Elastic Scattering Diffraction

Neutron diffraction detects long-range order but it is sensitive also to less well-ordered systems such as two-dimensional fluids and multilayers. Recent studies, all on graphite substrates, have included He, Ar, Kr, 02, Nj, NO, NDj, CD, and the paraffins C2D6, CaDg, and C4Dio Diffraction 

---

Since the mass of the neutron (w , kg) is known, as are the neutron flight distances d, m), for an elastic scattering (diffraction) process the flight time t, ps) determines the neutron velocity (v ) and hence its energy E, cm ) since (cf Eq. 2.21)... 

Monoenergetic electrons ( 100 eV) Low energy electron diffraction (LEED) Elastic scattering Diffracted intensity Ordering... 

The maxima and minima in the angular variation of the polarization lie close to the maxima and minima of the differential elastic scattering diffraction patterns. 

On a microscopic scale, neutron spectroscopy has proved to be a very powerful tool for the determination of the positions (diffraction) and of the dynamics of hydrogen (inelastic and quasi-elastic scattering). Diffraction experiments on LaNi -H and related systems have been... 

Electrons interact with solid surfaces by elastic and inelastic scattering, and these interactions are employed in electron spectroscopy. For example, electrons that elastically scatter will diffract from a single-crystal lattice. The diffraction pattern can be used as a means of stnictural detenuination, as in FEED. Electrons scatter inelastically by inducing electronic and vibrational excitations in the surface region. These losses fonu the basis of electron energy loss spectroscopy (EELS). An incident electron can also knock out an iimer-shell, or core, electron from an atom in the solid that will, in turn, initiate an Auger process. Electrons can also be used to induce stimulated desorption, as described in section Al.7.5.6. 

When Davisson and Germer reported in 1927 that the elastic scattering of low-energy electrons from well ordered surfaces leads to diffraction spots similar to those observed in X-ray diffraction [2.238-2.240], this was the first experimental proof of the wave nature of electrons. A few years before, in 1923, De Broglie had postulated that electrons have a wavelength, given in A, of ... 

When high-energy electrons are injected into thin specimen, most of them tend to pass through without any perturbation occurring from the substances, because the cross section of atomic nuclei is small enough to such electrons. Some of the incident electrons are elastically scattered to be diffracted, and the others... 

Neutron diffraction is one of the most widely used techniques for the study of liquid structure. In the experiment, neutrons are elastically scattered off the nuclei in the sample and are detected at different scattering angles, typically 3° to 40°, for the purpose of measuring intermolecular structure whilst minimizing inelasticity corrections. The resultant scattering profile is then analyzed to provide structural information. 

X-ray diffraction occurs in the elastic scattering of X-ray photons by atoms in a periodic lattice. The scattered monochromatic X-rays that are in phase give constructive interference. Figure 4.4 illustrates how diffraction of X-rays by crystal planes allows one to derive lattice spacings by using the Bragg relation ... 

The STEM Is Ideally suited for the characterization of these materials, because one Is normally measuring high atomic number elements In low atomic number metal oxide matrices, thus facilitating favorable contrast effects for observation of dispersed metal crystallites due to diffraction and elastic scattering of electrons as a function of Z number. The ability to observe and measure areas 2 nm In size In real time makes analysis of many metal particles relatively rapid and convenient. As with all techniques, limitations are encountered. Information such as metal surface areas, oxidation states of elements, chemical reactivity, etc., are often desired. Consequently, additional Input from other characterization techniques should be sought to complement the STEM data. 

The capillary wave frequency is detected by an optical heterodyne technique. The laser beam, quasi-elastically scattered by the capillary wave at the liquid-liquid interface, is accompanied by a Doppler shift. The scattered beam is optically mixed with the diffracted beam from the diffraction grating to generate an optical beat in the mixed light. The beat frequency obtained here is the same as the Doppler shift, i.e., the capillary wave frequency. By selecting the order of the mixed diffracted beam, we can change the wavelength of the observed capillary wave according to Eq. (11). 

Besides the inelastic component, always a certain number of He atoms are elastically scattered in directions lying between the coherent diffraction peaks. We will refer to this scattering as diffuse elastic scattering. This diffuse intensity is attributed to scattering from defects and impurities. Accordingly, it provides information on the degree and nature of surface disorder. It can be used for example to study the growth of thin films or to deduce information on the size, nature and orientation of surface defects Very recently from the analysis of the diffuse elastic peak width, information on the diffusive motion of surface atoms has been obtained. ... 

Many such techniques have been developed and used. Low-Energy Electron Diffraction, in which electrons are elastically scattered off a surface, has been the most successful among those for surface crystallography. Inelastically scattered electrons also... 

---