Improved recovery time and sensitivity to H2 and NH3 at room temperature with SnOx vertical nanopillars on ITO

Nanostructured SnO2 is a promising material for the scalable production of portable gas sensors. To fully exploit their potential, these gas sensors need a faster recovery rate and higher sensitivity at room temperature than the current state of the art. Here we demonstrate a chemiresistive gas sensor based on vertical SnOx nanopillars, capable of sensing < 5 ppm of H2 at room temperature and 10 ppt at 230 °C. We test the sample both in vacuum and in air and observe an exceptional improvement in the performance compared to commercially available gas sensors. In particular, the recovery time for sensing NH3 at room temperature is more than one order of magnitude faster than a commercial SnO2 sensor. The sensor shows an unique combination of high sensitivity and fast recovery time, matching the requirements on materials expected to foster widespread use of portable and affordable gas sensors.

Free surfaces recast superconductivity in few-monolayer MgB2: Combined first-principles and ARPES demonstration

Two-dimensional materials are known to harbour properties very different from those of their bulk counterparts. Recent years have seen the rise of atomically thin superconductors, with a caveat that superconductivity is strongly depleted unless enhanced by specific substrates, intercalants or adatoms. Surprisingly, the role in superconductivity of electronic states originating from simple free surfaces of two-dimensional materials has remained elusive to date. Here, based on first-principles calculations, anisotropic Eliashberg theory, and angle-resolved photoemission spectroscopy (ARPES), we show that surface states in few-monolayer MgB2 make a major contribution to the superconducting gap spectrum and density of states, clearly distinct from the widely known, bulk-like σ- and π-gaps. As a proof of principle, we predict and measure the gap opening on the magnesium-based surface band up to a critical temperature as high as ~30 K for merely six monolayers thick MgB2. These findings establish free surfaces as an unavoidable ingredient in understanding and further tailoring of superconductivity in atomically thin materials.

Gas sensing at the nanoscale: engineering SWCNT-ITO nano-heterojunctions for the selective detection of NH3 and NO2 target molecules

The gas response of single-wall carbon nanotubes (SWCNT) functionalized with indium tin oxide (ITO) nanoparticles (NP) has been studied at room temperature and an enhanced sensitivity to ammonia and nitrogen dioxide is demonstrated. The higher sensitivity in the functionalized sample is related to the creation of nano-heterojunctions at the interface between SWCNT bundles and ITO NP. Furthermore, the different response of the two devices upon NO₂ exposure provides a way to enhance also the selectivity. This behavior is rationalized by considering a gas sensing mechanism based on the build-up of space-charge layers at the junctions. Finally, full recovery of the signal after exposure to NO₂ is achieved by UV irradiation for the functionalized sample, where the ITO NP can play a role to hinder the poisoning effects on SWCNT due to NO₂ chemisorption.

Solid state effects on the electronic structure of H2OEP

We present the results of a joint experimental and theoretical investigation concerning the effect of crystal packing on the electronic properties of the H2OEP molecule. Thin films, deposited in ultra high vacuum on metal surfaces, are investigated by combining valence band photoemission, inverse photoemission, and X-ray absorption spectroscopy. The spectra of the films are compared, when possible, with those measured in the gas phase. Once many-body effects are included in the calculations through the GW method, the electronic structure of H2OEP in the film and gas phase are accurately reproduced for both valence and conduction states. Upon going from an isolated molecule to the film phase, the electronic gap shrinks significantly and the lowest unoccupied molecular orbital (LUMO) and LUMO + 1 degeneracy is removed. The calculations show that the reduction of the transport gap in the film is entirely addressable to the enhancement of the electronic screening.

Evaluation of genotoxicity and cytotoxicity of water samples from the Sinos River Basin, southern Brazil

<p>Some water bodies in the Sinos River Basin (SRB) have been suffering the effects of pollution by residential, industrial and agroindustrial wastewater. The presence of cytotoxic and genotoxic compounds could compromise the water quality and the balance of these ecosystems. In this context, the research aimed to evaluate the genotoxicity and cytotoxicity of the water at four sites along the SRB (in the cities of Santo Antônio da Patrulha, Parobé, Campo Bom and Esteio), using bioassays in fish and cell culture. Samples of surface water were collected and evaluated <italic>in vitro</italic> using the <italic>Astyanax jacuhiensis</italic> fish species (micronucleus test and comet assay) and the Vero lineage of cells (comet assay and cytotoxicity tests, neutral red - NR and tetrazolium MTT). The micronucleus test in fish showed no significant differences between the sampling sites, and neither did the comet assay and the MTT and NR tests in Vero cells. The comet assay showed an increase in genetic damage in the fish exposed to water samples collected in the middle and lower sections of the basin (Parobé, Campo Bom and Esteio) when compared to the upper section of the basin (Santo Antônio da Patrulha). The results indicate contamination by genotoxic substances starting in the middle section of the SRB.</p>

