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New angle-resolved photoelectron spectroscopy (ARPES) data, recorded at several different photon energies from the Si(111)(7 × 7) surface, show that the well-known S1 and S2 surface states that lie in the bulk band gap are localised at specific (adatom and rest atom) sites on the reconstructed surface. The variations in the photoemission intensity from these states as a function of polar and azimuthal emission angle, and incident photon energy, are not consistent with Fermi surface mapping but are well-described by calculations of the multiple elastic scattering in the final state. This localisation of the most shallowly bound S1 state is consistent with the lack of significant dispersion, with no evidence of Fermi surface crossing, implying that the surface is not, as has been previously proposed, metallic in character. Our findings highlight the importance of final state scattering in interpreting ARPES data, an aspect that is routinely ignored and can lead to misleading conclusions.

Our group has revealed an unprecedented one-dimensional (1D) Si atomic arrangement solely comprising highly perfect alternating pentagons residing in the missing row troughs of the reconstructed surface Ag(1 1 0). It is the first pure pentagonal phase ever found for silicon low-dimensional structures, initially theoretically supported by density functional theory (DFT) calculations compared to scanning tunneling microscopy observations, further rapidly confirmed by surface X-ray diffraction measurements. In fact, until now such a structure has only been obtained synthetically as 1D nanoribbons (1D-NRs) grown on a silver (1 1 0) substrate. These NRs adopt a highly ordered chiral arrangement in single- and/or double-strands. We thus simultaneously demonstrate the existence of penta-silicene, a recently conjectured novel pentagonal silicon allotrope, which remained unveiled for more than one decade, and which materializes a paradigmatic shift from normal hexagonal silicene. The discovery of 1D-penta-silicene NRs increases the chances of the future isolation of this new low-dimensional Si allotrope, provided these epitaxial NRs can be detached from the silver surface.

Here we report low secondary electron emission yields of a nanostructured graphite and metal-dielectric composites coatings of high aspect ratio deposited on aluminium substrates. In this work, the reduction of SEY due to charging of dielectric domains embedded in conducting surfaces is also studied. The charging of the dielectric domains of these composites inhibits most of the secondary emission from the surface, which still keeps its conductive properties. The SEY as a function of the primary electron energy curves of the nanostructured coatings show SEY

The reduction of the total secondary electron emission during electron-matter interactions is required to improve the maximum power limit of the vacuum RF equipments prone to multipactor discharge. In this work, a chemical deposition technique was developed to create the appropriate micron or submicron surface roughness to significantly improve the typical characteristics of the flat silver coatings used for high-power microwave devices for space applications. Rough silver coated RF filters with a high surface aspect ratio, >3, was achieved. It is found that the secondary electron emission yield (SEY) remains lower than 1 throughout the primary electron energy range and therefore multipactor electron avalanche is avoided. The influence of aging on the multipactor discharge is also drastically reduced in rough silver coatings. An experimental linear correlation was found between the multipactor power level and the minimum interaction energy for which the number of incident and emitted electrons is equal.

[EN] The interaction of ionizing radiation with matter is of critical importance in numerous areas of science and technology like space and vacuum technology and even medicine and biotechnology. Secondary electron emission is a consequence of electron irradiation on materials. We achieve extremely low secondary electron emission yield values smaller than 0.2, even up to incident electron energies ~1 keV, due to an undocumented synergy between neighbouring metal and dielectric domains in composite samples. To investigate this experimental discovery, we propose a simple 3D model where the dielectric and metallic domains are arranged in parallel and interleaved. The proposed surface profile has a triangular shape to model the surface roughness. We obtain a continuous equation to describe the electric field that arises between grounded conductors and charged dielectrics domains. The calculated trajectories of secondary electrons in this 3D geometry are used to predict dynamic secondary emission yield, which strongly depends on the charge accumulated in the dielectric domains. This research paves the way to design new materials of low secondary emission yield, addressing the technological problem not yet resolved to inhibit the electron avalanche in RF equipment that limit their maximum working power., This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness of Spain under “Programa Estatal de Fomento de la Investigación Científica y Técnica de Excelencia”. Projects No ESP2015- 67842-P, RTI2018-095903-B-I00 and AYA2012-39832-C02-01. L.O. acknowledge support from the Spanish Ministry of Economy, Industry and Competitiveness, No BES-2013-063612

