Organic primer coatings loaded with environmentally harmful Cr(VI) corrosion inhibitive pigments still play an important role in corrosion protection of aluminium alloys for the aerospace industry. A potential green alternative coating system has recently been developed, loaded with lithium salt corrosion inhibitors. Under exposure to neutral salt spray, lithium salts leach from the organic coating into coating defects to induce the formation of a corrosion protective layer. In this work the composition and growth of this protective layer is investigated by time-of- ight secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS imaging is successfully applied to monitor the lateral spread of leaching lithium salts in artificial one-millimeter-wide scribes. The chemical composition of the protective layer is revealed by comparing the mass spectra of salt spray exposed scribe areas to the mass spectra of pseudoboehmite and aluminium-lithium layered double hydroxide reference samples. The insights obtained in this work have led to a thorough understanding of the formation mechanism of the protective layer and provide local chemical and structural information which can be linked to corrosion protection behavior.
Street canyons are generally highly polluted urban environments due to high traffic emissions and impeded dispersion. Green infrastructure (GI) is one potential passive control system for air pollution in street canyons, yet optimum GI design is currently unclear. This review consolidates findings from previous research on GI in street canyons and assesses the suitability of different GI forms in terms of local air quality improvement. Studies on the effects of various GI options (trees, hedges, green walls, green screens and green roofs) are critically evaluated, findings are synthesised, and possible recommendations are summarised. In addition, various measurement methods used for quantifying the effectiveness of street greening for air pollution reduction are analysed. Finally, we explore the findings of studies that have compared plant species for pollution mitigation. We conclude that the influences of different GI options on air quality in street canyons depend on street canyon geometry, meteorological conditions and vegetation characteristics. Green walls, green screens and green roofs are potentially viable GI options in existing street canyons, where there is typically a lack of available planting space. Particle deposition to leaves is usually quantified by leaf washing experiments or by microscopy imaging techniques, the latter of which indicates size distribution and is more accurate. The pollutant reduction capacity of a plant species largely depends on its macromorphology in relation to the physical environment. Certain micromorphological leaf traits also positively correlate with deposition, including grooves, ridges, trichomes, stomatal density and epicuticular wax amount. The complexity of street canyon environments and the limited number of previous studies on novel forms of GI in street canyons mean that offering specific recommendations is currently unfeasible. This review highlights a need for further research, particularly on green walls and green screens, to substantiate their efficacy and investigate technical considerations.
The ultra-low-angle microtomy (ULAM) technique has been developed to impart a cross-sectional, ultra-low-angle taper through polymeric materials such as coatings and paints. ULAM employs a conventional rotary microtome in combination with high-precision, angled sectioning blocks to fabricate the ultra-low-angle tapers. Subsequent investigation of the tapers produced by ULAM may be used in conjunction with X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (ToF-SIMS), for compositional depth profiling or ‘buried’ interface analysis. Variation in the selection of the ULAM taper angle and/or the analysis interval size employed enables depth resolution at the nanometre or micrometre scales to be achieved. In the work described here scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been employed to investigate the morphology and topography of the surfaces resulting from the ULAM tapering process. It is demonstrated that a correctly mounted polymeric sample, sectioned with a sharp microtome knife, displays little perturbation of the resulting polymeric surface after ULAM processing. Additionally, SEM analysis of the interface region between a poly(vinylidene fluoride) (PVdF) topcoat and polyurethane (PU) primer exposed by ULAM processing reveals that the interface region between the two coatings possesses a well-defined boundary. No evidence of polymeric smearing across the interface is observed. XPS compositional depth profiling across a ‘buried’ PVdF/PU interface, exposed by ULAM processing, is employed to demonstrate the utility of the ULAM technique.
The very thin native oxide film on stainless steel, of the order of 2 nm, is known to be readily modified by immersion in aqueous media. In this paper, XPS and ToF-SIMS are employed to investigate the nature of the air-formed film and modification after water emmersion. The film is described in terms of oxide, hydroxide and water content. The preferential dissolution of iron is shown to occur on immersion. It is shown that a water absorbed layer and a hydroxide layer are present above the oxide-like passive film. The concentrations of water and hydroxide appear to be higher in the case of exposure to water. A secure method for the peak fitting of Fe2p and Cr2p XPS spectra of such films on their metallic substrates is described. The importance of XPS survey spectra is underlined and the feasibility of C60+ SIMS depth profiling of a thin oxide layer is shown.
This study investigates the formation of a chromate conversion coating at Al–Cu–Fe–Mn intermetallic sites of an Al2219 alloy and the corrosion initiation at these sites in a 3.5% NaCl solution, using SEM, AES and EDX. Changes in the surface chemistry were monitored after progressive exposures to the solution up to 42 h. The coating was found to be thinner and more defective on the intermetallic. Initially, Al is dissolved and Al(OH)3 deposited on and around the intermetallic. After 42 h of exposure, Al(OH)3, Fe and Mn oxides and small particles of elemental Cu are deposited as corrosion products.
To investigate the role of intermetallic particles in the localised corrosion of AA7075-T6, three particles were monitored over 16 hours immersion in 3.5 wt.% KCl solution. These were examined using Auger electron spectroscopy, energy dispersive x-ray spectroscopy, scanning Kelvin probe force microscopy and focused ion beam-scanning electron microscopy. Despite similar Volta potential measurements, the corrosion microchemistry varied significantly with composition. A Al7Cu2Fe intermetallic resulted in trenching while a (Al,Cu)6(Fe,Cu) intermetallic showed crevice corrosion and sub-surface intergranular corrosion and a Al12Fe3Si intermetallic appeared to be galvanically inactive but showed crevice formation at the matrix interface and sub-surface intergranular corrosion.
Lithium scribed in vacuum and a particle of lithium oxide were analysed by AES and lithium metal exposed to atmosphere for <1 min was analysed by XPS. The oxide particle embedded in the host metal was analysed at low and high take off angles. AES spectra acquired demonstrate the change in the KLL structure with increasing oxygen concentration. Survey spectra as well as high resolution narrow spectra were acquired and are presented. The presence of lithium carbonate, together with the oxide, formed in air, was confirmed by XPS as it is not easily resolvable using AES.
As-received beryllium and beryllium oxide were analysed by X-ray photoelectron spectroscopy and Auger electron spectroscopy. Additionally, beryllium metal was scribed in vacuum and analysed by AES. Survey spectra together with high-resolution spectra were acquired in XPS and AES mode and are presented here. The binding energies of the beryllium and the beryllium oxide Be 1s peaks were found to be 110.5 and 113.4 eV respectively, as collected by XPS, and the kinetic energies of the primary metal and oxide KLL Auger transitions were found to be 103.0 and 93.6 eV respectively, as collected by AES. Three loss peaks are also observed at 87.1, 78.0 and 67.2 eV in the AES spectrum of beryllium oxide
Herein we report the construction of a Wagner chemical state plot for beryllium containing the: metallic, oxide, nitride and carbide forms of beryllium by combining electron beam induced AES and XPS data. AES and XPS values were collected from metallic beryllium mechanically abraded in vacuum, bulk and native beryllium oxide and homogeneous secondary-phase beryllium nitride and beryllium carbide inclusions. XPS data for beryllium nitride and carbide were obtained from the literature.
As-received beryllium, beryllium scribed in vacuum and beryllium oxide were analysed by Auger Electron Spectroscopy. As-received beryllium was analysed at low and high take off angles. Spectra produced demonstrate the change in the KLL structure with increasing oxygen concentration. Survey spectra as well as high resolution Be KLL and O KLL transitions were collected and are presented.
Four samples of well-defined silicon-germanium alloys were used as standards for calibration purposes to allow accurate quantification of silicon-germanium-on-insulator (SGOI) microelectronic devices using Auger electron spectroscopy. Narrow Si KLL and the Ge LMM, high resolution Si KL_2,3L_2,3 and Ge L_3M_4,5M_4,5 together with survey spectra were collected and are presented from each sample. A matrix effect was observed for silicon in germanium and calculated as 0.85 and 0.95 for the Ge77.5Si22.5 Ge52.4Si47.6 alloys respectively.
SFA Sani, GA Mahdiraji, ASS Shafiqah, GW Grime, V Palitsin, SJ Hinder, N Tamchek, HAA Rashid, MJ Maah, JF Watts, DA Bradley (2015)XPS and PIXE Analysis of Doped Silica Fibre for Radiation Dosimetry, In: JOURNAL OF LIGHTWAVE TECHNOLOGY33(11)pp. 2268-2278
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Most tyre models used in vehicle dynamics simulations are parameterised with data obtained on a flat-track test rig, where the tyre is commonly driven on sandpaper. The resultant models are typically very accurate at low to medium slip conditions. At high slip, the prediction of forces and moments of a tyre rolling on surfaces other than sandpaper is less reliable as this condition is dominated by the rubber-road friction characteristics. To extend the validity of tyre models derived from sandpaper surface measurements to road surfaces, this paper explores the use of frictional behaviour of tread rubber obtained with a purpose-built rubber friction measurement system. Since rubber friction depends on many variables, tests have been carried out under controlled conditions in order to obtain accurate and repeatable data. Friction measurements were performed on sandpaper and incorporated into a brush-type tyre model to recreate the flat-track measurements of the full tyre. Preliminary results indicate the benefits and potential of detailed knowledge on the frictional behaviour for accurately modelling tyre forces and moments.
