Graphene as a Mechanically Active, Deformable Two-Dimensional Surfactant

In crystal growth, surfactants are additive molecules used in dilute amount or as dense, permeable layers to control surface morphologies. We investigate the properties of a strikingly different surfactant: a 2D and covalent layer with close atomic packing, graphene. Using in situ, real-time electron microscopy, scanning tunneling microscopy, kinetic Monte Carlo simulations, and continuum mechanics calculations, we reveal why metallic atomic layers can grow in a 2D manner below an impermeable graphene membrane. Upon metal growth, graphene dynamically opens nanochannels called wrinkles, facilitating mass transport while at the same time storing and releasing elastic energy via lattice distortions. Graphene thus behaves as a mechanically active, deformable surfactant. The wrinkle-driven mass transport of the metallic layer intercalated between graphene and the substrate is observed for two graphene-based systems, characterized by different physicochemical interactions, between graphene and the substrate and between the intercalated material and graphene. The deformable surfactant character of graphene that we unveil should then apply to a broad variety of species, opening new avenues for using graphene as a 2D surfactant forcing the growth of flat films, nanostructures, and unconventional crystalline phases.

Modificazioni Indotte Dall'1–4 Dimetansulfonossibutano SUL Quadro Istologico del Testicolo di MUS Musculus Albinus

Testes of albino mice treated with 1–4 dimethansulfonoxybutane for different periods (15 and 30 days) and with different doses (25-50-100 γ) have been histologically studied. After 15 days treatment unsignificant lesions were observed independently of the employed dose, while after 30 days the seminiferous epithelium had disappeared and azoospermia with remarkable hyperplasia of the leydighian system were noticed. On the basis of the results obtained some considerations are exposed.

Rothmund-Thomson Syndrome: Insights from New Patients on the Genetic Variability Underpinning Clinical Presentation and Cancer Outcome

Biallelic mutations in RECQL4 gene, a caretaker of the genome, cause Rothmund-Thomson type-II syndrome (RTS-II) and confer increased cancer risk if they damage the helicase domain. We describe five families exemplifying clinical and allelic heterogeneity of RTS-II, and report the effect of pathogenic RECQL4 variants by in silico predictions and transcripts analyses. Complete phenotype of patients #39 and #42 whose affected siblings developed osteosarcoma correlates with their c.[1048_1049del], c.[1878+32_1878+55del] and c.[1568G>C;1573delT], c.[3021_3022del] variants which damage the helicase domain. Literature survey highlights enrichment of these variants affecting the helicase domain in patients with cancer outcome raising the issue of strict oncological surveillance. Conversely, patients #29 and #19 have a mild phenotype and carry, respectively, the unreported homozygous c.3265G>T and c.3054A>G variants, both sparing the helicase domain. Finally, despite matching several criteria for RTS clinical diagnosis, patient #38 is heterozygous for c.2412_2414del; no pathogenic CNVs out of those evidenced by high-resolution CGH-array, emerged as contributors to her phenotype.

Electronic properties of single-layer tungsten disulfide on epitaxial graphene on silicon carbide

This work reports an electronic and micro-structural study of an appealing system for optoelectronics: tungsten disulfide (WS₂) on epitaxial graphene (EG) on SiC(0001). The WS₂ is grown via chemical vapor deposition (CVD) onto the EG. Low-energy electron diffraction (LEED) measurements assign the zero-degree orientation as the preferential azimuthal alignment for WS₂/EG. The valence-band (VB) structure emerging from this alignment is investigated by means of photoelectron spectroscopy measurements, with both high space and energy resolution. We find that the spin-orbit splitting of monolayer WS₂ on graphene is of 462 meV, larger than what is reported to date for other substrates. We determine the value of the work function for the WS₂/EG to be 4.5 ± 0.1 eV. A large shift of the WS₂ VB maximum is observed as well, due to the lowering of the WS₂ work function caused by the donor-like interfacial states of EG. Density functional theory (DFT) calculations carried out on a coincidence supercell confirm the experimental band structure to an excellent degree. X-ray photoemission electron microscopy (XPEEM) measurements performed on single WS₂ crystals confirm the van der Waals nature of the interface coupling between the two layers. In virtue of its band alignment and large spin-orbit splitting, this system gains strong appeal for optical spin-injection experiments and opto-spintronic applications in general.

