Showing papers in "Acta Physica Polonica A in 1990"

HgFeSe ― A system with mixed valence

Abstract: L'impurete de Fe se comporte comme un donneur resonnant avec la bande de conduction. Formation d'une structure de Wigner de type verre des donneurs ionises a partir des interactions coulombiennes interioniques dans un regime ou la valence mixte du systeme de donneurs est realise pour des niveaux de dopage suffisamment eleves. Description de la correlation dans ce systeme a n corps par utilisation d'une simulation numerique et d'un modele analytique simple. Calcul de l'equilibre d'energie, de la structure, de la densite d'etats, de la concentration d'electrons de conduction et de la mobilite

The nonlinear dielectric effect applied to study the pretransitional effects in the isotropic phase of the MBBA-benzene solutions

Abstract: Application de l'effet dielectrique non lineaire a l'etude des proprietes critiques de melanges contenant des composants nematogenes et non mesogeniques. Etude de la temperature de surfusion du melange vis-a-vis de la composition chimique

Electron paramagnetic resonance of copper(II) in YBa2Cu3O7−x high-temperature superconducting ceramics

Abstract: Room-temperature X-band EPR spectra for six samples of YBa 2 Cu 3 O 7−x ceramics from different sources are presented. The spectra differ among each oter in symmetry, EPR parameters and intensity, and are compared with spectra of CuO, BaCuO 2 , Y 2 Cu 2 O 5 , Y 2 BaCuO 5 and YBa 2 Cu 3 O 6 also measured in this work. EPR signals of the studied YBa 2 Cu 3 O 7−x (x=0.1) ceramics are due to impurity phases, mainly to Y 2 BaCuO 5 , YBa 2 Cu 3 O 6 and Y 2 Cu 2 O 5 with varying amount of these compounds in the superconducting samples. The spectra are practically not affected by superconducting transition

Deep level transient spectroscopy measurements of p-type InP

Abstract: Determination des parametres des six pieges a trous de l'echantillon dope au Fe et avec diffusion de Ni. Proposition d'un niveau accepteur Ni 3+/2+ avec une energie d'activation 0,48 eV et d'un niveau accepteur Fe 3+/2+ avec une energie d'activation de 0,63 eV

Neutron depolarization study of static magnetization fluctuations in ferromagnets

Abstract: Neutron depolarization studies using pulsed polarized neutrons have been performed to get information on mean magnetization, static magnetization fluctuations and magnetic anisotropy in plate-like ferromagnetic samples. The approach to magnetic saturation of polycrystalline ferromagnets ((Fe 50 Ni 50 ) 96 Cr 4 , and MnZn-ferrit) was studied by analyzing the field dependence of depolarization parameters

Characterization of deep traps in semi-insulating GaAs and InP by photoinduced transient spectroscopy (PITS)

Abstract: Etude des niveaux profonds des pieges dans GaAs dope au Cr et InP dope au Fe. Tentative d'identification des niveaux observes

Photoionization spectra of iron doped InP and GaAs

Abstract: Observation des bandes d'absorption larges correspondant a un processus photoionisant Fe 3+ (3d 5 )→Fe 2+ (3d 6 ) pour les transitions a un etat fondamental ( 5 E) et a un etat excite ( 5 T 2 ) de l'etat Fe 2+ . Discussion de la nature des raies d'absorption ne correspondant pas a celles des transitions photoionisantes: a 0,78 et 1,14 eV dans InP, a 0,87 eV dans GaAs

Structural stability analysis in a stationary diffusion limited aggregation

Abstract: An approach through stationary diffusion field (Laplacian operator) with Dirichlet as well as Neumann boundary condition to the diffusion limited aggregation (DLA) has been presented. The influence of finiteness of the diffusional field on the aggregation process has been investigated. The so called structural of Mullins-Sekerka (M-S) stability analysis has also been provided

Magnetic and optical properties of 50CB

Abstract: Magnetic susceptibility and optical birefringence studies have been conducted on liquid crystal 4'-pentyloxy-4-cyanobiphenyl. Diamagnetic susceptibilities at different temperatures have been measured with the help of a sensitive torsional balance set up by us. From our experimental refractive index and density data we have calculated the polarizability values using both Vuks' and Neugebauer's relations. Finally, we have calculated the orientational order parameter, , from optical and magnetic data

Concentration depolarization of the fluorescence, delayed fluorescence and phosphorescence of acridine yellow and proflavine in polyvinyl alcohol films

Abstract: The results obtained were interpreted in terms of Jablonski's model of luminescent centre in which the participation of the intermediary triplet state was taken into account. In the case of fluorescence and phosphorescence, the concentration depolarization is described by the same equation, whereas for the delayed fluorescence the magnitude of the concentration depolarization depends on the relative fluorescence quantum yield

Pyroelectric properties, domain structure and ferroelectricity of (CH3NH3)3Bi2Br9 single crystals

Abstract: Pyroelectric measurements and domain structure observations have been performed in (CH 3 NH 3 ) 3 Bi 2 Br 9 crystals in a wide temperature range. Pyroelectric measurements revealed polarity of the crystals in the phases II, III and IV. The phase IV pyroelectric along the c-axis is also ferroelectric one in the plane a*c. The ferroelectric axis forms an angle about 7 o with the a* axis. The microscopic investigations disclosed the 180 o and 120 o domains in ferroelectric phase

