Spectromicroscopic investigation of (NH4)2S treated polycrystalline Cu(In1−xGax)Se2

Device-grade polycrystalline thin-film Cu(In_1−xGa_x)Se₂ was treated with (NH₄)₂S at 60°C to determine the resulting microscopic surface composition/morphology. Scanning electron microscopy was used to evaluate the resultant macroscopic surface morphology. Modification of the surface and grain boundary chemistry of the Cu(In_1−xGa_x)Se₂ polycrystalline films was investigated with scanning photoemission spectromicroscopy. The submicrometer lateral resolution of this technique allows us to directly characterize not only the surface chemistry of the treated films on the submicron scale, but also to probe the grain boundary chemistry. Chemical maps depicting the distribution of chemical species on the surface and at grain boundaries were obtained by monitoring the S 2p, Se 3d, In 4d/Ga 3d and Cu 3d (valence band) photoelectrons while scanning the sample. Background maps were also acquired of each of the peak energies to separate chemical contrast from topographic contrast. Results show that S has been incorporated at the surface, possibly creating a wider bandgap Cu(In_1−xGa_x)(Se_1−yS_y)₂ surface layer, and along the grain boundaries. The purpose of this investigation is to find an environmentally safe replacement for the toxic CdS overlayer commonly used for heterojunction devices without sacrificing overall device performance and reliability.     

Optical and vibrational properties of CdxHg1-x-y ZnyTe solid solutions

The lattice dynamics of Cd_xHg_1-x-y Zn_yTe solid solutions is studied theoretically and experimentally. The frequencies of the basic optical phonons of Cd_xHg_1-x-y Zn_yTe are calculated in terms of a modified random-element isodisplacement model. As a result, all basic vibrations of the crystal lattice that substantially affect the optical properties of this material in the spectral region corresponding to one-phonon resonance are identified. The optical properties of epitaxial Cd_xHg_1-x-y Zn_yTe layers grown by liquid-phase epitaxy on Cd_1-x Zn_xTe substrates are studied. The calculated and experimental spectral dependences of the dielectric function of Cd_xHg_1-x-y Zn_yTe solid solutions of various compositions are compared at 295 and 78 K, and good agreement between them is reached. The additional lattice vibrations whose frequencies in the phonon density of states are lower than that of the HgTe mode are shown to be caused by the lattice defects of the Cd_xHg_1-x-y Zn_yTe solid solutions.     

Band edge offsets in strained (InGa)As-(AlGa)As heterostructures

The excitonic transitions between the ground electron and hole quantum well sublevels in strained In_xGa_1-xAs-Al_yGa_1-yAs multiple quantum well structures (x = 0.12−0.35 and y = 0.2−0.35) have been investigated by means of photoluminescence and photoconductivity measurements. The molecular beam epitaxy grown structures contained an Al_yGa_1-yAs matrix with one unstrained GaAs and three strained In_xGa_1-xAs quantum wells one of which was in the GaAs cladding layers. The ratio of the conduction band edhe line up to the band gap offset for the strained In_xGa_1-xAs-unstrained Al_yGa_1-yAs interface has been found to be 0.67 ± 0.08 for the studied regions of x and y.     

Solid solutions on the base of bismuth vanadate: Preparation, structure, phase transitions, dielectric and transport properties

Ceramic solid solutions (Bi_1-yLa_y)₄(V_1-xMe_x)₂O_11-y with x, y < 0.2, Me-Zr, Ga, Fe, Cu, have been prepared by the solid state reaction method. Crystal structure parameters, phase transitions, dielectric and transport properties of ceramic samples have been studied. Concentration and temperature stability regions of monoclinic α-, orthorhombic β- and tetragonal γ- or γ’- polymorph modifications have been determined.Annealing of samples, containing large amount of Cu and/or La dopants, at 973 K in the reducing atmosphere resulted in their decomposition, though compositions containing low content of La, Ga or Zr dopants, remained pretty stable.     

Investigation of the cation distribution in perovskite-like oxides with Mössbauer spectroscopy

Complex perovskite-like oxides, such as LnFe_2/3Mo_1/3O₃ orthoferrites, Ln_8?ySr_yCu_8?xFe_xO₂₀ (8-8-20), Pr₄BaCu₄FeO_13-δ(4-1-5), YBa_2-yLa _y Cu_3-xFe _x O_7-δ and Y_1-yCa _y Ba _y La _y Cu_3-xFe _x O_7-δ (1-2-3), are studied by means of Mössbauer spectroscopy. At room temperature, the spectra of the orthoferrites contain only magnetic components. The spectra of the 1-2-3 compounds contain only magnetically disordered components: iron atoms substitute for copper at Cu(1) sites, taking various configurations: planar squares, quadratic pyramids, and octahedra. Cuprates 8-8-20 and 4-1-5 have a wide diversity of spectra. In the 8-8-20 oxides, a phase related to the pyramidal environment of the iron cations is present at any iron concentration. In all the perovskites, iron cations become magnetically ordered only at octahedral sites of the structure.     

