Metalizable Polymer Thin Films in Supercritical Carbon Dioxide

We report an environmentally “green” method to improve adhesion at a polymer/metal interface by using supercritical carbon dioxide (scCO₂). Spun-cast polystyrene (PS) and poly(methyl methacrylate) (PMMA) thin films on cleaned Si wafers were used for this study. Film thicknesses of both polymer films were prepared in the range of 100 Å to 1600 Å. We exposed the films to scCO₂ in the pressure-temperature (P–T) range corresponding to the density-fluctuation ridge, where the excess swelling of both polymer films occurred, and then froze the swollen structures by quick evaporation of CO₂. A chromium (Cr) layer with film thickness of 300–400 Å was deposited onto the exposed film by using an E-beam evaporator. X-ray reflectivity (XR) measurements showed that the interfacial width between the Cr and exposed polymer layers increased by a factor of about two compared with that without exposure to scCO₂. In addition, the large interfacial broadening was found to occur irrespective of the thickness of both polymer films. After the XR measurements, the dewetting structures of the PS/Cr films induced by additional annealing were characterized by using atomic force microscopy, showing improved surface morphology in the exposed films. Contact angle measurements showed that a decrease in interfacial tension with exposure to scCO₂ accompanied the increase in interfacial width.     

Contact angle characteristics and breaking strength of paint plastic film

The advancing contact angle of water on plastic film coatings on metal was measured against both the air and the metal side surfaces after their being peeled off from the metal substrate. The plastic used was a methacrylate copolymer, and it was baked on cadmium, aluminum, nickel, iron, and gold. Contact angle for the air side was about 74° at 25°C. for all metals, but the values on the metal side differed considerably, ranging from 76° for gold to 50° for cadmium. At the same time the static breaking strengths of the same films were investigated by applying a knife-edge vertically to the film with increasing load and measuring the weight at which the electric resistance through the film became zero. Increasing film thickness gave increasing strength, but further thickening made the film weaker with a tendency for crack formation. The film–metal combinations of larger contact angle difference generally also showed the higher breaking strength.     

Relationship between thickness of polymer films and their oxidation on copper substrate

This research was undertaken to understand how the thickness of polyethylene films oxidized on a copper substrate influences the accumulation of carbonyl groups (measured by an IR‐spectroscopy technique) and of metal from the substrate (determined by polarography analysis). It was found that the whole polymer became inhibited by the time the copper stopped transferring into the specimen. Plots of copper concentration versus film thickness have two thickness sections: section I is found between 0 and 70 μm and section II between 80 and 170 μm. Between these two sections the metal concentration varies drastically. This situation can be explained by two schemes by which PE changes to inhibited condition. According to Scheme I (for section I, short oxidation time) this change has only one step: the inhibited layer gradually becomes thicker beginning from the interface and moving toward the outer surface. The second scheme (for section II) shows that the polymer becomes inhibited in two steps. It is typical of thicker films. In this case the oxidation process shifts and localizes in the outer surface because of longer treatment. As a result, transfer of metal and formation of an inhibited layer are interrupted for some time. The metal accumulation in the film only resumes when low‐molecular‐weight products of thermooxidative degradation—formed in the specimen outer surface—enter the region of adhesional contact. A so‐called second transfer stage for metal is realized during which the whole polymer becomes inhibited. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 671–675, 2003     

Electrical currents resulting from reduction/oxidation processes of tested particles on electrodes modified with metal-containing polymer films

Metal-containing films are considered as systems including a multitude of microelectrodes, the role of which is played by metal clusters distributed in both the film interior and film interfaces. In the case of electrode reactions occurring exclusively on the surface of such metal inclusions and the film thickness significantly exceeding clusters’ radii, it is shown that the concentration of species participating in such processes (tested particles, further on) satisfies a diffusion equation complicated with an accompanying electrochemical reaction. By assuming reversibility of the electron transfer processes between polymer fragments, one can arrive at solutions of the derived equation and calculate the corresponding currents resulting from tested particles’ reactions. The role of such factors of inclusion of metal clusters into conducting polymer films, as its density and inhomogeneity is discussed in the context of their influence on the measured currents of reduction/oxidation processes of tested particles. Non-stationary effects that might be observed in cycling voltammetry and potential clamp measurements with electrodes modified by metal-containing films are also analyzed. The performed analysis shows that electrochemical properties of the modified electrodes in question practically coincide with those of the electrodes made of the corresponding metals and immersed into the same solutions.     

