Electron Spin Resonance Measurements Research Articles

The Drug-Loaded Electrospun Poly(ε-Caprolactone) Mats for Therapeutic Application.

Diclofenac sodium salt (DSS)-loaded electrospun nanofiber mats on the base of poly(ε-caprolactone) (PCL) were investigated as biocompatible nanofibrous mats for medical applications with the ability to inhibit bacterial infections. The paper presents the characteristics of fibrous mats made by electrospinning and determines the effect of medicament on the fiber morphology, chemical, mechanical and thermal properties, as well as wettability. PCL and DSS-loaded PCL nanofibrous mats were characterized using scanning electron microscopy, transmission electron microscopy, attenuated total reflectance-Fourier transform infrared spectrometry, dynamic mechanical analysis, and contact angle measurements. Electron paramagnetic resonance measurements confirmed the lifetime of DSS before and after application of high voltage during the electrospinning process. In vitro biocompatibility was studied, and it was proved to be of good viability with ~92% of the diploid human cells culture line composed of lung fibroblast (MRC 5) after 48 h of incubation. Moreover, the significant activity of DSS-loaded nanofibers against cancer cells, Ca Ski and HeLa, was established as well. It was shown that 12.5% (m/V) is the minimal concentration for antibacterial activity when more than 99% of Escherichia coli (Gram-negative) and 99% of Staphylococcus aureus (Gram-positive) have been exterminated.

ESR Investigations of (BaSnO3)x/(Cu, Tl) 1223 composite in the normal and superconducting state

ABSTRACT (BaSnO3)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ superconducting composites (0.00 ≤ x ≤ 1.50 wt.%) were prepared by the solid-state reaction technique. The crystalline structure and superconducting transition temperature were investigated by X-ray powder diffraction (XRD) and dc-electrical resistivity measurements, respectively. X-Band electron spin resonance (ESR) measurements were carried out at different temperatures 103 ≤ T ≤ 298 K. ESR spectra are dominated by a single asymmetric line corresponding to Cu2+ ions at the rhombic site. The temperature dependence of the g factors allowed the determination of the pseudo-gap onset temperature T*. The results of T* are compatible with those obtained from resistivity and thermoelectric power measurements. The contribution of delocalized electrons from Cu2+ ions in the disordered part of the impurity phases BaCuO2 and Ba2CuO3 is significant for the high addition of nanoparticles. Moreover, the number of spins N participating in ESR and the activation energy Ea were enhanced with the addition of BaSnO3.

Dual nonradical degradation of acetaminophen by peroxymonosulfate activation with highly reusable and efficient N/S co-doped ordered mesoporous carbon

This work demonstrates for the first time the potential application of a novel nonradical oxidation system consisting of N/S co-doped ordered mesoporous carbon (NS-CMK-3) and peroxymonosulfate (PMS). The results showed that the NS-CMK-3 catalyst effectively activated PMS to completely degrade pharmaceutical acetaminophen (ACT). The catalytic performance of NS-CMK-3 was ~20 and 10 times better than that of pristine CMK-3 and single N-doped one (N-CMK-3), respectively. The oxidative system could also remove other pollutants (i.e., sulfathiazole, trans-ferulic acid, orange G, and phenol). A higher content of N (5.3 at.%) and a distribution of graphite-N (28.1%) were determined in NS-CMK-3 than in N-CMK-3. The synergistic effect of N/S co-doping (i.e., graphite-N and thiophene-S) resulted in the enhanced catalytic performance. The activation of PMS by NS-CMK-3 primarily followed two nonradical pathways (i.e., singlet oxygen and catalyst surface-bound reactive PMS complexes), supported by quenching experiments and electron paramagnetic resonance measurements. The p-benzoquinone (p-BQ) and ACTdimer were main degradation products. The removal of total organic carbon (TOC) was ≈27%, suggesting nonradicals could mineralize ACT. The NS-CMK-3 not only demonstrated superior stability owing to a removal efficiency that was still as high as 98% in the fifth recycle run, but also significantly decreased the potential effects of water constituents (e.g., Cl−, NO3−, HCO3−, and humic acid) on the removal process. The NS-CMK-3/PMS oxidative system offers a novel strategy to carry out environmental remediation via nonradical processes.

