Region Of Absorption Edge Research Articles

Effect of preparation conditions on the surface morphology and edge absorption of ZnGa2O4:Cr thin films

Thin ZnGa2O4:Cr films were obtained by RF ion-plasma sputtering in argon and argon-oxygen atmospheres mixtures on single-crystal NaCl and amorphous υ-SiO2 substrates. The surface morphology of the films was studied by atomic force microscopy. It was found that during the annealing of ZnGa2O4:Cr films on υ-SiO2 substrates in oxygen, the grains forming the film grow along the film surface, and during annealing in an argon atmosphere, the growth of grains is observed normal to the film surface. The region of the fundamental absorption edge was studied by optical spectroscopy. The variation of the optical band gap of Eg depending on the deposition and annealing atmosphere was determined. The total effective mass of free charge carriers and the concentration of free charge carriers are estimated. It is shown that the shift of the fundamental absorption edge in ZnGa2O4:Cr thin films after annealing in an argon atmosphere and when oxygen is added to the sputtering atmosphere is due to the Burstein-Moss effect.

Cr and Mg codoped bismuth tantalate pyrochlores: Thermal expansion and stability, crystal structure, electrical and optical properties, NEXAFS and XPS study

A series of Bi2Cr1-xMgxTa2O9+Δ solid solutions with the pyrochlore structure was synthesized by the method of solid-phase synthesis. Structural parameters of the disordered pyrochlore were determined by the Rietveld method (space group Fd-3m:2 (No. 227), Z = 8). As the magnesium content increases, the unit cell parameter rises continuously from 10.4596 ± 0.0001 Å (x = 0.3) to 10.5463 ± 0.0001 (x = 1.0) according to the Vegard rule. The grain size varies in the range of 0.5–2 μm, regardless of the magnesium/chromium(III) ratio. Chromium ions increase the range of thermal stability of ceramics up to 1110 °C.The thermal expansion coefficient in the range of 30–1110 °C increases continuously from 4.1 to 8.6 × 10−6 °C−1 (for x = 0.5). The oxidation states of ions were determined by X-ray spectroscopy (XPS and NEXAFS). It was shown that bismuth and magnesium ions in the pyrochlore are in the Bi(+3), Mg(+2) charge states, and for chromium the states Cr(+3), Cr(+6) are most probable. Based on the presence of an energy shift in the region of Ta4f, Ta5p and Ta5d absorption edges by ΔЕ∼0.7 eV and ∼1 eV, respectively, it was concluded that the oxidation degree of the Ta(+5-δ) ion decreased. The band gap for the samples in the case of direct allowed electronic transitions is in the range of 2.14–2.29 eV. At RT and in the frequency range (102–106 Hz), the dielectric permittivity of the samples is practically constant and it decreases with increasing amount of chromium from 20 (x = 0.7) to 16 (x = 0.3) at 1 MHz.In the high-frequency region (≥105 Hz), the dielectric loss tangent for all samples is independent on frequency and takes low values of ∼0.004 (1 MHz). The activation energy of conductivity for the samples varies in the range of 1.39–1.48 eV. The ability to adsorb water was found for chromium pyrochlores.

Structural, optical and luminescent properties of undoped Gd3AlxGa5-xO12 (x = 0,1,2,3) and Gd2YAl2Ga3O12 single crystals

The studies of structural, optical and luminescent properties of undoped Gd3AlxGa5-xO12 (x = 0,1,2,3) and Gd2YAl2Ga3O12 mixed crystals were carried out. Mixed crystals composition and lattice parameters were determined using EDX and XRD techniques. The distribution of cations between sites with different symmetry was obtained using Rietveld method. The spectral dependence of refraction coefficients was determined using the multiangle spectrophotometry method and Cauchy equation. Optical band gap values were determined from the absorption spectra in the region of fundamental absorption edge. Presence of two non-equivalent Gd3+ emission centers was supposed from the analysis of emission spectra. The energies of exciton creation and band gap energies were obtained from the luminescence excitation spectra analysis.

On the Temperature Behavior of Optical Gap in Arsenic Sulfide Glasses

Temperature behavior of optical transmission in the fundamental optical absorption edge region is studied for a broad range of As–S glass compositions covering the entire glass‐forming interval. It is shown that temperature dependences of optical gap values for all bulk glasses can be well fitted by the one‐phonon approximation based on Bose–Einstein statistics. Correlation of fitting parameters with thermodynamic data and compositional structural development published earlier is discussed.