A new protocol using time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been developed to identify the deposition order of a fingerprint overlapping an ink line on paper. By taking line scans of fragment ions characteristic of the ink molecules (m/z 358.2 and 372.2) where the fingerprint and ink overlap and by calculating the normalised standard deviation of the intensity variation across the line scan, it is possible to determine whether or not a fingerprint is above ink on a paper substrate. The protocol adopted works for a selection of fingerprints from four donors tested here and for a fingerprint that was aged for six months; for one donor, the very faint fingerprints could not be visualized using either standard procedures (ninhydrin development) or SIMS and therefore the protocol correctly gives an inconclusive result.
The interactions of polymeric methylene diphenyl di‐isocyanate (pMDI) and a model Fe–Cr alloy have been studied by X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Films of two different thicknesses have been investigated: one with an extremely thin pMDI layer in which the interfacial chemistry can be probed directly and a thicker one in which sputter profiling using cluster ions is necessary to expose the interface chemistry for direct analysis. Multivariate analysis (MVA), using principal component analysis (PCA) and nonnegative matrix factorisation (NMF), has been used to identify specific ions associated with the interfacial region of the ToF‐SIMS sputter depth profile and chemical species from the XPS sputter depth profile. As an unsupervised method, this avoids an unconscious bias on the part of the analyst. Specific ions associated with pMDI interactions with both Fe and Cr allow the proposal of two complementary reaction mechanisms, supported by the XPS data. A range of cluster ions is used in this investigation, but the bulk of the work used argon clusters for the XPS depth profiles and Buckminster Fullerene projectiles for the ToF‐SIMS analyses. To ensure that such data were directly comparable, the ToF‐SIMS sputter profiles were repeated in a different system of the same type using argon cluster ions.
The present work has been conducted in order to investigate the quality of impregnation of unsaturated polyester resin across the bleached alfa pulpboard, and evaluate the potential for the obtained compound to serve a purpose as a useful composite material.
The ultra-low-angle Microtomy (ULAM) method was used to study the quality of impregnation of alfa fibres by unsaturated polyester resin. The cross-section through the bleached alfa pulpboard/unsaturated polyester material, which emphasised the impregnation zone, was analysed using X-ray photoelectron spectroscopy (XPS). The profiles obtained by the XPS line scan analysis of the tapered surface show a well-defined impregnation region. The depth of this region has been characterised using two chemical constituent peaks, which showed an approximate depth of impregnation of about 20 to 40 μm, on the basis of C-OH/C-O-C, components which are exactly complementary to the β-shifted carbon signal, employed as an analogue for the unsaturated polyester. A comparative study was also carried out between the mechanical and tribological properties of the composite material and the pure unsaturated polyester resin, in order to complement the results obtained by surface analysis. The comparison shows better stiffness, tensile strength at break and wears resistance in the reinforced unsaturated polyester resin.
The results of this research demonstrate a good quality of impregnation of unsaturated polyester resin across the short alfa fibres which present the matrix and reinforcement of the studied composite material.
Porosity was measured for 21 AA2319 wire and arc additive manufacture (WAAM) panels built using different wire batches, cold metal transfer (CMT) modes, wire feed speed (WFS) and travel speed (TS). Image analysis software was used to measure the porosity across two different planes, totalling an area of 84 mm2 approximately 20 layers in height. Porosity was not strongly dependent on CMT mode, WFS and WFS to TS ratio within the ranges tested but batch-to-batch variability in feedstock wire had a significant influence on area of porosity and size distribution. Wire characterisation showed that porosity did not appear to depend on bulk composition but was influenced by surface finish. Surface finish could affect hydrogen content on the wire surface and arc stability which would affect porosity. Further investigation of the relationships between surface finish and surface hydrogen content, and surface finish and arc stability is required to understand porosity formation in aluminium WAAM components.
New concepts of surface modifications aimed at the enhancement of alkali resistance of basalt fibresrequire research work on chemical composition of interacting surface layers as well as knowledge aboutfundamental processes of basaltic glass dissolution. Therefore, two model basalt fibres manufactured outof subalkaline and alkaline rock material were leached in NaOH solution at a temperature of 80◦C for upto 11 days. The formation of a corrosion shell was observed in both cases and was analyzed by SEM/EDX.The model fibres out of subalkaline rocks show dissolution kinetic, which is two-staged, whereas themore alkaline fibre reflects a linear one. The complex composition of basalt fibre is detected by EDX andXPS. The surface of basalt fibres is rich in Si and Al. XPS high resolution spectra provide information onoxidation state of iron.
Timber is a composite material ordered over many length scales. The basic building blocks of timber are wood fibres, hollow tube like elements which are responsible for both water transport and load bearing within trees, (Ansell, 2015). The fibres can be separated from bulk timber in a process known as defibrilation, a key industrial process for the production of Medium Density Fibreboard (MDF). MDF is a composite material formed of fibres and adhesive, which is used widely in the construction industry among innumerable others.
A dual purpose mass spectrometer chamber capable of performing molecular beam scattering (MBS) and temperature programmed desorption (TPD) is detailed. Two simple features of this design allow it to perform these techniques. Firstly, the diameter of entrance aperture to the mass spectrometer can be varied to maximize signal for TPD or to maximize angular resolution for MBS. Secondly, the mass spectrometer chamber can be radially translated so that it can be positioned close to the sample to maximize signal or far from the sample to maximize angular resolution. The performance of this system is described and compares well with systems designed for only one of these techniques.
Wood fibers are of the order of a few millimeters in length and a hundred micrometers in width, which makes it difficult to mechanically characterize them using standard methods, such as tensile testing. This work, builds on the development of a novel method to evaluate the stiffness of wood fibers, which uses the cantilever of an atomic force microscope (AFM) to carry out three-point bending. This is done by placing the fibers across a two millimeter trench, whereupon the AFM engages to the center and both applies loads and records the resulting displacements. Testing using this method has been confined to a single species of wood, pinus sylvestris (Scots pine), but there is a significant spread in the modulus of the fibres tested. This is not entirely surprising as a sample of wood consists of several different types of fibre, including, for example, heartwood and sapwood, early wood and latewood. These different fibres vary slightly in size and wall thickness.
Here, Weibull statistics is used to investigate the correlation between samples in a dataset, and describe the magnitude of the correlation, in order to distinguish between fibre types and to provide greater clarity of the modulus associated with different types of fibre.
The effects of flame treatment on the surface characteristics of four injection moulded, automotive grade, polypropylene samples, pigmented with carbon black, have been studied. The changes in wettability have been monitored by water contact angle and Dyne inks, whilst XPS has been used to establish the changes in oxygen surface concentration as a function of flame treatment. As expected carbon pigmented and carbon plus talc filled samples showed a significant increase in oxygen concentration and surface wettability with increasing flame treatment. For the glass filled sample this effect was not so pronounced. Inspection of the XPS valence band shows initial attack in the flame treatment process to be at the pendant methyl group of the poly(propylene) molecular architecture. XPS in conjunction with cluster ion bombardment shows the depth of surface treatment to range from ca. 7 nm at one pass of flame treatment to some 15 nm following seven passes. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) shows the segregation of characteristic additives during the injection moulding process which are subsequently greatly reduced during the flame treatment. As treatment level increases oxygen increases from mono-atomic to diatomic attachment. This work extends the understanding of the flame treatment of moulded polyolefines and establishes that the beneficial properties conferred are the result of the conjoint effect of the oxygenation of the bulk polymer along with the removal of surface segregated processing aids.
Timber is one of the oldest building materials used by mankind, and its environmental and sustainable credentials are certainly more persuasive than those of concrete or brick. One only has to survey the historic building stock in the UK to see that, with good design, timber framed structures can last for many hundreds of years. However, when degradation sets in, the majority of the existing historic UK timber framed buildings receive repairs that are either resin assisted, screwed, or bolted. This is frequently required at beam ends, where the timber has traditionally been interfacing with a moisture absorbent and retaining material, such as brick, which focuses and exacerbates degradation processes.
Enhancement of the surface wettability and surface free energy of thermoplastic materials is an effective way of improving their adhesion and consequently the adhesive joint strength. A nanosecond pulsed Nd:YAG laser was selected in this work to provide energetic treatment of PEEK surfaces, in order to investigate its effectiveness in increasing the performance of lap shear adhesive joints. The laser was used to irradiate the PEEK, by rastering a spot of ca. 1 mm diameter across a large area. The resulting surfaces were characterised using single lap shear testing, confocal laser scanning microscopy, contact angle analysis, FT-IR, XPS and ToF-SIMS. Single lap shear testing of PEEK joints showed that the strength of adhesively bonded joints is greatly improved by laser treatment, up to 13 times that of untreated PEEK. Confocal laser scanning microscopy showed that the higher laser powers intensities (≥ 107 W mm-2) disrupted the surface of the PEEK more than the lower laser powers intensities (< 107 W mm-2), but also showed that, as expected, only some of the surface is treated by the laser. Contact angle analysis showed a decrease in water contact angle with increasing laser power intensity, and the derived surface free energy increased accordingly. FT-IR in the specular reflectance mode showed no discernible change but XPS and ToF-SIMS did, suggesting that laser treatment only affects the near surface at the extremity of the 1-2 μm sampling depth. XPS showed a decrease in the carbon/oxygen ratio of PEEK on treatment, indicating that oxygen-containing functional groups were being created at the surface. XPS also suggested a cleaning mechanism at a laser intensity of 7.83 x 10⁶ W mm-², progressing to surface modification from a laser intensity of 107 W mm-² and above. ToF-SIMS confirmed that laser treatment cleans the surface of PEEK of extraneous material.
