Die optischen Eigenschaften von Gold,Silber und Gold-Silber-Legierungen zwischen 2 und 40eV aus Energieverlustmessungen

The energy loss functions Im \(\left( { - \frac{1}{\varepsilon }} \right)\) of Au, Ag and Ag-Au alloys are determined from energy loss spectra of fast electrons, using different methods in the energy regions 2 to 4 eV and 4 to 40 eV. The optical constants ?₁ und ?₂ are calculated from the energy loss functions by Kramers-Kronig analysis. The experimental results show a different dependence in the optical behaviour of the alloy on the alloying component: if Au is added to Ag, the effect on the optical properties is stronger than in the reverse case. Between 50 and 70 at.% Au in the alloy the specific properties of Ag and Au vanish completely. An interpretation of the energy loss maxima as surface plasma oscillation, volume plasma oscillation and interband transition is attempted.     

Optical properties of solid benzene derived from electron energy losses

From energy loss measurements of fast electrons on polycrystalline benzene films the energy loss function Im(?1/?) and the dielectric constants ?=?₁+i?₂ are calculated up to 40 eV. The results are discussed in terms of ?₂ and are compared with the corresponding ?₂-spectrum of benzene vapour.     

Effect of substitution group variation on the optical functions of -5-sulfono-7-(4-x phenyl azo)-8-hydroxy quinoline thin films

-5-Sulfono-7-(4-x phenyl azo)-8-hydroxy quinoline (SAHQ)-x ligands, x = NO₂ or CH₃ or Cl have polycrystalline structure in as synthesized condition. Thermally evaporated thin films of SAHQ-x have crystal structure depending on the substitution group; SAHQ-NO₂ and SAHQ-Cl films have nano-crystalline structure with different degree of crystallinity and SAHQ-CH₃ film has amorphous structure. The changes in optical functions and therefore optical constants with substitution group variation have been calculated by using spectrophotometer measurements of the transmittance and reflectance at nearly normal incidence of light in the wavelength range 200–2500 nm. Substitution group variation influences the refractive index, dispersion parameters, optical functions and bond length of SAHQ. It has no influence on mobility, relaxation time and plasma frequency of charge carriers. The obtained optical energy gaps for SAHQ-x ligands, x = NO₂ or CH₃ or Cl are 1.89, 2 and 2eV, respectively.     

An ab initio study of the structural,elastic, electronic and optical properties of the newly synthesized nitridoaluminate LiCaAlN2

The structural parameters, elastic constants, electronic structure and optical properties of the recently reported monoclinic quaternary nitridoaluminate LiCaAlN₂ are investigated in detail using the ab initio plane-wave pseudopotential method within the generalized gradient approximation. The calculated equilibrium structural parameters are in excellent agreement with the experimental data, which validate the reliability of the applied theoretical method. The chemical and structural stabilities of LiCaAlN₂ are confirmed by calculating the cohesion energy and enthalpy of formation. Chemical band stiffness is calculated to explain the pressure dependence of the lattice parameters. Through the band structure calculation, LiCaAlN₂ is predicted to be an indirect band gap of 2.725 eV. The charge-carrier effective masses are estimated from the band structure dispersions. The frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for polarized incident light in a wide energy range. Optical spectra exhibit a noticeable anisotropy. Single-crystal and polycrystalline elastic constants and related properties, including isotropic sound velocities and Debye temperatures, are numerically estimated. The calculated elastic constants and elastic compliances are used to analyse and visualize the elastic anisotropy of LiCaAlN₂. The calculated elastic constants demonstrate the mechanical stability and brittle behaviour of the considered material.     

Structural,elastic, electronic and optical properties of the cubic perovskites CaXO3 (X=Hf and Sn)

The structural, elastic, electronic and optical properties of CaXO₃ compounds with the cubic perovskites structure have been investigated, by employing a first principles method, using the plane wave pseudo potential calculations (PP-PW), based on the density functional theory (DFT), within the local density approximation (LDA). The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk, shear and Young’s moduli for ideal monocrystalline and for polycrystalline CaXO₃ aggregates which we have classified as ductile in nature. Band structures reveal that these compounds are indirect energy band gap (R-G) semiconductors; the analysis of the site and momentum projected densities, valence charge density bond length, bond population and Milliken charges, shows that bonding is of covalent–ionic nature. We have found that the elastic constants C₁₁, C₁₂, C₄₄ are in good correlation with the bonding properties. The optical constants, including the dielectric function, optical reflectivity, refractive index and electron energy loss, are calculated for radiation up to 20 eV.     

