Deposition mechanism of nanostructured thin films from tetrafluoroethylene glow discharges

Abstract

Nanostructured polytetrafluoroethylene (PTFE)-like thin films can be deposited, in certain experimental conditions, by modulated discharges fed with tetrafluoroethylene (TFE). These coatings are characterized by a unique morphology consisting of highly twisted micron-long ribbons, which leads to an extremely high water repellency of the surface. In the present work, the diagnostics of the plasma phase is presented, coupled with that of the coating, in order to understand the film growth mechanism in different discharge regimes. When the duty cycle (DC) is increased in modulated C2F4 plasmas, the monomer depletion increases, too, and many recombination reactions take place at progressively higher rates, resulting in the formation of CF4, C2F6, C3F6, C3F8, and C4F10; the formation of powders in the homogeneous phase, however, was never evidenced. The modulation of C2F4 plasmas strongly affects the morphology of the resulting coating, as revealed by atomic force microscopy (AFM), ranging from bumpy to ribbon-like structures. The latter, moreover, are found to be more PTFE-like with respect to the remaining part of the film. In the last part of the paper, a deposition mechanism is proposed, where low radical densities in the plasma and surface migration of the precursors are the keys for the growth of ribbon-like structures

Hierarchical micro and nano structured, hydrophilic, superhydrophobic and superoleophobic surfaces incorporated in microfluidics, microarrays and lab on chip microsystems

“…3(i) and (ii)). In addition to the early works mentioned above, we note also the work of Favia [54], and Milella for modulated plasmas exploring the mechanisms to deposit ribbon-like or bumpy fluorocarbon layers [55], as reviewed also by the same author later on [56]. Vacuum deposition of superhydrophobic coatings was also reviewed by Cigala et al [57], and Kylian et al [18].…”

“…3(ii)); however a long deposition time was necessary (over 1 h) [60]. Mechanisms of plasma deposited nanotexture formation and transition from bump to ribbon structures were discussed by Milella [55].…”

Methods to Investigate the Adhesion of Soft Nano‐Coatings on Metal Substrates – Application to Polymer‐Coated Stents

“…These ribbon-like structures are formed during the plasma polymerization and are also visible on non-deformed samples. [26,[72][73][74][75][76] The topographical changes at the metal surface, which increased the roughness, proved to influence the adhesion properties and the coating integrity, leading to coating failures. As observed in Figure 3f, a crack aligned with the slip band was observed in the 15 min coated sample, indicating a lack of cohesion.…”

Nanostructured plasma polymers

“…The deposition parameters (pressure and flow (Figure 4) [24][25][26][27]. It was suggested that under the above conditions low ion bombardment, and a low concentration of CF 2 radicals incident at the surface triggered diffusion-mediated film growth.…”