Oxidation of gallium arsenide in a plasma multipole device. Study of the MOS structures obtained

The oxygen plasma oxidation of GaAs was studied in order to obtain extremely high frequency responses with MOS devices. In the multipole system a homogeneous oxygen plasma of high density can easily be obtained in a large volume. This system is thus convenient for the study of plasma oxidation of GaAs. The electrical properties of the MOS diodes obtained in this way are controlled by interface states, located mostly in the upper half of the band gap where densities in the 10 to the 13th power/(sq cm) (eV) range can be estimated. Despite these interface states the possibility of fabricating MOSFET transistors working mostly in the depletion mode for a higher frequency cut-off still exists

UtpA and UtpB chaperone nascent pre-ribosomal RNA and U3 snoRNA to initiate eukaryotic ribosome assembly

Early eukaryotic ribosome biogenesis involves large multi-protein complexes, which co-transcriptionally associate with pre-ribosomal RNA to form the small subunit processome. The precise mechanisms by which two of the largest multi-protein complexes—UtpA and UtpB—interact with nascent pre-ribosomal RNA are poorly understood. Here, we combined biochemical and structural biology approaches with ensembles of RNA–protein cross-linking data to elucidate the essential functions of both complexes. We show that UtpA contains a large composite RNA-binding site and captures the 5′ end of pre-ribosomal RNA. UtpB forms an extended structure that binds early pre-ribosomal intermediates in close proximity to architectural sites such as an RNA duplex formed by the 5′ ETS and U3 snoRNA as well as the 3′ boundary of the 18S rRNA. Both complexes therefore act as vital RNA chaperones to initiate eukaryotic ribosome assembly

Combination of Nanoindentation and Quantitative Backscattered Electron Imaging Revealed Altered Bone Material Properties Associated with Femoral Neck Fragility

Osteoporotic fragility fractures were hypothesized to be related to changes in bone material properties and not solely to reduction in bone mass. We studied cortical bone from the superior and inferior sectors of whole femoral neck sections from five female osteoporotic hip fracture cases (74–92 years) and five nonfractured controls (75–88 years). The typical calcium content (CaPeak) and the mineral particle thickness parameter (T) were mapped in large areas of the superior and inferior regions using quantitative backscattered electron imaging (qBEI) and scanning small-angle X-ray scattering, respectively. Additionally, indentation modulus (E) and hardness (H) (determined by nanoindentation) were compared at the local level to the mineral content (CaInd) at the indent positions (obtained from qBEI). CaPeak (−2.2%, P = 0.002), CaInd (−1.8%, P = 0.048), E (−5.6%, P = 0.040), and H (−6.0%, P = 0.016) were significantly lower for the superior compared to the inferior region. Interestingly, CaPeak as well as CaInd were also lower (−2.6%, P = 0.006, and –3.7%, P = 0.002, respectively) in fracture cases compared to controls, while E and H did not show any significant reduction. T values were in the normal range, independent of region (P = 0.181) or fracture status (P = 0.551). In conclusion, it appears that the observed femoral neck fragility is associated with a reduced mineral content, which was not accompanied by a reduction in stiffness and hardness of the bone material. This pilot study suggests that a stiffening process in the organic matrix component contributes to bone fragility independently of mineral content

Plasma anodization of silicon at room temperature

Room temperature plasma anodization of silicon (growth rate of a few nm/min.) is possible through a thin calcia stabilized zirconia (CSZ) layer. The anodization kinetics, the composition and the electrical properties of the anodic SiO 2 films are studied. Constant voltage or low current anodization lead to quasi defect free films with reduced surface roughness. The dielectric breakdown field of as grown SiO2 is about 5 x 106 V/cm. The minimum of density of traps at the SiO2/Si interface is in the 1010-1011 cm-2. eV-1 range after hydrogen annealing at 470 °C for 30 min. This is comparable to high temperature (above 400 °C) plasma grown SiO2. The protective filter effect of the CSZ against contamination has also been demonstrated. In addition, thick (above 0.3 μm) SiO2 layers can be obtained in a reasonable time (about 30 min.) at moderate temperatures

INTERACTIONS OF Si (III) SURFACE WITH H2, NH3, SiH4 MULTIPOLAR PLASMAS STUDIED BY IN SITU ELLIPSOMETRY

Un système ultra vide formé d'une chambre plasma couplée à une chambre d'analyse permet l'étude de l'interaction de différents plasmas multipolaires (NH3-H2-SiH4) avec la surface (1,1,1) de silicium. Les cinétiques d'interaction peuvent être suivies en temps réel par ellipsométrie "in situ" à 310 nm. Le même appareillage permet d'analyser l'échantillon par ellipsométrie spectroscopique. La chambre d'analyse est équipée d'un spectromètre Auger (CMA) et d'un système RHEED.An ultra high vacuum system consisting in a plasma chamber and an analysis chamber is used to study the interactions of various multipolar plasmas (NH3- H2SiH4) with Si surfaces. The kinetics of interaction can be followed in real time by in situ ellipsometry at 310 nm. Using the same set up the sample can be analyzed in situ by spectroscopic ellipsometry. The analysis chamber is equipped with an Auger spectrometer (CMA) and a RHEED set up

Analysis of the near-intrinsic and extrinsic photocapacitance due to the EL2 level in boron implanted GaAs

A detailed analysis of the photocapacitance signal at the near‐band and extrinsic energetic ranges in Schottky barriers obtained on horizontal Bridgman GaAs wafers, which were implanted with boron at different doses and annealed at several temperatures, has been carried out by using the optical isothermal transient spectroscopy, OITS. The optical cross sections have been determined as well as the quenching efficiency of the EL2 level which has been found to be independent of the annealing temperature. Moreover, the quenching relaxation presents two significant features: (i) a strong increase of the quenching efficiency from 1.35 eV on and (ii) a diminution of the quenching transient amplitude in relation with that shown by the fundamental EL2 level. In order to explain this behavior, different cases are discussed assuming the presence of several energy levels, the existence of an optical recuperation, or the association of the EL2 trap with two levels located, respectively, at Ev+0.45 eV and Ec−0.75 eV. The theoretical simulation, taking into account these two last cases, is in agreement with the experimental photocapacitance data at low temperature, as well as at room temperature where the EL2 filling phototransient shows an anomalous behavior. Moreover, unlike the previous data reported for the EL2 electron optical cross section, the values found using our experimental technique are in agreement with the behavior deduced from the theoretical calculation. The utilization of the OITS method has also allowed the determination of another level, whose faster optical contribution is often added to that of the EL2 level when the DLOS or standard photocapacitance is used

Recent synchrotron radiation microdiffraction experiments on polymer and biopolymer fibers

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