Metallic Atomic Planes and Surfaces: FCC

1
Metallic Atomic Planes and Surfaces FCC
Which fcc atomic planes are expected to have
lowest surface energy, ?? Why?
Relative Surface Energies ?110 gt ?100 gt ?111

• From packing arguments only, clearly the most
  close-packed planes are 111, then 100,
  followed last by 110.
• Following packing, must considers bonding (e.g.,
  Ru(0001)), covalency and ionicity (e.g.
  InSd(111)).
• Metals rarely reconstruct on CP planes. Simply
  relaxing redistributes itinerant e.
• one rare exception is Au(110) 1x1 to 2x1 at
  650K (continuously)

Finnis and Heine, 1974
2
Ru(0001) Non-reconstructing Metallic Surfaces
revisit
Kr 4d7 5s1

• Ru(0001) surface is equivalent to fcc (111)
  planes.
• Hence, this is most-closed packed plane.
• bulk Ru(0001) has mostly non-bonding d-orbitals
• Expect no reconstruction
• Ru(0001) is stable, non-reactive substrate for
  ML growth studies.

3
FCC Au(110) reconstruction
(Campuzano et al, 1985)
(111) facets formed
sketch
1x1 to 2x1 surface reconstruction follows
Onsagers exact solution (solid line) for 2-D
Ising model. Argument does not depend on fact
that this is Au.
LEED intensity
Temperature
4
Surface structure of W(100) high-T 1x1 phase and
low-T v2 x v2 - R450
relaxed surface atoms
Related to Jahn-Teller Or Peierls distortion
unrelaxed surface atoms
5
Various FCC surface adsorption sites
fcc 001
fcc 110
fcc 111

• We now can consider
• Types of molecules
• Types of bonds in molecule and surface
• Types of bonds at metal surface, e.g. dz2

Atop 4-fold hollow hcp 3-fold hollow fcc 3-fold
hollow
x
Also, Rate of diffusion as measured by the
diffusion coefficient increases in
order Stepped lt (100) lt (110) lt
111) Increasing diffusion coefficient Increasing
surface roughness
6
Overlayer structures on fcc surfaces due to
adsorption
fcc 001
v2 x v2 structures
2x2 structures
3x3 structures black and grey
Experiments, such as LEED, cannot distinguish
these cases
7
Case Study CO on Ni(001)