Synthesis of Antimonene on Germanium

The lack of large-area synthesis processes on substrates compatible with industry requirements has been one of the major hurdles facing the integration of 2D materials in mainstream technologies. This is particularly the case for the recently discovered monoelemental group V 2D materials which can only be produced by exfoliation or growth on exotic substrates. Herein, to overcome this limitation, we demonstrate a scalable method to synthesize antimonene on germanium substrates using solid-source molecular beam epitaxy. This emerging 2D material has been attracting a great deal of attention due to its high environmental stability and its outstanding optical and electronic properties. In situ low energy electron microscopy allowed the real time investigation and optimization of the 2D growth. Theoretical calculations combined with atomic-scale microscopic and spectroscopic measurements demonstrated that the grown antimonene sheets are of high crystalline quality, interact weakly with germanium, exhibit semimetallic characteristics, and remain stable under ambient conditions. This achievement paves the way for the integration of antimonene in innovative nanoscale and quantum technologies compatible with the current semiconductor manufacturing.

Corrigendum: Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures

This corrects the article DOI: 10.1038/nnano.2015.315.

Subfilamentary Networks Cause Cycle-to-Cycle Variability in Memristive Devices

A major obstacle for the implementation of redox-based memristive memory or logic technology is the large cycle-to-cycle and device-to-device variability. Here, we use spectromicroscopic photoemission threshold analysis and operando XAS analysis to experimentally investigate the microscopic origin of the variability. We find that some devices exhibit variations in the shape of the conductive filament or in the oxygen vacancy distribution at and around the filament. In other cases, even the location of the active filament changes from one cycle to the next. We propose that both effects originate from the coexistence of multiple (sub)filaments and that the active, current-carrying filament may change from cycle to cycle. These findings account for the observed variability in device performance and represent the scientific basis, rather than prior purely empirical engineering approaches, for developing stable memristive devices.

Comparing Fourier optics and contrast transfer function modeling of image formation in low energy electron microscopy

A theoretical understanding of image formation in cathode lens microscopy can facilitate image interpretation. We compare Fourier Optics (FO) and Contrast Transfer Function (CTF) approaches that were recently adapted from other realms of microscopy to model image formation in low energy electron microscopy (LEEM). Although these two approaches incorporate imaging errors from several sources similarly, they differ in the way that the image intensity is calculated. The simplification that is used in the CTF calculation advantageously leads to its computational efficiency. However, we find that lens aberrations, and spatial and temporal coherence may affect the validity of the CTF approach to model LEEM image formation under certain conditions. In particular, these effects depend strongly on the nature of the object being imaged and also become more pronounced with increasing defocus. While the use of the CTF approach appears to be justified for objects that are routinely imaged with LEEM, comparison of theory to experimental observations of a focal image series for rippled, suspended graphene reveals one example where FO works, but CTF does not. This work alerts us to potential pitfalls and guides the effective use of FO and CTF approaches. It also lays the foundation for quantitative image evaluation using these methods.

Controlling second-harmonic generation at the nanoscale with monolithic AlGaAs-on-AlOx antennas

We review recent achievements in the field of nanoscale nonlinear AlGaAs photonics based on all-dielectric optical antennas. After discussing the motivation and main technological challenges for the development of an AlGaAs monolithic platform for χ ⁽²⁾ nonlinear nanophotonics, we present numerical and experimental investigations of the second-order nonlinear response and physical reasons for high efficiency of second-order nonlinear interactions in the AlGaAs nano-antennas. In particular, we emphasize the role of the dipolar resonances at the fundamental frequency and the multipolar resonances at the second harmonic wavelength. We also discuss second-harmonic generation directionality and show possible strategies to engineer the radiation pattern of nonlinear antennas.

Polarization properties of second-harmonic generation in AlGaAs optical nanoantennas

Manipulating light at the nanoscale by means of dielectric nanoantennas recently received renewed attention thanks to the development of key enabling fabrication tools in semiconductor technology, combined with the extremely low losses exhibited by dielectrics in the optical regime. Nanostructures based on III-V type semiconductors, characterized by an intrinsic broken symmetry down to a single elementary cell, has already demonstrated remarkable nonlinear conversion efficiencies at scales well below the operating wavelength. In this Letter, we thoroughly investigate the emission properties of second-harmonic generation (SHG) in AlGaAs monolithic nanoantennas. Our findings point toward the pivotal role of volume susceptibility in SHG, further unraveling the physics behind the nonlinear processes in these systems. The extremely high SHG efficiency attained, together with the control over the polarized emission in these nanoantennas, constitute key ingredients for the development of tunable nonlinear metasurfaces.

