Influence of focus offset on the microstructure of an intermetallic gamma-TiAl based alloy produced by electron beam powder bed fusion

It is well established in literature that, when processing intermetallic gamma-TiAl components by electron beam powder bed fusion, a banded microstructure is frequently formed because of an inhomogeneous Al distribution since more pronounced evaporation of Al occurs at the top of the melt pool. This feature is particularly promoted when highly energetic process parameters (high beam currents, slow beam speeds, narrow line offsets) are used. Therefore, an approach already suggested in the literature to reduce the Al loss is to minimize the energy level of the process parameter during production. However, there is a limit to such kind of approach: minimizing the beam current or increasing the beam speed, or increasing the line offset will, at a certain point, results in not being able to achieve a completely dense material and thus some process -induced porosity, the so-called lack-of-fusion defects, starts to occur in the produced parts.In this study, the effect of an additional parameter of the electron beam powder bed fusion process is taken under consideration: the focus offset (FO), i.e. the distance between the focusing plane of the electron beam with respect to the powder bed. The effect of the FO on the residual porosity, microstructure, phase composition, hardness as well as chemical composition is investigated, thus having the possibility to demonstrate that also the FO can affect the Al loss and play a fundamental role in the generation of a homogenous microstructure, contributing to mitigate the appearance of a banded microstructure

Analysis of effective mobility and hall effect mobility in high-k based In0.75Ga0.25As metal-oxide-semiconductor high-electron-mobility transistors

We report an In0.75Ga0.25As metal-oxide-semiconductor high-electron-mobility transistor with a peak Hall mobility of 8300 cm(2)/Vs at a carrier density of 2 x 10(12) cm(-2). Comparison of split capacitance-voltage (CV) and Hall Effect measurements for the extracted electron mobility have shown that the split-CV can lead to an overestimation of the channel carrier concentration and a corresponding underestimation of electron mobility. An analysis of the electron density dependence versus gate voltage allows quantifying the inaccuracy of the split-CV technique. Finally, the analysis supported by multi-channel conduction simulations indicates presence of carriers spill over into the top InP barrier layer at high gate voltages. (C) 2011 American Institute of Physics. (doi: 10.1063/1.3665033

Analysis of electron mobility in HfO2/TiN gate metal-oxide-semiconductor field effect transistors: The influence of HfO2 thickness, temperature, and oxide charge

We report a new analysis of electron mobility in HfO2/TiN gate metal-oxide-semiconductor field effect transistors (MOSFETs) by investigating the influence of HfO2 thickness (1.6-3 nm), temperature (50-350 K), and oxide charge (similar to 1x10(11)-8x10(12) cm(-2)) in the high inversion charge region. The fixed oxide charge and interface state densities are deliberately increased using negative-bias-temperature stress, allowing the determination of the Coulomb scattering term as a function of temperature for various oxide charge levels. The temperature dependence of the Coulomb scattering term is consistent with the case of a strongly screened Coulomb potential. Using the experimentally determined temperature dependence of Coulomb scattering term, a model is developed for the electron mobility, including the effects oxide charge (mu(C)), high-k phonon (mu(Ph-Hk)), silicon phonon (mu(Ph-Si)), and surface roughness scattering (mu(SR)). The model provides an accurate description of the experimental data for variations in HfO2 thickness, temperature, and oxide charge. Using the model the relative contributions of each mobility component are presented for varying oxide charge and high-k thickness. Scaling of the HfO2 physical thickness provided a reduction in the oxide charge and high-k phonon scattering mechanisms, leading to an increase in electron mobility in HfO2/TiN gate MOSFETs

Low-frequency noise in junctionless multigate transistors

Low-frequency noise in n-type junctionless multigate transistors was investigated. It can be well understood with the carrier number fluctuations whereas the conduction is mainly limited by the bulk expecting Hooge mobility fluctuations. The trapping/release of charge carriers is related not only to the oxide-semiconductor interface but also to the depleted channel. The volume trap density is in the range of 6-30 x 10(16) cm(-3) eV(-1), which is similar to Si-SiO2 bulk transistors and remarkably lower than in high-k transistors. These results show that the noise in nanowire devices might be affected by additional trapping centers. (C) 2011 American Institute of Physics. (doi:10.1063/1.3569724

Development and characterization of iron-pectin beads as a novel system for iron delivery to intestinal cells

