Multiple scattering x-ray photoelectron diffraction study of the SrTiO3(100) surface

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The atomic surface structure of SrTiO3(100) after annealing at 630 degrees C in vacuum is investigated by x-ray photoelectron diffraction (XPD) using the Sr 3d(5/2) core level. The photoelectron diffraction peaks are successfully assigned by considering the forward scattering of photoelectrons by the atomic potential near the emitter atom in the lattice. The strongest diffraction peaks are aligned along the single crystal internuclear axes. We compare the results of photoelectron multiple scattering calculations (MSC) of SrO and TiO2 terminated SrTiO3(100) surfaces, including surface relaxation and rumpling, with the experimental data. For TiO2 and SrO terminated SrTiO3(100) surfaces, all top-layer cations relax inward, whereas second-layer atoms relax outward. The surface rumpling for SrO- and TiO2-terminated surfaces agrees well with low-energy electron diffraction results. Using a genetic algorithm the best agreement of MSC to the experimental XPD data is obtained for a SrO terminated surface with a 30% coverage of 3 ML SrO(100) islands.1063Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)European Commission [NMP3-CT-2005-013862]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [0554993-4]European Commission [NMP3-CT-2005-013862

Tool steel ion beam assisted nitrocarburization

The nitrocarburization of the AISI-H13 tool steel by ion beam assisted deposition is reported. In this technique, a carbon film is continuously deposited over the sample by the ion beam sputtering of a carbon target while a second ion source is used to bombard the sample with low energy nitrogen ions. The results show that the presence of carbon has an important impact on the crystalline and microstructural properties of the material without modification of the case depth. (C) 2007 Elsevier B.V. All rights reserved.4654167119419

In situ photoemission electron spectroscopy study of nitrogen ion implanted AISI-H13 steel

In this paper we report the effect of hydrogen on the structural properties of AISI-H13 steel nitrogen-implanted samples in low oxygen partial pressure atmosphere. The samples were implanted in a high vacuum chamber by using a broad ion beam source. The H-2(+)/N-2(+) ion composition of the beam was varied and the surface composition studied in situ by photoemission electron spectroscopy (XPS). The samples were also ex situ analyzed by X-ray diffraction and scanning electron microscopy (SEM), including energy-dispersive spectroscopy measurements. It was found that hydrogen has the effect of modifying the amount of retained nitrogen at the surfaces. This result shows that hydrogen plays a role beyond the well-established effect of oxygen etching in industrial machines where vacuum is relatively less well controlled. Finally, an optimum concentration of 20-40% [H-2]/[H-2+N-2] ion beam composition was determined to obtain maximum nitrogen incorporation on the metal surface. (c) 2004 Elsevier B.V. All rights reserved.20072566257

Microstructure of tool steel after low temperature ion nitriding

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The microstructural development in H13 tool steel upon nitriding by an ion beam process was investigated. The nitriding experiments were performed at a relatively low temperature of similar to 400 degrees C and at constant ion beam energy (400 eV) of different doses in a high vacuum preparation chamber; the ion source was fed with high purity nitrogen gas. The specimens were characterised by X-ray photoelectron spectroscopy, electron probe microanalysis, scanning and transmission electron microscopy, and grazing incidence and Bragg-Brentano X-ray diffractometry. In particular, the influence of the nitrogen surface concentration on the development of the nitrogen concentration depth profile and the possible precipitation of alloying element nitrides were discussed.256726732Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)DAADConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [97/12069-0

Precipitates Temperature Dependence in Ion Beam Nitrited AISI H13 Tool Steel

AISI H13 tool steel samples were nitrided using broad nitrogen ion beams in a high-vacuum chamber at different temperatures. At 400 degrees C, a thin epsilon-Fe(2-3)N phase forms on the top of a shallow nitrided layer and the nitrogen distribution follows a complementary error function. At 500 degrees C, deviations from this behavior are observed and a thick epsilon-Fe(2-3)N layer is formed. At 600 degrees C, no epsilon-Fe(2-3)N phase is formed and the nitrogen profile is step-like. At such a temperature, coarse nitride precipitates are observed. Also, carbon losses (decarburizing) are observed upon nitriding at and above 500 degrees C.41S736S74

