Die kristallisationsgeschwindigkeit des bestrahlten glasigen selens

At the temperature of 90°C the crystallization rate of γ-irradiated (0–154.5 Mrad) vitreous selenium has been studied by the calorimetric method. The obtained results satisfy the Avrami's equation x = 1 ? exp(? L·C_Kr·τ^z). It was found that radiation induced changes of vitreous selenium structure bring about the decrease of the exponent z and the increase of the value L·c_Kr.The relationship between the above results and structural changes of vitreous selenium was discussed.     

Die einwirkung der struktur auf die kristallisationskinetik des glasigen selens

By means of a calorimetric method the rate of crystallization of vitreous selenium samples remelted at various temperatures t_U (225–3502C) was studied at a temperature of 90.0°C. To describe the kinetics the Avrami equation was used. The samples remelted at t_U < 260°C crystallized in one stage, A. For the samples remelted at t_U ? 260°C two stages, A and B, were observed. The rate constants k_Kr = z(L · c_Kr)$\text{1}\text{2}$ and the coefficients z were calculated from the Avrami equation. For the samples remelted at t_U = 225, 250 and 330°C, the activation energy e_kr was determined.The values of z, k_Kr and z · E_Kr were found to decrease as the temperature t_U increased. The kinetics of crystallization probably depend upon the structure of vitreous selenium (i.e. on the number of crystalline regions and on content of the small rings), which in turn is dependent on the temperature _U. This supposition was confirmed mathematically.     

Diffusion Control of Homogeneous Crystallization in Nanoconfined Domains of Block Copolymers

Abstract

Confined crystallization in a poly(oxyethylene)‐b‐poly(oxybutylene)/poly(oxybutylene) blend (E₁₁₅B₁₀₃/B₂₈, φ_E = 0.14) with bcc morphology and in a polystyrene‐b‐poly (oxyethylene)‐b‐polystyrene (S‐E‐S) triblock copolymer (S₄₀E₁₃₆S₄₀, φ_E = 0.407) with lamellar morphology was studied using differential scanning calorimetry (DSC). Two types of confined crystallization with different characteristic Avrami exponents were identified in both systems. At higher crystallization temperature (T _c), the Avrami exponent is 1.0 and the overall crystallization rate is controlled by the homogeneous nucleation rate. At lower T _c, the Avrami exponent is 0.5, which is attributed to diffusion‐controlled confined crystallization. This shows that diffusion has a great influence on the overall crystallization rate when chain mobility is reduced, which can be caused either by lower T _c or by constrained microstructure.     

Differential scanning calorimetric study of Ga5Se95 glass

Results of differential scanning calorimetry, at different heating rates, α, on Ga₅Se₉₅ glass are reported and discussed. From the heating rates dependence of values of T_g and T_p, the glass activation energy, E_g and the crystallization activation energy, E_c, are derived. The crystallization results are interpreted in terms of recent analyses developed for non-isothermal crystallization and also for the evaluation of E_c. The crystallization mechanism is then characterized. From the obtained results, the glassy Ga₅Se₉₅ has two-dimensional growth, the average value of the order of crystallization mechanism, n is 3. The average value of the glass activation energy, E_g and crystallization activation energy, E_c, for Ga₅Se₉₅ glass are 189±4 and 69±5 kJ/mol, respectively.     

Viscosity of liquid selenium and selenium-sulphur mixtures

The viscosity of selenium has been studied in the liquid state, and the effect of thallium and sulphur additives was investigated. The rotating cylinder method was used. Experimental measurements show that the viscosity of liquid selenium with sulphur admixtures is higher than that for pure selenium, and a complex molecular structure is formed. The results were explained on the basis of the free volume model and the data for liquid selenium were fitted to the model withE _act=0.6 eV.     

Die keimbildungskinetik im glasigen selen mit der beimischung des jods

The rate of crystallization of vitreous selenium containing 2 at.% of iodine was studied by calorimetric method in the temperature range 60–90°C. The obtained results satisfy an equation of Avrami. It was found that the exponential parameter z in this equation decreases as the temperature of crystallization increases. It was assumed in the discussion that the parameter z does not depend on the number of all processes occurring during nucleation. It depends only on slowly occurring processes. The increase of temperature probably causes a decrease of the number of slow processes and thus the value of the parameter z is diminished.The activation energy of crystallization is equal to $\text{E}{}_{\mathrm{kr}}\text{= 80}\text{kJ}\text{mol}$ with the standard deviation $\text{s}{}_{\mathrm{E}}\text{= 5.0}\text{kJ}\text{mol}$.     

