Decrease In Linewidth Research Articles

Exploring the Crystal Structure, Thermodynamics, and Molecular Dynamics of NH(CH3)3CuCl3·2H2O Organic-Inorganic Hybrid Perovskite.

Understanding the physical properties of the organic-inorganic hybrid NH(CH3)3CuCl3·2H2O is necessary for its potential applications. Initially, the monoclinic structure of this crystal was discussed via single-crystal X-ray diffraction. Moreover, the previously unknown phase transition temperature was 350 K, as revealed by differential scanning calorimetry and powder X-ray diffraction. Attributed to ferroelasticity, domain walls were observed between the temperatures T c (Low) (223 K) and T c (High) (350 K). Furthermore, changes in chemical shifts for 1H and 13C indicated alterations in the molecular environment, whereas a notable decrease in line width was attributed to increased molecular motion freedom. Subsequently, spin-lattice relaxation times (T 1ρ values) for 1H and 13C (indicative of energy transfer) were influenced by tumbling motions. The high activation energy barrier for molecular reorientation was associated with the tumbling motion of methyl groups around the triple symmetry axis. These foundational properties guide the development of efficient organic-inorganic hybrids suitable for practical applications.

Zn-Ti co-substituted LiZn microwave ferrites: Sintering characteristics and gyromagnetic properties

To meet the low-loss and high-frequency application requirements of modern electronic information systems for integrated microwave devices, Zn-Ti co-substituted LiZn microwave ferrites were prepared in this work. The results demonstrated that Zn-Ti co-substitution promoted the grain growth and densification process during sintering, leading to a decrease in the pore-induced linewidth (ΔHp) of LiZn composite microwave ferrites; the introduction of non-magnetic Zn2+ and Ti4+ ions lowered the content of Fe3+ ions in the ferrites, which reduced the magnetocrystalline anisotropy constant |K1| and thus diminished the anisotropy-induced linewidth (ΔHa). Besides, the dielectric loss of the material decreased with increasing Zn-Ti substitution amounts (x) due to the reduction of Fe2+ ion content. As a result, when x = 0.35, the FMR linewidth was decreased from ∼251 Oe to ∼97 Oe, and the dielectric loss was greatly reduced from >100×10−4 to ∼3.82×10−4 in the ferrites. The material also exhibited excellent properties including high saturation magnetization (∼3913 Gauss), high Curie temperature (∼304 °C), and low coercivity (∼2.05 Oe).

Control of sintering characteristics and gyromagnetic properties of LiZn-based microwave ferrite ceramics by Nb2O5 doping

In this study, a new strategy of trace amounts of Nb2O5 doping was employed to control microwave loss of Ti-Mn-Bi co-substituted LiZn-based ferrite ceramics sintered at 890 °C. The results revealed the distribution of doped Nb in the spinel ferrites. Partial Nb5+ ions entered the lattices and induced the generation of Fe2+ ions, resulting in a decrease in the magnetocrystalline anisotropy linewidth (ΔHa). The rest of Nb2O5 remained at grain boundaries and formed high resistance layers, which contributed to lowering the dielectric loss (tanδε). Due to the particular distribution of Nb, a dual-structure and higher densification were observed, and thus the porosity-induced line broadening contributions (ΔHp) was reduced. Notably, by doping with 0.15 wt.% Nb2O5, the LiZn-based ferrites presented excellent magnetic properties (ΔH = 87 Oe, tanδε = 3.24 × 10-4, 4πMs = 3799 Gauss, Br/Bs = 0.9), which shows promising potential for low-loss microwave ferrite devices.

7.4 nm linewidth Pt nanowires by electron-beam lithography using non-chemically amplified positive-tone resist and post-exposure bake

Abstract 7.4 nm linewidth Pt nanowires were demonstrated on SiO2/Si substrates via electron-beam lithography using a non-chemically amplified positive resist ZEP520A and post-exposure bake (PEB) treatment. The effect of the PEB treatment conditions on the nanowires’ characteristics was investigated. As the PEB temperature and time increased, a decrease in the mean linewidth and an improvement of the line-width (line-edge) roughness of the nanowires were observed. Pt nanowires with an ultrafine linewidth of 7.4 nm were successfully fabricated using the optimal condition of 100 °C for 2 min, verifying the effectiveness of PEB for fabricating sub-10 nm linewidth robust metal nanowires.