A number of analytical techniques were applied to investigate changes to the surface of unsized boron-free E-glass fibres after thermal conditioning at temperatures up to 700 °C. Novel systematic studies were carried out to investigate the fundamental strength loss from thermal conditioning. Surface chemical changes studied using X-ray photoelectron spectroscopy (XPS) showed a consistent increase in the surface concentration of calcium with increasing conditioning temperature, although this did not correlate well with a loss of fibre strength. Scanning electron microscopy fractography confirmed the difficulty of analysing failure-inducing flaws on individual fibre fracture surfaces. Analysis by atomic force microscopy (AFM) did not reveal any likely surface cracks or flaws of significant dimensions to cause failure: the observation of cracks before fibre fracture may not be possible when using this technique. Fibre surface roughness increased over the whole range of the conditioning temperatures investigated. Although surface roughness did not correlate precisely with fibre strength, there was a clear inverse relationship at temperatures exceeding 400 °C. The interpretation of the surface topography that formed between 400–700 °C produced evidence that the initial stage of phase separation by spinodal decomposition may have occurred at the fibre surface.
G Rebord, N Hansrisuk, B Lindsay, C Lekakou, GT Reed, JF Watts (2008)Electrofunctional Polymer Nanocomposites, In: ESTC 2008: 2ND ELECTRONICS SYSTEM-INTEGRATION TECHNOLOGY CONFERENCE, VOLS 1 AND 2, PROCEEDINGSpp. 1401-1405
The current work examines using the natural features of wood to form a ‘speckle pattern’ for Digital Image Correlation (DIC) techniques, rather than using a spray applied paint. The work further investigates the impact of applying a spray painted speckle pattern and the impact on both the timber under investigation and the corresponding results.
An advanced method for joining fibre reinforced polymers to metallic substrates has been investigated. The solution was shown to offer improvements in strength, toughness (as indicated by the area under the load-displacement curve) and damage tolerance (residual strength after impact) under a range of test conditions.
Data produced using both unsized and aminopropyltriethoxysilane (APS) coated fibre will be shown and discussed. By applying a novel method of single fibre thermal conditioning (sf-TC) it was found that retained fibre strength is, in some cases, underestimated and that the temperature range 400-500 °C is the most critical for thermally induced strength loss. This is not related to degradation of the APS surface coating, but rather is likely linked to fundamental changes occurring in the glass network or at the fibre surface. X-ray Photoelectron Spectroscopy (XPS) analysis of treated fibres was performed, but it was not possible to measure any significant changes in surface chemical state. Analysis of water volatilized from unsized fibre was performed using a furnace connected to quadropole mass spectrometer. An asymptotic minimum in volatilized water is reached between 400-500 °C.
The surface of 316 stainless steel has been modified using cold atmospheric plasma (CAP) to increase the surface free energy (by cleaning the and chemically activating the surface)IN preparation for subsequent processes such as painting, coating or adhesive bonding. The analyses carried out, on CAP treated 316 stainless steel surfaces, includes X-ray photoelectron spectroscopy (XPS), imaging XPS (iXPS), and surface free energy (SFE) analysis using contact angle measurements.The CAP treatment is shown to increase the SFE of as-received 316 stainless steel from ~39 mJ m-1 to >72 mJ m-1 after a short exposure to the plasma torch. This was found to correlate to a reduction in adventitious carbon, as determined by XPS analysis of the surface. The reduction from ~90 at% to ~30% and ~39 at%, after being plasma treated for 5 minutes and 15 seconds respectively, shows that the process is relatively quick at changing the surface. It is suggested that the mechanism that causes the increase in surface free energy is chain scission of the hydrocarbon contamination triggered by free electrons in the plasma plume followed by chemical functionalisation of the metal oxide surface and some of the remaining carbon contamination layer.
Advanced hybrid joints, which incorporate a specially designed array of macro-scale pins that provide mechanical interlocking reinforcement, have been developed in order to address the challenges associated with joining fibre reinforced composites to metals. In the present work, important joint characteristics including strength, mechanical fatigue, damage tolerance and durability have been studied and discussed. The results indicate that with advanced hybrid joints it is possible to achieve the benefits of the respective bonded and bolted systems but with virtually zero net weight gain, or conceivably a weight reduction as the increased performance of the hybrid scheme could facilitate smaller joints. The authors also present initial results from a comprehensive manufacturing and scalability trial, and demonstrate that low-cost, large-scale manufacture of hybrid joints is now feasible.
The interfacial region of a model, multilayer coating system on an aluminium substrate has been investigated by high resolution time-of-flight secondary ion mass spectrometry (ToF-SIMS). Employing ultra-low-angle microtomy (ULAM), the interface between a poly(vinylidene difluoride) (PVdF) based topcoat and a poly(urethane) (PU) based primer ‘buried’ over 20μm below the PVdF topcoat’s air/coating surface was exposed. Imaging ToF-SIMS and subsequent post-processing extraction of mass spectra of the ULAM exposed interface region and the PVdF topcoat and PU primer bulks indicates that the material composition of the polymer-polymer interface region is substantially different to that of the bulk PVdF and PU coatings. Analysis of the negative ion mass spectra obtained from the PVdF/PU interface reveals the presence of a methacrylate based component or additive at the interface region. Reviewing the topcoat and primer coating formulations reveals the PVdF topcoat formulation contains methyl methacrylate (MMA)/ethyl acrylate (EA) acrylic co-polymer components. Negative ion ToF-SIMS analysis of an acrylic co-polymer confirms it is these components that are observed at the PVdF/PU interface. Post-processing extraction of ToF-SIMS images based on the major ions of the MMA/EA co-polymers reveals these components are observed in high concentration at the extremities of the PVdF coating i.e. at the polymer-polymer interface but are also observed to be distributed evenly throughout the bulk of the PVdF topcoat. These findings confirms that a fraction of the MMA/EA acrylic co-polymers in the formulation segregate to the topcoat-primer interface where they enhance the adhesive properties exhibited by the PVdF topcoat towards the underlying PU primer substrate.
Ni3s, Ni3p and Ni2p x-ray photoelectron spectra of mono-and binuclear carboxylate complexes of nickel with various geometry of metal ions environment are obtained. The spectra are calculated in an isolated ion approximation. The dependence of the spectral profiles and the structure of the charge-transfer satellites on the structure of the immediate environment of nickel atoms is established. The data obtained support the results of X-ray diffraction and magnetic studies.
There is a growing desire for wearable sensors in health applications. Fibers are inherently flexible and as such can be used as the electrodes of flexible sensors. Fiber-based electrodes are an ideal format to allow incorporation into fabrics and clothing and for use in wearable devices. Electrically conducting fibers were produced from a dispersion of poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT: PSS). Fibers were wet spun from two PEDOT: PSS sources, in three fiber diameters. The effect of three different chemical treatments on the fibers were investigated and compared. Short 5 min treatment times with dimethyl sulfoxide (DMSO) on 20 μm fibers produced from Clevios PH1000 were found to produce the best overall treatment. Up to a six-fold increase in electrical conductivity was achieved, reaching 800 S cm−1, with no loss of mechanical strength (150 MPa). With a pH-sensitive polyaniline coating, these fibers displayed a Nernstian response across a pH range of 3.0 to 7.0, which covers the physiologically critical pH range for skin. These results provide opportunities for future wearable, fiber-based sensors including real-time, on-body pH sensing to monitor skin disease.
Bowei Li, Yuren Xiang, Imalka Jayawardena, Deying Luo, John Watts, Steven Hinder, Hui Li, Victoria Ferguson, Haitian Luo, Rui Zhu, Ravi Silva, Wei Zhang (2020)Tailoring Perovskite Adjacent Interfaces by Conjugated Polyelectrolyte for Stable and Efficient Solar Cells, In: Solar RRL
Interface engineering is an effective means to enhance the performance of thin‐film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open‐circuit voltage (Voc), short‐circuit current density (Jsc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35–55% at room temperature. All of these improvements are attributed to the functional PFN‐I layers as they provide favorable interface contact and defect reduction.
Scanning Kelvin probe force microscopy has been employed to examine the galvanic activity of a range of second phase particles present in beryllium that are believed to have a role in the localised corrosion of the metal. These particles were characterised by means of scanning electron microscopy, energy dispersive x-ray spectroscopy and scanning Kelvin probe force microscopy. The particles were found to have a range of potentials which varied with the particle type. All particles were found to be more noble than the beryllium matrix.
S Diplas, S Jorgensen, J Tafto, T Tonnessen, T Knutsen, J Lehrmann, T Valand, ML Abel, JF Watts (2006)Probing the electronic structure of Ni-X, (X = B, S, P) catalysts with XPS, In: SURFACE AND INTERFACE ANALYSIS38(4)pp. 238-242
The nuclear industry has used hard chromium plate for many years but is seeking alternatives, due to the adverse health effects of Cr(VI) employed in electroplating. In this study, testing and analysis regimes for the comparison of the sliding wear performance of candidate materials have been established and the performance of WC-(W,Cr)2C-Ni has been compared with that of hard chromium plate.
