Mass Of Bombarding Ions Research Articles

Spectromicroscopy Study of Induced Defects in Ion-Bombarded Highly Aligned Carbon Nanotubes.

Highly aligned multi-wall carbon nanotubes were investigated with scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after bombardment performed using noble gas ions of different masses (argon, neon and helium), in an ultra-high-vacuum (UHV) environment. Ion irradiation leads to change in morphology, deformation of the carbon (C) honeycomb lattice and different structural defects in multi-wall carbon nanotubes. One of the major effects is the production of bond distortions, as determined by micro-Raman and micro-X-ray photoelectron spectroscopy. We observe an increase in sp3 distorted bonds at higher binding energy with respect to the expected sp2 associated signal of the carbon 1s core level, and increase in dangling bonds. Furthermore, the surface damage as determined by the X-ray photoelectron spectroscopy carbon 1s core level is equivalent upon bombarding with ions of different masses, while the impact and density of defects in the lattice of the MWCNTs as determined by micro-Raman are dependent on the bombarding ion mass; heavier for helium ions, lighter for argon ions. These results on the controlled increase in sp3 distorted bonds, as created on the multi-wall carbon nanotubes, open new functionalization prospects to improve and increase atomic hydrogen uptake on ion-bombarded multi-wall carbon nanotubes.

Electron-induced secondary electron emission coefficient of lithium, tungsten and stainless steel surfaces exposed to low-pressure plasmas

The secondary electron emission (SEE) coefficient by electron impact of Li, W and stainless steel (SS) surfaces exposed to a glow discharge is evaluated and analyzed in the energy range of Ee<200eV. While the values of the SEE coefficient for SS and W show a small increase with respect to their vacuum value, an enhancement of this parameter up to a factor of 6 has been deduced for clean Li surfaces. Experiments with different plasma gas discharges (He, Ar and H2) are undertaken in order to address the possible mechanisms related to such enhancement. No major effect of the bombarding ion mass or incident electron flux is observed. The implications of these findings on the use of Li as a plasma-facing component in fusion devices are addressed.

Origin of surface electrical degradation of insulators due to ionic bombardment

Insulator materials required for ITER and beyond must operate in a significant radiation field, extending well beyond the first wall. As a result, these materials will be subjected not only to neutron and gamma irradiation, but also to particle bombardment, due mainly to ionization of the residual gas and acceleration of the resulting ions by local electric fields. A systematic study was carried out on the main insulating candidate materials for ITER (Al 2O 3, SiO 2, BeO, and AlN), in order to assess this potential surface degradation issue, and clarify possible mechanisms. Severe surface optical and electrical degradation has previously been reported for these materials bombarded with H +, D +, and He + ions, at different energies, temperatures, and dose rates, as well as for electron irradiation. In all cases, dramatic degradation has been found and related to loss of oxygen (nitrogen) from the implanted/irradiated zone due to preferential radiolytic anion sputtering. In the work reported here, a model is presented to explain the surface electrical degradation of insulators under ion bombardment. A general mathematical expression for the evolution of the surface conductivity with time (dose) of an insulator or extrinsic semiconductor subjected to preferential sputtering has been obtained. Very good agreement between the experimental data and the theoretical model has been obtained, and a clear dependence of the sputtering cross-section on the bombarding ion mass has been identified.

Generation processes of super-high-energy atoms and ions in magnetron sputtering plasma

Energy distribution function (EDF) of ion species (Ar +, Kr +, Xe +) in a rare gas magnetron plasma is measured at a substrate position, 0.1 m away from the target surface, by energy-resolved mass spectrometry. The measured ion EDF contains, besides a bulk low-energy part (<10 eV), a tail part of super-high energy on an order of 100 eV, depending on the mass ratio of ion species to target material (tungsten, permalloy (80% Ni, 20% Fe)). A weak electric field in a diffusion region of magnetron plasma cannot accelerate slow bulk ions of ∼0.2 eV to such high energies. Origin of large kinetic energies is attributed to the backscattering process on the target surface where, e.g., Ar + ions impinging on the target are neutralized and reflected as fast Ar atoms of the kinetic energy approximately given by a two-body collision model. Subsequently, a part of fast atoms may be converted to fast ions in three possible collision processes in the diffusion region: (i) electron impact ionization (ii) resonant charge exchange, and (iii) ionization of slow atoms by fast atoms. Among them, the third process is found to be dominant from Monte Carlo simulations where the backscattering process is evaluated by the TRIM code. Furthermore, when the target mass is larger than the bombarding ion mass, the substrate is bombarded by the super-high-energy atoms having a flux 2–4 orders of magnitude larger than the fast-ion flux.

Resonance in the efficiency of the conduction-state formation in ion-bombarded crystalline quartz

A resonance in the ion conductivity as function of the bombarding-ion mass number was observed in ion-irradiated crystalline quartz. The resonance is observed at the optimum ratio of the energy losses for the nuclear and electron stopping of the impinging ions interacting with crystalline quartz in the range of ion mass numbers from 35 to 45 amu.

