A comprehensive experimental study was made of the Si(001)-c(4 x 4) surface reconstruction by using scanning tunnelling microscopy (at room temperature and elevated temperatures), Auger electron spectroscopy, reflection high-energy electron diffraction and low-energy electron diffraction. The Si(001) samples were kept under ultra-high vacuum at around 550C until the c(4 x 4) reconstruction appeared. Scanning tunnelling microscopic contrast of the c(4 x 4) reconstruction was strongly influenced by electronic effects, and changed considerably over a range of bias voltages. The c(4 x 4) surface reconstruction was a result of stress that was caused by the incorporation of impurities or adsorbates in sub-surface locations. The resultant c(4 x 4) reconstruction in the top layer was a pure silicon structure. The main structural element was a 1-dimer vacancy. At this vacancy, second-layer Si-atoms re-bonded and caused the adjacent top Si-dimers to brighten in the scanning tunnelling microscopic images at low bias voltages. At higher bias voltages, the contrast was similar to that of Si-dimers on the (2 x 1) reconstructed Si(001). Therefore, as well as the 1-dimer vacancy, and the 2 adjacent Si-dimers, another Si-dimer under tensile stress could complete the 4x unit cell. This was a refinement of the missing dimer model.

The Si(001) c(4 x 4) Surface Reconstruction - a Comprehensive Experimental Study. H.Nörenberg, G.A.D.Briggs: Surface Science, 1999, 430[1-3], 154-64