Hyperfine magnetic fields on Cd impurity in the Pd2MnIn1-xSnx and Pd2MnSn1-ySby heusler alloys

The TDPAC technique was used to measure the magnetic hyperfine field (mhf) acting on Cd impurity in the Heusler alloys Pd₂MnIn_1-xSn_x and Pd₂MnSn_1-ySb_y for various values of x and y in the range 0 ? x, y ? 1. The alloys of Pd₂MnIn_1-xSn_x are antiferromagnetic at the In-rich end and ferromagnetic at the Sn-rich end, with a transition region x ≈ 0.5?0.7 where both phases coexist; the alloys containing Sn/Sb are ferromagnetic for all values of y. The mhf on the Cd impurity in the antiferromagnetic, transition and ferromagnetic regions of Pd₂MnIn_1-xSn_x are respectively zero, -150 and -200 kOe. For the Sn/Sb alloys the field changes from -200 at the Sn-rich end to -235 kOe at the Sb-rich end. The values of the field very closely follow the trend of the ferromagnetic Curie temperatures for the same alloys as a function of the s-p electron concentration. The observed large distribution of field intensities (～20%) and the lower values of the field in the region x = 0.5?0.6 are attributed mainly to the effect of antiferromagnetic domains. The results are compared with previous Mössbauer mhf measurements at the sites of Sn and Sb in the same alloys as well as with measurements in other Heusler alloys.     

Magnetic field dependence of the energy levels in CdTe-Cd(Mn)Te double quantum well structures

We show that if the valence band offset between CdTe and Cd_1-xMn_xTe alloys is not too large, magneto-photoluminescence experiments performed on CdTe-Cd_1-xMn_xTe-Cd_1-yMn_yTe double quantum wells should yield direct informations on this offset: the structure changes from a type I configuration (where electron and hole are mostly localized within CdTe layer) prevailing at zero magnetic field to a type II configuration (electron in CdTe layer, hole in Cd_1-yMn_yTe layer) at large magnetic field.     

Iron substitution effects and Mössbauer spectroscopy in Bi−Sr−Ca−Cu ceramic oxides

Mössbauer spectroscopy spectra of the ceramic Bi₂Sr₂Ca(Cu_1-x Fe _x )₂O_8+y forx=0, 0.005, 0.02 and 0.05 shows two doublets, that can be assigned to two different environments for the substituting ion. One of the sites is identified as a single Fe ion replacing a Cu ion in the CuO plane. The other site is associated with the dopant in an interstitial position in the plane, in slightly different environments. This last configuration, which increases with increasingx, is related with adverse effects upon the conductive properties of these materials.     

Galvanomagnetic and thermoelectric properties of multicomponent n-type solid solutions based on Bi and Sb chalcogenides

The galvanomagnetic and thermoelectric properties of n-Bi_2-x Sb_xTe_3-y-z Se_yS_z multicomponent solid solutions with atomic substitutions (Sb → Bi; Se, S → Te) are studied. The principal components of the effective mass tensor (m ₁, m ₂, m ₃) for the isotropic mechanism of charge carrier scattering are determined within a many-valley model of the energy spectrum for compositions 0.08 ≤ x ≤ 0.4 and 0.06 ≤ y = z ≤ 0.15. The effect of a variation in the parameters of the constant-energy surface on the thermoelectric efficiency is analyzed for different compositions and carrier concentrations in solid solutions.     

X-ray photoelectron diffraction (XPED) patterns from: III-V compound mixed crystals (Ga1-xAlxAs AND GaAs1-yPy). Comparison of experiment and single scattering calculations

X-ray photoelectron diffraction (XPED) measurements, together with single scattering calculations, were made for two III—V group compound semiconductor mixed crystals (Ga_1-xAl_xAs(110) and GaAs_1-yP_y(001)). Each pair of photoelectrons excited at equivalent atomic sites in the crystal (Ga 3d and Al 2p in Ga₁-xAl_xAs, and As 3d and P 2p in GaAs₁-yP_y) showed essentially the same XPED patterns. Single scattering calculations reproduced the observed XPED patterns fairly well. An obvious site dependence of XPED patterns was observed in both the experimental and calculated results. These results clearly show that, for a given kinetic energy, XPED patterns mainly depend on the site of emitter atoms in the crystal, not on the species of emitter atoms. Thus, XPED measurements can be used for crystal site determinations in a fingerprint manner.     