Monolithic AlGaAs second-harmonic nanoantennas

We demonstrate monolithic aluminum gallium arsenide (AlGaAs) optical nanoantennas. Using a selective oxidation technique, we fabricated epitaxial semiconductor nanocylinders on an aluminum oxide substrate. Second harmonic generation from AlGaAs nanocylinders of 400 nm height and varying radius pumped with femtosecond pulses delivered at 1554-nm wavelength has been measured, revealing a peak conversion efficiency exceeding 10^-5 for nanocylinders with an optimized geometry.

Growth and characterization of epitaxially stabilized ceria(001) nanostructures on Ru(0001)

We have studied (001) surface terminated cerium oxide nanoparticles grown on a ruthenium substrate using physical vapor deposition. Their morphology, shape, crystal structure, and chemical state are determined by low-energy electron microscopy and micro-diffraction, scanning probe microscopy, and synchrotron-based X-ray absorption spectroscopy. Square islands are identified as CeO2 nanocrystals exhibiting a (001) oriented top facet of varying size; they have a height of about 7 to 10 nm and a side length between about 50 and 500 nm, and are terminated with a p(2 × 2) surface reconstruction. Micro-illumination electron diffraction reveals the existence of a coincidence lattice at the interface to the ruthenium substrate. The orientation of the side facets of the rod-like particles is identified as (111); the square particles are most likely of cuboidal shape, exhibiting (100) oriented side facets. The square and needle-like islands are predominantly found at step bunches and may be grown exclusively at temperatures exceeding 1000 °C.

Fragmentation of magnetism in artificial kagome dipolar spin ice

Geometrical frustration in magnetic materials often gives rise to exotic, low-temperature states of matter, such as the ones observed in spin ices. Here we report the imaging of the magnetic states of a thermally active artificial magnetic ice that reveal the fingerprints of a spin fragmentation process. This fragmentation corresponds to a splitting of the magnetic degree of freedom into two channels and is evidenced in both real and reciprocal space. Furthermore, the internal organization of both channels is interpreted within the framework of a hybrid spin–charge model that directly emerges from the parent spin model of the kagome dipolar spin ice. Our experimental and theoretical results provide insights into the physics of frustrated magnets and deepen our understanding of emergent fields through the use of tailor-made magnetism.

By nanofabricating arrays of dipolar-coupled bistable single-domain nanomagnets, artificial model systems exhibiting collective ordering may be realized. Here, the authors present signatures of spin fragmentation in low-energy states of an artificial kagome ice.

Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures

Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometre size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetization at the nanoscale. Chiral skyrmion structures have so far been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films, and under an external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral Néel internal structure, which we explain as due to the large strength of the Dzyaloshinskii-Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions.

Coupling dynamics of 1D surface plasmon polaritons in hybrid graphene systems

We describe the coupling dynamics of one-dimensional surface plasmon polaritons supported by a pair of hetero-junctions between two-dimensional media. We first discuss the unique symmetry properties of the supermodes of such structures, and then we exploit the possibility of electrically tuning the conductivity of graphene to demonstrate tailoring and manipulation of light propagation in a graphene/graphene platform.

Fabrication of 2D Heterojunction in Graphene via Low Energy N2(+) Irradiation

Substitutional doping in graphene is locally induced with very low energy nitrogen ions. Irradiated and nonirradiated areas exhibit different charge carrier densities and are separated by a sharp boundary, stable up to 750 °C. The way towards lithographic control of the electronic properties of graphene by ion irradiation is paved, providing a proof of principle for the fabrication of 2D graphene-based heterojunctions.

