Metal-polymer Interface Research Articles

Lubrication and slip flow during extrusion of plasticized PVC compounds in the presence of lead stabilizer

The main point of interest when discussing lubrication is to understand what lubricants do in a compound, particularly during processing. Among lubricants, we can find metal soaps, which are often heat stabilizers of PVC. In order to study the influence of lubricants on the flow properties, it is of particular interest to analyse the behaviour of the material at the die walls, where slip may be observed. Then, in the present paper, the lubricating ability of a lead stabilizer during extrusion of a plasticized PVC formulation was investigated through an instrumented die, which allowed us to have the apparent flow properties at the wall. Rough and smooth surfaces of the die were used in order to prevent or promote slip at the metal surface. From this method, it was possible to observe the slip phenomenon above a critical concentration, whereas the analysis of the die surface through SEM coupled energy dispersive x-ray spectroscopy shows that lead stabilizer migrates even at low concentration. So, slip occurs when the lubricant layer forms a continuous solid layer which modifies the polymer–metal interface properties.

Electroluminescence in polyethylene subjected to impulse voltages

Electroluminescence (EL) from HDPE (high-density polyethylene) films subjected to repetitive rectangular-shaped impulse voltages has been investigated at electric fields <80 kV/mm in order to clarify the temporal behavior of carriers injected into the polymer. EL emission was distinctly observed during the voltage rise and fall phases. During the voltage plateau and the zero voltage phases, the EL intensity did not instantly decrease to zero but a very weak EL emission lasted for at least 3 ms. The number of EL pulses was determined by the amplitude of the impulse voltage, whereas the EL intensity strongly depended on the temporal variation rate of the voltage. The total number of EL pulses during both phases of the voltage rise and fall was almost equal. The EL spectra did not depend on the phase and the amplitude of the impulse voltage. The above behavior of EL emission can be explained qualitatively by the electron-hole recombination in the metal-polymer interface region and showed the picture of temporal behavior of carriers, carrier injection and transport, in the interface region for the field relaxation at the interface.

Evidence for metal interaction in gold metallized polycarbonate films: An x-ray photoelectron spectroscopy investigation

The interfacial interactions between in situ thermally evaporated Au and polycarbonate (PC) film, a technologically important polymeric material, is studied by x-ray photoelectron spectroscopy (XPS). Angle resolved XPS is performed to investigate the Au reactivity if any, in forming the metal-polymer interface. The spectral evidence from the above suggests that the metal interacts predominantly with the carbonyl carbon of the monomeric unit with only minor interactions with the phenyl carbons without any complex formation. In contrast to previous findings of Au to be inert at the M-polymer interfaces, this work emphasizes the salient charge transfer type interactions of Au (as electron injector) at the C=O as the primary interaction site, distributing a net charge density to C=O with the formation of a Au-CO π-back bond. The conclusions are supported by the observed new C 1s feature at 282.6 eV and the O 1s and Au 4f7/2 XPS spectral changes. The growth mode of Au on PC was proceeded by the metal monolayer deposition with cluster growth on the already weakly bonded Au onto the C=O carbon of the polymeric backbone.

Transistor por efeito de campo e fotocondutor de poli(o-metoxianilina).

RESUMO: Esse artigo apresenta resultados sobre fabricação e caracterização de um transistor por efeito de campo (FET) tendo a poli(o-metoxianilina) - POMA - como material ativo. Uma adaptação de processos de microeletrônica tradicional foi feita para a confecção desse dispositivo. O FET desenvolvido apresentou modulação por voltagem de porta Vg, mas operou mesmo em Vg=0. A corrente de dreno I D aumentou significativamente sob iluminação na região da radiação visível e infravermelho próximo, mostrando o caráter fotocondutor da POMA dopada e, portanto, do dispositivo. Um modelo teórico baseado nos mecanismos de condução eletrônica da POMA, e de efeitos de interface metal-polímero foi elaborado, ajustando-se muito bem aos resultados experimentais.

Adhesion Improvement of Poly(Phenylene-Vinylene) Substrates Induced by Argon-Oxygen Plasma Treatment

Copper films evaporated on argon-oxygen plasma-treated poly(phenylene-vinylene) films have been studied by scratch test, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The adhesion of the metallic film to the polymer substrate was greatly enhanced after treatment and found to increase with the treatment time. SEM observation of the treated samples revealed that the morphology of the polymer surface was gradually changed with the treatment time as compared with that of the bare polymer film. On the other hand, XPS analysis of the polymer-metal interface showed that the bonding between carbon, oxygen and copper were subsequently modified as compared with those obtained in untreated samples. The high adhesion strength observed on these substrates was related to the modification in the surface morphology on the one hand and to the formation of new compounds at the polymer-metal interface on the other. The nature of the interfacial layer and its influence on the adhesion of the copper layer was discussed by comparing the results with those obtained in poly(phenylene-vinylene) (PPV)-Al systems.

