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This critical analysis of the traditional pathophysiological approach to the diagnosis and treatment of cardiogenic pulmonary edema calls into question some long-established ideas and interventions that ought to be replaced by better evidence-based concepts. [ABSTRACT FROM AUTHOR]

Abstract: As part of a search for new spintronic materials, highly ordered films of Cr x Ti1−x O2 in both the rutile and anatase structures and for several Cr concentrations ranging from x =0.02 to 0.16 were grown by oxygen plasma assisted molecular beam epitaxy. X-ray photoelectron diffraction data of the Cr 2p level exhibit the same patterns and the same modulation amplitudes as those observed for Ti 2p, providing a strong indication that a large fraction of the Cr atoms occupy substitutional lattice sites in both structures. The Cr 2p core-level spectra as well as a Cr 3d related dopant signal above the valence band of TiO2 are characteristic of Cr3+ ions. At room temperature, Cr-doped anatase films exhibit ferromagnetic order with a saturation magnetization of ∼0.6 μB per Cr atom and strong in-plane anisotropy. [Copyright &y& Elsevier]

A computational method is presented for angle-resolved photoemission spectra (ARPES) and photoelectron diffraction (PED) in the ultraviolet regime. The one-step model is employed and both initial valence and final continuum states are calculated using the finite-cluster, real-space multiple scattering method. Thereby the approach is versatile and provides a natural link to core-level PED. The method is applied to the Cu(111) valence band and good agreement with experiment is found for both ARPES spectra and PED patterns. When the PED patterns are integrated over a filled band of a single-orbital symmetry, such as Cu-3d, we show, both numerically and analytically, that the exact theory with delocalized initial states can be replaced by the much simpler, core-level-type theory where the initial states are taken as localized. [ABSTRACT FROM AUTHOR]

Abstract: Diamondoids are nanometer-sized, hydrogen terminated diamond-like molecules consisting of fused adamantane units. The thiolated diamondoid [121]tetramantane-6-thiol shows negative electron affinity behavior, i.e. population of unoccupied states directly leads to spontaneous electron emission. We present time-resolved photoemission data from self-assembled monolayers of [121]tetramantane-6-thiol in order to shed light on the emission process: A photon energy threshold for electron emission of 5.6–5.8eV was observed, and the electron affinity was estimated to be −0.21 to −0.57eV for Ag and Au substrates, respectively. Electrons are emitted after excitation in the metal substrate through the molecular orbitals within a few femtoseconds. [Copyright &y& Elsevier]

The quantitative analysis of spin-polarized photoemission data is discussed. An angle-resolving photoelectron spectrometer equipped with a three-dimensional (3D) spin polarimeter produces complete data sets consisting of photoemission intensities as well as spin asymmetry curves for three orthogonal vector components. In a two-step fitting routine, the photoemission spectrum is first dissected into individual peaks and background. Assigning trial spin polarization vectors to each of them, the asymmetry curves can be modeled until the best fit is reached. This procedure is crucial when analyzing strongly overlapping peaks or weak signals sitting on a large unpolarized background, especially in the presence of non-collinear spins. It is robust against strong intensity variations due to matrix element effects because it references the spin polarization contribution of each band to the measured peak intensity. The method is applied to 2D systems where spin-orbit effects lead to spin splittings and complex momentum-dependent spin structures. Presented case studies include surface alloys of Bi and Pb on Ag(111) that show a giant Rashba effect. [ABSTRACT FROM AUTHOR]

Abstract: Single sheets of hexagonal boron nitride on transition metals provide a model system for single layer dielectrics. The progress in the understanding of h-BN layers on transition metals of the last 10 years is shortly reviewed. Particular emphasis lies on the boron nitride nanomesh on Rh(111), which is a corrugated single sheet of h-BN, where the corrugation imposes strong lateral electric fields. Fermi surface maps of h-BN/Rh(111) and Rh(111) are compared. A h-BN layer on Rh(111) introduces no new bands at the Fermi energy, which is expected for an insulator. The lateral electric fields of h-BN nanomesh violate the conservation law for parallel momentum in photoemission and smear out the momentum distribution curves on the Fermi surface. [Copyright &y& Elsevier]

