Reflection high-energy electron diffraction (RHEED)

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$Reflection and Refraction Maxwell's equations lead to definition for ...$

4.6.2 Instrumentation for EXAFSTunable x-ray source (electron storage ring - synchrotron)- pulsed, plane polarized outputX-ray monochromator (< few eV resolution)Detector for I and I 0 - ion chamber (total ion current α intensity)4.6.3 Surface EXAFS (SEXAFS)Basic problem in making EXAFS surface sensitive is removing contributionfrom bulk absorptiond# Bulk ~ (V x ρ/AW) x N# Surface ~ 6 x (1/d) 2AFor 1 x 1 x 1 cm 3 Au: (NN distance = 2.89 Å, AW = 197 g·mol -1 , ρ = 19.3g·cm -3 ) # bulk atoms = 6x10 22 , number surface atoms = 6x10 15 (0.1 ppm)CEM 924 7.14 Spring 2001
The conventional EXAFS technique can be made more surface sensitive bygrazing incidence- by varying incidence angle, surface sensitivity can be altered from nmto mm- can detect reflected beam directly or x-ray fluorescence (α absorption)- photons have long pathlength in solids (1-100 µm)One way is to measure x-ray fluorescence from atom known to be present onsurface only- fluorescence from O or C atoms for c(2x2)CO-Ni(100)Another way is to measure low energy photoelectrons coming from surfaceLow energy electrons have short inelastic mean free path (IMFP), λ, in solids(used in LEED to give surface sensitivity, remember?)CEM 924 7.15 Spring 2001
Page 1 and 2: 4.5 Reflection High Energy Electron
Page 3 and 4: a = 2πd=2π3.56 Å / 2= 2.49 Å
Page 5 and 6: - theory less well developed than L
Page 7 and 8: In this case, growth proceeds by Fr
Page 9 and 10: 4.6.1 Extended X-ray Absorption Fin
Page 11 and 12: E = hν photon − hν thresholdλ
Page 13: CEM 924 7.13 Spring 2001
Page 17 and 18: Need dynamical calculations to dete
Page 19: BUTRequires synchrotron for tunable

Reflection high-energy electron diffraction (RHEED)

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