DNA damage in Wistar rats exposed to dithiocarbamate pesticide mancozeb

Pesticides are used in large amounts in agriculture and the evaluation of their toxic effects is of major concern to public and environmental health. The aim of the present study was to investigate the genotoxic potential of a commercial formulation of the fungicide mancozeb by the micronucleus test in bone marrow and the comet assay in total blood of Wistar rats. Adult male Wistar rats were treated with a solution of mancozeb at a concentration of 40 mg/kg/day, administered intraperitoneally for 18 consecutive days, and compared to a control group. The results indicate that mancozeb induced significantly higher DNA damage as detected by the comet assay and increased the frequency of micronuclei. The results show that mancozeb is genotoxic and may adversely affect the DNA integrity of exposed organisms.

Excitation spectra of transition-metal atoms on the Ag (100) surface controlled by Hund's exchange

We report photoemission experiments revealing the valence electron spectral function of Mn, Fe, Co, and Ni atoms on the Ag (100) surface. The series of spectra shows splittings of higher energy features which decrease with the filling of the 3d shell and a highly nonmonotonic evolution of spectral weight near the Fermi edge. First principles calculations demonstrate that two manifestations of Hund's exchange J are responsible for this evolution. First, there is a monotonic reduction of the effective exchange splittings with increasing filling of the 3d shell. Second, the amount of charge fluctuations and, thus, the weight of quasiparticle peaks at the Fermi level varies nonmonotonically through this 3d series due to a distinct occupancy dependence of effective charging energies U(eff).

Apolipoprotein B is a new target of the GDNF/RET and ET-3/EDNRB signalling pathways

BACKGROUND

GDNF/RET and Endothelin-3 (ET-3)/EDNRB regulate survival, differentiation, migration, and proliferation of neural crest-derived cells. Although several RET and EDNRB signalling mediators have been characterized, most of the genes targeted by these two pathways are still largely unknown. We focused our study on apolipoprotein B (APOB) as a novel target gene of the RET and EDNRB pathways, based on previous data obtained using a Caenorhabditis elegans strain mutant for the homologue of mammalian ECE1.

METHODS

Molecular and cellular studies of Apob were performed in the murine Neuro2a cells, an in vitro model for studying neural crest-derived cell development, along with a mouse knock-in for the Hirschsprung-associated mutation Ret(C620R). Silencing for Apob and Ret has been performed via shRNA.

KEY RESULTS

GDNF/RET and ET-3/EDNRB cooperated in inducing neuronal differentiation resulting in Apob activation in Neuro2a cell line. Apob expression was downregulated in mouse embryos homozygous for the Ret(C620R) mutation and presenting a severe Hirschsprung phenotype. Ret silencing prevented Apob expression increase. MAPK P38 kinase activation evoked Apob expression via GDNF/RET signalling in Neuro2a cells. A p53-dependent repressor element in Apob promoter resulted in a reduced Apob expression. Silencing of Apob reduced HuD protein expression.

CONCLUSIONS & INFERENCES

Apob is a novel downstream target of the RET/EDNRB pathways with a role in neuronal survival and maintenance, as indicated by its effect on HuD expression. Our data provide a conceptual framework to investigate and establish the role of APOB gene in severe gut dysmotility.

Functional K-doping of eumelanin thin films: Density functional theory and soft x-ray spectroscopy experiments in the frame of the macrocyclic protomolecule model [corrected]

We demonstrate the possibility to achieve the doping of eumelanin thin films through K(+) incorporation during the electrodeposition of the film. K-doping changes the optical properties of the eumelanin thin films, reducing the energy gap from 1.0 to 0.6 eV, with possible implications for the photophysical properties. We have identified the doping-related occupied and unoccupied electronic states and their spectral weight using resonant photoemission spectroscopy (ResPES) and x-ray absorption at the C and N K-edges (near edge x-ray absorption fine spectroscopy, NEXAFS). All data are consistently interpreted by ab initio calculations of the electronic structure within the frame of the macrocycle model developed for the eumelanin protomolecule. Our analysis puts in evidence the intercalation of K with one specific oligomer (a tetramer composed of one indolequinone and 3 hydroquinone monomers) in correspondence of the nitrogen macrocycle. The predicted variation of the tetramer spacing is also in agreement with the recent x-ray diffraction experiments. The charge donation from K to N and C atoms gives rise to new electronic states at the top of the valence band and in NEXAFS resonances of the unoccupied orbitals. The saturation of the tetramer macrocycles leaves an excess of K that bind to N and C atoms in alternative configurations, as witnessed by the occurrence of additional spectral features in the carbon-related ResPES measurements.

