The atomic structure of the room temperature (2 × 1) reconstruction of Ge(001) has been investigated with X-ray diffraction measurements by collecting an extensive and accurate set of diffracted intensities. The structural model that best agrees with the data consists of a buckled array of disordered dimers: there is a 0.5 probability of finding one of the two dimer orientations (positive and negative tilt angles) in any unit cell. The dimer tilt angle is found to be 15.6±0.6°, its bond length is expanded by 4% compared to the bulk bond length, the reconstruction is found to extend to eight atomic layers and the maximum distortion of the bonds has been found to be less than 6%. The model is compared with similar models, and the dynamical and ordered models and the dynamics of the dimer flipping are discussed.
Torrelles, X., Van Der Vegt, H. A., Etgens, V. H., Fajardo, P., Alvarez, J., & Ferrer, S. (1996). The structure of the Ge(001)-(2 × 1) reconstruction investigated with X-ray diffraction. Surface Science, 364(3), 242–252. https://doi.org/10.1016/0039-6028(96)00650-4