Formation of Ge35In8S57 amorphous films for optical applications

Thin films of In-doped Ge-S in the form of Ge₃₅In₈S₅₇ with different film thickness were deposited using an evaporation method. The X-ray diffraction studies demonstrate that the as-prepared films are amorphous in nature for these films. Some optical constants were calculated at a thickness of 150, 300, 450 and 900?nm and annealing temperature of 373, 413, 437 and 513?K. Our optical observations show that the mechanism of the optical transition obeys the indirect transition. It was found that the energy gap, E_g, decreases from 2.44 to 2.20?eV with expanding the thickness of the film from 150 to 900?nm. On the other hand, it was found that E_g increases with annealing temperature from 373 to 513?K. The increment in the band gap can be attributed to the gradual annealing out of the unsaturated bonds delivering a decreasing the density of localized states in the band structure. Using the single oscillator model, the dispersion of the refractive index is described. The dispersion constants of these films were calculated with different both thickness and annealing temperatures. Additionally, both of nonlinear susceptibility, χ⁽³⁾ and nonlinear refractive index, n₂ were calculated.     

Annealing temperature effect on the structural, optical and electrical properties of ZnS thin films

Zinc sulfide thin films were prepared on glass substrates at room temperature using a chemical bath deposition method. The obtained films were annealed at temperatures ranging from 100 to 500 °C in steps of 100 °C for 1 h. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray analysis (EDX), optical absorption spectra, and electrical measurements. X-ray diffraction analysis indicates that the deposited films have an amorphous structure, but after being annealed at 500 °C, they change to slightly polycrystalline. The optical constants such as the refractive index (n_r), the extinction coefficient (k), and the real (ε₁) and imaginary (ε₂) parts of the dielectric constant are calculated depending on the annealing temperature. Aside from the ohmic characteristics of the I-V curve, a nonlinear I-V curve owing to the Schottky contact is also found, and the barrier heights (?_bn) for Au/n-ZnS and In/n-ZnS heterojunctions are calculated. The conductivity type was identified by the hot-probe technique.     

Structure and bonding of hydrocarbon plasma generated carbon films: An electron energy loss study

Electron energy loss spectroscopy has been used to study the structure and the bonding in hard amorphous carbon films (aC:H) prepared by plasma decomposition of benzene. EXAFS spectra indicate an amorphous and not a microcrystalline structure for aC:H films. The near-edge structure of the carbon K-amsorption edge reveals a considerable amount of π bonding in the aC:H films. The optical constants were derived by a Kramers-Kronig analysis of the loss functions for energies less than 40 eV. From the sum rule for ε₂, we derive that $\text{1}\text{3}$ of the carbon atoms are trigonally bonded and 273 of the carbon atoms are tetrahedrally bonded.     

On the validity of the random phase approximation for pairing vibrations of closed shell nuclei

Energy loss measurements on solid xenon applying 51 keV-electrons are reported. The spectrum shows excitonic structure and a plasma loss. From the energy loss function —Im1/g3 optical constants are calculated by means of a Kramers-Kronig transform. They are compared with optical absorption spectra and found to be in good agreement. An appendix gives detailed information about the calculation of —Im 1/g3 from energy loss measurements.     

Dependence of the optical properties of Fe<Subscript>78</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy on its structural state

The optical properties of Fe₇₈Si₁₀B₁₂ ferromagnetic alloy in amorphous, crystalline, and intermediate structural states have been investigated by ellipsometry in the spectral range of 0.22–18 μm. It is established that alloy crystallization leads to a significant change in the optical constants and the frequency dependences of the dielectric functions calculated based on these optical constants. The structural reconstruction under heat treatment leads to an increase in the intensity and shift of interband absorption bands. The plasma and relaxation frequencies of conduction electrons are determined; their numerical values also depend on the degree of atomic ordering.     