A 7T interleaved fMRS and fMRI study on visual contrast dependency in the human brain

Abstract Introduction: Functional magnetic resonance spectroscopy (fMRS) is a non-invasive technique for measuring dynamic changes in neurometabolites. While previous studies have observed concentration changes in metabolites during neural activation, the relationship between neurometabolite response and stimulus intensity and timing requires further investigation. To address this, we conducted an interleaved fMRS and functional magnetic resonance imaging (fMRI) experiment using a visual stimulus with varying contrast levels. Methods: A total of 20 datasets were acquired on a 7T MRI scanner. The visual task consisted of two STIM blocks (30 s/20 s ON/OFF, 4 min), with 10% or 100% contrast, interleaved with a 5 min REST block. A dynamic fitting approach was used for fMRS data analysis. For metabolite level changes, the STIM conditions were modeled in two different ways: either considering the full STIM block as active condition (full-block model) or only modeling the ON blocks as active condition (sub-block model). For linewidth changes due to the BOLD effect, STIM conditions were modeled using the sub-block model. Results: For both models, we observed significant increases in glutamate levels for both the 10% and 100% visual contrasts, but no significant difference between the contrasts. Decreases in aspartate, and glucose, and increases in total N-acetylaspartate and total creatine were also detected, although less consistently across both 10% and 100% visual contrasts. BOLD-driven linewidth decreases and fMRI-derived BOLD increases within the MRS voxel were observed at both 10% and 100% contrasts, with larger changes at 100% compared to 10% in the fMRI-derived BOLD only. We observed a non-linear relation between visual contrast, the BOLD response, and the glutamate response. Conclusion: Our study highlights the potential of fMRS as a complementary technique to BOLD fMRI for investigating the complex interplay between visual contrast, neural activity, and neurometabolism. Future studies should further explore the temporal response profiles of different neurometabolites and refine the statistical models used for fMRS analysis.

Bose Condensation of Upper-Branch Exciton-Polaritons in a Transferable Microcavity.

Exciton-polaritons are composite quasiparticles that result from the coupling of excitonic transitions and optical modes. They have been extensively studied because of their quantum phenomena and potential applications in unconventional coherent light sources and all-optical control elements. In this work, we report the observation of Bose-Einstein condensation of the upper polariton branch in a transferable WS2 monolayer microcavity. Near the condensation threshold, we observe a nonlinear increase in upper polariton intensity accompanied by a decrease in line width and an increase in temporal coherence, all of which are hallmarks of Bose-Einstein condensation. Simulations show that this condensation occurs within a specific particle density range, depending on the excitonic properties and pumping conditions. The manifestation of upper polariton condensation unlocks new possibilities for studying the condensate competition while linking it to practical realizations in polaritonic lasers. Our findings contribute to the understanding of bosonic systems and offer potential for the development of polaritonic devices.

Formation and evolution mechanism of persistent free radicals in biochar during biomass pyrolysis: Insights from biochar’s element composition and chemical structure

The persistent free radicals (PFRs) in biochar can play a crucial role during biochar’s utilization, but the formation and evolution mechanism of PFRs in biochar are poorly understood because of biochars’ element specificity and chemical structure complexity. In order to further understand the formation and evolution mechanism of PFRs, the PFRs characteristics, chemical structure and element composition of six types of biomasses were investigated. The results revealed that the changing trend of the PFRs types, concentration and line width with pyrolysis temperature is similar for all six feedstocks. The difference in the feedstocks’ properties just affects the absolute value of PFRs’ characteristic parameters. The arrangement and combination of elements and carbon skeleton structure in biochar determine the evolution of PFRs in the pyrolysis process. Additionally, the (H + O)/C atomic ratio of the biomass feedstock and the content of substitutional groups on aromatic rings were found to influence the types of PFRs in biochar. When biochar has a similar O/C atom ratio, a higher H content can reduce the carbon-centered PFRs in biochar. Besides, the reduction in O element content contributes to a decrease in line width due to the reduction in the effect of heteroatoms. The good correlation between O/C atomic ratio, H/C atomic ratio, chemical structure and PFRs characteristics can be used to predict the PFRs characteristics. Combining the changing characteristics in PFRs concentration and carbon skeleton structure of biochar, a three-stage model of PFRs formation and evolution was constructed.

