The geometric structure of pure SF6 and mixed Ar/SF6 clusters investigated by core level photoelectron spectroscopy

The S 2p core level photoelectron spectra of Sulphurhexafluoride clusters have been investigated together with heterogeneous Ar/SF₆ clusters, created by doping Ar host clusters (with a mean size of 3600 atoms) with the molecule. Surface and bulk features are resolved both in the argon 2p and the sulphur 2p core level photoelectron spectra. For the latter level such features were only observed in the pure cluster case; a single feature characterizes the S 2p core level spectra of SF₆ doped argon clusters. From the chemical shifts, investigated with respect to SF₆ doping pressure. It can be concluded that the host clusters get smaller with increasing doping pressures and that the SF₆ molecules predominantly stay below the cluster surface, whereas the Argon core stays intact. We have neither observed features corresponding to SF₆ on the cluster surface, nor features corresponding to molecules deep inside the bulk in any of the spectra from the pick-up experiments.     

The structure of ordered Au films on TiOx

The growth of Au on an ultra-thin, ordered Mo(1 1 2)-(8 × 2)-TiO_x, was investigated using scanning tunneling microscopy (STM), low energy ion scattering spectroscopy (LEISS), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Wetting of the TiO_x surface by Au was observed with STM and LEISS, and the ordering of the Au films was atomically resolved with STM. TPD showed that Au binds more strongly to the reduced TiO_x film than to bulk TiO₂, but more weakly than to the Mo substrate. The Au-TiO_x binding energy is greater than Au-Au in bulk Au. The oxidation state of Ti in the TiO_x film was deduced by XPS and from the Ti-O phonon shifts relative to bulk TiO₂. The TiO_x/Mo(1 1 2) film structure and those for the (1 × 1)- and (1 × 3)-Au/TiO_x/Mo(1 1 2) surfaces are discussed.     

The effect of Co ion implantation on Ge1−xMnx films

Ge_1−xMn_x (x = 0, 0.013, 0.0226, 0.0339, 0.0565, 0.0678, 0.0904, 0.113) films prepared by magnetron sputtering at 773 K had a Ge cubic structure except for x = 0.1130. Co ion implantation into these films can effectively prevent the formation of a second phase. Both single-doped and co-doped samples were ferromagnetic at room temperature. The d-d exchange interaction between the interstitial Mn (MnT) and the substituted Mn (Mn_Ge) resulted in ferromagnetism in the sputtered films. Since Co ion implantation destroyed the Mn_T-Mn_Ge-Mn_T complex, the saturated magnetization decreased. Hall measurements revealed that the Co ion implanted films were n-type semiconductors, and the anomalous Hall Effect (AHE) suggested the ferromagnetism was carrier-mediated in the implanted films.     

Preparation and characterization of CrNxOy thin films: The effect of composition and structural features on the electrical behavior

Metallic oxynitrides have attracted the attention of several researchers in the last decade due to their versatile properties. Through the addition of a small amount of oxygen into a transition metal nitride film, the material's bonding states between ionic and covalent types can be tailored, thus opening a wide range of electrical, optical, mechanical and tribological responses. Among the oxynitrides, chromium oxynitride (CrN_xO_y) has many interesting applications in different technological fields. In the present work the electrical behavior of CrN_xO_y thin films, deposited by DC reactive magnetron sputtering, were investigated and correlated with their compositional and structural properties. The reactive gas flow, gas pressure, and target potential were monitored during the deposition in order to control the chemical composition, which depend strongly on reactive sputtering process. Depending on the particular deposition parameters that were selected, it was possible to identify three types of films with different growth conditions and physical properties. The electrical resistivity of the films, measured at room temperature, was found to depend strongly on the chemical composition of the samples.     

Band structure of semiconductor alloys beyond the virtual crystal approximation. effect of compositional disorder on the energy gaps in GaPxAs1−x

A general method to study the band structure of compositionally disordered semiconductors is proposed. The effects of chemical disorder are added to the virtual-crystal band structure using the pseudopotential method and second order perturbation theory. In GaP_xAs_1?x, chemical disorder is shown to give a significant contribution to the experimentally observed non-linear behaviour of the lowest energy gaps as function of composition.     

