Fundamental Criteria for the Propagation of Telephone Cord Buckles Beneath DLC Films on Glass Substrates
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Fundamental Criteria for the Propagation of Telephone Cord Buckles beneath DLC Films on Glass Substrates
Myoung-Woon Moon1 , Kyang-Ryel Lee2, Jin-Won Chung2, And Kyu Hwan Oh1 1 Material Science and Engineering, Seoul National University, Seoul 151-742, KOREA. 2 Korea Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul 130-650, KOREA.
ABSTRACT The topology of telephone cord buckles that form beneath compressed diamond-like carbon films (DLC) on glass substrates has been characterized with Atomic Force Microscopy (AFM) and with the Focused Ion Beam (FIB). Using AFM with 2nm resolution, the wavelength and amplitude of the buckles and their profiles have been measured. It has been found that, within each wavelength, the profile has symmetric and asymmetric segments. These changes have been related to differences in local mode mixity around the periphery of each repeat unit along the buckle, resulting in a fundamental rationale for the factors governing the wavelength. Sections made through various segments of the buckle by using the FIB imaging system result in local changes in the shape and size of the buckles that provide further insight into the buckle propagation criterion.
INTRODUCTION Residually compressed thin films on thick substrates may buckle. The buckles propagate beneath the film if the induced energy release rate exceeds the interface fracture toughness. The associated mechanics has been documented [1-8]. The buckles exhibit several configurations: ranging from circular, to linear to telephone cord. Straight buckles propagate with curved front. The conditions at the stationary side and the circular front have been modeled and rationalized in terms of mode mixity and energy release rate [5, 6]. The corresponding mechanics for telephone cord buckles (figure 1a) are less well developed. The purpose of this study is to provide some insight into the buckle propagation criterion by performing experimental measurements on thin films of diamond-like carbon (DLC) deposited onto nominally flat slide glass substrates. The profiles of telephone cord buckles are characterized along different chords, by using the atomic force microscope L2.4.1
(AFM). To make a direct comparison between telephone cord and straight-sided buckles, the focused ion beam (FIB) imaging system has been used to create two parallel (damage free) cuts, converting a section of the telephone cord buckle into the straight-sided buckle. Changes in the profile before and after cutting can be used to correlate the two configurations, with all other variables fixed.
EXPERIMENTS Diamond-like carbon films were deposited on glass microscope slides by using a capacitively-coupled glow discharge of CH 4 and C6 H 6 plus N2, at a deposition pressure of 1.33Pa, with negative self bias voltage controlled in the range from -100 to -700V by adjusting the r. f. power [9]. For these conditions, the film thickness is in the range, 0.13 to 0.46 ยต m, and the residual compression between 1 and 3GPa, resulting in telephone cord buckles. Images of re
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