Millimeter-Wave Band Resonator with Surface Coil for DNP–NMR Measurements

In this study, we developed a surface coil with a meanderline shape for nuclear magnetic resonance (NMR) combined with a Fabry–Perot resonator (FPR) for millimeter-wave band electron-spin resonance (ESR). Our goal was to perform both NMR and ESR measurements with high sensitivity, in particular for thin samples, such as a silicon wafer. We measured NMR signals using a variety of meanderline coil shapes and determined the optimal turn number of the meanderline as well as the clearance length between the lines. The FPR consisted of spherical and flat mirrors, where the latter was constructed of a thin gold layer with the meanderline underneath. We observed that the meanderline provided high sensitivity when the gold layer was sufficiently thin at approximately 16 nm. We also measured millimeter-wave ESR from a thin sample of phosphorous-doped silicon with the developed FPR with the meanderline.

Quantum Sensing of Insulator‐to‐Metal Transitions in a Mott Insulator

AbstractNitrogen vacancy (NV) centers, optically active atomic defects in diamond, have attracted tremendous interest for quantum sensing, network, and computing applications due to their excellent quantum coherence and remarkable versatility in a real, ambient environment. Taking advantage of these strengths, this paper reports on NV‐based local sensing of the electrically driven insulator‐to‐metal transition (IMT) in a proximal Mott insulator. The resistive switching properties of both pristine and ion‐irradiated VO2 thin film devices are studied by performing optically detected NV electron spin resonance measurements. These measurements probe the local temperature and magnetic field in electrically biased VO2 devices, which are in agreement with the global transport measurement results. In pristine devices, the electrically driven IMT proceeds through Joule heating up to the transition temperature while in ion‐irradiated devices, the transition occurs nonthermally, well below the transition temperature. The results provide direct evidence for nonthermal electrically induced IMT in a Mott insulator, highlighting the significant opportunities offered by NV quantum sensors in exploring nanoscale thermal and electrical behaviors in Mott materials.

Engineering Z-scheme silver oxide/bismuth tungstate heterostructure incorporated reduced graphene oxide with superior visible-light photocatalytic activity

Photocatalytic degradation of multiple organic contaminants has received extensive research attention and rational design of visible-light driven photocatalyst has been considered as an efficient approach. In this study, a visible-light Ag2O/Bi2WO6 heterostructure incorporated reduced graphene oxide (ABW-RGO) composite photocatalyst was prepared through a facile hydrothermal method for the first time and exhibited synergetic degradation behavior for contaminants in aqueous solutions. Under visible light, Tetracycline antibiotics has degraded 95.3% within only 40 min, and dye pollutants including Crystal Violet (cationic dye) and Congo Red (anionic dye) reached over 98.5% decomposition. The synthesized composite is also highly efficient in a wide pH range and multi-components system, maximizing the utilization of common sunlight, which make it suitable for industrial wastewater. The reactive oxidant species (ROS) experiment and electron spin resonance (ESR) measurement revealed the critical role of hydroxyl and superoxide radicals, clarifying the degradation pathway and mechanism analysis. The superior photocatalytic activity could be attributed to the formation of effective Z-scheme heterostructure and the excellent sorption capacity and conductivity of reduced graphene oxide. This research provides the design pathway to a novel catalyst using semiconductors composite and graphene support material, which can be extended to the energy-saving treatment of various organic pollutants.

Experimental and Theoretical Evidence for an Unusual Almost Triply Degenerate Electronic Ground State of Ferrous Tetraphenylporphyrin.