Influence of valence electron concentration on elastic, electronic and optical properties of the alkaline-earth tin oxides A3SnO (A=Ca, Sr and Ba): A comparative study with ASnO3 compounds

By employing first principles method of the plane wave pseudo potential calculations (PP-PW), based on the density functional theory (DFT), within the local density approximation (LDA), the correlation between valence electron concentration and structural, elastic, electronic as well as optical properties of A₃SnO and ASnO₃ compounds where A=Ca, Sr and Ba are investigated. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk, shear and Young's moduli for ideal monocrystalline and for polycrystalline A₃SnO and ASnO₃ aggregates. Band structures reveal that alkaline-earth tin oxides A₃SnO are direct energy band gap (G-G) materials.The hardness of these compounds was explained using chemical bonding properties and Milliken charges transfer. The optical constants, including the dielectric function, optical reflectivity, refractive index and electron energy loss, are calculated for radiation up to 20 eV. We have found that the static dielectric constants of all these compounds are in good agreement with Penn model.     

Effect of crystallization of amorphous Fe5Co75Si4B16 alloy on its optical properties

The optical properties of ferromagnetic Fe₅Co₇₅Si₄B₁₆ alloy in the amorphous state and after temperature treatments have been investigated by spectroscopic ellipsometry in the energy range of 0.073–5.64 eV. It is shown that alloy crystallization changes significantly the frequency dependences of the optical constants and the dielectric functions calculated based on them. The atomic ordering is accompanied by a significant increase in the intensity of the fundamental band of quantum light absorption. The plasma and relaxation frequencies of conduction electrons have been calculated.     

Compositional dependence of the optical properties of the amorphous GexTe1−x system

Optical absorption at room temperature of vacuum evaporated Ge_xTe_1−x (0.125?x?0.225) amorphous thin films has been studied as a function of composition. It was found that the optical absorption is due to a direct transition. The real and imaginary parts of the dielectric constant were determined. The single-oscillator energy (E_o) and the energy dispersion parameter (E_d) have been calculated and discussed in terms of the Wemple and Di-Domenico model. The relationship between the optical gap, the average heat of atomization and the coordination numbers has been determined. The optical properties of the amorphous thin films do not change monotonically with increasing Ge content. The observed behavior of the optical properties in the range of compositions studied are explained on the basis of the Bond Constraint Theory (BCT) and rigidity theory, which provide a powerful framework for understanding the structure and properties of amorphous materials. The non-monotonic variation of the optical properties indicates that a transition from floppy to rigid occurs in the Ge_xTe_1−x films.     

First-principles calculations of structural, elastic, electronic and optical properties of the antiperovskite AsNMg3

The density functional theory (DFT) calculations of structural, elastic, electronic and optical properties of the cubic antiperovskite AsNMg₃ has been reported using the pseudo-potential plane wave method (PP-PW) within the generalized gradient approximation (GGA). The equilibrium lattice, bulk modulus and its pressure derivative have been determined. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline AsNMg₃ aggregate. We estimated the Debye temperature of AsNMg₃ from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNMg₃ compound, and it still awaits experimental confirmation. Band structure, density of states and pressure coefficients of energy gaps are also given. The fundamental band gap (Γ-Γ) initially increases up to 4 GPa and then decreases as a function of pressure. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. The all results are compared with the available theoretical and experimental data.     

Thickness-dependent electrical and optical properties of Ge8Sb2Te11 thin films

The amorphous Ge₈Sb₂Te₁₁thin films with varying thickness are thermally deposited on well-cleaned glass substrate from its polycrystalline bulk. Absence of any sharp peak confirms the amorphous nature of deposited films. Thickness-dependent electrical and optical properties including dc-activation energy, sheet resistivity, optical band gap, band tailing parameter, etc. of Ge₈Sb₂Te₁₁thin films have been studied. The optical parameters have been calculated from transmission, reflection and absorbance data in the spectral range of 200–1100 nm. It has been found that optical band gap and band tailing parameter decreases with the increase in Ge₈Sb₂Te₁₁thin films thickness. The dc-activation energy and sheet resistivity decreases while the crystallization temperature of the amorphous Ge₈Sb₂Te₁₁ films increases with the increase in thickness of the films. The decrease of the sheet resistivity has been substantiated quantitatively using the classical size-effect theory. These results have been explained on the basis of rearrangements of defects and disorders in the amorphous chalcogenide system.     

