Plasma fluorination of diamond-like carbon surfaces: mechanism and application to nanoimprint lithography

Abstract

Diamond-like carbon (DLC) films, used as molds for nanoimprint lithography, were treated with a fluorocarbon-based plasma in order to enhance their anti-adhesion properties. While elllipsometry and AFM measurements showed negligible changes in thickness and surface roughness after plasma processing, contact angle measurement found fluorine plasma-treated DLC surfaces to be highly hydrophobic, with surface energy values reduced from ~ 45 mJ/m 2 for untreated films to ~ 20-30 mJ/m2 after fluorination. XPS revealed a thin (from ~ 0.5 nm to ~ 3 nm) fluorocarbon layer on the DLC surface. Proposed mechanisms for the formation of this layer include two competing processes: etching of DLC and deposition of fluorocarbon material, with one or the other mechanism dominant depending on the plasma conditions. Fluorocarbon plasma-treated DLC molds for nanoimprint lithography were used to pattern sub-20 nm size features with a high degree of repeatability, demonstrating an extended lifetime of the anti-adhesion coating.

Cell adhesion and growth on surfaces modified by plasma and ion implantation

“…For the DLC-O, the contact angle obtained was (63 6 2) (SFE ¼ 39 6 1 mN/m) and, for the DLC-F, was (90 6 1) (SFE ¼ 27 6 2 mN/m), which is compatible with the literature results. [42][43][44] These results agree with those previously reported by Duailibi et al, 45 showing that hydrophilic surfaces benefit cell growth. Concerning to the DLC without plasma treatment, cell growth presented different behaviors for each of the three independent experiments.…”

Work function and electron affinity of the fluorine-terminated (100) diamond surface

“…The solid lines illustrate how the low-energy electron cut-off was determined from the intersection of the baseline with the leading edge of the low energy peak. The presence of adsorbed fluorocarbon has been reported for some F-terminated diamond samples, 19,20 but not for others, 1,10,11,14 and seems to be a peculiarity of the fluorination technique employed here. The deposition of fluorocarbon adlayers from fluorocarbon plasmas has also been described briefly by Schvartzman et al 20 For the case at hand, it is plausible that hydrocarbon molecules in the preparation vacuum chamber are fluorinated along with the sample and adsorb onto its surface as the sample cools.…”

“…The fluorocarbon adlayer has been suggested to act as a protective layer that prevents oxidation and reduction of the surface. 19,20 While the presence of an adsorbed fluorocarbon has only a small effect of the work function and electron affinity of the surface, as a hydrophobic layer it may play an important role in protecting the underlying fluorineterminated diamond surface, yet it can be removed by moderate annealing in-vacuo as we have demonstrated.…”

“…9 A variety of techniques have been reported for the preparation of F-terminated diamond surfaces with varying degrees of success. These have been based on the exposure of surfaces to fluorine-containing gases (atomic F, 10-12 F 2 , 2,13 HF, 13 and XeF 2 [14][15][16] ), molecules (fluorocarbons 17 and fluorofullerenes 18 ), and plasmas (CF, 6,19 CHF 3 ,5,20 and C 4 F 8 1,20 ). However, many of these techniques are known to damage or etch the surface and provide unsaturated disordered surfaces with an adsorbed fluorocarbon layer.…”

Single-crystal diamond nanomechanical resonators with quality factors exceeding one million

“…The air annealing step has the added benefit of removing organic and graphitic contamination from the surface leading to a general improvement of surface quality. Fluorine termination was achieved using exposure to a CF 4 plasma 37 . Polycrystalline diamond cantilevers: polycrystalline diamond reference cantilevers were produced from ultrananocrystalline (3-5 nm grain size) material, available as a DOI wafer from Advanced Diamond Technology, using applicable steps from our DOI method.…”