Characteristics of Laser-Ablated Plasma and Properties Of Diamond-Like Carbon Film In Pulsed Laser Deposition
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CHARACTERISTICS OF LASER-ABLATED PLASMA AND PROPERTIES OF DIAMOND-LIKE CARBON FILM IN PULSED LASER DEPOSITION Yukihiko Yamagata, Tamiko Ohshima, Tomoaki Ikegami, Raj K. Thareja, Kenji Ebihara Ajay Sharma1, Robert M. Mayo2 and Jagdish Narayan1 Department of Electrical and Computer Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, JAPAN 1 NSF Center of Advanced Materials and Smart Structures, North Carolina State University, Raleigh, NC 27695-7916, U.S.A. 2 Department of Nuclear Engineering, North Carolina State University, Raleigh, NC 27695-7909, U.S.A. ABSTRACT Characteristics of laser-ablated carbon plasma and properties of diamond-like carbon film in KrF pulsed laser deposition were investigated using laser-induced fluorescence (LIF) and optical emission spectroscopy. Two-dimensional LIF images of C2 (Swan band, d 3Πg – a 3Πu) and C3 (Comet Head System, A 1Πu – X 1Σg+) molecules were detected as a function of laser energy density by narrow band pass filters and an intensified CCD camera. C2 LIF intensity is found to be weaker in the central part of the plume than that at the periphery at incident energy greater than 6 J/cm2. It is conjectured that C2 molecules are dissociated by collision with energetic species in the central part of the ablation plume, and degrade the diamond-like property of deposited films. INTRODUCTION Hydrogen-free diamond-like carbon (DLC) films with attractive properties, such as extreme hardness, very low electrical conductivity, chemical inertness, optical transparency, and low electron affinity, have great potential for applications in mechanical and optical coatings, electronic devices, and field emitters. Pulsed laser deposition (PLD) has many advantages, such as low temperature processing, low levels of contamination, stoichiometry preservation, and reproducibility of film characteristics compared with the other deposition methods. Since the average energy of laser-ablated species is much higher than kT and a certain fraction of these species is ionized, it is possible to form metastable phases such as DLC [1-10]. Consequently, PLD has been regarded as one of the most successful techniques to synthesize novel and metastable materials and structures. Because the dynamics of laser-ablated plasma plume affect the properties of deposited thin films, there are many investigations aiming to understand the PLD process and to correlate the characteristics of laser-ablated plasma and the properties of deposited films. The mechanism of the PLD process, however, has not yet been understood in detail, especially in the case of DLC deposition. In order to prepare high-quality thin films and to improve the potential of PLD, it is desirable to diagnose and establish a correlation between plasma composition and properties of deposited film. We have systematically investigated the characteristics of laser-ablated carbon plasma and the properties of hydrogen-free DLC film prepared by KrF-PLD [1-4]. Characteristics of laserablated carbon plasma have been diagnosed using laser-induced
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