Double-crystal diffractometric and topographic studies of (111) oriented synthetic diamonds

Two new experimental diffraction methods for a precise measurement of crystal perfection

We have developed a lattice image analysis method that gives lattice parameters directly from the lattice image of multiple quantum well (MQW) laser diodes, in order to judge whether the strain‐compensated structure is adopted or not. The method can handle a large amount of image data. The noise element in the lattice image is removed when the one‐dimensional Fourier transform is applied, and the lattice parameter value is obtained with good precision and good accuracy. The distribution of lattice parameters is valuable for evaluating the structure. Copyright © 2003 John Wiley & Sons, Ltd.

The nucleation and initial stage of GaN growth on sapphire was investigated by atomic force microscopy, X-ray diffraction and photoluminescence. A 15 to 30 nm thick GaN buffer layer deposited at proper conditions was extremely smooth and nearly amorphous. Proper post deposition annealing resulted in the buffer crystallized. The buffer layer deposition temperature, thickness and annealing time and temperature must be coordinated. Low deposition temperature and/or insufficient annealing of the buffer results in a GaN wafer which has fine spiking surface morphology with an RMS of 3.4 nm for 1.4 μm wafer, strong yellow luminescence and wide xray rocking curve FWHM. High deposition temperature, longer crystallization time, and a low growth rate results in a wafer which exhibits strong band edge luminescence without noticeable yellow luminescence, and a narrow (002) diffraction rocking curve. However, the surface morphology exhibits well developed hexagonal feature with RMS roughness of 14.3 nm for a 570 nm thick layer. X-ray rocking curve analysis revealed buffer crystallization, domain coalescence and alignment process. The FWHM of the ω–scan of GaN (101) diffraction was 1700–2000 arc seconds for 200–1400 nm wafers which indicates that the twist of the domains is not changing much with the growth.

The device described incorporates a helium gas flow cryostat for measurements down to 4.2K. By setting the crystal on the flank of the rocking curve, the change in lattice parameter is deduced from the change in intensity of the diffracted beam during rotation of a magnetic field of up to 1.25 T flux density. Even in crystals with rocking curves 30 seconds of arc in width, a strain sensitivity of about 10-6 can be achieved. The feasibility of the technique has been assessed by measuring the magnetostriction of a substituted rare earth iron garnet film.

Tuning of CeO2 buffer layers for coated superconductors through doping

We have observed the apparently anomalous behavior of sputtered AlN thin films that exhibit poor piezoelectric response in spite of having (0002) preferred orientation and narrow rocking curve with full width at half maximum below 2°; however, other AlN films with weak 0002 x-ray diffraction peak and rocking curve as wide as 8° provide a good value of the piezoelectric coefficient d31 (2.1pm∕V). The critical difference between both types of films is the presence of traces of non-(0002) reflections in the x-ray diffraction patterns of the former. Non-(0002) reflections may be related to defects (probably, inversion domains) that significantly reduce the net piezoelectric field.

Fabrication and characterization of heteroepitaxial bilayers of La–Ca–Mn–O/Y–Ba–Cu–O

AlN films, grown by metalorganic chemical vapour deposition on c-plane sapphire, were investigated by high-resolution X-ray diffraction. In Ω-scans very narrow peaks superimposed on a broader diffraction signal were found. The occurrence of very narrow rocking curves is explained in terms of coherent X-ray scattering. This phenomenon is caused by a small rotational out-of-plane disorder resulting in a resolution-limited component of the rocking curve. The tilt (out-of-plane disorder) of individual crystallites is caused by a rotation with small angles around an axis lying parallel to the substrate surface. The diffuse component of the rocking curve was used for the structural characterization of the epitaxial films and a detailed determination of structural imperfection by X-ray diffraction could be obtained by measuring asymmetric reflections. The structural properties of the AlN films are confirmed by atomic force microscopy and transmission electron microscopy.

Spatial fluctuations of the Si 004 lattice spacing, strain, and lattice tilt around through-Si vias (TSVs) in wafer-on-wafer (WOW) structures annealed at different temperatures were quantitatively investigated using X-ray microbeam diffraction. The TSVs were found to induce spatial fluctuations in the base and bonded wafers, and a strain of approximately 0.1% and lattice tilt with a long undulation period of 40 µm were clearly observed. Furthermore, annealing at approximately 100 °C effectively reduced the spatial fluctuation, strain, and lattice tilt in the WOW structure.