Monolayer germanene, a novel graphene-like germanium allotrope akin to silicene has been recently grown on metallic substrates. Lying directly on the metal surfaces the reconstructed atom-thin sheets are prone to lose the massless Dirac fermion character and unique associated physical properties of free standing germanene. Here, we show that few layer germanene, which we create by dry epitaxy on a gold template, possesses Dirac cones thanks to a reduced interaction. This finding established on synchrotron-radiation-based photoemission, scanning tunneling microscopy imaging and surface electron diffraction places few layer germanene among the rare two-dimensional Dirac materials. Since germanium is currently used in the mainstream Si-based electronics, perspectives of using germanene for scaling down beyond the 5 nm node appear very promising. Other fascinating properties seem at hand, typically the robust quantum spin Hall effect for applications in spintronics and the engineering of Floquet Majorana fermions by light for quantum computing., Funding from the 2D NANOLATTICES project within the 7th Framework Programme for Research of the European Commission, under FET-Open grant number 270749 has been greatly appreciated. M.E.D. acknowledges support from the Projects No. AYA2012-39832-C02-01and 02 of MINECO of Spain.

Objetivo Determinar las manifestaciones orales y caries dental en ninos expuestos al virus de inmunodeficiencia humana (VIH). Metodos Se estudiaron 37 ninos que acuden a la consulta pediatrica del programa nacional de control de SIDA (PRONASIDA-Lara). Se informo a padres y representantes sobre los objetivos del estudio y su caracter confidencial. El examen de la cavidad oral lo realizo un odontologo, quien ademas indago sobre historia de manifestaciones bucales y corroboro la informacion con la historia clinica. Resultado La edad promedio fue 5,15±3,79 anos, 62,2 % era del genero masculino. Se infectaron por trasmision vertical 91,8 %. La mayoria de los ninos pertenecian a la categoria clinica A (35,1 %). El mayor porcentaje (37,8 %) de ninos se encontro en la categoria 15-24 % de linfocitos CD4. Entre las manifestaciones orales mas prevalentes se encontro la candidiasis oral, queilitis angular, eritema gingival lineal y parotiditis. Se observo diferencia estadisticamente significativa entre el porcentaje de linfocitos CD4 y queilitis angular (p

Objetivo Con el propósito de determinar el nivel de conocimiento (NC) que sobre la Influenza A (H1N1) 2009 tienen las personas en el municipio Iribarren del Estado Lara, se realizó una investigación descriptiva transversal. Metodología La población estuvo constituida por 1 800 personas. La muestra la conformaron 665 personas quienes fueron divididas en tres grupos: grupo I: 300 alumnos; grupo II: 141 profesores y personal administrativo y grupo III conformado por 224 miembros de la comunidad. Se aplicó un instrumento con preguntas sobre la gripe AH1N1, modo de transmisión, prevención y control. Resultados Los resultados muestran que la edad promedio de los participantes fue 25,19± 13,88; 54,4 % eran varones. Setenta y tres coma siete por ciento (73,3 %) reportó NC “Regular”. Al analizar el NC sobre modo de trasmisión se observó que 66,8 % reporta un NC “Deficiente”. Se observó diferencia estadísticamente significativa entre el NC y los grupos en estudio. El análisis no paramétrico de Kruskal Walis reportó diferencia estadísticamente significativa entre los grupos en estudio y el valor promedio del NC. Conclusiones Los hallazgos del estudio, corroboran que es necesario reforzar las estrategias de difusión de la información sobre la Influenza A (H1N1) 2009. Por otra parte, se hace necesario continuar con las medidas de control y prevención impartidas por las autoridades de salud para reducir el riesgo a contagio de la enfermedad.

Carbon and silicon pentagonal low-dimensional structures attract a great interest as they may lead to new exotic phenomena such as topologically protected phases or increased spin–orbit effects. However, no pure pentagonal phase has yet been realized for any of them. Here we unveil through extensive density functional theory calculations and scanning tunnelling microscope simulations, confronted to key experimental facts, the hidden pentagonal nature of single- and double-strand chiral Si nano-ribbons perfectly aligned on Ag(110) surfaces whose structure has remained elusive for over a decade. Our study reveals an unprecedented one-dimensional Si atomic arrangement solely comprising almost perfect alternating pentagons residing in the missing row troughs of the reconstructed surface. We additionally characterize the precursor structure of the nano-ribbons, which consists of a Si cluster (nano-dot) occupying a silver di-vacancy in a quasi-hexagonal configuration. The system thus materializes a paradigmatic shift from a silicene-like packing to a pentagonal one., The atomic structure of Si nanoribbons on metallic surfaces has been disputed for years and yet remained elusive. Here, the authors unveil the nature of aligned Si nanoribbons on Ag(110), shifting the focus from a hexagonal silicene-like arrangement to a 1D phase solely comprising Si pentagons.