Influence of the process temperature on the steel microstructure and hardening in pulsed plasma nitriding

In this paper we report the influence of temperature (260 to 510 degrees C) on the AISI H13 steel microstructure and hardness in pulsed plasma nitriding processes. The experimental results show that bulk nitrogen penetration is well represented by a temperature-activated law. Even at the lowest studied temperatures, grain boundary diffusion causes nitrogen to move relatively deep in the bulk sample. The microstructure was studied by X-ray diffraction analysis at grazing angle and in the Bragg-Brentano configuration. Scanning Electron Microscopy with spatially resolved Xray energy disperse spectroscopy was also employed to map nitrogen influence on the morphology of the material. Also, surface (frontal) and profiling nano-indentation was utilized to elucidate the effect of the temperature on the nitrited material hardness. (c) 2005 Elsevier B.V. All rights reserved.2014167145245

Growth of nitrogenated fullerene-like carbon on Ni islands by ion beam sputtering

The synthesis and properties of fullerene-like carbon materials containing nitrogen deposited by ion beam sputtering in a high-vacuum chamber are reported. The samples are grown on Si substrate by sequentially depositing a titanium nitride thin film, nanometric nickel particles, and carbon. The carbon nanostructured samples were prepared by sputtering a carbon target in nitrogen and helium-nitrogen atmospheres. The effect of the noble gas on the nanostructure formation is reported. X-ray photoelectron spectroscopy performed in an ultra high-vacuum chamber, attached to the deposition system, reveals the incorporation of nitrogen in the carbon layer coating the nickel particles. Atomic force microscopy shows dome-like shaped structures. Raman spectroscopy and high-resolution transmission electron microscopy show multi-wall graphenes covering the nickel particles. The field emission properties of the structures are reported. (C) 2007 Elsevier Ltd. All rights reserved.45132678268

Effect of Carbon on the Compound Layer Properties of AISI H13 Tool Steel in Pulsed Plasma Nitrocarburizing

Due to the mechanical and inertness properties of the epsilon-Fe(2-3)N phase, its formation as a compact monolayer is most wanted in plasma surface treatments of steels. This phase can be obtained by the inclusion of carbon species in the plasma. In this work, we present a systematic study of the carbon influence on the compound layer in an AISI H13 tool steel by pulsed plasma nitrocarburizing process with different gaseous ratios (0% <= [CH(4)]/[N(2)_CH(4)_H(2)] <= 4%). The plasma treatment was carried out for 5 h at 575 degrees C. The microstructure and phase composition of the modified layers were studied by scanning electron microscopy and X-ray diffraction, respectively. X-Ray photoelectron spectroscopy was used to measure the relative concentration of carbon and nitrogen on the surface. The hardening profile induced by the nitrocarburized process is also reported.41S728S73

Spatial modulation of above-the-gap cathodoluminescence in InP nanowires

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We report the observation of light emission on wurtzite InP nanowires excited by fast electrons. The experiments were performed in a scanning transmission electron microscope using an in-house-built cathodoluminescence detector. Besides the exciton emission, at 850 nm, emission above the band gap from 400 to 800 nm was observed. In particular, this broad emission presented systematic periodic modulations indicating variations in the local excitation probability. The physical origin of the detected emission is not clear. Measurements of the spatial variation of the above-the-gap emission points to the formation of leaky cavity modes of a plasmonic nature along the nanowire length, indicating the wave nature of the excitation. We propose a phenomenological model, which fits closely the observed spatial variations.2550Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)National Agency for Research under the program of future investment TEMPOS-CHROMATEM [ANR-10-EQPX-50]European Union Seventh Framework Programme [FP7/2007-2013]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2007/58962-1, 2008/55023-7, 2011/05989-5]National Agency for Research under the program of future investment TEMPOS-CHROMATEM [ANR-10-EQPX-50]European Union Seventh Framework Programme [FP7/2007-2013