Electron Spin Resonance Characteristics Research Articles

Investigations on single and multi-grain optically stimulated luminescence (OSL) sensitivity and electron spin resonance (ESR) signals in quartz derived from sandstones: Insights on provenance of quartz in ancient depositional systems

Trapped charge techniques of luminescence and electron spin resonance (ESR) are classic tools for dating Quaternary deposits. Over the past decade, these techniques have been routinely applied to investigate provenance and/or the sedimentary history of quartz grains based on their different luminescence and ESR characteristics. Of these, optically stimulated luminescence (OSL) sensitivity is one of the most widely investigated parameter for luminescence-based provenance approach. A majority of studies on this parameter are based on evaluation of multi-grain quartz OSL sensitivity of the samples. This is particularly concerning because single-grain quartz luminescence studies have shown that the luminescence signal of a multi-grain aliquot is contributed by less than ∼1–10% of the total grains. Since the sole criteria for discrimination of sources based on luminescence sensitivity relies on its intensity, therefore the results based on multi-grain analysis will most likely be skewed depending on the ‘proportion’ and ‘brightness’ of a few grains. This demands a need to evaluate the potential of single-grain quartz OSL sensitivity in provenance studies. In this study, we investigate single and multi-grain quartz OSL sensitivity from compositionally different sandstones with well-characterised sources based on U–Pb zircon ages. We further complement this analysis with characterisation of ESR centres commonly used in quartz provenance, namely E′1 and [AlO4]0 centres. Our study shows that single-grain quartz OSL sensitivity can help distinguish between sediments that have a predominant input from a single source as compared to those with contribution from multiple sources, which otherwise cannot be inferred from multi-grain studies. Moreover, our results on characterisation of quartz-based ESR intensity of E′1 and saturated [AlO4]0 centres successfully differentiates between sandstones and further complements the luminescence-based characterisation.

Особенности электронного спинового резонанса в биообъектах Pleurotus ostreatus, выращенных на субстрате с добавлением магнетит

Особенности электронного спинового резонанса в биообъектах Pleurotus ostreatus, выращенных на субстрате с добавлением магнетит

Antioxidative Properties of Melanins and Ommochromes from Black Soldier Fly Hermetia illucens.

A comparative study of melanin and ommochrome-containing samples, isolated from the black soldier fly (BSF) by enzymatic hydrolysis, alkaline and acid alcohol extraction or by acid hydrolysis, was carried out. Melanin was isolated both as a melanin-chitin complex and as a water-soluble melanin. Acid hydrolysis followed by delipidization yielded a more concentrated melanin sample, the electron spin resonance (ESR) signal of which was 2.6 × 1018 spin/g. The ommochromes were extracted from the BSF eyes with acid methanol. The antiradical activity of BSF melanins and ommochromes was determined by the method of quenching of luminol chemiluminescence. It has been shown that delipidization of water-soluble melanin increases its antioxidant properties. A comparison of the antioxidant activity of BSF melanins and ommochromes in relation to photoinduced lipid peroxidation was carried out. The ESR characteristics of native and oxidized melanins and ommochromes were studied. It is assumed that H. illucens adult flies can be a useful source of natural pigments with antioxidant properties.

Thermal stability and temperature dependent electron spin resonance characteristics of the As acceptor in geological 2H-MoS2

Electron spin resonance (ESR) results are presented on the thermal stability and temperature dependence of the ESR spectral characteristics of the As acceptor dopant (As substituting for S site) in geological 2H-MoS2. Under sequential isochronal heating in H2 (1.1 atm), the As dopant density is found to remain unaffected for anneal temperatures (Tans) up to 525 °C, above which the density moderately decreases (∼3 times) for Tan → 840 °C. In turn, vacuum annealing is seen to result in a gradual increase (2–3 times) of the As acceptor density for Tan increasing from 400 °C → 840 °C, pointing to a positive ‘regain’ of misconfigured As impurities in pristine geo-MoS2. Finally, meticulous monitoring of the ESR signal intensity versus tempertaure at X-band confirms the previously inferred As acceptor activation energy of 0.7 ± 0.2 meV at K-band. The appropriateness of the latter ESR probing and analysis approach has been consolidated by application to the archetypal case of decoupled P donors in n-Si, resulting in an ESR-determined activation energy (42 ± 4 meV) well in agreement with the generally accepted one. In light of these findings, As is confirmed as a promising candidate for stable covalently bonded p-type doping of MoS2.

