Danka Slavínská

Plasma polymer films and their future prospects

Abstract Plasma polymerization processes began their fast development in the 1950s. They have been widely recognized during the last 20 years and several successful applications have emerged. Two special groups of plasma polymers that have received increased attention in recent years are treated in detail here. First, the deposition process and basic properties such as the structure, morphology, electrical and optical properties, and ageing of metal (Ag, Ni, Mo) and semiconductor (Ge)/hard plasma polymer (C:H) composites are described consisely. The deposition process is based on unbalanced magnetron sputtering with the target operated in an argon/n-hexane working gas mixture. Second, the preparation of plasma polymer films by radio-frequency sputtering from polymeric targets is introduced and their basic properties, especially structure and morphology, are revealed. Most attention is paid to fluorocarbon plasma polymer films sputtered from polytetrafluoroethylene (PTFE). For both groups of plasma polymers, application possibilities are discussed. The whole range of plasma polymers and their future prospects are summarized, starting from those resembling conventional polymers that are prepared at low power, and ending with the new materials prepared at high power.

The influence of pulse parameters on film composition during pulsed plasma polymerization of diaminocyclohexane

Abstract Plasma polymerization of diaminocyclohexane was investigated in order to deposit the amine groups rich plasma polymer films for biomedical applications. The obtained films were characterized by FTIR and XPS in dependence on duty cycle ranging from continuous wave mode (CW) to 0.1 and ton varied from 0.02 to 10 ms. The concentration of primary and secondary amine groups was determined by the derivatization technique using trifluoromethyl benzaldehyde (TFBA) and trifluoroacetic anhydride (TFAA). It has been shown that the concentration of both follows the same curve with the minimum at ton=0.5 ms (duty cycle 0.1). The plasma polymerization process likely differs here from the processes for higher and lower ton. The highest primary amine concentration reached is 8%. The films prepared at ton=0.5 ms are shown to be less stable due to aging by oxidation as shown by XPS on films kept in open air. The FTIR analysis confirms the same dependence of amine groups’ concentration as above. As the deposition rate increases for decreased ton it will be advantageous to prepare the plasma polymer films with the higher amine group concentrations at decreased ton below 0.5 ms.

Rf magnetron sputtering of polytetrafluoroethylene under various conditions

Abstract Deposition of fluorocarbon plasma polymer films by means of rf sputtering of polytetrafluoroethylene (PTFE) has been performed in argon, nitrogen and in a self-sputtering mode. The average temperature of the target was found to be below the melting point of PTFE. Energy resolved mass spectrometry revealed the differences between the cases of argon and nitrogen working gases. The CFN compound and increased concentration of CFx fragments were observed in the plasma using N2. High resolution XPS analysis revealed CN in these films and enhanced amount of CF2 groups. Wettability by means of contact angle of water droplet was assessed. Static contact angles approaching 105° and 100° were measured for fluorocarbon plasma polymer films sputtered in argon and nitrogen, respectively.

Plasma deposition and properties of composite metal/polymer and metal/hard carbon films

- The growing interest in novel materials has promoted the investigation of two-component composite materials formed by small metal inclusions incorporated in an organic insulating medium. In this paper the recent knowledge of composite thin films composed of metal grains dispersed in the matrix of a plasma deposited polymer or a hard carbon is reviewed. The most important deposition techniques are presented and the relation between the deposition processes, the film microstructure and resulting film properties (especially optical and electrical) are discussed. The film characteristics are illustrated by the latest results from our laboratory.

Vacuum Thermal Degradation of Poly(ethylene oxide)

Thermal degradation of poly(ethylene oxide) (PEO) was studied under vacuum conditions. PEO macromolecules degrade predominantly by random chain scission of a backbone with elimination of oligomer fragments. The reactions include the mechanism of radical termination by disproportionation. The eliminated fragments form thin film deposits which have chemical composition close to the original PEO. Activation of the evaporated flux with a glow discharge leads to further fragmentation and recombination of the released species and can be used to tune the properties of the resulting thin films.