WC-(W,Cr)2C-Ni was applied to Inconel 625 substrates using a detonation gun thermal spray technique. Sliding wear testing was performed using a ball-on-flat configuration reciprocating tribometer at 20 °C in three environments: dry, deionised water and simulated nuclear reactor water chemistry. Wear rates have been evaluated, using both mass and volume loss, and the worn samples were analysed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).
The WC-(W,Cr)2C-Ni coating had a broadly comparable wear performance to hard chromium plate in all three environments. There were differences between deionised and borated water, such that the latter needs to be used in further evaluation. SEM and XPS analyses enabled the wear mechanisms for WC-(W,Cr)2C-Ni and HCP to be elucidated, including pull-out and tribolayer formation. XPS has shown that the tribolayer on WC-(W,Cr)2C-Ni is stratified and undergoes chemical changes as a result of wear.
DR Baer, AS Lea, JD Geller, JS Hammond, L Kover, CJ Powell, MP Seah, M Suzuki, JF Watts, J Wolstenholme (2010)Approaches to analyzing insulators with Auger electron spectroscopy: Update and overview, In: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA176(1-3)pp. 80-94
ELSEVIER SCIENCE BV
This paper provides an updated overview, intended to be of practical value to analysts, of methods that can be applied to minimize or control the build-up of near-surface electrical charge during electron-induced Auger electron spectroscopy (AES). Although well-developed methods can be highly effective, dealing with insulating or ungrounded samples for which high spatial resolution is needed remains a challenge. Examples of the application of methods involving low-energy ion sources and sample thinning using a focused ion beam that can allow high-resolution measurements on a variety of samples are highlighted. The physical bases of newer and traditional methods are simply described along with strengths and limitations of the methods. Summary tables indicate methods that can be applied to most AES spectrometers, methods that require special instrumental capabilities and methods that require special sample preparation or mounting.
X-ray photoelectron spectroscopy (XPS) was carried out to analyse a commercially available pentanedioic acid powder. XPS spectra were obtained using incident monochromatic Al Ka radiation at 1486.6 eV. A survey spectrum together with O 1s and C 1s core level spectra are presented.
The potential for the use of X-ray photoelectron spectroscopy (XPS) in forensic science is reviewed, taking as a starting point a series of examples and case histories this review speculates on other areas where XPS may be able to make a contribution. The topics that are considered include chemical speciation of fingerprints, thin layers deposited on substrates as a result of explosions and/or fire, particulate materials and cosmetics and finally sequestration of marker elements and molecules on surfaces. It is concluded that XPS has much to offer the forensic science community but investigations may be hampered by the need to compare crimes scene specimens with known standards. Until this issue is addressed it is likely that XPS will continue to be used on an ad hoc basis for particularly challenging specimens in high profile cases.
Thin films of LiH and its corrosion products were studied using temperature programmed decomposition (TPD), x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Thin films were grown on Ni(100) in an ultra high vacuum system using an electron beam evaporator. Characteristic Li KLL AES peaks were identified for Li, LiH, Li2O and LiOH which facilitated identification of thin film composition. XPS of the O 1s region revealed three distinct chemical shifts which were attributed to Li2O, LiOH and chemisorbed H2O. We show that exposing LiH to very low H2O partial pressures results in formation of LiOH/Li2O domains on LiH. We also show that these XPS peaks can be linked to reaction mechanisms in the TPD profiles. TPD traces have been explicitly modelled to determine the activation energies of the reactions and compare favourably with previous measurements on bulk LiH samples.
Izabela Jurewicz, Rosa Garriga, Matthew J Large, Jake Burn, Niki Bardi, Alice AK King, Eirini Velliou, John Watts, Steven Hinder, Edgar Muñoz, Alan B Dalton (2018)Functionalization of Silver Nanowire Transparent Electrodes with Self-Assembled 2-Dimensional Tectomer Nanosheets, In: ACS Applied Nano Materials1(8)pp. 3903-3912
American Chemical Society
Here, we describe the unusual self-assembly of amine-terminated oligoglycine peptides into extended two-dimensional sheets in the presence of silver nanowires. The resulting tectomer sheets are shown to have a strong affinity for the nanowires through a charge-transfer interaction as evidenced by X-ray photoelectron spectroscopy. We show that extended assemblies of metal-peptide hybrids offer additional augmentative functionalities, for instance, the tectomer sheets are hydrophobic in nature and act as a protective layer preventing oxidation and degradation of the nanowires when exposed to atmospheric conditions. Moreover, for silver nanowire percolating networks the presence of the peptide markedly increases the overall electrical conductivity through mechanical squeezing of wire-wire junctions in the network. The peptide-metal interface can be controlled by pH stimulus thus potentially offering new directions where silver nanowire assemblies are used for transparent electrodes ranging from antimicrobial coatings to biosensors.
X-ray photoelectron spectroscopy (XPS) was carried out to analyse a commercially available propanedioic acid (malonic acid) powder. XPS spectra were obtained using incident monochromatic Al Ka radiation at 1486.6 eV. A survey spectrum together with O 1s and C 1s core level spectra are presented. The presence of characteristic carbon and oxygen photoelectrons peaks allows the use these results as a reference for dicarboxylic acids.
Post-manufacturing thermal treatments are commonly employed in the production of hip replacements to reduce shrinkage voids which can occur in cast components. Several studies have investigated the consequences of these treatments upon the alloy microstructure and tribological properties but none have determined if there are any biological ramifications. In this study the adsorption of proteins from foetal bovine serum (FBS) on three Co-Cr-Mo ASTM-F75 alloy samples with different metallurgical histories, has been studied as a function of protein concentration. Adsorption isotherms have been plotted using the surface concentration of nitrogen as a diagnostic of protein uptake as measured by X-ray photoelectron spectroscopy. The data was a good fit to the Langmuir adsorption isotherm up to the concentration at which critical protein saturation occurred. Differences in protein adsorption on each alloy have been observed. This suggests that development of the tissue/implant interface, although similar, may differ between as-cast (AC) and heat treated samples.
Commercially grown, multi-walled carbon nanotubes (MWNTs), available in kilogramme quantities from three commercial suppliers have been characterised using a number of analytical techniques. The catalysts used in the growth of the MWNTs are identified by energy dispersive X-ray spectroscopy (EDX) and different growth mechanisms are postulated to explain the various structures present in the MWNT stock in its as-supplied form. A tightening of the agglomerate structures during purification and functionalisation is shown using scanning electron microscopy (SEM) and confirmed more qualitatively using pore-size distributions obtained using the Brunauer–Emmett–Teller (BET) method and non-local density functional theory (NLDFT) calculations. Differences in thermal stability are shown using thermogravimetric analysis (TGA) and are related back to the residual catalysts present. X-ray photoelectron spectroscopy (XPS) is used to confirm functionalisation of certain grades and Raman spectroscopy is used to investigate the level of defects present.
Peak-fitting has been performed on a series of peaks obtained by ToF-SIMS analysis in order to assess whether information may be obtained from this procedure on the samples’ characteristics. A variety of samples were examined including a range of treatments for aluminium leading to different surface roughnesses, polymer films with a range of polydispersities, molecular weight and thicknesses as well as aluminium samples with adsorbed adhesion promoters on the surface. Variation of peak-fitting was assessed by varying the peak intensity, full width at half maximum and peak asymmetry. Although further studies are needed it is possible to say that the peak width increases with roughness whereas peak asymmetry seems to be related to oxide thickness. Polymer characteristics do not seem to influence the width whereas the peak asymmetry increases either versus molecular weight or polydispersity. A possible assumption is that the peak asymmetry relates to the ion formation processes. Additional work with varying polymer films thickness indicates that both FWHM and peak asymmetry may be related to sample charging and this could be used for assessment of film thicknesses. Finally, peak-fitting was used to obtain a more reliable peak area when peaks are too close in mass to use current methods.
Early stage oxidation of a dilute depleted uranium-molybdenum alloy was analysed in situ under UHV conditions by AES and XPS. At the equivalent of less than 300 ns at 1 atm O2, U-5Mo oxidises to form stoichiometric UO2. No molybdenum oxidation is observed. After an oxygen dose of approximately 39 L, the oxide layer approached a limiting thickness of approximately 2.4 nm. The oxidation kinetics followed a logarithmic rate law, with the best fit to the experimental data for the oxide thickness, d, being given by d = 1.26 log(0.12t + 0.56). Changes in oxygen KLL and 1s peak positions associated with transformation from chemisorbed oxygen to metal oxide were observed at similar oxygen doses of 2.3 and 2.6 L O2 by AES and XPS respectively, which opens up the possibility of using well characterised XPS chemical information to inform Auger peak shifts.
X-ray photoelectron spectroscopy (XPS) was carried out to analyse a commercially available butanenedioic acid (succinic acid) powder. XPS spectra were obtained using incident monochromatic Al Ka radiation at 1486.6 eV. A survey spectrum together with O 1s and C 1s core level spectra are presented. The presence of characteristic carbon and oxygen photoelectrons peaks allows the use these results as a reference for dicarboxylic acids.
This paper considers the effects of an atmospheric plasma treatment (APT) on the surface properties of an amine cured carbon fibre/epoxy resin composite, and how those effects manifest over time. In particular, the ability of the APT to remove a thin layer of silicone-containing, proprietary, release agent (Chemlease® 41 EZ), typically used in the production of composite components, has been investigated. It was concluded that the reduction in water contact angle (WCA) after APT for both the solvent wiped and contaminated surfaces was as a result of an increase in oxygen containing species at the surface, as determined through X-ray photoelectron spectroscopy (XPS). Further, it was found that the APT slightly reduced the failure strength of lap shear specimens for solvent wiped surfaces, whereas an increase in failure strength was observed for silicone contaminated samples. WCA and XPS results suggest that the contaminant layer was not removed, but instead transformed to a more stable inorganic form.
