H. Metzger

The static Debye-Waller factor of defect-induced lattice displacements

The attenuation of Bragg scattering intensities due to static displacements is discussed for interstitially dissolved point-defects. It is shown that in the single defect approximation the static Debye-Waller factor (DWF) exp (−2L) decreases linearly with the defect concentrationc and quadratically with the scattering-vectorK (for smallK andc). From a model calculation of the displacements around H in Nb the static DWF is shown to be primarily due to the displacements closest to the impurity. Therefore the measurement of the static DWF can be used as a method to determine these displacements. From X-ray measurements of the integrated Bragg intensities of NbHx single crystals we obtained the displacements of the four nearest neighbours around a tetrahedral interstitial site to beu1=0.1Å. This is in good agreement with the results of our model calculation.

Grazing incidence diffraction of X-rays at a Si single crystal surface: Comparison of theory and experiment

To test the grazing incidence diffraction scheme for applications to surface studies we have measured with high resolution the angular dependence (“rod profile”) of the [220] Bragg intensity of X-rays under the condition of total reflection from the [001] surface of a Si single crystal. The experimental data agree quantitatively with predictions of the dynamical scattering theory, which takes into account a natural oxide layer and a tilt of the [220] lattice planes.

Investigation of a semiconductor superlattice by use of grazing incidence X-ray diffraction

Abstract A GaInAs/InP superlattice with 10 periods grown by a MOCVD technique on [001] InP was measured by X-ray diffraction under grazing incidence. The details of the GID technique are explained and the results on the superlattice real structure are interpreted in terms of a kinematical scattering approach. Because the depth probed by the X-rays is extremely reduced to a near-surface region both the thickness of the supercell (44 ± 1 monolayers) and of the (GaIn)As quantum wells (2 ± 1 monolayers) can be determined with monolayer accuracy. By successively increasing the penetration depth of the X-rays, the vertical density profile is probed in different regions below the sample surface. The measurements indicate that the thickness of the solid solution layer varies by about 1–2 monolayers laterally and in depth. The composition of the layers is different from that expected from the growth conditions.

Huang Diffuse Scattering of Neutrons

Huang diffuse neutron scattering was measured for the first time on niobium with interstitially dissolved deuterium as well as on MgO after neutron irradiation and Li7F afterγ-irradiation. With Huang diffuse scattering the strength and symmetry of the distortion field around lattice defects can be determined. Our results clearly demonstrate that this method is feasible with neutrons.The present results are compared with X-ray experiments and the advantages of using neutrons is discussed in some detail.

X-ray investigation of the mean square thermal displacements in VDx, NbHx and TaHx interstitial alloys

Abstract X-Ray measurements of the integrated Bragg intensities from V, Nb and Ta single crystals as a function of hydrogen (D) concentration and temperature have been carried out. Two different methods were applied: (i) the usual angular dispersive method using MoKα1 characteristic radiation; and (ii) the energy dispersive method using the white spectrum of the Mo tube and an intrinsic Ge detector. From the results the thermal Debye-Waller factor for the three metals and its change with hydrogen concentration are determined. The mean square of the thermal displacements (u2) decreases with hydrogen (D) concentration. For NbHx(Dx) this agrees well with (u2) values as determined from measured phonon density of states spectra. The results are also given in terms of a Debye temperature depending on H(D) concentration.

Near Surface Structure of Ion Implanted Si Studied by Grazing Incidence X-Ray Scattering

X-rays incident on a surface under grazing angle may undergo total external reflection and excite an interior wave field damped exponentially into the bulk. These evanescent waves are a sensitive probe for the study the real structure in the near surface region. We report results on the influence of implantation defects on Bragg diffracted and on diffuse intensities. By detailed comparison of Bragg intensities with predictions of dynamical scattering theory we detect the presence of amorphous layers and determine their thickness. For the first time defect induced diffuse scattering underconditions of grazing incidence andexit is observed and compared to recent theoretical results. Strength and symmetry of implantation induced defects can be determined as well as their depth distribution which is compared to results of a TRIM simulation: the defect distribution is found to agree with that of the deposited collisional energy.

Lattice dynamics and ordering effects in high-concentrated α′-NbD x -alloys

The phonon dispersion of NbDx (0.57≦x≦0.77) in [110]-direction has been determined by inelastic neutron scattering after in situ loading of the sample. Two quasioptical excitations with Γ-point frequencies of ν=3.8 THz and ν=4.2 THz, respectively, are observed along with a threefold splitting of the longitudinal acoustic branch. At the zone boundary two of these branches are getting soft when increasing the deuterium concentration. The elastic constants extracted from the initial slopes of acoustic phonon branches exhibit an anomalous behavior in the concentration range under consideration.

Grazing incidence X-ray diffraction on silicon after ion implantation and thermal annealing

Abstract X-ray diffraction under grazing incidence and exit angles was measured on Si [001] wafers directly after implantation with 100 keV si+ and after rapid thermal annealing at different temperatures. By comparison with model calculations based on the dynamical scattering theory depth-resolved information on the structure and perfection of the crystal lattice is obtained. From as-implanted samples the thickness of the amorphized top layer (2200 ± 200 A) and the extension of the amorphous/crystalline interface (320 ± 40 A) was determined. Recrystallization after rapid annealing at different temperatures has been studied. Here we observed dynamic scattering effects from the recrystallized parts of the sample indicating the high perfection of the regrown lattice. The thickness of the remaining amorphous layer and the interface regions was determined.

Unusual softening of the Nb and V lattice due to dissolved hydrogen (deuterium)

We report on X-ray Bragg intensity measurements in the high concentration range of NbHx and VDx as a function of temperature andH(D) concentrationx. The mean square thermal displacements of the metal atoms decrease with increasingH(D) concentration. For concentrations higher thanx∼0.7 a sharp increase was observed. The metal lattice first stiffens withH(D) dissolution and then becomes very soft.