Surface Structure of Tetrahedral-Coordinated Amorphous Diamond-Like Carbon Films Grown by Pulsed Laser Deposition
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T. W. MERCER*, N. J. DiNARDO*,**, L. J. MARTINEZ-MIRANDA***, F. FANG****, T. A. FRIEDMANN ..... , J. P. SULLIVAN ..... , AND M. P. SIEGAL*""' * Drexel University, Department of Physics and Atmospheric Science, **
Philadelphia, PA 19104 University of Pennsylvania, Department of Materials Science and Engineering, Philadelphia, PA 19104 Kent State University, Department of Physics, Kent, OH 44242 and University of Maryland, Department of Materials and Nuclear Engineering, College Park, MD 20742 University of Pennsylvania, Department of Electrical Engineering, Philadelphia, PA 19104 Sandia National Laboratories, Albuquerque, NM 87185-0345
ABSTRACT The structure and composition of tetrahedral-coordinated amorphous diamondlike carbon films (a-tC) grown by pulsed laser deposition (PLD) of graphite has been studied with atomic force microscopy (AFM). The nanometer-scale surface structure has been studied as a function of growth parameters (e.g., laser energy density and film thickness) using contact-mode and tapping-mode AFM. Although the surfaces were found to be generally smooth, they exhibited reproducible structural features on several size scales which correlate with the variation of laser energy and the effects of excited ion etching. Introduction Due to significant developments in the area of high powered ultra-violet (UV) excimer lasers, the technique of pulsed laser deposition (PLD) has become a very effective means for depositing high-quality hydrogen-free tetrahedral-coordinated amorphous diamond-like carbon (a-tC) films. A critical factor for deposition is the creation of a high flux beam of energetic carbon ions in the fractional keV range. In this study, we have examined the surfaces of several films grown by PLD at a variety of laser energy densities. These films are grown by ablation of a graphite target with a KrF (248 nm) pulsed excimer laser. Films approximately 1400 A thick were grown on commercial grade Si(100) wafers at three different laser energy densities of 46 J/cm 2, 2 2 27J/cm and 11 J/cm
Experiment The PLD process is described elsewhere.1 After a-tC deposition, the samples were oxygen plasma etched for a period of 360 seconds in order to remove graphitic carbon. 2 This procedure was performed in a Denton Model PE-120 plasma chamber 863 Mat. Res. Soc. Symp. Proc. Vol. 358 ©1995 Materials Research Society
with an oxygen pressure of 400 ± 20 mTorr and an RF power of 50 W. The set of samples under study were etched simultaneously to assure identical etching conditions. After etching, the samples were imaged with a Digital Instruments Nanoscope III atomic force microscope (AFM). When the AFM was operated in the contact mode, it was found that the SiN 3 tips were susceptible to a significant amount of damage inhibiting the ability to obtain images with acceptable spatial resolution. This occurs because of rapid tip wear due to the extreme hardness of these surfaces. In order to avoid this problem, tapping mode (intermittent-contact imaging) was utilized to improve image quality. Before etching,
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