Model samples of the interface of an adhesive joint containing small levels of aminopropyl triethoxysilane (APS) have been prepared in order to examine the interface formed with an aluminium substrate. X-ray photoelectron (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS) has been used to analyse and image the interface region in between the aluminium and an epoxy adhesive in order to ascertain the reactions by the organosilane, present as a minor component within the system. It was found that APS was present at the interface between the adhesive and the substrate and that it had reacted with the substrate forming a covalent bond and was also crosslinked within the adhesive. Evidence of near to full hydrolysis of APS is also present within the spectra.
Mechanical properties of individual wood fibres and the characterisation of the interaction between wood fibres and resins are of interest to the composite wood panel industry and others involved in the fabrication of engineered wood products. However, the size of such fibres typically a few millimetres in length, makes characterisation of their mechanical properties difficult. Gripping fibres is problematic, not to mention the measurement of meaningful load displacement data. Using a novel three point bend test technique, the Young’s moduli of single wood fibres were determined. Fibres were placed on a specially designed test rig and a scanning probe microscope was used to apply a load and to measure the deflection at the centre of each fibre. A model of the fibre was produced in order to facilitate data analysis. The technique proved to be feasible, resulting in an average Young’s modulus value of 24.4 GPa for Pinus Sylvestris softwood fibres. This compares well with other values in the literature, but there is scope for improvement in the methodology to lead to more accurate measurements.
Time of flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) have been employed to study the interfacial interaction between polymeric methylene diphenyl diisocyanate (PMDI) and aluminium produced by the deposition of a thin PMDI layer on the aluminium, in order to improve adhesion and/or abhesion performance. When the PMDI concentration increases, the intensity ratio fragments indicative of the reaction product with water (m/z = 106 u: C7H8N+) to that of isocyanate group (m/z = 132 u: C8H6NO+) decreases. A very thin MDI layer on oxidised aluminium samples exhibits lower 106/132 ratio than degreased samples as a result of less hydroxide/hydroxyl spices on the surface. This suggests that water reactions occur both at the surface of PMDI and at the PMDI/aluminium interface. The variation of the PMDI chemistry has also been studied by exposing PMDI treated samples to the air for various periods of time (a few hours to 14 days), in order to assess the reaction of the PMDI surface and PMDI/aluminium interface. At the interface, the yield of reaction with water is limited because of the finite amount of hydroxyl groups on the aluminium surface, and the water reaction is completed in a short period of time. However, the PMDI surface continues to react with water from the atmospheric. This methodology was also used to establish the presence of specific interactions at the PMDI/aluminium interface, and a fragment indicative of covalent bond formation between PMDI and aluminium (AlCHNO3-) is observed at the interface.
Advanced hybrid joints, which incorporate a specially designed array of macro-scale pins that provide mechanical interlocking reinforcement, have been developed in order to address the challenges associated with joining fibre reinforced composites to metals. In the present work, important joint characteristics including strength, mechanical fatigue, damage tolerance and durability have been studied and discussed. The results indicate that with advanced hybrid joints it is possible to achieve the benefits of the respective bonded and bolted systems but with virtually zero net weight gain, or conceivably a weight reduction as the increased performance of the hybrid scheme could facilitate smaller joints. The authors also present initial results from a comprehensive manufacturing and scalability trial, and demonstrate that low-cost, large-scale manufacture of hybrid joints is now feasible
Thin films of aminopropyltriethoxysilane (APS) have been deposited on grit-blasted aluminium and dried at four different temperatures: room temperature (RT), 50, 93 and 120°C respectively. These specimens were prepared in order to assess the occurrence of the three important reactions known to take place when using silanes as films and/or primers: hydrolysis in the absence of water, condensation with the substrate, i.e. covalent bond formation and crosslinking or self-condensation. Analyses performed using X-ray photoelectron spectroscopy (XPS) indicate that the films reduce in thickness with temperature and that the type of silicon bonding changes mostly above 50°C. Time of flight secondary ion mass spectrometry (ToF-SIMS) reveals that covalent bonding of APS on aluminium occurs at all temperatures used in this study as well as showing that the films are close to being fully hydrolysed. It is also possible to assess the presence of crosslinking within the films.
The migration and segregation of a minor silicone containing additive in a multilayer, organic coating system has been investigated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The silicone containing additive employed was the most compatible thermally stable, polyester modified poly(dimethyl siloxane) (PDMS) flow agent. A polyester/polyurethane (PU) based primer and a poly(vinylidene difluoride) (PVdF) based topcoat on an aluminium substrate were used as a model, multilayer, organic coating system. XPS and SIMS characterisation of the PU primer formulation (with and without addition of the PDMS based flow agent), confirmed that the PDMS based flow agent segregated to the PU primers air/coating surface. Characterisation of the PVdF topcoats air/coating surface, after application and curing over the PU primers, revealed the presence of the PDMS based flow agent at the PVdF air/coating surface when the topcoat was applied to the PU primer containing the PDMS based flow agent. Ultra-low-angle microtomy (ULAM) was employed to produce an ultra-low-angle taper that passes through the entire thickness of the PVdF topcoat (~20 µm). XPS linescan analysis along the ULAM taper indicated that the PDMS based flow agent had migrated from the PU primer surface into the bulk of the PVdF topcoat. Analysis of the shape of the silicon concentration profile revealed the existence of a silicon concentration gradient and indicated that the PDMS based flow agent was segregating towards the PVdF topcoats air/coating surface. Such migration and segregation phenomena have major implications for formulators in the coatings/paint industries.
This work presents a data analysis extension to a well-established methodology for the assessment of organic coatings using imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS). Such an approach produced results that can be analysed using a multivariate analysis (MVA) procedure that performs the simultaneous processing of spatially and chemically related datasets. The coatings consist of two commercial resins that yield extremely similar spectra and there are no peaks of sufficient intensity that are uniquely diagnostic of either material to provide an unambiguous identification of each. In order to resolve the problem, in addition to microtome-based sample preparation steps of tapers for the analysis through sample thickness, standard samples in cured and uncured conditions are introduced and measured in the same fashion as the specimens under investigation. The resulting ToF-SIMS imaging datasets have been processed using non-negative matrix factorisation (NMF), which enabled identification of phase separation in the cured coatings.
The strength of intercoat adhesion exhibited between a series of polyester/polyurethane (PU) based primer formulations and a standard poly(vinylidene difluoride) (PVdF) based topcoat formulation has been investigated by X-ray photoelectron spectroscopy (XPS). An initial XPS study of changes in surface elemental composition (induced by variation of the peak metal temperature (PMT) achieved during thermal curing), on a subset of the PU primers employed, indicates that beyond a PMT of 232°C changes in PU primer surface composition are negligible. A reference PU primer coating formulation and four variations of this formulation, produced by including, excluding or substituting components/additives in the reference formulation, are characterised by XPS. The PU primer formulation in which a flow agent additive is included exhibits segregation of the flow agent to the primer surface. The PU primer and PVdF topcoat intercoat adhesion failure surfaces resulting from failure at or near the PVdF/PU interface as a result of a peel test are also characterised by XPS. Additionally the PVdF topcoat air-coating surface is characterised by XPS. The interface analyses for the flow agent containing PU primer formulation indicates stripping of the flow agent layer from the PU primer and transfer of the flow agent to the PVdF topcoat interfacial failure surface. Similarly, PU primer formulations in which the concentrations of a crosslinking resin are changed demonstrate that the transfer of carbon and oxygen containing materials from the PU primer to the PVdF topcoat occurs, due to insufficient crosslinking of the polyester component of the PU primer formulation. These results suggest a correlation between the nitrogen concentration at the PU primer surface and the strength of the intercoat adhesion exhibited by the PU primer towards the PVdF topcoat.
The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and the surface properties of the material. After single crystal fabrication and mechanical polishing, modification of the surface to remove damage and reduce the surface leakage current is generally achieved through chemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have been chemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were 0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120 s. Angle resolved XPS and sputter depth profiling has been employed to characterize the surfaces for the different exposure conditions. A Te rich surface layer was formed for all exposures and the layer thickness was found to be independent of exposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rate against a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layer thickness was determined to be 1.3 ± 0.2 and 1.8 ± 0.2 nm, respectively. The BM etched surfaces have subsequently been passivated in a 30 wt.% HO solution employing exposure time of 15 s. The oxide layer thickness has been calculated using two standard XPS methodologies, based on the Beer-Lambert expression. The TeO thickness calculated from ARXPS data are slightly higher than the thickness obtained by the simplified Beer-Lambert expression. For BM exposures of 30-120 s followed by a passivation treatment of 30 wt. % HO solution employing an exposure time 15 s, the ARXPS method gave an average TeO thickness value of 1.20 nm and the simplified Beer-Lambert expression gave an average thickness value of 0.99 nm. © 2012 Elsevier B.V. All rights reserved.
