In this work, a systematic study of the influence of growth conditions on the anomalous formation of ternary In x Ga 1-x As nanowires is presented. Free-standing nanowires, of nominal InAs composition, were grown by molecular beam epitaxy on GaAs (111)B substrates at different temperatures and As 4 beam equivalent pressures. The morphology, chemical composition, and crystal structure of the nanowires were investigated by scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction techniques. It was found that a strong incorporation of Ga occurs during the growth creating a homogeneous ternary In x Ga 1-x As alloy in the nanowires with very low residual strain. The GaAs molar fraction was found to increase with the growth temperature and to decrease with the As 4 beam equivalent pressure. A nanowire growth model, taking into account the creation and diffusion of Ga adatoms from the substrate surface toward the nanowires, was used to explain the incorporation of Ga atoms and the formation of the ternary alloy. This model predicts that the GaAs/InAs composition ratio in the nanowires follows an Arrhenius law as a function of the growth temperature with an inverse square root dependency of the As 4 beam equivalent pressure as a pre-exponential factor. The theory was found to fit well the experimental data with an activation energy of 1 eV. It is also shown that the activation energy corresponds to the energy necessary to create Ga adatoms on the surface of the GaAs (111)B substrate. Both experimental and theoretical results show that in this range of growth conditions the limiting factor for the formation of the In x Ga 1-x As alloy in the nanowires is not the diffusion length of the Ga and In adatoms on the substrate surface and nanowires side walls but the density of available Ga adatoms on the substrate surface.

In order to improve the characteristics of future integrated circuits, low dielectric constant (low-k) materials are employed. In this paper we describe in detail the characteristics of k = 2.0, SICOH films treated by capacitively coupled Ar/N2 and Ar/H2 plasmas, which were applied in order to modify the top surface of the film. New insights were obtained about the porous structure of the pristine and the plasma treated films: analyses indicated that the investigated plasma treatments reduced the pore size in the top ten nm of the films, while partial carbon depletion was found down to a few tens of nm inside the film. For the integration of metal barriers deposited by Atomic Layer Deposition in interconnect technologies, precursor penetration into the porous low-k dielectric should be avoided. We investigated precursor penetration in the pores during TaN Atomic Layer Deposition on the pristine and the plasma treated porous low-k films. Detailed analyses showed that the plasma induced modifications resulted in a local growth enhancement and pore sealing during the first cycles of the atomic layer deposition process.

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A long x-ray pathway based on an x-ray back-diffraction cavity for coherent x-ray beam experiments is presented. In the present work, such a setup was tested and used for propagation-based x-ray phase contrast imaging (PBI). This setup showed to be useful for PBI purposes, with the advantage of being compact (3 m long) when compared with long x-ray synchrotron beamlines with dimensions from tens to hundreds of meters.

An analyzer-based x-ray phase contrast imaging ͑PCI͒ setup based on channel-cut crystals at the Laboratorio Nacional de Luz Sincrotron ͑LNLS-Brazilian Synchrotron͒ is presented. The contrast, visibility, signal-to-noise ratio and spatial resolution of the acquired images were characterized. The potential of PCI for enhancing details of different features with the same x-ray attenuation coefficient is exploited together with cross section simulations of the PCIs acquired at different angular positions on the rocking curve ͑RC͒. The present results show that this setup can be used as a standard PCI setup at the LNLS.