Parameterization of photobleaching and photodarkening in-situ kinetics in thermally deposited GeSe2 thin films

Thermally evaporated chalcogenide glass thin films are known to be highly photosensitive revealing both metastable and transient photoinduced changes of optical transmission at the fundamental absorption edge region. In-situ kinetics of metastable photobleaching and transient photodarkening as well as following light-off relaxations for as-deposited GeSe2 thin films were studied and fitted with the stretched exponential function. Dependences of kinetic parameters β and τ on film thickness, temperature, sample prehistory and wavelength of light irradiation were analyzed. The obtained results were discussed within current approaches to mechanisms of photoinduced kinetic phenomena and structural relaxation in glasses.

Band Gap of (In2S3)x(AgIn5S8)1 –x Single-Crystal Alloys

In2S3, AgIn5S8, and (In2S3)x(AgIn5S8)1 – x-alloy single crystals are grown by the Bridgman method. The composition and structure of the crystals are determined. It is established that both the initial compounds and their alloys crystalize with the formation of the cubic spinel structure. The unit-cell parameters of the single crystals are calculated, and the dependences of these parameters on the alloy composition are constructed. It is shown that, in the system, Vegard’s law is satisfied. The transmittance spectra of the crystals in the region of the fundamental absorption edge are studied at room temperature, and the band gap (Eg) is determined. It is shown that Eg varies with the composition parameter x, with some deviation from a linear dependence.

Growth, Structure, and Temperature Dependence of the Band Gap of Mn0.3Ag0.7In4.1S6.8 Single Crystals

Mn0.3Ag0.7In4.1S6.8 single crystals were grown by directed melt crystallization. Their composition and crystal structure were determined. It was established that the Mn0.3Ag0.7In4.1S6.8 single crystals crystallized in the cubic spinel structure. The band gap of the single crystals was estimated and its temperature dependence was constructed using transmission spectra in the region of the fundamental absorption edge in the range 20–320 K. The temperature dependence of the band gap was shown to have the form characteristic of semiconductor materials.

Influence of spin orbit splitting and satellite transitions on nickel soft X-ray optical properties near its L2,3 absorption edge region.

Transition elements exhibit strong correlations and configuration interactions between core and valence excited states, which give rise to different excitations inside materials. Nickel exhibits satellite features in its emission and absorption spectra. Effects of such transitions on the optical constants of nickel have not been reported earlier and the available database of Henke et al. does not represent such fine features. In this study, the optical behaviour of ion beam sputter deposited Ni thin film near the L2,3-edge region is investigated using reflection spectroscopy techniques, and distinct signatures of various transitions are observed. The soft X-ray reflectivity measurements in the 500-1500 eV photon energy region are performed using the soft X-ray reflectivity beamline atthe Indus-2 synchrotron radiation source. Kramers-Kronig analysis of the measured reflectivity data exhibit features corresponding to spin orbital splitting and satellite transitions in the real and imaginary part of the refractive index (refraction and absorption spectra). Details of fine features observed in the optical spectra are discussed. To the best of our knowledge, this is the first study reporting fine features in the measured optical spectra of Ni near its L2,3-edge region.

High accuracy determination of photoelectric cross sections, X-ray absorption fine structure and nanostructure analysis of zinc selenide using the X-ray extended range technique.

Measurements of mass attenuation coefficients and X-ray absorption fine structure (XAFS) of zinc selenide (ZnSe) are reported to accuracies typically better than 0.13%. The high accuracy of the results presented here is due to our successful implementation of the X-ray extended range technique, a relatively new methodology, which can be set up on most synchrotron X-ray beamlines. 561 attenuation coefficients were recorded in the energy range 6.8-15 keV with measurements concentrated at the zinc and selenium pre-edge, near-edge and fine-structure absorption edge regions. This accuracy yielded detailed nanostructural analysis of room-temperature ZnSe with full uncertainty propagation. Bond lengths, accurate to 0.003 Å to 0.009 Å, or 0.1% to 0.3%, are plausible and physical. Small variation from a crystalline structure suggests local dynamic motion beyond that of a standard crystal lattice, noting that XAFS is sensitive todynamic correlated motion. The results obtained in this work are the most accurate to date with comparisons with theoretically determined values of the attenuation showing discrepancies from literature theory of up to 4%, motivating further investigation into the origin of such discrepancies.

Morphology control of WO3 nanoplate film on W foil by oxalic acid for photocatalytic gaseous acetaldehyde degradation

WO3 film with reasonable morphology could be a promising photocatalytic material for indoor air purification. Herein, we constructed WO3 nanoplate film for photocatalytic degradation of gaseous acetaldehyde. The WO3 nanoplate film was prepared by nitric acid corrosion of W foil using oxalic acid for morphology regulation. SEM, XRD, and XPS evidenced that the monoclinic phase WO3 nanoplates grew on W foil. The oxalic acid anchored on the specific faces of the tungsten oxide hydrate facilitated for forming high quality larger and thinner WO3 nanoplates. UV–vis diffuse reflection spectra (DRS) manifested that the oxalic acid modulated WO3 nanoplate films possess smaller absorption edge and wider solar light absorption region. The oxalic acid contributed to obtain efficient WO3 nanoplate film photocatalyst for gaseous acetaldehyde decomposition under simulated solar light irradiation, which was response for the increased crystallinity and more surface reactive sites as well as the enhanced light absorption. The morphology modulation by oxalic acid will pave the way for synthesis of practical WO3 films in environment purification.