The aim of this study is to investigate the processability of silica-thermoset polymer matrix nanocomposites in terms of dispersion of silica nanoparticles and their effect on curing. Two thermosetting resins were considered, an epoxy and a polyester resin, with 5 % silica, although 1% silica was also used in preliminary studies in the polyester system. Various combinations of mechanical mixing and sonication were investigated for the dispersion of silica nanoparticles under different processing conditions and times in solvent-free and solvent-containing systems. It was found that the best dispersion route involved a solvent-aided dispersion technique. Consequently, different procedures for the solvent removal were investigated. Optical microscopy and SEM were used to characterize the resulting nanocomposites. DSC and rheological DMTA tests demonstrated that the silica nanoparticles shorten the gel time and promote curing in these thermosetting systems.
Bowei Li, Yuren Xiang, K.D.G. Imalka Jayawardena, Deying Luo, Zhuo Wang, Xiaoyu Yang, John F. Watts, Steven Hinder, Muhammad T. Sajjad, Thomas Webb, Haitian Luo, Igor Marko, Hui Li, Stuart A.J. Thomson, Rui Zhu, Guosheng Shao, Stephen J. Sweeney, S. Ravi P. Silva, Wei Zhang (2020)Reduced bilateral recombination by functional molecular interface engineering for efficient inverted perovskite solar cells, In: Nano Energy105249
Interface-mediated recombination losses between perovskite and charge transport layers are one of the main reasons that limit the device performance, in particular for the open-circuit voltage (VOC) of perovskite solar cells (PSCs). Here, functional molecular interface engineering (FMIE) is employed to retard the interfacial recombination losses. The FMIE is a facile solution-processed means that introducing functional molecules, the fluorene-based conjugated polyelectrolyte (CPE) and organic halide salt (OHS) on both contacts of the perovskite absorber layer. Through the FMIE, the champion PSCs with an inverted planar heterojunction structure show a remarkable high VOC of 1.18 V whilst maintaining a fill factor (FF) of 0.83, both of which result in improved power conversion efficiencies (PCEs) of 21.33% (with stabilized PCEs of 21.01%). In addition to achieving one of the highest PCEs in the inverted PSCs, the results also highlight the synergistic effect of these two molecules in improving device performance. Therefore, the study provides a straightforward avenue to fabricate highly efficient inverted PSCs.
A thermodynamic study of the adsorption of an epoxy acrylate resin used for UV-cured coatings on two different anticorrosion pretreatments on aluminium alloys relevant to aerospace industry has been undertaken. Aluminium alloy Al2219 specimens, treated with an inorganic chromate based conversion coating (Alodine 1200S) and an organic titanium based conversion coating (Nabutan STI/310), were immersed in solutions of different concentrations of the resin and adsorption isotherms were determined by assessing the uptake of the adsorbate, as a function of solution concentration, by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show different behaviour for the two substrates, which can be attributed to the organic component of the titanium based coating. In the case of the inorganic conversion coating a clear plateau is achieved at relatively low concentrations and at a lower level of adsorption than for the hybrid coating. The data for both the coatings conform well to the Langmuir model, the organic coating, as well as showing a higher level of adsorption of the resin, also presents oscillatory behaviour at low concentration, which is shown to be complementary to the behaviour of the reactive diluent included with the epoxy acrylate to aid processing. A discussion of this competitive adsorption of the epoxy resin and the diluent on the different substrates is presented, based on considerations of the chemistry of the systems under investigation.
Scanning Kelvin probe force microscopy has been employed to examine the behaviour of second phase carbide particles in beryllium at different relative humidity levels and after exposure to deionised water. Carbides are believed to have a role in the localised corrosion of beryllium as a result of their hydrolysis when exposed at the metal surface. The presence of beryllium carbide was confirmed by means of Auger electron spectroscopy and the particles were further characterised by scanning electron microscopy, energy/wavelength dispersive x-ray spectroscopy and scanning Kelvin probe force microscopy. The particles were found to have a more noble Volta potential than the beryllium matrix and a decrease in the Volta potential difference between the second phase particles and the matrix was observed as the humidity was increased. A thick beryllium oxide/hydroxide layer then formed on the particles following exposure to water significantly reducing their potential.
Coil Coating is an industrial process widely used to apply a paint layer to metal coil stock, in order to improve the resistance to corrosion as well as the aestetics of the surface. Three thermally cured coatings, formulated on a low Tg ispophtalic based polyester, were investigated by XPS and ToF-SIMS. A model formulation was employed for all three coatings investigated, however, the crosslinking agents used were varied for each formulation. Hexamethoxymethyl melamine (HMMM), tris isocyanurate (TIC) and a combination of HMMM and TIC were included as the cross linking agents in the three coating formulations. The use of TIC alone required a Sn based catalyst to promote the curing reaction. The aim of this work was to investigate the difference in the surface composition of the three coatings and the different behaviour of the different crosslinking agents used. This was in preparation for further studies which will involve interfacial analysis in order to elucidate the mechanism behind intercoat adhesion. The XPS analysis of the air/coating surfaces revealed a nitrogen concentration consistent with the concentration expected from the formulation for the coating containing HMMM. In the other two formulations a lower concentration then that calculated from the formulation was observed. The surface concentration of the two crosslinking agents is not influenced by the presence of the others, indeed the formulation containing both crosslinking agents is, in term of nitrogen concentration, merely a simple combination of the other two coatings. Peaks diagnostic of the cross linking agents were observed in ToF-SIMS spectra acquired from the air/coating surfaces. The coating with HMMM revealed peaks not present on the coating with TIC and vice versa, however the coating with a combination of HMMM and TIC showed all the peaks, with different relative intensities. In the positive spectrum of the sample with TIC the characteristic pattern of the tin catalyst can be observed. By XPS and ToF-SIMS analysis, we have been able to determinate that the HMMM and the TIC have a different distribution on the coating/air surface. Their distribution is not affected by the presence of the other crosslinking agent.
High quality single crystal silicon-germanium-on-insulator has the potential to facilitate the next generation of photonic and electronic devices. Using a rapid melt growth technique we engineer tailored single crystal silicon-germanium-on-insulator structures with near constant composition over large areas. The proposed structures avoid the problem of laterally graded SiGe compositions, caused by preferential Si rich solid formation, encountered in straight SiGe wires by providing radiating elements distributed along the structures. This method enables the fabrication of multiple single crystal silicon-germanium-on-insulator layers of different compositions, on the same Si wafer, using only a single deposition process and a single anneal process, simply by modifying the structural design and/or the anneal temperature. This facilitates a host of device designs, within a relatively simple growth environment, as compared to the complexities of other methods, and also offers flexibility in device designs within that growth environment.
S Diplas, M Avice, A Thogersen, JS Christensen, U Grossner, BG Svensson, O Nilsen, H Fjelivag, S Hinderc, JF Watts (2008)Interfacial studies of Al2O3 deposited on 4H-SiC(0001), In: SURFACE AND INTERFACE ANALYSIS40(3-4)pp. 822-825
JOHN WILEY & SONS LTD
Al2O3 films deposited on 4H-SiC(0001) by atomic layer deposition (ALD) were characterized by x-ray photoelectron spectroscopy (XPS), and high resolution transmission electron microscopy (HRTEM). The effect of medium and high temperature (873, 1273 K) annealing on samples with oxide thicknesses of 5-8nm and 100-120nm was studied. XPS indicated presence of a thin (~1nm) SiOx layer on the as-grown samples which increased to ~3 nm after annealing above crystallization temperature (1273 K) in Ar atmosphere. Upon annealing the stoichiometry of the interfacial oxide approaches that of SiO2. HRTEM showed that the thickness of the interfacial oxide formed after annealing at 1273 K was not uniform. No significant increase in the thickness of the interfacial oxide, was observed after annealing at 873 K in a N2 (90%) / H2 (10%) atmosphere.
Protecting an aircraft from the extremes of environments during service begins at the interface between topcoat and environment. The topcoat considered here is an aliphatic polyurethane (PU) based matte coating. This paper examines the degradation of the PU topcoat through the use of a novel HyperTest which combines ultra-violet (UV) and ozone as the degradation method. To benchmark the technique against accepted accelerated testing methods, QUV was used and samples were tested between two and 56 days. For The HyperTest, samples were degraded at increments between one to 120 minutes. X-ray photoelectron spectroscopy (XPS) determined that 56 days of UV exposure was equivalent, in terms of the extent of the chemical degradation of the topcoat, to one to two minutes of UV/ozone (UV/O3) exposure. There was a significant increase in carbonyl component with increasing oxygen concentration for samples treated with The HyperTest, whereas no clear degradation trend was observed for the samples exposed to UV alone. After 60 minutes of UV/O3 exposure a steady-state mechanism is established as the oxidative decomposition of the PU coating. The proposed degradation mechanism of the PU topcoat, through UV/O3 exposure, is the reaction of atomic oxygen with the polymer matrix/binder through hydrogen abstraction producing a hydroxyl group. This further decomposes to produce a carbonyl component observed in the XPS analysis. The products of degradation are simple volatile molecules such as CO2 and H2O for both testing methods used here. However, the efficient nature of The HyperTest, requiring only minutes to degrade samples as shown here, proves it to be a viable complementary technique to established methods of laboratory accelerated testing.
