Complex investigation of multilayer nanostructure of a‐Si/SiO1.9 by probe and spectroscopic analysis techniques. Visualization of the band structure. Studying of the band structure of the suboxide border layers

This article describes an integrated approach to the study of multilayer nanostructures of a‐Si/SiO_1.9 as a potential model to study the influence of the effects arising at the interface of Si/SiO₂ under the influence of ionizing radiation. The results of the functional layers of amorphous silicon and silicon dioxide surface topology investigation have been disclosed. The possibility of application of a band gap contrast in electron probe studies by means of electron energy filtering during the detection process has been demonstrated. Changes in valence band and band gap through depth of the a‐Si/SiO_1.9 nanostructure have been registered. As part of the study, density of states of the a‐Si/SiO_1.9 multilayer nanostructures and depth distribution of surface suboxide layers of native oxide of amorphous silicon have been reconstructed using the determination of an effective mean free path of the electrons by the TPP2M algorithm in conjunction with PARXPS and REELS measurements. Copyright © 2015 John Wiley & Sons, Ltd.     

Area radiation monitoring on ISS Increments 17 to 22 using PADLES in the Japanese Experiment Module Kibo

The measurement of radiation environmental parameters in space is essential to support radiation risk assessments for astronauts and establish a benchmark for space radiation models for present and future human space activities. The Japan Aerospace Exploration Agency (JAXA) is performing a continuous area radiation monitoring experiment using the “PAssive Dosimeters for Lifescience Experiments in Space” (PADLES) system inside the Japanese Experiment Module Kibo on board the International Space Station (ISS). The PADLES dosimeter consists of thermoluminescent dosimeters (TLDs) and CR-39 plastic nuclear track detectors (PNTDs). JAXA has run the Area PADLES experiment since the Kibo module was attached to the ISS in June 2008, using 17 dosimeters in fixed locations on the Pressurized Module (PM) and the Experiment Logistics Module-Pressurized Section (ELM-PS) of Kibo, which are replaced every 6 months or every Increment, respectively. For three monitoring periods, known as Area PADLES experiment series #1 to #3, of 301, 180, and 232 days in June 2008 to April 2010 over ISS Increments 17 to 22, the average absorbed dose (dose equivalent) rates of 12 positions in the PM of Kibo were 319 ± 30 μGy/day (618 ± 102 μSv/day), 276 ± 30 μGy/day (608 ± 94 μSv/day), and 293 ± 33 μGy/day (588 ± 84 μSv/day), respectively. The radiation measurement in the ELM-PS was conducted in only Area PADLES experiment series #3 from August 2009 to April 2010 (232 days) over ISS Increments 21 to 22, the average absorbed dose (dose equivalent) rates of 5 positions was 297 ± 28 μGy/day (661 ± 65 μSv/day). The directional dependence of the radiation field was also investigated by installing PADLES dosimeters located in the zenith of ELM-PS of Kibo.     

Neutron-induced complex reaction analysis with 3D nuclear track simulation

Complex (multiple) etched tracks are analysed through digitised images and 3D simulation by a purpose-built algorithm. From a binary track image an unfolding procedure is followed to generate a 3D track model, from which several track parameters are estimated. The method presented here allows the deposited energy, that originated from particle fragmentation or carbon spallation by means of induced tracks in commercially available PADC detectors, to be estimated. Results of evaluated nuclear tracks related to ¹²C () reaction are presented here. The detectors were exposed on the ISS in 2001.     

Silica poisoning of oxygen membranes

Perovskite oxide membranes (La_0.6Sr_0.4Co_0.2Fe_0.8O₃) are used for the separation of oxygen from air. In oxygen permeation experiments these membranes showed a peculiar behavior. Besides poor performance, a characteristic coloring also appeared on the surface of the membranes. In order to understand what was happening to the surface of the membranes, they were analysed with Low-Energy Ion Spectroscopy (LEIS) and X-ray Photoelectron Spectroscopy (XPS). The analyses showed that the surface of the LSCF membrane was covered with a SiO₂ layer, which obviously reduced the performance and caused the coloring. It was established that the source of the silicon was siloxane containing grease that was used in the manual valves of the setup. In a new improved permeation setup, where grease-free valves were used, the LSCF membranes showed remarkably better performance. The LEIS measurements showed also that the permeation experiment of 300 h did not affect the surface composition of the membranes. The contamination-free LSCF membranes only showed the presence of La, Sr and O in the outermost atomic layer. The observed absence of Co and Fe suggests that further improvement of the membrane performance is possible.     

Input-to-state stability of impulsive systems with hybrid delayed impulse effects

The goal of this paper is to study properties of input-to-state stability (ISS) and integral input-to-state stability (iISS) of impulsive systems with hybrid delayed impulses, and a set of Lyapunov-based sufficient conditions ensuring ISS/iISS properties are obtained. Those conditions reveal the effects of hybrid delayed impulses on ISS/iISS and establish the relationship between impulsive frequency and the time delay existing in hybrid impulses. When the continuous dynamics of the system are stabilizing, the ISS property can be retained under the impulse scheme even if there exist destabilizing impulses. Conversely, when the impulse dynamics are stabilizing, but the continuous dynamics are not, the ISS property can be obtained if the interval between impulses are not overly long. Two illustrative examples are presented, with their numerical simulations, to demonstrate the effectiveness of the main results.     

Cosmic ray studies on the ISS using SSNTD, BRADOS projects, 2001–2003

The BRADOS 1–3 projects were organised by the Russian Space Agency (RZA) between 2001 and 2003. The aim was to study the contribution of the primary galactic cosmic rays and of the secondary particles to the dose received by the crew of the International Space Station (ISS). Several laboratories participated in these experiments. Two different stacks (constructed by the team of the Atomic Energy Research Institute, AERI, Budapest, Hungary) composed of solid-state nuclear track detectors (SSNTD) were exposed inside the Service Module at different locations. The calibrations were made at the CERN high-energy neutron reference field named CERF (Geneva, Swiss). Applying a multiple track etching technique (2–20 h etching time) and a sophisticated image analyser, the secondary neutron dose was deduced. The composition of stacks, the evaluation methods and the results will be presented here or referenced to previous papers.     

The fundamental surface science of wurtzite gallium nitride

A review is presented that covers the experimental and theoretical literature relating to the preparation, electronic structure and chemical and physical properties of the surfaces of the wurtzite form of GaN. The discussion includes the adsorption of various chemical elements and of inorganic, organometallic and organic species. The focus is on work that contributes to a microscopic, atomistic understanding of GaN surfaces and interfaces, and the review concludes with an assessment of possible future directions.