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.
A new scheme for x‐ray grazing incidence diffraction
A new scheme for x‐ray grazing incidence diffraction (GID) under total external reflection conditions is presented. This simple scheme allows the grazing angles and the scattering angles to be adjusted independently so that the structural and/or the chemical profiles of materials can be determined at controlled depths. As an example, Si1−xGex/Si superlattice materials were studied. Both commensurate and incommensurate growths between the two quantum wells in the strained‐layer superlattice were observed by the GID technique.
X-ray diffraction under specular reflection conditions. Ideal crystals
The theory of X-ray diffraction by ideal crystals under the conditions when the incident and diffracted beams are directed at small angles to the entrance surface of a crystal has been developed. Besides the diffracted wave propagating inside the crystal (i.e. Laue-case diffraction) there are two specular reflected waves arising from incident and diffracted waves respectively. Such a diffraction scheme has been recently put into practice [Marra, Eisenberger & Cho (1979). J. Appl. Phys. 50, 6927-6933]. It is found that at small glancing angles of incidence there exist directions in which the intensity of the reflected diffracted wave is close to the incident wave intensity, while both the specular reflected wave and diffracted wave intensities are close to zero. The analytical expressions are obtained for the diffraction curve shape. It is shown that for diffraction curve measurements high collimation through the glancing angle of incidence of X-rays on the crystal, Φ, is sufficient. There is no need to provide collimation through parameter a denoting deviation from exact Bragg conditions. Owing to the rigid relation between α, Φ and the angle of emergence of the reflected diffracted wave from the entrance surface of the crystal, Φ′, Φ2 = α + Φ′2, when measuring the intensity of the reflected diffracted wave as a function of Φ, the intensity is obtained as a function of α. Measurement of Φ′ with the accuracy of about 30′′ corresponds to accuracy through α of about 0.1′′. These facts sufficiently simplify the performance of experiment and open wide prospects for studies of crystal structure of thin subsurface layers with unique accuracy.