RF sputtering of hydrocarbon polymers and their derivatives

RF sputtering of polymeric targets was discussed from the point of view of history and present status of the field. RF sputtering of polytetrafluorethylene (PTFE) was mentioned in self-sputtering mode, argon, nitrogen and other gases. The emission of fragments from the target observed by means of quadrupole mass spectroscopy and target surface as observed by SEM were described. Columnar morphology of the sputtered films at substrate temperatures below room temperature was mentioned. Deposition rate of sputtered PTFE films was found up to one order of magnitude higher than polyimide (PI) sputtered films. Results of PI sputtering process and films characterization in terms of tribological coatings were reviewed. Polyethylene (PE) and polypropylene (PP) sputtering was found below 100 W power more than three times slower than PTFE sputtering. The films are hydrocarbon plasma polymers containing a lot of oxygen and OH groups. Above 100 W the co-evaporation from the erosion zone of the target took place and deposited films resemble much more the parent target as observed by FTIR. Finally, co-sputtering of metal and polymer that results in nanocomposite metal/plasma polymer films and sputtering of SiO2/PTFE composite target is shortly discussed.

Plasma polymers prepared by RF sputtering of polyethylene

Hydrocarbon plasma polymer thin films were deposited by means of magnetron sputtering of polyethylene (PE) using Ar as the working gas. AFM, ESCA, FTIR techniques were applied to investigate the films properties and composition. The films sputtered at Radio frequency (RF) power up to 100 W have a plasma polymer structure whereas further increase of RF power results in hydrocarbon plasma polymers more resembling conventional PE.

Rf sputtering of composite SiOx/plasma polymer films and their basic properties

Abstract Composite SiOx/PTFE films were deposited by rf sputtering in argon using balanced magnetron equipped with a PTFE/SiO2 target. The composition of deposited films, found by XPS and FTIR, ranged from fluorocarbon plasma polymers with very small SiOx content up to coatings with a greater incorporation of SiOx. The hardness of fluorocarbon polymer films with increased concentration of SiOx was 2400 N/mm2. This is between two to three times higher than in the case of fluorocarbon plasma polymers with very low SiOx content. The static contact angle of water ranges from 112 to 95° and the refractive index from 1.49 to 1.43, when incorporation of SiOx into fluorocarbon plasma polymer matrix decreases.

RF magnetron sputtering of polymers

Abstract RF sputtering of polymeric materials such as polytetrafluoroethylene (PTFE) and polyethylene (PE) has been studied. Threshold powers of 220 and 80 W for the self-sputtering glow discharge mode were found for PTFE and PE, respectively. FTIR absorption data using polarized light disclosed a structural anisotropy of the sputtered PTFE films. A simple structural model is proposed. The first results obtained by FTIR spectroscopy of sputtered PE films are presented.

Composite Ag/C:H films prepared by DC planar magnetron deposition

Abstract Composite Ag/C:H films were deposited by means of an unbalanced magnetron operated in a gas mixture of argon and n -hexane. We used a gradual coating (‘poisoning’) of the target by a carbonaceous layer to deposit films with decreasing rate of silver sputtering. Rate of deposition of the films decreases with the covering of the magnetron target. XPS measurements were performed with the aim to study the composition of the films. The surface energy of the films was estimated from static water and formamide contact angles, which were measured using the droplet method. Values of the water contact angle were found to be in the range from 88° to 66°. Absorption spectra in the visible, near UV and IR region were studied as a function of silver concentration. FTIR spectroscopy was employed to investigate the composite films and monitor their aging. CH 2 /CH 3 stretching and deformation bands are present in all infrared spectra of the films. Evolution of the FTIR spectra with aging shows a high influence of concentration and size of the metallic inclusions on the absorption bands of the carboxyl and carbonyl groups.