Auger electron spectroscopic analysis of chemical vapour deposited diamond/substrate interfaces

Auger electron spectroscopy has been used to identify the allotropes of carbon in chemical vapour deposited diamond films deposited on copper and tungsten wires and on SiC and silica fibres and to measure the thickness and composition of the diamond/substrate reaction layers. The significance of these results for the manufacture of diamond fibres is discussed.     

Adhesion mechanisms at soft polymer interfaces

Based on several significant examples, we analyse the adhesion mechanisms at soft polymer interfaces with a special emphasis first on the role of connector molecules, that is, polymer chains bound to the interface and which transmit stress through a stretching and extraction mechanism, and second on the necessary relay that must be taken by additional dissipation mechanisms acting at larger scales if one wants to reach typical fracture toughnesses in the range of a few 10 J m(-2). Examples of such bulk dissipation mechanisms will be discussed for interfaces between polymer melts and for pressure-sensitive adhesives in contact with a solid surface. We shall particularly point out the fact that the level of adhesion results from a competition between adhesive failure usually driven by both the interactions and the friction properties of the interface and bulk strong deformations which take place in the bulk of the adhesive layer. Controlling the friction properties of the interface then becomes a tool to finely tune adhesive properties.     

Adhesion along metal–polymer interfaces during plastic deformation

In this paper a numerical study is presented that concentrates on the influence of the interface roughness that develops during plastic deformation of a metal, on the work of adhesion and on the change of interface energy upon contact with a glassy polymer. The polymer coating is described with a constitutive law that mimics the behavior of Poly-Ethylene Terephthalate. It includes an elastic part, a yield stress, softening and hardening with increasing strains. For the interface between the metal and the polymer a mixed-mode (mode I and II) stress-separation law is applied that defines the interface energy and an interaction length scale. At the onset of deformation the surface of the substrate has a self-affine roughness characterized by the so-called Hurst exponent, a correlation length and an rms roughness amplitude, that evolves as a function of increasing strain. The findings are the following: the interface energy decreases until the strain at yield of the polymer coating. Interestingly, after yielding as the polymer starts to soften macroscopically, the decreasing average stress levels result in partial recovery of the interface energy at the interface. At higher strains, when macroscopic hardening develops the recovery of the interface stops and the interface energy decreases. The effect of coating thickness is discussed as well as the physical relevance of various model parameters.     

Fracture of metal/ceramic interfaces

The present paper examines metal/ceramic interfaces. Energy release rates are calculated with the finite element method for different elastic–plastic material laws of the metal. The local strain field of the metal is measured during a four-point bending test with an optical method and compared with results from the simulations. The aim of the work is to understand the influence of interface strength and material properties on the energy release rate.     

Combined spectroscopic characterization of electron transfer at hybrid CuPcF(16)/GaAs semiconductor interfaces

We characterize photoinduced charge injection at the interface between a fluorinated copper phthalocyanine (CuPcF(16)) film deposited over a GaAs(100) wafer by means of pump-probe spectroscopy combined with ultraviolet photoemission spectroscopy (UPS) and electromodulated transmission spectroscopy. UPS characterization of the hybrid interface demonstrates that the CuPcF(16) 's lowest unoccupied molecular level (LUMO) is almost aligned with the GaAs conduction band. Upon photoexcitation of the hybrid interface with 150 fs pulses we observe an efficient photoinduced electron transfer from CuPcF(16) to GaAs. The evolution of interfacial CuPcF(16) charges appear to be strongly influenced by energy level alignment at the GaAs/CuPcF(16) heterojunction.     

Erratum to: Charge transfer in graphene/polymer interfaces for CO2 detection

Nano Research - The order of the authors in the original version of this article was unfortunately incorrect on the first page and the first page of the ESM. Instead of Myungwoo Son1, Yusin Pak1,...     

