Variation of relative intensities between surface and bulk plasmon losses due to crystal orientations for aluminium in low energy electron reflection loss spectroscopy

The contrast change of secondary electron images due to the crystal orientations is observed by the ultra high vacuum scanning electron microscope (UHV-SEM) for crystal grains of clean surface of polycrystalline Al in the primary energy E_p of 200 eV to 5 keV. The low energy electron loss spectra are measured by the cylindrical mirror analyzer. The relative intensity ratio between surface and bulk plasmon loss spectra was dependent on the crystal orientations. The SEM images taken by the surface and bulk plasmon signals at E_p = 230 eV show the inverse contrast depending on the grains. The inversion of the relative intensities between the surface and bulk plasmon losses is explained qualitatively by taking into account of variation of the penetration depth of the incident beam caused by the electron channeling.     

Variation of electron energy loss spectra of Ni (100) with increasing primary energy

Electron energy loss spectra of clean Ni(1 0 0) show for the first time a 17 eV peak, which is attributed to an interband transtiion. All the observed peaks are shifted to higher energies as the primary electron energy E_p increases from 102 to 2045 eV. This shift is explained by a continuous decay in energy of the primary electrons inside the crystal. At E_p ? 700 eV, the decay takes place in the surface region of the crystal, while at E_p > 700 eV it takes place mainly in the bulk. The rate of decay increases with increasing temperature of the crystal between 300 and 900 K.     

Optical polarized properties related to the oxygen vacancy in the CaMoO4 crystal

The electronic structures, dielectric functions and absorption spectra for the CaMoO₄ (CMO) crystal with and without oxygen vacancy V_O²⁺ have been calculated using the CASTEP code with the lattice structure optimized. The calculated results indicate that the optical properties of the CMO crystal show anisotropy and its optical symmetry coincides with the lattice structure geometry of the CMO crystal. The calculated absorption spectra indicate that the perfect CMO crystal does not display absorption band in the visible and near-ultraviolet range. However, in this range, the absorption spectra of the CMO crystal containing V_O²⁺ exhibit one peak at about 1.84 eV (673 nm). It predicates that the 680 nm absorption band is related to the existence of V_O²⁺ in the CMO crystal.     

Mössbauer effect in poly-and single crystals YBa2(Cu1−x Fe x )3O7−y

Angle dependence of Mössbauer spectra parameters on angle δ_O between the ψ-rays wave vectork and the unit cellc-axis of single crystal YBa₂(Cu_0.98Fe_0.02)₃O_7?y is studied at room temperature. The present results give more detailed information about the correct manner of spectra fitting and EFG tensor parameters in positions of Fe-atoms in 1-2-3 crystal matrix.     

Electron energy loss spectroscopy of A {111} oriented aluminum single crystal

Recently, the electron energy loss spectroscopy (ELS) and secondary electron spectroscopy (SES) of the interaction of oxygen with polycrystalline aluminum were reported for primary energies in the range 30 ? E_p ? 250 eV. Two new transitions were resolved in the ELS spectra (one at 4 eV for clean aluminum and the other at 12 eV for oxide-covered aluminum) for low primary energies (E_p ~ 30 eV). In this paper we report on experiments utilizing a {111} oriented single crystal of aluminum that confirm the existence of these loss peaks for low primary energies and show that the 4 eV peak position for pure aluminum depends on the primary beam energy. This suggests that this low energy loss peak is due to direct nonvertical inter- and intraband transitions which differs from the previous assignment.     

Infrared absorption studies on the superionic conductor ZrO2−Y2O3 crystal

Infrared absorption spectra of (1−x)ZrO₂−xYO_1.5, which is one of the superionic conductors, have been studied using thin films evaporated on Si plates. From absorption spectra obtained at normal incidence and at oblique incidence it is shown that ZrO₂−Y₂O₃ crystals have well-defined TO and LO infrared active phonons, though they have many defects. From the analysis of the spectra, x-dependences of the force constant and the effective charge are obtained, and it is found that the concept of the virtual ion crystal model is very useful to understand the infrared properties of the superionic conductor ZrO₂−Y₂O₃ crystal.     

