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

Steering effect on the shape of islands for homoepitaxial growth of Cu on Cu(100)

The steering effect on the growth of islands is investigated by combining molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations. Dynamics of depositing atoms and kinetics of atoms on a substrate are realized by MD and KMC, respectively. The reported experimental results on the asymmetric island growth [van Dijken {\it et al.}, Phys. Rev. Lett. {\bf 82}, 4038 (1999).] is well reproduced. A salient phenomenon, the reversal of the asymmetry, is found as the island size increases, and attributed to the asymmetric flux on the lower terrace of island.Comment: 5 figur

Anomalous strong repulsive step-step interaction on slightly misoriented Si(113)

We have used scanning tunneling microscopy to study Si(113) 0.2° misoriented towards [11-bar0]. Rapid quenching of this surface from 1500–1575 K to room temperature results in a uniformly stepped single-domain surface, whereas slower cooling gives rise to clustering of steps. The thermally induced step wandering and the terrace width distribution of the uniformly stepped surface are analyzed in order to determine the strength of the energetic and entropic step-step interactions. Beside the short-range attractive step-step interaction found by Song and Mochrie [Phys. Rev. Lett. 73, 995 (1994)] on Si(113) misoriented 1°–5° towards [001], we found an anomalously strong long-range repulsive step-step interaction on Si(113) 0.2° misoriented towards [11-bar0]. The coexistence of a long-range repulsive and a short-range attractive step-step interaction may explain the transition from a uniformly stepped surface at high freeze in temperature to a faceted surface at lower freeze in temperatures

Spin waves in CoFeB on ferroelectric domains combining spin mechanics and magnonics

Spin dynamics controlled by magnetoelastic coupling and applied electric fields might play a vital role in future developments of magnonics, i.e., the exploitation of spin waves for the transmission and processing of information. We have performed broadband spin-wave spectroscopy on a magnetostrictive CoFeB alloy grown on a ferroelectric BaTiO3 substrate causing elastic strain with a quasi-periodic modulation. We find characteristic eigenfrequencies and spin-wave modes with large group velocities and small damping. These results suggest bright perspectives for electric-field control of reprogrammable magnonics.Peer reviewe

d0 Ferromagnetic Interface Between Non-magnetic Perovskites

We use computational and experimental methods to study d0 ferromagnetism at a charge- imbalanced interface between two perovskites. In SrTiO3/KTaO3 superlattice calculations, the charge imbalance introduces holes in the SrTiO3 layer, inducing a d0 ferromagnetic half-metallic 2D electron gas at the interface oxygen 2p orbitals. The charge imbalance overrides doping by vacancies at realistic concentrations. Varying the constituent materials shows ferromagnetism to be a gen- eral property of hole-type d0 perovskite interfaces. Atomically sharp epitaxial d0 SrTiO3/KTaO3, SrTiO3 /KNbO3 and SrTiO3 /NaNbO3 interfaces are found to exhibit ferromagnetic hysteresis at room temperature. We suggest the behavior is due to high density of states and exchange coupling at the oxygen t1g band in comparison with the more studied d band t2g symmetry electron gas.Comment: 5 pages, 5 figure

Irreversible nucleation in molecular beam epitaxy: From theory to experiments

Recently, the nucleation rate on top of a terrace during the irreversible growth of a crystal surface by MBE has been determined exactly. In this paper we go beyond the standard model usually employed to study the nucleation process, and we analyze the qualitative and quantitative consequences of two important additional physical ingredients: the nonuniformity of the Ehrlich-Schwoebel barrier at the step-edge, because of the existence of kinks, and the steering effects, due to the interaction between the atoms of the flux and the substrate. We apply our results to typical experiments of second layer nucleation.Comment: 11 pages. Table I corrected and one appendix added. To be published in Phys. Rev. B (scheduled issue: 15 February 2003

Effects of deposition dynamics on epitaxial growth

The dynamic effects, such as the steering and the screening effects during deposition, on an epitaxial growth (Cu/Cu(001)), is studied by kinetic Monte Carlo simulation that incorporates molecular dynamic simulation to rigorously take the interaction of the deposited atom with the substrate atoms into account. We find three characteristic features of the surface morphology developed by grazing angle deposition: (1) enhanced surface roughness, (2) asymmetric mound, and (3) asymmetric slopes of mound sides. Regarding their dependence on both deposition angle and substrate temperature, a reasonable agreement of the simulated results with the previous experimental ones is found. The characteristic growth features by grazing angle deposition are mainly caused by the inhomogeneous deposition flux due to the steering and screening effects, where the steering effects play the major role rather than the screening effects. Newly observed in the present simulation is that the side of mound in each direction is composed of various facets instead of all being in one selected mound angle even if the slope selection is attained, and that the slope selection does not necessarily mean the facet selection.Comment: 9 pages, 10 figure

Sensitivity of the Relationship Between Antarctic Ice Shelves and Iron Supply to Projected Changes in the Atmospheric Forcing

Upward advection or mixing of iron-rich deep waters due to circulation changes driven by the rate of basal ice shelf melt was shown to be a primary control on chlorophyll a production in coastal polynyas over the Antarctic continental shelf. Here, the effects of atmospheric changes projected in 2100 on this relationship were examined with a 5-km resolution ocean/sea ice/ice shelf model of the Southern Ocean with different simulated dissolved iron sources and idealized biological uptake. The atmospheric changes are added as idealized increments to the forcing. Inclusion of a poleward shift and strengthening of the winds, increased precipitation, and warmer atmospheric temperatures resulted in doubling of the heat advected onto the continental shelf and an 83% increase in the total Antarctic ice shelf basal melt. The total dissolved iron supply to the surface waters over the continental shelf increased by 62%, while the surface iron supply due just to basal melt driven overturning increased by 48%. However, even though the ice shelf driven contribution becomes less important to the total iron supply on average (29% of total), the ice shelf involvement becomes relatively even more important in some locations, such as the Amundsen and Bellingshausen Seas. The modified atmospheric conditions also produced a reduction in summer sea ice extent and a shoaling of the summer mixed layers. These simulated responses to projected changes suggest relief of light and nutrient limitation for phytoplankton blooms over the Antarctic continental shelf and perhaps an increase in annual production in years to come