Iron deficiency is the most common nutritional deficit worldwide. The goal of this work was to obtain iron-pectin beads by ionic gelation and evaluate their physiological behavior to support their potential application in the food industry. The beads were firstly analyzed by scanning electronic microscopy, and then physical-chemically characterized by performing swelling, thermogravimetric, porosimetry, Mössbauer spectroscopy and X-ray fluorescence analyses, as well as by determining the particle size. Then, physiological assays were carried out by exposing the beads to simulated gastric and intestinal environments, and determining the iron absorption and transepithelial transport into Caco-2/TC7 cells. Iron-pectin beads were spherical (diameter 1-2 mm), with high density (1.29 g/mL) and porosity (93.28%) at low pressure, indicating their high permeability even when exposed to low pressure. Swelling in simulated intestinal medium (pH 8) was higher than in simulated gastric medium. The source of iron [FeSO4 (control) or iron-pectin beads] did not have any significant effect on the mineral absorption. Regarding transport, the iron added to the apical pole of Caco-2/TC7 monolayers was recovered in the basal compartment, and this was proportional with the exposure time. After 4 h of incubation, the transport of iron arising from the beads was significantly higher than that of the iron from the control (FeSO4). For this reason, iron-pectin beads appear as an interesting system to overcome the low efficiency of iron transport, being a potential strategy to enrich food products with iron, without altering the sensory properties.Centro de Investigación y Desarrollo en Criotecnología de Alimento

Contour models of cellular adhesion

The development of traction-force microscopy, in the past two decades, has created the unprecedented opportunity of performing direct mechanical measurements on living cells as they adhere or crawl on uniform or micro-patterned substrates. Simultaneously, this has created the demand for a theoretical framework able to decipher the experimental observations, shed light on the complex biomechanical processes that govern the interaction between the cell and the extracellular matrix and offer testable predictions. Contour models of cellular adhesion, represent one of the simplest and yet most insightful approach in this problem. Rooted in the paradigm of active matter, these models allow to explicitly determine the shape of the cell edge and calculate the traction forces experienced by the substrate, starting from the internal and peripheral contractile stresses as well as the passive restoring forces and bending moments arising within the actin cortex and the plasma membrane. In this chapter I provide a general overview of contour models of cellular adhesion and review the specific cases of cells equipped with isotropic and anisotropic actin cytoskeleton as well as the role of bending elasticity.Comment: 24 pages, 9 figures. arXiv admin note: text overlap with arXiv:1304.107

Development and characterization of iron-pectin beads as a novel system for iron delivery to intestinal cells

Iron deficiency is the most common nutritional deficit worldwide. The goal of this work was to obtain iron-pectin beads by ionic gelation and evaluate their physiological behavior to support their potential application in the food industry. The beads were firstly analyzed by scanning electronic microscopy, and then physical-chemically characterized by performing swelling, thermogravimetric, porosimetry, Mössbauer spectroscopy and X-ray fluorescence analyses, as well as by determining the particle size. Then, physiological assays were carried out by exposing the beads to simulated gastric and intestinal environments, and determining the iron absorption and transepithelial transport into Caco-2/TC7 cells. Iron-pectin beads were spherical (diameter 1-2 mm), with high density (1.29 g/mL) and porosity (93.28%) at low pressure, indicating their high permeability even when exposed to low pressure. Swelling in simulated intestinal medium (pH 8) was higher than in simulated gastric medium. The source of iron [FeSO4 (control) or iron-pectin beads] did not have any significant effect on the mineral absorption. Regarding transport, the iron added to the apical pole of Caco-2/TC7 monolayers was recovered in the basal compartment, and this was proportional with the exposure time. After 4 h of incubation, the transport of iron arising from the beads was significantly higher than that of the iron from the control (FeSO4). For this reason, iron-pectin beads appear as an interesting system to overcome the low efficiency of iron transport, being a potential strategy to enrich food products with iron, without altering the sensory properties.Centro de Investigación y Desarrollo en Criotecnología de Alimento

Mapping the Complex Morphology of Cell Interactions with Nanowire Substrates Using FIB-SEM

Using high resolution focused ion beam scanning electron microscopy (FIB-SEM) we study the details of cell-nanostructure interactions using serial block face imaging. 3T3 Fibroblast cellular monolayers are cultured on flat glass as a control surface and on two types of nanostructured scaffold substrates made from silicon black (Nanograss) with low- and high nanowire density. After culturing for 72 hours the cells were fixed, heavy metal stained, embedded in resin, and processed with FIB-SEM block face imaging without removing the substrate. The sample preparation procedure, image acquisition and image post-processing were specifically optimised for cellular monolayers cultured on nanostructured substrates. Cells display a wide range of interactions with the nanostructures depending on the surface morphology, but also greatly varying from one cell to another on the same substrate, illustrating a wide phenotypic variability. Depending on the substrate and cell, we observe that cells could for instance: break the nanowires and engulf them, flatten the nanowires or simply reside on top of them. Given the complexity of interactions, we have categorised our observations and created an overview map. The results demonstrate that detailed nanoscale resolution images are required to begin understanding the wide variety of individual cells' interactions with a structured substrate. The map will provide a framework for light microscopy studies of such interactions indicating what modes of interactions must be considered