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...

Sputtering of W Mo alloy under ion bombardment

The distribution of plasma density in the vicinity of the W Mo alloy source in the process of double glow discharge plasma surface alloying was diagnosed using the moveable Langmuir probe. The sputtering law, surface composition and morphological variation of the W Mo alloy source was studied. The experimental results show that there exists obvious preferential sputtering on the surface of the W Mo alloy source under the argon ion bombardment; the stable period is reached after a transitional period, and the preferential sputtering occurs in a definite range of composition(mole fraction): 70%～75% Mo, 22%～25% W; there appears segregation on the surface of the W Mo alloy source.

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.

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.

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.

4-20 Light Emission from Sputtered Aluminum Atoms and Ions Produced by Kr13+ Ion Bombardment

When solid surface is bombarded by energetic projectile ions, a fraction of the sputtered particles leaves the surface in electronically excited states. The optical emission in front of the target surface is due to the radiative decay of these sputtered particles[1;2]. The optical emission identifies the target by measurement of wavelength.

Impact of Low-Energy Ion Beam Implantation on the Expression of Ty1-copia-like Retrotransposons in Wheat(Triticum aestivum)

Retrotransposon-like elements are major constituents of most eukaryotic genomes. For example, they account for roughly 90% of the wheat （Triticum aestivum） genome, Previous study on a wheat strain treated by low-energy N^＋ ions indicated the variations in AFLP （Amplified Fragment Length Polymorphism ） markers, One such variation was caused by the re-activation of Tyl-copia-like retrotransposons, implying that the mutagenic effects of lowenergy ions might work through elevated activation of retrotransposons, In this paper an expression profile of Tyl-copia-like retrotransposons in wheat treated by low-energy N^＋ ions is reported, The reverse transcriptase （RT） domains of these retrotransposons were amplified by reverse-transcriptional polymerase chain reaction （RT-PCR） and sequentially cloned, 42 and 65 clones were obtained from the treated （CL） and control materials （CK）, respectively, Sequence analysis of each clone was performed by software. Phylogeny and classification were calculated responding to the sequences of the RT domains. All the results show that there is much difference in the RT domain between the control sample and the treated sample, Especially, the RT domains from the treated group encode significantly more functional ORF （open reading frames） than those from the control sample, This observation suggests that the treated sample has higher activation of retrotransposons, possibly as a consequence of low-energy ion beam irradiation, It also suggests that retrotransposons in the two groups impact the host gene expression in two different ways and carry out different functions in wheat cells.

Damage of low-energy ion irradiation on copper nanowire:molecular dynamics simulation

Physical and chemical phenomena of low-energy ion irradiation on solid surfaces have been studied systematically for many years, due to the wide applications in surface modification, ion implantation and thin-film growth. Recently the bombardment of nano-scale materials with low-energy ions gained much attention. Comared to bulk materials, nano-scale materials show different physical and chemical properties. In this article, we employed molecular dynamics simulations to study the damage caused by low-energy ion irradiation on copper nanowires. By simulating the ion bombardment of 5 different incident energies, namely, 1 keV, 2 keV, 3 keV, 4 keV and 5 keV, we found that the sputtering yield of the incident ion is linearly proportional to the energies of incident ions. Low-energy impacts mainly induce surface damage to the nanowires, and only a few bulk defects were observed. Surface vacancies and adatoms accumulated to form defect clusters on the surface, and their distribution are related to the type of crystal plane, e.g. surface vacancies prefer to stay on （100） plane, while adatoms prefer （110） plane. These results reveal that the size effect will influence the interaction between low-energy ion and nanowire.

Improvement of L(+)-Lactic Acid Production of Rhizopus Oryzae by Low-Energy Ions and Analysis of Its Mechanism

The wild type strain Rhizopus oryzae PW352 was mutated by means of nitrogen ion implantation （15 keV, 7.8×10^14 ～ 2.08 ×10^15 ions/cm^2） to find an industrial strain with a higher L（＋）-lactic acid yield, and two mutants RE3303 and RF9052 were isolated. In order to discuss the mechanism primarily, Lactate Dehydrogenase of Rhizopus oryzae was studied. While the two mutants produced L（＋）-lactic acid by 75% more than the wild strain did, their specific activity of Lactate Dehydrogenase was found to be higher than that in the wild strain. The optimum temperature of Lactate Dehydrogenase in Rhizopus oryzae RF9052 was higher. Compared to the wild strain, the Michaelis constant （Km） value of Lactate Dehydrogenase in the mutants was Changed. All these changes show that L（＋）-lactic acid production has a correlation with the specific activity of Lactate Dehydrogenase. The low-energy ions, implanted into the strain, may improve the specific activity of Lactate Dehydrogenase by influencing its gene structure and protein structure.