The Nitrogen Acceptor in 2H‐Polytype Synthetic MoS2: Frequency and Temperature Dependent ESR Analysis

In extending on recent electron spin resonance (ESR) work which has revealed the N acceptor (N substituting for S site) in 2H‐polytype bulk synthetic MoS2, the dopant is extensively analyzed in terms of its frequency, temperature (T), and magnetic field B angular dependent ESR spectral characteristics. For B∥c‐axis, the multi‐frequency analysis confirms the ESR spectrum as being composed of a 14N hyperfine (hf) triplet with hf splitting constant A∥ = 14.7 ± 0.2 G (B∥c‐axis) and making up ≈74% of the total spectrum intensity, superimposed on a central line centered at about equal g‐value [g∥ = 2.032(2)]. The presence of the latter signal, points to some non‐uniformity in dopant distribution, that is, clustering, with about ≈26% of the total N response not originating from N incorporated in the preferred “isolated” dopant configuration. Angular dependent measurements reveal distinct anisotropy of the hf matrix, whereas ESR probing over a wide T‐range exposes drastic signal broadening with increasing T above ≈150 K. Detailed study of the N acceptor signal intensity versus T at Q‐band reveals an activation energy Ea = 50 ± 10 meV, herewith consolidating the value reported initially. Besides unveiling the S‐site substitutional N impurity as an appropriate p‐type dopant for MoS2, the total of the ESR work establishes a basic frame of the N acceptor ESR characteristics, giving way for further in‐depth theoretical perusal.

Colloidal Organolead Halide Perovskite with a High Mn Solubility Limit: A Step Toward Pb-Free Luminescent Quantum Dots.

Organolead halide perovskites have emerged as a promising optoelectronic material for lighting due to its high quantum yield, color-tunable, and narrow emission. Despite their unique properties, toxicity has intensified the search for ecofriendly alternatives through partial or complete replacement of lead. Herein, we report a room-temperature synthesized Mn2+-substituted 3D-organolead perovskite displacing ∼90% of lead, simultaneously retaining its unique excitonic emission, with an additional orange emission of Mn2+ via energy transfer. A high Mn solubility limit of 90% was attained for the first time in lead halide perovskites, facilitated by the flexible organic cation (CH3NH3)+ network, preserving the perovskite structure. The emission intensities of the exciton and Mn were influenced by the halide identity that regulates the energy transfer to Mn. Homogeneous emission and electron spin resonance characteristics of Mn2+ indicate a uniform distribution of Mn. These results suggest that low-toxicity 3D-CH3NH3Pb1-xMnxBr3-(2x+1)Cl2x+1 nanocrystals may be exploited as magnetically doped quantum dots with unique optoelectronic properties.

(Invited) Probing Dopants in 2H MoS2 Crystals and 2D Layers by Electron Paramagnetic Resonance: Identification and Quantification

Low-temperature electron spin resonance (ESR) study on the atomic nature of doping in geological p-type 2H MoS2 crystals reveals two main types of responses. The major one, of axial symmetry, stems from As acceptors, with As substituting for S, which, occurring with density ~2.4x1017 cm-3, predominantly accounts for the p-type doping. Its ESR spectrum points to manifest non-uniform As dopant distribution, i.e., substantial clustering, with only ~13% of the As response originating from single decoupled As impurities. A second, much weaker so far unknown signal, of spin density ~5x1014 cm-3, shows lower than axial symmetry, likely orthorhombic (C 2v). Based on salient ESR characteristics, it is assigned to the Pb impurity substituting for Mo, the center operating as acceptor. The dopant activation energy, Ea, was assessed through cautious monitoring of the signal intensity vs. temperature. For As, this resulted in Ea = 0.7 ± 0.2 meV, unveiling As as a noticeable shallow acceptor. The adduced insight may contribute to developing tunable, robust p-type doping strategies for few-layer MoS2 application in future nano-electronic devices.

