Selective and wideband UV sensors

It is shown that thin-film photoelectric devices can be constructed on the basis of wide-gap A^IIB^VI semiconductor compounds grown on a narrow-gap quasi-single-crystal substrate. The potential barrier ΔE _v existing at the interface of a multilayer heterostructure blocks the contribution of the narrow-gap component to the total photocurrent. Based on these heterostructures, selective and wideband UV sensors requiring no additional filters are developed for the first time.     

Synthesis and characterization of some chalcogenides of AIB2IICIIID4VI composition

A number of quaternary diamond-like semiconducting phases of A^IB₂^IIC^IIID₄^VI composition (A^I = Cu,Ag; B^II = Zn, Cd; C^III = Ga, In; D^VI = Se,Te) were investigated. Microstructure, DTA and roentgenographic examinations, carried out on samples obtained by direct synthesis, show that the characteristics of homogeneity and single-phase seem to be restricted to copper (CuB₂^IIC^IIID₄^VI) and silver (AgCd₂InTe₄) based compositions, characterized by a generally incongruent metling and by cubic or hexagonal cells.     

Physical chemistry of magnesium and calcium uranophosphate and uranoarsenate AII(BVUO6)2·nH2O

Temperature dependences of the isobaric heat capacity of A^II(B^VUO₆)₂·nH₂O (A^II = Mg, Ca; B^V = P, As) was measured. The standard entropies and Gibbs energies of formation of the compounds were calculated. From these values, the solubility of the compounds in water at T = 25°C was evaluated.     

Initial Stage of Condensation of C60 Films on Semiconducting Substrates of Different Chemical Nature

Abstract

Conditions of growing C₆₀ films deposited from the gas‐dynamic vapor flow on different substrates [layered GaSe substrates with inactive surface, A^IIB^VI (CdS, CdSe) crystals, silicon substrates of (1 1 1) orientations, porous Si substrate] are studied. The condensate structure and growth mechanisms for different substrate are compared. It is shown that the high‐quality epitaxial films of the fullerenes can be prepared by using GaSe layered crystals as substrates.     

Ferromagnetism in (Zn,Cr)Se Layers Grown by Molecular Beam Epitaxy

Magnetization measurements of MBE grown epilayers of (Zn,Cr)Se with relatively large Cr content of 0.014 and 0.021 are presented. We evidence the presence of a strong ferromagnetic coupling between Cr ions, but also suggest a significant clustering due to a pronounced superparamagnetic behavior found in the layers. We estimate the intraparticle Curie temperature to be about 100 K, which combined with other arguments appears to indicate that some magnetic properties of Cr-rich layers might be dominated by the presence of small grains of A^II–Cr₂–B₄ ^VI spinels.     

Structure,composition and electrophysical properties of heat-treated single-crystal AB films

The results of electron diffraction investigations and a study of the electrophysical properties (specific resistance ?, mobility of charge carriers μ) of original and air annealed epitaxial A^IIB^VI (CdS, CdSe, ZnS and ZnSe) films are reported.     

New ferromagnetics based on manganese-alloyed chalcopyrites A<Superscript>II</Superscript>B<Superscript>IV</Superscript>C<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>

This review describes the principles of semiconductor spintronics, represents the physicochemical properties of materials based on manganese-alloyed A^IIB^IVC₂^V compounds, considers the results from theoretical simulation of magnetic properties of A^IIB^IVC₂^V alloyed with 3d metals, summarizes the basic approaches to explanation of ferromagnetism with Curie points above room temperature arising in A^IIB^IVC₂^V:Mn, and indicates promising ways to synthesize and study magnetic semiconductors based on chalcopyrites A^IIB^IVC₂^V in order to produce a suitable material for spintronic devices.     

Thermelectric power in ultrathin films ofA 3 II B 2 V semiconductors in the presence of a quantizing magnetic field

An attempt is made to study theoretically the thermoelectric power in ultrathin films ofA ₃ ^II B ₂ ^V semiconductors in the presence of a quantizing magnetic field by formulating a new magneto-dispersion law, within the framework ofk · p formalism incorporating the anisotropies in the band parameters. It is found, taking ultrathin films ofn-Cd₃P₂ as an example, that the same power decreases with increasing surface electron concentration and changes in an oscillatory manner with film thickness and quantizing magnetic field. In addition, the well-known results for parabolic energy bands have also obtained from our expressions as special cases.     

Bulk modulus and hardness of chalcopyrite structured solids

The bulk modulus and microhardness can be represented by an empirical linear relation that is a simple function of melting temperature T_m, atomic volume Ω and product of ionic charges (Z₁Z₂Z₃). Values of bulk modulus B and microhardness H of A^IB^IIIC₂^VI and A^IIB^IVC₂^V chalcopyrite semiconductors exhibit a linear relationship when plotted against the k_BT_m/Ω (k_B = Boltzmann's constant), but fall on two straight lines according to the product of ionic charges of the compounds. This correlation is similar in form to other correlations in the literature for diffusion data of materials that indicate the significance of the melting temperature as a scaling or lattice dynamic properties of materials. The calculated results are compared with available experimental data and previous calculations based on phenomenological models.     

