[en] A series of studies were conducted for surface valency in blue tungsten oxides by using photoemission technique. Results show that, the blue tungsten oxide contains not only one kind of valency, but conbination of two valences, namely the conbination of W⁺⁵ and W⁺⁶, and also the process of argon ion etching and high temperature treatment all induced the loss of oxygen in W-chemical reduction process, which causes W transfer from high valence to low valence. Meanwhile, the density of state near Fermi level increases with the change from high valence to low valence

[en] X-ray photoelectron spectroscopy has been used to investigate the interactions between Ti and bismuth-based superconductors. It is shown that Ti adatoms leach oxygen from the underlying superconductors, forming Ti-O bond on the surface. In the interface region. Cu-O and Bi-O bonds are destroyed, Cu²⁺ and Bi³⁺ are reduced to metallic atoms. The electronic structures of the superconductors are disrupted by the Ti adatoms. By using the standard four-probe method, it is found that after Ti deposition, the transition temperature of the thin film is 10 K lower and the zero resistance can not be reached

[en] Breakdown in ablative pulsed plasma thrusters (APPTs) must be studied in order to design new types of APPTs and measure particular parameters. In this paper, we studied a parallel-plate ablative pulsed plasma thruster that used a coaxial semiconductor spark plug. By operating the APPT about 500 times with various capacitor voltages and electrode gaps, we measured and analyzed the voltage of the spark plug, the voltage between the electrodes, and the discharge current. These experiments revealed a time delay (∼1–10 μs) between spark plug ignition and capacitor discharge, which may affect the performance of high-pulsing-rate (>10 kHz) and double-discharge APPTs, and the measurements of some of the APPT parameters. The delay time decreased as the capacitor voltage increased, and it increased with an increasing electrode gap and increasing number of ignitions. We explain our results through a simple theoretical analysis

[en] The influence of doping lanthana on valent state of CeO₂ surface has been studied by using x-ray photoelectron spectroscopy. It was found that La³⁺ doping in host CeO₂ lattice can promote to convert Ce⁴⁺ into Ce³⁺ and enhance adsorbing-carbonyl capacity of the materials. However, the inversion of Ce⁴⁺ to Ce³⁺ is depressed by dopant La³⁺ during argon ion bombardment

[en] The deposition of Cu at room temperature on a Cr₂O₃(0001) substrate is studied by x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and low-energy-electron diffraction. The results indicate that at RT Cu is highly dispersed on the substrate at initial deposition. X-ray induced Auger spectra, Auger parameter and ultraviolet photoelectron spectroscopy show that at the initial coverage the deposited Cu is in the Cu(I) state due to the interaction of Cu with the Cr₂O₃ substrate; Cu becomes metallic at Cu coverages of > 4 monolayer equivalent. The formation of Cu two-dimensional or quasi-2D patches is followed by the formation of Cu three-dimensional clusters. Cu grows epitaxially on the Cr₂O₃(0001) films as Cu(111)R 30 deg. as observed by low-energy-electron diffraction

[en] The interactions of V with Cr₂O₃(0001) films and Cr with V₂O₃(0001) films at room temperature are studied using x-ray photoelectron spectroscopy and low-energy-electron diffraction. The results show that the deposited V is oxidized and the Cr₂O₃(0001) surface is reduced at the initial coverage due to the interaction of V with the Cr₂O₃ substrate; V becomes metallic at V coverage greater than 5 monolayer equivalent. Full oxidization of the deposited vanadium cannot be achieved by O₂ exposure at room temperature for 20 min. However, V₂O₃(0001) films have been observed after heating the sample to 600-700 K in oxygen ambient at 1x10^-7 mbar. Similar results have been obtained for the Cr/V₂O₃(0001)/Re(0001) system. (author)