Iron porphyrins exhibit unrivalled catalytic activity for electrochemical CO2-to-CO conversion. Despite intensive experimental and computational studies in the last 4 decades, the exact nature of the prototypical square-planar [FeII(TPP)] complex (1; TPP2- = tetraphenylporphyrinate dianion) remained highly debated. Specifically, its intermediate-spin (S = 1) ground state was contradictorily assigned to either a nondegenerate 3A2g state with a (dxy)2(dz2)2(dxz,yz)2 configuration or a degenerate 3Egθ state with a (dxy)2(dxz,yz)3(dz2)1/(dz2)2(dxy)1(dxz,yz)3 configuration. To address this question, we present herein a comprehensive, spectroscopy-based theoretical and experimental electronic-structure investigation on complex 1. Highly correlated wave-function-based computations predicted that 3A2g and 3Egθ are well-isolated from other triplet states by ca. 4000 cm-1, whereas their splitting ΔA-E is on par with the effective spin-orbit coupling (SOC) constant of iron(II) (≈400 cm-1). Therfore, we invoked an effective Hamiltonian (EH) operating on the nine magnetic sublevels arising from SOC between the 3A2g and 3Egθ states. This approach enabled us to successfully simulate all spectroscopic data of 1 obtained by variable-temperature and variable-field magnetization, applied-field 57Fe Mössbauer, and terahertz electron paramagnetic resonance measurements. Remarkably, the EH contains only three adjustable parameters, namely, the energy gap without SOC, ΔA-E, an angle θ that describes the mixing of (dxy)2(dxz,yz)3(dz2)1 and (dz2)2(dxy)1(dxz,yz)3 configurations, and the ⟨rd-3⟩ expectation value of the iron d orbitals that is necessary to estimate the 57Fe magnetic hyperfine coupling tensor. The EH simulations revealed that the triplet ground state of 1 is genuinely multiconfigurational with substantial parentages of both 3A2g (<88%) and 3Eg (>12%), owing to their accidental near-triple degeneracy with ΔA-E = +950 cm-1. As a consequence of this peculiar electronic structure, 1 exhibits a huge effective magnetic moment (4.2 μB at 300 K), large temperature-independent paramagnetism, a large and positive axial zero-field splitting, strong easy-plane magnetization (g⊥ ≈ 3 and g∥ ≈ 1.7) and a large and positive internal field at the 57Fe nucleus aligned in the xy plane. Further in-depth analyses suggested that g⊥ ≫ g∥ is a general spectroscopic signature of near-triple orbital degeneracy with more than half-filled pseudodegenerate orbital sets. Implications of the unusual electronic structure of 1 for CO2 reduction are discussed.

Comparatively singlet oxygen efficiency by sono-photochemical and photochemical studies of new lutetium (III) phthalocyanines

This study performs a sono-photochemical method to get more effective therapeutic outcomes for cancer treatment. Additionally, sonochemical and sono-photochemical properties of lutetium phthalocyanines have been presented in this study for the first time. Although it aims to synthesize a series of new peripherally/non-peripherally mono lutetium (III) phthalocyanines (1-3Lu), the related double-decker lutetium (III) phthalocyanines (1′-3′Lu) were simultaneously synthesized. Characterization of the resulting macromolecules was carried out using diverse spectroscopic approaches including NMR (1H and 13C NMR; for 1-3Lu), UV–Vis, FT-IR, and Mass spectroscopy. The double-decker lutetium (III) phthalocyanines (1′-3′Lu) were also characterized by performing electron spin resonance (ESR) measurements. The solubility of all the new macromolecules was studied using different polar and non-polar organic solvents. The photophysicochemical properties of the resulting mono lutetium (III) complexes were analyzed and photochemical, sonochemical, and sono-photochemical properties were investigated to determine the efficiencies of singlet oxygen. When the data were compared, the highest singlet oxygen quantum yields (ΦΔ = 0.86 for 1-Lu, 0.96 for 2-Lu, 0.83 for 3-Lu) were obtained for the sono-photochemical studies. The results prove that sono-photochemical properties improve the therapeutic effects compared to photochemical ones.