自旋-Peierls化合物GeCuO3电子结构的第一性原理研究

采用平面波赝势方法对自旋-Peierls化合物GeCuO₃的电子结构进行了第一性原理研究.计算结果表明：Cu²⁺的3d轨道自由度被冻结,未配对电子填充d_x²-y²轨道.自旋向上和向下的d_x²-y²轨道间的交换劈裂导致了体系的绝缘性.费米能级附近的Cu 3d态与O(2) 2p态存 关键词： 3')" href="#">GeCuO₃ 自旋-Peierls相变 第一性原理计算 共价绝缘体     

Effect of Substitution of Zr and Pr on magnetic properties of R2Co17(R=Er,Yb)

Magnetic properties (saturation magnetizations, Curie temperatures and anisotropy fields) have been measured for the ternary systems Er₂Co_17-xZr_x and Yb₂Co_17-xZr_x and for the quaternary system Er_2-yPr_yCo_16.4Zr_0.6. Introduction of Zr expands the lattice and diminishes the Curie temperature, both indicating Zr replaces Co. Saturation magnetization is diminished, when Zr replaces Co, more rapidly than simple dilution, suggesting Co d-band filling by electron transfer from Zr. The anisotropy field (H_A) is sharply increased when Co replaces Zr, indicating that both preferential substitution and band structure effects are involved. Replacement of Er by Pr enhances H_A, presumably because of preferential replacement of Er at the 2d site. H_A of 42 kOe (at 295 K) was achieved for Er_1.6Pr_0.4Co_16.4Zr_0.6.     

Valence band structure of fractional Wannier-Stark effect shallow InGaAs/InGaAs superlattices

Strain induced effects on the valence band structure of In_xGa_1-xAS/In_yGA_1-yAs (x ≈ 0.47, y ≈ 0.6) shallow superlattices are analyzed by optical spectroscopy. The formation of minibands and the spatially indirect nature of the electron-light-hole transition are observed by photocurrent experiments. Field induced spectral changes of the photocurrent spectra are attributed to Wannier-Stark localization. Heavy hole related fan diagrams are derived for all samples. In contrast, the electron-light-hole Wannier-Stark ladder appears to be very sensitive to material parameters. These results are compared with theoretical calculations of the excitonic absorption coefficient.     

Charge-transfer hole-lifetime broadening of the Cu Auger-electron spectra of high Tc superconductors

The satellite intensity in the Cu L₂₃-VV Auger-electron spectrum of the high T_c superconductor (YBa₂Cu₃O_7−x, 123) is much more enhanced as compared to that of CuO. This enhancement was previously interpreted by Ramaker et al. [D.E. Ramaker, N.H., Turner, F.L. Hutson, Phys. Rev. B 38 (1988) 11368] as a result of the mixing between the ddp and dpp states. Here, d is a hole in the Cu 3d band and p is a hole in the O 2p band. However, the dramatic Auger electron spectroscopy (AES) spectral lineshape change from CuO to 123 is not only in the charge-transfer (CT) satellite but also in the main-line width. The change arises from the transit of the “pairing” of two bound d holes in the ddp state to that of two bound p holes in the dpp state. As a result, in CuO there is no CT satellite but the dd state becomes a resonant state broadened by the CT hole-lifetime broadening, whereas in 123 the dd state becomes a mixture of a resonant-like state and nonresonant band states. The present many-body theory can explain the overall AES lineshape change from CuO to 123.     

LixNayCoO2的制备和热电性质

用固相反应方法，成功地合成了具有交互生长结构的Li_xNa_yCoO₂单相多晶系列样品. 热电势测量表明，该系统的室温热电势比Na_xCoO₂体系约高出60μV/K. 基于空穴载流子具有O2p特征，提出Li_xNa_yCoO₂中额外的热电势来源于氧空穴的占位熵. 关键词： xNa_yCoO₂')" href="#">Li_xNa_yCoO₂ 热电势 热电材料     

Event patterns extracted from top quark-related spectra in proton-proton collisions at 8 TeV

We analyze the transverse momentum(p _T)and rapidity(y)spectra of top quark pairs,hadronic top quarks,and top quarks produced in proton-proton(pp)collisions at center-of-mass energys~(1/2)=8 Te V.For p _(T )spectra,we use the superposition of the inverse power-law suggested by the QCD(quantum chromodynamics)calculus and the Erlang distribution resulting from a multisource thermal model.For y spectra,we use the two-component Gaussian function resulting from the revised Landau hydrodynamic model.The modelling results are in agreement with the experimental data measured at the detector level,in the fiducial phase-space,and in the full phase-space by the ATLAS Collaboration at the Large Hadron Collider(LHC).Based on the parameter values extracted from p _(T )and y spectra,the event patterns in three-dimensional velocity(β_x-β_y-β_z),momentum(p_x-p_y-p_z),and rapidity(y_1-y_2-y)spaces are obtained,and the probability distributions of these components are also obtained.     