Tracking the excitation dynamics in the Mn:Ge(111) metallic interface by resonant electron spectroscopy

Resonant photoemission from the valence band of a (√3 × √3)R30° reconstructed Mn:Ge(111) metallic interface has been carefully analyzed with the aim to track the transition from resonant Raman to normal Auger emission. The transition energy has been compared with the Mn 2p binding energy, as well as with the Mn L(3) absorption edge energy. Close similarities emerge with respect to the case of elemental Mn thin films, suggesting that the excitation dynamics is dominated by the electronic properties of Mn 3d states, in spite of the bonding with Ge atoms. The switching from the resonant Raman Auger (RRAS) to the normal Auger regime is found about 2 eV below the Mn L(3) absorption edge. A change of the lineshape due to the transition from an overall N - 1 electron final state (RRAS channel) to an N - 2 electron final state (normal Auger channel) is evidenced by the analysis of the experimental data, which also allowed the ratio to be tracked between charge delocalization and core-hole time scales as the photon energy is tuned across the Mn L(3) edge.

Spectral functions of isolated Ce adatoms on paramagnetic surfaces

We report photoemission experiments revealing the full valence electron spectral function of Ce adatoms on Ag(111), W(110), and Rh(111) surfaces. A transfer of Ce 4f spectral weight from the ionization peak towards the Fermi level is demonstrated upon changing the substrate from Ag(111) to Rh(111). In the intermediate case of Ce on W(110) the ionization peak is found to be split. This evolution of the spectra is explained by means of first-principles theory, which clearly demonstrates that a reliable understanding of magnetic adatoms on metal surfaces requires simultaneous low and high energy spectroscopic information.

A multibiomarker approach in rats to assess the impact of pollution on Sinos River, Southern Brazil

The aim of this study was to determine the feasibility of combining water quality analysis with different biomarkers to characterise the relationship between anthropogenic contamination and biotic response in the Sinos River, southern Brazil. Wistar rats were studied using three biomarkers combined with physical, chemical and microbiological analysis to assess the effects of pollution at four sampling sites. The induction of oxidative stress was quantified by MDA levels in peripheral blood, lymphocyte DNA damage was determined using the comet assay, and histopathological changes were analysed in the liver. After sampling, animals were allowed to drink the river water during a 48 hours period. No increase in oxidative stress and DNA damage was observed. However, liver damage was observed in the animals exposed to water samples, indicating that the Sinos River is contaminated with hepatotoxic substances. Water analyses confirmed that water quality decreased downriver.

The attenuation length of low energy electrons in Yb

Photoelectron emission spectra in a photon energy range between 7.5 and 21 eV are measured for in situ grown polycrystalline Yb films. By comparing bulk and surface core level shifted 4f components we give an estimation of the effective attenuation length (EAL) for low energy (6-20 eV) electrons in Yb, establishing a moderate increase of the EAL upon electron energy decrease. The experimental EAL data are found to be a factor of four smaller than those predicted from the so-called 'universal curve'.

Sensing gases with carbon nanotubes: a review of the actual situation

Here we review the possible application of carbon nanotubes (CNTs) as chemiresistor and field-effect transistor chemical sensors. The endeavor of this paper is to understand the key facts emerging from the literature that seem to demonstrate the high sensitivity of CNTs to several molecular species, with the effort to catch the results in a correct manner.

Quasiparticles at the Mott transition in V2O3: wave vector dependence and surface attenuation

We present an angle resolved photoemission study of V2O3, a prototype system for the observation of Mott transitions in correlated materials. We show that the spectral features corresponding to the quasiparticle peak in the metallic phase present a marked wave vector dependence, with a stronger intensity along the GammaZ direction. The analysis of their intensity for different probing depths shows the existence of a characteristic length scale for the attenuation of coherent electronic excitations at the surface. This length scale, which is larger than the thickness of the surface region as normally defined for noncorrelated electronic states, is found to increase when approaching the Mott transition. These results are in agreement with the behavior of quasiparticles at surfaces as predicted by Borghi et al.