Poly(methyl methacrylate) as masking material for microelectromechanical system (MEMS) fabrication

In the present study direct current (dc) sputtered poly(methyl methacrylate) (PMMA) films deposited on silicon substrates were evaluated as masking materials for anisotropic etching of silicon in aqueous potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAH) solutions. Sputtered PMMA films were characterized by FTIR to ascertain the bonding, by X‐ray photoelectron spectroscopy (XPS) for the elemental composition, and by the contact angle for measuring the adhesion of the film with the substrate. FTIR and XPS data showed the presence of a poly(tetrafluoroethylene)‐like film on the silicon substrate. The interfacial tension was calculated from the contact angle value, which was 0.82 dyne/cm, confirming good adhesion of the film and the substrate. A pattern was lithographically transferred through the masking material on the silicon substrate, and the etch rate of the masking layer was calculated from the masking time data of the films. The etch rate value of 4 Å/min obtained for the masking material is low compared to the etch rate of the conventional masking materials (60 Å/min for SiO₂ and 8 Å/min for Si₃N₄). © 2006 Wiley Periodicals Inc. J Appl Polym Sci 102: 2094–2098, 2006     

Studies of the development of fibrillar structure in nylon 6

Very thin films of poly(vinyl alcohol) could be prepared by utilizing the adsorption of polymer molecules at air/water interface from the aqueous solutions of the poly(vinyl alcohol) derived from vinyl trifluoroacetate. The films prepared by the bubble method were thinner than those obtained by the frame method. The minimum thickness of the former films was 260 Å and that of the latter was 1800 Å. These very thin films resisted water at temperatures below 55°C. The maximum Young's modulus of the drawn/annealed films prepared from these samples was 30 GPa. The permeability of water, J_w/δP, was 2–6 × 10^?3 cm · s^?1 atm^?1 (0–55°C) for the untreated film (thickness: 1800 Å) prepared by the frame method and 0.8–2.2 × 10^?2cm · s^?1 · atm^?1 (5–55°C) for the untreated film (360 Å) prepared by the bubble method, and depended on the thickness of film.     

Preparation of Unsupported Metal Organic and Ceramic Thin Film Specimens for TEM Observation

A method for preparing TEM specimens from fragile metal organic resin and metal-organic-derived ceramic films is described. Unsupported films can be easily prepared by spin coating a metal organic solution onto a camphor substrate followed by separating the film by subliming the substrate. The method involves encapsulating the fragile film fragments in a low-viscosity, thermosetting, epoxy-hardener solution to obtain mechanical integrity. The encapsulated film can be easily hand polished to approximately 20-μm thickness in less than 1 h. Electron-transparent TEM specimens can then be prepared by ion-beam thinning the encapsulated film, after mounting it on a slotted copper grid.     

Transfer of copper and zinc in polymeric materials oxidized in contact with brass

Transfer particularities were investigated for zinc and copper in polymeric films oxidized in contact with brass. Inversion in selectivity of alloy component transfer proved to be the fact for a wide range of polymers. The results obtained are explained by an irregular development of oxidative transformations within the polymer layer, thus leading to a two-stage mode of transfer in the case of catalytically active metals. The influence of various factors (e.g., oxidation temperature, polymer film thickness, polymer origin) on the level of ultimate concentrations of copper and zinc accumulated in polymers was considered. © 1995 John Wiley & Sons, Inc.     

