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Surface self-assembly of spherical nanoparticles of sizes below 10 nm into hierarchical heterostructures is under arising development despite the inherent difficulties of obtaining complex ordering patterns on a larger scale. Due to template-mediated interactions between oil-dispersible superparamagnetic nanoparticles (MNPs) and polyethylenimine-stabilized gold nanoparticles (Au(PEI)NPs) at the water–oil interface of microemulsions, complex nanostructured films can be formed. Characterization of the reverse microemulsion phase by UV–vis absorption revealed the formation of heteroclusters from Winsor type II phases (WPII) using Aerosol-OT (AOT) as the surfactant. SAXS measurements verify the mechanism of initial nanoparticle clustering in defined dimensions. XPS suggested an influence of AOT at the MNP surface. Further, cryo-SEM and TEM visualization demonstrated the elongation of the reverse microemulsions into cylindrical, wormlike structures, which subsequently build up larger nanoparticle superstructure arrangements. Such WPII phases are thus proven to be a new form of soft template, mediating the self-assembly of different nanoparticles in hierarchical network-like filaments over a substrate during solvent evaporation.
Low-cost, high-efficient catalysts for water splitting can be potentially fulfilled by developing earthabundant metal oxides. In this work, surface galvanic formation of Co-OH on K0.45MnO2 (KMO) was achieved via the redox reaction of hydrated Co2+ with crystalline Mn4+. The synthesis method takes place at ambient temperature without using any surfactant agent or organic solvent, providing a clean, green route for the design of highly efficient catalysts. The redox reaction resulted in the formation of ultrathin Co-OH nanoflakes with high electrochemical surface area. X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the changes in the oxidation state of the bulk and
surface species on the Co-OH nanoflakes supported on the KMO. The effect of the anions, such as chloride, nitrate and sulfate, on the preparation of the catalyst was evaluated by electrochemical and spectrochemical means. XPS and Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis demonstrated that the layer of CoOxHy deposited on the KMO and its electronic structure strongly depend on the anion of the precursor used during the synthesis of the catalyst. In particular, it was found that Cl- favors the formation of Co-OH, changing the rate-determining step of the reaction, which enhances the catalytic activity towards the OER, producing the most active OER catalyst in alkaline media.
Small-area/spot photoelectron spectroscopy (SAXPS) is a powerful tool for the investigation of small surface features like microstructures of electronic devices, sensors or other functional surfaces. For evaluating the quality of such microstructures, it is crucial to know whether a small signal in a spectrum is an unwanted contamination of the field of view (FoV), defined by the instrument settings, or it originated from outside. The aperture has a major influence on the signal-contribution from the outside. For the evaluation of the FoV, we determined the Au4f intensities measured with the center of the FoV aligned with the center of the spot and normalized to the Au4f intensity determined on the Au-film. With this test specimen, it was possible to characterize the FoV: The signal-contribution from the outside is reduceable down to lower than 50 %, when the aperture is 30 % of the structure dimension for our Kratos AXIS Ultra DLD system.
Imaging and small-spot (small area) XPS have become increasingly important components of surface chemical analysis during the last three decades, and its use is growing. Some ambiguity in the use of terminology, understanding of concepts, and lack of appropriate reference materials leads to confusing and not always reproducible data. In this paper, it is shown that by using existing knowledge, appropriate test specimens, and standardized approaches, problems of comparability and such reproducibility issues recently observed for XPS data reported in the scientific literature can be overcome. The standardized methods of ISO 18516:2019, (i) the straight-edge, (ii) the narrow-line, and (iii) the grating method, can be used to characterize and compare the lateral resolution achieved by imaging XPS instruments and are described by reporting examples. The respective measurements are made using new test specimens. When running an XPS instrument in the small-spot (small area) mode for a quantitative analysis of a feature of interest, the question arises as to what contribution to the intensity originates from outside the analysis area. A valid measurement approach to control the intensity from outside the nominal analysis area is also described. As always, the relevant resolution depends on the specific question that needs to be addressed. The strengths and limitations of methods defining resolution are indicated.
