Isabel Montero

Behavior of oxygen doped SiC thin films: An x-ray photoelectron spectroscopy study

Thin silicon carbide films have been deposited by chemical vapor deposition on p-type (100) silicon substrates. The composition and bonds formed in these films have been analyzed by x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy. The native surface oxide on the silicon carbide surface induced by air exposure has also been studied. Several phases are detected in the near-surface region: elemental Si, Si oxides (mainly SiO2), Si carbide (SiC) and Si oxicarbides (SiOxCy). Quantitative XPS analysis results indicate that, for atomic oxygen fractions <0.15, the Si–C phases are dominant in the films. Above this value no silicon oxicarbide is observed, but a multiphase material formed by elemental Si, Si oxides and Si carbides is observed. In spite of the film being a complex phase mixture, a simple relationship is found between the overall carbon and oxygen compositions. The carbon atomic fraction in the film decreases quasilinearly as the oxygen content increases, with a slope of about −1. An ...

An XPS study of carbon nitride synthesized by ion beam nitridation of C60 fullerene

Abstract Carbon nitride thin films were obtained using low-energy nitrogen ion beams (0.05–3.0 keV) and simultaneous sublimation of fullerene (C 60 ) on Si substrates. By comparing the N 1s peak positions with reference data on nitrogen containing polymers and organic molecules, it is shown that the two main components of the N 1s spectra at 400.6 and 398.5 eV correspond to nitrogen bonded to sp 2 and sp 3 carbon, respectively. It is also suggested that a third component related to ion beam-induced defects should be considered in an intermediate position (399.3 eV). This component disappears at temperatures above 500 K and reappears when the annealed samples are bombarded with Ar + ions (1.0 keV). C 1s core level spectra do not show discrete chemical shifts but an overlapping distribution producing a broad line shape, whose centroid shifts to higher binding energies with increasing nitrogen content. The samples were determined to be amorphous by X-ray diffraction and Infrared Absorption Spectroscopy.

Patterns of Infection in Patients With Myelodysplastic Syndromes and Acute Myeloid Leukemia Receiving Azacitidine as Salvage Therapy. Implications for Primary Antifungal Prophylaxis

Incidence, etiology, and outcome of infectious episodes in patients with myeloid neoplasms receiving azacitidine are uncertain, with no prospective data available in this group of patients. The aim of the current study was to analyze the incidence and factors related to the probability of infection in a cohort of patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) treated with azacitidine who did not receive any type of antimicrobial prophylaxis. Significantly, the group of patients who received prior intensive chemotherapy had more infectious episodes (P = 10(-4)), and particularly, invasive aspergillosis (P = .015), than patients who received frontline azacitidine. Primary antifungal prophylaxis might be recommended in MDS and AML patients receiving azacitidine as salvage therapy after intensive regimens.

X-ray photoelectron spectroscopy study of low-temperature molybdenum oxidation process

The low-temperature oxidation during deposition by evaporation of molybdenum thin films has been investigated. Analysis by x-ray photoelectron spectroscopy and x-ray diffraction reveals that small differences in the substrate temperature during deposition may give rise to important changes in the final composition and structure of the molybdenum oxide. Changes in binding energy and line shape of the Mo 3d5/2−Mo 3d3/2 doublet attributed to oxygen incorporation have been studied. Two principal steps can be distinguished, with a transition temperature of ∼310 °C. Up to substrate temperatures of ∼310 °C, the superficial Mo remains almost unaffected, with some oxygen dissolved. At ∼310 °C, mixing of Mo0 metal and molybdenum oxide (Moδ+0<δ<4) clusters or islands is observed. Finally, above this temperature a surface layer of molybdenum oxide, Mo6+, is formed. In addition, an abrupt change in d100 interplanar parameter of Mo is observed.

Aging of porous silicon in physiological conditions: Cell adhesion modes on scaled 1D micropatterns †

The surface properties of porous silicon (PSi) evolve rapidly in phosphate-buffered saline. X-ray photoelectron spectra indicate the formation of a Si-OH and C-O enriched surface, which becomes increasingly hydrophilic with aging time. Multiscale stripe micropatterns of Si and PSi have been fabricated by means of a high-energy ion-beam irradiation process. These micropatterns have been aged in physiological conditions and used to analyze human mesenchymal stem cell (hMSC) adhesion. The actin cytoskeleton of hMSCs orients following the uniaxial micropatterns. In the wider Si stripes, hMSCs are dominantly located on Si areas. However, for reduced Si widths, adhesion is avoided on PSi by a split assembly of the actin cytoskeleton on two parallel Si areas. These results confirm that nanostructured Si-OH/C-O-rich surfaces with hydrophilic character are specially adapted for the creation of cell adhesion surface contrasts.