Passive behaviour of niobium

The passive behaviour of niobium at electrode potentials from −1 to 4 V (sce) in aqueous solutions of pH 0–13 at 25°C has been studied by quasi-steady (20 h) and transient polarization measurements, dc capacitance determinations and some AES depth profile investigations. Niobium exhibits a quasi-steady passive current varying little with the electrode potential and pH. After potential (or current) steps, transient superpolarization occurs. The transient data accord with the Cabrera-Mott equation and fit reasonably with λ = 1.5 Å and z = 5 for metal ion transfer at the metal—oxide interface. The capacitance data satisfy a simple insulator model, reveal the main charge distribution in the passive electrode, and combine with film thickness data to give ε = 46 for the static dielectric constant of the passive film. The anodization ratio is 37 Å V⁻¹ under quasi-steady conditions. The passive niobium electrode seems mostly to carry a net negative charge. Anodic oxygen evolution does not occur.     

Growth of anodic oxide films on oxygen-containing niobium

The present study is directed at understanding of the influence of oxygen in the metal on anodic film growth on niobium, using sputter-deposited niobium containing from about 0-52 at.% oxygen, with anodizing carried out at high efficiency in phosphoric acid electrolyte. The findings reveal amorphous anodic niobia films, with no significant effect of oxygen on the field strength, transport numbers, mobility of impurity species and capacitance. However, since niobium is partially oxidized due to presence of oxygen in the substrate, less charge is required to form the films, hence reducing the time to reach a particular film thickness and anodizing voltage. Further, the relative thickness of film material formed at the metal/film interface is increased by the incorporation of oxygen species into the films from the substrate, with an associated altered depth of incorporation of phosphorus species into the films.     

Study of transient currents in discharging mode in pure and iodine doped ethyl cellulose films

A study of transient currents in discharging mode in vacuum aluminized pure and iodine doped ethyl cellulose (EC) films, approximately 20 μm in thickness, measured at various temperatures (303–353K) and applied fields (2.0 × 10⁴?4.5 × 10⁴ V/cm) is described. The order of current has been found to increase considerably with increase in poling temperature, field and iodine mixing. The currents have been found to show I ∝? t^?n (i.e. Curie–Von Schweidler law) time dependence with different slopes in the short and long time regions. The conductivity of the films is increased on doping with iodine. The dopant molecules are considered to act as additional trapping centres and provide a link between the polymer molecules in the amorphous region, thus resulting in the formation of a charge transfer complex. The results of the experiments and the mechanisms involved are discussed on the basis of available theories.     

Surface passivation of nylon‐6,6 films by graft copolymerization for reduction of moisture sorption

To improve the moisture sorption property of nylon‐6,6 film, ally pentafluorobenzene (APFB) was incorporated on the argon plasma‐pretreated nylon film by UV or thermally induced surface graft copolymerzation. The plasma pretreatment introduced peroxides that were degraded into radicals to initiate the graft copolymerization of APFB on the nylon surface. The modified surfaces were characterized by X‐ray photoelectron spectroscopy (XPS) and contact angle measurement. The moisture sorption was assessed by the coulometric test method. The efficiency of surface graft copolymerization was affected by plasma pretreatment time of the nylon substrate, as well as by the UV or thermal graft copolymerization time. The UV graft‐copolymerized nylon film exhibited a significantly lower extent of moisture sorption when compared to that of the pristine films, even at low graft concentration. However, the moisture sorption behavior for the thermally graft copolymerized films was similar to that of the pristine films. Contact angle and XPS measurements suggested that the reduction in moisture sorption for the UV graft‐copolymerized nylon‐6,6 film was attributable to the fact that the hydrophobic polymer layer was formed on the nylon surface, and the hydrophobic layer of an appropriate thickness could serve as an effective barrier to moisture. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1366–1373, 2000     

