Summary: Reader

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• 2 From solids to solid surfaces

• 2.3 Geometric structure of surfaces and 2.4

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• What is surface relaxation?

  The first layer of atoms move further away from the remaining neighbors or closer towards them. The periodicity of the surface or its symmetry is not changed.
  

• What is surface reconstruction?

  This involves changes in periodicity and/or symmetry of the surface structure. The surface unit cell becomes bigger. (superstructure)
  

• Why does surface reconstruction occur?

  The simple reconstructions can often be explained by a reduction of the coordinative unsaturation of the surface atoms by bond formation between adjacent atoms.
  

• 2.5 Defects

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• Name different defects origination form surface.

  Vacancy, kinks, stepedges, ledge atom, adatom
  

• Name two defects originating from the bulk.

  • Edge dislocations

  • Screw dislocations

• 2.7 Quasi crystals

• What is a quasi cristal?

  A structure that is long range ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry.
  While crystals, according to the classical crystallographic restriction theorem, can possess only two, three, four, and six-fold rotational symmetries, the Bragg diffraction pattern of quasicrystals shows sharp peaks with other symmetry orders, for instance five-fold.
  

• 3 electronic structure of surfaces

• 3.5 Work function

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• What is the work function?

  Energy needed to remove an electron from a surface (like ionizing individual atoms/molecules)
  

• 3.7 Smoluchowski effect

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• What is the Smoluchowski effect?

  On surfaces with a strong corrugation it is favorable for the electrons to re-distribute in a way that creates a smoother charge density at the surfaces (this effect also contributes to surface relaxation). This charge smoothening is called Smoluchowski effect.

• 3.8 Measuring work function

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• How is the work function determined with the photo-electric effect?

  Radiate material with photons with fixed energy (wavelength ). Photons kick electrons out of the material. Threshold energy (minimum energy required) is equal to the work function.
  

• How can the work function be determined with thermionic emission?

  Higher T, electrons get above Fermi level. High enough T electrons can be kicked out -> gives current density which is exponentially dependent on the work function. Slope of log plot (Fowler-Nordheim plot) gives value of work function.