A study of the effect of methanol solution composition (in terms of methanol and water proportions) on the hydrolysis of γ-glycidoxy propyl trimethoxy silane (GPS) was conducted using proton nuclear magnetic resonance (H1 NMR). In conjunction with this study, adsorption experiments were performed with the same solutions and the films deposited on aluminium surfaces studied by both X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Hydrolysis experiments were performed until completion of the hydrolysis reaction and it is shown that the addition of methanol to an aqueous silane solution prevents hydrolysis and slows down the hydrolysis kinetics dramatically when added at a proportion of 90% (v/v). The use of a pure methanolic solution, however, stops the reaction totally. XPS data also indicated that adsorption from a solution containing methanol is less favourable than in pure water. An unexpected "inversion" of the adsorption isotherm plateaux obtained for solutions containing 10% and 90% methanol, respectively, as well as with the variation of the fragment ions characteristic of the silane epoxy and silicon atom suggest a variation in the adsorption conformation. A correlation was obtained between the state of hydrolysis deduced from both NMR data and ToF-SIMS intensities of specific fragments. This indicates that the concentrations in solution and the amount adsorbed are either correlated or anti-correlated according to the molecule under consideration. These correlations are more convincing when fragments characteristic of no hydrolysis or with one silanol are considered. © 2005 Elsevier Ltd. All rights reserved.
DA Pankhurst, Z Yuan, D Nguyen-Manh, ML Abel, G Shao, JF Watts, DG Pettifor, P Tsakiropoulos (2005)Electronic structure and bonding in Mo3Si, Mo5Si3, and Mo(Si,Al)2 alloys investigated by x-ray photoelectron spectroscopy and density-functional theory, In: PHYSICAL REVIEW B71(7)ARTN 0pp. ?-?
AMERICAN PHYSICAL SOC
X-ray sources are used for both scientific instrumentation and inspection applications. In X-ray photoelectron spectroscopy (XPS), aluminum Kα X-rays are generated through electron beam irradiation of a copper-based X-ray anode incorporating a thin surface layer of aluminum. The maximum power operation of the X-ray anode is limited by the relatively low melting point of the aluminum. Hence, optimization of the materials and design of the X-ray anode to transfer heat away from the aluminum thin film is key to maximizing performance. Finite element analysis has been employed to model the heat transfer of a water-cooled copper-based X-ray anode with and without the use of a CVD (chemical vapour deposited) diamond heat spreader. The modeling approach was to construct a representative baseline model, and then to vary different parameters systematically, solving for a steady state thermal condition, and observing the effect of on the maximum temperature attained. The model indicates that a CVD diamond heat spreader (with isotropic thermal properties) brazed into the copper body reduces the maximum temperature in the 4 μm aluminum layer from 613 °C to 301 °C. Introducing realistic anisotropy in the TC (thermal conductivity) of the CVD diamond has no significant effect on heat transfer if the aluminum film is on the CVD diamond growth face (with the highest TC). However, if the aluminum layer is on the CVD diamond nucleation face (with the lowest TC), the maximum temperature is 575 °C. Implications for anode design are discussed.
Linear saturated dicarboxylic acids are a class of organic chemical compounds with two carboxyl functional groups (-COOH) at the extremities of their aliphatic chains. This class of organic acids can be represented by the general molecular formula HOOC-(CH2)n-COOH. The most common values for n with their respective acid names are present in Table I. The general chemical behavior and reactivity of these compounds are similar to monocarboxylic acids, and they are all widely used in the production of copolymers, such as polyamides and polyesters (Refs. 1–3). The easy conversion of carboxyl groups to esters has industrial importance since many esters are used as taste and odor enhancers. Carboxylic acids are also used as catalysts, replacing ecologically unfavorable organic halides (Ref. 4). Over the last three decades, interest in such acids has increased, specifically regarding their application to improve the corrosion resistance of metallic substrates such as zinc, copper, iron, and aluminum (Refs. 5–12). Research has also shown that carboxylic acids can be used as additives for the electro synthesis of polymeric protective coatings. Such coatings promote passivation of different metallic substrates, allowing the oxidation of the carboxylic acid monomers without concomitant reactions (Refs. 10–13). More recently, carboxylic acids have been used to generate hydrophobic surfaces on various metallic substrates (Fe, Al, Cu, Mg, Zn, Ti, etc.) forming self-assembled layers by adsorption, via carboxyl groups, to the positively charged metal surfaces (Refs. 14–18).
The extent to which an organosilane surface treatment regime can promote durability enhancement of an adhesively bonded aluminium alloy system has been determined. Results have revealed the range of application and film-conditioning parameters which contribute to joint durability in a simple Boeing wedge joint. Organosilane solution parameters relating to solvent type, solution concentration, pH and hydrolysis time have all been shown to influence resultant durability. Interestingly, parameters such as film drying temperature and in-process time delay (time interval between application of the organosilane to the alloy surface and subsequent bonding) have little influence on joint performance. The factors responsible for the durability variations observed have been considered using various surface analytical techniques. Superficially, failure surfaces indicative of interfacial failure between substrate and adhesive have been observed. More detailed characterisation using both XPS and SIMS has indicated failure processes associated with a 'diffusion zone' comprising aluminium oxide and the organosilane. Crown Copyright © 2005 Published by Elsevier Ltd. All rights reserved.
Bowei Li, Yuren Xiang, K. D. G. Imalka Jayawardena, Deying Luo, John F. Watts, Steven Hinder, Hui Li, Victoria Ferguson, Haitian Luo, Rui Zhu, S. Ravi P. Silva, Wei Zhang (2020)Tailoring Perovskite Adjacent Interfaces by Conjugated Polyelectrolyte for Stable and Efficient Solar Cells, In: Solar RRL, Solar RRL4(5)
John Wiley & Sons, Ltd
Interface engineering is an effective means to enhance the performance of thin-film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9-bis(3?-((N,N-dimethyl)-N-ethyl-ammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]di-iodide (PFN-I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35?55% at room temperature. All of these improvements are attributed to the functional PFN-I layers as they provide favorable interface contact and defect reduction.
In recent years, gas cluster ion beams (GCIB) have become the cutting edge of ion beam technology to sputter etch organic materials in surface analysis. However, little is currently known on the ability of argon cluster ions (Arn+) to etch metal oxides and other technologically important inorganic compounds and no depth profiles have previously been reported. In this work, XPS depth profiles through a certified (European standard BCR-261T) 30 nm thick Ta2O5 layer grown on Ta foil using monatomic Ar+ and Ar1000+ cluster ions have been performed at different incident energies. The preferential sputtering of oxygen induced using 6 keV Ar1000+ ions is lower relative to 3 keV and 500 eV Ar+ ions. The depth profiling etch rate and depth resolution is substantially better for the monatomic beam compared to the cluster beam. Ar+ ions exhibit a steady state O/Ta ratio through the bulk oxide but Ar1000+ ions show a gradual decrease in the O/Ta ratio as a function of depth. Higher residual O concentrations are observed on the Ta bulk metal for the Ar1000+ profiles compared to the Ar+ profiles.
D Luo, W Yang, Z Wang, A Sadhanala, Q Hu, R Su, R Shivanna, G Trindade, John Watts, Z Xu, T Liu, K Chen, F Ye, P Wu, L Zhao, J Wu, Y Tu, Y Zhang, X Yang, Wei Zhang, R Friend, Q Gong, H Snaith, R Zhu (2018)Enhanced photovoltage for inverted planar heterojunction perovskite solar cells, In: Science360(6396)pp. 1442-1446
American Association for the Advancement of Science
The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (Voc). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in Voc by up to 100 millivolts. We achieved a high Voc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.
Coffee is the most widely traded tropical agricultural commodity in the world with global production for 2016 of over 151 million 60 kg bags, according to the International Coffee Organization. Such popularity and its chemical complexity demands the development of analytical chemistry methodologies for the characterisation of different coffee compounds. This paper proposes the use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) for this purpose. The main steps involving sample preparation and spectra acquisition are described alongside initial multivariate analysis results.
Time of flight secondary ion mass spectrometry (ToF-SIMS) has been employed for the study of the adsorption of epoxy resin molecules, diglycidyl ether of bisphenol A (DGEBA), on aluminium substrates treated with an organosilane, γ-glycidoxypropyltrimethoxysilane (GPS). Both the kinetics of adsorption and the thermodynamics have been examined, by the construction of adsorption isotherms. The kinetics of adsorption was investigated to establish an exposure equilibrium time for DGEBA adsorption onto GPS-treated aluminium. Specimens were treated with three different concentrations of DGEBA solution and six times of treatment. It was found that DGEBA molecules were adsorbed on the aluminium substrate and reached a true adsorption equilibrium after 10 min. Adsorption isotherms were then produced to define the type of adsorption. Two possible types of adsorption isotherms, Langmuir and Temkin, were examined, and DGEBA adsorption was found to be of the Langmuir type, providing a better fit than Temkin adsorption. Using a modified form of the Langmuir equation, the fractional monolayer coverage of DGEBA molecules was determined. © 2005 Elsevier Ltd. All rights reserved.
The present work has used an accelerated test method, based upon cyclic-fatigue testing using a fracture-mechanics approach, to study the durability of organosilane-pretreated joints which were adhesively-bonded using a hot-cured epoxy-film adhesive. The silane primer investigated was γ-glycidoxypropyltrimethoxysilane (GPS). The cyclic-fatigue tests were mainly conducted in (a) a 'dry' environment of 25±2 °C with a relative humidity of 55±5% and (b) a 'wet' environment where the joints were fully immersed in distilled water at 28±2 °C. However, tests were also undertaken by varying the relative humidity of the environment. The loci of failure of the joints were identified using various surface specific techniques. The use of the GPS-pretreatment has been shown to be effective in increasing the joint durability, compared with a simple grit-blast and degrease (GBD) treatment and, indeed, gives comparable results to using a chromic-acid etch (CAE) pretreatment. Crown Copyright © 2005 Published by Elsevier Ltd. All rights reserved.
