China
Africa
Explore chapters and articles related to this topic
Detector Characterization
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
Another type of scan that is closely related to a θ-2θ scan is a rocking curve (RC) scan. By passing over maxima, the intensity distribution displays a narrow peak whose angular width is a measure of the crystalline quality of the material. This peak is known as the rocking curve and is obtained in practice by keeping the scattering angle fixed and “rocking” the crystal from side to side. Rocking curves measure the amount of mosaicity in the crystal, an angular measure of the degree of long-range order of the unit cells. Lower mosaicity indicates better-ordered crystals and hence better X-ray diffraction. From a rocking curve measurement, it is possible to determine the mean spread in orientation of the different crystalline domains of a non-perfect crystal. If the crystalline particles are very small, it is possible to determine their size from an RC scan. RC scans also measure the underlying curvature in the lattice planes and give indirect information on strains that manifest themselves in the broadening of the peak. In order to obtain the RC, one need not perform a θ-2θ scan first, since the position for diffraction is usually well known. In this case, the detector is moved to the diffraction peak. Then, data are acquired by varying the orientation of the sample by an angle Δθ around its equilibrium position, whilst keeping the detector position fixed. For RC scans, the detector does not need to have a small angular acceptance, since we are not measuring a scattering angle or lattice parameter. RC scans can also be very useful for determining the efficacy of crystal-processing techniques. For example, in Fig. 7.4 we show double- and triple-axis XRD RCs for a Cd1-xZnxTe crystal before and after various post-processing treatments have been applied to remove surface damage. Triple-axis RC is generally only used on the highest quality crystals for which intrinsic width is very small (< 14 arc seconds) and can give quantitative information on mosaicity and strain in the crystal.
Subamorphous Thermal Conductivity of Crystalline Half-Heusler Superlattices
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
E. Chavez-Angel, N. Reuter, P. Komar, S. Heinz, U. Kolb, H.-J. Kleebe, G. Jakob
A cross-sectional transmission electron microscope (TEM) image of one SL with a roughness of η = 5.9 nm and period thickness L = 4.5 nm is displayed in Figure 1a. As it is displayed in the inset of Figure 1a, there is an intermixing of the SL layers, however, the SL still keeps the crystal and epitaxial quality as shown in the rocking curve in Figure 1b and its inset. The rocking curves reveal the broadening of a given diffraction peak. Defects such as mosaicity, atomic intermixing dislocations, among others, lead to spreading of crystal planes and thus a broadening of the linewidth [40]. In addition, the presence of the (002) and (004) film reflections around 2θ = 30º and 60º, respectively, confirm the crystallinity of all the samples discarding amorphization of the crystal structure (see Figure S3, S4 and S6 in the supporting information). The crystal quality can also be appreciated in the high resolution TEM image, where it is possible to observe the well-ordered crystal structure (see inset Figure 1a).