Comparison of chromospheric diagnostics in a 3D model atmosphere

Context. The Hα line, one of the most studied chromospheric diagnostics, is a tracer of magnetic field structures, while the intensity of its line core provides an estimate of the mass density. The interpretation of Hα observations is complicated by deviations from local thermodynamic equilibrium (LTE) or instantaneous statistical equilibrium conditions. Meanwhile, millimetre (mm) continuum radiation is formed in LTE, and therefore the brightness temperatures from Atacama Large Millimetre-submillimetre Array (ALMA) observations provide a complementary view of the activity and the thermal structure of stellar atmospheres. These two diagnostics together can provide insights into the physical properties of stellar atmospheres, such as their temperature stratification, magnetic structures, and mass density distribution. Aims. In this paper, we present a comparative study between synthetic continuum brightness temperature maps at mm wavelengths (0.3 mm to 8.5 mm) and the width of the Hα 6565 Å line. Methods. We used the 3D radiative-transfer codes Multi3D and Advanced Radiative Transfer (ART) to calculate synthetic spectra for the Hα line and the mm continua, respectively, from an enhanced network atmosphere model with non-equilibrium hydrogen ionisation generated with the state-of-the-art 3D radiation magnetohydrodynamics (rMHD) code Bifrost. We use a Gaussian point spread function (PSF) to simulate the effect of ALMA’s limited spatial resolution and calculate the Hα versus mm continuum correlations and slopes of scatter plots for the original and degraded resolution of the whole box, quiet sun, and enhanced network patches separately. Results. The Hα linewidth and mm brightness temperatures are highly correlated and the correlation is highest at a wavelength of 0.8 mm, that is, in ALMA Band 7. The correlation systematically increases with decreasing resolution. On the other hand, the slopes decrease with increasing wavelength. The degradation of resolution does not have a significant impact on the calculated slopes. Conclusions. With decreasing spatial resolution, the standard deviations of the observables, Hα linewidth, and brightness temperatures decrease and the correlations between them increase, but the slopes do not change significantly. These relations may therefore prove useful in calibrating the mm continuum maps observed with ALMA.

Extremely powerful flare phenomenon of H2O maser in W49N near −40 km s−1

ABSTRACT As a result of detailed observations of the water vapour maser at the 22-m Simeiz radio telescope from 2017 June to 2019 December, two powerful flares were recorded in the Galactic source W49N, which occurred near the high-velocity feature −40 km s−1. The extremely powerful flare had an ultrashort duration of about 2 d and reached a flux density of 110 kJy. An ultrashort flare occurred at the top of a less powerful, but ten times longer one. To our knowledge, a flare of a water maser with such extreme characteristics has never been reported before. A correlation between the exponential increase and decrease in the flare flux density and decrease in line widths with increasing flux density, which is characteristic of an unsaturated maser, is found. The maser of the third flare was in a saturated state and provided a large input flux density 9.5 kJy for the occurrence of two powerful flares, the masers of which were in an unsaturated state. New data have been obtained concerning the physical characteristics of the water maser phenomenon during powerful flares.

Strain-Induced Indirect-to-Direct Bandgap Transition, Photoluminescence Enhancement, and Linewidth Reduction in Bilayer MoTe2.