Analysis of a Partial Male-Sterile Mutant of Arabidopsis thaliana Isolated from a Low-Energy Argon Ion Beam Mutagenized Pool

A screen for Arabidopsis fertility mutants, mutagenized by low-energy argon ion beam, yielded two partial male-sterile mutants tc243-1 and tc243-2 which have similar phenotypes. tc243-2 was investigated in detail. The segregation ratio of the mutant phenotypes in the M2 pools suggested that mutation behaved as single Mendelian recessive mutations, tc243 showed a series of mutant phenotypes, among which partial male-sterile was its striking mutant characteristic. Phenotype analysis indicates that there are four factors leading to male sterility, a. Floral organs normally develop inside the closed bud, but the anther filaments do not elongate sufficiently to position the locules above the stigma at anthesis, b. The anther locules do not dehisce at the time of flower opening （although limited dehiscence occurs later）, c. Pollens of mutant plants develop into several types of pollens at the trinucleated stage. as determined by staining with DAPI （4＇,6-diamidino-2-phenylindole）. which shows a variable size. shape and number of nucleus. d. The viability of pollens is lower than that of the wild type on the germination test in vivo and vitro.

Surface Etching and DNA Damage Induced by Low-Energy Ion Irradiation in Yeast

Bio-effects of survival and etching damage on cell surface and DNA strand breaks were investigated in the yeast saccharomyces cerevisiae after exposure by nitrogen ion with an energy below 40 keV. The result showed that 16% of trehalose provided definite protection for cells against vacuum stress compared with glycerol. In contrast to vacuum control, significant morpho- logical damage and DNA strand breaks were observed, in yeast cells bombarded with low-energy nitrogen, by scanning electron microscopy （SEM） and terminal deoxynucleotidyl transferase- mediated dUTP nick end labeling （TUNEL） immunofluorescence assays. Moreover, PI （propidium iodide） fluorescent staining indicated that cell integrity could be destroyed by ion irradiation. Cell damage eventually affected cell viability and free radicals were involved in cell damage as shown by DMSO （dimethyl sulfoxide） rescue experiment. Our primary experiments demonstrated that yeast cells can be used as an optional experimental model to study the biological effects of low energy ions and be applied to further investigate the mechanism（s） underlying the bio-effects of eukaryotic cells.

A Preliminary Study of the Application of a Model Animal-Caenorhabidity elegans'Exposure to a Low-Energy Ion Irradiation System

Because of the lack of suitable animal models adapted to high vacuum stress in the low-energy ion implantation system, the bio-effects ion irradiation with an energy less than 50 keV on multi-cellular animal individuals have never been investigated so far. The nematode Caenorhabditis elegans has proved to be an excellent animal model used for the study of a broad spectrum of biological issues. The purpose of this work was to investigate the viability of this animal under ion irradiation. We studied the protection effects of glycerol and trehalose on the enhancement of nematodes＇ ability to bear the vacuum stress. The results showed that the survival of the nematodes was enhanced remarkably under long and slow desiccation, even without glycerol and trehalose. 159 glycerol showed a better anti-vacuum stress effect on the nematodes than trehalose did under short-time desiccation. Low-temperature pre-treatment or post-treatment of the samples had no obvious effect on the survival scored after argon ion irradiation. Moreover, little effect was induced by 15% glycerol- and vacuum-exposure on germ cell apoptosis, compared to the untreated control sample. It issuggested that such treatment would provide relatively low background for genotoxic evaluations with ion irradiation.

