F. Palumbo

Deposition of super-hydrophobic fluorocarbon coatings in modulated RF glow discharges

Superhydrophobic coatings were deposited in modulated RF glow discharges fed with tetrafluorothylene. Such coatings are characterized by a high fluorination degree, ribbon-like randomly distributed surface microstructures, and a certain crystallinity. Combined high fluorination degree and surface texture/roughness leads to the super hydrophobic behaviour, as attested by water contact angle values of 150° and more. The coatings were characterized by means of XPS, FT-IR and X-ray diffraction, while time resolved optical emission spectroscopy was utilized to investigate the plasma phase.

Morphological and structural study of plasma deposited fluorocarbon films at different thicknesses

The growth of fluorocarbon thin films has been obtained by continuous and modulated r.f. plasmas fed with C2F4. The kinetics surface morphology of the coatings has been investigated and analyzed on films of various thicknesses. Such a study has allowed the evolution of structures in size and shape to be followed. Specifically, it has been observed that modulated plasmas with the proper duty cycles (⩽7%) lead to the formation of micrometer-long ribbon-shaped nanostructures. The precursors of the ribbons are nuclei that align into a spiral-mimic. Highly nanostructured films with an optimal thickness and ribbon density exhibit a super-water repellent surface with contact angles up to 170°. The surface roughness and smoothing of fluorocarbon films are strongly affected by the modulated and continuous plasmas, respectively.

Deposition of SiOx : films from hexamehtyldisiloxane/oxygen radiofrequency glow discharges: process optimization by plasma diagnostics

Optical emission and Fourier transform infrared absorption diagnostics have been carried out in hexamethyldisiloxane/oxygen RF discharges for studying the effects of the feed composition and the power on the deposition of SiO2—like thin films. Ex situ FTIR absorption has been utilized to monitor organic moieties and silanol groups in the film. It is shown that carbon-free films can be obtained by highly diluting the monomer in oxygen, while medium-to-high power is necessary to abate silanol groups. These two conditions represent the optimization criterion to obtain excellent barrier films for food packaging applications.

Process control for plasma processing of polymers

Abstract PE-CVD processes of a variety of coatings — fluoropolymers, SiO x , PEO- and Ag-PEO-like, COOH functional layers — are described, as well as plasma treatments aimed to selectively graft NH 2 groups on polymers, with the use of spectroscopic plasma- and surface-diagnostics parameters of potential use for process transfer and control in industrial applications.

Deposition mechanism of nanostructured thin films from tetrafluoroethylene glow discharges

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.

Immobilization of Heparin and Highly-Sulphated Hyaluronic Acid onto Plasma-Treated Polyethylene

Heparin and highly-sulphated hyaluronic acid have been successfully immobilized onto plasma-processed polyethylene via a diamine polyethyleneglycol (PEG) spacer molecule. Two different plasma-processes have been utilized, i.e. a treatment and a deposition process, for providing polyethylene surface with the COOH groups necessary for the immobilization reactions. XPS integrated with derivatization procedures, ATR-FTIR and Water Contact Angle measurements have been carried out for characterizing each modification step: 1) the plasma-process, 2) the immobilization of the spacer molecule and 3) the immobilization of the biomolecules. The thrombin time of the modified surfaces has been measured, and their platelet activation characteristics evaluated. The results indicate a certain nonthrombogenic character of the biomolecule-immobilized polyethylene samples.

Diagnostics and insights on PECVD for gas-barrier coatings

In this work, we report on our last results concerning the polyethyleneterephtalate barrier performance optimization as a function of the chemistry of the SiOx coating, deposited by means of hexamethyldisiloxane/oxygen-fed plasmas ignited in an RF capacitively coupled parallel plates reactor. The influence of the gas feed composition and power on the plasma phase/coating chemistry and on the O2 gas transmission rate has been investigated. The plasma phase has been studied by means of Fourier transform infrared absorption (FT-IR) and optical emission spectroscopies (OES), and the results have been coupled to the film chemistry investigated by means of FT-IR spectroscopy. These techniques show excellent potentialities in the correlation of the plasma phase and film chemistries with the barrier properties of the SiOx-coated polymer, especially when a very good barrier level is required.

GC-MS Investigation of Hexamethyldisiloxane-Oxygen Fed Plasmas

This paper deals with the determination of by-products formed in plasmas fed with hexamethyldisiloxane (HMDSO), oxygen, and Ar. The gas effluent has been sampled by means of a cold trap and analyzed using gas chromatography-mass spectrometry. The results indicate that under the experimental conditions utilized, HMDSO is not activated by reactions with oxygen but mainly by electron collisions. Oxygen controls the overall chemistry of the plasma since it influences the quali-quantitative distribution of by-products. Many linear and cyclic oligomers have been observed and most of them contained one or more―Me2SiO― groups. The concentration of detected by-products, except trimethylsilylformate, decreases with O2 addition.

Deposition of gold-containing siloxane thin films

Abstract Thin films containing gold clusters dispersed in a SiO x matrix have been deposited by simultaneous plasma-enhanced chemical vapour deposition of hexamethyldisiloxane-O 2 -Ar mixtures and r.f. sputtering of a gold target. The effect of deposition conditions on film composition and on some physical properties have been investigated. The results show that the films are mainly composed of an inorganic SiO x matrix which contains gold clusters, carbon and hydrogen atoms. By changing the gold content of the film the d.c. electrical conductivity follows the trend reported in the literature for other metal-containing plasma polymers, while the optical absorption in the UV-Vis region shows some differences from published data.

Plasma-assisted deposition of tungsten-containing siloxane thin films

Abstract Composite films containing tungsten clusters dispersed in an organosilicon matrix have been deposited by simultaneous plasma-enhanced chemical vapour deposition of hexamethyldisiloxane-O2-Ar mixtures and r.f. sputtering of a tungsten target. The effect of plasma conditions on the deposition process and film composition has been investigated. It is shown that actinometry can conveniently be utilized as an in-situ process parameter.