Lattice-matching periodic array of misfit dislocations: Heteroepitaxy of Bi(111) on Si(001),
In spite of the large lattice mismatch between Bi and Si, it is possible to grow expitaxial Bi(111) films on Si(001) substrates, which are atomically smooth and almost free of defects. The remaining lattice mismatch of 2.3% is accommodated by the formation of a periodic array of edge-type dislocations confined to the interface. The strain fields surrounding each dislocation cause a weak periodic surface undulation, which results in the splitting of all spots in low-energy electron diffraction (LEED). From a high resolution spot profile analyzing LEED study, an amplitude of 0.66 Å and a separation of 200 Å were derived. Comparison with elasticity theory gives a full lattice spacing of the Si surface as a Burgers vector b⃗=1/2 of the misfit dislocation array. With increasing thickness, the Bi film relaxes toward its bulk lattice constant.
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