Incident Photon Energy Dependence Research Articles

Complex dielectric, electric modulus, impedance, and optical conductivity of Sr3−x Pb x Fe2TeO9 (x = 1.50, 1.88 and 2.17)

Abstract Sr3−x Pb x Fe2TeO9 (x = 1.50, 1.88 and 2.17) were synthesized in polycrystalline form via the solid-state reaction route in air, and were studied at room temperature using powder X-ray diffraction and ultraviolet visible spectroscopy techniques. The crystal structures were resolved by the Rietveld refinement method; x = 1.50 and 1.88 adopt a tetragonal phase (space group I4/mmm) while x = 2.17 adopts a hexagonal phase (space group R 3 ̄ $\bar{3}$ m). The direct bandgap energy (E g) of ∼1.89 eV for (x = 1.50), ∼1.87 eV for (x = 1.88) and ∼1.74 eV for (x = 2.17) was estimated from the Tauc plots of (αhʋ)2 versus photon energy. The Urbach energy (E U) was determined from the plots of logarithmic absorption coefficient versus hυ. Plots of the incident photon energy dependence of optical parameters such as refractive index, extinction coefficient, real and imaginary parts of the dielectric function, dielectric loss, real and imaginary parts of the complex optical conductivity, linear and nonlinear optical susceptibilities, real and imaginary parts of the electric modulus, real and imaginary parts of the impedance were obtained by means of ultraviolet visible spectrophotometer experiments. Additionally, the estimated values of the single oscillator energy, dispersion energy, static refractive index and high-frequency dielectric constant were obtained from the linear portion of the (n 2 − 1)−1 versus (hυ)2 plots using the Wemple–DiDomenico model.

Excited-state exchange interaction in NiO determined by high-resolution resonant inelastic x-ray scattering at the Ni M2,3 edges

The electronic and magnetic excitations of bulk NiO have been determined using the ${}^{3}{A}_{2g}$ to ${}^{3}{T}_{2g}$ crystal-field transition at the Ni ${M}_{2,3}$ edges with resonant inelastic x-ray scattering at 66.3- and 67.9-eV photon energies and 33-meV spectral resolution. Unambiguous assignment of the high-energy side of this state to a spin-flip satellite is achieved. We extract an effective exchange field of $89\ifmmode\pm\else\textpm\fi{}4$ meV in the ${}^{3}{T}_{2g}$ excited final state from empirical two-peak spin-flip model. The experimental data is found consistent with crystal-field model calculations using exchange fields of 60--100 meV. Full agreement with crystal-field multiplet calculations is achieved for the incident photon energy dependence of line shapes. The lower exchange parameter in the excited state as compared to the ground-state value of 120 meV is discussed in terms of the modification of the orbital occupancy (electronic effects) and of the structural dynamics: (A) With pure electronic effects, the lower exchange energy is attributed to the reduction in effective hopping integral. (B) With no electronic effects, we use the $S=1$ Heisenberg model of antiferromagnetism to derive a second-nearest-neighbor exchange constant ${J}_{2}$ = $14.8\ifmmode\pm\else\textpm\fi{}0.6$ meV. Based on the linear correlation between ${J}_{2}$ and the lattice parameter from pressure-dependent experiments, an upper limit of 2% local Ni-O bond elongation during the femtosecond scattering duration is derived.

Energy band diagram for SiO2/Si system as evaluated from UPS analysis under vacuum ultraviolet with variable incident photon energy

We have studied the energy band diagram for the Si surface and SiO2/Si system by using ultraviolet photoelectron spectroscopy (UPS) measurements. In the UPS measurements, monochromatized vacuum ultraviolet with variable incident photon energies below 10.50 eV was used in order to increase the detection limit of the depth from the surface and to understand the electronic states not only at the surface but also in the region near the interface of the stacked structure. From the incident photon energy dependence of the UPS spectral width, the energy level of the valence band top of the H-terminated Si surface and the electrical potential change in the SiO2/Si structure has been evaluated. Also, the vacuum work function value of the hetero-epitaxial Ag(111) surface has been investigated to check this measurement technique.