Defect correlated with positive charge trapping in functional HfO2 layers on (100)Si revealed by electron spin resonance: Evidence for oxygen vacancy?

We report on the results of low-temperature K- and Q-band electron spin resonance (ESR) measurements on three types of device-grade HfO2 films deposited on p-(100)Si by chemical vapor deposition (CVD) using different precursors. The study has been carried out in combination with ex situ contactless charge injection, complemented with various post-growth irradiation treatments, with the intent to assess the presence and atomic nature of occurring charge trapping centers. In HfO2 layers grown by atomic layer (AL) and metal-organic (MO) CVD, this reveals the reproducible appearance of a paramagnetic center, termed H5, in firm correlation with alternate positive/negative charge injection, i.e., distinct signal intensity increase/decrease, respectively. Simulation of the observed powder pattern for both K- and Q-band consistently points to a defect of orthorhombic symmetry characterized by g1=1.880±0.006, g2=1.900±0.006, g3=1.981±0.0015. Analysis based on the inferred spectroscopic ESR characteristics in comparison with previous theoretical work leads to the suggestion that the observed center may concern an O-vacancy defect, closest perhaps to the 4-fold 1+ charged O-vacancy (VO4+). The revealed defect may account, at least partly, for the previously reported distinct propensity of positive charge trapping in Si/hafnia structures grown by ALCVD and MOCVD.

Multi‐frequency electron spin resonance study of inherent Si dangling bond defects at the thermal (211)Si/SiO2 interface

AbstractMultifrequency low temperature electron spin resonance (ESR) studies were carried out to atomically assess inherent point defects at the thermal ‘higher index' (211)Si/SiO2 interface. This reveals, as dominant imperfections, Pb‐type centers (generic entity Si3≡Si•, the dot representing an unpaired sp3‐like hybrid) occurring in densities of ∼1 × 1013 cm–2 for oxidation temperatures ∼400 °C. On the basis of the pertinent ESR characteristics, the inherent basic defect is typified as the Pb0(211) variant, resembling closely the Pb0 center in standard (100)Si/SiO2. At the higher index (211)Si/SiO2 interface, these defects predominantly pertain to defected Si atoms located at (111)‐face terraces. Combination of angular and frequency (ν) dependent studies show the Pb0(211) peak‐to‐peak line width ΔBpp to be composed of a residual width (ν→0) of 2.2 ± 0.1 G, to which dipolar broadening contributes an essential part, and a substantial inhomogeneous broadening component due to g distribution, predominantly in g⊥, induced by non‐uniform interface strain –also similar to the Pb0(100) properties. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Microscopic Characterization of Printable Low-Voltage Electrolyte-Gated Transistors by Electron Spin Resonance

We have investigated the microscopic properties of printable low-voltage electrolyte-gated transistors using electron spin resonance (ESR). The utilized devices were ion gel-gated regioregular poly(3-hexylthiophene) (RR-P3HT) thin-film transistors. We performed simultaneous mesurements of field-induced ESR (FI-ESR) and device characteristics using the same device. Clear FI-ESR signals due to hole carriers (positive polarons) were observed by applying a negative gate voltage. The anisotropy of the ESR linewidth indicated two-dimensional magnetic interactions between high density charges. The magnetism of the majority of hole carriers at a high charge density was found to be nonmagnetic from the simultaneous measurements of FI-ESR and transfer characteristics. The anisotropy of the g value of the ESR signal at a high gate voltage indicated the disordered molecular orientation of RR-P3HT where paramagnetic holes exist. These results provide insight into the charge transport mechanism of RR-P3HT polymer semiconductors with high charge densities.