Carbon Dots Detect Water-to-Ice Phase Transition and Act as Alcohol Sensors via Fluorescence Turn-Off/On Mechanism.

Highly fluorescent carbon nanoparticles called carbon dots (CDs) have been the focus of intense research due to their simple chemical synthesis, nontoxic nature, and broad application potential including optoelectronics, photocatalysis, biomedicine, and energy-related technologies. Although a detailed elucidation of the mechanism of their photoluminescence (PL) remains an unmet challenge, the CDs exhibit robust, reproducible, and environment-sensitive PL signals, enabling us to monitor selected chemical phenomena including phase transitions or detection of ultralow concentrations of molecular species in solution. Herein, we report the PL turn-off/on behavior of aqueous CDs allowing the reversible monitoring of the water-ice phase transition. The bright PL attributable to molecular fluorophores present on the CD surface was quenched by changing the liquid aqueous environment to solid phase (ice). Based on light-induced electron paramagnetic resonance (LEPR) measurements and density functional theory (DFT) calculations, the proposed kinetic model assuming the presence of charge-separated trap states rationalized the observed sensitivity of PL lifetimes to the environment. Importantly, the PL quenching induced by freezing could be suppressed by adding a small amount of alcohols. This was attributed to a high tendency of alcohol to increase its concentration at the CD/solvent interface, as revealed by all-atom molecular dynamics simulations. Based on this behavior, a fluorescence "turn-on" alcohol sensor for exhaled breath condensate (EBC) analysis has been developed. This provided an easy method to detect alcohols among other common interferents in EBC with a low detection limit (100 ppm), which has a potential to become an inexpensive and noninvasive clinically useful diagnostic tool for early stage lung cancer screening.

Deciphering the H-Bonding Preference on Nucleoside Molecular Recognition through Model Copper(II) Compounds.

The synthetic nucleoside acyclovir is considered an outstanding model of the natural nucleoside guanosine. With the purpose of deepening on the influence and nature of non-covalent interactions regarding molecular recognition patterns, three novel Cu(II) complexes, involving acyclovir (acv) and the ligand receptor N-(2-hydroxyethyl)ethylenediamine (hen), have been synthesized and thoroughly characterized. The three novel compounds introduce none, one or two acyclovir molecules, respectively. Molecular recognition has been evaluated using single crystal X-ray diffraction. Furthermore, theoretical calculations and other physical methods such as thermogravimetric analysis, infrared and UV-Vis spectroscopy, electron paramagnetic resonance and magnetic measurements have been used. Theoretical calculations are in line with experimental results, supporting the relevance of the [metal-N7(acv) + H-bond] molecular recognition pattern. It was also shown that (hen)O-H group is used as preferred H-donor when it is found within the basal coordination plane, since the higher polarity of the terminal (hen)O-H versus the N-H group favours its implication. Otherwise, when (hen)O-H occupies the distal coordination site, (hen)N-H groups can take over.

Structural, dielectric, and magnetic properties of LaCo0.2Mn0.8O3 and La2CoMnO6 perovskite materials

Herein report, we aim to study the structural, dielectric, and magnetic properties for multifunctional perovskite materials LaCo0.2Mn0.8O3 and La2CoMnO6 nanoparticles, which were synthesized by a modified sol–gel route. Citric acid was processed as the chelating agent; gelation slurry formed by irradiation process which exposed to a total gamma radiation dose of 25 kGy at a dose rate of ~1.2 Gy/h to obtain more stability and high purity multifunctional perovskite materials. XRD notarizes the genesis of one pure phase orthorhombic perovskite structure. A full agreement between the particle sizes was investigated by HRTEM and the XRD data was observed. Raman spectra result assigned to the antisymmetric stretching mode and symmetric stretching mode of the (Co/Mn) O6 octahedra, which related to lattice distortions. The as-prepared perovskite materials exhibit ferromagnetic nature with different values of magnetization. Electron Spin Resonance (ESR) measurements are also carried out in the LCMO multifunctional nanoparticle systems, which suggests the occurrence of Jahn–Teller glass analogous to the spin-glass behavior. The complex impedance displayed high impacts on the electrical properties. The high value of dielectric constant for LCMO prepared nanoparticle systems may be used in electric tunable devices.

