THE STRUCTURE OF THE GE(001)-(2X1) RECONSTRUCTION INVESTIGATED WITH X-RAY-DIFFRACTION

The atomic structure of the room temperature (2 x 1) reconstruction of Ge(001) has been investigated with X-ray diffraction measurements by collecting an extensive and accurate set of diffracted intensities. Th e structural model that best agrees with the data consists of a buckle d array of disordered dimers: there is a 0.5 probability of finding on e 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 degre es, 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%. Th e model is compared with similar models, and the dynamical and ordered models and the dynamics of the dimer flipping are discussed.