Heteroepitaxial nucleation and growth of twin-free diamond on Ir(111) is reported. The bias enhanced nucleation (BEN) technique was applied in a microwave plasma chemical vapor deposition setup to induce diamond nucleation on the new multilayer stack Ir/YSZ/Si(111). We demonstrate that the gathering of the diamond nuclei in so-called “domains,” a pattern formation process unique for diamond nucleation on iridium, is also present on Ir(111). The 1–2 nm thick carbon layer deposited by BEN does not show any crystalline diamond structures in electron diffraction and high resolution lattice imaging microscopy. In contrast, x-ray photoelectron diffraction (XPD) measurements yield C 1s diffractograms with clear threefold symmetry. The main features are comparable to measurements on diamond (111) single crystal surfaces. The weaker fine structure in the XPD patterns of the BEN layers is attributed to some disorder due to the harsh ion bombardment. However, this ion bombardment did not induce any measurable amount of twinning as deduced from the threefold symmetry. After 3 h diamond growth, the signal due to twins in the x-ray diffraction pole figures is still below the noise level of ∼1%. Negligible twinning and the low mosaic spread of 0.96° (tilt) and 1.85° (twist) indicate that these films mark a breakthrough toward heteroepitaxial diamond films with (111) orientation. They provide interesting growth substrates, e.g., for phosphorous doped diamond or for the formation of heterojunction devices by deposition of wurtzite-type wide band gap semiconductor materials. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the enhancement of the structural sensitivity of x-ray photoelectron diffraction through the acquisition of a full hemispherical diffraction pattern of chemically shifted core levels. Background on diamondlike carbon films; Discussion on complex systems to resolve the local order per element and per chemical environment; Effects of the sample temperature and ion dose on the structure of deposited layers.

Epitaxial ferromagnetic films of Cr-doped TiO2 anatase (CrxTi1-xO2-x/2) were grown on LaAlO3(001) using oxygen-plasma-assisted molecular-beam epitaxy. Cr K-shell x-ray absorption near-edge spectroscopy shows that the formal oxidation state of Cr is +3 throughout the films, with no evidence for either elemental Cr or half-metallic CrO2. Cr is found to substitute for Ti in the lattice, with uniform distribution throughout the doped region of the film. The Cr-doped anatase films exhibit room-temperature ferromagnetism aligned in-plane, with a saturation magnetization of ∼0.6 μB/Cr atom. [ABSTRACT FROM AUTHOR]

What is the spatiotemporal limit of a macroscopic model that describes the optoelectronic interaction at the interface between different media? This fundamental question has become relevant for time-dependent photoemission from solid surfaces using probes that resolve attosecond electron dynamics on an atomic length scale. We address this fundamental question by investigating how ultrafast electron screening affects the infrared field distribution for a noble metal such as Cu(111) at the solid-vacuum interface. Attosecond photoemission delay measurements performed at different angles of incidence of the light allow us to study the detailed spatiotemporal dependence of the electromagnetic field distribution. Surprisingly, comparison with Monte Carlo semiclassical calculations reveals that the macroscopic Fresnel equations still properly describe the observed phase of the 1R field on the Cu(111) surface on an atomic length and an attosecond time scale. [ABSTRACT FROM AUTHOR]

Objective Whether or not a high risk of falls increases the risk of bleeding in patients receiving anticoagulants remains a matter of debate. Methods We conducted a prospective cohort study involving 991 patients ≥65 years of age who received anticoagulants for acute venous thromboembolism ( VTE) at nine Swiss hospitals between September 2009 and September 2012. The study outcomes were as follows: the time to a first major episode of bleeding; and clinically relevant nonmajor bleeding. We determined the associations between the risk of falls and the time to a first episode of bleeding using competing risk regression, accounting for death as a competing event. We adjusted for known bleeding risk factors and anticoagulation as a time-varying covariate. Results Four hundred fifty-eight of 991 patients (46%) were at high risk of falls. The mean duration of follow-up was 16.7 months. Patients at high risk of falls had a higher incidence of major bleeding (9.6 vs. 6.6 events/100 patient-years; P = 0.05) and a significantly higher incidence of clinically relevant nonmajor bleeding (16.7 vs. 8.3 events/100 patient-years; P < 0.001) than patients at low risk of falls. After adjustment, a high risk of falls was associated with clinically relevant nonmajor bleeding [subhazard ratio ( SHR) = 1.74, 95% confidence interval ( CI) = 1.23-2.46], but not with major bleeding ( SHR = 1.24, 95% CI = 0.83-1.86). Conclusion In elderly patients who receive anticoagulants because of VTE, a high risk of falls is significantly associated with clinically relevant nonmajor bleeding, but not with major bleeding. Whether or not a high risk of falls is a reason against providing anticoagulation beyond 3 months should be based on patient preferences and the risk of VTE recurrence. [ABSTRACT FROM AUTHOR]

