Abstract
We have carried out investigations aimed at understanding the mechanism responsible for a water contact angle increase of up to ten degrees and a decrease in dielectric constant in silicon modified hydrogenated amorphous carbon films compared to unmodified hydrogenated amorphous carbon films. Our investigations based on surface chemical constituent analysis using Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), SIMS, FTIR, contact angle / surface energy measurements and spectroscopic ellipsometry suggests the presence of hydrophobic chemical entities on the surface of the films. This observation is consistent with earlier theoretical plasma chemistry predictions and observed Raman peak shifts in the films. These surface hydrophobic entities also have a lower polarizability than the bonds in the un-modified films thereby reducing the dielectric constant of the silicon modified films measured by spectroscopic ellipsometry. Ellipsometric dielectric constant measurement is directly related to the surface energy through Hamaker's constant. Our current finding is expected to be of benefit to understanding stiction, friction and lubrication in areas that range from nano-tribology to microfluidics.
Highlights
Diamond-like carbon films (a-C:H or DLC) have been reported to be very promising starting materials for fabricating micro-electromechanical (MEMS) devices.[1,2] They generally exhibit high hardness, wear-resistance, chemical inertness and low residual stresses
Our Raman spectroscopy investigation on the deposited Si-DLC films confirmed the theoretical argument of Friedel,[16] who used the method of moments to estimate changes in the density of states in a carbon-silicon system and deduced that the amount of sp[3] bonding should increase in a silicon-carbon network
Based on an earlier model that suggested that a-C:H films consist mainly of sp[2] bonded planar clusters, which connect to each other by sp[2] and sp[3] bonds,[17] the present authors proposed based on Raman spectroscopy investigation that the modification of the a-C:H structure by silicon leads to two interpenetrating network based on silicon and carbon.[17]
Summary
Diamond-like carbon films (a-C:H or DLC) have been reported to be very promising starting materials for fabricating micro-electromechanical (MEMS) devices.[1,2] They generally exhibit high hardness, wear-resistance, chemical inertness and low residual stresses. A high wear and impact resistance, is a desirable property for MEMS devices. Many MEMS applications will involve repetitive contact, encountered by nano-devices like nano-gears or micro-channels conveying fluids. The ease of patterning and etching of DLC films reported by Mousinho et al.,[2] combined with the above identified properties, make DLC films a promising starting material for the fabrication of MEMS devices. Micro-gears and micro-channels have already been fabricated from DLC films by lithography and plasma-etching.[2] It has been reported that stiction, friction and wear are the major sources of failure of MEMS devices. According to the meniscus theory of stiction, high stiction at aCorresponding author. 2158-3226/2012/2(3)/032128/8
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