Enhanced second-harmonic generation from magnetic resonance in AlGaAs nanoantennas

We designed AlGaAs-on-aluminium-oxide all-dielectric nanoantennas with magnetic dipole resonance at near-infrared wavelengths. These devices, shaped as cylinders of 400nm height and different radii, offer a few crucial advantages with respect to the silicon-on-insulator platform for operation around 1.55μm wavelength: absence of two-photon absorption, high χ((2)) nonlinearity, and the perspective of a monolithic integration with a laser. We analyzed volume χ((2)) nonlinear effects associated to a magnetic dipole resonance in these nanoantennas, and we predict second-harmonic generation exceeding 10(-3) efficiency with 1GW/cm(2) of pump intensity.

p53-dependent and p53-independent anticancer activity of a new indole derivative in human osteosarcoma cells

Osteosarcoma (OS) is the most common primary malignant tumor of bone, occurring most frequently in children and adolescents. The mechanism of formation and development of OS have been studied for a long time. Tumor suppressor pathway governed by p53 gene are known to be involved in the pathogenesis of osteosarcoma. Moreover, loss of wild-type p53 activity is thought to be a major predictor of failure to respond to chemotherapy in various human cancers. In previous studies, we described the activity of a new indole derivative, NSC743420, belonging to the tubulin inhibitors family, capable to induce apoptosis and arrest of the cell cycle in the G2/M phase of various cancer cell lines. However, this molecule has never been tested on OS cell line. Here we address the activity of NSC743420 by examine whether differences in the p53 status could influence its effects on cell proliferation and death of OS cells. In particular, we compared the effect of the tested molecule on p53-wild type and p53-silenced U2OS cells, and on SaOS2 cell line, which is null for p53. Our results demonstrated that NSC743420 reduces OS cell proliferation by p53-dependent and p53-independent mechanisms. In particular, the molecule induces proliferative arrest that culminate to apoptosis in SaOS2 p53-null cells, while it brings a cytostatic and differentiating effect in U2OS cells, characterized by the cell cycle arrest in G0/G1 phase and increased alkaline phosphatase activity.

Island Ripening via a Polymerization-Depolymerization Mechanism

In catalytic methanol oxidation on ultrathin vanadium oxide layers on Rh(111) (Θ_{V}≈0.2 monolayer equivalent) we observe a 2D ripening of the VO_{x} islands that is controlled by the catalytic reaction. Neighboring VO_{x} islands move under reaction conditions towards each other and coalesce. The motion and the coalescence of the islands are explained by a polymerization-depolymerization equilibrium that is sensitive to gradients in the adsorbate coverages.

Nanobubbles at GPa Pressure under Graphene

We provide direct evidence that irradiation of a graphene membrane on Ir with low-energy Ar ions induces formation of solid noble-gas nanobubbles. Their size can be controlled by thermal treatment, reaching tens of nanometers laterally and height of 1.5 nm upon annealing at 1080 °C. Ab initio calculations show that Ar nanobubbles are subject to pressures reaching tens of GPa, their formation being driven by minimization of the energy cost of film distortion and loss of adhesion.

Mode matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation

Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear nanoscale sources, approaches that enhance the electromagnetic field intensity and counter the lack of phase matching in nanoplasmonic systems are often employed. However, the high degree of symmetry in the crystalline structure of plasmonic materials (metals in particular) and in nanoantenna designs strongly quenches second harmonic generation. Here, we describe doubly-resonant single-crystalline gold nanostructures with no axial symmetry displaying spatial mode overlap at both the excitation and second harmonic wavelengths. The combination of these features allows the attainment of a nonlinear coefficient for second harmonic generation of ∼5 × 10(-10) W(-1), enabling a second harmonic photon yield higher than 3 × 10(6) photons per second. Theoretical estimations point toward the use of our nonlinear plasmonic nanoantennas as efficient platforms for label-free molecular sensing.

Role of antenna modes and field enhancement in second harmonic generation from dipole nanoantennas

We study optical second harmonic generation from metallic dipole antennas with narrow gaps. Enhancement of the fundamental-frequency field in the gap region plays a marginal role on conversion efficiency. In the symmetric configuration, i.e., with the gap located at the center of the antenna axis, reducing gap size induces a significant red-shift of the maximum conversion efficiency peak. Either enhancement or inhibition of second-harmonic emission may be observed as gap size is decreased, depending on the antenna mode excited at the harmonic frequency. The second-harmonic signal is extremely sensitive to the asymmetry introduced by gap's displacements with respect to the antenna center. In this situation, second-harmonic light can couple to all the available antenna modes. We perform a multipolar analysis that allows engineering the far-field SH emission and find that the interaction with quasi-odd-symmetry modes generates radiation patterns with a strong dipolar component.