Theoretical study of the effects of electron-phonon and electron-photon interaction in optoelectronic properties of armchair graphene nano-flakes –a renormalization method

Abstract In this work, we study the effects of electron-phonon and electron-photon interaction on the electronic and optoelectronic properties of nano systems consisting of graphene nano-flakes (small length armchair graphene nanoribbons) connected to two semi-infinite metal electrodes. Our calculations are based on the use of non-equilibrium Green's function formalism. The non-interacting Hamiltonian is written within the nearest neighbor tight binding approximation. The full interacting Hamiltonian is then obtained by addition the electron-phonon and electron –photon interaction to the above non-interacting Hamiltonian. Using unitary transformations the interacting Hamiltonian is renormalized into a non-interacting tight-binding form with effective onsite energy and hopping parameter which contain the interacting effects. The Landuer-Buttiker formalism can now be used for the system with renormalized non-interacting Hamiltonian for calculating the electronic current. Within the above framework, we calculate the electron current, density of states (DOS) and photocurrent in the presence and absence of electron-phonon interaction in a nano-system consisting of graphene nano-flake with different width as central molecule. Our results show that electron-phonon interaction leads to decreasing the number of peaks in the DOS. Also the photocurrent has oscillatory behavior versus electron-photon coupling for different widths of the nano-flake. Finally, incident photon energy dependence of threshold electron-photon coupling (i.e photocurrent becomes larger than Ballistic case) and its increasing trend versus photon energy are studied.

Incident angle and photon energy dependence of polariton lasing in an organic microcavity

Organic semiconductor microcavities forming strongly coupled exciton-polaritons are interesting systems due to their nonlinear coherent emission observed even at room temperature. Here, we investigate the incident angle and photon-energy-dependent photoemission from a planar organic microcavity to evaluate the relaxation efficiency towards the bottom of the lower polariton branch. We observe nonlinear increase in the vertical emission from the microcavity when the sample is pumped resonantly to the lower polariton branch with an incident angle of 30 to 55°. The observed results support the fast and efficient relaxation of organic microcavity polaritons within the lower polariton branch.

Investigation on energy dependency of dose enhancement factor produced by gold nanoparticle

In this present study, we are elaborating the incident photon energy dependence of gold nanoparticle dose enhancement at 7mg/g concentration by using different radionuclide’s such as Co-60, Pd- 103, I-125, Cs-137,Ir-192,Au-198,Yb-169 and external beam energies 40, 50, 60, 70, 80, 90, 100, 110, 120 KeV & 6-MeV X-rays. Mass energy absorption coefficient (µen/ϼ) and mass attenuation coefficients (µ/ϼ) are generated by using WinXCOM software. Kerma relative to air value was calculated and results are discussed. Our results suggest that maximum dose enhancement was found at following source 40 KeV, I-125, 50 KeV, Pd-103, 60 KeV it was 2.07, 2.017, 1.98, 1.83, 1.8 respectively. For higher energy 6 MeV X-ray DEF almost negligible it was around 1.01.

Neutron shielding qualities and gamma ray buildup factors of concretes containing limonite ore

Neutron dose transmissions for fast neutrons produced by 5.486MeV alpha particles on beryllium are measured in concrete samples with and without limonite ore to investigate their neutron shielding qualities. Using measured values, macroscopic removal cross-sections (ΣR, cm−1) have been determined experimentally and also ΣRvalues have been calculated theoretically using the elemental composition of the concrete mixes. The best neutron shielding property of concrete sample containing 100% limonite ore (FCL: fine and coarse limonite) was found. Additionally, energy absorption buildup factor (EABF) and exposure buildup factor (EBF) of concrete sample were calculated using the five-parameter Geometric Progression (G-P) approximation in the energy range of 0.015–15MeV for penetration depths up to 40 mean free path (mfp). The incident photon energy and penetration depth dependence of buildup factors were examined. Finally, we observed that concrete samples have maximum values of buildup factors in the intermediate energy region around 0.1–0.3MeV. FCL has the minimum values of both of the buildup factors. FCL has the excellent gamma shielding properties compared to the concrete samples.

