, including KrF (248 nm) and XeCl (308 nm) pulsed excimer lasers,4"7 Nd: YAG (1064 and 532 nm) lasers,8"10 and pulsed ruby laser (683 nm) laser11 as well as CO 2 CW laser.12 The wavelength ranges from the ultraviolet to the infrared, and the power density from 108 W/cm 2 to 1011 W/cm 2 . In general, the degree of diamond-like character (mainly the fraction J. Mater. Res., Vol. 8, No. 9, Sep 1993
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of sp3 hybridized carbon bonding in a film) varies considerably with the deposition parameters. Commonly, it is believed that pulsed laser deposition is an energetic process.13 The laser power density plays a vital role in controlling the film properties. There is a threshold at 1011 W/cm 2 in order to grow high-quality DLC films.8"10 In this paper we report the results of pu
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