Principles of differential energy-dispersive X-ray spectroscopy (DEDXS)

Cousins, C S G

doi:10.1107/s0021889888005643

Cited by 8 publications

(4 citation statements)

References 6 publications

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“…As shown above the variation of the integral intensity ∆R/R is of the order of the experimental error of common structure analysis procedure. Therefore a modulation technique was used as introduced by Fujimoto [11,12] and also applied by Mahlberg [1]. In fig.…”

mentioning

confidence: 99%

Electric-field–induced electron density response of GaAs and ZnSe

Stahn¹,

Pucher²,

Geue³

et al. 1998

Europhys. Lett.

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The response of the electron densities of GaAs and ZnSe to an external electric field was probed by measuring the variation of the integral intensity of several weak X-ray structure factors due to a field parallel to [1 1 1]. In the range −3 kV/mm < E < +3 kV/mm we found a nearly linear dependence of the relative intensity variation ∆R/R on E for low indexed reflections (2 2 2, 0 6 0) and an additional E 2 -dependence for higher-indexed ones (4 4 2, 6 6 6). The results are interpreted in terms of a bond-charge model. The linear effect can be interpreted by the redistribution of valence charges from bonds parallel to E into bonds lying oblique (bond-charge transfer) whereas the origin of the non-linear effect is still unclear. After the exclusion of lattice effects (piezo-electric effect, internal strain) it ought to be allocated to a charge density response of the core region.

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mentioning

confidence: 99%

Electric-field–induced electron density response of GaAs and ZnSe

Stahn¹,

Pucher²,

Geue³

et al. 1998

Europhys. Lett.

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“…For the piezoelectric effect ͑creation of an electric field in the crystal by the application of external pressure͒ the ''internal strain effect'' as a result of an uniaxial stress along ͓111͔ has already been measured. [9][10][11][12][13][14] In this case, the anion sublattice does not completely follow the cation sublattice upon compression or expansion as expected for a homogeneously deformed system. This means, that the bond lengths remain almost fixed but the unit-cell distortion is mainly associated with a change in the bond angles.…”

Section: Introductionmentioning

confidence: 89%

“…Since the relative intensity variation (⌬R/R)(E,) due to the external electric field is of the order of 1% or less, a modulation demodulation technique was used. 13,15 This means that for each point on the rocking curve the external field was switched on and off 100 times with a frequency of about 20 Hz. After ͑dis-͒ chargement of the plate capacitorlike sample the detected signal was collected in different counters for each external voltage.…”

Section: Methodsmentioning

confidence: 99%

Electric-field-induced charge-density variations in covalently bonded binary compounds

et al. 2001

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Extended data sets for the relative intensity variation of x-ray Bragg reflections of GaAs and ZnSe caused by an external electric field were collected using a modulation demodulation technique. In particular, the functional dependence of the intensity variation on field strength and wavelength of the synchrotron radiation was determined. The wavelength dependence allows to determine the phases of the difference-structure factors. An interpretation of all data using a semiempirical model leads to the following conclusions: The main contribution to the measured effects comes from a displacement of the anion sublattice relative to the cation sublattice. The response of the electron density to an external electric field is negligibly small according to density functional theory calculations with both, clamped and ''free'' ions. This effect is much smaller than the redistribution of the electron density in the bond region associated with the displacements of the atoms causing a change in overlap. The dependence of the sublattice displacement on the strength of the external electric field Eʈ͓111͔ is estimated to be 1.5ϫ10 Ϫ8 Å/V mm Ϫ1 for GaAs and 13.5ϫ10 Ϫ8 Å/V mm Ϫ1 for ZnSe. For the mainly covalent GaAs the inverse piezoelectric effect can be explained by this bond-length variation, in contrast to the much more ionic compound ZnSe for which this is not the case.

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“…With this method, one loses the advantage of the quasisimultaneous detection for the different ®eld values but increases considerably the number of measured re¯ections within a given time. Cousins (1988) proposed the use of an energy-dispersive Laue technique, allowing the simultaneous measurements of a re¯ection and its harmonics. However, only a few results have been reported (Hamichi et al, 1994;Addison et al, 1995).…”

Section: Experimental Techniquesmentioning

confidence: 99%

Studies of electric field induced structural and electron-density modifications by X-ray diffraction

2004

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During the last two decades, a number of X-ray diffraction studies on the response of a crystal to an applied electric field have been carried out. In a few cases, the electron-density polarizations could be determined. The analysis of the induced variations of the structural properties on an atomic scale are of prime importance in order to acquire a better understanding of physical properties like the piezoelectric and dielectric properties of crystals. This article reviews the experimental technique used and the modelling methods of the Bragg scattering variations induced by the field. Some noteworthy results are presented that illustrate the possibility of detecting subtle structural changes, for example as small as 0.1 degrees in bond angles arising from applying a strong field, 10-40 kV cm(-1), as well as the pitfalls of such an approach for clarifying the relevance of the structural properties in physical mechanisms.

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Principles of differential energy-dispersive X-ray spectroscopy (DEDXS)

Cited by 8 publications

References 6 publications

Electric-field–induced electron density response of GaAs and ZnSe

Electric-field–induced electron density response of GaAs and ZnSe

Electric-field-induced charge-density variations in covalently bonded binary compounds

Studies of electric field induced structural and electron-density modifications by X-ray diffraction

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