Electronic excitations in synthetic eumelanin aggregates probed by soft X-ray spectroscopies

Electronic excitations of condensed phase eumelanin aggregates are investigated with soft X-ray spectroscopies. Resonant photoemission data indicate that mechanisms of charge delocalization may occur when electrons are excited about 3 eV above the first unoccupied electronic level. An average, lower limit value of 1.6 fs was estimated for the lifetime of the excited C 1s-pi* states.

Insulating ground state of Sn/Si(111)-(square root 3 x square root 3)R30 degrees

The Sn/Si(111)-(square root 3 x square root 3)R30 degrees surface was so far believed to be metallic according to the electron counting argument. We show, by using tunneling spectroscopy, scanning tunneling microscopy, photoemission, and photoelectron diffraction, that below 70 K this surface has a very low density of states at the Fermi level and is not appreciably distorted. The experimental results are compatible with the insulating Mott-Hubbard ground state predicted by LSDA+U calculations [G. Profeta and E. Tosatti, Phys. Rev. Lett. 98, 086401 (2007)].

Phase separation in potassium-doped ZnPc thin films

In this study synchrotron radiation was used to investigate the electronic properties of a thin film of zinc-phthalocyanine (ZnPc) deposited on Si(001)-2x1 and progressively doped with K atoms. The molecular orientation was probed by angular-dependent x-ray absorption spectroscopy and the molecules were found to lie with the macrocycle plane roughly perpendicular to the surface. The evolution of the electronic properties of the film was then followed by measuring the photoemission spectra upon in situ evaporation of K atoms on the pristine ZnPc film. The results show that doping proceeds through charge donation from the K atoms to the molecular units whose lowest unoccupied molecular orbital (LUMO) becomes progressively filled. Despite the fact that the LUMO spectral weight increases as the stoichiometry x in the K(x)ZnPc compound varies from about 1 to 4 (as determined by core level photoemission), no detectable density of states was observed at the Fermi level, showing that the film remains insulating for all the investigated stoichiometries. On the other hand the C 1s spectra, which appear merely broadened at the earliest stages of doping (x approximately 1), clearly develop two distinct components when x exceeds 2, suggesting that the charge state is not the same for all the molecules. At the same time, the modification of the valence band points towards the coexistence of two distinct phases with x=2 and x=4.

Element-Specific Probe of the Magnetic and Electronic Properties of Dy incar-Fullerenes

The magnetic and electronic properties of a single atom and a pair of Dy atoms encapsulated inside fullerene carbon cages have been examined using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) as well as resonant photoelectron spectroscopy (RESPES) across the Dy M(4,5)-edge. The comparison of the measured XAS spectra with multiplet calculations indicates that the encaged Dy has a 4f( 9) configuration. The presence of Dy 5d spectral weight in the valence band is not detected by RESPES, indicating that Dy is in a formally trivalent state. The evolution of the encaged Dy orbital and spin moments of the 4f orbitals as a function of the applied magnetic field and temperature has been obtained from XMCD measurements. At 6.9 T and 4 K, both the orbital and the spin magnetic moments of the encaged Dy 4f electrons are dramatically smaller than those expected for the free Dy(3+) at saturation.

Electronic properties of a pure and sodium-doped C70 single layer adsorbed on Al polycrystalline surface

Core level and valence band photoemission measurements combined with near edge x-ray absorption fine structure measurements were performed on a single C(70) layer adsorbed on polycrystalline Al (1 ML-C(70)/Al) (ML-monolayer), pure and doped with sodium atoms. The data obtained from the pure ML chemisorbed on Al surface show a semiconducting behavior of the system, which is characterized by a covalent bond between the adsorbate and the substrate. The same data show also that the C(70) molecules tend to orient themselves with the C(5v) axis perpendicular to the surface in analogy to what observed for 1 ML-C(70)/Cu(111). By doping the sample with sodium atoms a charge transfer from the alkali atoms to the lowest unoccupied molecular orbital (LUMO) of the C(70) molecules takes place, as underlined by the gradual increasing intensity of the C(70) LUMO peak as a function of doping. Nevertheless, no metallic phases are observed for any doping step.

