Influence of cyclic ignition and steady-state operation on a 1–2 A barium tungsten hollow cathode

Booming low-power electric propulsion systems require 1–2 A hollow cathodes.Such cathodes are expected to go through more frequent ignitions in the low orbit,but the impact of cyclic ignitions on such 1–2 A barium tungsten hollow cathodes with a heater was not clear.In this study,a 12,638-cyclic ignition test and a 6,000-hour-long life test on two identical cathodes were carried out.The discharge voltage of the cathode and the erosion of the orifice after cyclic ignition were all larger than that of the cathode after stable operation.This indicated that the impact of cycle ignition on the discharge performance of a low current BaO-W cathode with a heater was higher than that of stable operation.The results of the ion energy distribution function measured during the ignition period indicated that the main reason for the orifice expansion was ion bombardment.Therefore,it was necessary to pay attention to the number of ignitions for the lifetime of this kind of cathode.

Degradation of the Emission Current from the Field Emitter Caused by Ion Bombardment

In field emission devices, the emission current sometimes degrades with the time. The mechanism of the current degradation is complicated. In this paper, a program is used to simulate the movement of the electron beam from a field emitter. According to the current distribution and the trajectories of the primary electron beam, it is shown that the residual gas is ionized and the ion pairs are generated. The trajectories of the positive ions are simulated. With the different locations and kinetic energy of i...

Formation of nanocrystalline microstructure in arc ion plated CrN films

Applying negative bias voltages caused significant microstructure changes in arc ion plated CrN films. Nanocrystalline microstructures were obtained by adjusting the negative bias voltage. Structural characterizations of the films were carried out using X-ray diffractometry (XRD) and high-resolution transmission electron microscopy (HR-TEM). The results indicated that increasing ion bombardment by applying negative bias voltages resulted in the formation of defects in the CrN films, inducing microstructure evolution from micro-columnar to nanocrystalline. The microhardness and residual stresses of the films were also affected. Based on the experimental results, the evolution mechanisms of the film microstructure and properties were discussed by considering ion bombardment effects.

Effect of Ar＋, He＋, and S＋ Irradiation on n-InP Single Crystal

The irradiation effects of Ar＋, He＋, and S＋ with energy from 10 eV to 180 eV on n-InP（100） surface are analyzed by X-ray photoelectron spectroscopy and low energy electron diffraction. After irradiation on the n-InP surface, damage on the surface, displacement of the Fermilevel and formation of sulfur species on S＋ exposed surface are found and studied. Successive annealing is done to suppress the surface states introduced by S＋ exposure. However, it is unsuccessful in removing the damage caused by noble ions. Besides, S＋ ions can efficiently repair the Ar＋ damaged surface, and finally form a fine 2×2 InP surface.

Response of HD-V2 radiochromic film to argon ions

A two-dimensional dose detector for ion beam is required in many high energy density physics experiments.As a solid detector,the GAFChromic film offers a good spatial resolution and dosimetric accuracy.For an absolute dose measurement,the relative effectiveness,which represents the darkening efficiency of the film to a radiation source,needs to be taken into consideration.In this contribution,the dose-response of HD-V2 to argon ions is presented for the first time.The calibration was taken over the dose range of 65 Gy-660 Gy with 8-keV argon ions.The response of net optical density is from 0.01 to 0.05.Triple-color dose-response functions are derived.The relative effectiveness for the argon ion beams is about 5%,much lower than that of protons and carbon ions.To explain this effect,the inactivation probability based on track theory of ion bombardment is proposed.Furthermore,a theoretical prediction of the relative effectiveness for single ion is presented,showing the dependence of the darkening efficiency on the atomic number and the incident energy of ions.

Simulation of Isotopic Angular Effects under Ion Bombardment of a^(92)Mo-^(100)Mo Target

Under 5 keV Ar ion bombardment of a 92Mo-100Mo target, we have investigated isotopic angular effects by means of the static and the dynamic Monte Carlo programs. Our calculated results are in quantitative agreement with the measured and other calculated results. The conclusion consistences among theories. simulations and measurements are also discussed.