Light emission in PE with a needle-like microvoid at the metal-polymer interface under impulse voltages

Light emission from polyethylene with a needle-like microvoid has been investigated under the application of a negative impulse voltage in order to examine the temporal behavior of discharge in the microvoid at the metal-polymer interface. The light emission was observed distinctly during the voltage rise and fall phases with a period of no light emission between the two light emitting phases. The emitted light consisted of sequential light pulses which appeared regularly, according to the temporal variation rate of the voltage. The sequential light pulses corresponded to the sequential discharge in the microvoid which occurred to keep the voltage across the microvoid below the discharge inception voltage. The characteristics of light emission revealed the occurrence of intermittent discharges in the microvoid during the voltage variation phase of the impulse voltage, caused by charge deposition on the polymer surface of the microvoid.

XPS/AFM study of the PET surface modified by oxygen and carbon dioxide plasmas: Al/PET adhesion

The formation of the interface between aluminium and O2 or CO2 plasma-modified poly(ethylene terephthalate) (PET) has been investigated by X-ray photoelectron spectroscopy (XPS). As demonstrated by the changes in the C 1s, O 1s, and A1 2p core level spectra upon A1 deposition, the metal was found to react preferentially with the original ester, with the plasma-induced carboxyl and carbonyl groups to form interfacial complexes. The phenyl ring at the modified PET surface was seen to be involved in the formation of the interface, but to a lesser extent. This confirms the high reactivity of the oxygen-containing groups towards the deposited A1 atoms. The adhesion between A1 and the plasma-modified PET films was evaluated by means of a 180° peel test. A considerable (up to ten times) improvement in adhesion was achieved by plasma treatment of the PET substrate, but for either plasma gas the adhesion strength was found to depend strongly on the plasma power and treatment time. The results are discussed in terms of the concentration of oxygen-containing groups at the polymer surface, the surface topography, and the possible presence of low-molecular-weight materials at the metal-polymer interface.

Ta and TaN adhesion to high-temperature fluorinated polyimides. Surface and interface chemistry

The practical adhesion of Cu/Ta to high-temperature fluorinated polyimides (FPIs) was initially good but failed after the reliability test involving treatment under the FPI curing condition five times (T5). But a thin layer (40 nm) of TaN greatly improved the reliability of the Cu/Ta-to-FPI adhesion. Both CF4 and in situ Ar plasma treatments of FPIs prior to metal deposition enhanced the metal-to-FPI adhesion strength. CF4 plasma enriches the FPI surface with fluorine atoms and most of fluorine is bound to carbon as CF3, CF2, and CF. Ar plasma first destroys CF3 and then C=O groups of the FPIs to yield a polar surface. The locus of failure by a 90° peel test was found to be within the Ar-plasma-modified FPI layer but it moved toward the bulk of FPI, i.e. away from the metal-polymer interface, after the T5 reliability test. The locus of failure in the case of weak adhesion where no plasma treatment was done on FPI films was in the near-interface region within the FPI layer, and the failure seemed to occur in the weak boundary layers of FPI surfaces. Plasma treatment removes weak boundary layers and also increases FPI surface roughness. These two effects combined improved the metal-to-FPI practical adhesion.

Degradation of nonencapsulated polymer-based light-emitting diodes: Noise and morphology

We show that the degradation of a nonencapsulated polymer-based light-emitting diode (LED) is accompanied by the appearance of strong fluctuations,—that is noise both in the radiance and in the film resistance. We demonstrate a correlation between the morphological changes which occur during the degradation process and the noise, suggesting that the sampling of noise during LED operation can be used as a very efficient tool to predict the approaching failure of LEDs in real-life applications. The morphological changes in LED degradation are essentially a two-stage process. First, there is formation of “bubbles” at the metal–polymer interface due to delamination of the polymer film from the metal surface. Second, carbonized areas in the form of “black spots” are formed. Accumulation of carbonized areas leads to short and/or open circuits and final LED failure.

