The Si(001) c(4 x 4) surface reconstruction:: a comprehensive experimental study

We have carried out a comprehensive experimental study of the Si(001) c(4 x 4) surface reconstruction by scanning tunneling microscopy (STM) (at room temperature and elevated temperatures). Auger electron spectroscopy (AES), reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED). Si(001) samples were kept under ultra-high vacuum (UMV) at around 550 degrees C until the c(4 x 4) reconstruction appeared. STM contrast of the c(4 x 4) reconstruction is strongly influenced by electronic effects and changes considerably over a range of bias voltages. The c(4 x 4) surface reconstruction is a result of stress which is caused by incorporation of impurities or adsorbates in sub-surface locations. The resulting c(4 x 4) reconstruction in the top layer is a pure silicon structure. The main structural element is a one-dimer vacancy (1-DV). At this vacancy, second layer Si-atoms rebond and cause the adjacent top Si-dimers to brighten up in the STM image at low bias voltages. At higher bias voltage the contrast is similar to Si-dimers on the (2 x 1) reconstructed Si(001). Therefore, besides the 1-DV and the two adjacent Si-dimers, another Si-dimer under tensile stress may complete the 4 x unit cell. This is a refinement of the missing dimer model. (C) 1999 Elsevier Science B.V. All rights reserved.