Red and green light emission from samarium-doped amorphous aluminum nitride films

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X-ray photoelectron spectroscopic study of rare-earth-doped amorphous silicon-nitrogen films

Amorphous silicon-nitrogen (a-SiN) films independently doped with different rare-earth (RE) elements (Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) have been prepared by cosputtering. The films were investigated in detail by x-ray photoelectron spectroscopy employing 1486.6 eV photons. Additional information was also achieved by optical techniques and ion beam analyses. As a result of the deposition method and conditions, the films present similar contents of Si and N, and rare-earth concentrations below 1.0 at. %. In spite of this relatively low concentration, and taking advantage of the high photoionization cross section of the rare-earth elements at 1486.6 eV, the signal of several different core-levels and Auger transitions could be detected and analyzed. The electronic states at the top of the valence band of the RE-doped a-SiN films were also investigated with 1486.6 eV photons. Compared to the spectroscopic data of pure metals, the RE-related core levels of the present a-SiN films exhibit an energy shift typically in the 0.8-2.5 eV range, which is attributed to the presence of nitrogen atoms. According to the experimental data, most of the RE ions remain in the 3+ state. The only clear exception occurs in the Yb-doped a-SiN film, where a large fraction of Yb2+ coexisting with Yb3+ ions is evident. (C) 2003 American Institute of Physics.9341948195

Aluminium-induced nanocrystalline Ge formation at low temperatures

The present work contributes to establishing the role of hydrogenation and of the substrates in the aluminium-induced crystallization process of amorphous germanium layers. For such a purpose, four series of a-Ge(Al) samples, deposited under identical nominal conditions, were studied: hydrogenated samples, H-free samples, and samples deposited on crystalline silicon and on glass substrates, respectively. On purpose, the impurity concentration was kept at a doping level (10(-5) < [Al/Ge] < 2 x 10(-3)). Furthermore, the films were submitted to isochronal cumulative thermal annealing in the 200-550 degrees C range. Raman scattering spectroscopy was used to characterize the crystallization process. The role of Al impurity as a precursor seed for the crystallization of a-Ge:H has been clearly established, confirming that the metal-induced crystallization ( MIC) phenomenon occurs at an atomic level. Moreover, it has been found that hydrogenation and the periodic nature of the substrate play a fundamental role in the appearance of crystal seeds at low temperatures. The evolution of crystallization with annealing temperature and the analysis of the distribution of crystallite sizes indicate that the formation of crystal seeds occurs at the amorphous film-substrate interface. The importance of fourfold-coordinated aluminium as the embryo of nanocrystal formation is discussed.19

Comprehensive spectroscopic study of nitrogenated carbon nanotubes

Carbon nanotubes with different nitrogen contents were produced by the arc-discharge technique. The samples were first submitted to a concentration process (purification) and analyzed by x-ray photoelectron spectroscopy, electron-energy-loss spectroscopy, electron transmission, and scanning electron microscopy to study the materials structure and morphology. Measured values of nitrogen concentration were below 5 at. % and varied with the nitrogen partial pressure inside the arc-discharge chamber. Using an optical microscope, highly localized regions of the samples (similar to1 mm(2)) were irradiated by an Ar ion laser. Controlling the laser intensity, further local purification was induced and information about the evolution of the structural order of the nanotube samples with different contents of nitrogen was obtained.69

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