Ions Bombardment in Thin Films and Surface Processing

Ions bombardment is very important in thin films and surface processing. The ion energy and ion flux are two important parameters in ion bombardment. The ion current density mainly dependent on the plasma density gives the number of energetic ions bombarding the substrate. The self-bias voltage in plasma sheath accelerates plasma ions towards the substrate. RF discharge can increase plasma density and RF bias can also provide the insulator substrate with a plasma sheath. In order to choose and control ion energy, ion density, the angle of incidence, and ion species, ion beam sources are used. New types of electrodeless ion sources (RF, MW, ECR-MW) have been introduced in detail. In the last, the effects of ion bombardment on thin films and surface processing are presented.

MICROSTRUCTURE OF Ti－B－NFILM AND INTERFACEFORMED BY N ION BOMBARDMENTON A Ti－B FILM

Ti-B-N film was deposited on W18Cr4 V high speed steels by using N ion bombardment on an EB-ion plating Ti-B film. It was found that Ti, B and N in the film are homogeneous, but there exists an extended diffusion zone at the film / substrate interface on the basis of the results of IPMA, EPMA and TEM. The boron content of the film is 9.5 at.%, as given by nuclear reaction analysis. The ratio of nitrogen to titanium of the film is about 0.94, as given by EPMA. The width of a high N concentration region in the Ti-B-N film fowned by N ion bombardment of a Ti-B film is about 100 nm; N and Ti penetrates into the substrate, resulting in a wide interfacial diffusion zone. The width of the diffusion zone obtained with TEM and EDAX is about 20 nm. μ-diffraction patterns of the interface show that FeTi, Fe_2 Ti, and Ti_2N existin the interfacial diffusion zone. TEM observation of film and interface show a dense and fine nano-crystalline structure of the film and a dense close interfactal bonding of the film to substrate. Electron diffraction patterns and the values of electrun binding energy by XPS show that the film consists mainly of fcc TiN, with dispersed simple orthorhombic TiB, cubic BN and simple hexagonal Ti-B-N phases. The results show that the N ion hombardment extends the film / substrate interfacial diffusion zone and stimulates chemical reaction both in the film and interface.

ENHANCING ADHESION OF TETRAHEDRAL AMORPHOUS CARBON FILMS

Objective The high energy ion bombardment technique is applied to enhancing the adhesion of the tetrahedral amorphous carbon (TAC) films deposited by the filtered cathode vacuum arc (FCVA). Methods The abrasion method, scratch method, heating and shaking method as well as boiling salt solution method is used to test the adhesion of the TAC films on various material substrates. Results The test results show that the adhesion is increased as the ion bombardment energy increases. However, if the bombardment energy were over the corresponding optimum value, the adhesion would be enhanced very slowly for the harder material substrates and drops quickly, for the softer ones. Conclusion The optimum values of the ion bombardment energy are larger for the harder materials than that for the softer ones.

Monte Carlo simulation of lattice analysis of complex LaCeTh0.1CuOy using ion bombardment technique

Ion bombardment analysis of perovskite materials is challenging owing to their peculiar structure.This shortcoming renders the reliability on the technique somewhat questionable.In this research,three structured modifications(i.e.,scan angle,low energy,and large ion bombardment)were adopted to improve the ion bombardment analysis of 99,999 ions using Monte Carlo simulations.The modified technique was used to analyze the effects of a chemically pressurized‘‘A’’site in the perovskite lattice system.The LaCeTh0.1Cu2Oy compound was used in this experiment.Despite the low probing energy,it was observed that the high number of ions bombarding the material resulted in external pressure on the lattice structure of the material.Moreover,the chemically pressurized‘‘A’’site perovskite material was characterized by lattice mismatch,lattice fluctuations,grain boundary collapse,and oxygen displacement.The novel discovery of this research is the inter-and intra-extended lattice mismatches that are likely to connect.Hence,further investigation of the connection between inter-and intraextended lattice mismatches is recommended as they may enable fabrication of room-temperature superconductors.

The role of ions in plasma catalytic carbon nanotube growth： A review

While it is well-known that the plasma- enhanced catalytic chemical vapor deposition （PECVD） of carbon nanotubes （CNTs） offers a number of advantages over thermal CVD, the influence of the various individual contributing factors is not well understood. Especially the role of ions is unclear, since ions in plasmas are generally associated with sputtering rather than with growing a material. Even so, various studies have demonstrated the beneficial effects of ion bombardment during the growth of CNTs. This review looks at the role of the ions in plasma- enhanced CNT growth as deduced from both experimental and simulation studies. Specific attention is paid to the beneficial effects of ion bombardment. Based on the available literature, it can be concluded that ions can be either beneficial or detrimental for carbon nanotube growth, depending on the exact conditions and the control over the growth process.