물리적 확인시험법을 이용한 시판 유통 중인 고춧가루의 방사선 조사여부 판별 모니터링

Ten commercially available red pepper powders were investigated using photostimulated-luminescence (PSL), thermoluminescence (TL) and electron spin resonance (ESR) analyses to confirm their irradiation status. The application of PSL, TL, and ESR analyses was also confirmed by in-house irradiation. In PSL-based screening, all samples gave negative photon counts (<700 PCs). The PSL calibration dose (1 kGy) showed a low sensitivity of 4 samples, while the others provided reliable screening results. TL glow curves demonstrated maximum peaks after 250 o C for the 6 samples; however 4 samples gave complex TL glow curves with maximum peaks in the range of 185-260 o C (radiation-specific), which could be the effect of an irradiated component in low concentration as the TL ratios of all samples were <0.1. Radiation-specific ESR features were absent in the all commercial samples. Variable irradiation detection properties were found; where the TL analysis showed the possible presence of an irradiated component in 4 samples requiring further monitoring and investigation.

Evaluation of Microscopic Properties of Organic Solar Cells by Light-Induced Electron Spin Resonance

We have investigated organic thin-film solar cells from the microscopic viewpoint with light-induced electron spin resonance (ESR). The utilized cell structures are indium–tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM)/Pd/LiF/Al. We performed simultaneous measurements of light-induced ESR and device characteristics using the same device. Under simulated solar irradiation, the light-induced ESR intensity of a solar cell increases, while the short-circuit current and open-circuit voltage of the cell concomitantly decrease with increasing duration of irradiation. We have successfully observed a clear correlation between the light-induced ESR intensity and the device characteristics. Trapping sites of photogenerated hole carriers (positive polarons) are ascribed to P3HT by the analysis of the ESR signals.

Charge Formation in Pentacene Layers During Solar‐Cell Fabrication: Direct Observation by Electron Spin Resonance

AbstractMicroscopic characterization of charge carriers in solar cells is useful for high‐performance cell fabrication because the formation and accumulation of charges in cells greatly affect the device performance. Electron spin resonance (ESR) is suitable for such characterization because it can directly observe charge carriers with spins in these cells. In this work, the ESR method is applied to organic thin‐film solar cells to investigate charge formation in such devices. Heterojunction cells of indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS)/pentacene/C60/bathocuproine (BCP)/Al are investigated. Clear ESR signals are observed by inserting a typical PEDOT:PSS hole buffer layer. From analysis of the dependence of the ESR characteristics on the external magnetic field direction, the bias voltage, and the duration of solar‐simulated irradiation, the charges (mobile holes) in pentacene layers are successfully identified and it can be deduced that these holes are formed at the PEDOT:PSS/pentacene interface during device fabrication. This ESR analysis provides useful knowledge for understanding device operation and improving device performance at the microscopic level.

High-Frequency ESR Measurements of S = 1/2 1-D Heisenberg Antiferromagnetic Zig-Zag Chain (VO)(SO4)(2,2-bpy)

High-frequency electron spin resonance (ESR) measurements of S = 1/2 one-dimensional Heisenberg antiferromagnetic zig-zag chain substance (VO)(SO4)(2,2-bpy) were performed in the temperature region from 1.8 to 265 K. ESR measurements at 265 K show typical powder pattern spectra of the V4+ ion and g || = 1.925 ± 0.001 and g ⊥ = 1.976 ± 0.001 were obtained. Although the magnetic susceptibility shows a maximum at 3.1 K suggesting the existence of a short-range order, no g-shift and line width broadening were observed down to 1.8 K. We suggest that these temperature-independent features of ESR can be attributed to the result of frustration in (VO)(SO4)(2,2-bpy).

Quantum confinement and electron spin resonance characteristics in Si-implanted silicon oxide films

The nature of electron and hole trapping in silicon ion–implanted silicon oxide (SiO2) with a dose of 1016 cm−2 were studied using photoluminescence and electron spin resonance (ESR) measurements. We observed an ESR signal with g = 2.006 after hole and electron injections. These results unambiguously imply that the Si nanoclusters created by the high-dose Si implants are both electron and hole traps in the SiO2 films.

