Atom-beam diffraction

Diffraction, by X-rays or neutrons, has been the standard method for determining the structures of crystals. The mean free path of X-rays and neutrons is very long, and thus is not sensitive to surfaces. To probe the structures of surfaces, the probing particles must have a very short mean free path in solids. Two methods are extensively used for determining surface structures low-energy electron diffraction (LEED) and atomic-beam diffraction. A helium 

The de Broglie relation, p = ftk, is valid for any particle. An beam of particles with mass M and kinetic energy E is associated with a wavelength 

An electron beam with energy 150 eV has a wavelength of 1 A, which is suitable to probe crystallographic structures. The typical electron energy used in LEED is 20-500 eV. The mean free path of such electrons in metals is 5-10 A. The electrons scatter elastically from the surface. LEED has been discussed in many textbooks (Ashcroft and Mermin, 1985 Zangwill, 1988). 

Using a nozzle. He beams with narrow kinetic energy distribution can be obtained. The de Broglie wavelength of He with kinetic energy E is 

The typical kinetic energy of a He beam generated by a nozzle is between 20 and 200 meV, corresponding to wavelength ranges between 0.1 and 1.0 A. By directing an atomic beam to a solid surface, diffraction occurs. 

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Atomic-beam diffraction was first demonstrated in 1930, as a verification of the concept of the de Broglie wave (Estermann and Stem, 1930). In the 1970s, it was developed into an extremely informative method for determining topography and atomic structure of solid surfaces (Steele, 1974 Goodman and Wachman, 1976). 

Fig. 4.12. Atomic-beam diffraction. A nearly monochromatic beam of helium, generated by a nozzle, falls on the solid surface with an angle of incidence. The diffracted beam is collected at an outgoing angle. The angular distribution of the diffracted helium beam contains the information about the topography and structure of the...

Lapujoulade, J., Salanon, B., and Gorse, D. (1984). Surface structure analysis by atomic beam diffraction. In The Structure of Surfaces, edited by Van Hove, M. A., and Tong, S. Y., Springer-Verlag, Berlin. 

See Atomic metallic ion emission Anomalous corrugation theory 31, 142 breakdown 146 graphite, and 31, 144 Apparent barrier height 63,171 anomalously low 171 attractive force, and 49, 209 definition 7 image force, and 72 repulsive force, and 171, 198, 209 square-barrier problem, in 63 Apparent radius of an atomic state 153 Atom charge superposition I 11 analytic form 111 Au(lll), in 138 in atomic beam scattering 111 Atom-beam diffraction 107 apparatus 109... 

Atomic beams are suitable for diffraction experiments. The repulsive interaction with the surface is so strong that low-energy atoms are already reflected by the topmost atomic layer. Due to its pronounced sensitivity to the topmost surface layer, the method of atomic beam diffraction is especially useful for the study of adsorbates and superlattices. Typical energies of the incident atoms are under 0.1 eV. At such low energies no radiation damage occurs. In... 

A thermal energy atomic beam (20-200 meV) has a wavelength on the order of inter-atomic distances. The atomic beam diffracts from a contour of the surface potential corresponding to the beam energy. This contour is located 3-4 A above the ion cores in the outermost layer of the surface. Atomic beam diffraction patterns are normally interpreted using model surface scattering calculations, where the scattering is described as a Van der Waals interaction. 

Such waves can be used to probe the structure of crystal surfaces, through low-energy electron diffraction (LEED) or atomic beam diffraction. The latter is usually confined to He atoms, but even Ar atom diffraction can be discerned... 

Farias D, Rieder KH (1998) Atomic beam diffraction from solid surfaces. Rep Prog Phys 61 1575... 

RIE Rieder, K. H. Surface structural research with atom beam diffraction helium versus neon Surf. Rev. Lett. 1 (1994) 51. 

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