Defect structure of rare-earth gallium germanium garnets

The garnet structure (cation distributions overc, a, andd sites; valence states of ions; etc.) was modeled using a semiempirical relation between the lattice parameter and Shannon’s radii of the cations occupying dodecahedral, octahedral, and tetrahedral sites and earlier experimental data. The nature of the defect species present and their concentrations are assessed and the competition between defects in R₃Ga₅0_12-δ-based garnets is examined. It is shown that the dominant defect species in Gd_3-xCa _x Ga_5-xZr _x O_{12- δ} (0<x < 0.8) garnets area-site Ga vacancies and Gd _VI ³⁺ . Partial substitution of In _VI ³⁺ for Ga _VI ³⁺ leads to the formation of □ _VI ^In , vacancies. Additional doping with Ge⁴⁺ changes the dominant defect species from □ _VI ^Ga to □ _VI ^Ge . The mechanisms of these processes are discussed.     

Solubility of Uranovanadates AII(VUO6)2·nH2O (AII = Mg,Ca, Sr,Ba, Co,Ni, Cu,Pb) in Water and Aqueous Solutions

Solubility of uranovanadates A^II(VUO₆)₂·nH₂O (A^II = Mg, Ca, Sr, Ba, Co, Ni, Cu, Pb) in water and acid aqueous solutions under various conditions was studied. Based on these data, the standard Gibbs energies of formation of the uranovanadates were calculated, which would allow analysis of their state under conditions that were not studied experimentally.     

Estimative calculations of the dispersion limit for A<Superscript>II</Superscript>B<Superscript>VI</Superscript> and A<Superscript>III</Superscript>B<Superscript>V</Superscript> crystals

Estimative calculations are carried out for the critical sizes of crystalline grains of some semiconductor compounds A^IIB^VI and A^IIIB^V, a further decrease in which leads to a crystalline-amorphous transition. The correlation between the critical grain size and the band gap of a semiconductor is found. Values of critical grain sizes are in agreement with sizes of the disordered (amorphous) phase appearing at the initial stage of growth of epitaxial films (Si and CdHgTe) on different substrates.     

Influence of Oxygen Annealing in the Superconductivity and Electronic States of Mo0.3Cu0.7Sr2YCu2O y

We report the effect of oxygen-annealing in the superconductivity and electronic states for the Mo_0.3Cu_0.7Sr₂YCu₂O _y compound. The influence of oxygen annealing in the electronic states for Mo_0.3Cu_0.7Sr₂YCu₂O _y associated with a nonsuperconducting to superconducting state transformation has been investigated by means of X-ray photoelectron spectroscopy, powder X-ray diffraction, magnetic susceptibility, and resistivity measurements. We unambiguously show the preeminence of the Mo^V state over the Mo^VI one; annealing under an oxygen atmosphere enhances both the Mo^VI and Cu^II amounts. The enhancement of Mo^VI after oxygen annealing is in close relation with the decrease in the O 2p→Cu 3d charge-transfer energy resulting in superconducting properties. Oxygen annealing is then seemed to reduce the copper plane hole concentration of the overdoped as-prepared sample, which induces superconductivity in the Cu–O planes.     

Bibliography on AIIBIVC22 V ternary compounds

In the introduction, some of the applications of the A^IIIB^V compounds are indicated. Their limitations are mentioned and two possibilities are suggested for overcoming these. In view of the A^IIIB^V compounds' outstanding contribution in recent years, the investigation of their isoelectric analogues, the A^IIB^IVC ₂ ^V compounds, is suggested as a logical step. CdSnAs₂ is shown to be the most investigated compound in this group, although several phosphides have potentialities as materials with energy gaps in the visible region of the spectrum. A comprehensive bibliography of the published work on A^IIB^IVC_2/suV compounds is given.     

High resolution electron microscopy of bismuth oxides with perovskite layers

Layered bismuth oxides of the general formula (Bi₂O₂)²⁺ (A _n−1B_nO_3n+1)²⁻ whereA = Bi or Ba,B = Ti, Fe, W andn = number of perovskite layers have been investigated by high resolution electron microscopy. Lattice images obtained forn = 1 to 6 members show stacking of (n − 1) perovskite layers sandwiched between dark bands due to the (Bi₂O₂)²⁺ layers. It has been possible to resolve the perovskite layer structures in some of the oxides. A highly ordered structure is observed upto then = 3 member, whereas higher members show superstructures, dislocations and stacking faults arising from the side-stepping of (Bi₂O₂)²⁺ layers as well as ferroelectric domain walls. Contribution No. 73 from Materials Research Laboratory.     

Mixed mode interface crack in a pure power-hardening bimaterial

Analytical and numerical analysis of the dominant singularity solutions of the stress and strain field near an interface crack in a pure power-hardening bimaterial indicates that the crack stress singularity is –1/(n _II+1) for hardening power of n _I and n _II(n _I<n _II). This result is obtained by solving the non-linear eigenvalue equations of the stress field near a plane crack while observing the conservation properties of the J-integral and the continuity conditions of the interface. Numerical results are presented for the distribution of stress, strain and displacement field of various mixed mode interface cracks when n _I=1 and n _II=5. Possible further destruction of the bimaterial with interface cracks is also discussed.