The effect of Er doping on the spin reorientation transition in Ho1−xErxAl2

The magnetothermal properties of pseudo binary Ho_1−xEr_xAl₂ alloys have been investigated by heat capacity measurements. Two anomalies are observed in the heat capacity of HoAl₂. A sharp peak at 20 K represents the first order spin reorientation transition, and a second order anomaly occurs in the vicinity of the ferromagnetic transition at 32 K. As Ho is partially replaced by Er in Ho_1−xEr_xAl₂ the sharpness of the first order heat capacity peak diminishes with increasing Er concentration, while the temperature of this transition remains practically unaffected. The second order ferromagnetic transition shifts to higher temperature region with increasing Er concentration. The observed behaviors are explained considering the geometry of 4f charge densities of Ho³⁺ and Er³⁺ and the easy magnetization directions of HoAl₂ and ErAl₂.     

A survey on the effect of vanadium content on the magnetoelastic properties of YFe12−xVx alloys

Experimental results on the thermal expansion and magnetostriction of YFe_12−xV_x (1.5≤x≤3.5) alloys are reported. The results show that the anisotropic magnetostriction (Δλ) at a finite field (1.5 T) increases with increasing vanadium content in the range of x<2. But for x>2, a decrease in the magnetic anisotropy with increasing vanadium content causes a decrease in the saturation values of Δλ. In addition, the thermal expansion coefficient becomes a minimum for x≈2. Experimental curves exhibit that the forced volume magnetostriction (ΔV/V) is positive and increases linearly with the applied field at high fields. But in the low field region (≤0.5 T), a minimum appears in the isothermal curves of ΔV/V around the saturation field. The results are explained by considering the influence of vanadium content on the magnetization anisotropy of YFe_12−xV_x compounds.     

The effect of addition of gallium on the thermal stability and crystallization kinetic parameters of GaxSe100−x glass system

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation for Ga_xSe_100−x glass system (x=0, 2.5 and 5 at%). The kinetic parameters of Ga_xSe_100−x glass system under non-isothermal conditions are analyzed by the model-free and model-fitting models at different constant heating rates (5-50 K/min). A strong heating rate dependence of the effective activation energy of crystallization was observed. The analysis of the present data shows that the effective activation energy of crystallization is not constant but varies with the degree of crystallization and with temperature as well. The crystallization mechanisms examined using the local Avrami exponents indicate that one mechanism (volume nucleation with one-dimensional growth) is responsible for the crystallization process for heating rates 5-50 K/min for Se glass and two mechanisms (volume nucleation with two- and one-dimensional growth) are working simultaneously during the amorphous-crystalline transformation of the Ga_2.5Se_97.5 and Ga₅Se₉₅ glasses (5-50 K/min). The reaction model that may describe crystallization process of all the compositions of Ga_xSe_100−x glass system is Avrami-Erofeev model (g(α)=[−ln(1−α)]^1/n) with n=2 for Se glass. While for Ga_2.5Se_97.5 and Ga₅Se₉₅ glasses, the values of n are equal to 3 and 2 for the heating rates 5-20 and 35-50 K/min, respectively. A good agreement between the experimental and the reconstructed (α-T) curves has been achieved. The transformation from amorphous to crystalline phase in Ga_xSe_100−x glass system demonstrates complex multi-step involving several processes.     

Breit相互作用对类氦离子亚稳态1s2s 3S1电子碰撞激发截面的影响

利用新近发展的基于全相对论扭曲波方法研究电子-离子碰撞激发过程的计算程序,通过对Breit相互作用的考虑,计算了类氦等电子序列离子从亚稳态1s2s³S₁激发2s电子到n=2,3壳层的电子碰撞激发截面;研究了不同入射电子能量时Breit相互作用对碰撞激发截面的影响,进一步总结了沿等电子序列变化时,Breit相互作用对截面影响的一般规律.部分计算结果与实验结果进行了比较,得到了很好的一致性. 关键词： 全相对论扭曲波方法 Breit相互作用 电子碰撞激发截面     

Effect of Cu deficiency on the optical properties and electronic structure of CuIn1−xGaxSe2

Spectroscopic ellipsometry measurements of CuInSe₂ (CIS) and CuIn_1−xGa_xSe₂ (CIGS) over a range of Cu compositions reveal that there are important differences in electronic and optical properties between α-phase CIS/CIGS and Cu-poor CIS/CIGS. We find a reduction in the imaginary part of the dielectric function ?₂ in the spectral region, 1-3 eV. This reduction can be explained in terms of the Cu-3d density of states. An increase in band gap is found for Cu-poor CIS and CIGS due to the reduction in repulsive interaction between Cu-3d and Se-4p states. We also characterize the dielectric functions of polycrystalline thin-film α-phase CuIn_1−xGa_xSe₂ (x=0.18 and 0.36) to determine their optical properties and compare them with similar compositions of bulk polycrystalline CuIn_1−xGa_xSe₂. The experimental results have important implications for understanding the functioning of polycrystalline optoelectronic devices.     

