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

Initial stages of Pt growth on Ge(001) studied by scanning tunneling microscopy and density functional theory

We have studied the initial stages of submonolayer Pt growth on the Ge(001). We have observed several stable and meta-stable adsorption configurations of Pt atoms at various temperatures. Calculations indicate relatively high binding energies of Pt atoms onto the Ge lattice, at different adsorption sites. Our results show that through-the-substrate bonding (concerted bonding) of two Pt atoms is more favored on Ge(001) surface then a direct Pt-Pt bond. Both our experiments and calculations indicate the breaking of Ge-Ge bonds on the surface in the vicinity of Pt adsorbates. We have also observed the spontaneous generation of 2 + 1 dimer vacancy defects at room temperature that cause the ejection of Ge atoms onto the surface. Finally we have studied the diffusion of Pt atoms into the bulk as a result of annealing and found out that they get trapped at subsurface sites

A two-qubit Bell inequality for which POVM measurements are relevant

A bipartite Bell inequality is derived which is maximally violated on the two-qubit state space if measurements describable by positive operator valued measure (POVM) elements are allowed rather than restricting the possible measurements to projective ones. In particular, the presented Bell inequality requires POVMs in order to be maximally violated by a maximally entangled two-qubit state. This answers a question raised by N. Gisin.Comment: 7 pages, 1 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

Field induced phase segregation in ferrofluids

We study the phase segregation in magnetite ferrofluids under the influence of an external magnetic field. A phase with lower nanoparticle density and corresponding higher optical transmission is formed in the bottom of a glass cell in the presence of only a very modest magnetic field gradient (smaller than 25 T/m). The flux density in our magnetic configuration is simulated using finite element methods. Upon switching off the external magnetic field, the low-density phase develops into a ‘bubble’-like feature. The kinetics of this ‘bubble’ in the absence and presence of a magnetic field are described and analyzed in terms of a simple model, which takes into account buoyancy and drag force

Electric field assisted nanocolloidal gold deposition

The deposition of nanocolloidal gold particles under the influence of an externally applied electric field is studied in situ by means of spectroscopic ellipsometry. The variation of the relative coverage with time, as a function of applied potential, is determined using a principal component analysis. Calibration of the absolute coverage is done by means of ex situ electron microscopy. The results reveal that the deposition rate is directly related to the electrochemical current. A threshold potential exists for current and therewith also deposition to occur. The spatial distribution of nanoparticles deposited in an applied field exhibits a higher degree of order as compared to the random, irreversibly deposited nanocolloids at chemically functionalized surfaces. The experimental findings are discussed in terms of a simple electrochemical model

Stationary Properties of a Randomly Driven Ising Ferromagnet

We consider the behavior of an Ising ferromagnet obeying the Glauber dynamics under the influence of a fast switching, random external field. Analytic results for the stationary state are presented in mean-field approximation, exhibiting a novel type of first order phase transition related to dynamic freezing. Monte Carlo simulations performed on a quadratic lattice indicate that many features of the mean field theory may survive the presence of fluctuations.Comment: 5 pages in RevTex format, 7 eps/ps figures, send comments to "mailto:[email protected]", submitted to PR