Analytical transmission electron microscopy at organic interfaces

Organic materials are ubiquitous in all aspects of our daily lives. Increasingly there is a need to understand interactions between different organic phases, or between organic and inorganic materials (hybrid interfaces), in order to gain fundamental knowledge about the origin of their structural and functional properties. In order to understand the complex structure–property–processing relationships in (and between) these materials, we need tools that combine high chemical sensitivity with high spatial resolution to allow detailed interfacial characterisation. Analytical transmission electron microscopy (TEM) is a powerful and versatile technique that can fulfil both criteria. However, the application of analytical TEM to organic systems presents some unique challenges, such as low contrast between phases, and electron beam sensitivity. In this review recent analytical TEM approaches to the nanoscale characterisation of two systems will be discussed: the hybrid collagen/mineral interface in bone, and the all-organic donor/acceptor interface in OPV devices.     

Electrical properties of polymer/metal interface in polymer light-emitting devices: electron injection barrier suppression

The electrical characterization of a high efficient multilayer polymer light emitting diode using poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] as the emissive layer and an anionic fluorinated surfactant as the electron transport layer was performed. For the sake of comparison, a conventional single layer device was fabricated. The density current vs. voltage measurements revealed that the conventional device has a higher threshold voltage and lower current compared to the surfactant modified device. The effective barrier height for electron injection was “suppressed”. The influence of the interfaces and bulk contributions to the dc and high frequencies conductivities of the devices was also discussed.     

Theoretical study of charge-induced defects at metal/polymer interface

Conducting polymers have attracted much attention concerning the possibility of their use as active components of electronic and optoelectronic devices. We use a molecular dynamics method with semi-empirical quantum chemistry at CNDO (complete Neglect of differential overlap) level to study the chemical interactions between aluminium atoms and trans-polyacetylene during the interface formation. Our results suggest that aluminium dimer (Al₂) bound to a polymer chain is energetically more favourable than the adsorption of isolated aluminium atoms. In both cases, the compound formation is accompanied by charge transfer between metal and polymer. As a result charge rearrangement among the polyacetylene atoms is induced. We shall describe the charge-induced structural relaxation of the trans-polyacetylene backbone which is accompanied by a local change in the electronic structure of the polymer, commonly called defects.     

Thermal conductance of metal interfaces at low temperatures

In the present work the dependence of the heat transfer coefficient between Cu and Sn, Cu and Pb, and Cu and W on the temperature and an external magnetic field has been measured. The preparation of the metal-metal junctions has been performed by melting so that a close contact at the interface was guaranteed. The heat transfer coefficient has been found by a steady-state measuring method. In the case of the Cu-Pb junction the heat transfer coefficient could be measured both in the superconducting and normal states. For all the metal—metal junctions in the normal state a linear temperature dependence of the heat transfer coefficients on the temperature has been found. In the superconducting state a strong reduction of the heat transfer coefficient has been observed. In addition, a theoretical calculation of the heat transfer coefficient on metal-metal interfaces is given. First we consider the scattering of electrons on a steplike potential barrier between two gases of free electrons. Then the thermal conductance due to scattering in an alloy layer is calculated. Such an alloy layer may arise from diffusion during the contact preparation. Comparison of these two cases with the experiments shows the thermal conductance at the interface is mainly determined by the electron scattering on lattice irregularities in the diffusion layer.     

A molecular perspective of water at metal interfaces

Water/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as corrosion, lubrication, heterogeneous catalysis and electrochemistry. Although many fields have contributed to rapid progress in the fundamental knowledge of water at interfaces, detailed molecular-level understanding of water/solid interfaces comes mainly from studies on flat metal substrates. These studies have recently shown that a remarkably rich variety of structures form at the interface between water and even seemingly simple flat surfaces. In this Review we discuss the most exciting work in this area, in particular the emerging physical insight and general concepts about how water binds to metal surfaces. We also provide a perspective on outstanding problems, challenges and open questions.     