NMR and EPR reveal a compaction of the RNA-binding protein FUS upon droplet formation.

Many RNA-binding proteins undergo liquid-liquid phase separation, which underlies the formation of membraneless organelles, such as stress granules and P-bodies. Studies of the molecular mechanism of phase separation in vitro are hampered by the coalescence and sedimentation of organelle-sized droplets interacting with glass surfaces. Here, we demonstrate that liquid droplets of fused in sarcoma (FUS)-a protein found in cytoplasmic aggregates of amyotrophic lateral sclerosis and frontotemporal dementia patients-can be stabilized in vitro using an agarose hydrogel that acts as a cytoskeleton mimic. This allows their spectroscopic characterization by liquid-phase NMR and electron paramagnetic resonance spectroscopy. Protein signals from both dispersed and condensed phases can be observed simultaneously, and their respective proportions can be quantified precisely. Furthermore, the agarose hydrogel acts as a cryoprotectant during shock-freezing, which facilitates pulsed electron paramagnetic resonance measurements at cryogenic temperatures. Surprisingly, double electron-electron resonance measurements revealed a compaction of FUS in the condensed phase.

Synthesis and investigation of small g-values for smart spinel ferrite nanoparticles

Smart spinel and hexagonal ferrite nanoparticles (NPs) have been fabricated by ethylenediaminetetraacetic acid (EDTA) and cetyltrimethylammonium bromide (CTAB) assisted hydrothermal route by using NaOH solution. Electron spin resonance (ESR) measurements of the spinel and hexagonal ferrite NPs have been performed by a high sensitive conventional x˗band (~9.5–9.8 GHz) spectrometer at room temperature (RT). The measured five small g-values by ESR spectra at RT may be relevant for quantum information processing. Quantum computing and relativistic quantum computing by two-level system (qubit) have been realized by spinel type NPs at RT. Temperature evolution of magnetic hysteresis loops, magnetization, coercivity (HC), saturation field (HS), saturation magnetization (MS) and remanent magnetization (Mr) have been investigated.

Frustrated magnetism of the triangular-lattice antiferromagnets α-CrOOH and α-CrOOD

We report a comprehensive investigation of the frustrated magnetism on the delafossite oxides, α-CrOOH and α-CrOOD, which experimentally realize the S = 3/2 nearly-Heisenberg antiferromagnetic (J 1 > 0) model on a triangular lattice with weak single-ion anisotropy (D). The electron spin resonance (ESR), neutron scattering, and specific heat (C m) measurements on both α-CrOOH and α-CrOOD consistently indicate that the long-range 120° Néel order is significantly suppressed and both systems are in the vicinity of a spin-liquid phase with C m ∼ T 2 at low temperatures. The strength of D is quantitatively determined from fitting the high-temperature ESR linewidth and magnetic susceptibility, and its minus sign (D < 0, easy-axis type) is suggested by the low-energy (E ⩽ 2 meV) spin excitations. This easy-axis anisotropy (D/J 1 ∼ −5%) competes with the 120° Néel order and thus enhances the quantum spin fluctuations at low temperatures.

