Hydrogen adsorption configurations on Ge(001) probed with STM

The adsorption of hydrogen on Ge(001) has been studied with scanning tunneling microscopy at 77 K. For low doses (100 L) a variety of adsorption structures has been found. We have found two different atomic configurations for the Ge-Ge-H hemihydride and a third configuration that is most likely induced by the dissociative adsorption of molecular hydrogen. The Ge-Ge-H hemihydride is either buckled antiparallel or parallel to the neighboring Ge-Ge dimers. The latter configuration has recently been predicted by M. W. Radny et al. [J. Chem. Phys. 128, 244707 (2008)], but not observed experimentally yet. Due to the presence of phasons some dimer rows appear highly dynamic

Erratum: (2x1)-(1x1) Phase Transition on Ge(001): Dimer Breakup and Surface Roughening [Phys. Rev. Lett. 91, 116102 (2003)]

Using low energy electron microscopy, we have investigated the (2×1)-(1×1) phase transition occurring above 925 K on Ge(001). Dimer breakup has been identified as the physical origin of this transition. A quantitative description of the dimer concentration during the transition involves configuration entropy of random monomers within the dimer matrix. The dimer formation energy amounts to 1.2±0.3  eV. Dimer breakup promotes reversible surface disorder by step proliferation and irreversible surface roughening above 1130 K

Thermal roughening of {001} surfaces

Within the framework of a solid-on-solid model that incorporates nearest- (epsilon) and next-nearest-neighbor (delta) interactions we have determined the free energy of the high-symmetry steps on a (001) surface of a cubic crystal. We have found a simple expression that allows one to determine the thermal roughening temperature TR of a (001) surface (2e¿(epsilon/2+delta)/kbTR¿e¿(epsilon+2delta)/kbTR+2e¿(epsilon+delta)/kbTR=1). In a more refined analysis we have explicitly included step-edge overhangs. This results in a slightly lower thermal roughening temperature. Our results are also applicable to the two-dimensional Ising spin system

Influence of dimer buckling on dimer diffusion: A scanning tunneling microscopy study

The diffusion of Ge dimers along the substrate dimer rows of Ge(001) has been investigated with scanning tunneling microscopy. The jump frequency of on-top Ge dimers along symmetric dimer rows at room temperature is found to be eight times higher than the diffusion along asymmetric dimer rows (0.36 s–1 versus 0.044 s–1). We ascribe this difference to limitations associated with the rocking motion that a dimer has to perform while diffusing along asymmetric dimer rows