Aluminum metal/polymer interfaces

Metal thin films deposited on polymers are widely used in various industrial domains such as microelectronics (capacitors), magnetic recording, packaging, etc. Despite much attention that has been paid in the recent literature on the adhesive properties of metals films on polyimide (PI)( 1 - 5 ) and polyethyleneterephtalate (PET)((L) it appears that a better knowledge of the metal/polymer interface is needed. In this paper we focus ourself on the relationship between the adhesion and the structural properties of the aluminum films evaporated (or sputtered) on commercial bi-axially stretched PET (Du Pont de Nemours (Luxembourg) S.A.). A variety of treatment (corona, fluorine,etc.) have been applied in order to improve the adhesion of the metallic layer to the polymer. The crystallographic... 

Electrified interfaces are predominantly built up by mobile charged species which in the case of metal/polymer interfaces may be identified with ions embedded in the polymeric matrix. Therefore, electrochemically driven reactions prevail in environments which allow the presence of such species. Furthermore, the conservation of charge may require the presence of ion-transfer reactions and this condition is almost always satisfied for reactive metals such as iron, copper, zinc, and aluminum. 

In the present paper. Static Secondary Ion Mass Spectrometry (SSIMS) is used to investigate the interfacial chemistry between vacuum-deposited Al and Cu on PET by following the initial stages of metallization in the submonolayer and monolayer regimes. From the SIMS intensity variations with the deposited metal flux, information on the initial growth mechanisms of the metal layer Is expected. Two metals, copper and aluminum, have been chosen In order to investigate the influence of the metal reactivity on the metal-polymer interface formation. Aluminum with its electropositive sp band is known to react strongly with the carbonyl functionalities of the whereas copper is an inert metal and its Interaction is believed to be much weaker. ... 

In the many reports on photoelectron spectroscopy, studies on the interface formation between PPVs and metals, focus mainly on the two most commonly used top electrode metals in polymer light emitting device structures, namely aluminum [55-62] and calcium [62-67]. Other metals studied include chromium [55, 68], gold [69], nickel [69], sodium [70, 71], and rubidium [72], For the cases of nickel, gold, and chromium deposited on top of the polymer surfaces, interactions with the polymers are reported [55, 68]. In the case of the interface between PPV on top of metallic chromium, however, no interaction with the polymer was detected [55]. The results concerning the interaction between chromium and PPV indicates two different effects, namely the polymer-on-metal versus the metal-on-polymer interface formation. Next, the PPV interface formation with aluminum and calcium will be discussed in more detail. 

Usually, for metallic surfaces such as steel and aluminum, most polymers adhere well due to adequate chain adsorption. Even polyethylenes apparently achieve sufficient chain adsorption on bare metallic walls for stresses up to 0.5 MPa. This means that only a coil-stretch transition may occur to produce disentanglement and to cause complete interfacial slip on metallic walls. Since the coil-stretch transition requires exertion of sufficient forces on each adsorbed or stagnant chain at the interface, it is not possible to observe on clean metallic surfaces in any geometry other than capillary (or slit) dies. It is well known [14]... 

Metallized polymers are used nowadays in numerous industrial applications (food packaging, capacitors, magnetic tapes etc...). The adhesion and the durability of metal/polymer systems represent the most important concepts that concern many research groups (1-3). Obviously, any aggressive medium which corrodes the metal film will be directly related to some loss of adhesion and durability. The aim of this work is to investigate the influence of corrosive environments on aluminum layers evaporated onto PET film and especially on both the A1 surface and interface. 

The construction of a cell permitting both FTIR measurements and electrochemical impedance measurements at buried polymer/metal interfaces has been described [266]. Ingress of water and electrolyte, oxidation (corrosion) of the aluminum metal layer, swelling of the polymer and delamination of the polymer were observed. A cell suitable for ATR measurements up to 80°C has been described [267]. The combination of a cell for ATR measurements with DBMS (see Sect. 5.8.1) has been developed [268]. It permits simultaneous detection of stable adsorbed species and relatively stable adsorbed reaction intermediates (via FTIR spectroscopy), quantitative determination of volatile species with DBMS and elucidation of overall reaction kinetics. An arrangement with a gas-fed electrode attached to the ATR element and operated at T = 60°C has been reported [269]. In this study, the establishment of mixed potentials at an oxygen consuming direct methanol fuel cell in the presence of methanol at the cathode was investigated. With infrared spec-... 

The rate of electron transfer reactions (ETRs) is strongly influenced by the surface composition of the metal. As most materials are covered by oxides, their electronic properties will determine the rate of ETR. Therefore, metals that are covered by electron conducting or semiconducting oxides such as iron or zinc will show a higher ETR rate at the substrate-polymer interface in comparison to materials that form highly insulating oxides such as aluminum. 

Theoretical Studies of Metal/Conjugated Polymer Interfaces Aluminum and Calcium Interacting with 7i-Conjugated Systems... 

Fahlman, M., et al. 2000. Polyaniline-metal interfaces Implications on corrosion protection of steel and aluminum alloys. Polym Prepr Am Chem Soc Div Polym Chem 41 (2) 1753. 

Inverted Device Structures The conventional device structure for PSCs is indium tin oxide (ITO)/PEDOT PSS/polymer blend/Al, where a conductive high-work-function PEDOTPSS layer is used for anode contact, and a low-work-function metal as the cathode. Both the PEDOTPSS layer and the low-work-function metal cathode can cause the degradation of PSCs [110-112]. The acidic PEDOTPSS was reported to etch the ITO and cause interface instability through indium diffusion into the polymer active layer. Low-work-fiinction metals, such as calcium and aluminum, are easily oxidized when exposed to air, increasing the series resistance at the metal/BHJ interface and degrading device performance. 

The often used FPL etdi of an aluminum-lithium alloy bonded with polysulfone leads to interfacial (at the metal oxide/polymer interface) failure (38) which is a surprisingly uncommon type of failure. The results leading to this assignment are shown as XPS C Is and O Is narrow scan spectra in Figure 15. This definitive assignment of failure mode is based on the fact that one failure surfece has an oi gen photopeak similar to the pretreated adherend before bonding and the other failure surfece has an 0 gen photopeak similar to the adhesive. 

In failure analysis the possibility to record all elements is advantageous, not least in combination with 3D imaging (i.e., a TOF-SIMS instrument with dual-beam capability is the instrument of choice). An example is the investigation of black spots in OLEDs where a fluorine-based polymer was sandwiched between a metallic cathode consisting of Ba and A1 and a poly(3,4-ethylenedioxythiophene)/ITO anode. From the recorded raw data, depth profiles can be reconstructed as well as two-dimensional (2D) images in any depth or a 3D representation of all interesting signals. It was found that aluminum was oxidized at the Al/polymer interface [220]. 

C. Fredriksson and J. L. Bredas, Metal/conjugated polymer interfaces a theoretical investigation of the interaction between aluminum and trans-polyacetylene oligomers, J. Chem. Phys. 98 4253 (1993). 

---