The adhesion of metal/alumina interfaces

Cylinders of copper and nickel have been melted under various conditions to form sessile drops on alumina plaques. The resultant metal/ceramic adhesion at room temperature has been measured using the commonly adopted test in which the drops are pushed off the ceramic plaques. The stress system involved in the test has been analysed and it has been shown that the standard interpretation of the test, as a measure of interfacial shear strength, is not valid; the revised interpretation makes it a measure of adhesion in tension. Results for the Cu/Al₂O₃ and Ni/Al₂O₃ systems show that non-wetted interfaces can be strong and have strengths that are independent of contact-angle changes caused by wetting-temperature variations.     

The strength of metal/alumina interfaces

The room-temperature strengths of interfaces formed by melting aluminium, cobalt, gold, iron, nickel, palladium, silver, and uranium in contact with alumina have been measured. Correlations were sought between the strengths and the physical properties of the systems. Metals which formed void-free interfaces and were not subject to martensitic transformations bonded well to alumina. Metals subject to martensitic transformations (cobalt and uranium) were virtually non-adherent at room temperature.     

Crack propagation along polymer/non-polymer interfaces

Mechanisms of the propagation of crack fronts along interfaces between a glassy polymer and metal or glass are discussed. Specifically, the systems studied are Poly-Ethylene Terephthalate (PETG) spin-coated on Al, PETG-glass and PETG hot-pressed on Cr-sputtered glass. Cracks studied propagate in an Assymetric Double Cantilever Beam (ADCB) geometry. Dependence of microscopic crack front geometry on propagation speed is found. The local stress state is found to have an impact on macroscopic as well as microscopic crack front geometry. Simple lattice model calculations of propagating crack fronts illustrate the impact of disorder and residual stress state on propagation mechanisms and macroscopic crack front shape respectively.     

Surface analysis of polysiloxane/metal oxide interfaces

The interfaces between various types of silane-based primers and abraded mild-steel surfaces have been investigated using two surface-specific techniques in an attempt to ascertain the bonding mechanism between primer and metal. The XPS technique gave semi-quantitative information about the relative concentrations of primer and exposed steel while the SSIMS technique enabled the chemical state of the first few monolayers of surface to be elucidated. From some primer/metal systems the presence of FeSiO⁺ radicals was detected by SSIMS and it was found that the environmental resistance of structural adhesive joints, employing the various silane-based primers, could be directly related to the presence or absence of this radical.     

Heating rate dependent delamination of metal–polymer interfaces: experiments and modeling

Bimaterial interfaces in microelectronics packages are the most common regions of failure under thermo-mechanical excursions. In this work, we report experimentally observed role of heating rate on the delamination initiation and propagation across a metal-polymer interface in a microelectronic package. We observe that the rate of delamination propagation increases with increasing heating rate. When the heating rate increases, in addition to the higher amount of delamination growth per unit time, experimental results suggests that higher growth will also incur per unit temperature (loading). Correspondingly, the temperature at which complete delamination occur decreases. Using finite element modeling with cohesive interfaces, we provide a plausible explanation to this observed phenomenon. The analyses indicate that the mechanical behavior of the bimaterial interface is sensitive to both temperature and thermal rate.     

Local delamination on heavily deformed polymer–metal interfaces: evidence from microscopy

In this work the microstructure of interfaces present in heavily bi-axially deformed polymer-coated metal is studied. Cross sections of deformed polymer-coated steel are prepared using several polishing strategies, including the use of focused ion beam, and are imaged using optical microscopy and scanning electron microscopy. We find that the interfaces show significant details right down to the smallest scale observable with the preparation techniques used of about ~10 nm. Local delamination events at these deformed interfaces are observed and are found to be preferentially associated with overhanging parts on the interface. Overhanging parts are frequently observed, but only below a certain length-scale on the interfaces that are otherwise found to be self-affine up to a certain correlation length. The smallest detail includes the tail of the size distribution of the overhanging features. Together this suggests that the physical mechanisms determining the formation of critical features for adhesion operate at sub-grain level as well as at grain level.