The bottom-up growth of edge specific graphene nanoribbons

The discovery of ballistic transport in graphene grown on SiC(0001) sidewall trenches has sparked an intense effort to uncover the origin of this exceptional conductivity. How a ribbon's edge termination, width, and topography influence its transport is not yet understood. This work presents the first structural and electronic comparison of sidewall graphene grown with different edge terminations. We show that armchair and zigzag terminated ribbons, grown from SiC, have very different topographies and interact differently with the substrate, properties that are critical to device architecture in sidewall ribbon electronics.

Reversible switching of in-plane polarized ferroelectric domains in BaTiO3(001) with very low energy electrons

The switchable bipolar ground state is at the heart of research into ferroelectrics for future, low-energy electronics. Polarization switching by an applied field is a complex phenomenon which depends on the initial domain ordering, defect concentration, electrical boundary conditions and charge screening. Injected free charge may also to be used to reversibly switch in-plane polarized domains. We show that the interaction between the initial domain order and the bulk screening provided by very low energy electrons switches the polarization without the collateral radiation damage which occurs when employing a beam of high energy electrons. Polarization switching during charge injection adds a new dimension to the multifunctionality of ferroelectric oxides.

Cathode lens spectromicroscopy: methodology and applications

The implementation of imaging techniques with low-energy electrons at synchrotron laboratories allowed for significant advancement in the field of spectromicroscopy. The spectroscopic photoemission and low energy electron microscope, SPELEEM, is a notable example. We summarize the multitechnique capabilities of the SPELEEM instrument, reporting on the instrumental aspects and the latest developments on the technical side. We briefly review applications, which are grouped into two main scientific fields. The first one covers different aspects of graphene physics. In particular, we highlight the recent work on graphene/Ir(100). Here, SPELEEM was employed to monitor the changes in the electronic structure that occur for different film morphologies and during the intercalation of Au. The Au monolayer, which creeps under graphene from the film edges, efficiently decouples the graphene from the substrate lowering the Dirac energy from 0.42 eV to 0.1 eV. The second field combines magnetism studies at the mesoscopic length scale with self-organized systems featuring ordered nanostructures. This example highlights the possibility to monitor growth processes in real time and combine chemical characterization with X-ray magnetic circular dichroism-photoemission electron microscopy (XMCD-PEEM) magnetic imaging by using the variable photon polarization and energy available at the synchrotron source.

Growth, reaction and nanowire formation of Fe on the ZnS(1 0 0) surface

The growth and reaction of Fe on a ZnS(1 0 0) substrate are studied in situ and with high lateral resolution using low energy electron microscopy (LEEM), micro low energy electron diffraction ( μLEED), x-ray photoemission electron microscopy (XPEEM), microprobe x-ray photoelectron spectroscopy ( μXPS) and x-ray magnetic circular dichroism PEEM (XMCDPEEM) for complementary structural, chemical, and magnetic characterization. Initially, a two-dimensional (Fe, Zn)S reaction layer forms with thickness that depends on growth temperature. Further growth results in the formation of a variety of three-dimensional crystals, most of them strongly elongated in the form of 'nanowires' of two distinct types, labeled as A and B. Type A nanowires are oriented near the ZnS[1 1 0] direction and are composed of Fe. Type B nanowires are oriented predominantly along directions a few degrees off the ZnS[0 0 1] direction and are identified as Greigite (Fe3S4). Both types of nanowires are magnetic with Curie temperatures above 450 °C. The understanding of the reactive growth mechanism in this system that is provided by these investigations may help to develop growth methods for other elemental and transition metal chalcogenide nanostructures on ZnS and possibly on other II-VI semiconductor surfaces.

Size distribution of magnetic charge domains in thermally activated but out-of-equilibrium artificial spin ice

A crystal of emerging magnetic charges is expected in the phase diagram of the dipolar kagomé spin ice. An observation of charge crystallites in thermally demagnetized artificial spin ice arrays has been recently reported by S. Zhang and coworkers and explained through the thermodynamics of the system as it approaches a charge-ordered state. Following a similar approach, we have generated a partial order of magnetic charges in an artificial kagomé spin ice lattice made out of ferrimagnetic material having a Curie temperature of 475 K. A statistical study of the size of the charge domains reveals an unconventional sawtooth distribution. This distribution is in disagreement with the predictions of the thermodynamic model and is shown to be a signature of the kinetic process governing the remagnetization.