Determination of local lattice tilt in Si1−xGex virtual substrate using high resolution channeling contrast microscopy

Measurements have been made of the changes in X-ray lattice parameter which result when a PdHx alloy is taken on a path in the PdHx phase diagram which traverses the mixed ( alpha + beta )-phase region to reach beta -phase concentrations (0.70<x<0.92). The changes were followed by comparing the lattice parameter values for alloys which had been taken along such a path with lattice parameter values of alloys taken along paths avoiding the mixed-phase region in reaching beta -phase concentrations of comparable value. From previous experience with the mixed ( alpha + beta )-phase region and the observed diffraction line broadening and magnitude and direction of the lattice parameter shifts, it can be inferred that the lattice parameter changes are due to internal stresses resulting from the progression of the alpha to beta phase change as the alloy is moved through the mixed-phase region. A discussion is given of some implications of the observations for the use of lattice parameter measurements in locating coexistence curves for M-H alloys.

Remote and van der Waals epitaxy are promising approaches for synthesizing single crystalline membranes for flexible electronics and discovery of new properties via extreme strain; however, a fundamental challenge is that most materials do not wet the graphene surface. We develop a cold seed approach for synthesizing smooth intermetallic films on graphene that can be exfoliated to form few nanometer thick single crystalline membranes. Our seeded GdAuGe films have narrow X-ray rocking curve widths of 9-24 arc seconds, which is 2 orders of magnitude lower than their counterparts grown by typical high temperature methods, and have atomically sharp interfaces observed by transmission electron microscopy. Upon exfoliation and rippling, strain gradients in GdAuGe membranes induce an antiferromagnetic to ferri/ferromagnetic transition. Our smooth, ultrathin membranes provide a clean platform for discovering new flexomagnetic effects in quantum materials.

Superconducting copper fluoride ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{1.3}{\mathrm{Cu}(\mathrm{O},\mathrm{F})}_{4+\ensuremath{\delta}}$ with ${T}_{c}=55$ K had been synthesized via the solid phase fluorination of ${\mathrm{La}}_{0.7}$${\mathrm{Sr}}_{1.3}$Cu${\mathrm{O}}_{3.25}$ with Cu${\mathrm{F}}_{2}$ at relatively low temperature. The fluoride is a derivative of its precursor, but its lattice constant a is expanded from 3.7547(5) to 3.9368(7) \AA{}, while its lattice parameter $c$ is expanded from 12.896(3) to 13.075(4) \AA{}. The obvious difference in lattice parameters and crystal structure seems to distinguish this compound from the superconducting ${\mathrm{Sr}}_{2}\mathrm{Cu}{\mathrm{O}}_{2}{\mathrm{F}}_{4+\ensuremath{\delta}}$ reported in a recent study. It gives strong evidence for superconductivity with reduced Cu${\mathrm{O}}_{2}$ sheets while in the presence of apical oxygen or fluorine.

The positions of Higher Order Laue Zone (HOLZ) Lines, visible in the bright field discs of Convergent Beam Electron Diffraction (CBED) patterns, are frequently used to determine the lattice parameters or strain present in phases observed in the Analytical Electron Microscope (AEM). The technique usually relies upon the use of a “standard” sample of known lattice parameter that has the same crystal structure as the unknown phase and is of similar average atomic number. The relative movement of particular HOLZ lines in the unknown phase with respect to the standard are used to calculate the difference in lattice parameters between the standard and the unknown. The thickness of the samples is not taken into consideration. This paper describes the results of both computer simulations and cold stage experiments in the AEM which lead us to conclude that the HOLZ lines are not independent of thickness, particularly in the presence of highly dynamical zero layer diffraction effects.

Crystallographic properties such as lattice constants, degree of c-axis orientation, and c/a ratio of tetragonal Pb1−xLaxTiO3 (PLT, x=0–0.28) epitaxial thin films grown by pulsed laser deposition on single-crystal substrates such as MgO(001) and SrTiO3(001) were evaluated. General x-ray-diffraction techniques—θ-2θ scan and Φ scan—were used to confirm the epitaxial relations between films and substrates. The epitaxial relations were PLT(001) or (100)//substrate (001) and PLT[100] or [001]//substrate[100]. Then, using the {303} asymmetric rocking curve technique, more quantitative crystallographic informations of PLT films could be obtained. The c/a ratio and lattice constant along the a axis of c-axis-oriented PLT tetragonal unit cell were calculated from the peak location of {303} rocking curve, which is slightly different from that of the powder or bulk PLT. The existence of a-axis-oriented domains was also verified in PLT films grown on SrTiO3 substrate by {303} rocking curve. The origin of the observed ferroelectric domain structures is discussed based on transformation and thermal strains involved in the film preparation.