The setup of an apparatus for chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) and its characterization on four-inch wafers in ultra high vacuum (UHV) environment is reported. It provides well-controlled preparation conditions, such as oxygen and argon plasma assisted cleaning and high temperature annealing. In situ characterization of a wafer is accomplished with target current spectroscopy. A piezo motor driven x-y stage allows measurements with a step size of 1 nm on the complete wafer. To benchmark the system performance, we investigated the growth of single layer h-BN on epitaxial Rh(111) thin films. A thorough analysis of the wafer was performed after cutting in atmosphere by low energy electron diffraction, scanning tunneling microscopy, and ultraviolet and X-ray photoelectron spectroscopies. The apparatus is located in a clean room environment and delivers high quality single layers of h-BN and thus grants access to large area UHV processed surfaces, which had been hitherto restricted to expensive, small area single crystal substrates. The facility is versatile enough for customization to other UHV-CVD processes, e.g., graphene on four-inch wafers. [ABSTRACT FROM AUTHOR]

We present time-resolved photoemission experiments from a peculiar bismuth surface, Bi(114). The strong one-dimensional character of this surface is reflected in the Fermi surface, which consists of spin-polarized straight lines. Our results show that the depletion of the surface state and the population of the bulk conduction band after the initial optical excitation persist for very long times. The disequilibrium within the hot electron gas along with strong electron-phonon coupling cause a displacive excitation of coherent phonons, which in turn are reflected in coherent modulations of the electronic states. Beside the well-known A1g bulk phonon mode at 2.76 THz, the time-resolved photoelectron spectra reveal a second mode at 0.72 THz which can be attributed to an optical surface phonon mode along the atomic rows of the Bi(114) surface. [ABSTRACT FROM AUTHOR]

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi2Se3 from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature. [ABSTRACT FROM AUTHOR]

The recently discovered three-dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into a topological state by modulating the spin-orbit interaction or the crystal lattice, driving the system through a topological quantum phase transition. By directly measuring the topological quantum numbers and invariants, we report the observation of a phase transition in a tunable spin-orbit system, BiTL(S1-δSeδ)2, in which the topological state formation is visualized. In the topological state, vortex-like polarization states are observed to exhibit three-dimensional vectorial textures, which collectively feature a chirality transition as the spin momentum-locked electrons on the surface go through the zero carrier density point. Such phase transition and texture inversion can be the physical basis for observing fractional charge (±e/2) and other fractional topological phenomena. [ABSTRACT FROM AUTHOR]

We report high-resolution spin-resolved photoemission spectroscopy (spin-ARPES) measurements on the parent compound Sb of the recently discovered three-dimensional topological insulator Bi1-xSbx (Hsieh et al 2008 Nature 452 970, Hsieh et al 2009 Science 323 919). By modulating the incident photon energy, we are able to map both the bulk and the (111) surface band structure, from which we directly demonstrate that the surface bands are spin polarized by the spin-orbit interaction and connect the bulk valence and conduction bands in a topologically non-trivial way. A unique asymmetric Dirac surface state gives rise to a k-splitting of its spin-polarized electronic channels. These results complement our previously published works on this class of materials and re-confirm our discovery of topological insulator states in the Bi1-xSbx series. [ABSTRACT FROM AUTHOR]

Background: We reviewed the current evidence on the benefit and harm of pre-hospital tracheal intubation and mechanical ventilation after traumatic brain injury (TBI). [ABSTRACT FROM PUBLISHER]