Two-dimensional (2D) layered materials provide an ideal platform for engineering electronic and optical properties through strain control because of their extremely high mechanical elasticity and sensitive dependence of material properties on mechanical strain. In this paper, a combined experimental and theoretical effort is made to investigate the effects of mechanical strain on various spectral features of bilayer MoTe2 photoluminescence (PL). We found that bilayer MoTe2 can be converted from an indirect to a direct bandgap material through strain engineering, resulting in a photoluminescence enhancement by a factor of 2.24. Over 90% of the PL comes from photons emitted by the direct excitons at the maximum strain applied. Importantly, we show that strain effects lead to a reduction of the overall linewidth of PL by as much as 36.6%. We attribute the dramatic decrease of linewidth to a strain-induced complex interplay among various excitonic varieties such as direct bright excitons, trions, and indirect excitons. Our experimental results on direct and indirect exciton emission features are explained by theoretical exciton energies that are based on first-principles electronic band structure calculations. The consistent theory-experimental trend shows that the enhancement of PL and the reduction of linewidth are the consequences of the increasing direct exciton contribution with the increase of strain. Our results demonstrate that strain engineering can lead to a PL quality of the bilayer MoTe2 comparable to that of the monolayer counterpart. The additional benefit of a longer emission wavelength makes the bilayer MoTe2 more suitable for silicon-photonics integration due to the reduced silicon absorption.

Effect of the sudden change of ambient atmosphere on free radicals in coal body by CO2 fire prevention gas injection

ABSTRACT The coal body’s gas environment transforms during the CO2 fire prevention procedure from an oxygenated ambience to a CO2 gas ambience, which in turn prevents the coal body from continuously oxidizing. To investigate the effect of sudden changes in the gas environment to which the coal body is exposed on the microscopic group reactions, the free radical parameters such as ESR in situ spectra, line widths, g-factors, and free radical concentrations of the coal bodies during the gas atmosphere transition at different temperature moments were measured. The findings are as follows: as the injection temperature point for CO2 rises, the spectral peak height increases, and the paramagnetic center of coal shifts at lower temperature in CO2 atmosphere than in dry air atmosphere. After the abrupt change of gas environment, free radical levels first decrease and subsequently rise. Furthermore, the general development rate of free radicals can be slowed down by injecting CO2 at lower temperatures. Meanwhile, at lower temperatures, the higher the temperature point of the minimum g value is, the smaller the maximum g value is. Changes in a gas atmosphere, sudden decrease in line width of ESR spectra of coal bodies, and the line width finally stabilizes around 0.45. CO2 injection at 70°C has the best inhibitory effect on free radicals.

The role of resonant coupling in vibrational sum-frequency-generation spectroscopy: Liquid acetonitrile at the silica interface

Vibrational sum-frequency-generation (VSFG) spectroscopy is a versatile technique for probing molecular organization at interfaces. There is a growing recognition that dynamic phenomena, such as reorientation and intermolecular vibrational coupling, can also influence VSFG spectra. The silica/liquid acetonitrile interface is a useful system for exploring these effects in more detail. The organization of acetonitrile at this interface has been well studied, and is known to resemble that of a supported lipid bilayer in many ways. Here isotopic dilution is used to explore the influence of resonant intermolecular coupling of methyl symmetric stretches on the VSFG spectroscopy of this system. VSFG spectra in the methyl stretching region at this interface show a blue shift, a decrease in linewidth, and a higher-than-expected intensity upon dilution in deuterated acetonitrile. We demonstrate that resonant coupling influences VSFG spectral shifts through the infrared transition. Using molecular simulations, we show that our experimental observations are consistent with resonant coupling between methyl transition dipoles being a significant, but not the dominant, contribution to the observed spectral shift upon isotopic dilution. Furthermore, our molecular simulations demonstrate that resonant coupling accounts partially for changes in linewidth and intensity. These classical molecular dynamics simulations also elucidate the behavior of the isotropic Raman spectrum in the bulk liquid upon isotopic dilution. We further simulate the resonant coupling among cyano stretches in this system. These simulations match the experimental shift due to the Raman non-coincidence effect shift of the CN stretch in the bulk liquid, but suggest that the corresponding resonant-coupling-induced shift in the VSFG spectrum at the silica interface is minimal. Our experimental and simulation results indicate that proximity to an interface can cause substantial changes in the resonant coupling of vibrations in a liquid.