Electrical switching and thermal studies on Ge22Te78−xIx chalcohalide glasses: The effect of iodine on network-topology

Investigations on the electrical switching behavior and thermal studies using Alternating Differential Scanning Calorimetry have been undertaken on bulk, melt-quenched Ge₂₂Te_78−xI_x (3≤x≤10) chalcohalide glasses. All the glasses studied have been found to exhibit memory-type electrical switching. The threshold voltages of Ge₂₂Te_78−xI_x glasses have been found to increase with the addition of iodine and the composition dependence of threshold voltages of Ge₂₂Te_78−xI_x glasses exhibits a cusp at 5 at.% of iodine. Also, the variation with composition of the glass transition temperature (T_g) of Ge₂₂Te_78−xI_x glasses, exhibits a broad hump around this composition. Based on the present results, the composition x=5 has been identified as the inverse rigidity percolation threshold at which Ge₂₂Te_78−xI_x glassy system exhibits a change from a stressed rigid amorphous solid to a flexible polymeric glass. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy () of Ge₂₂Te_78−xI_x glasses at x=5, which is suggestive of a thermally reversing window at this composition.     

The mixed-spin ternary-alloy in the form of ABpC1−p on the Bethe lattice

The AB_pC_1−p type of mixed ferromagnetic-ferrimagnetic ternary-alloy with A (spin-3/2), B (spin-1) and C (spin-5/2) ions was studied on the Bethe lattice with the odd numbered shells containing only A ions, while the even numbered shells either containing B or C ions randomly. The phase diagrams were obtained on the (R=|J_AC|/J_AB,kT_c/J_AB) and (p, kT_c/J_AB) planes for given values of p and R, respectively, with the coordination numbers z=3, 4, 5 and 6. The explicit dependence of the phase diagrams on z and each shell of the Bethe lattice having only one type of ion lead to some differences when compared with the previous works. The model presents one or two compensation temperatures for appropriate values of the system parameters.     

The effect of Mn substitution on thermoelectric properties of Ca3MnxCo4−xO9 at low temperatures

The effects of partial substitution of Mn for Co on the thermoelectric properties of Ca₃Mn_xCo_4−xO₉ (x=0, 0.03, 0.9), prepared by sol-gel process, were investigated at the temperatures from 380 K down to 5 K. The results indicate that the substitution of Mn for Co results in increase in thermopower at temperatures >∼80 K, and substantial (23-31% at 300 K) decrease in lattice thermal conductivity in the whole temperature range investigated. The temperature behavior of ZT suggests that Ca₃Mn_xCo_4−xO₉ with light Mn substitution would be a promising candidate for high-temperature thermoelectric applications.     

The influence of isotope substitution of neon atom on the integral cross sections of rotational excitation in Ne-Na2 collisions

This paper applies the multiple ellipsoid model to the 16 Ne (20 Ne,28 Ne,34 Ne)-Na 2 collision systems,and calculates integral cross sections for rotational excitation at the incident energy of 190 meV.It can be seen that the accuracy of the integral cross sections can be improved by increasing the number of equipotential ellipsoid surfaces.Moreover,by analysing the differences of these integral cross sections,it obtains the change rules of the integral cross sections with the increase of rotational angular quantum number J,and with the change of the mass of isotope substitution neon atom.Finally,the contribution of different regions of the potential to inelastic cross sections for 20 Ne-Na 2 collision system is investigated at relative incident energy of 190 meV.     

The influence of Al substitution on the phase transitions and magnetocaloric effect in Ni43Mn46Sn11−xAlx alloys

The effects of Al substitution on the phase transitions and magnetocaloric effect of Ni₄₃Mn₄₆Sn_11−xAl_x (x=0-2) ferromagnetic shape memory alloys were investigated by X-ray diffraction and magnetization measurements. With the increase of Al content, the cell volume decreases due to the smaller radius of Al, and the martensitic transformation temperature increases rapidly, while the Curie temperature of austenitic phase shows a small increase. A large positive and a negative magnetic entropy change were observed near the first-order martensitic transition and the second-order magnetic transition, respectively. The magnetic entropy changes, hysteresis behavior, and refrigerant capacity near the two transitions are compared.     

