Y. Ufuktepe

Resonant Photoemission Studies of Thulium Monochalcogenides around the Tm 4d Threshold

Electronic structures of thulium monochalcogenides (TmS, TmSe, TmTe) were studied both experimentally and theoretically using a resonant photoemission technique in the photon energy range around Tm 4 d edge (100–190 eV). The experimental results show a large resonant enhancement of 4 f photoelectron emission around the 4 d threshold with sharper multiplet structures than those reported before. The calculated results are in good agreement with the experimental ones both for divalent and trivalent features of Tm ions. We observed different types of valence structures for TmS, TmSe and TmTe compounds, due to change in mean valence. We have estimated the mean valence of each sample from absorption spectra and from off-resonant photoemission spectra. The meaning of these values is discussed as compared with those for the values obtained from the measurements of magnetic susceptibilities.

Photoemission Study of Mixed-Valent Tm-monochalcogenides: Evidence of Electron-Correlation Effect in Different Tm-Core Levels

Systematic results of the photoemission spectra for different core levels such as, Tm 4 p , 5 p and 3 d in the mixed valent Tm-monochalcogenides (TmS, TmSe and TmTe) obtained by both experimentally and theoretically are reported. The effects of the electron–electron correlation due to the interaction between core-holes and 4 f -electrons or the interaction between different configurations are considered to explain the spectral features, depending on the principal ( n ) and orbital quantum numbers of the core levels. Any sharp peak corresponding to a spin–orbital term is not observed especially from the n =4 states. Instead, the multiplet structures are dominantly observed, and the physical identity of the spin–orbital peaks is totally or partially dissolved into the multiplets. Moreover, the electron-correlation effect is found to be dependent on the valence components (Tm 2+ and Tm 3+ ). In the case of the Tm 4 p core level, in which the principal quantum number is identical with the valence 4 f , the co...

4d Core-level resonant photoemission spectroscopy of thulium monochalcogenides around the Tm3d threshold

Abstract We report the results of 4d core-level photoemission spectra for thulium monochalcogenides, TmX (X = S, Se, Te) around the3 d –4 f absorption edge. The resonance effect for Tm4 d emission occurs through partial decay channels of the3 d –4 f excited states. The lifetime-broadening phenomenon, which depends strongly on the binding energy, is also employed here for elucidation of4 d photoelectron spectral features. The behavior of a particular decay channel, referred to as3 d –4 d 4 f , followed by preferential excited states was studied extensively.

Resonant photoemission studies of thulium monochalcogenides around the Tm3d threshold

Abstract We have studied4 f photoemission spectra of thulium monochalcogenides at excitation photon energies of the3 d –4 f resonance region ( hv = 1450–1520 eV). The experimental results are compared with theoretical calculations. The contributions from the4 f divalent part and the trivalent part in the3 d –4 f resonance are more clearly distinguished and resolved than for the4 d -4 f resonant photoemission. The calculated results are in good agreement with the experimental ones both for divalent and trivalent features of thulium ions. We have estimated the mean valence of TmS, TmSe and TmTe samples from3 d absorption spectra and from off-resonant photoemission spectra. The latter should reflect more bulk-sensitive information than that reported for the4 d -4 f resonance region. It is concluded that the3 d –4 f resonant photoemission is a more useful technique to investigate4 f electronic structures than the4 d -4 f photoemission. When we perform the experiments with relatively higher energy resolution.

Morphological and Structural Properties of NbN Thin Films Deposited by Pulsed Laser Deposition

Niobium nitride (NbN) films were deposited on Nb using pulsed laser deposition (PLD), and the effect of substrate deposition temperature on the preferred orientation, phase, and surface properties of NbN films were explored by x-ray diffraction (XRD) and atomic force microscopy (AFM). It was found that the substrate deposition temperature has a significant influence on properties of the NbN films, leading to a pronounced change in the preferred orientation of the crystal structure and the phase. We find that substrate temperature is a critical factor in determining the phase of the NbN films. For a substrate temperature of 650 °C 850 °C, the NbN film formed in the cubic δ-NbN phase mixed with the β-Nb2N hexagonal phase. With an increase in substrate temperature, NbN layers became β-Nb2N single phase. Essentially, films with a mainly β-Nb2N hexagonal phase were obtained at deposition temperatures above 850 °C. Surface roughness and crystallite sizes of the β-Nb2N hexagonal phase increased as the deposition temperatures increased.

Pulsed laser deposition of niobium nitride thin films

Niobium nitride (NbNx) films were grown on Nb and Si(100) substrates using pulsed laser deposition. NbNx films were deposited on Nb substrates using PLD with a Q-switched Nd:YAG laser (λ = 1064 nm, ∼40 ns pulse width, and 10 Hz repetition rate) at different laser fluences, nitrogen background pressures and deposition substrate temperatures. When all the fabrication parameters are fixed, except for the laser fluence, the surface roughness, nitrogen content, and grain size increase with increasing laser fluence. Increasing nitrogen background pressure leads to a change in the phase structure of the NbNx films from mixed β-Nb2N and cubic δ-NbN phases to single hexagonal β-Nb2N. The substrate temperature affects the preferred orientation of the crystal structure. The structural and electronic, properties of NbNx deposited on Si(100) were also investigated. The NbNx films exhibited a cubic δ-NbN with a strong (111) orientation. A correlation between surface morphology, electronic, and superconducting propertie...

The Electronic Structure of Wurtzite MnS

Manganese sulfide thin films have been investigated by X‐ray Absorption Fine Structure spectroscopy (XAFS). XAFS provides a description of the structure of the films. The paper also presents a structural characterisation of the wurtzite MnS thin films and their crystallisation behaviour by annealing at increasing temperatures. The x‐ray absorption fine structure (XAFS) of Mn K‐edge and S K‐edge in wurtzite MnS have been investigated. The full multiple scattering approach has been applied to the calculation of Mn K edge XANES spectra of MnS. The calculations are based on different choices of one electron potentials according to Mn coordinations by using the real space multiple scattering method FEFF 8.0 code. The crystallographic and electronic structure of the MnS are tested at various temperature ranges from 300 to 573 K. We have found prominent changes in the XANES spectra of Mangeanese sulfide thin films by the change of the temperature. Such observed changes are explained by considering the structural...

Study of magnetic linear dichroism (MLD) for different thickness of Ni thin film grown on ferromagnetic Co (001) in element specific photoemission

Abstract The magnetic linear dichroism (MLD) was used to study the magnetic properties of Ni-ultrathin film grown on ferromagnetic substrate Co(001). The MLD in photoemission has been measured for either the valence Ni3d states around the Ni3p threshold or 3p core level. Our dichroism measurements of the valence Ni3d states conclude that the resonance effect is present on MLD for ‘6 eV-satellite’ in the valence band photoemission whereas the main valence band peak shows nearly same MLD signal for the both on and off resonance. It is shown for the thinner film that the dichroism from Ni and Co3p core levels shows same sign with each other. This means that the Ni and Co are ferromagnetically coupled.

4d–4f and 3d–4f resonant photoemission of TmX (X = S, Se, Te)

The electronic structures of thulium monochalcogenides (TmX; X = S, Se, Te) were studied both experimentally and theoretically using resonant photoemission around the Tm 4d and 3d absorption edges. The fundamental electronic structures and the mean valences are analyzed.