CuO nanowires for inhibiting secondary electron emission

Copper oxide nanowires (NWs) grown on copper to avoid the secondary electron emission were investigated. Optimal temperatures for NW growth were found to be in the range 700–800 K. NW surface coverage of 102 µm−2 is required to strongly reduce the secondary electron yield. A total secondary electron emission coefficient below 1 was obtained for NW aspect ratio higher than 103.

Clinical Prognostic Factors for Survival and Risk of Progression to Acute Myeloid Leukemia in Patients With Myelodysplastic Syndromes With 10% Marrow Blasts and Non-Unfavorable Cytogenetic Categories

UNLABELLED Prognosis of myelodysplastic syndromes (MDS) is an area of ongoing interest. Identification of patients with poor outcome in the categories of lower risk disease is critical. In this study, we classify a cohort of 332 lower risk MDS into 3 groups with differences in survival and risk for leukemic progression that could drive treatment approaches to improve prognosis in a fraction of these patients. BACKGROUND Prognosis of MDS and particularly in patients categorized as lower risk (< 10% blasts or low and intermediate-1 International Prognostic Scoring System [IPSS]) is very heterogeneous and includes patients with very different outcomes with current scoring systems. Recently, a new cytogenetic classification has been proposed for the revised IPSS in predicting the outcome for MDS. PATIENTS AND METHODS To evaluate the prognostic significance of multiple variables for survival and risk of progression to acute myeloid leukemia, we analyzed baseline characteristics of 332 lower risk MDS patients within the lower risk cytogenetic categories by IPSS and the recent proposal for the new cytogenetic classification. RESULTS In multivariate analysis, severity of cytopenias, age > 60 years, bone marrow blasts (5%-9%) and transfusion dependency significantly influenced outcome. The combination of these variables allowed development of a model which categorizes patients in 3 different groups with median survival of 95, 44, and 13 months for groups 1, 2, and 3, respectively (P < .001). In addition, this score also stratified patients for their risk for leukemic progression, estimated at 2 years in 3.1%, 7.6%, and 21.3% for each group (P = .024). CONCLUSION Although karyotype remains the main prognostic factor in MDS, the current study identifies clinical parameters predicting outcome among patients with the better cytogenetic profile. Degree of cytopenias, blasts 5%-9% and transfusion dependence might identify a subset of patients within the nonadverse karyotype, in which early or more aggressive approaches could possibly be required to improve survival or prevent disease progression.

Whiskers in indium tin oxide films obtained by electron beam evaporation

Indium tin oxide thin films consisting mainly of whiskers have been deposited on glass by electron beam evaporation. Low deposition rates (35 A/min) and substrate temperatures in the 120–400 °C range were used. Morphology by scanning electron microscopy, crystal structure, energy dispersive analysis of x-rays, and x-ray photoelectron spectroscopy compositions, optical and conducting properties of films have been studied as a function of temperature of growth and further annealing in air. Whiskers associate and produce flatter surfaces, the grain size increases from ≈390 A to ≈790 A, keeping however its fibrous structure after 400 °C-30 min annealing. In films deposited at temperatures below 200 °C, next to cubic In2O3, tetragonal Sn and cubic In2Sn2O(7−x) appear. During growth and after air annealing Sn4+ segregates to the surface, attaining Sn/In concentration ratios of 4.6. On air annealing the optical transmittance and electrical resistance increase, in some cases from 2% to 90% and by a factor of abou...

Secondary electron emission and photoemission studies on surface films of carbon nitride

The secondary electron emission yield of fullerene, graphite, and diamondlike carbon after low-energy N2+ ion bombardment was studied for antimultipactor applications. Nitrogen incorporation into the carbon thin films decreases their secondary emission yield, contrary to the hydrogen or oxygen effect. Carbon nitride surface textured to a nanometric scale had the property of hindering secondary electron emission. Valence bands obtained from photoemission spectroscopy using synchrotron radiation were correlated with secondary electron emission measurements. Multipactor threshold power for carbon nitride was 7.5kW.

Multipactor Susceptibility Charts of a Parallel-Plate Dielectric-Loaded Waveguide

In this paper, we investigate the dependence of multipactor susceptibility charts of a parallel-plate dielectric-loaded waveguide on the different geometrical and electrical parameters of the waveguide under study. Susceptibility charts are obtained for different properties of the dielectric material loading the structure (i.e., different height, dielectric constant, and secondary emission yield (SEY) responses are considered). Realistic susceptibility charts are also computed employing experimental SEY measurements from different metallic and dielectric materials.