The electronic band structure of different types of graphite samples have been investigated in order to identify the origin of non-dispersive density of states recently reported in the literature. A systematic series of synchrotron radiation angle resolved photoemission spectroscopy (ARPES) measurements on graphite single crystal, highly oriented graphite (HOPG) and epitaxial grown graphite single crystal on 6H–SiC(0 0 0 1) samples, have been carried out as well as compared with theoretical tight binding calculations. Our results indicate that these localized states are present in all the graphite-investigated samples showing the same non-dispersive character and at the same binding energies. The photoemission data taken at several photon energies demonstrate that these states are not surface states nor due to indirect photoemission processes. It seems that they are closely related to the level of impurities present in the studied samples.

Thermogravimetry, X-ray and electron diffraction and high resolution electron microscopy show that the reduction process from perovskite La0.5Ca0.5MnO3 to brownmilleriteLa0.5Ca0.5MnO2.5 is a reversible topotactic process. Two series of monophasic La0.5Ca0.5MnO3–δ oxygen-deficient perovskites were stabilized in the 0 ≤ δ ≤ 0.12 range, either from reduction of La0.5Ca0.5MnO3 or oxidation of La0.5Ca0.5MnO2.5. Soft X-ray absorption spectroscopy shows that Mn oxidation states differ as a function of the synthetic pathway. Temperature dependence of the magnetization as a function of anionic vacancies concentration at constant doping level are reported together with the evolution of high-resolution O K-edge and Mn L-edge spectra. Our results show dramatic changes in the magnetic behaviour due to the stabilization of different Mn oxidation states.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The realization of the first Field Effect Transistors operating at room temperature, based on a single layer silicene channel, open up highly promising perspectives, e.g., typically, for applications in digital electronics. Here, we describe recent results on the growth, characterization and electronic properties of novel synthetic two-dimensional materials beyond graphene, namely silicene and germanene, its silicon and germanium counterparts., Conference paper presented at the SPIE DEFENSE + SECURITY, held on April 20-24th, 2015, in Baltimore, Maryland, United States.

Atomically thin 2D materials are emerging as a new frontier of materials science. They offer ultimate thickness scaling for nanoelectronic devices that could substantially improve electrostatic control and enable a number of low-power versatile applications, such as ultra-thin-channel field-effect transistors, optoelectronic devices, and solar cells.1 Graphene, the archetypal 2D material, cannot be used in conventional transistor technology because of the inherent difficulty of opening an electronic bandgap in this gapless material. Typically, the chalcogenides (that is, sulfides, selenides, and telluride), with bandgaps comparable to those of conventional group IV or group III–V semiconductors, may have the potential of scaling down to a truly atomic scale. However, in practice these materials are challenging to integrate with existing silicon-based electronics.

A large set of highly oriented graphite (HOPG) samples with different degree of defects has been studied according to their transport properties. The samples showed a dramatic decrease of their conductivity as the degree of defects is increased. For extreme cases, well-ordered HOPG samples displayed a metallic behavior as a function of the temperature, while poorly ordered samples exhibited a reversible semiconductor dependence of their conductivity as a function of temperature changes. Focusing on those samples with either a net metallic or semiconductor behavior, we have carried out a systematic study of their valence band structure by using angle resolved photoemission spectroscopy (ARPES). For those two types of samples, our results reveal an apparent difference of the density of states very close to the Fermi level. Samples with metallic character, show an additional electronic state at the Fermi level, which is quenched, as a higher disorder degree is present.

Two series of oxygen deficient perovskites with composition La 0.5 Ca 0.5 MnO 3− δ have been prepared by different synthetic routes. Magnetic measurements indicate that samples with same degree of anionic vacancies (identical δ value) have different behavior. A systematic study of a large set of samples shows that depending on the synthesis protocol followed to induce the anionic vacancies different species of manganese can be stabilized. To confirm this assumption, a detailed XANES study has been carried out together with X-ray diffraction, electron diffraction and thermogravimetric analysis, for a large set of samples. Our results indicate the coexistence of Mn 2+ , Mn 3+ and Mn 4+ species for those samples obtained from a La 0.5 Ca 0.5 MnO 2.5 parent compound. However, only Mn 3+ and Mn 4+ species are stabilized when the synthesis is based on direct reduction of La 0.5 Ca 0.5 MnO 3 . Reduction and oxidation mechanism and magnetic properties are discussed as a function of the Mn oxidation states.

