40 research outputs found
Ion distribution preferences in ternary crystals Zn xCd 1−x Te, Zn 1−x Hg xTe and Cd 1−x Hg xTe
No full textSimilar ternary semiconductors are sometimes associated with widely different structures characterized by different site occupation preferences. We have used far-infrared (FIR) spectra to determine the site occupation preference coefficients for three ternary semiconductor alloys: ZnCdTe, ZnHgTe and CdHgTe and, in the case of ZnHgTe, have validated it by X-ray absorption fine structure (EXAFS) analysis. While ZnCdTe spectra exhibit the canonical configuration with eight phonon lines free of vibrational defect lines and only a slight departure from a random ion distribution, CdHgTe spectra show the eight canonical phonon modes plus an additional vibrational defect line and constant preference coefficients. In contrast, two defect lines and only four modes characterize ZnHgTe spectra, as extreme preferences prevent the formation of two of the five expected tetrahedral configuration arrangements. Moreover, for this system, comparison with EXAFS data points out the vibrational nature of both the extra lines. The analysis clearly shows that assuming a Bernoulli distribution of the component configurations of semiconductors may lead to wrong assessments of the evolution of its properties with relative content.JRC.D.5 - Food Safety and Qualit
EXAFS data resolved into individual site occupation preferences in quaternary compounds with tetrahedral coordinated structure
No full textFilter method and silicon detectors to measure the temperature of a hot dense thermal deuterium plasma from its quantum bremsstrahlung
No full textHigh resolution spectra of defects in CdTe obtained in far-infrared region using synchrotron radiation
No full textThe present work analyses the lattice deformations induced in the crystals with tetrahedral coordination by the presence of impurity hydrogen and oxygen atoms. Such deformations can be monitored by analyzing of far-infrared (FIR) vibration spectra. FIR experiments carried out on hydrogenated CdTe crystals that successfully revealed the presence and localization of hydrogen atoms within the lattice. (c) 2006 Elsevier B.V. All rights reserved
Occupation preference values in doped CmIm' multinaries from EXAFS and FTIR correlative analysis
No full textWe discuss which x-ray absorption fine structure (EXAFS) data of binary doped CmIm' compound structures can be unfolded to determine elemental bond distances and the deviations from random configurations due to site preference occupations (SOPs). SOP-deviation estimations can be further confirmed by independent Fourier transform infrared (FTIR) data analysis. The limits and restrictions of our model are presented and discussed.The authors would like to thank A. Balerna for constructive comments. The work was partially supported by the European Community Research Infrastructure Integrating Activity “Study of Strongly Interacting Matter–Hadron Physics” (cf. contract number RII-CT-2004-506078) of the Sixth Framework Programme (FP6)
Occupation preference values in doped CmIm' multinaries from EXAFS and FTIR correlative analysis
No full textWe discuss which x-ray absorption fine structure (EXAFS) data of binary doped CmIm' compound structures can be unfolded to determine elemental bond distances and the deviations from random configurations due to site preference occupations (SOPs). SOP-deviation estimations can be further confirmed by independent Fourier transform infrared (FTIR) data analysis. The limits and restrictions of our model are presented and discussed.The authors would like to thank A. Balerna for constructive comments. The work was partially supported by the European Community Research Infrastructure Integrating Activity “Study of Strongly Interacting Matter–Hadron Physics” (cf. contract number RII-CT-2004-506078) of the Sixth Framework Programme (FP6)
Occupation preference values in doped CmIm' multinaries from EXAFS and FTIR correlative analysis
No full textWe discuss which x-ray absorption fine structure (EXAFS) data of binary doped CmIm' compound structures can be unfolded to determine elemental bond distances and the deviations from random configurations due to site preference occupations (SOPs). SOP-deviation estimations can be further confirmed by independent Fourier transform infrared (FTIR) data analysis. The limits and restrictions of our model are presented and discussed.The authors would like to thank A. Balerna for constructive comments. The work was partially supported by the European Community Research Infrastructure Integrating Activity “Study of Strongly Interacting Matter–Hadron Physics” (cf. contract number RII-CT-2004-506078) of the Sixth Framework Programme (FP6)
Statistical strained-tetrahedron model of local ternary zinc blende crystal structures
No full textThe statistical strained-tetrahedron model was developed to overcome two common assumptions
of previous models: 1) rigid undistorted ion sublattice of regular tetrahedra throughout all
five configurations and 2) random ion distribution. These simplifying assumptions restrict the
range of applicability of the models to a narrow subset of ternary alloys for which the constituent
binaries have their lattice constants and standard molar enthalpies of formation (∆fH₀) equal or
quasi-equal. Beyond these limits predictions of such models become unreliable, in particular, when
the ternary exhibits site occupation preferences. The strained-tetrahedron model, free from rigidity
and stochastic limitations, was developed to better describe and understand the local structure
of ternary zinc blende crystals, and interpret experimental EXAFS and far-IR spectra. It considers
five tetrahedron configurations with the shape and size distortions characteristic of ternary zinc
blende alloys, allows nonrandom distributions and, hence, site occupation preferences, conserves
coordination numbers, respects stoichiometry, and assumes that next-neighbor values determine
preferences beyond next-neighbor. The configuration probabilities have three degrees of freedom.
The nineteen inter-ion crystal distances are constrained by tetrahedron structures; to avoid destructive
stresses, we assume that the average tetrahedron volumes of both sublattices relax to
equal values. The number of distance free-parameters ≤ 7. Model estimates, compared to published
EXAFS results, validate the model. Knowing the configuration probabilities, one writes the dielectric
function for far-infrared absorption or reflection spectra. Constraining assumptions restrict
the number of degrees of freedom. Deconvolution of the experimental spectra yields site-occupation-
preference coefficient values and/or specific oscillator strengths. Validation again
confirms the model.Part of the work was supported by the EU TARIproject
contract HPRI-CT-1999-00088
Local crystalline structure of multinary semiconducting alloys: Random vs. ordered distributions
No full text