Electron-energy-loss spectroscopy of KxC60 and K-halides: comparison in the K3p excitation region

We have investigated the electronic structure of K_xC₆₀ (x=0–6) using low-energy electron energy loss spectroscopy (LEELS), especially focusing on the K_3p core-electron excitation spectra. It is found that the structure of the K_3p-excitation spectrum of K_xC₆₀ quite differs from that of KCl. Furthermore, the K_3p-excitation LEELS of K₃C₆₀ has been revealed to be different from that of K₆C₆₀. K_3p electrons are excited into K_4s- and K_3d-derived empty states in both K_xC₆₀ and KCl, but in the case of K_xC₆₀ the K_3d-derived empty states have a rather complicated structure where several levels are not well separated. Consequently, K_3p-excitation LEEL spectra of K_xC₆₀ show wide-spread plateau-like structures. The difference in the K_3p-excitation spectra of K₃C₆₀ and K₆C₆₀ is considered to originate from the different crystal field around K⁺ cations in the C₆₀ molecular crystal.     

Lowering of magnetic field intensity at the surfaces of α-Fe2O3 and FeBO3 single crystals

Depth-selective conversion electron Mössbauer spectroscopy was used to study magnetic properties of the thin surface layers of the α-Fe₂O₃ and FeBO₃ single crystals. An analysis of the experimental spectra indicates that the magnetic properties of the layers at a depth of more than ～100 nm from the surface are similar to the properties of crystal bulk, and the corresponding spectra consist of narrow lines. The lines gradually broaden as the crystal surface is approached. The spectra of the ～10-nm-thick surface layers consist of broad lines, indicating a wide distribution δ=2.1 T of the effective magnetic field about its mean value of 32.2(4) T. The experimental spectra were used to determine the effective magnetic fields (H _eff) for the iron ions situated in the surface layers of thickness ～100 nm. The effective fields in these layers were found to gradually decrease at room temperature (291 K) as the crystal surface was approached. The H _eff values in the 2.4(9)-nm-thick surface layer of the α-Fe₂O₃ crystal and 4.9(9)-nm layer of FeBO₃ are 0.7(2) and 1.2(3)%, respectively, smaller than for the nuclei of the ions in the bulk of these crystals.     

Direct evidence for controlled band filling in the mixed crystal NMPxPhen1−xTCNQ

Raman spectra of the segregated stack mixed crystal NMP_xPhen_1?xTNCQ and the mixed stack compound Phen TCNQ are presented. By means of the relation between charge transfer and line shift, we give for the first time a direct proof for controlled band filling in the mixed crystal series, whereas for Phen TCNQ a zero charge transfer is obtained. Raman spectra of Phenazine and the related NMP⁺ have also been measured and used for comparison.     

Unified calculations of the optical and electron paramagnetic resonance spectral data for Ce ion in Y3Ga5O12 crystal

Seven crystal field energy levels (obtained from the optical spectra) and three g factors g_x, g_y and g_z (obtained from electron paramagnetic resonance (EPR) spectra) for Ce³⁺ ion in Y₃Ga₅O₁₂ crystal are calculated together by diagonalizing a complete energy matrix. The Hamiltonian of this energy matrix includes all the interactions for 4f¹ ion Ce³⁺ in rhombic crystal field and under an external magnetic field, and so the optical and EPR data can be studied in a unified way. The calculated crystal field energy levels are in better agreement with the experimental values than the calculated values in the previous paper, and the g factors (which have not been calculated previously) are explained reasonably. The results are discussed.     

Ein quantitativer Vergleich der Energieverlustspektren von Elektronen in Aluminium und Kalium mit der dielektrischen Theorie

The energy loss spectra of 34 kV electrons inelastically scattered by thin foils of Aluminium and Potassium were measured and compared with loss intensities, calculated by the dielectric theory from the dielectric constantsε ₁ andε ₂ depending on energy. One obtains a good quantitative agreement of the measured spectra with the calculated energy loss intensities.     

The electronic structure of highly-symmetrical compounds of the lanthanides and actinides—VII: The electronic Raman spectra of the lanthanide elpasolites of the type Cs2NaLn(III)Cl6

The low-temperature Raman spectra of all lanthanide elpasolites of the type Cs₂NaLn(III)Cl₆ have been measured and the observed electronic Raman bands have been identified on the basis of crystal field theory. The corresponding crystal field parameters have been calculated.     