Upon deposition of silicon onto the (1 1 0) surface of a silver crystal we have grown massively parallel one-dimensional Si nanowires. They are imaged in scanning tunnelling microscopy as straight, high aspect ratio, nanostructures, all with the same characteristic width of 16 A, perfectly aligned along the atomic troughs of the bare surface. Low energy electron diffraction confirms the massively parallel assembly of these self-organized nanowires. Photoemission reveals striking quantized states dispersing only along the length of the nanowires, and extremely sharp, two-components, Si 2p core levels. This demonstrates that in the large ensemble each individual nanowire is a well-defined quantum object comprising only two distinct silicon atomic environments. We suggest that this self-assembled array of highly perfect Si nanowires provides a simple, atomically precise, novel template that may impact a wide range of applications.

In this article, we review some of the most recent progress and understanding in the low temperature surface phase transitions at prototypical metal-semiconductor interfaces. We essentially focus on quantitative surface structural information obtained by using a significant variety of specialised techniques for the individual phases of a model system, namely, tin on Ge(1 1 1) substrates. The strengths and limitations of the structural results obtained by using scanning tunnelling microscopy, photoelectron diffraction and surface X-ray diffraction are discussed in relation to their support with respect to possible mechanisms recently invoked in the literature as being at the origin of the phase transition. These investigations show that a large progress has been made in this field, taking into account the very valuable experimental and theoretical contributions provided by different groups. There remain, however, essential unresolved problems, which will be analysed in the light of the limitations of these structural methods and the difficulty presented by the complex adsorbate systems studied.

Reflection high energy electron diffraction (RHEED) and synchrotron radiation photoemission spectroscopy (SRPES) have been used to investigate the evolution of the crystallinity and interface reaction of Co thin films deposited on Sb/GaAs(1 1 0). The RHEED images have allowed us to qualitative observe an improvement of the Co bcc crystal structure compared to the deposition on the bare substrate. Additionally, the use of high energy resolution synchrotron radiation photoemission spectroscopy has shown that the interdiffusion process behaves differently from that observed for the non-passivated surface.

We have examined, using angular scanned photoelectron diffraction (PED), the effect of the saturation of dangling bonds of Si(1 1 1) surfaces with atomic As on the Ag thin films growth. The intensity variation of the Ag 3d core-level was monitorised in a full emission cone of a 60° polar angle and a 360° azimuthal angle. From a detailed analysis of the intensity modulation patterns, we deduce that silver films grow following a Volmer–Weber mechanism, even at the very early stage of the interface formation. All investigated silver films show a good epitaxial growth, giving rise to the coexistence of two fcc (1 1 1) single crystal domains, which are rotated 60° from each other. A quantitative analysis shows that the As-mediated silver film growth promotes the preferential development of A-type domain.

We present in this article a comprehensive review of the dynamical fluctuations in the atomic positions that may take place, even at very low temperatures, at the clean silicon or germanium (100) surfaces or at their (111) surfaces decorated with Sn or Ag adatoms. We also elucidate the intriguing, hitherto unexplained differences observed between the two, seemingly similar, Sn/Si(111) and Sn/Ge(111) [Formula: see text] surfaces. We also describe the surprising behaviors of silver ultrathin films grown on different semiconductor surfaces, displaying in certain cases a bcc phase, a one-dimensional quasicrystalline superstructure and/or well-defined quantum size effects.

We have carried out simulations of the angle-scanned photoemission spectrum of Cu(1 0 0) within the framework of the one-step model at the He I energy of 21.2 eV for unpolarized photons. Comparison with the corresponding measurements reveals differences with respect to the theoretical predictions of our state-of-the-art computations. The main discrepancy is associated with the details of the Shockley type surface state, localized around the X symmetry point on Cu(1 0 0), which are not well described within our model. However, refinement of the potential in the surface region yields a good level of accord with the experimental results.