Lattice coupling and Franck–Condon effects in K-edge resonant inelastic x-ray scattering

In this paper, we discuss our recent Cu K-edge resonant inelastic x-ray scattering (RIXS) results for CuB2O4, a model system consisting of electronically isolated CuO4 plaquettes, which exhibits anomalies in the incident photon energy dependence that are not captured by electron-only models. We show that these anomalous features can be qualitatively described by extending the electron-only considerations to include the lattice degrees of freedom. Our findings have important general implications for the interpretation of K-edge RIXS results for electronically higher-dimensional transition metal oxides.

CopperKand OxygenKResonant Inelastic X-ray Scattering of One-Dimensional Cuprates

Resonant inelastic X-ray scattering (RIXS) using the Cu K shell of one-dimensional cuprates is compared with that using the O K shell on the basis of numerically-exact diagonalization calculations applied for a finite-size cluster model. Particular attention is paid to the effects of Cu 3 d orbital degeneracy on the Cu K RIXS and the incident photon energy dependence of the Cu K RIXS. Inclusion of the Cu 3 d (3 z 2 - r 2 ) orbital results in the d d excitation in the Cu K RIXS, which is in accordance with the O K RIXS. However the excitation mechanism differs for the Cu K RIXS and O K RIXS. The d d excitation in the Cu K RIXS is caused through the mixing between the Zhang–Rice singlet (ZRS) and Cu 3 d (3 z 2 - r 2 ) bands, while it is mainly caused by the optical dipole transition process in the case of O K RIXS. Moreover, mixing between the ZRS and Cu 3 d (3 z 2 - r 2 ) bands induces new structures, whose binding energy is higher than that of the structure due to electron–hole pair excitations from the Z...

Charge-Transfer Excitations in the Model SuperconductorHgBa2CuO4+δ

We report a Cu $K$-edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa$_2$CuO$_{4+\delta}$ at optimal doping ($T_{\rm c} = 96.5 $ K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly-dispersive ($ < 0.5$ eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitation suggests the existence of a charge-transfer pseudogap deep in the superconducting phase. Quite generally, our data demonstrate the importance of exploring the incident photon energy dependence of the RIXS cross section.

Incident Photon-Energy Dependence of the Electronic Density of States in Pd&lt;SUB&gt;42.5&lt;/SUB&gt;Ni&lt;SUB&gt;7.5&lt;/SUB&gt;Cu&lt;SUB&gt;30&lt;/SUB&gt;P&lt;SUB&gt;20&lt;/SUB&gt; Metallic Glass

Incident photon-energy dependence of photoemission spectra of Pd 42.5 Ni 7.5 Cu 30 P 20 metallic glass was measured using a synchrotron radiation facility. Compared to the elemental Pd, Ni, or Cu metal, the electronic density of states of this extremely good glass-former is highly suppressed at the Fermi energy, which indicates the existence of covalent bonds in this metallic mixture. From the incident photon-energy dependence of the spectra, partial density of states of the Pd, Ni, and Cu elements can be estimated, which suggests the selective formation of Pd-P bonds using the Pd 4d states.

Simulation study of angle-resolved photoemission spectra and intramolecular energy-band dispersion of a poly(tetrafluoroethylene) oligomer film.