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Résumé On procède à una analyse théorique et numérique des solutions de singularité dominantes dans les champs de contraintes et de dilatation voisins d'une fissure d'interface dans un complexe bimétallique répondant à une loi simple de durcissement parabolique. On montre que la singularité de la contrainte vaut –1/n _II+1 pour des modules d'écrouissage n _I et n _II(n _I<n _II).On obtient ce résultat en résolvant les équations non linéaires d'eigenvalues du champ de contraintes au voisinage d'une fissure plane, tout en respectant les propriétés de conservation de l'intégrale J, et les conditions de continuité numérique pour la distribution des champs de contraintes, de dilatations et de déplacements correspondant à diverses fissures d'interfaces sollicitées selon des modes mixtes, avec n _I=1 et n _II=5.On discute également d'une destruction ultérieure possible du bimatériau en présence de fissures d'interface.

     

Probing the electronic properties of ternary AnM3n−1B2n (n = 1: A = Ca,Sr; M = Rh,Ir and n = 3: A = Ca,Sr; M = Rh) phases: observation of superconductivity

Abstract

We follow the evolution of the electronic properties of the titled homologous series when n as well as the atomic type of A and M are varied where for n = 1, A = Ca, Sr and M = Rh, Ir while for n = 3, A = Ca, Sr and M = Rh. The crystal structure of n = 1 members is known to be CaRh₂B₂-type (Fddd), while that of n = 3 is Ca₃Rh₈B₆-type (Fmmm); the latter can be visualized as a stacking of structural fragments from AM₃B₂ (P6/mmm) and AM₂B₂. The metallic properties of the n = 1 and 3 members are distinctly different: on the one hand, the n = 1 members are characterized by a linear coefficient of the electronic specific heat γ ≈ 3 mJ mol^?1 K^?2, a Debye temperature θ_D ≈ 300 K, a normal conductivity down to 2 K and a relatively strong linear magnetoresistivity for fields up to 150 kOe. The n = 3 family, on the other hand, exhibits γ ≈ 18 mJ mol^?1 K^?2, θ_D ≈ 330 K, a weak linear magnetoresistivity and an onset of superconductivity (for Ca₃Rh₈B₆, T_c = 4.0 K and H_c2 = 14.5 kOe, while for Sr₃Rh₈ B₆, T_c = 3.4 K and H_c2 ≈ 4.0 kOe). These remarkable differences are consistent with the findings of the electronic band structures and density of state (DOS) calculations. In particular, satisfactory agreement between the measured and calculated γ was obtained. Furthermore, the Fermi level, E_F, of Ca₃Rh₈B₆ lies at almost the top of a pronounced local DOS peak, while that of CaRh₂B₂ lies at a local valley: this is the main reason behind the differences between the, e.g., superconducting properties. Finally, although all atoms contribute to the DOS at E_F, the contribution of the Rh atoms is the strongest.     

Giant Room‐Temperature Magnetodielectric Response in a MOF at 0.1 Tesla

A giant room‐temperature magnetodielectric (MD) response upon the application of a small magnetic field is of fundamental importance for the practical application of a new generation of devices. Here, the giant room‐temperature magnetodielectric response is demonstrated in the metal–organic framework (MOF) of [NH₂(CH₃)₂]_n [Fe^IIIFe^II_{(1?x )}Ni^II_x (HCOO)₆]_n (x ≈ 0.63–0.69) ( 1) with its MD coefficient remaining between ?20% and ?24% in the 300–410 K temperature range, even at 0.1 T. Because a room‐temperature magnetodielectric response has never been observed in MOFs, the present work not only provides a new type of magnetodielectric material but also takes a solid step toward the practical application of MOFs in a new generation of devices.     

Photodiodes based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructures grown using rare-earth elements for the 1.1–2.4 μm spectral range

Photodiodes sensitive in the wavelength range of 1.1–2.4 μm have been created based on n-GaSb/n-GaInAsSb/p-AlGaAsSb heterostructures with a narrow-gap n-GaInAsSb layer (E _g ≅ 0.5 eV) grown in the presence of a rare-earth element (holmium). The electron concentration in the narrow-gap layer is n = 1 × 10¹⁶ cm⁻³, which is about one-fourth of that in an analogous structure grown without the rare-earth element. The proposed structure is characterized by increased quantum efficiency and response speed.     

State of uranyl phosphates and arsenates in aqueous solutions

The state of uranyl phosphates and arsenates (UO₂)₃(PO₄)₂·nH₂O and (UO₂)₃(AsO₄)₂·nH₂O in aqueous solutions in the interval of pH 1–14 was studied by X-ray diffraction, IR spectroscopy, thermography, and chemical analysis. The composition and structure of the initial solid phases vary depending on the solution acidity. The equilibrium constants of the reactions occurring in the heterogeneous systems (UO₂)₃(B^VO₄)₂·nH₂O (B^V = P, As)-aqueous solution were calculated. The speciation diagrams of the solid phases and equilibrium solutions were plotted.