Magnetic order in palladium-based heusler alloys: Part 2: Pd2MnIn1−ySby

Magnetization, susceptibility, X-ray and neutron-diffraction measurements have been on the Heusler alloy series Pd₂MnIn_1?ySb_y, for 0 < y < 1. All the alloys were chemically and magnetically ordered with a moment of ?4.2μ_B located at the Mn sites. Their magnetic structures change from antiferromagnetic fcc type 2 at the In rich end, to antiferromagnetic fcc type 3A and then to ferromagnetism as the Sb content is increased. The results closely parallel those already reported on the isostructural series Pd₂MnIn_1-xSn_x and Pd₂MnSn_1-xSb_x with the changes in magnetic structures o ccurring at the same conduction electron concentrations. The results strongly support the postulate that the exchange interactions in Heusler alloys are essentially dependent upon the conduction electron concentration. The correlation between the data and an indirect double resonance exchange coupling mechanism is discussed.     

Microstructure and magnetic characterization of the Sm-CoMn co-substituted SrCaM hexagonal ferrites

A series of Sm-CoMn substituted hexagonal ferrites with chemical composition of Sr_0.85-xCa_0.15Sm_xFe_12-y(Co_0.5Mn_0.5)_yO₁₉ (0.00?≤?x?≤?0.60, (0.00?≤?y?≤?0.50) were synthesized by the solid-state reaction method. Microstructure and magnetic properties of the hexaferrites have been investigated by the X-ray diffraction, field emission scanning electron microscopy and a permanent magnetic measuring system. A single magnetoplumbite phase is exhibited in the hexaferrites with the substitutiom of Sm (0.00?≤?x?≤?0.12) and CoMn (0.00?≤?y?≤?0.10) contents. For the hexaferrites containing Sm (x?≥?0.24) and CoMn (y?≥?0.20), impurity phases are observed in the structure. The FESEM micrographs exhibit that the hexaferrites with different Sm-CoMn contents have formed hexagonal structures and the grain size of the hexaferrites remains unchanged with increasing Sm-CoMn content. The remanence (B_r), H_k/H_cj ratios, and maximum energy product [(BH)_max] decrease with increasing Sm-CoMn content (0.00?≤?x?≤?0.60, (0.00?≤?y?≤?0.50). Instrinsic coercivity (H_cj) and magnetic induction coercivity (H_cb) increase with increasing Sm-CoMn content (0.00?≤?x?≤?0.12, 0.00?≤?y?≤?0.10), and then decrease with increasing Sm-CoMn content (0.12?≤?x?≤?0.36, 0.10?≤?y?≤?0.30), while for the hexaferrites with Sm (x?≥?0.36) and CoMn (y?≥?0.30), with increasing Sm-CoMn content, H_cj increases and H_cb decreases.     

Formation and lithuim ionic conduction of the antifluorite type solid electrolytes,Li2+x-y-z[(NH)1-x-y-zNxClyHz]

Antifluorite type solid electrolytes, Li_2+x-y-z[(NH)_1-x-y-zN_xCl_yH_z] have been synthesized from Li₃N, LiCl and LiCl·H₂O or $\text{Li}{}_2\text{[(}\text{NH}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{H}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$]. Either of the last two compounds introduces NH^2- ions into the product and is indispensable to form the antifluorite type structure. The lattice parameter decreases with increasing amount of NH^2- ions in the compound, reflecting the difference of anion sizes between Cl^- and NH^2- ions. Activation energies of Li⁺ diffusive motion, derived from both conductivity and NMR measurements, increase with concentration of NH^2- ions, although the values differ by a factor of ≈2 netween the both methods.     

Synthesis,structure, and properties of BIFENBVOX

Solid solutions Bi₄V_2-x Fe _x/2Nb _x/2O_11-δ (х?=?0.05–1.0) and Bi₄V_2-х-y Fe _x Nb _y O_11–δ (with fixed x or y?=?0.2 and variable х or y?=?0.2–0.5 with step 0.1) were synthesized by the standard ceramic technology in the temperature range 773–1113 K and by mechanochemical activation method using Bi₂O₃, V₂O₅ Fe₂O₃, and Nb₂O₅ oxides as initial compounds. The formation of solid solutions was studied. Ranges of stability and temperature values of phase transitions for different polymorphous modifications were defined using dylatometric and thermo gravimetric studies. The morphology and the local chemical composition of the ceramic samples were studied. Samples with concentration of dopants x?>?0.3 contain two phases; both major and impurity phases are solid solutions of the BIFENBVOX type although the dopants atoms distribution between them is random. The thermal expansion coefficients (TEC) were measured. The electrical conductivity of ceramic samples was investigated in a wide range of temperatures. The highest conductivity values among the studied solid solutions are observed for the sample with a small amount of dopants x?=?0.25.