Theoretical simulations of the angle-resolved ultraviolet photoemission spectra (ARUPS) for the oligomer of poly(tetrafluoroethylene) [(CF(2))(n); PTFE] were performed using the independent-atomic-center approximation combined with ab initio molecular orbital calculations. Previously observed normal-emission spectra for the end-on oriented sample (with long-chain axis perpendicular to the surface) showed the incident photon-energy (hnu) dependence due to the intramolecular energy-band dispersion along the one-dimensional chain, and the present simulations successfully reproduced this hnu dependence of the observed spectra. We employed the experimentally observed helical structure for PTFE oligomers for the simulations. We also calculated the density of states (DOS) for the planar zigzag structure, and examined the changes in the electronic structure due to the difference in the molecular structure by comparing the DOS for the helical and planar zigzag structures. Only a small change in the DOS was found between these structures, showing little change of the electronic structure between these conformations. We also evaluated the inner potential V(0), which is the parameter defining the energy origin of the free-electron-like final state, and checked the validity of the value of -10 eV estimated in our previous study using the experimentally observed hnu dependence of the peak intensity. The estimation of V(0) was performed by pursuing the best agreement between the energy-band dispersion [E=E(k)] relation along the chain direction obtained from the simulated spectra and the experimentally deduced one. An excellent agreement in the topmost band was achieved when the assumed inner potential V(0) was set at about zero. This value of V(0) is much different from the value of V(0)=-10 eV in the previous study, suggesting the invalidity of the previous assumption at the estimation of V(0) from the peak intensity variation with hnu. Using the presently obtained V(0), we could derive more reliable E=E(k) dispersion relation from the observed ARUPS spectra. The comparison of this newly derived relation gave good agreement with theoretically calculated E=E(k) relations, in contrast to the poor agreement for the previous results with V(0)=-10 eV.

INTRAMOLECULAR ENERGY BAND DISPERSION IN ORIENTED THIN FILM OF n-CF3(CF2)22CF3 STUDIED BY ANGLE-RESOLVED UPS AND THEORETICAL SIMULATION

Electronic structure of perfluorotetracosane [n- CF 3 ( CF 2)22 CF 3; PFT], which is an oligomer of poly(tetrafluoroethylene) (PTFE), was investigated by angle-resolved photoemission spectroscopy (ARUPS) with synchrotron radiation. Theoretical simulations of ARUPS spectra were also performed by the independent atomic center (IAC) approximation combined with ab initio molecular orbital (MO) calculations. Measured normal-emission spectra for end-on oriented (the long-chain axis of PFT is perpendicular to the surface) films showed an incident photon energy dependence due to the intramolecular energy band dispersion. The energy band structure along the long-chain direction of PFT obtained from measured and calculated spectra is also discussed.

Incident photon energy dependence of the resonant x-ray magnetic scattering cross section of a samarium film

Resonant x-ray magnetic scattering is widely used as an element selective probe of magnetism in solids. The present work deals with a different, less frequently addressed aspect: the electronic shell selectivity. Due to the complexity of the atomic effects inherent to the resonant process and at the origin of the electronic shell selectivity, the data are generally considered on a qualitative basis. Here, we try to extend the arguments to a semiquantitative level. We show, through a detailed spectroscopic study of the resonance at the ${L}_{2}$ and ${L}_{3}$ edges of samarium in a single-crystal epitaxial film, how the exploitation of the atomic effects can lead to a deeper understanding of long-range magnetic order in this material. At the ${L}_{2,3}$ edges of rare earths, dipole resonances carry information on the polarization of the $5d$ band, whereas quadrupole resonances reflect the polarization of the $4f$ shell. The narrow width of the $4f$ band permits the interpretation of the quadrupole resonance below the ${L}_{3}$ edge using atomic considerations. A systematic study of the dependence of the $4f$ quadrupole resonance on wave-vector transfer shows that, within our resolution, the magnitude of the $4f$ moments in samarium is independent of the local environment (cubic or hexagonal). On the other hand, the energy dependence of the dipole resonance at and above the ${L}_{2}$ and ${L}_{3}$ absorption edges shows two maxima and is interpreted in the framework of an extended density of $5d$ states. Finally, the relative temperature dependences of the dipole and quadrupole resonances sheds light upon the respective contributions of the $4f$ and $5d$ levels to the long-range magnetic order in samarium.