This paper investigates electrochemical double-layer capacitors (EDLCs) including two alternative types of carbon-based fibrous electrodes, a carbon fibre woven fabric (CWF) and a multiwall carbon nanotube (CNT) electrode, as well as hybrid CWF-CNT electrodes. Two types of separator membranes were also considered. An organic gel electrolyte PEO-LiCIO4-EC-THF was used to maintain a high working voltage. The capacitor cells were tested in cyclic voltammetry, charge-discharge, and impedance tests. The best separator was a glass fibre-fine pore filter. The carbon woven fabric electrode and the corresponding supercapacitor exhibited superior performance per unit area, whereas the multiwall carbon nanotube electrode and corresponding supercapacitor demonstrated excellent specific properties. The hybrid CWF-CNT electrodes did not show a combined improved performance due to the lack of carbon nanotube penetration into the carbon fibre fabric.
This work combines large area ToF-SIMS imaging with multivariate analysis methods in order to characterise a cold-atmospheric plasma treatment of the surface of an automotive grade polypropylene. Data pre-processing steps are also presented alongside their main challenges. The results enabled the investigation of the spatial distribution of the treatment for different standoff distances as well as the effects of plasma plume mixing with atmosphere.
Kovar is widely used as a metal for glass-to-metal seals because of its compatible coefficient of thermal expansion. A thick, well adhering oxide is desired on the metal to form a strong bond to glass. Surface oxide formed on Kovar samples preoxidised at 700 and 800 °C for ten minutes have been analysed. Each sample showed the presence of Fe_2O_3, CoO and NiO. XPS survey spectra and high resolution narrow scans were collected and are presented.
Chemical throwing power, being the distance over which an inhibitor is able to protect a defect effectively, is an important parameter for active protective coatings. This study investigates the chemical throwing power of lithium-based leachable corrosion inhibitors exhibiting different leaching kinetics, from coatings at different inhibitor loading concentrations. The results demonstrate that Li-salt loaded coatings provide corrosion protection of defect areas up to a width of 6 mm. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to detect the lateral spread of Li in the defect areas and provide the chemical speciation of corrosion protective layers in the defect areas.
Organic-inorganic hybrid nano-particles have been synthesized via a modified Stöber method. Nano-particles have been prepared from silica precursors with different organic functionalities. Methyl, ethyl, vinyl and phenyl modified silicas have been synthesized with a view to using these particles as modifiers for polymers and polymer matrix composites. Nano-composites have been produced using polyester as a matrix. The effect of the nano-particles on the toughness of the polyester has been investigated and it is shown that the incorporation of nano-particles leads to an improvement in toughness. For the methyl, ethyl and vinyl ormosils (organically modified silicas) the improvement is minor. The phenyl ormosil gives a greater improvement. This is attributed to different toughening mechanisms.
Transverse (z) alignment of PEDOT grains was demonstrated in inkjet printed PEDOT:PSS. This explained the superior transverse charge conduction mode in inkjet printed PEDOT:PSS films, best fitted by the Efros-Shklovskii 1D-VRH (variable range hopping) model in this study compared with spin coated PEDOT:PSS films, which have demonstrated layers of generally in-plane aligned PEDOT:PSS grains. The findings of this study, regarding the microstructure of inkjet printed PEDOT:PSS films and their transverse charge transport model, justify measurements of the transverse conductivity of inkjet printed films in this study being 600 times higher than that of spin coated films. In addition, it was found that the addition of 5 wt% DMSO in the printing PEDOT:PSS ink lowers the workfunction by 3% approximately.
The interfacial interactions between methylene diphenyl di-isocyanate (MDI) and polymeric MDI (PMDI) with 316L stainless steel have been studied in order to understand the adhesion properties of polyurethane based adhesives (containing free isocyanate groups) on metal surfaces. A thin (< 5 nm) layer of MDI and PMDI was deposited on the surface of clean 316L stainless steel and then analysed by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). By using density functional theory (DFT) methods for the interpretation of XPS data, the presence of specific interactions between the adsorbate and the substrate was established. The reaction between isocyanate and metal hydroxyl groups with the formation of urethane-like bonding with the metal was observed. The formation of hydrogen bonds between the isocyanate nitrogen and the hydroxyl groups and the formation of nitrogen-metal double bond, as consequence of the cycloaddition reaction between isocyanate and metal oxide, are also proposed.
Surface mass spectrometry methods can be difficult to use effectively with low cost, portable mass spectrometers. This is because commercially available portable (single quadrupole) mass spectrometers lack the mass resolution to confidently differentiate between analyte and background signals. Additionally, current surface analysis methods provide no facility for chromatographic separation and therefore are vulnerable to ion suppression. Here we present a new analytical method where analytes are extracted from a sample using a solvent flushed across the surface under high pressure, separated using a chromatography column and then analysed using a portable mass spectrometer. The use of chromatography reduces ion suppression effects and this, used in combination with in-source fragmentation, increases selectivity, thereby allowing high sensitivity to be achieved with a portable and affordable quadrupole mass spectrometer. We demonstrate the efficacy of the method for the quantitative detection of cocaine and benzoylecgonine in urine and oral fluid. The method gives relative standard deviations below 15% (with one exception), and R2 values above 0.998. The limits of detection for these analytes in oral fluid and urine are <30 ng/ml, which are comparable to the cut-offs currently used in drug testing, making the technique a possible candidate for roadside or clinic-based drug testing..
The durability of adhesively bonded aluminium-alloy joints have been investigated by undertaking cyclic-fatigue tests in liquid water and in 55% RH, to establish the threshold adhesive fracture energy, Gth, below which crack growth will not occur. Three surface pretreatments were employed: grit-blast and degreasing (GBD), phosphoric-acid anodising (PAA), and PAA followed by the application of an anti-corrosion primer (PAAP). The ranking of the durability for the six systems, as assessed by the value of Gth, is as follows: PAAP55%RH = PAA55%RH > PAAPH2O = PAAH2O > GBD55%RH > GBDH2O X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-filtered transmission-electron microscopy have been used to assess the nature of the locus of failure and the mechanisms of failure. For the GBD pretreated joints, tested in both the liquid water and in 55% RH environments, failure occurs predominantly by the thermodynamic displacement of the adhesive from the metal substrate, according to the well-established principles of interfacial thermodynamics. In the case of the PAA and PAAP surface pretreatments, the anodising process provides additional adhesion forces and stability to the interface, which involves the formation of a microcomposite interphase region, and failure is shown to occur in a cohesive manner entirely within the adhesive for the tests undertaken in the 55% RH environment. For the specimens tested in liquid water, in the threshold region, the joints show loci of failure which are predominantly within the adhesive but with small areas of interfacial failure and oxide failure. The differences in durability for the PAAP and PAA when exposed to 55% RH or liquid water is ascribed to the kinetics of aggregation of water in the environs of the metal/adhesive interface, this phenomenon occurring much more rapidly for exposure to liquid water during the cyclic-fatigue process than for the exposure to water vapour at 55% RH. A method based on the XPS analysis of failure surfaces has been used to assess the extent of interfacial failure of the joint prepared from anodised stock. This is shown to be up to 95% depending on treatment and exposure conditions.
The development of state-of-art time-of-flight secondary ion mass spectrometry (ToF-SIMS) results in extremely large datasets. In order to perform multivariate analysis of such datasets without loss of mass and spatial resolution, appropriate data handling methods must be developed. The work in this paper presents an approach that can be taken to perform non-negative matrix factorisation (NMF) of large ToF-SIMS datasets. A large area stage raster scan of a chemically contaminated fingerprint is used as an example and the results show that the fingerprint signal was successfully separated from the substrate signal. Pre-processing challenges and artefacts that arises from the results are also discussed and an alternative approach, using the MapReduce programming model, is suggested for even larger datasets.
The effect on the Volta potential, measured from second phase particles in beryllium, by the thin layer of hydrocarbon contamination pyrolised onto the surface under the action of an electron beam during secondary electron imaging has been investigated. Despite being only a few nanometres thick, this contamination has a significant influence on the Volta potential of second phase particles of interest. This work shows that such contamination can have a substantial effect on the measured potential of particles, acting to increase or decrease the Volta potential difference compared to the metallic matrix
Polymeric methylene diphenyl diisocyanate (PMDI) is the major component of polyurethane formulations and as a result the adhesion, or indeed abhesion, of polyurethanes, in a variety of forms (foams, coatings and adhesives), to metal substrates will be a function of the interactions between PMDI and metal surfaces. In this paper the adsorption of PMDI on oxidised metal (aluminium and iron) substrates has been investigated. The thermodynamics of adsorption has been examined by the construction of adsorption isotherms derived from ToF-SIMS data. At low solution concentration, the adsorption isotherns of PMDI are not of the Langmuir type, but are shown to conform to Langmuir adsorption at higher solution concentrations (> 1 g L-1). The interaction between the PMDI and iron is probably an acid-base interaction, and thus the adsorption of small PMDI molecules is displaced by larger PMDI molecules on the iron surface above a critical solution concentration. By contrast, such displacement is small on the aluminium surface as a result of dominance of covalent bond formation between PMDI and the metal substrate.