Electron mobility in inversion channels of p-Hg1−xCdxTe MISFET's

Abstract: Calcul de la mobilite des electrons base sur les caracteristiques de transfert de la structure MISFET avec des structures de tunnel MIS ou des jonctions p-n comme source et drain. Utilisation de modele de gaz d'electrons bidimensionnel pour expliquer les resultats

Rigid and relaxed hardness parameters of molecular fragments

Abstract: On donne les expressions explicites pour la durete rigide et relaxee de fragments moleculaires, en termes de la durete et de la molesse d'atomes dans une molecule (AIM)

Phase transitions in dimethylammonium halogenoantimonates. III

Abstract: Detection des transformations irreversibles a haute temperature vers de nouvelles structures pour DMCA (complexe nerochloro), et DMABA (complexe nerobromo), lesquelles ne montrent pas de comportement ferroelectrique mais revelent d'autres sequences de transitions. DMAHBA (complexe hexabromo) montre deux transitions reversibles a haute temperature pendant le refroidissement

Electroluminescence in semiconductors

Abstract: Analyse des transitions radiatives et application aux composes II-VI des donnees concernant les composes III-V. Apercu des mecanismes physiques dans les panneaux electroluminescents a couches minces, et des problemes provenant des poudres

Magnetic susceptibility of Hg1−xFexSe

Abstract: Mesure de la susceptibilite magnetique a champ faible pour 0,3%≤x≤2%. Explication qualitative en termes de susceptibilite de van Vleck des ions Fe 2+ superposee a la susceptibilite de type Curie des ions Fe 3+ pour x=0,3%. Pour des valeurs de x plus elevees et au-dessous de 10 K, une augmentation de la susceptibilite en fonction de la temperature decroissante est plus grande que celle attendue, ce qui peut suggerer une presence d'impuretes magnetiques etrangeres ou des complexes incluant du Fe trivalent

Crystal growth and characterization ofsome novel AIBIICV semiconductors

Abstract: Estimation des bandes interdites des cinq echantillons etudies et determination de quelques caracteristiques electriques

CdTe Valence band structure in the direction Γ-K-X determined by angle-resolved photoemission

Abstract: Determination de la decomposition spin-orbite Γ 7 -Γ 8 et les energies de plusieurs points critiques. Comparaison des resultats experimentaux a ceux obtenus par calcul

Vibronic couplings in an excited state of hydrogen bond dimeric systems

Abstract: The theory is used to reproduce experimental absorption and experimental emission spectra of a hydrogen bond monomeric system and two different hydrogen bond dimeric systems. Relative energies of vibronic transitions and relative intensity distributions of both the absorption and the emission spectra are calculated

Magnetic-dipole and electric-quadrupole interaction constants and lifetime of the 92D5/2 state in 87Rb

Abstract: The hyperfine structure of the 9 2 D 5/2 state in 87 Rb was measured by the quantum beat method in a zero magnetic field. The resulting values of the magnetic-dipole and electric-quadrupole interaction constants are determined

The TLS contribution to electrical resistivity in Nb3Ge

Abstract: The two level systems contribution to electrical resistivity of amorphous Nb 3 Ge has been calculated in the framework of a second order scaling theory. The buildup of a TLS distribution below a certain crossover temperature, is carried out according to a renormalization procedure. A negative temperature coefficient of resistivity is found in good agreement with experimental data

On the exact calculation of the scattering lengths for long range potentials. I, The inverse power potentials

Abstract: The potentials which fall off asymptotically as const r −−s , s>3, are considered and an exact method of calculating of the scattering lengths for them is presented

Microwave dielectric dispersion in [(CH3)2NH2]5Cd3Cl11 crystals

Abstract: The paper presents the results of the investigations of the complex dielectric permittivity of [(CH 3 ) 2 NH 2 ]Cd 3 Cl 11 crystal in a frequency range 20 MHz to 42 GHz in the temperature region 127 K to 360 K. The Debye-type dielectric dispersion was found in the c-direction with two relaxation times. The observed temperature dependence of the dynamical complex dielectric permittivity can be interpreted in terms of the potential barriers between orientations of different dipole groups

Temperature dependence of silicon etching rate by fluorine atoms

Abstract: It is shown that the temperature dependence of silicon etching rate measured in work [1] can be explained by multiphonon relaxation of impinging atom energy. This result supports the statement of the authors concerning nonactivated behaviour of silicon etching by fluorine atoms

Charge transfer transitions in rare earth-doped ZnS

Abstract: Analyse de la position des niveaux des terres rares (RE) 2+/3+ dans la bande interdite. Estimation de l'energie des bandes de transfert de charge a partir de la theorie sur l'energie d'appariement de spins de Jorgensen

Raman scattering in α-Zn3As2 crystals

Abstract: Attribution des bandes a basses frequences (0-100 cm −1 ) aux modes normaux avec contribution predominante des vibrations atomiques de Zn; tandis que les bandes a hautes frequences (200-300 cm −1 ) sont dues a la contribution des vibrations atomiques de As

Inter-donor interactions ― Source of electron mobility increase under pressure

Abstract: On montre que l'ordre spatial induit par l'interaction des charges dans un systeme de donneurs partiellement rempli conduit a une augmentation de la mobilite avec la pression dans les deux cas: U positif et U negatif (U etant l'interaction intra-impurete) des centres DX