Experimental and density functional theory investigations on the antioxidant mechanism of carbon nanotubes

Carbon nanotubes (CNTs) could improve the antioxidant properties of polymers because of their radical scavenging activities, but the interaction between CNTs and radicals is ambiguous. We investigated the thermal-oxidative aging resistance of fluorosilicone rubber (FSR) with and without multi-wall carbon nanotubes (MWCNTs), and tracked the concentration of peroxy radicals using chemiluminescence measurements. The results showed that 0.1–0.5 wt% of MWCNTs could block the auto-oxidation degradation of FSR by scavenging the alkyl radicals, thereby showing an antioxidant effect. Based on the structural characterizations of nanocarbons, a set of polycyclic aromatic phenols and polycyclic aryloxy radicals (PArO·) were constructed and optimized to mimic CNTs. The spin density distribution, spin population, and the formation and reaction of PArO· were calculated using density functional theory (DFT). The results indicated that the CNTs were an open-shell system with a spin density distribution focused on the aryloxy groups and nearby sp2-hybridized carbon atoms. Those atoms with spin populations ranging from 0 to 0.6 a.u. were inert but could react with high-reactivity radicals, including alkyl radicals. This mechanism was confirmed by electron spin resonance measurements of the nanocarbons and heat-treated pyrenols. This study contributed to the development of nanocarbons in antioxidants, catalysts, and reactive oxygen species scavengers.

Inactive Cu2O Cubes Become Highly Photocatalytically Active with Ag2S Deposition.

Previously, Cu2O cubes have been shown to remain photocatalytically inert toward methyl orange degradation even after surface decoration with ZnO, ZnS, CdS, and Ag3PO4 nanostructures. Surprisingly, when Ag2S nanoparticles are lightly deposited on Cu2O cubes as seen through scanning electron microscopy (SEM) images, the heterostructures become highly photocatalytically active. X-ray diffraction (XRD) patterns show mainly Cu2O diffraction peaks due to lightly deposited Ag2S, but Ag2S peaks can emerge with increased Ag2S deposition. X-ray photoelectron spectroscopy (XPS) analysis also supports Ag2S formation on Cu2O crystals. The Ag2S-deposited Cu2O octahedra and rhombic dodecahedra show the expected activity enhancement. Electron paramagnetic resonance (EPR) measurements, as well as electron, hole, and radical scavenger tests, all confirmed the emergence of photocatalytic activity from the Ag2S-Cu2O cubes. Photoluminescence lifetimes are shortened after Ag2S deposition. Electrochemical impedance measurements revealed a large decrease in charge transfer resistance for Cu2O cubes after the Ag2S deposition. Unexpectedly, the separately synthesized Ag2S particles are also photocatalytically inactive. No specific lattice planes of Ag2S are formed directly over the {100} face of Cu2O. Diffuse reflectance and ultraviolet photoelectron spectral data were used to construct band diagrams of different Cu2O crystals and Ag2S nanoparticles. A Z-scheme charge transfer mechanism may be involved at the heterojunction interface to promote charge carrier separation. However, to explain the sudden appearance of photocatalytic activity from the Ag2S-deposited Cu2O cubes, a large change in the {100} surface band bending after Ag2S deposition should be used. This work illustrates that an unusual photocatalytic outcome is possible to semiconductor heterojunctions, where two photocatalytically inert components can become highly active when joined together.

UV and X-ray excited red persistent luminescence in Mn2+ doped MgGeO3 material synthesized in air and reducing atmosphere

Materials with long persistent luminescence (PersL) have caused widespread interest among scientists and industry for decades. Currently, there is widely available information on the long persistent luminescence materials with emission in the blue and green spectral range, while the number of publications on the afterglow in the red and near-infrared spectral range is considerably lower. In the course of this work MgGeO3 material doped with 0.1 mol% Mn2+ was produced using solid-state reaction synthesis in ambient and reducing atmospheres. The material exhibits a broad luminescence band with a peak around 680 nm, excited by either X-rays or UV. After cessation of irradiation, the afterglow up to 6 h when excited by UV and 15 h in the case of excitation by X-rays can be observed. Decay kinetics of the samples indicate that persistent luminescence in this material is a complex process that includes several different traps. Different thermally stimulated luminescence (TSL) techniques, such as Tstop – Tmax and Hoogenstraaten's methods were employed to draw conclusions about the nature of the traps and properties of the material. It was concluded that multiple traps with activation energy between 0.60 and 1.55 eV are present in the samples, furthermore the synthesis in reducing atmosphere promotes creation of additional closely overlapping deep traps, which, based on electron paramagnetic resonance (EPR) measurements, most likely are related to oxygen vacancies.