On the Growth and Properties of FeIn2S3.6Se0.4 Single Crystals

FeIn2S3.6Se0.4 single crystals are grown by planar crystallization of the melt (the vertical Bridgman method). The composition and crystal structure of the crystals are determined. It is established that the single crystals crystallize with the formation of the cubic spinel structure. From the transmittance spectra in the region of the fundamental absorption edge, the band gap of the single crystals is determined. Thermal expansion of the FeIn2S3.6Se0.4 single crystals is studied by the dilatometric technique in the temperature range from 80 to 550 K, and the coefficients of thermal expansion are determined. From the coefficients of thermal expansion determined, the Debye temperatures and the root-mean-square (rms) dynamic displacements of atoms are calculated. It is shown that, as temperature is elevated, the Debye temperatures decrease and the rms dynamic displacements of atoms increase. Magnetic studies show that the FeIn2S3.6Se0.4 single crystals are paramagnetic materials at temperatures down to 12.4 K.

Выращивание и свойства монокристаллов FeIn-=SUB=-2-=/SUB=-S-=SUB=-3.6-=/SUB=-Se-=SUB=-0.4-=/SUB=-

Abstract FeIn_2S_3.6Se_0.4 single crystals are grown by planar crystallization of the melt (the vertical Bridgman method). The composition and crystal structure of the crystals are determined. It is established that the single crystals crystallize with the formation of the cubic spinel structure. From the transmittance spectra in the region of the fundamental absorption edge, the band gap of the single crystals is determined. Thermal expansion of the FeIn_2S_3.6Se_0.4 single crystals is studied by the dilatometric technique in the temperature range from 80 to 550 K, and the coefficients of thermal expansion are determined. From the coefficients of thermal expansion determined, the Debye temperatures and the root-mean-square (rms) dynamic displacements of atoms are calculated. It is shown that, as temperature is elevated, the Debye temperatures decrease and the rms dynamic displacements of atoms increase. Magnetic studies show that the FeIn_2S_3.6Se_0.4 single crystals are paramagnetic materials at temperatures down to 12.4 K.

Features of the edge photoconductivity of gamma-irradiated layered crystals GaS and GaS:Yb under the strong electric field

The influence of the surface electric field on the edge photoconductivity (PC) in undoped and ytterbium-doped (N[Formula: see text][Formula: see text] 10[Formula: see text] cm[Formula: see text]) layered GaS crystals at T = 77 K irradiated with gamma quanta was investigated. It was found that the PC of layered crystals in the absorption edge region due to charge exchange of surface levels is formed as a result of electric smoothing of fluctuations in the potential of surface energy bands. The degree of smoothing of the surface bending of the zones depends on the dose of [Formula: see text]-irradiation, the concentration of impurity atoms and also on the magnitude and direction of the transverse electric field.

Band-fluctuations model for the fundamental absorption of crystalline and amorphous semiconductors: a dimensionless joint density of states analysis

We develop a band-fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless joint density of states formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p-type GaAs and nano-crystalline Ga1-xMnxN, as examples for direct bandgap materials, as well as amorphous Si:Hx, SiC:Hx and SiNx, are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edge.

Discrimination of DNA and RNA distribution in a mammalian cell by scanning transmission soft X-ray microscopy.

Soft X-ray spectromicroscopy was applied to study the distribution of DNA and RNA in a mammalian cell at the spatial resolution of 400 nm. The relative distribution of DNA and RNA was examined by the SVD (singular value decomposition) method in aXis2000 program using combined full spectra of DNA and RNA at the absorption edge regions of carbon, nitrogen and oxygen. The absorption of nucleic acid was evaluated using 1s-π* transitions in the NEXAFS spectra at the nitrogen K absorption edge and distributed to DNA and RNA according to the relative level obtained above. The present results revealed the usefulness of the SVD method to discriminate closely related molecules such as DNA and RNA.