Objective To determine the knowledge of people living with HIV/AIDS (PLWHIV/AIDS) towards the disease. Methods A cross-sectional study was designed for a sample of 260 persons. A validated questionnaire, developed by the authors was used; it was structured into 35 questions regarding generalities and the mode of transmission of the disease. Results A high proportion of the participants were males (59.6 %), the mean age was 35.45±10.90 years, the median time of diagnosis of the participants was 3 years. 30 % of the participants had an elementary school educational level. 3.5 % had a "good" general knowledge. Statistically significant difference was observed between "deficient" and "fair" knowledge and educational level (p0.000). 10.5 % of the females did not know that "HIV is transmitted through breast feeding", however, a statistically significant difference was observed between genders (p0.009). 67.6 % did not know the most frequent opportunistic disease of the oral cavity among PLWHIV/AIDS. No statistically significant difference (p0.05) was observed between educational level and the knowledge about questions related to CD4 cells. Statistically significant difference was observed between time of diagnosis and breast feeding as mode of transmission. Conclusion There is a need to develop educational programs geared towards PLWHIV/AIDS in order to improve their knowledge towards the disease and their quality of life.

We present novel strategies for obtaining materials with low secondary electron emission under electron beam irradiation for advanced technological applications. Apart from the promising low secondary electron emission yield (SEY) of amorphous carbon coatings deposited on rough surfaces, graphene nanoplatelets are shown to be very effective in reducing the SEY even over flat substrates. Here, we report very low SEY from coatings of graphene platelets exposed to the air, indicating a 60% reduction of the SEY respect to the uncoated flat surfaces. The shape of the SEY curve as a function of primary energy looks like the inverted image of a typical SEY curve. © 2013 Elsevier B.V., This work was supported by the European Space Agency (ESA) and MICIIN of Spain Projects No. AYA2009-14736-C02-01 and AYA2009-14736-C02-02.

A scanned-energy mode photoelectron diffraction study has been conducted of the Ni(111)(2 × 2)O chemisorption phase using O 1s modulation spectra recorded in a range of different emission directions. The O atom is found to occupy the “fcc” hollow site, directly above third layer Ni atoms. The exact ONi outermost layer spacing and the possible magnitude of outermost substrate layer “rumpling” and lateral distortions have been investigated through comparisons with the results of multiple scattering theory calculations. The values obtained are compared with those given by several recent LEED studies, and the relative sensitivity of the two methods to some of these parameters is discussed. In particular, the problem of parameter-coupling in structure determination is investigated. The combination of the present results and those of the most recent LEED studies indicate that there is no significant lateral distortion of the outermost Ni layer.

The growth of Mn nanostructures on a 1D grating of silicon nano-ribbons is investigated at atomic scale by means of scanning tunneling microscopy, low energy electron diffraction and core level photoelectron spectroscopy. The grating of silicon nano-ribbons represents an atomic scale template that can be used in a surface-driven route to control the combination of Si with Mn in the development of novel materials for spintronics devices. The Mn atoms show a preferential adsorption site on silicon atoms, forming one-dimensional nanostructures. They are parallel oriented with respect to the surface Si array, which probably predetermines the diffusion pathways of the Mn atoms during the process of nanostructure formation. © 2013 IOP Publishing Ltd.

A detailed quantitative structure determination of the Ni(111)c(4 × 2)-CO structure has been undertaken using scanned energy mode photoelectron diffraction from the C 1s state over a wide range of emission angles. Analyses of these data by approximate direct methods, and by two independent multiple scattering trial-and-error fitting optimisations lead to a consistent structure in which the CO occupies both types of hollow site on the surface in equal amounts with a C-Ni top layer spacing of 1.29 ± 0.05 A. This structure is therefore essentially the same as that for Ni(111)c(4 × 2)-NO, and provides further evidence that simple use of the intramolecular stretching frequencies of such adsorbed molecules, which had been interpreted in both cases as indicative of bridge site adsorption, is not always a reliable indicator of local adsorption site.