The influence of gamma radiation on organic compounds having carbon ring and its application in dosimetry

Abstract The formation of highly oxidizing radicals in multifunctional-solid compounds upon irradiation with gamma-ray had been investigated. Five organic compounds having a single carbon ring had been used in the present investigation; these materials are 1-chloro-4-nitrobenzene, 4′-aminoacetophenone, 3′-hydroxyacetophenone, n-anthranilic acid, and triphenylmethane. These material were irradiated using 60Co radiation with different doses between 20 and 100 kGy. Electron spin resonance spectroscopy spotted increases of the resonance absorption having landé factor around 2.0113 ± 0.003 upon irradiation with the increasing of dose. This resonance absorption was related to the formation of long-lived oxygen radicals that were attached to one of the radiation synthesized compounds. The method of infrared absorption spectroscopy emphasized the formation of cyclic and aliphatic hexane in addition to the active oxygen radicals. n-Anthranilic acid was found to be suitable for radiation the dosimetry with long-lasting radiation signature as electron spin and also to determine the exposure dose. The time-lapse infrared and electron spin resonance measurements had been used to tracked the formation of active species within the time-lapsed after the end of exposure; results showed that the dosimetric signature may be used as a tracker for the time when the exposure happens.

High-pressure Ar passivation to enhance the photoluminescence of Si nanocrystals

Photoluminescence (PL) enhancement of Si nanocrystals (Si–NCs) embedded in SiO2 matrix by high-pressure (30 bar) Ar passivation at moderately high temperatures has been observed. For the same pressure, time and temperature of passivation, the PL enhancement of Si–NCs for the Ar passivated sample is even larger than that for the regular H2 passivated one. Electron paramagnetic resonance (EPR) measurement shows that high-pressure Ar passivation causes more reduction in density of dangling bonds which are non-radiative recombination centers, than the regular H2 one. Elemental depth profile analysis shows deep diffusion of Ar atoms into the sample after Ar passivation. The depth profile of PL enhancement after Ar passivation correlates properly with the Ar depth distribution. This effect of inert gas passivation also holds for the case of Kr passivation. The mechanism of such an effect could be that Ar atoms inside the sample alter Si dangling bonds into paired Si ones by a kind of annealing process of thermal atomic collision.

Iron oxidation state in La0.7Sr1.3Fe0.7Ti0.3O4 and La0.5Sr1.5Fe0.5Ti0.5O4 layered perovskites: Magnetic properties

La0.5Sr1.5Fe0.5Ti0.5O4 and La0.7Sr1.3Fe0.7Ti0.3O4 solid solutions with the layered perovskite structure were synthesized using a solid state method. Structural properties of obtained samples were characterized using X-ray diffraction and X-ray fluorescence analyses. Magnetic properties were investigated using magnetometry, electron spin resonance (ESR) and Mössbauer spectroscopy methods. Based on magnetization and ESR measurements it was suggested the presence of Fe4+ ions in addition to trivalent iron ions that was exactly confirmed by Mössbauer spectroscopy investigations. Based on all experimental results one can suggest the presence of the electronic phase separation in the investigated samples – the simultaneous existence of the paramagnetic phase and magnetically correlated regions, which form due to the mixed-valence iron ions. So the paramagnetic phase with strong antiferromagnetic correlation exists in both samples, while the second phase is ferromagnetically and ferrimagnetically correlated regions in La0.5Sr1.5Fe0.5Ti0.5O4 and La0.7Sr1.3Fe0.7Ti0.3O4, respectively.