Influence of 120 MeV S9+ ion irradiation on structural, optical and morphological properties of zirconium oxide thin films deposited by RF sputtering

The calibrated and controlled swift heavy ions (SHI) beam irradiation generate defects which can cause modifications in various properties of the materials such as structural, optical, magnetic, morphological, and chemical etc. The passage of ion through the target material causes the nuclear energy losses (Sn) and electronic energy losses (Se). The Se dominates over Sn in SHI irradiation. In the present study, ZrO2 thin films were grown on silicon and glass substrate by using RF sputtering deposition technique. For the purpose of modifications induced by swift heavy ions, these films were irradiated by a 120 MeV S9+ ion beam of 1 pnA current, with varying ion fluences from 5E12 to 1E13 ions/cm2, using the tandem accelerator at the Inter University Accelerator Center (IUAC), New Delhi, India. The X-ray diffraction (XRD) patterns confirmed the formation of monoclinic and tetragonal phases and it was observed that XRD peaks intensity increased up to the fluence of 5E12 ions/cm2 followed by opposite behavior at higher fluences. Atomic force microscope (AFM) study revealed the increased surface roughness after SHI irradiation. In addition to it, the formation of electronic transition states in optical band gap region and enhancement of absorption edge was observed from UV-visible spectroscopy (UV-Vis) results due to which direct band gap energy value decreased from those of un-irradiated samples. Photoluminescence (PL) broad emission spectra were determined using the excitation wavelength at 290 nm with the prominent peak at 415 nm which can be ascribed to Zr vacancies due to band edge emission as a result of free-exciton recombination. Rutherford backscattering spectrometry (RBS) technique was used for depth profiling and elemental composition in zirconia thin films. The expected role of electronic energy loss during ion irradiation is to modify the properties of the material has been discussed.

On the Growth of FeIn2S2Se2 Single Crystals and the Study of their Properties

FeIn2S2Se2 single crystals are grown for the first time by the Bridgman method, and their composition and properties are determined. It is found that the single crystals are hexagonal in structure. The arrangement of Fe ions in the structure of the FeIn2S2Se2 crystals is studied by nuclear γ-resonance spectroscopy. From the transmittance spectra in the region of the fundamental absorption edge, the band gap of the single crystals grown in the study is determined.

Soft x-ray optical constants of sputtered chromium thin films with improved accuracy in the L and M absorption edge regions

In this study, we determine with improved accuracy the complex index of refraction n = 1 − δ + iβ of sputtered chromium thin films for photon energies ranging from 25 eV to 813 eV. These data include the first absolute measurements of the absorption fine structure near the Cr-L edge. First, we verified by combining Rutherford Backscattering Spectrometry and grazing-incidence x-ray reflectometry that the sputtered thin films were pure Cr with a density consistent with tabulated values. Then, we demonstrated that the Cr surface oxide layer remains stable when the samples are exposed to air for up to 4 years. The Cr absorption coefficient β was determined from the transmittance of freestanding Cr thin films with various thicknesses, measured at the ALS synchrotron radiation source. A model is proposed to correct the transmittance data from the spectral contamination of the source. Finally, we used the new β values, combined with theoretical and tabulated data from the literature, in order to calculate the δ values by the Kramers-Kronig relation. The improvement in the accuracy of β values is demonstrated by the f-sum rule. An additional validation of the new Cr optical constants (δ, β) is performed by comparing the simulated and experimental reflectance of a Cr/B4C multilayer mirror near the Cr-L2,3 edge.

Crystal Structure and Band Gap of (MnIn2S4)1–x • (AgIn5S8)x Alloys

The (MnIn2S4)1–x • (AgIn5S8)x alloy single crystals are grown for the first time by the Bridgman method in the entire range of component concentrations. The composition of the single crystals and their crystal structure are determined. It is shown that the alloy crystallizes in the cubic spinel structure. The unit-cell parameter of the single crystals (a) is calculated, and its dependence on the composition parameter (x) is determined. It is established that the parameter a linearly varies with x. From the transmittance spectra in the region of the fundamental absorption edge, the band gap (Eg) of the MnIn2S4 and AgIn5S8 compounds and (MnIn2S4)1–x • (AgIn5S8)x alloys is determined, and the dependence of Eg on the parameter x is constructed. It is found that the band gap Eg nonlinearly varies with x and has a maximum at x = 0.6.

Interband optical transitions in Gd2O3: Er nanoparticles – prospective system for energy convertors

The features of electron transitions in the region of fundamental absorption edge as well as vibrational characteristics are investigated in Gd2O3 nanoparticles doped with Er3+ ions at 0.25-8 mol% concentration. The analysis of initial reflection data is performed for cases of direct and indirect interband transitions. The dependences of corresponding energy gaps on activator concentration are obtained. The effect of strong decrease in the phonon frequency under doping of matrix with a small amount of Er3+ is found. The obtained data open new opportunities for improving the efficiency of energy conversion devices.