[en] To illuminate the thermal transfer mechanism of devices adopting polytetrafluoroethylene (PTFE) as ablation materials, the thermal radiation properties of PTFE plasma are calculated and discussed based on local thermodynamic equilibrium (LTE) and optical thin assumptions. It is clarified that line radiation is the dominant mechanism of PTFE plasma. The emission coefficient shows an opposite trend for both wavelength regions divided by 550 nm at a temperature above 15 000 K. The emission coefficient increases with increasing temperature and pressure. Furthermore, it has a good log linear relation with pressure. Equivalent emissivity varies complexly with temperature, and has a critical point between 20 000 K to 25 000 K. The equivalent cross points of the average ionic valence and radiation property are about 10 000 K and 15 000 K for fully single ionization. (paper)

[en] This paper focuses on the net electron-emission current as a function of bias voltage of a plasma source that is being used as the cathodic element in a bare electrodynamic tether system. An analysis is made that enables an understanding of the basic issues determining the current–voltage (C–V) behaviour. This is important for the efficiency of the electrodynamic tether and for low impedance performance without relying on the properties of space plasma for varying orbital altitudes, inclinations, day–night cycles or the position of the plasma contactor relative to the wake of the spacecraft. The cathodic plasma contactor considered has a cylindrical discharge chamber (10 cm in diameter and ∼11 cm in length) and is driven by a hollow cathode. Experiments and a 1D spherical model are both used to study the contactor's C–V curves. The experiments demonstrate how the cathodic contactor would emit electrons into space for anode voltages in the range of 25–40 V, discharge currents in the range of 1–2.5 A, and low xenon gas flows of 2–4 sccm. Plasma properties are measured and compared with (3 A) and without net electron emission. A study of the dependence of relevant parameters found that the C–V behaviour strongly depends on electron temperature, initial ion energy and ion emission current at the contactor exit. However, it depended only weakly on ambient plasma density. The error in the developed model compared with the experimental C–V curves is within 5% at low electron-emission currents (0–2 A). The external ionization processes and high ion production rate caused by the discharge chamber, which dominate the C–V behaviour at electron-emission currents over 2 A, are further highlighted and discussed. (paper)

[en] Pulsed plasma thrusters (PPTs) are an attractive form of micro-thrusters due to advantages such as their compactness and lightweight design compared to other electric propulsion systems. Experimental investigations on their plasma properties are beneficial in clarifying the complex process of plasma evolution during the micro-second pulse discharge of a PPT. In this work, the multi-dimensional evolutions of the light intensity of the PPT plasma with wavelength, time, and position were identified. The plasma pressure was obtained using an iterative process with composition calculations. The results show that significant ion recombination occurred in the discharge channel since the line intensities of CII, CIII, CIV, and FII decreased and those of CI and FI increased as the plasma moved downstream. At the center of the discharge channel, the electron temperature and electron density were in the order of 10 000 K and 10¹⁷ cm⁻³, respectively. These had maximum values of 13 750 K and 2.3 × 10¹⁷ cm⁻³ and the maximum temperature occurred during the first half-cycle while the maximum number density was measured during the second half-cycle. The estimated plasma pressure was in the order of 10⁵ Pa and exhibited a maximum value of 2.69 × 10⁵ Pa. (paper)

[en] Based on the three-dimensional particle-in-cell (PIC) method and Compute Unified Device Architecture (CUDA), a parallel particle simulation code combined with a graphic processor unit (GPU) has been developed for the simulation of charge-exchange (CEX) xenon ions in the plume of an ion thruster. Using the proposed technique, the potential and CEX plasma distribution are calculated for the ion thruster plume surrounding the DS1 spacecraft at different thrust levels. The simulation results are in good agreement with measured CEX ion parameters reported in literature, and the GPU's results are equal to a CPU's. Compared with a single CPU Intel Core 2 E6300, 16-processor GPU NVIDIA GeForce 9400 GT indicates a speedup factor of 3.6 when the total macro particle number is 1.1×10⁶. The simulation results also reveal how the back flow CEX plasma affects the spacecraft floating potential, which indicates that the plume of the ion thruster is indeed able to alleviate the extreme negative floating potentials of spacecraft in geosynchronous orbit