High-resolution photoemission study of the valence-band electronic structure of AxC60 (A=K or Cs; x

Determining oral manifestations and dental caries amongst children exposed to the immunodeficiency virus (HIV).Thirty-seven (n=37) children attending the Colombian AIDS Control Program (PRONASIDA-Lara) pediatric service were studied. Parents and guardians were informed about the purpose of the study and its confidentiality. An oral examination was conducted by a dentist; parents/guardians were asked about their children's history of oral manifestations and this was corroborated with their clinical charts.The mean age was 5.15±3.79; 62.2 % were males. Ninety-eight point eight percent had become vertically infected. Most of the children were classified in the A immune suppression category (35.1 %). The highest percentage (37.8 %) of children were in the 15 %-24 % total CD4+ lymphocyte category. The most prevalent oral manifestations were oral candidiasis, angular cheilitis, linear gingival erythema and parotid enlargement. There was a significant statistical difference between percentages of CD4 lymphocytes and angular qualities (p0.05). Forty-five point nine percent had dental caries and 54.1 % were in "urgent" need of dental treatment. The Index of Orthodontic Treatment Need (IOTN) showed that ¾ of the children needed dental treatment.The results of the study led to concluding that there was a need for an oral manifestation management-based strategy focusing on clinical and preventative treatment, as oral manifestations are frequent in children suffering from HIV infection.

Although the C-O stretching frequency for the system Ni>{111}c(4>x2)-CO falls in the so-called bridge region, a structure determination with photoelectron diffraction shows that the CO molecules are actually adsorbed in threefold hollow sites. These, and other recent data, seriously call into question the practice of adsorption site assignment solely on the basis of the stretching frequency of an internal mode.

Descriptive research was conducted for determining the level of knowledge (LK) held by people from Iribarren in the state of Lara, Venezuela, regarding influenza A (H1N1) 2009.The population consisted of 1,800 people. The sample of 665 people was divided into groups: group 1 consisted of 300 high-school students, group 2 of 141 elementary school teachers, administrative personnel and white-collar workers and group 3 consisted of 224 people from the local community. A questionnaire containing questions about influenza A (H1N1)-2009, its mode of transmission prevention and control was applied.The results showed that participants' mean age was 25.19±13.88; 54.4 % were male. 73.3 % reported "fair" LK. When analyzing LK mode of transmission, 66.8 % reported "deficient" LK. A statistically significant difference was observed between LK and the groups being studied. The Kruskal-Wallis non-parametric test revealed a statistically significant difference between the groups being studied and average LK value.The study's findings confirmed that influenza A (H1N1)-2009 diffusion strategies should be reinforced. Health authorities' prevention and control measures should also be continued to reduce disease transmission risk.

Silicene, a monolayer of silicon atoms tightly packed into a two-dimensional honeycomb lattice, is the challenging hypothetical reflection in the silicon realm of graphene, a one-atom thick graphite sheet, presently the hottest material in condensed matter physics. If existing, it would also reveal a cornucopia of new physics and potential applications. Here, we reveal the epitaxial growth of silicene stripes self-aligned in a massively parallel array on the anisotropic silver (110) surface. This crucial step in the silicene gold rush could give a new kick to silicon on the electronics road-map and opens the most promising route towards wide-ranging applications. A hint of superconductivity in these silicene stripes poses intriguing questions related to the delicate interplay between paired correlated fermions, massless Dirac fermions and bosonic quasi-particules in low dimensions.

We review our recent discovery of silicene in the form of silicon nano-ribbons epitaxially grown on silver (1 1 0) or (1 0 0) surfaces, which paves the way for the growth of graphene-like sheets. We further draw some perspectives for this unique novel material upon mild hydrogenation.

Silicene, a monolayer of silicon atoms packed into a two-dimensional honeycomb lattice is the challenging hypothetical reflection in the silicon realm of graphene, a one-atom thick graphite sheet, presently the hottest new material in condensed matter physics and nanotechnology. If existing, it would also reveal a cornucopia of new physics and potential applications. Here, we reveal the catalytic growth of graphene-like silicon nano-ribbons self-aligned in a massively parallel array on the anisotropic Ag(110) surface. We compare with one-dimensional (1D) structures formed, more classically, the other way around, upon depositing gold or silver on the silicon (111) surface. Finally, we envisage wide ranging applications for these novel silicene stripes.

A descriptive investigation was conducted for determining the prevalence of dental caries amongst mentally retarded (MR) people and those suffering from Down's syndrome (DS).A special school located in Morán county in the State of Lara was visited. The inclusion criteria involved dental examination of 60 students and their parents/or the person responsible for them being interviewed.Participants' mean age was 14.5 +/- 8.17; 48.3% were from a blue collar level. Regarding oral health, 53.0% had dental caries, 51.7% being in the molars. Moderately MR people had the highest proportion of dental caries (75%). About 53% of the females and 46.2% of males, 644% and 31.9% of RM and DS participants had caries. 28.3% needed non-urgent dental treatment and 45% were using public dental health services.People suffering from MR and DS have precarious oral health; it is thus recommended that health programmes be created which are specifically directed towards these people.