Fluorescence in colloidal solutions: Scattering vs physicochemical effects on line shape

Line shapes of anionic fluorescein fluorescence in suspensions of polystyrene nanoparticles (PSNP), anionic and cationic micelles, lipid vesicles, and of laurdan in lipid vesicles were investigated. Computed second harmonic of measured spectra indicated three lines for fluorescein and two for laurdan. Accordingly, fluorescein spectra were fit to three Gaussians and laurdan spectra to two lognormal distributions. Resolved line parameters were examined against particle concentration. Scattering, although wavelength dependent, affected intensity but not line shape. Inner filter effects of scattering on line shape are insignificant because multiple scattering, redirection of scattered photons into the detector, and inclusion of scattered photons in collection and detection minimize wavelength dependent effects. Dominant effects on line width and peak positions are due to physicochemical effects of dye-particle-solvent interactions rather than scattering. Fluorescein does not interact with anionic micelles and lipid vesicles, but remains in the aqueous phase, and responds to pH increase induced by these additives. Blue shift in peak position, decrease in line width, and increase in emission intensity in these systems are like those in NaOH solutions. Fluorescein does interact with cationic micelles and hydrophobic PSNP, and its emission is red shifted. Laurdan in lipid vesicles senses interface polarity. Blue shift and decrease in line width of its emission line indicate decreasing polarity with lipid concentration. Scattering, as well as interactions affect emission intensity. Physicochemical effects distort line shape and modify intrinsic spectra. Line shape changes are better markers than intensity to investigate interactions and reactions.

Effect of vacuum annealing on the optical properties of tungsten oxide films

• Annealing of WO 3– x films in vacuum initiates their coloration in blue. • Colored film absorption band is adequately described by the Breit-Wigner distribution. • Annealing temperature rise nonlinearly increases the absorption band intensity. • Decrease in the spectral line width is saturated when annealing temperature increases. • Asymptote of refractive index dispersion decreases in proportion to the temperature. In this work, the thermochromic properties of tungsten oxide films are studied. The goal of this work is to study the influence of vacuum annealing on optical properties of amorphous WO 3– x films deposited on silica glass substrates. These dependences of the absorption index were approximated using the Breit-Wigner distribution. An increase in the annealing temperature led to an increase in the intensity and a decrease in the width of the absorption band in the near infrared range of the film transmission spectrum. This changed the dispersion of absorption and refractive indices.

Iron oxide-Palladium core-shell nanospheres for ferromagnetic resonance-based hydrogen gas sensing

Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe3O4–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe3+ acetylacetonate in the presence of a reducing agent to produce the Fe3O4 core, followed by the reduction of a Pd2+ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H2 gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe3O4–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas.

Parameter Optimization of Laser Direct-Write Patterning on Indium Tin Oxide/Polycarbonate Thin Films Using Multi-Performance Characteristics Analysis

Indium tin oxide (ITO) thin films on polycarbonate (PC) substrates were patterned using the laser direct-write (LDW) technique to form an isolation line. The effect of the LDW parameters (power, pulse repetition rate, and defocusing distance) on the isolation line width, depth and roughness of the PC within the line was investigated. Additionally, the Taguchi method of experimental design was applied to determine the optimal parameters of LDW. Results showed that increasing the power led to an increase in the isolation line width and decrease in the surface roughness of the PC within the line. The increase in the pulse repetition rate and defocusing distance caused a decrease in the isolation line width. The optimal parameters were found to be A2B3C3, consisting of power of 5 W, pulse repetition rate of 100 kHz, and defocusing distance of +3 mm. Under these parameters, we obtained an isolation line width of 48.4 μm, and a surface roughness of Ra 38 nm of the PC within the isolation line. We confirmed that the ITO films separated by the isolation lines attained electrical isolation.

Electric Fields Influence Intramolecular Vibrational Energy Relaxation and Line Widths.