Effect of Corrosive Medium on Properties of Metal-Plastics Laminates

The mechanical properties of Alors-laminated pressed systems composed of thin aluminium alloys alternating with layers of organic fiber reinforced plastic has been investigated. The investigation included three main stages. At the first stage, the effect of Alors composition on the fatigue strength, adhesive strength and deformability was studied. The second stage included the shortcut cyclic corrosion tests. It was found that bending loads inhibited corrosion development at polymer metal interface. The third test stage included long term exposure certification tests in a warm damp climate. The effects of true impact of outdoor corrosion environment were determined and Alors properties stability under operating conditions was proven.

X-ray absorption spectroscopy (NEXAFS) of polymer surfaces

The application of X-ray absorption spectroscopy (NEXAFS) in surface analysis of polymers is demonstrated by means of selected examples. High resolution NEXAFS spectra of poly(ethylene), poly(butadiene) and poly(styrene) are presented. The effect of oxygen plasma treatment on the surface of polypropylene foils was investigated. It is shown that angle resolved NEXAFS spectroscopy can be used to observe preferential orientations of segments of macromolecules at the surface of a poly(ethylene terephthalate) foil. Finally, the formation of a polymer-metal interface was observed in a model study of chromium evaporated onto a poly(bisphenol-A-carbonate) film surface. NEXAFS spectroscopy and XPS are complementary tools in surface analysis of polymers. NEXAFS polymer spectra can be used in parallel electron energy loss spectroscopy (PEELS) to control for electron beam damage.

Thermally stable liquid crystalline thermosets based on aromatic copolyesters: Preparation and properties

The synthesis and physical properties are described for a thermally stable liquid crystalline (LC) thermoset based on all aromatic ester units. The persistence of the liquid crystalline phase throughout the curing process was monitored with polarizing optical microscopy. The applicability of these new liquid crystalline thermosets has been evaluated for use as an adhesive for bonding metals, namely titanium. The failure of the adhesive bonds always occurs within the polymer; thus it can be inferred that bonding at the polymer-metal interface is very good. This strong interfacial bonding is attributed to low cure shrinkage and CTE matching of the underlying substrate by the LC resins. The cohesive properties and strength of the cured resin can be greatly enhanced by the addition of filler materials.

Conjugated polymer surfaces and interfaces

The doping of a conjugated polymer, polyacetylene, to a state of high electrical conductivity in 1977 marked a distinct step in interest in the electronic and transport properties of electrically conducting organic materials. Since 1990, however, undoped semiconducting conjugated polymers have emerged as potentially useful electronic materials in a variety of electronic and optoelectronic applications. In the context of polymer–based electronic device applications, it is of critical importance to understand the nature of the electronic structure of the polymer surface and the polymer–metal interface. It has been shown that, especially for conjugated polymers, photoelectron spectroscopy provides a maximum amount of both chemical and electronic structural information within a single measurement technique. This contribution contains an overview of some details of the early stages of interface formation with metals on the surfaces of conjugated polymers and model molecular solids, as studied using photoelectron spectroscopy. The materials chosen are especially of interest in connection with polymer-based light emitting devices, or LEDs. Specifically, the materials involved include poly( p –phenylenevinylene), or PPV, and a series of substituted PPVs, as well as a diphenylpolyene molecule for PPV, namely, α,ω–diphenyltetradecaheptaene. Some general trends in the behaviour of light–metal atoms on the clean surfaces of conjugated polymers are pointed out. Some consequences, based upon the information obtained in the studies reviewed, are highlighted. Finally, two recent issues, which are studied by the methods used for the metal–on–polymer interfaces studies, are covered: the role of water vapour on the electronic structure of PPV; and the use of phase–separated polymer blends to increase the quantum efficiency of blue light emitting diodes.

Electrical conductivity in the metal-polymer-metal system: The role of boundary conditions

We study a new type of charge instability in electroactive polymers, an instability caused by a change in the boundary condition at the metal-polymer interface. The change in the boundary conditions is achieved by melting one of the electrodes in a measuring cell of the metal-polymer-metal sandwich type. Charge instability manifests itself in the form of an insulator-metal phase transition, which emerges when one of the electrodes is melted. We list the results of numerous studies of the role of artifacts. Finally, we propose a model that explains several features of the phenomenon.