Visualization of surface modifications may be very challenging for coating/substrate systems of either almost identical optical constants, e.g. transparent films on substrates of the same material, or minor film thickness, substance quantity and affected area, e.g. ultra-thin or island films. Methods for visualization are optical microscopy (OM), imaging ellipsometry (IE), and referenced spectroscopic ellipsometry (RSE). Imaging ellipsometry operates at oblique incidence near Brewster angle of the bare, clean or unmodified substrate. In this configuration, reflected intensities are rather weak. However, the contrast to add-on and sub-off features may be superior. Referenced spectroscopic ellipsometry operates in a two-sample configuration but with much higher intensities. In many cases, both ellipsometric techniques reveal and visualize thin films, printed-pattern, laser-induced changes, and impurities better than optical microscopy. In particular for stratified homogeneous modifications, ellipsometric techniques give access to modelling and hence thickness determination. Modifications under investigation are polymer foil residue on silicon, laser-induced changes of ta-C:H coatings on 100Cr6 steel, imperfections of ta-C:H on thermal silicon oxide, degradation of glass, thin film tin oxide pattern on silicon, printed and dried pattern of liquids such as deionized water, cleaning agents, and dissolved silicone. © 2016 Elsevier B.V. All rights reserved.
The paper addresses the “Conventional Single-Sample vs. Multiple-Sample Hardness Testing: Hardness Testing Machine vs. Centrifuge” and the follow points are discussed in more detail: Principle of the centrifuge test, components of the centrifuge test, indenter geometries, microscopic measurement of Brinell and Vickers indents, and hardness testing: conventional vs. centrifuge.
Industrial quality control (QC) nowadays requires the visualization of surface modifications from the macro-scopic to the microscopic or even nanoscopic scale. This is a prerequisite to the evaluation of functionality and reliability, the detection of defects and their separation of artefacts. The diversity of applications ranges from low-E glazings and solar panels, micro- and optoelectronics, micro- and smart devices to sensor-on-chip and lab-on-chip systems [1]. Optical microcopy (light, confocal laser scanning, white light interference) as established QC-tool is operated at normal incidence, i.e. p- and s-polarization are undistinguishable. Either light-intensity in terms of grey scale and colour or intensity-correlated effects of phase shifts are used. In case of ellipsometry, operated at oblique incidence, p- and s-polarization matter, and amplitude ratios and phase shifts upon reflection are measured. Hence, information content must be much higher.
The visualization of surface modifications may be very challenging for coating/substrate systems of either al-most identical optical constants, e.g. transparent films on substrates of the same material, or minor film thick-ness, substance quantity and affected area, e.g. ultra-thin or island films. Ellipsometry gives access to the con-trast of intensity (I), amplitude ratio (Ψ), and phase shift (Δ) with nanometer-scaled vertical and micrometer-scaled lateral sensitivity, one is able to identify tiny changes within an unmodified surface. As both mapping ellipsometry (ME) and imaging ellipsometry (IE) are operated in the optical far-field, surface inspection is also possible on the macroscopic scale. Near the Brewster-angle of the bare, undamaged, clean, and fresh substrate, the contrast to add-on and sub-off features is superior.
Fig. 1 shows three examples of ellipsometric imaging, i.e. a thin SnO:Ni film on SiO2/Si (Fig. 1a), a dried stain of an anti-body solution on cyclo-olefin-polymer (COP) shown in Fig. 1b, and a polyimide film residue on SiO2/Si (Fig. 1c). For all of these examples, ellipsometry provides much better contrast between substrate and surface modification than optical microscopy, sometimes primarily caused by the oblique incidence (Figs. 1a and 1c), in other cases related to the phase sensitivity of ellipsometry (Fig. 1b). Other examples are laser surface modifications and the corrosion of glass. In these cases, optical microscopy and IE yield to similar results, how-ever only ellipsometry gives access to modelling.
Further investigated coating/substrate systems are 100Cr6 steel, native oxide on silicon, borosilicate glass, and the polymer polycarbonate with deposited films of graphene and ta-C:H, printed and dried pattern of liquids such as water, cleaning agents, and dissolved silicone. Besides imaging ellipsometry, referenced spectral ellipsometry (RSE) has been applied, combining the advantages of both optical microscopy (fast measurement) and ellipsometry (high sensitivity to tiny modifications).