Intramolecular vibrational energy relaxation (IVR) is fundamentally important to chemical dynamics. We show that externally applied electric fields affect IVR and vibrational line widths by changing the anharmonic couplings and frequency detunings between modes. We demonstrate this effect in benzonitrile for which prior experimental results show a decrease in vibrational line width as a function of applied electric field. We identify three major channels for IVR that depend on electric field. In the dominant channel, the electric field affects the frequency detuning, while in the other two channels, variation of anharmonic couplings as a function of field is the underlying mechanism. Consistent with experimental results, we show that the combination of all channels gives rise to reduced line widths with increasing electric field in benzonitrile. Our results are relevant for controlling IVR with external or internal fields and for gaining a more complete interpretation of line widths of vibrational Stark probes.

Effect of Oxygen on Radical Reaction during Oxidation of Different-rank Coals

ABSTRACT The spontaneous combustion disaster caused by low-temperature oxidation of coal often leads to mine fire which poses a serious threat to the safe mining of underground coal resources. Due to the complexity of coal and the variability of gas atmosphere, it is difficult to prevent the spontaneous combustion of residual coal in goaf. In this paper, the radical characteristics during oxidation of lignite, bitumite, and anthracite in anaerobic, anoxic, and normal oxygen atmospheres were measured by preparing mixed gases with different oxygen concentrations. On this basis, the spontaneous combustion characteristics of different-rank coals under different oxygen concentrations were explored. The experimental results show that the primary radical concentrations of different-rank coals are quite different in the initial stage of oxidation. Among the three types of coals, anthracite has the highest primary radical concentration while lignite has the lowest primary radical concentration. As the oxidation proceeds, the radical concentration of lignite grows at a significantly higher rate than those of bitumite and anthracite. In addition, the g factor values of the three types of coal all increase slightly with the rise of temperature, and the g factor value of lignite is always greater than those of bitumite and anthracite. During coal oxidation, the ΔH values of lignite, bitumite and anthracite vary in the range of 0.78–0.70, 0.6–0.48, and 0.70–0.50, respectively. The ΔH value of lignite is larger than those of bitumite and anthracite, but it experiences a smaller decrease than bitumite and anthracite. With the increase of oxygen concentration, the radical concentration and g factor of coal increase while the line width decreases. Through the analysis, the growth rate of radical concentration and g factor, instead of radical concentration, were used to evaluate the oxidation capacity of coal. The results reveal that the radical reaction in lignite is more sensitive to oxygen than those in bituminous and anthracite.

Molecular Motion of Azetidinium Ion and Phase Transition in [(CH2)3NH2]2KCo(CN)6 with Double Perovskite Structure

Abstract Molecular dynamics of azetidinium ion (AzH+), a four-membered-ring ammonium, in a cyano-bridged double perovskite compound (AzH)2KCo(CN)6 is studied by spin-lattice relaxation time measurements of 1H NMR as well as 14N NQR in relation to the phase transition associated with considerable change of dielectric property. AzH+ ions are in static and dynamic disorder, respectively, below and above Tc = 199 K. Below Tc, a ring-puckering motion of AzH+ takes place with the activation energy Ea = 17.5 kJ mol−1 and the correlation time τc/s = 2.8 × 10−14 exp(Ea/RT). On the other hand, from sudden decrease of 1H NMR linewidth above Tc, a C3 reorientation of AzH+ ion is shown to be activated in high-temperature phase. The activation energy of the C3 reorientation is estimated to be 18 kJ mol−1 from the temperature dependences of 1H NMR as well as 14N NQR spin-lattice relaxation times T1 and T1Q.

Influence of temperature on the magnetic properties of Mn3O4 nanowires

Single crystalline Mn3O4 nanowires have been synthesized with tetragonal hausmannite structure using a solvothermal method. The structural and morphological evolution of Mn3O4 nanowires have been characterized using powder X-ray diffraction, transmission electron microscopy, and electron resonance spectroscopy. The nanowires were grown uniformly along the (200) direction with a diameter of 5–10 nm range. A relatively broad and intense electron spin resonance (ESR) signal was observed at room temperature, with the g ≈ 2.0. As the synthesis temperature increases from 150 to 250 °C, a decrease in ESR signal intensity and line widths were observed. Mn3O4 displayed a positive Curie-Weiss temperature, θ, which decreases with the increase of synthesis temperature.