(Invited) Identification of Intrinsic Point Defects at GexSi1-x/Oxide Interfaces by ESR Probing

We report on the obvervation by electron spin resonance (ESR) of two paramagnetic Ge dangling bond (DB)-type defects at Ge/oxide interfaces. One, detected in SiO2/(100)GexSi1-x/SiO2/Si hetero-structures grown by the condensation method, exhibits monoc-linic-I (C2v) symmetry, with principal g values g1=2.0338(3), g2=2.0386(6), g3=2.0054 and g3 axis (DB) direction 24{plus minus} 2{degree sign} off a <111> direction towards the [100] interface normal. The defect reaches maximum densities for x~0.7, to disappear for x{less than or equal to}0.45 and x{greater than or equal to}0.87. It is suggested to concern a Ge Pb1-type center, i.e., not a trigonal basic Ge Pb(0)-type center (Ge3≡Ge•), thus exposing a unique interface mismatch adaptation as function of substrate Ge fraction. The second one, observed at the interface of epitaxially grown Ge3N4/(111)Ge entities with nm-thin Ge3N4 layers, shows trigonal (C3v) symmetry characterized by g//~2.0023 and g⊥~2.0032. Based on comparision of its salient ESR features with previous theoretical results, the defect is suggested to concern the Ge K center.

Effects of gamma radiation on solid trisodium citrate dihydrate: radical kinetics, radiosensitivity and dosimetry

In the present work, radiosensitivity and dosimetric potential of solid trisodium citrate dihydrate (SC) were explored through a detailed electron spin resonance (ESR) study performed at various temperatures. Irradiated SC was observed to exhibit an ESR spectrum consisting of many intense and weak resonance lines spread over a magnetic field range of 7 mT and centered at g = 2.0039. An evaluation technique based on the variations of the characteristic resonance line intensities and the spectrum area under different experimental conditions was adopted, to determine the spectroscopic, kinetic and dosimetric features of radical species responsible for the observed experimental ESR spectrum. Radicals exhibiting similar ESR characteristics to those reported in the literature for irradiated tricarboxilic acids and their organic compounds were shown to be also produced in gamma-irradiated SC.

ESR investigations on doped conjugated polymers diluted in a solid matrix

The electron spin resonance (ESR) properties of a polystyrene (PS) blend of iodine-doped regiorandom (RRa) poly(3-octylthiophene) (P3OT) are investigated to reveal the intrachain spin dynamics of conjugated polymers. The PS blends exhibits broader and anisotropic ESR spectra compared to the isotropic spectrum of the pure RRa-P3OT film. Spectral simulations are performed to reveal the ESR features of the PS blend. It is concluded that intrachain spin motion is less active than interchain motion. In addition, the spin dynamics of the pure film are dominated by intrachain spin motion at low temperature and interchain motion at high temperature.

Electron spin resonance in silver-doped PbS nanorods

The electron spin resonance characteristics of silver (Ag)-doped PbS nanorods have been investigated here. We show that both Ag0 and Ag2+ centres can be simultaneously created in PbS nanorod structures grown in polymers. Structural investigations reveal that strain-induced distortion of PbS lattice can lead to the formation of hole traps in as-grown samples. Large strain-induced binding of the Ag+ ions into the Pb2+ vacancies lowers the activation energy of diffusion significantly. The isomorphic substitution of Ag+ in PbS host is then converted into Ag0 and Ag2+ paramagnetic centres to maintain the charge neutrality and cation–anion ratio, confirmed by electron spin resonance investigations.

Electron spin resonance in CuCrS2 chrome-copper disulphides synthesized by different methods

The electron spin resonance (ESR) in CuCrS2 disulphides is found to be strongly dependent on a synthesis method used. At a temperature of 300 K, a polycrystalline CuCrS2 sample is paramagnetic with a g-value of 1.95 at 40 K, it undergoes the magnetic transition. In the temperature range 4.2–290 K, a single-crystal sample prepared by a chemical vapor transport method exhibits the ESR features typical of a ferromagnet. It is shown that these features are related to the presence of a small amount of the single-crystal CuCr2S4 impurity in the CuCrS2 single crystal.