ssp_9y - 3 Continued 3.4 Experimental methods Fig. 3.15....

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3 Continued
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3-18 3.4 Experimental methods Fig. 3.15. The de Broglie wavelength of photons, electrons, neutrons and helium atoms as a function of the particle energies. The arrow shows the energy for a thermal beam at room temperature (eV scale). sin Θ= λ 2 1 d hkl Photons: λ = c / ν E = h ⋅ν λ (12 keV) 0.1 nm 1 keV < E < 100 keV Neutrons / light atoms: λ = h / p de Broglie E = p 2 / 2m λ (0.1 eV) 0.1 nm 10 meV < E < 1 eV Electrons: λ (150 eV) 0.1 nm 10 eV < E < 1 keV } λ = hc / E } λ= hE m /2
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3-19 Photons: Penetration depth up to some mm I Z 2 problems for H Sources: X-ray tube (characteristic lines + bremsstrahlung), synchroton (high I , variable E , strongly collimated, 100% polarized) Neutrons: Large penetration depth f α for all elements of same order of magnitude f α varies non-systematically with Z Large experimental effort (reactor or spallation source) Small cross section (no charge, only interaction with core and magnetic moment) Electrons: 10 eV - 1 keV: large cross section (charged particle) 1 - 5 nm penetration depth ideal for surface studies! Atom beams: Very large cross section studies of first monolayer at surface
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3-20 Laue technique Fig. 3.16. Illustration of a set-up for Laue technique and diffraction pattern on the photo plates. Source: λ -continuum (e.g., X-ray bremsstrahlung) reflexes from all cystallographic planes Application: orientation of single cystals (of known structure) k 0 n-fold axis diffraction pattern has same symmetry as crystal No structure determination!
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3-21 Rotating crystal technique Fig. 3.17. Set-up for the rotating crystal technique and diffraction pattern. A peak is obtained if during crystal rotation a reciprocal lattice point intersects with the surface of the Ewald sphere (cf. Fig. 3.4).
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This note was uploaded on 01/19/2010 for the course MATERIALS M504 taught by Professor Adelung during the Spring '02 term at Uni Kiel.

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ssp_9y - 3 Continued 3.4 Experimental methods Fig. 3.15....

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