Coexistence of multiple silicene phases in silicon grown on Ag(1 1 1)

Silicene, the silicon equivalent of graphene, is attracting increasing scientific and technological attention in view of the exploitation of its exotic electronic properties. This novel material has been theoretically predicted to exist as a free-standing layer in a low-buckled, stable form, and can be synthesized by the deposition of Si on appropriate crystalline substrates. By employing low-energy electron diffraction and microscopy, we have studied the growth of Si on Ag(1 1 1) and observed a rich variety of rotationally non-equivalent silicene structures. Our results highlight a very complex formation diagram, reflecting the coexistence of different and nearly degenerate silicene phases, whose relative abundance can be controlled by varying the Si coverage and growth temperature. At variance with other studies, we find that the formation of single-phase silicene monolayers cannot be achieved on Ag(1 1 1).

Tuning of surface plasmon polaritons beat length in graphene directional couplers

We investigate the tuning of the coupling of surface plasmon polaritons between two spatially separated graphene layers. We demonstrate that by slightly changing the chemical potential, a graphene coupler can switch from the bar to the cross state; as a consequence, the coupling coefficient in such structures can be easily controlled by means of an applied electrical signal.

[Ocular manifestations in chronic granulomatous disease]

Chronic granulomatous disease (CGD) is a rare genetic immune deficiency due to defective oxygen metabolism in phagocytic cells. It results in recurrent severe bacterial and fungal infections in patients from an early age on. Inflammatory lesions are also observed, with the formation of granulomas. Diagnosis relies on the demonstration of a deficiency in the oxidative properties of phagocytes. Pulmonary infections are the most frequent clinical manifestations of the disease, yet all organs can be involved, such as the eye, with either infections or inflammatory chorioretinal lesions. The treatment of CGD relies on prophylaxis to avoid infections, and on the rapid management of infectious and inflammatory episodes. The only cure to date is allogenetic bone marrow transplant, which requires a compatible donor and can only be considered in certain clinical situations.

Temperature-driven reversible rippling and bonding of a graphene superlattice

In order to unravel the complex interplay between substrate interactions and film configuration, we investigate and characterize graphene on a support with non-three-fold symmetry, the square Ir(100). Below 500 °C, distinct physisorbed and chemisorbed graphene phases coexist on the surface, respectively characterized by flat and buckled morphology. They organize into alternating domains that extend on mesoscopic lengths, relieving the strain due to the different thermal expansion of film and substrate. The chemisorbed phase exhibits exceptionally large one-dimensional ripples with regular nanometer periodicity and can be reversibly transformed into physisorbed graphene in a temperature-controlled process that involves surprisingly few C-Ir bonds. The formation and rupture of these bonds, rather than ripples or strain, are found to profoundly alter the local electronic structure, changing graphene behavior from semimetal to metallic type. The exploitation of such subtle interfacial changes opens new possibilities for tuning the properties of this unique material.

Spectromicroscopy of pulses transporting alkali metal in a surface reaction

The NO + H2 reaction on a potassium promoted Rh(110) surface is shown to sustain the formation of spatio-temporal periodic patterns leading to mass transport phenomena. The excitation of pulses and the mass transport mechanism are studied in the 10(-7) and 10(-6) mbar pressure range, with the potassium coverage varying between θK = 0.05 and θK = 0.12 ML. Using spectroscopic photoemission and spectroscopic low energy electron microscopy (SPELEEM) as well as related microprobe diffraction techniques, we show that the excitation mechanism comprises a cyclic structural transformation: K + O-coadsorbate → (2 × 1)-N → c(2 × 4)-2O,N → K + O coadsorbate. Laterally resolved spectroscopy demonstrates that potassium is accumulated in front of the nitrogen pulses, suggesting that adsorbed nitrogen acts as a diffusion barrier for potassium.

The effect of magnetic anisotropy on the spin configurations of patterned La(0.7)Sr(0.3)MnO3 elements

We study the effect of magnetocrystalline anisotropy on the magnetic configurations of La0.7Sr0.3MnO3 bar and triangle elements using photoemission electron microscopy imaging. The dominant remanent state is a low energy flux-closure state for both thin (15 nm) and thick (50 nm) elements. The magnetocrystalline anisotropy, which competes with the dipolar energy, causes a strong modification of the spin configuration in the thin elements, depending on the shape, size and orientation of the structures. We investigate the magnetic switching processes and observe in triangular shaped elements a displacement of the vortex core along the easy axis for an external magnetic field applied close to the hard axis, which is well reproduced by micromagnetic simulations.