Stable field emission of ion-sputtering-induced Si nanocone arrays

Silicon nanocone arrays with metal silicide （Fe and Cr）-enriched apexes are fabricated on Si （100） substrate by the Ar＋ ion bombardment method. The nanocone arrays show excellent field emission properties. A high current density （J） of -0.03 mA/cm^2 under a field of -3 V/μm, a very low turn-on field of -1.4 V/μm, and a very large enhancement factor of -9466 are also obtained. The emission J of Si nanocone arrays remains extremely stable for long periods of time （24 h）.

A review on recent progress of thermionic cathode

As the performance of vacuum electron devices is essentially governed by the properties of their cathodes,developing efficient and durable thermionic cathode is necessary and highly desired to meet the boosting requirements of vacuum electron devices.This review summarized the progress made in the past decades with a detailed discussion on the occurred various thermionic cathodes and their features,and the understandings of the correlation between the emission properties and the composition,where structure and synthesis method are well illustrated.Furthermore,dispenser cathodes with novel structures and emission mechanism are highlighted to indicate the recent achievement in this area of research,and Sc-cathode is considered as a promising candidate for the next-generation vacuum electron devices due to the greatly improved efficiency.However,challenges still exist to meet the ever-growing demands of thermionic cathode with collaborative requirement of high performance,easy fabrication and inadequate reproducibility.

Effects of ion bombardment on microcrystalline silicon growth by inductively coupled plasma assistant magnetron sputtering

Hydrogenated microcrystalline silicon （mc-Si：H） thin films were deposited by inductively coupled plasma assistant magnetron sputtering （ICP-MS） in an Ar-H2 gas mixture. The role of ion bombardment in the growth of mc-Si：H films was studied with increasing negative bias voltages on the substrate holder from 0 to -100 V. Raman scattering, X-ray diffraction （XRD）, Fourier transform infrared （FTIR） spectroscopy and transmission electron microscopy （TEM） were performed to investigate the microstructure changes of deposited Si films. Raman scattering showed that the high energy ion bombardment resulted in crystalline degradation of Si films. The XRD results showed the decrease and even elimination of preferential growth orientation of crystalline Si films with ion bombardment energy increase. The SiH bonding configuration changes and the increase of bonded hydrogen concentration were determined with the analysis of FTIR spectra. Furthermore, the dramatic evolution of cross-sectional morphology of Si thin films was detected by TEM observation.

Stereochemical effects in mass spectrometry——Ⅺ.Negative ion fast atom bombardment mass spectrometry of saccharides and glycosides using phenylboronic acid as reagent

The negative ion fast atom bombardment (NIFAB) mass spectra of mono-,di-saccharides and glycosides using phenylboronic acid (PBA) as reagent have been studied.In the ion source,PBA reacts stereospecifically with the molecules containing cis-vicinal glycols to form characteristic ions, from which the stereo-isomers of saccharides can be definitely distinguished.Disaccharides and glyco- sides with β-glycosidic linkage seem to be unfavorabale to react with PBA,therefore,by comparison of the abundances of the characteristic ions,the configuration of the glycosidic linkage in these compounds may be inferred.

Dependency of photoluminescence from SiO2 thin films containing Si1-xGex quantum dots on Ge/Si doping ratio

SiO2 thin films containing Si1-xGex quantum dots （QDs） are prepared by ion implantation and annealing treatment. The photoluminescence （PL） and microstructural properties of thin films are investigated. The samples exhibit strong PL in the wavelength range of 400-470 nm and relatively weak PL peaks at 730 and 780 nm at room temperature. Blue shift is found for the 400-nm PL peak, and the intensity increases initially and then decreases with the increase of Ge-doping dose. We propose that the 400-470 nm PL band originates from multiple luminescence centers, and the 730- and 780-nm PL peaks are ascribed to the Si=O and GeO luminescence centers.