Helical Dirac fermions—charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum—are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose–Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene or bismuth. It has recently been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators—materials with a bulk insulating gap of spin–orbit origin and surface states protected against scattering by time-reversal symmetry—and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime. However, helical Dirac fermions have not been observed in existing topological insulators. Here we report the realization and characterization of a tunable topological insulator in a bismuth-based class of material by combining spin-imaging and momentum-resolved spectroscopies, bulk charge compensation, Hall transport measurements and surface quantum control. Our results reveal a spin-momentum locked Dirac cone carrying a non-trivial Berry’s phase that is nearly 100 per cent spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers point and can be driven to the long-sought topological spin transport regime. The observed topological nodal state is shown to be protected even up to 300 K. Our demonstration of room-temperature topological order and non-trivial spin-texture in stoichiometric Bi2Se3.Mx (Mx indicates surface doping or gating control) paves the way for future graphene-like studies of topological insulators, and applications of the observed spin-polarized edge channels in spintronic and computing technologies possibly at room temperature. [ABSTRACT FROM AUTHOR]

A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry-based classification of condensed matter. Exotic spin-transport phenomena, such as the dissipationless quantum spin Hall effect, have been speculated to originate from a topological order whose identification requires a spin-sensitive measurement, which does not exist to this date in any system. Using Mott polarimetry, we probed the spin degrees of freedom and demonstrated that topological quantum numbers are completely determined from spin texture-imaging measurements. Applying this method to Sb and Bi1-xSbx, we identified the origin of its topological order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a topological quantum Berry's phase and definite spin chirality, which are the key electronic properties component for realizing topological quantum computing bits with intrinsic spin Hall-like topological phenomena. [ABSTRACT FROM AUTHOR]

Abstract: The carbon layer formed during the bias enhanced nucleation (BEN) procedure on iridium has been studied by different electron diffraction techniques. In reflection high energy electron diffraction (RHEED) and low energy electron diffraction (LEED) the carbon nucleation layer does not give any indication of crystalline diamond even if the presence of domains proves successful nucleation. In contrast, X-ray photoelectron diffraction (XPD) shows a clear C 1s pattern when domains are present after BEN. The anisotropy in the Ir XPD patterns is reduced after BEN while the fine structure is essentially identical compared to a single crystal Ir film. The change in the Ir XPD patterns after BEN can be explained by the carbon layer on top of a crystallographically unmodified Ir film. The loss and change in the fine structure of the C 1s patterns as compared to a single crystal diamond film are discussed in terms of mosaicity and a defective structure of the ordered fraction within the carbon layer. The present results suggest that the real structure of the BEN layer is more complex than a pure composition of small but perfect diamond crystallites embedded in an amorphous matrix. [Copyright &y& Elsevier]

The growth of hexagonal boron nitride (h-BN) on Ni(1 1 1) at submonolayer coverages results in triangular islands with two different orientations. In combining X-ray photoelectron diffraction and scanning tunneling microscopy it is demonstrated that these two island types correspond to fcc and hcp domains of h-BN/Ni(1 1 1). The domain boundaries appear as defect lines that are also present in complete h-BN monolayers. Based on the experimental data, structural models for the two domains and the defect lines are discussed. [Copyright &y& Elsevier]

Abstract: The structure of hexagonal boron nitride (h-BN) on Pd(111) was studied with low energy electron diffraction (LEED), photoelectron spectroscopy and scanning tunnelling microscopy (STM). h-BN forms flat monolayers on the Pd(111) surface in contrast to Rh(111) where a complex self-assembled double layer structure, the nanomesh [M. Corso, W. Auwärter, M. Muntwiler, A. Tamai, T. Greber, J. Osterwalder, Science 303 (2004) 217], appears. The LEED patterns reveal a dominating 10×10 h-BN superstructure, with a second, distinct structure rotated by 30° and further azimuthally randomly oriented h-BN overlayers. This is consistent with STM images which show several different Moiré patterns associated with different rotation angles of the overlayer. Additionally the use of thin Pd(111) films instead of single crystal substrates was studied. No significant differences in the h-BN film quality were found. [Copyright &y& Elsevier]