LEEM image phase contrast of MnAs stripes

Low energy electron microscopy (LEEM) imaging of strained MnAs layers epitaxially grown on GaAs(001) reveals striped contrast features that become more pronounced and vary systematically in width with increasing defocus, but that are completely absent in focus. Weaker subsidiary fringe-like features are observed along the stripe lengths, while asymmetric contrast reversal occurs between under-focus and over-focus conditions. A Fourier optics calculation is performed that demonstrates that these unusual observations can be attributed to a phase contrast mechanism between the hexagonal α phase and orthorhombic β phase regions of the MnAs film, which self-organize into a periodic stripe array with ridge-groove morphology. The unequal widths of the α and β phase regions are determined accurately from the through focus series, while the height variation in this system can also be determined in principle from the energy dependence of contrast.

Graphene sustained nonlinear modes in dielectric waveguides

We discuss the existence of nonlinear modes sustained by graphene layers in dielectric waveguides. Taking advantage of the almost two dimensional nature of graphene, we introduce the nonlinear effect as a parameter in the continuity equations. We then apply our modeling to a simple slab waveguide to enlighten how graphene can be used to induce huge nonlinear phase shifts at easily accessible power levels.

Fine tuning of graphene-metal adhesion by surface alloying

We show that bimetallic surface alloying provides a viable route for governing the interaction between graphene and metal through the selective choice of the elemental composition of the surface alloy. This concept is illustrated by an experimental and theoretical characterization of the properties of graphene on a model PtRu surface alloy on Ru(0001), with a concentration of Pt atoms in the first layer between 0 and 50%. The progressive increase of the Pt content determines the gradual detachment of graphene from the substrate, which results from the modification of the carbon orbital hybridization promoted by Pt. Alloying is also found to affect the morphology of graphene, which is strongly corrugated on bare Ru, but becomes flat at a Pt coverage of 50%. The method here proposed can be readily extended to several supports, thus opening the way to the conformal growth of graphene on metals and to a full tunability of the graphene-substrate interaction.

Graphene-assisted control of coupling between optical waveguides

The unique properties of optical waveguides electrically controlled by means of graphene layers are investigated. We demonstrate that, thanks to tunable losses induced by graphene layers, a careful design of silicon on silica ridge waveguides can be used to explore passive PT-symmetry breaking in directional couplers. We prove that the exceptional point of the system can be probed by varying the applied voltage and we thus propose very compact photonic structures which can be exploited to control coupling between waveguides and to tailor discrete diffraction in arrays.

Hypertension negatively affects the pregnancy outcome in patients with antiphospholipid syndrome

The impact of hypertension in the pregnancies from autoimmune patients is not unequivocally defined. We have prospectively followed 168 pregnancies from 135 patients from four Italian centres to verify the potential impact of hypertension in the antiphospholipid syndrome (APS). The rate of preeclampsia, mean neonatal weight and gestational age at delivery were significantly lower in patients with both APS and hypertension than in patients with hypertension or APS alone. This information may be relevant for counselling and care of these patients.

Barrett's esophagus: surgical treatments

The following on surgical treatments for Barrett's esophagus includes commentaries on the indications for antireflux surgery after medical treatment; the effects of the various procedures on the lower esophageal sphincter; the role of impaired esophageal motility and delayed gastric emptying in the choice of the surgical procedure; indications for associated highly selective vagotomy, duodenal switch, and gastric electrical stimulation; therapeutic strategies for detection and treatment of shortened esophagus; the role of antireflux surgery on the regression of metaplastic mucosa and the risk of malignant progression; the detection of asymptomatic reflux brfore bariatric surgery; the role of non-GERD symptoms on the results of surgery; and the indications of Collis gastroplasty and choice of the type of fundoplication.

Valence band circular dichroism in non-magnetic Ag/Ru(0001) at normal emission

For the non-magnetic system of Ag films on Ru(0001), we have measured the circular dichroism of photoelectrons emitted along the surface normal, the geometry typically used in photoemission electron microscopy. Photoemission spectra were acquired from micrometer-sized regions having uniformly thick Ag films on a single, atomically flat Ru terrace. For a single Ag layer, we find a circular dichroism that exceeds 6% at the d-derived band region around 4.5 eV binding energy. The dichroism decreases as the Ag film thickness increases to three atomic layers. We discuss the origin of the circular dichroism in terms of the symmetry lowering that can occur even in normal emission.