Hynek Biederman

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.

RF sputtering of polymers and its potential application

Abstract Plasma polymerization processes are commonly used for the deposition of thin films of plasma polymers that have been proposed for a variety of applications ranging from surface modifications for biomedical purposes to optical coatings and variable and protective films in electronics. RF sputtering of polymeric materials in an inert gas (Ar) or in its own fragmented polymer vapours can be applied in order to avoid the conventional supply of gaseous monomer. Volatile fragments of polymeric target serve as plasma polymerization precursors in the case of RF sputtering. RF sputtering of polytetrafluoroethylene (PTFE), polyimide (PI), etc. are rewieved. Recent results from our laboratory on balanced and unbalanced magnetron RF sputtering of polytetrafluoroethylene and polyethylene (PE) are presented. The dependence of structure and morphology of RF sputtered plasma polymers on plasma parameters and substrate temperature is discussed. In conclusion potential applications are summarized.

Sputter process diagnostics by negative ions

We measured the energy distributions of negative ions during reactive sputtering of silicon in oxygen. Various oxygen containing negative ions are formed in the cathode sheath or directly at the sputter target, respectively. These negative ions are accelerated away from the cathode by the electrical field, and can be detected using a mass spectrometer facing the sputter magnetron. The origin of each ion can be determined from peak structures in the energy distribution. Additionally the flux of different negative ions provides information on poisoning of the target by oxide films.

Substrate-Independent Approach for the Generation of Functional Protein Resistant Surfaces

A new route for coating various substrates with antifouling polymer layers was developed. It consisted in deposition of an amino-rich adhesion layer by means of RF magnetron sputtering of Nylon 6,6 followed by the well-controlled, surface-initiated atom transfer radical polymerization of antifouling polymer brushes initiated by bromoisobutyrate covalently attached to amino groups present in the adhesion layer. Polymer brushes of hydroxy- and methoxy-capped oligoethyleneglycol methacrylate and carboxybetaine acrylamide were grafted from bromoisobutyrate initiator attached to a 15 nm thick amino-rich adhesion layer deposited on gold, silicon, polypropylene, and titanium-aluminum-vanadium alloy surfaces. Well-controlled polymerization kinetics made it possible to control the thickness of the brushes at a nanometer scale. Zero fouling from single protein solutions and a reduction of more than 90% in the fouling from blood plasma observed on the uncoated surfaces was achieved. The feasibility of functionalization with bioactive compounds was tested by covalent attachment of streptavidin onto poly(oligoethylene glycol methacrylate) brush and subsequent immobilization of model antibodies and oligonucleotides. The procedure is nondestructive and does not require any chemical preactivation or the presence of reactive groups on the substrate surface. Contrary to current antifouling modifications, the developed coating can be built on various classes of substrates and preserves its antifouling properties even in undiluted blood plasma. The new technique might be used for fabrication of biotechnological and biomedical devices with tailor-made functions that will not be impaired by fouling from ambient biological media.

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.

Metal doped polymer films prepared by simultaneous plasma polymerization of tetrafluoromethane and evaporation of gold

Abstract The incorporation of gold from an evaporation source during plasma polymerization of tetrafluoromethane CF 4 in an rf (20 MHz) glow discharge excited by means of a planar magnetron has been investigated. Optical emission spectroscopy was used to monitor the deposition process in situ . The structure of the films was studied by transmission electron microscopy (TEM) observations. The sheet resistance and optical transmission measurements have been performed showing a dramatic influence of gold concentration on the film properties. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analysis were used for determining the concentration depth profiles through the films. It has been shown that the presence of gold in the layers substantially reduces the fluorine content. The effect of various gold incorporation methods on the film characteristics has been discussed.

The properties of films prepared by the rf sputtering of PTFE and plasma polymerization of some freons

Fluorocarbon films were prepared by rf sputtering of PTFE at 6.65 Pa in glow discharges operated in the target emission alone and with argon or nitrogen added. A 75 mm dia target and an rf supply of 20 MHz with different power inputs between 100 and 500 W were used. Blank and aluminium-covered glass substrates were rested on grounded or biased supports above the target. The refractive index (NaD) and absorption of each film in the near uv and uv regions of light were measured. Electrical properties like I–V characteristics, dielectric constant and dielectric strength in the sandwich configuration Al-film-Al were also studied. In the second set of experiments the same properties of films prepared by plasma polymerization of certain freons (CF3Cl, CF2Cl2) at a pressure of 15 Pa and higher were investigated at various flow rates and power inputs for comparison.

Polymer films prepared by plasma polymerization and their potential application

Abstract The basic features of plasma polymerization are described and the main theoretical models briefly discussed. Principal experimental arrangements are taken into account. Physical properties of organosilicon, halocarbon, hydrocarbon and composite (metal-doped) plasma polymer films are concisely reviewed. Proposed applications of these films in optics and electronics are presented.

Effect of different surface nanoroughness of titanium dioxide films on the growth of human osteoblast-like MG63 cells †‡

Cell behavior depends strongly on the physical and chemical properties of the material surface, for example, its chemistry and topography. The authors have therefore assessed the influence of materials of different chemical composition (i.e., glass substrates with and without TiO(2) films in anatase form) and different surface roughness (R(a) = 0, 40, 100, or 170 nm) on the adhesion, proliferation, and osteogenic differentiation of human osteoblast-like MG63 cells. On day 1 after seeding, the largest cell spreading area was found on flat TiO(2) films (R(a) = 0 nm). On TiO(2) films with R(a) = 170 nm, the cell spreading area was larger and the number of initially adhering cells was higher than the values on the corresponding uncoated glass. On day 3 after seeding, the cell number was higher on the TiO(2) films (R(a) = 0 and 40 nm) than on the corresponding glass substrates and the standard polystyrene dishes. On day 7, all TiO(2) films contained higher cell numbers than the corresponding glass substrates, and the cells on the TiO(2) films with R(a) = 40 and 100 nm also contained a higher concentration of β-actin. These results indicate that TiO(2) coating had a positive influence on the adhesion and subsequent proliferation of MG63 cells. In addition, on all investigated materials, the cell population density achieved on day 7 decreased with increasing surface roughness. The concentration of osteocalcin, measured per mg of protein, was significantly lower in the cells on rougher TiO(2) films (R(a) = 100 and 170 nm) than in the cells on the polystyrene dishes. Thus, it can be concluded that the adhesion, growth, and phenotypic maturation of MG63 cells were controlled by the interplay between the material chemistry and surface topography, and were usually better on smoother and TiO(2)-coated surfaces than on rougher and uncoated glass substrates.