X-RAY DIFFRACTION A N A L Y S I S OF THIN CLAY FILMS FROM DILUTE SUSPENSIONS USING G L A N C I N G INCIDENCE DIFFRACTION
-X-ray diffraction (XRD) analysis of small quantities of clay mounted on glass slides using conventional Bragg-Brentano geometry generally produces unsatisfactory low-intensity reflections masked by amorphous substrate scatter. Glancing-incidence asymmetric Bragg diffraction, an alternative uncoupled geometry, uses a fixed low-incidence angle and parallel-beam optics to increase path length through the sample and decrease X-ray penetration into the substrate. To evaluate this technique on thin soil clay films, results from conventional Bragg-Brentano and glancing-incidence diffraction (GID) were compared for progressively diluted clay suspensions separated from 2 southeastern soils with typical mineral assemblages. Patterns produced by GID showed overall higher reflection intensities and reduced substrate scatter, especially at higher 20 angles within the amorphous glass region, Using GID, positive identification of clay minerals was obtained from sample quantities as small as 0.005 mg cm 2 and suspensions as dilute as 29 mg L 1. Key Words--GID, Thin Films, XRD.
Depth‐resolved measurement of lattice relaxation in Ga1−xInxAs/GaAs strained layer superlattices by means of grazing‐incidence x‐ray diffraction
The state of relaxation in two different superlattices (SLs) of a system with large lattice mismatch, Ga0.8In0.2As/GaAs grown on GaAs [001] by molecular beam epitaxy, has been investigated by surface‐sensitive grazing‐incidence diffraction (GID). The SL is squeezed between the substrate and a thick GaAs top layer. The thickness of individual GaInAs layers ta (active layer) is the same in both samples, while the GaAs barrier thickness tb is different. We have studied the influence of the thickness ratio tb/ta on the state of relaxation for different distances from the sample surface. We find that for thick barriers the whole SL remains coherently strained and for the thinner barrier thickness the SL is partially relaxed against the the GaAs top layer. The GID technique was applied for the first time to obtain depth resolution of the lateral lattice parameter in a SL. It is demonstrated to be especially well suited for SL systems with a small difference of the average electron density between the sublayers....
Dynamical X-Ray Diffraction Profiles for Asymmetric Reflection form Crystals under Grazing Incidence Conditions
Dynamical X-ray diffraction during total external reflection has been studied by measuring rocking curves from Bragg planes nearly perpendicular to the flat surface of a germanium single crystal. The rocking-curve profiles for both the diffracted and specular beams observed from slightly asymmetric Bragg planes were found to be quite different from those from the symmetric plane. Experiments using a parallel X-ray beam and a surface passivated sample confirmed the rocking-curve features arising from the excitation and de-excitation of the wave fields in shallow surface layers of the bulk crystal.