Cigdem Toparli

Optical absorption spectroscopy at interfaces

This chapter summarises the physical principles of optical absorption spectroscopy and its use for the characterisation of surfaces and interfaces. After a brief discussion of the fundamentals of absorption spectroscopy and its relation to quantum mechanics, the chapter discusses the basics of optics at interfaces, focusing on the absorption of light by molecules in the interfacial region. Because of fundamental similarities, the chapter will touch on spectroscopy of both electronic and vibrational transitions, with a strong focus on infrared absorption experiments. There is a brief discussion, with reference to examples, of experiments in internal and external reflection geometry, including a brief discussion of the measurement of spectra on different classes of substrates (metallic vs. transparent).

Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles by means of hydrogen reduction assisted ultrasonic spray pyrolysis (USP-HR)

Abstract Fe/metal oxide nanocomposite particles were produced by means of hydrogen reduction assisted ultrasonic spray pyrolysis. Fe/Fe0.761Mg0.239O and Fe/MgO nanocomposite particles were obtained at 600 and 800 °C, respectively. The thermodynamics of the formation reactions were investigated. Increasing the reaction temperature allowed efficient reduction of the precursor to metallic iron that induces the formation of pure MgO phase. The crystallite sizes of the Fe in the composite structures slightly increased, and also the crystallite sizes of the oxides decreased with elevating temperature. The nanocomposite particles exhibited spherical morphology and their particle sizes were slightly different. All of the samples showed ferromagnetic characteristics and the results indicate that the amount of metal and metal oxide phases most affected the saturation magnetizations of the composite particles which were lower than pure iron.

Cyclodextrin inhibits zinc corrosion by destabilizing point defect formation in the oxide layer

Corrosion inhibitors are added in low concentrations to corrosive solutions for reducing the corrosion rate of a metallic material. Their mechanism of action is typically the blocking of free metal surface by adsorption, thus slowing down dissolution. This work uses electrochemical impedance spectroscopy to show the cyclic oligosaccharide β-cyclodextrin (β-CD) to inhibit corrosion of zinc in 0.1M chloride with an inhibition efficiency of up to 85%. Only a monomolecular adsorption layer of β-CD is present on the surface of the oxide covered metal, with Raman spectra of the interface proving the adsorption of the intact β-CD. Angular dependent X-ray photoelectron spectroscopy (ADXPS) and ultraviolet photoelectron spectroscopy (UPS) were used to extract a band-like diagram of the β-CD/ZnO interface, showing a large energy level shift at the interface, closely resembling the energy level alignment in an n–p junction. The energy level shift is too large to permit further electron transfer through the layer, inhibiting corrosion. Adsorption hence changes the defect density in the protecting ZnO layer. This mechanism of corrosion inhibition shows that affecting the defect chemistry of passivating films by molecular inhibitors maybe a viable strategy to control corrosion of metals.

How to probe structure, kinetics and dynamics at complex interfaces in situ and operando by optical spectroscopy

Techniques using light in a large spectral range are well suited to study interfaces. Photon-based techniques have a special strength when it comes to application in situ and operando. This article introduces some of the most commonly used experimental techniques. Absorption spectroscopy in the far-, mid-, and near-infrared (IR), in the visible (VIS) and ultraviolet (UV) is a simple method to obtain the interface equivalent to the type of information normally obtained by the respective bulk method. Also photoluminescence/fluorescence is used to study interfaces. Polarization, for example, in ellipsometry, or polarization-modulated spectroscopy can increase the interface specificity. The same could be achieved by surface enhancement, for example, in surface-enhanced Raman spectroscopy. IR/VIS sum frequency generation spectroscopy (SFG) has intrinsic surface specificity. Main working principles of these techniques are introduced, with reference to more detailed coverage elsewhere, and examples of application. Overall, the techniques are suitable to yield qualitative and quantitative information on which species are present at interfaces, in which conformation state or which defects develop in solids. Frequently, also information on orientation of species can be obtained.