We used angle-resolved photoemission spectroscopy to measure theelectronic dispersion and single-particle spectral function in a liquidmetal. A lead monolayer supported on a copper (111) surface wasinvestigated as the temperature was raised through the meltingtransition of the film. Electron spectra and momentum distribution mapsof the liquid film revealed three key features of the electronicstructure of liquids: the persistence of a Fermi surface, the filling ofband gaps, and the localization of the wave functions upon melting.Distinct coherence lengths for different sheets of the Fermi surfacewere found, indicating a strong dependence of the localization lengthson the character of the constituent atomic wave functions. [ABSTRACT FROM AUTHOR]

On Cu(2 2 1) it is possible to grow long ordered one-dimensional chains of C60 molecules aligned along the steps of this vicinal template. By scanning tunneling microscopy (STM) a unit cell with two distinctly imaged molecules is found. From distribution of the rare defects a bond energy difference of the two types of molecules is inferred. At least in one of the two species, the molecules have a well-defined orientation as determined by X-ray photoelectron diffraction (XPD). [Copyright &y& Elsevier]

The electronic structure of an incommensurate Pb layer on Cu(1 1 1) is investigated by means of angle scanned ultraviolet photoemission. Despite of the rather complex atomic structure with three competing periodicities, we observe a well defined band structure, reflecting essentially the fundamental (1 × 1)-periodicity of the adlayer. Comparison with band structure calculations for a free standing Pb-layer shows that all observed bands can be fully attributed to the overlayer. [Copyright &y& Elsevier]

The magnetic and electronic properties of itinerant ferromagnets and their interplay have been studied in the last few years by spin resolved electron spectroscopy on one hand and by high-resolution angle-resolved photoemission experiments on the other. We discuss how the two approaches can be combined in a high resolution electron spectrometer with spin resolution for angle-scanned Fermi surface mapping experiments. We have built this new instrument, which allows an advance into a deeper understanding of magnetic thin film or multilayer systems, where band structures become intricately dense in momentum space and where the magnetization direction can change from layer to layer. Spin-resolution is thus required to arrive at a correct assignment of spectral features. A fully three-dimensional polarimeter makes the instrument ‘complete’ in the sense that all properties of the photoelectron are measured. First experiments on Ni(111) conclusively confirm previous band and spin assignments at the Fermi level and demonstrate the correct functioning of the apparatus. [Copyright &y& Elsevier]

The growth of cobalt on a monolayer of hexagonal boron nitride on Ni(1 1 1) has been studied in a combination of scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS). A detailed picture of the growth kinetics is obtained. The Co sticking coefficient strongly decreases at high substrate temperatures. Co deposition results in two different morphologies: (i) three-dimensional clusters that grow on top of the hexagonal boron nitride (h-BN) film and often align themselves to form chains and (ii) islands with a more two-dimensional character, which are intercalated below the h-BN film dominate at higher substrate temperatures. From XPS measurements at different deposition temperatures an activation energy for intercalation of ∼0.24 eV is inferred. The influence of observed defect lines in the h-BN overlayer on the growth kinetics is discussed. [Copyright &y& Elsevier]

Nickel (111) and the interface of hexagonal boron nitride on Ni(111) serve as model systems for an itinerant ferromagnet that is truncated with vacuum or a single layer insulator. These systems are investigated with angle-scanned He I and He II photoemission. Upon formation of the h-BN/Ni(111) interface the work function drops by 1.8 eV and the minority Ni Λ[sub 3] d-band shifts by 0.13 eV to higher binding energy. This indicates that the Ni magnetic moment decreases in the interface. Spin-polarized band structure calculations from bulk nickel identify the observed minority and majority bands. The experimental Fermi surface maps show that h-BN distorts a minority d-band in a way which is consistent with the decreasing magnetic moment. It can be seen that h-BN affects the scattering of the electrons. Effects in the photoemission final and initial state are recognized. [ABSTRACT FROM AUTHOR]

We present the design and performance tests of a miniaturized pulsed low-energy electron gun. Electrons photoemitted from a gold cathode are accelerated over a distance of 75 μm and then collimated by a microchannel plate. According to calculations, this novel concept will allow the time spread of the electron pulses to be kept below 5 ps for kinetic energies as low as 100 eV. The achievement of a minimum angular beam divergence (approx. 1°) along with an energy resolution of 1.1 eV has to be paid for by low signal intensities. We demonstrate the performance of the gun and the high electron-beam coherence by presenting low-energy-electron diffraction images taken from a submonolayer of lead adsorbed on the germanium (111) surface. We anticipate that this electron gun will open up new possibilities for following structural changes on solid surfaces in real time. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes the setup of an electron spectrometer for angle-resolved photoemission. Exploitation of a monochromatized high flux He discharge photon source; Quantification of the dispersion of the Shockley surface state on AG(111) above the Fermi energy.

