Compensation effect of boron and nitrogen codoping on the hardness and electrical resistivity of diamond-like carbon fil
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Jin-Nyoung Jang and MunPyo Hong Department of Display and Semiconductor Physics, Korea University, Sejong 339-700, Korea
Kwang-Ho Kwon Department of Control and Instrumentation Engineering, Korea University, Sejong 339-700, Korea (Received 10 June 2012; accepted 28 September 2012)
Nitrogen (N) and boron (B) codoped diamond-like carbon (DLC) films were prepared on silicon oxide substrates by RF magnetron sputtering to optimize the electrical conductivity and hardness of DLC film. The electrical conductivity and hardness of the N–B codoped DLC films were controlled simultaneously by varying N2 flow rate with fixed B target power and varying B target power with fixed N2 flow rate. The electrical resistivity of the B-doped DLC films showed a cup-shaped relationship with B target power and a U-shaped relationship with the N–B codoped DLC film. However, hardness of the B-doped DLC films showed a decreasing behavior but it was maintained almost constant for the N–B codoped DLC film. These particular electrical and hardness behaviors of the N–B codoped DLC films could be explained by a neutralization effect of N and B codoping.
I. INTRODUCTION
Diamond-like carbon (DLC) has a unique combination of properties including extreme hardness, optical transparency, high electrical resistivity, and chemical inertness, and it is therefore widely used for a variety of applications such as biomedical engineering, protective coating, microelectromechanical systems, cutting tool, antireflective coating, and as a field emission source for emitter.1–5 There are also several types of bonds in DLC that confer a wide range of properties. DLC is an amorphous carbon material with sp2- or sp3-bonded carbon and hydrogen. The chemical structure of DLC, which corresponds to a bond ratio of sp3:sp2, is important because it produces the unique properties of DLC.6 The strong directional sp3 bonding of diamond gives it many unique properties such as extreme hardness, optical transparency, high electrical resistivity, and chemical inertness. In contrast, the sp2 bonding of graphite produces weak interlayer bonding, making it useful as a lubricant.6 The properties of DLC have been reported to be significantly dependent on the deposition conditions because the energy of carbon species plays an important role in determining the sp3:sp2 ratio in DLC films.7,8 Also, incorporation of Si, B, N, and F into DLC films has been shown to change the sp3:sp2 ratio. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.348 J. Mater. Res., Vol. 27, No. 23, Dec 14, 2012
Addition of Si and F shows different behavior on the change in the ratio of sp3:sp2 DLC. For example, an addition of Si increases the sp3:sp2 ratio but an addition of F decreases the ratio.9,10 As the proportion of sp2 bonds increases, the electrical conductivity of the DLC film increases but the diamond-like properties decrease. If the diamond-like properties of the film could be maintained while enhancing the electrical conductivity, the DLC films could be used for chemical se
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