Gallium arsenide cleaves easily along planes

PHYSICS · Multi-part · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Crystal structure, bonding and diffraction · Crystal structure, bonding and diffraction

Solid State Physics, Ch Seeing atoms: electron and scanning-probe microscopy

Problem

Gallium arsenide cleaves easily along

(110)

planes, exposing alternating rows of Ga and As atoms in the surface unit cell, each row separated by the surface lattice repeat

a_s

. A scanning tunnelling microscope operated at

-2.0\,\mathrm{V}

sample bias (a filled-state image) shows one row of atoms as bright protrusions. On the same area, an image taken at

+2.0\,\mathrm{V}

sample bias (an empty-state image) shows bright protrusions on the other row, laterally displaced by

a_s/2

relative to the filled-state image. ((a)) Using the Tersoff-Hamann description of the tunnel current, explain why the two bias polarities light up different rows of atoms. ((b)) A colleague claims the two images prove that the Ga and As atoms physically shift by

a_s/2

when the bias is reversed. Is this correct? Justify the answer in one or two sentences.

Browse the problem library