Passive behaviour of zirconium

The title subject has been studied by quasi-steady (20 h stabilization) and transient polarization measurements and dc capacitance determinations over potentials from −1 to 2 V (sce) in aqueous solutions of pH 0–13 at 25°C. A few AES investigations of oxide films formed are also included. The quasi-steady data reveal an essentially potential and pH independent passive current and a superimposed current of oxygen evolution appearing already at rather low overvoltages for this reaction. The transients accord with the Cabrera-Mott equation and suggest charge transfer by Zr(IV) ions at sites of relatively fast responding field or current dependent density at the metal/oxide interface (no superpolarization). The transient polarization fits with a value of about 1.5 Å for the activation (half-jump) distance. The capacitance data largely satisfy a simple insulator model, reveal the main charge distribution in the passive zirconium electrode, and combine with previous film thickness data to give about 28/r (r being the roughness factor) for the dielectric constant of the passive film. Comparisons are made to the passive behaviour of titanium and aluminium.     

Positive and negative photoresist applications of thin films surface-photopolymerized from hexachlorobutadiene

Polymeric films deposited from the vapor of C₄Cl₆ by the surface-photopolymerization technique are electrically and mechanically continuous on various substrates when very thin. The thickness of the films depends upon irradiation time with wavelengths in the region 2000-3000Å. Re-irradiation in oxygen (air) of the polymeric films with light of these low wavelengths leads to patterned removal of the films. Since films 500Å thick and less can resist etchants for various substrates, a new and extremely thin positive photoresist system is possible. Resolution of etched substrates to lines a few microns wide has been demonstrated. If the polymeric films from C₄Cl₆ are deposited from the monomeric vapor at lower substrate temperatures they are soluble in various solvents. Re-irradiation with UV light with the films in vacuum produces a patterned fixing of the polymer with respect to acetone. A negative photoresist system is therefore possible. Again, films of thickness 500Å and less can resist various etchants such that substrates can be etched to high resolution.     

Model treatment of double layer charging in electroactive polymer films with two kinds of charge carriers

To calculate such phenomenological parameters of the polymer film impedance theory, as charge transfer resistances and interfacial capacities, a well-known model of homogeneous electroactive films with two kinds of charge carriers is used. General representations of the electrochemical kinetics are applied to describe the injection processes of charge carriers into the films. The exchange current densities (i.e. inverse values of the charge transfer resistances) and the interfacial capacities are calculated as functions of the electrode potential and the bathing electrolyte solution concentration for films with both cationic and anionic nature of counter-ions. In both cases, the exchange current density of electrons as a function of the electrode potential may have an extremum or be monotonous, depending on particular values of the partition coefficient of electrons, while the capacity of the substrate/film interface is a monotonic function of the potential. On the contrary, the exchange current density of counter-ions is a monotonic function of the electrode potential, whereas the capacity of the film/solution interface might depend on the potential in a non-monotone way. The obtained results can be useful for a quantitative treatment of experimental data on the charge transfer resistance and the double layer capacity often observed in the Nyquist plots of the polymer film impedance. Some restrictions of the model used are also discussed.     

On the thickness and spatial distribution of a fluoropolymer film deposited by solution dipping

Poly-1H,1H-pentadecafuorooctyl methacrylate is a barrier compound used to prevent silicone oil from creeping to relay contacts. It is essentially a methyl methacrylate polymer with a fluorocarbon side chain substituted for one of the methyl hydrogens. It is applied by dipping the part into a solution, with Freon TF as the solvent and the fluorocarbon polymer as the solute. This work considers the spatial distribution of the resulting film of barrier compound when it is deposited in this manner. The specific variables considered are concentration and withdrawal velocity. The samples were withdrawn from the solution with velocity perpendicular to the surface, and we show that the macrosopic uniformity and thickness of the film is dependent on this velocity. There exists a critical velocity (dependent on concentration) above which the film is nonuniform and below which the film is macroscopically uniform. Below the critical velocity, the thickness varies with velocity with approximately a v^2/3 dependence. The critical velocity is about 13 mm/sec for a concentration of 0.2%. For macroscopically uniform films, a microscopic nonunitormity exists with a coverage of about 1/4 for an average film thickness of 90 Å.     