Structural,optical and electrical properties of laser irradiated Pb doped Ga–Se chalcogenide thin films

Using the Transverse Electrical Excitation at Atmospheric Pressure (TEA) nitrogen laser, we had irradiated the amorphous thin films of Ga₁₀Se₈₁Pb₉ chalcogenide glass and the results have been discussed in terms of the structural aspects of Ga₁₀Se₈₁Pb₉ glass. The observed changes are associated with the interaction of the incident photon and the lone-pairs electrons which affects the band gap. The X-ray structural characterization revealed the amorphous nature of as prepared films and polycrystalline nature of the laser irradiated films. The optical band gap of these thin films is measured by using the absorption spectra as a function of photon energy in the wavelength region 400–1200 nm. It is found that the optical band gap decreases while the absorption coefficient increases with increasing the irradiation time. The decrease in the optical band gap has been explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase in exposure time. The dc conductivities and activation energies of these thin films are measured in temperature range 303–403 K. It has been found that the activation energy in Ga₁₀Se₈₁Pb₉ chalcogenide thin films decreases whereas the dc conductivity increases at each temperature by increasing the irradiation time.     

Energieverluste von 50 keV-Elektronen an Ge und Si

Electron-Energy loss spectra of Ge and Si (amorphous, polycristalline and monocristalline) are measured in the low energy region of the band-band transitions and in the energy region of the plasma losses. These spectra are compared with the loss curve calculated from optical data: Discrepancies in the absolute values of the height and in the width of the plasma losses are found; the structures of the region of the bandband excitations show an agreement in the positions of the maxima, but not in their height. Additional electron energy loss maxima are observed.     

Structural,elastic, electronic,optical and thermal properties of c-SiGe<Subscript>2</Subscript>N<Subscript>4</Subscript>

We have investigated the structural, elastic, electronic, optical and thermal properties of c-SiGe₂N₄ by using the ultrasoft pseudopotential density functional method within the generalized gradient approximation. The calculated structural parameters, including the lattice constant, the internal free parameter, the bulk modulus and its pressure derivative are in agreement with the available data. The independent elastic constants and their pressure dependence, calculated using the static finite strain technique, satisfy the requirement of mechanical stability, indicating that c-SiGe₂N₄ compound could be stable. We derive the shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients for ideal polycrystalline c-SiGe₂N₄ aggregate in the framework of the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of this compound from the average sound velocity. Band structure, density of states, Mulliken charge populations and pressure coefficients of energy band gaps are investigated. Furthermore, in order to understand the optical properties of c-SiGe₂N₄, the dielectric function, refractive index, extinction coefficient, optical reflectivity and electron energy loss are calculated for radiation up to 40 eV. Thermal effects on some macroscopic properties of c-SiGe₂N₄ are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account. We have obtained successfully the variations of the primitive cell volume, volume expansion coefficient, heat capacities and Debye temperature with pressure and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first time, the numerical estimates of the elastic constants and related parameters, and the thermal properties are performed for c-SiGe₂N₄.     

金属有机分解法制备的SrTiO3薄膜的光学特性

采用金属有机分解法（MOD）在石英衬底上沉积了SrTiO3薄膜。所制备的薄膜是晶格常数为a=b=c=3.90?的多晶结构。通过测量190—1100nm波段内的透射光谱，采用包络方法计算了薄膜的光学常数（折射率n和消光系数k）。结果表明，采用MOD方法制备的薄膜的折射率大于采用射频磁控溅射、溶胶—凝胶和化学气相沉积方法制备的薄膜的折射率；薄膜的折射率色散关系满足单振子模型，其中振子强度S0为0.88′1014m-2，振子能量E0为6.40eV；薄膜的禁带宽度为3.68eV。     

Electron energy loss measurements on PbF2, PbCl2, PbBr2 and PbI2

The results of electron energy loss measurements on polycrystalline films of PbF₂, PbC1₂, PbBr₂ and PbI₂ are present and the calculated dielectric functions are discussed in relation to their band structures and optical data.