The effect of oxygen stoichiometry on electrical transport and magnetic properties of La0.9Te0.1MnOy

The effect of the variation of oxygen content on structural, magnetic and transport properties in the electron-doped manganites La_0.9Te_0.1MnO_y has been investigated. All samples show a rhombohedral structure with the space group The Curie temperature T_C decreases and the paramagnetic-ferromagnetic (PM-FM) transition becomes broader with the reduction of oxygen content. The resistivity of the annealed samples increases slightly with a small reduction of oxygen content. Further reduction in the oxygen content, the resistivity maximum increases by six orders of magnitude compared with that of the as-prepared sample, and the ρ(T) curves of samples with y=2.86 and y=2.83 display the semiconducting behavior (dρ/dT<0) in both high-temperature PM phase and low-temperature FM phase, which is considered to be related to the appearance of superexchange ferromagnetism and the localization of carriers. The results are discussed in terms of the combined effects of the increase in the Mn²⁺/(Mn²⁺+Mn³⁺) ratio, the partial destruction of double exchange interaction, and the localization of carriers due to the introduction of oxygen vacancies in the Mn-O-Mn network.     

Low voltage electrodeposition of CNx films and study of the effect of the deposition voltage on bonding configurations

Carbon nitride (CN_x) films were deposited from acetonitrile at low voltage (150-450 V) through electrodeposition. The films were characterized by atomic force microscopy (AFM), Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. AFM investigations revealed that the grain size was ∼200 nm and roughness was ∼10 nm. The films were found to be continuous and close packed. IR spectra revealed existence of strong sp³, sp² type bonding and weak sp type carbon nitrogen bonds and these bonds were found to increase with voltage. The fraction of sp³-bonded species in the sample increased in low voltage range and after reaching maximum at 350 V, decreased for higher voltages. However, the concentration of sp² CN ring structures in the film increased with increasing voltage. Also, the peak width decreased at low voltages reaching a minimum and increased thereafter. It was observed that the voltage dependent increase in the concentration of polymeric type sp² CN (chain) structures was much more pronounced than that of graphitic type sp² CN (ring) structures. Raman spectra showed the presence of both the D and G bands. The shift in the G band indicated the presence of nitrogen in the film. The I_D/I_G ratio was found to increase with the incorporation of nitrogen. Auger electron spectroscopy (AES) showed a clear increase in the nitrogen content with increase in the voltage. The formation of the film could be explained on the basis of dissociation of electrolyte under applied voltage.     

Effects of spin-phonon interaction on transport, magnetic properties and the oxygen isotope effect in R1−xAxMnO3

We consider the spin-phonon (s-p) coupling as an important correction to the double exchange and the dynamic Jahn-Teller effect in colossal magnetoresistance systems R_1−xA_xMnO₃. The effect of s-p on transport, magnetic properties and the oxygen isotope effect has been studied by utilizing the perturbation theory and mean field theory. It is indicated that (i) a formula for the shift of the ferromagnetic (FM) transition temperature T_c is given, from which it could be seen that the s-p coupling could yield an excitation gap for long-wavelength acoustic spin waves and an applied field could improve T_c, (ii) the relation T_c∼m^−1/2 (m is the mass of the anion) is obtained, which suggests that the oxygen isotope effect is dominated by both the s-p and e-p interaction, (iii) it could cause the hardening of phonon frequency in the FM state, (iv) s-p could lead to the increase of the resistivity which is proportional to T³ at low temperature and proportional to T at high temperature in the ferromagnetic metallic region of R_1−xA_xMnO₃.     

The dependence of the structural and optical properties on the Te mole fraction in ZnS1−xTex/GaAs heterostructures

Lattice-mismatched ZnS_1−xTe_x epilayers with various Te mole fractions on GaAs (100) substrates were grown by double well temperature gradient vapor deposition. X-ray diffraction patterns showed that the grown ZnS_1−xTe_x layers were epitaxial films. The photoluminescence spectra showed that the peak position of the acceptor-bound exciton (A⁰, X) varied dramatically with changing the Te mole fraction and that the behavior of the (A⁰, X) peak position of the ZnS_1−xTe_x epilayers with a small amount of the Te mole fraction was attributed to a bowing effect. The reflectivity and ellipsometry spectra showed that the absorption energy peak was significantly affected due to the Stoke's effect. These results provide important information on the structural and optical properties of ZnS_1−xTe_x/GaAs heterostructures for improving optoelectronic device efficiencies operating in the spectral range between near ultraviolet and visible regions.     

The effect of Co2+ on the Verwey transition of CoxFe3−xO4 (x ⩽ 0.04) single crystals

The Verwey transition of Co_xFe_3?xO₄ single crystals with x = 0.005; 0.01; 0.02; 0.03; and 0.04 has been determine by means of dilatation measurements. The transition temperature shows a linear dependence on x.