Grazing incidence of X-rays

The enhanced surface sensitivity obtained by grazing-incidence of X-rays on an air/bulk interface can be understood by standard textbook optics [59]. Only the essentials of the theory are outlined here, for details see [8, 13, 15, 16, 18, 60]. For X-rays of wavelength X. 1 A the refractive index, n, of matter is slightly less than unity [15, 60] ... 

For a detailed description of the reflection at grazing incidence of X-rays see, e.g., [4.37]. X-ray astronomy began after the Second World War with rockets. The first X-ray source, scorpius X-1, was discovered more by accident during a rocket experiment conducted by NASA. These discoveries established the X-ray astronomy and opened up the new research field of X-ray imaging optics. 

For a detailed description of the reflection at grazing incidence of X-rays, see e.g. [4.37]. X-ray astronomy began after World War II with rockets. The... 

Fig. 39. Grazing incidence angle x-ray diffraction (XRD) pattern of an InAslO/InSblO-41x superlattice.

A detailed study of the growth process and the structural evolution of silicalite-1 (MFI) films was undertaken with the aid of grazing incidence synchrotron X-ray diffraction. [65] The diffraction data of the adsorbed and grown zeolite films at different incident and exit angles reflect the distribution of the crystal orientation along the film thickness. The films were prepared via assisted adsorption of nanoscale MFI seed crystals, followed by calcination and subsequent hydrothermal synthesis on the seed layers. The adsorbed (multi-) layer of seed crystals consists of randomly oriented crystals. With progressing hydrothermal growth, the film surface becomes smoother and a preferred crystal orientation with the b-axis close to vertical to the substrate develops. 

LeveiUer, R, Jacquemain, D., Leiserowitz, L., Kjaer, K., and Als-Nielsen, J., Toward a determination at near atomic resolution of two-dimensional crystal structures of amphiphihc molecules on the water surface A study based on grazing incidence synchrotron x-ray diffraction and lattice energy calculations, J. Phys. Chem. 96,10380,1992. Als-Nielsen, J., Jacquemain, D., Kjaer, K. et al.. Principles and applications of grazing incidence x-ray and neutron scattering from ordered monolayers at the air-water interface, Phys. Rep. 246, 251, 1994. 

Fig. 35 Grazing incidence angle X-ray diffraction (XRD) pattern of an lnAslO/lnSblO-41X superlattice. The incident angle was 0.50°. (Adapted from Ref [52].)...

Bottom By grazing incidence the X-ray penetration depth A can be limited to a few nanometers. The evanescent wave is diffracted by the in-plane structure of the Langmuir film. 

The interface between pentacene and a layer of PEDOT PSS being spin coated onto Au source and drain contacts was analyzed by AFM, grazing incident angle x-ray diffraction and UPS. It was found that the PEDOT PSS interlayer reduced the hole-injection barrier and simultaneously led to increased crystalline domains of the semiconductor. Both changes improved the OFET characteristics. 

In this chapter, we first recall the basis of X-ray scattering under grazing incidence. The diffraction by a surface is next considered, with methods to quantitatively determine the surface atomic structure (roughness, relaxation or reconstruction). Experimental conditions are next discussed, in particular the sample requirements to obtain reliable quantitative measurements. 

---