Energy,momentum and angular momentum of gravitational radiation from a particle plunging into a non-rotating black hole

We have computed the energy ΔE, the momentum ΔP and the angular momentum ΔJ of gravitational radiation induced by a particle of mass μ and angular momentum μL_z plunging into a Schwarzschild black hole of mass M (?μ). It is found that the maximum value of ΔP is 4.5 × 10^?2 (μ/M) μc, ΔE/ΔJ ≈ 0.15c/(GM/c²), and a rotating ring plunging into a black hole emits less energy than a non-rotating one.     

Elastic constants of solid krypton at T = 77 K determined by inelastic neutron scattering

Long-wavelength acoustic phonons have been studied for each of the [ζ00]T, [ζ00]L, [ζζ0]L and [ζζ0]T₁ branches in solid Kr at T = 77 K by means of inelastic neutron scattering utilizing ‘cold neutrons’ as they are available in the long-wave length tail of the pile spectrum. The raw data have been corrected for resolution effects taking into account the curvature of the dispersion surface and variation of mode eigenvectors. It has turned out, that this yields appreciable shifts of the raw data. The results of our experiment give c₁₁ = 4·25 ± 0·10, c₄₄ = 2·04 ± 0·03, c₁₂ = 2·82 ± 0·12 and a value for B = (c₁₁ + 2c₁₂)/3 = 3·30 ± 0·09 × 10¹⁰ dyne/cm². Available thermodynamic data for Kr gives a derived value for B^ad = 2·58 ± 0·06 × 10¹⁰ dyne/cm² indicating a large difference between zero sound and first sound in solid Kr at high temperatures.     

Pressure experiment determination of the direct-indirect transition in the quarternary In1−xGaxP1−zAsz

Spontaneous and laser emission from In_1-xGa_xP_1-zAs_z double heterojunction diodes near the direct-indirect crossover (E_Γ = E_X, x ≡ x_c, z ≡ z_c) are studied at 77°K as a function of hydrostatic pressure up to 6 kbar. The pressure coefficients of the spontaneous emission peaks and of the laser modes are ～- 10.5 × 10^-6 eV/bar which is characteristics of the Γ band edge in III–V semiconductors. Laser threshold current is found to rise rapidly as pressure is applied owing to the decreasing Γ-X separation and the resultant carrier transfer to the X minima. Experimental lower limits for the direct-indirect crossover at three points in the In_1-xGa_xP_1-zAs_z quaternary system are determined. These three points and the established crossover in GaAs_1-yP_y (y_c ≈ 0.46, 77°K) give for the quaternary crossover (77°K) x_c ? 0.52z_c = 0.72. and the value x_c ≈ 0.72 for the limiting case of In_1-xGa_xP. Band edge bowing effects along the direct-indirect crossover in the In_1-xGa_xP_1-zAs_z system are discussed. The highest energy laser (77°K) for this quaternary system is estimated from pressure measurements to be ～ 2.155 eV (5752 Å).     

Laser excited Raman spectra of Gr. VI semiconducting compounds

Raman spectra of hexagonal layer compounds MoS₂, MoSe₂ and MoTe₂ were excited by a HeNe laser (6328Å). All the Raman active long-wave-length phonon frequencies were determined. These are A_1g, E¹_2g, E_1g and E²_g. The frequencies decrease as we pass from sulphur to tellurium and the quasiacoustical mode E²_2g has the lowest frequency. A comparison of the results with infrared spectra shows that the i.r. active mode for E ⊥ C is degenerate with one of the Raman active modes in the basal plane for all the compounds.     

Cliff and its inversion as rapid decay of fully developed chaos

We show analytically and numerically that the Lyapunov exponent (L) in one-parameter (r) families of one-dimensional maps, which exhibit for r = r′_c fully developed chaos (FDC) introduced by Györgyi and Szépfalusy, behaves near and below r = r′_c as $\text{L (r) ? L(r′}{}_{\mathrm{c}}\text{) ∝ (r′}{}_{\mathrm{c}}\text{? r)}{}^{\mathrm{<mtext>1</mtext><mtext>z</mtext>}}$, where z is the order of maximum in the maps. This is a new example of cliff, which we call type II. Averages of dynamical quantities other than L are also expected to show similar behavior, which is demonstrated numerically for a particular case. We also find that in certain one-parameter families FDC is less chaotic than nearby non-FDC in terms of L (inversion of cliff).     