One-dimensional Si quantum wires have been grown on silver single crystals upon deposition of ∼0.25 monolayer of Si on Ag(1 1 0) surfaces. Scanning tunneling microscopy (STM) clearly shows parallel 1D Si chains along the [−1 1 0] Ag crystallographic direction. Low Energy Electron Diffraction (LEED) confirms the massively parallel assembly of these selforganized Nanowires (NWs). We have characterized these nano-objects by measuring the dispersion of the NWs valence band at room temperature using Angle-Resolved PhotoEmission Spectroscopy (ARPES). Also, the Fermi Surface (FS) of the Ag(1 1 0) substrate has been mapped before and after the silicon deposition, trying to put in evidence the metallic or semiconductor character of the NWs silicon's states close to the Fermi level. Our results show the existence of well-defined quantum states associated to the silicon super-structure. Both LEED and ARUPS results confirm that the NWs have typical 1D features, however their metallic or semiconductor character could not be confirmed.

Objetivo Con el proposito de determinar la prevalencia de caries dental en personas con retraso mental (RM) y Sindrome de Down (SD) se realizo una investigacion descriptiva transversal. Metodos Se visito la escuela especial ubicada en el Municipio Moran, Estado Lara, Venezuela, la cual cumplia con los criterios de inclusion, se realizo el diagnostico de salud bucal de 60 alumnos y entrevisto a los padres y/o representantes. Resultados La edad promedio de los participantes fue de 14,5 ± 8,17 y 48,3 % pertenecen a la clase social obrero. En relacion con la salud bucal 53 % presentaba caries dental, de ellos 51,7 % en los molares. Las personas con RM moderado presentaron el mayor porcentaje de caries dental (75 %). Aproximadamente 53 % de las mujeres y 46,2 % de los varones, 64,4 % y 31,9 % de los participantes con RM y SD, tenian caries dental, respectivamente. Requerian tratamiento dental urgente 28,3 % de los participantes, y 45 % utilizaban los servicios odontologicos publicos. Conclusiones Las personas con RM y SD presentan una precaria salud bucal por lo que se recomienda la creacion de programas dirigidos a estas personas.

High resolution core level photoemission spectroscopy, photoelectron diffraction, and x-ray magnetic circular dicroism (XMCD) have been used to characterize the structural and magnetic properties of bcc-cobalt films grown on GaAs(110) substrates by using Sb as a surfactant. We have unambiguously disentangled the surfactant role played by the Sb which improves the crystallinity and reduces the lattice distortion of the metallic films as well as changes the interdiffusion process at the interface compared to the Co/GaAs(110) system. As a consequence of these combined effects, an improvement on the magnetic response of the grown Co thin films has been observed by XMCD measurements.

A quantitative analysis of the surface relaxation at the Yb(111) single-crystal films grown on W(110) has been undertaken applying energy-scan photoelectron diffraction technique using the two shifted components, i.e., surface and bulk of the lanthanide 4f core levels. Additional polar scans were recorded for a fixed photon energy along the crystal high-symmetry directions. The analysis of the data set following a trial and error fitting procedure confirmed a consistent fcc structure for all noncontaminated evaporated Yb films with the bulk lattice parameter corresponding to a value of a = (5.44′0.05) A, about 1% contracted respect to the bulk fcc Yb metal. A refinement of the structural analysis indicates an inward surface relaxation of the interlayer spacing for the first two top layers with respect to the bulk lattice parameter.

We have investigated the geometry and electronic structure of two different types of self-aligned silicon nanoribbons (SiNRs), forming either isolated SiNRs or a self-assembled 5 × 2/5 × 4 grating on an Ag(110) substrate, by scanning tunnelling microscopy and high resolution x-ray photoelectron spectroscopy. At room temperature we further adsorb on these SiNRs either atomic or molecular hydrogen. The hydrogen absorption process and hydrogenation mechanism are similar for isolated or 5 × 2/5 × 4 ordered SiNRs and are not site selective; the main difference arises from the fact that the isolated SiNRs are more easily attacked and destroyed faster. In fact, atomic hydrogen strongly interacts with any Si atoms, modifying their structural and electronic properties, while molecular hydrogen has first to dissociate. Hydrogen finally etches the Si nanoribbons and their complete removal from the Ag(110) surface could eventually be expected.