Orientation-dependent C60 electronic structures revealed by photoemission spectroscopy

We observe, with angle-resolved photoemission, a dramatic change in the electronic structure of two C60 monolayers, deposited, respectively, on Ag (111) and (100) substrates, and similarly doped with potassium to half filling of the C60 lowest unoccupied molecular orbital. The Fermi surface symmetry, the bandwidth, and the curvature of the dispersion at Gamma point are different. Orientations of the C60 molecules on the two substrates are known to be the main structural difference between the two monolayers, and we present new band-structure calculations for some of these orientations. We conclude that orientations play a key role in the electronic structure of fullerides.

Calorimetry at surfaces using high-resolution core-level photoemission

We have developed a method to measure simultaneously the internal energy of bulk and the first layer atoms of a crystal. The internal energy of bulk and the surface atoms of lithium (110) have been evaluated from 22 K up to above the melting transition, applying the Debye model to the thermal broadening of the respective 1s photoemission lines. Our measurements clearly reveal two phase changes: the known liquid to solid transition and the surface melting, occurring 50 K below the bulk melting point.

Band structure and Fermi surface of electron-doped C60 monolayers

C60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.

Core level photoemission evidence of frustrated surface molecules: a germ of disorder at the (111) surface of C60 before the order-disorder surface phase transition

Using high resolution core level photoemission, we investigated the disordering transition of the fullerene molecules at the (111) surface of C (60) films. The experimental evidence of a two-step mechanism for the rotational disordering of surface fullerene molecules is provided. The data are consistent with a recent model in which the rotational degrees of freedom of one molecule, out of the four inequivalent C (60) molecules of the low temperature (2x2) surface unit cell, melt about 100 K before the bulk phase transition.

Surface and bulk normal state transport properties in K(3)C(60)

The temperature dependence of the surface resistivity for a metallic K(3)C(60) ordered film in the nonsuperconducting state has been obtained by reflection electron energy loss spectroscopy. We demonstrate that the normal state electronic and transport properties of the top molecular layer of K(3)C(60) are similar to the corresponding properties measured with bulk sensitive techniques. These observations strengthen and give a general character to the experimental results obtained with surface sensitive techniques on fullerene compounds. In addition, the transport properties may deviate from the Fermi-liquid behavior above 500 K.

Temperature-dependent fermi gap opening in the c(6x4)-C60/Ag(100) two-dimensional superstructure

High-resolution angle-integrated photoemission of one monolayer of C (60) chemisorbed on Ag(100) shows the reversible opening of a gap at the Fermi level at temperatures 25< or =T< or =300 K. The gap reaches a maximum value of approximately 10 meV at T< or =70 K. This finding is the first evidence of an electronic phase transition in C60 monolayers and has implications on the ongoing debate about surface superconductivity in C60-based bulk materials.

Chemical shift resolved photoionization cross sections of amorphous carbon nitride

The various components in the N 1s photoemission spectra of amorphous carbon nitride are identified by measuring their photon energy dependence and comparing the experimental results with ab initio multiple scattering calculations. The intensity modulations with photon energy are due to the extended x-ray absorption fine structure effects.

Peripheral T-cell lymphomas. Clinico-pathologic study of 168 cases diagnosed according to the R.E.A.L. Classification

BACKGROUND

One hundred sixty-eight peripheral T-cell lymphomas (PTCLs) were reviewed according to the Revised European-American Lymphoma (R.E.A.L.) Classification.

PATIENTS AND METHODS

The cases, originally diagnosed on the basis of the Updated Kiel Classification (UKC), were all provided with histological preparations, immunophenotype, clinical information, and follow-up data. The slides were reclassified by five observers, who integrated the R.E.A.L. criteria with cell size measurements. The prognostic value of clinical and pathologic findings was assessed by univariate and multivariate analysis.

RESULTS

The R.E.A.L. Classification was reproducibly applied by all of the observers. Clinically, anaplastic large cell lymphomas (ALCLs) differed from the remaining PTCLs by mean age (29.5 vs. 52.9 years), bulky disease (52.3% vs. 11.3%; P = 0.000), mediastinal mass (52.7% vs. 32%; P = 0.004), and disease-free survival (68.0% vs. 38.2%; P = 0.0001). Although each histological type displayed specific clinical aspects, PTCLs other than ALCL were basically characterised by a poor clinical outcome which was not influenced by the UKC malignancy grade. At multivariate analysis, the risk of a lower complete remission rate was related to bulky disease (P = 0.001), histologic group (non-ALCL) (P = 0.01), and advanced stage (III-IV) (P = 0.0002).

CONCLUSIONS

The present study supports the classification of T-cell lymphomas proposed by the R.E.A.L. scheme.