Isothermal crystallization in Ce70Ga6Cu24 bulk metallic glass

The isothermal crystallization behaviors in a newly developed CeGaCu bulk metallic glass have been investigated through the classic differential scanning calorimeter(DSC) method. It is found that the apparent activation energy(Ea) strongly depends on the fraction(x) of isothermal crystallization. Johnson-Mehl-Avrami(JMA) formula was used to analyze the mechanism of crystallization and the obtained Avrami exponent(n) was discovered to show an obvious correlation with the crystallization fraction x. With the help of the relation between Ea and n, the nucleation and growth activation energies, En and Eg, were estimated to be 214–304 kJ/mol and 91 kJ/mol, respectively. This result suggests that the main energy barrier against crystallization in the present glass should be the nucleation of nucleates, rather than the growth of crystals. Such a large En is also believed to be responsible for the good glass forming ability of the CeGaCu alloy.     

Kinetic study of non-isothermal crystallization of BixSe100−x chalcogenide glasses

Results of differential thermal analysis (DTA) under non-isothermal conditions on four glasses of Bi_xSe_100−x (x=5, 10, 15 and 25 at%) are reported and discussed. The glass transition temperatures (T_g), the onset crystallization temperatures (T_c) and the peak temperatures of crystallization (T_p) were found to be dependent on the compositions and the heating rates. From the dependence on the heating rates of (T_g) and (T_p), the activation energy for glass transition, E_g, and the activation energy for crystallization, E_c, are calculated and their composition dependence is discussed. The crystalline phases resulting from DTA and scanning electron microscopy (SEM) have been identified using X-ray diffraction. According to the Avrami exponent (n), the results show a one-dimensional growth for the composition Bi₅Se₉₅ and two-dimensional growth for the compositions Bi₁₀Se₉₀, Bi₁₅Se₈₅ and Bi₂₅Se₇₅. The kinetic parameters determined have made it possible to discuss the glass-forming ability.     

Determination of the indirect band edge of GaAs by quantum-well bandfilling (Lz∼100Å)

Photoexcitation-bandfilling of a quantum-well Al_xGa_1?xAs-GaAs-Al_xGa_1?xAs (x～0.6, L_z～100Å) heterostructure is used to generate visible-red recombination radiation that cuts-off at high energy (1.864 eV, 4.2°K) due to electron transfer to indirect minima. This leads to an estimate of ΔE = E_L?E_Γ～310 meV.     

Multicomponent <Emphasis Type="Italic">n</Emphasis>-(Bi,Sb)<Subscript>2</Subscript>(Te,Se,S)<Subscript>3</Subscript> solid solutions with different atomic substitutions in the Bi and Te sublattices

The thermoelectric properties of n-Bi_{2 ? x} Sb _x Te_{3 ? y ? z} Se _y S _z solid solutions are studied in the temperature range 300–550 K. It is shown that an increase in the parameter β determining the figure-of-merit Z of the material is observed in compositions with the optimally related effective mass of the density of states m/m ₀, the carrier mobility μ₀, and the lattice thermal conductivity κ _L . Within the temperature range 300–350 K, the parameter β and the figure-of-merit Z are found to increase in solid solutions with substitutions in both bismuth telluride sublattices Bi → Sb and Te → Se, S (x = 0.16, y = z = 0.12) for optimum electron concentrations. An increase in the electron concentration and substitutions of atoms only in the tellurium sublattice bring about an increase in the β parameter and the value of Z at higher temperatures. Within the range 350–450 K, the parameters β and Z are observed to increase in a solid solution with a low content of substituted atoms in the tellurium sublattice Te → Se, S for y = z = 0.09 and, at higher temperatures up to 550 K, in compositions with tellurium substituted by selenium only, with increasing content of substituted atoms.     