Electrochemical impedance spectroscopic study of encapsulated triple tracks test (TTT) circuits

Electrochemical impedance spectroscopy (EIS) is effective for studying the reliability of protective coatings on microelectronic packaging devices. Triple track test (TTT) circuits were evaluated as a function of exposure time at 121/spl deg/C and 2 atm pressure. Specimens were deliberately contaminated by various chemicals and particles before coating. The impedance of some specimens decreased after the first 10 hours in the Pressure Cooker Test (PCT) while some lasted more than 150 hours in the PCT without an appreciable change in the impedance values. Impedance of the specimens changed appreciably due to water uptake in the epoxy coatings. The ionic contamination trapped under the coating caused faster failure in the TTT with respect to clean specimens. Water diffused to the polymer/gold interface causing a change in the dielectric properties of the specimen, shown as a shift in the EIS spectrum. This shift was observed in EIS spectra for most of the specimens which were exposed for more than 150 hours. The change suggests water that penetrated the coating made a conductive pathway to the interfacial region, a common cause of debonding between the metal (or ceramic) polymer interface. In one case (specimens contaminated by SiO/sub 2/ particles) the shift was not observed-suggesting that SiO/sub 2/ particles do not accelerate the adhesive failure at the metal (or ceramic)/polymer interface. The calculated saturated volume fraction of water at the metal (or ceramic)/polymer interface was 1.1/spl plusmn/0.1.

Fatigue crack propagation along polymer-metal interfaces in microelectronic packages

In this study, a fracture mechanics-based technique was used for characterizing fatigue crack propagation (FCP) at polymer-metal interfaces. Sandwich double-cantilever beam (DCB) specimens were fabricated using nickel and copper-coated copper substrates bonded with a thin layer of silica-filled polymer encapsulant. Under cyclic loading, crack propagation was found to occur at the polymer-metal interface. The interfacial failure mode was verified by scanning electron microscopy (SEM) analysis of the fatigue fracture surfaces. The crack growth rate was found to have a power-law dependence on the strain energy release rate range, and exhibited a crack growth threshold, much like the fatigue crack growth threshold stress intensity factor range for monolithic bulk metals, polymers, and ceramics. Interfacial FCP data for three candidate encapsulants predicted cracking resistances that were well correlated with package-level reliability tests. By varying the surface roughness of the copper and nickel plating, it was shown that interfacial FCP resistance increased with increasing roughness. The observed increases in FCP resistance were attributed to a reduction in the effective driving force for fatigue fracture along the rougher interfaces, and could be accounted for by a crack-deflection model.

Metal phase in electroactive polymer induced by change in boundary conditions

In the metal/polymer/metal structure the insulator-metal phase transition induced by 1 the change in the boundary conditions in the metal-polymer interface was realized. The boundary conditions were changed due to change in the metal work function at the metal melting point.

Electroluminescence in insulating polymers in ac electric fields

EL (electroluminescence) in several polymeric materials was investigated in the electric field range <90 kV/mm. We used polymeric films with semi-transparent gold electrodes: low density polyethylene, polypropylene, polytetrafluoroethylene and polyvinylchloride. The EL characteristics were very low EL inception fields (2 to 20 kV/mm) which strongly depend on the material and very low energy photon emission (mainly in the red region of 1.6 to 1.8 eV). These results reveal that EL emission occurs predominantly in the metal-polymer interface region rather than in the bulk of the polymer at the applied field. We present a model of EL emission in the metal-polymer interface region to explain our results qualitatively. In this model, the mechanism of EL emission is the radiative recombination of the electrons and holes trapped at the surface states of the polymer, which causes photon emission in the red region. The EL inception field and EL intensity depend on the density of the surface states of the polymers.

Interfacial effects in poly (p-phenylene-vinylene)-metal systems

The effect of vapour deposited metal (nickel and gold) on poly(p-phenylene-vinylene) (PPV) is investigated using X-ray photoelectron spectroscopy (XPS). Upon metallization, changes in the carbon and metal spectra are observed in comparison to the those recorded in the pristine ones, perhaps indicating an interaction at the polymer-metal interface. By comparison with earlier works, the formation of metal carbide in the polymer is postulated. The presence of such interactions appears to affect the behaviour of such metals when used as electrical contacts on a PPV substrate, as found from an I/V study of the characteristics of Cr-PPV-Au and Cr-PPV-Ni diodes.

Influence of the photo-oxidative degradation on the water barrier and corrosion protection properties of polyester paints

The barrier properties of a paint are strongly influenced by the presence of defects, by photo-oxidative phenomena and by the adhesive properties of the polymer-metal interface. Impedance spectroscopy is a flexible and efficacious instrument for assessing all these phenomena and is useful in supplying information on the mechanisms of deterioration as well as assessing the physical parameters associated with it. The wide use of paints in external environments that are exposed to the effects of solar radiation and humidity makes the study of the deterioration of organic coatings under these conditions important. The coefficients of humidity diffusion and the values of permeability and saturation for different ultraviolet (u.v.) radiation intervals have been calculated, starting from the impedance data and using appropriate models. The relationship is shown between these values and the effective long-term properties of protection from corrosion of the paints.