The orientation and the intramolecular relaxation due to adsorption of the chiral phenanthrene-derivative heptahelicene, C[sub 30]H[sub 18], on Cu(111) and Cu(332) surfaces have been investigated by means of angle-scanned full-hemispherical x-ray photoelectron diffraction. Although the C 1s diffraction patterns of the adsorbed submonolayer coverage helicene films exhibit scattering anisotropies of less than two percent, a detailed analysis involving simple molecular mechanics calculations of the atomic coordinates, photoelectron diffraction single-scattering cluster calculations and an R-factor analysis permits the determination of the helicene molecular orientation. On Cu(111), the molecules are found to bind to the substrate surface via their terminal phenanthrene group oriented parallel to the surface plane, while on Cu(332) the three terminal C-6 rings are oriented parallel to the (111) terrace plane. Six azimuthal molecular orientations are found to coexist on Cu(111), on Cu(332), however, the step–molecule interaction leads to a unique azimuthal alignment of the heptahelicene molecules. The heptahelicene on Cu(332) system thus represents a chiral surface with single-phase orientational order. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a method for controlled change of the doping level of high-temperature superconductors with ultraviolet radiation. Oxygen desorption caused by exposure of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+delta] samples to the light of a He gas-discharge lamp; Decrease of the doping levels of semiconductors caused by oxygen desorption.

Presents an abstract of the study 'Spin-Polarized Photoelectron Diffraction: A New Probe of Short-Range Magnetic Order,' by C.S. Fadley, B. Sinkovic, B.D. Hermsmeier and J. Osterwalder.

Coherent phonons are an excellent tool to investigate the interplay between electronic and structural dynamics. The displacive excitation of coherent phonons in elemental bismuth is one of the most widely studied processes for this purpose. We employ time-resolved photoelectron diffraction to access the structural dynamics by recording the photoemission intensity from one initial state as a function of emission angle. In comparison with tight-binding and single-scattering cluster calculations, this allows electronic and structural effects to be disentangled. Hence, the full dynamics of the hot electron gas and of coherently excited phonons can be accessed in a single experiment. As a major result the phase lag between the coherent phonons and the modulation of the electronic structure can be determined with high precision. The phonon phase lag with respect to the modulation of the electronic structure is about 2.85±0.21 rad, thus significantly smaller than π. The difference is not due to phonon decay by energy dissipation into low-energy modes, but rather caused by the very early evolution of the highly excited electron distribution. [ABSTRACT FROM AUTHOR]

The surface segregation profile of an intermetallic compound becomes vertically and laterally modulated upon epitaxial growth of a single-layer hexagonal boron nitride (h-BN) nanomesh. h-BN on PtRh(111) forms an 11-on-10 superhoneycomb, such as that on Rh(111) [Corso et al., Science 303, 217 (2004)], though with a smaller lattice constant of 2.73 nm. X-ray photoelectron diffraction shows that the h-BN layer reduces the Pt enrichment of the first layer by promoting site swapping of about 10 Pt-Rh pairs within the 10?10 unit cell between the first and second layers. This segregation profile is confirmed by density-functional-theory-based cluster-expansion calculations. Generally, a strong modulation of the h-BN bonding strength and a higher affinity to one of the constituents leads to self-assembly of top layer patches underneath the nanomesh pores. [ABSTRACT FROM AUTHOR]

Abstract: The hexagonal boron-nitride ‘nanomesh’ surface reconstruction on Rh(111) [Corso et al., Science 303 (2004) 217–220] has been investigated using surface X-ray diffraction utilizing synchrotron radiation. This unique structure has been found to be stable under ambient atmosphere which provides an important basis for technological applications like templating and coating. The previously suggested (12×12) periodicity of this reconstruction has been unambiguously confirmed and structural features are discussed in the light of the X-ray diffraction results. [Copyright &y& Elsevier]