Resonant X-ray Emission Spectroscopy in Hubbard Model

Resonant X-ray emission spectrum (RXES) is calculated for the one-dimensional single-band Hubbard model. The origin of each inelastic scattering peak can be explained as some intra-band or inter-band electron-hole pair excitation processes. However, the intensity of each peak is remarkably influenced by the core-hole potential effect in the intermediate state. In other words, the incident photon energy dependence of each inelastic peak gives direct information on the electron-hole pair excitations involved. Detailed experiments at and near the resonant condition are highly desired in highly-correlated electron systems.

Ultraviolet Photoelectron Spectra of Mono Metal Atom Encapsulated Fullerenes

Ultraviolet photoelectron spectra of mono metal atom encapsulated fullerenes, M@C82 (M = La, Gd and Sc), are measured with a synchrotron radiation light source. When the excitation energy is tuned, spectral intensity oscillation is observed in these mono metal atom encapsulated fullerenes as was in empty fullerene, C82. Their incident photon energy dependence is essentially the same. Their spectra deeper than 5 eV are almost identical and are similar to those of empty fullerene. The noticeable difference among the spectra is in the energy region between the Fermi level and 4 eV, which reveals the degree of electron transfer from the metal atom to the fullerene cage.

Galvanomagnetic, Optical Properties and Ultraviolet Photoelectron Spectra of Potassium-Oxygen-Graphite Intercalation Compounds

We investigated the Hall effect, the transverse magnetoresistance, the optical reflectivity and the ultraviolet photoelectron spectra for 1st and 2nd stage KO x -GICs (C 4 n KO x , stage number n =1, 2; x ∼2) in order to clarify the transport properties and the electronic structures. The Hall effect and the magnetoresistance indicate that the electrical conduction in KO x -GICs is governed by the majority electron carriers with low mobility in graphitic π bands and the minority hole carriers with high mobility in the intercalate bands, the latter of which originates mainly from the oxygen bands as suggested by the incident photon energy dependence of the ultraviolet photoelectron spectra. The optical reflectance spectra give the estimates of the Fermi energies, 1.9 eV and 1.35 eV for 1st and 2nd stage compounds, respectively, on the basis of the Drude-Lorentz model. The contribution of the intercalate hole carriers to the plasma frequency is small in good agreement with the Hall effect indicating the pres...

Resonant Light Scattering in InBr: Intensity Alternation of Multiple LO Phonon Scattering

The incident photon energy dependence of multiple LO phonon scattering lines has been investigated in InBr under the excitation in the first exciton region (2.331 eV, \(\bm{E}//\bm{c}\)) at 2 K. Each LO line shows strong outgoing resonance at the first exciton energy. The calculation of the cross section for the 2LO phonon scattering is carried out and it is indicated that the interband LO phonon scattering of exciton between p and s exciton states is the important relaxation process in InBr.

Resonance Raman and luminescence studies on the quasi-one dimensional crystals of [Pt(en) z][Pt(en) 2Cl 2](ClO 4) 4

Resonance Raman scattering, infrared luminescence and absorption spectra of [Pt(en) 2][Pt(en) 2Cl 2](ClO 4) 4 single crystals have been measured for polarized light at 2 K and room temperature. Contrary to the previous works on polycrystals, the incident photon energy dependence of the Raman cross section due to the symmetric ClPt IVCl stretching mode has a resonance peak at the charge-transfer absorption edge, which is well explained with the two-band model in a one-dimensional system. Two characteristic structures observed below the absorption edge are concluded not to be related to the charge-transfer transition by measurements of the excitation spectra both of the Raman scattering and of the luminescence. The origin of this luminescence is also discussed.

Multiple LO scattering in indium iodide

Resonant secondary emission is investigated in the energy range around the direct exciton in orthorhombic InI. Spectra at liquid nitrogen temperature exhibit multiple LO lines with characteristic intensity alternation as in InBr at 2K. Incident photon energy dependence of their scattering intensities is also studied. Pronounced outgoing resonance with 1 s exciton is found in each LO line.