Modeling of Inner Surface Modification of a Cylindrical Tube by Plasma-Based Low-Energy Ion Implantation

The inner surface modification process by plasma-based low-energy ion implantation（PBLEII）with an electron cyclotron resonance（ECR）microwave plasma source located at the central axis of a cylindrical tube is modeled to optimize the low-energy ion implantation parameters for industrial applications.In this paper,a magnetized plasma diffusion fluid model has been established to describe the plasma nonuniformity caused by plasma diffusion under an axial magnetic field during the pulse-off time of low pulsed negative bias.Using this plasma density distribution as the initial condition,a sheath collisional fluid model is built up to describe the sheath evolution and ion implantation during the pulse-on time.The plasma nonuniformity at the end of the pulse-off time is more apparent along the radial direction compared with that in the axial direction due to the geometry of the linear plasma source in the center and the difference between perpendicular and parallel plasma diffusion coefficients with respect to the magnetic field.The normalized nitrogen plasma densities on the inner and outer surfaces of the tube are observed to be about 0.39 and 0.24,respectively,of which the value is 1 at the central plasma source.After a 5μs pulse-on time,in the area less than 2 cm from the end of the tube,the nitrogen ion implantation energy decreases from 1.5 keV to 1.3 keV and the ion implantation angle increases from several degrees to more than 40°;both variations reduce the nitrogen ion implantation depth.However,the nitrogen ion implantation dose peaks of about 2×10^（10）-7×10^（10）ions/cm^2 in this area are 2-4 times higher than that of 1.18×10^（10）ions/cm^2 and 1.63×10^（10）ions/cm^2 on the inner and outer surfaces of the tube.The sufficient ion implantation dose ensures an acceptable modification effect near the end of the tube under the low energy and large angle conditions for nitrogen ion implantation,because the modification effect is mainly determined by the ion implantation dose,just as the mass transfer process in PBLEII is dominated by low-energy ion implantation and thermal diffusion.Therefore,a comparatively uniform surface modification by the low-energy nitrogen ion implantation is achieved along the cylindrical tube on both the inner and outer surfaces.

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.

ACHIEVEMENT OF LOW-ENERGY HEAVY-ION BIOLOGY

Generally,the interaction of low-energy ions with matter used to attract less attention than that of high-energy ions.In the 1980s,when the study of ion beam modification of materials was prosperous both at home and abroad,a new biological effect caused by ion beam implantation was discovered by Prof. Yu Zengliang and his postgraduates at CAS institute of Plasma Physics.In their research into the interaction between low energy ions and organism,they put forward and developed some new concepts,such as the bio damage model of mass-deposition and cell itching processing with ion beam.And they applied those principles in breeding new cultivars and made sig-

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.

Improvement of Vitamin K_2 Production by Escherichia sp.with Nitrogen Ion Beam Implantation Induction

Low-energy ion implantation as a novel mutagen has been increasingly applied in the microbial mutagenesis for its higher mutation frequency and wider mutation spectra. In this work, N^＋ ion beam implantation was used to enhance Escherichia sp. in vitamin K2 yield. Optimization of process parameters under submerged fermentation was carried out to improve the vitamin K2 yield of mutant FM5-632. The results indicate that an excellent mutant FM5-632 with a yield of 123.2±1.6 μg/L, that is four times that of the original strain, was achieved by eight successive implantations under the conditions of 15 keV and 60 ×2.6 ×10^13 ions/cm^2. A further optimization increased the yield of the mutant by 39.7%, i.e. 172.1±1.2 μg/L which occurred in the mutant cultivated in the optimal fermentation culture medium composed of （per liter）： 15.31 g glycerol, 10 g peptone, 2.89 g yeast extract, 5 g K2HPO4, 1 g NaCl, 0.5 g MgSO4·7H2O and 0.04 g cedar wood oil, incubated at 33 ℃, pH 7.0 and 180 rpm for 120 h.

HIGH ENERGY Xe^+ ENHANCED ADHESION OF Al AND Ag FILMS ON OPTICAL GLASS

The samples consisting of 100nm Al or Ag film on optical glass substrate were irradiated by a beam of Xe 5×1015 to 2×1016 cm-2 with energy 320 keV. The adhesion of films on substrates was tested by Xe+ irradiation. Optical character was measured by spectrophotometer. The ion mixing amount was measured by RBS. The results showed that after ion irradiating the adhesion of the film on the glass is enhanced. The adherent strength is greater than 10 kg/cm2. The thermal stability of the films is good. The irradiated film is more optically efficient, the surface is smooth and rendered more corrosion resistance. The mechanism of the film adhesion was discussed.