Plasma polymerized protective films for plated magnetic disks

Plasma polymerized protective films (PPP films) for magnetic disks have been investigated in order to improve weak durability of plated disk media to head friction and clash. The thickness heterogeneity of PPP films within 5% was realized around the all surface of 140 mm^? model substrates, determining the best discharge condition and apparatus geometry, which did not exert and aggravating influence upon head floating. The friction coefficients of PPP films to a ferrite slider of 0.3 ～ 0.4 were obtained in the thickness of above near 1500 Å, although PPP films are composed of hydrocarbon or fluorocarbon. As the results of contact start/stop cycle tests by a floating head, plasma polymerized toluene-2,4-diisocyanate films show good abrasive durability because of its superior adhesiveness to metal substrates, and PPP films in small thickness near 1000 Å give good protective films. The result of read/write tests indicated that the magnetic deterioration and instability of plated disk media did not occur by the process of plasma polymerization.     

Melt flow crystallization of ultrahigh molecular weight polyethylene under curvilinear flow conditions

Multiaxially oriented ultrahigh molecular weight polyethylene films were prepared recently under curvilinear flow conditions generated by the combined effects of compression and rotation. The films were prepared by melt flow crystallization in an optical apparatus specially designed for rheo-optical observations. Morphological studies indicate that the films were fibrillar with the fibrils oriented along the circular flow lines. The fibrils were lamellar, and their lamellar thickness (150–450 Å) and spacing (400–2000 Å) depended on the processing conditions. The film exhibited strong birefringence (1.4 × 10^?2) and had a Young modulus of 15–25 GPa along the flow lines and 3–5 GPa in the transverse direction.     

Cyclophosphazene-containing Polymers as Imprint Lithography Resists

We present the evaluation of a cyclophosphazene-containing polymer as a patternable resist for imprint lithography. Hexamethacryloxybutoxycyclotriphosphazene layers containing small amounts of photoinitiator can be applied to silicon wafers substrates by spin coating techniques and cured photochemically to give tough, network polymer thin films. The films were characterized by FT-IR. Thin films approximately 200 nm in thickness were subjected to anisotropic O₂ and CF₄ plasmas and the etch rates were determined. The polymer films etch at a rate of 21 Å/s in CF₄ plasma, and as low as 1.6 Å/s in O₂ plasma, which is comparable or lower than the rates observed with commercially available silicon-containing photoresists. The surface chemical composition was surveyed by X-ray photoelectron spectroscopy, which gave results consistent with the formation of an etch resistant phosphorus-rich layer during reaction with O₂ plasma. The polymer was processed by nano-contact molding imprint lithography and replicated 200 nm period test patterns. This report is the first demonstration of a cyclophosphazene-containing polymer as a resist candidate for high-resolution lithography.     

Grazing incidence X-ray diffraction studies on the structures of polyurethane films and their effects on adhesion to Al substrates

Grazing incidence X-ray diffraction was carried out to analyze the structure of polyurethane films as a function of X-ray penetration depth by varying the angle of incidence. Coherence lengths, interplanar spacings, and crystallinities were obtained for non-aged and aged films of OH numbers of 120, 375, and 600 bonded to an aluminum substrate. Aging led to the improvement of bulk crystallinity of all the samples, particularly in the case of the aged PU-375 film, for which a dramatic increase of the bond strength was observed. The crystallinity of non-aged samples varied from the air/polymer surface down to the polymer/aluminum interface. Invariance of coherence length from air surface to interface was observed for PU-120 and PU-375 samples, implying that substrate-induced ordering has little effect on the average crystallite size. As the X-ray penetration increases near the polymer/Al interface, interplanar spacing of (021) reflection in all the films approach the value found for a bulk polyurethane-urea by Ishihara et al. The bond strength of the polyurethane film to the aluminum was exponentially proportional to the crystallinity including the crystalline interphase formed near the substrate. It is also found that the polymer film containing more (100) planes provided higher bond strength.