Extraordinary photons with unusual angular momentum

A series of novel state-vector functions (SVFs), which is the general solution of the Schrödinger equation for a photon, are constructed. Each set of these functions consists of a triplet of eigen-SVFs: The triplet can be broken down into a pair of nonzero l-order functions and a single zero-order function. The photons, described with a triplet of eigen-SVFs, possess all the quantum characteristics of a photon: In addition to common attributes like energy E = ? _ω , and momentum p _z = ? _κ , they also exhibit different angular momenta (AM) L _z+ = l?, L _z? = l?, and L _z0 = 0, where l?1. In other words, in addition to usual eigenvalues L _z±= ±?, there are unusual nonzero l-order eigenvalues L _z± = ±l? and a zero-order eigenvalue L _z0 = 0 for AM of a photon. By a series of SVFs, the pattern from nonzero l-order and zero-order Laguerre-Gaussian modes of a laser beam is explained well from a quantum mechanical point of view.     

Crystal structure of 1-amino-2-phenyl benzocycloheptanol hydrobromide monohydrate

Crystals of 1-amino 2-phenyl benzocycloheptanol hydrobromide monohydrate are orthorhombic witha=6·927(17),b=30·947(40),c=30·990(40) Å,z=16 and the space group is Iba2.ρ=1·41 gm/ccρ _cal=1·403 gm/cc,μ for CuK_α=37.06 cm^?1. The structure was solved by heavy atom method using three dimensional x-ray intensity data and refined by block diagonal and full matrix least squares method to anR-index of 0·106. The structure is stabilised by a number of hydrogen bonds of the type N-H…O, O-H…Br, N-H…Br. The heptane rings in this molecule are in chair conformation.     

Mößbauereffekt in Eisenstilben und FeCl2·H2O

Using Mößbauer effect measurements in the temperature range between 3 °K and 310 °K the magnetic fields at the nucleus in iron-stilbene, FeCl₂·H₂O and FeCl₃ are determined to beH _T=0=(250±10) kOe, (252±18) kOe and (468±10) kOe; a Néel-temperature ofT _N=(23±1) °K is measured for iron-stilbene. The electric quadrupole splittings atT=0 °K for iron-stilbene and FeCl₂ ·H ₂ O, ΔE=(+2.52±0.02) mm/sec and (+2.50±0.05) mm/sec, yield electric field gradients at the iron nucleus ofq _z=+9.7·10¹⁷ V/cm² and +9.6·10¹⁷ V/cm², whereq _z⊥H; Debyetemperatures of θ=162 °K and 188 °K are obtained. The energy of the excited 3d-electron levels in iron-stilbene is estimated to Δ₁=309 cm^?1 and Δ₂=618cm^?1 as deduced from the temperature dependence ofΔE. In contrast to the suggestion ofEuler andWillstaedt bivalence of the iron in ironstilbene is found; its composition is shown to be 4(FeCl₂ ·H ₂O)·stilbene.     

Modification of anode surface in organic light-emitting diodes by chalcogenes

Influence of thin chalcogen X (S, Se, Te) interlayer between anode (indium-tin oxide, ITO) and a layer of N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) used as a hole-transport layer (HTL) on the operating characteristics of organic light-emitting diodes (OLEDs) of composition ITO/X/TPD/Alq₃/Yb (Alq₃ - aluminum 8-quinolinolate) has been investigated. It was found that the sulphur layer decreases operating voltage and enhances operating stability of a device while the selenium or tellurium interlayers impair these characteristics.     

Observation of phase separation in some Se-Te-Sn chalcogenide glasses

Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) techniques were employed here to investigate the glass transition behavior and crystallization kinetics of Se_80−x Te₂₀Sn_x (x=0.0, 2.5 and 5) alloys, which were prepared by the conventional melt quenching method. Two exothermic peaks have been observed in the DSC scans for the samples that contain Sn. Three crystalline phases (Se_7.68Te_0.32, SnSe and SnTe) were classified after heat treating the Se_77.5 Te₂₀Sn_2.5 glass at temperature corresponding to the second crystallization peaks for 3 h. All the characteristic temperatures such as glass transition temperature (T_g), crystallization temperature (T_c) and crystallization peak temperatures (T_p) were found to depend on both the heating rate and the composition. This dependence has been used to deduce the activation energy of the glass transition (E_g), the activation energy of crystallization (E_c), the Avrami exponent (n), thermal stability and the fragility index (F_i).