Electron spin resonance spectroscopy: a promising method for studying lipid oxidation in foods

Oxidative reactions that involve lipids are among the most important causes of deterioration of foods and affect both their shelf life and their organoleptic and nutritional properties. Radicals are intermediate key‐constituents in these reactions. Their detection is therefore essential in order to understand and predict early stages of these destructive oxidations. Several Electron Spin Resonance (ESR) methodologies (direct and indirect) make it possible to identify, quantify and measure the reactivity of radical species formed during oxidative‐reductive reactions. They are also used to evaluate the antiradical activity of antioxidants delaying lipid oxidation. An overview on the use of different ESR methodologies to study lipid oxidation in foods is reported in this paper.     

Kinetic Study of Hydroperoxide Degradation in Edible Oils Using Electron Spin Resonance Spectroscopy

Lipid oxidation is a complex phenomenon involving free radicals which are highly reactive molecular species. The life-time of these radical species is extremely short and their detection is therefore difficult. Several electron spin resonance (ESR) spectroscopy methodologies make it possible to identify, quantify and measure the reactivity of radical species formed during oxidation–reduction reactions. In this study we took advantage of the specificity of ESR spectroscopy to detect radical compounds in order to determine the rate constants of hydroperoxide degradation, a key reaction involved in lipid oxidation. The interaction of 5-doxyl stearic acid and lipid-derived radicals was studied by following the intensity of ESR spectra. A kinetic model was developed to simulate data analysis obtained by ESR and values of rate constants for hydroperoxide degradation were determined at 100 and 110 °C. This quantitative approach of ESR spectroscopy has produced useful information about new rate estimates for hydroperoxide degradation in edible oils.     

The impact of the discreteness of low-fluence ion beam processing on the spatial architecture of GaN nanostructures fabricated by surface charge lithography

We show that the descrete nature of ion beam processing used as a component in the approach of surface charge lithography leads to spatial modulation of the edges of the GaN nanostructures such as nanobelts and nanoperforated membranes. According to the performed Monte Carlo simulations, the modulation of the nanostructure edges is caused by the stochastic spatial distribution of the radiation defects generated by the impacting ions and related recoils. The obtained results pave the way for direct visualization of the networks of radiation defects induced by individual ions impacting a solid-state material.     

Fabrication of GaN nanowalls and nanowires using surface charge lithography

We demonstrate the possibility for controlled nanostructuring of GaN by focused-ion-beam treatment with subsequent photoelectrochemical (PEC) etching. The proposed maskless approach based on direct writing of surface negative charge that shields the material against PEC etching allows fabrication of GaN nanowalls and nanowires with lateral dimensions as small as 100 nm. The results obtained show that the occurrence of undercut etching inherent to gallium nitride PEC etching depends on the depletion length in doped GaN material, it being nearly fully suppressed in the structures below a critical size of about 200 nm for the investigated GaN layer of doping concentration of 1.7 × 10¹⁷ cm^− 3.     

Application of surface charge lithography to nanostructuring of GaN epilayers

It is shown that treatment of GaN epilayers by a low energy low dose focused ion beam with subsequent photoelectrochemical etching represent an efficient tool for GaN nanostructuring. Direct “writing” of a surface negative charge trapped by radiation defects allows one to fabricate thin GaN walls with a thickness as low as 100 nm using focused ion beam treatment. The obtained results show that the undercut etching inherent to GaN etching through windows defined by surface charge lithography depends on the depletion length in the doped GaN material and does not occur in the structures below a critical size of 200 nm in our case. The text was submitted by the authors in English.     

The impact of high energy ion irradiation upon CO gas sensitivity of nanostructured GaN epilayers

Photoelectrochemically nanostructured GaN epilayers were found to exhibit good sensitivity towards CO in the temperature range from 180 to 280°C. We show that subjection of nanostructured GaN samples to 166 MeV Xe⁺²³ ion irradiation causes considerable reduction of the gas sensitivity, while post-irradiation rapid thermal annealing results in sensitivity restoration, the effect being dependent upon the dose of irradiation and annealing temperature. A 50% restoration of the relative sensitivity is demonstrated after rapid thermal annealing for 1 min at 800°C in samples irradiated by Xe⁺²³ ions at a dose of 10¹² cm⁻². The article is published in the original.