An EPR study of different Gd3+ centers in LiNbO3

Electron Paramagnetic Resonance (EPR) and Zero-(magnetic)-Field (paramagnetic) Resonance (ZFR) spectra have been observed for LiNbO₃:Gd. EPR spectra measured at 9 and 35 GHz consisted of at least seven independent patterns; all of predominantly axial symmetry and all ascribed to Gd³⁺. The two most intense patterns have been analyzed in detail, and while one was found to be axially symmetric the other, though predominantly axial, had a small rhombic crystal field term. The ZFR spectrum, measured between 1 and 18 GHz, consisted of at least two patterns of zero field transitions. Both EPR and ZFR spectra were found to be insensitive to variations in LiNbO₃ stoichiometry, c- of a-axis crystal growth direction, and various sample treatments.     

Influence of exciton decay on the polariton luminescence spectra of CdTe crystal

The polariton luminescence spectra of CdTe crystals have been numerically calculated with allowance for the decay of mechanical excitons and compared with the known experimental low-temperature photoluminescence spectra of these crystals. The mechanism of formation of polariton luminescence in dependence of the optical parameters of crystal for the exciton resonance A _n=1 is discussed.     

Micro-Raman and photoluminescence spectra of Sm-doped β-BaB2O4 crystal lines written by YAG laser irradiation in glass

Nonlinear optical β-BaB₂O₄ (β-BBO) crystal straight lines are written in 10Sm₂O₃·40BaO·50B₂O₃ glass by irradiation of a continuous wave Nd:YAG laser operating at 1064 nm. The linearly polarized micro-Raman scattering spectra for β-BBO crystal lines are consistent with those for commercially available y-cut β-BBO bulk single-crystals, supporting that β-BBO crystal straight lines with the c-axis orientation along the YAG laser scanning direction might be single-crystals. The photoluminescence spectra with large intensities and Stark splitting are observed for β-BBO crystal lines, and it is concluded that some amounts of Sm³⁺ ions in the glass are incorporated into β-BBO crystal lines. Two-dimensional β-BBO crystal curved lines with a bending angle of 30° are successfully written in 10Sm₂O₃·42BaO·48B₂O₃ glass.     

Thermoreflectance of single crystal Gd

Thermoreflectance spectra for E∥c and E⊥c were measured on a Gd single crystal. The thermoconductance spectra, Δσ_∥ and Δσ_t], are very anisotropic. The strong interband edge at about 0.5 eV is shown to arise from a transition to or from the Fermi level for E⊥c. For E∥c additional effects occur.     

Zeeman splitting of a fluorescing level of CaF2 : U6+

Zeeman spectra for a pure electronic transition in the emission from a crystal of CaF₂ : U cooled to helium temperatures are reported for a magnetic field of 7.7 T along principal crystallographic directions. The polarized Zeeman spectra correspond to those of an E → A transition at a centre with trigonal and inversion symmetry.     

Thermal and optical properties of Tm: Li6Gd(BO3)3 crystal: A potential candidate for 1.83 μm lasers

Single crystal of Tm³⁺: Li₆Gd (BO₃)₃ was grown by the Czochralski method. The heat capacity was measured from 308 to 673 K. The absorption spectra of the crystal in three mutually perpendicular arbitrary directions were measured at room temperature. Based on the Judd-Ofelt theory and the spectra measured in three mutually perpendicular directions, the intensity parameters Ω_t (t=2, 4, 6), the line strengths, the oscillator strengths, the radiative rates, radiative lifetimes and fluorescent branching ratios were calculated. We calculated the emission cross-section by the reciprocity method and also obtained the gain cross-section.     

Photoluminescence and recombination centers in phosphorus-doped and undoped CdTe heat-treated under component vapour pressures

Photoluminescence spectra in heat-treated CdTe : P and undoped CdTe were studied at temperatures of 4.2–77 K in the edge emission and the exciton emission region. Temperature dependences and excitation intensity dependences were measured, and the recombination mechanism of each emission line was identified. A change in recombination centers with p_Cd was studied. In a heavily doped crystal an acceptor A₂ (66 meV) was dominant at low p_Cd and the phosphorus acceptor (78 meV) at high p_Cd. A rather deep donor (about 35 meV) was also observed. In a lightly doped crystal the spectra were intermediate between those of the undoped and the heavily doped crystas, and the emission line due to the phosphorus acceptor was not observed. In an undoped crystal an acceptor A₁ (52 meV) was dominat at low p_Cd and the A₂ acceptor at medium and high p_Cd.