![]() If you consider the backscattering of a wavefront from two adjacent atoms at a well-defined angle, \( θ\), to the surface normal then it is clear that there is a "path difference" ( d) in the distance the radiation has to travel from the scattering centres to a distant detector (which is effectively at infinity) - this path difference is best illustrated by considering two "ray paths" such as the right-hand pair of green traces in the above diagram. This is the simplest possible model for the scattering of electrons by the atoms in the topmost layer of a solid in which case the diagram below would be representing the solid in cross-section with the electron beam incident normal to the surface from the vacuum above. (Useful information: h = 6.62 x 10 -34 J s, e = 1.60 x 10 -19 C, m e = 9.11 x 10 -31 kg ).įrom the above examples the range of wavelengths of electrons employed in LEED experiments is seen to be comparable with atomic spacings, which is the necessary condition for diffraction effects associated with atomic structure to be observed.Ĭonsider, first, a one dimensional (1-D) chain of atoms (with atomic separation a ) with the electron beam incident at right angles to the chain. What is the wavelength of electrons of energy 200 eV ? What is the wavelength of electrons of energy 20 eV ? V - acceleration voltage ( = energy in eV ). ![]()
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