The Concept of Two Mobilities in Homoepitaxial Growth

A general kinetic concept is introduced which can be used to control growth modes in homoepitaxy. Its basic idea is that during growth of a layer, the characteristics length scale associated with nucleation is deliberately varied. The power of this concept lies in the fact that it can be realized experimentally in a variety of ways and is not restricted to special systems. It helps to understand various effects reported in the literature and may serve as a guideline for future methods of growth manipulation

Optical anisotropy induced by ion bombardment of Ag(001)

Grazing incidence ion bombardment results in the formation of nanoripples that induce an anisotropic optical reflection The evolution of the reflectance anisotropy has been monitored in situ with reflectance anisotropy spectroscopy. The Rayleigh-Rice theory (RRT) has been used to analyze the optical spectra quantitatively and provides the evolution of the average ripple period and root-mean-squared surface roughness. After an incipient phase, both the increase in the periodicity and the roughness vary roughly with the square root of the sputter time. Additional high-resolution low-energy electron diffraction (HR-LEED) measurements have been performed to characterize details of the average structure created by ion bombardment

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

Direct determination of the step-edge formation energies of the energetically stable and unstable double-layer step edges of Si(001)

Scanning tunneling microscopy images of 4.5° misoriented double B stepped Si(001) have been analyzed to determine the double-layer step-edge formation energies of the energetically stable double step (B-type) as well as the energetically unstable double step (A-type). The ordering of the various single- and double-layer step-edge formation energies is in accordance with semiempirical tight-binding-based total-energy calculations performed by Chadi [Phys. Rev. Lett. 59, 1691 (1987)]. Finally, the miscut angle at which the transition between the single- and double-layer stepped surface occurs as calculated using the experimentally obtained step-edge formation energies is in agreement with the experiment

Determination of surface stress anisotropy from domain wall fluctuations

The thermally induced meandering of domain walls between (2×1) and c(4×2) regions on Ge(001) is analyzed with a scanning tunneling microscope in order to extract the anisotropy of the surface stress tensor. On small length scales the domain walls exhibit random walker behavior, whereas on larger length scales (>100 Å) due to domain-wall repulsion originating from the anisotropy in the surface stress tensor a deviation from this one-dimensional random-walk behavior is observed. We have determined a value of 0.13±0.04eV/(1×1) cell for the stress anisotropy

Flux heterogeniety through incidence angle and particle energy in steering-enhanced growth

During growth Van der Waals forces between the incident atoms and the substrate lead to steering with sometimes important implications for the morphology of the molecular-beam-epitaxy- or sputter grown films. Deterministic classical trajectory calculations, modelling the atom-substrate interaction with a Lennard Jones potential, have been run to provide insight in the influence of the polar angle of incidence and the energy of the atoms on steering for 1 and 3 monolayer high islands. For low energies (10¿100 meV) substantial flux redistribution has been found. A major part of the flux directed to the ascending steps is transferred on top of the protrusion, while even reversal of the lateral velocity at the descending steps occurs. At grazing incidence strong deviations from geometric shadowing behavior is observed even for energies as high as 1 to 10 eV

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