Characterization of optically active defects created by noble gas ion bombardment of silicon

The modification in the G-line (969.5 meV) and the C-line (789.4 meV) photoluminescence (PL) intensities were studied as a function of the fluence, energy, and mass of the bombarding ions (He, Ne, Ar, and Kr). The intensities of the luminescent lines induced by 1 keV Ne bombardment were found to decrease with increasing dose after reaching a maximum at about 1×1012 ions/cm2. Considerable reductions in the intensities of the G- and C-lines were also recorded during bombardment using heavier noble gas ions and they have been attributed to the higher rates of nuclear energy deposition with increasing bombarding ion mass. The incident ion energy at which the PL intensities of the spectral lines reached their maximum values was found to be dependent on the ion mass and fluence. We have explained the decrease in PL intensities of the G-line and C-line to be due to the introduction of increased amounts of nonradiative recombination centers with increasing incident ion dose and mass. Further, the integral sum of defects induced during bombardment as a function of projected ion range and excitation depth of the Ar-ion laser has been used to qualitatively describe the decrease in the intensities of the two lines.

Formation cross sections of neutron deficient polonium isotopes in asymmetric and symmetrical heavy ion fusion

Excitation functions are measured for the fusion reactions 27Al+ 175Lu and 31P+ 169Tm leading to the isotopes 192–198Po. A comparison to the data for the reactions 100Mo + 92–100Mo shows that characteristics of the compound nucleus evaporation do not depend on the bombarding ion mass in the whole range of the entrance channel asymmetry up to the fully symmetrical systems. It is also shown that a satisfactory description of the experimental data is possible in the frame of the statistical deexcitation model only at an assumption involving, in comparison to theory predictions, a considerable reduction of macroscopic fission barriers for neutron-deficient isotopes of Bi.

Sputtering yield of optical materials: Sigmund’s model and experimental results

The main drawback of the ion beam assistance during optical thin film deposition is the stoichiometry alteration due to the different sputtering yield of elements which compose the film itself. In optical materials such effect causes both an increase of absorption coefficient and undesirable variation of refractive index. In order to maintain the advantages of the ion beam assistance (i.e., enhancement of adhesion, compactness, good control of optical properties) the sputtering phenomena should be modeled to recognize the parameters of the ion beam (energy, angle of incidence, and ion mass) that minimize the stoichiometry alteration. The Sigmund’s model is an analytical approach widely used to treat the modelling of the sputtering phenomenon. In this work the Sigmund’s model was applied to fit the experimentally measured sputtering yield of several materials typically employed to fabricate optical coatings: silicon dioxide (SiO2), yttrium oxide (Y2O3) and zinc selenide (ZnSe). The yield measurements were performed both at different angle of incidence of the beam (0°, 45°) and with different bombarding ion mass and energy. The experimental results appear well fitted by the relation of the sputtering yield (Sigmund’s model) at all considered angles and ion masses. Sputtering yields of the material components as for instance silicon (YSiion) and oxygen (YOion) for SiO2 material, were modeled as well as their behavior with either ion energy or ion mass.

Effects of ion bombardment on the chemical reactivity of gallium arsenide(100): variation of bombarding ion mass

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffects of ion bombardment on the chemical reactivity of gallium arsenide(100): variation of bombarding ion massJ. M. Epp, John G. Dillard, A. Siochi, R. Zallen, S. Sen, and L. C. BurtonCite this: Chem. Mater. 1990, 2, 2, 173–180Publication Date (Print):March 1, 1990Publication History Published online1 May 2002Published inissue 1 March 1990https://doi.org/10.1021/cm00008a019RIGHTS & PERMISSIONSArticle Views64Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Electron Ejection from Single Crystals Due to 1- to 10-keV Noble-Gas Ion Bombardment

The secondary-electron ejection coefficient $\ensuremath{\gamma}$ has been measured for the (110), (100), and (111) planes of Cu, Al, Ag, Ni, and Mo bombarded by the singly charged noble-gas ions ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$, ${\mathrm{Kr}}^{+}$, and ${\mathrm{Xe}}^{+}$ in the energy range from 1 to 10 keV. Surfaces were kept clean to within a fraction of a monolayer contamination by the sputtering action of the incident ion beams. The ratios $\frac{{\ensuremath{\gamma}}_{\mathrm{hkl}}}{{\ensuremath{\gamma}}_{{h}^{\ensuremath{'}}{k}^{\ensuremath{'}}{l}^{\ensuremath{'}}}}$ are quite constant, which would tend to indicate a theoretical model based on simple geometrical considerations of the opacity of the single-crystal planes. However, the fact that the ratios are relatively insensitive to the ion-bombardment energy indicates that a model based upon the transparency of the target is not sufficient to explain the phenomenon. The dependence of $\ensuremath{\gamma}$ on the bombarding-ion mass is also explored.

Secondary Positive Ion-Emission from Platinum

Mass analysis of the secondary particles ejected from Pt surfaces by inert gas ion bombardment or by heating revealed species characteristic of the base metal, of certain bulk and surface impurities, and of the bombarding beam (so-called ``reflected'' ions). The Pt+ ions seemed to come directly from the substrate rather than from surface compounds. Their yield increased with temperature, bombarding ion energy, and bombarding ion mass. The ratio of sputtered Pt ions to sputtered neutrals is estimated to be of the order of 1 to 1000 at room temperature. The kinetics of the formation and desorption of a certain surface compound [possibly Pt(CO)2] was studied by secondary ion analysis. The compound formed spontaneously on the surface from the background gas in the instrument (CO at 10—8 mm Hg). Its formation rate was greatly enhanced by inert gas ion bombardment. It desorbed readily at 1000°C with an activation energy of 0.74±0.05 ev. The ``reflected'' ions appeared to be sputtered rather than reflected. Their energy was always extremely low (&amp;lt;1 ev) and the dependence of their yield on ambient gas pressure and target temperature is consistent with the notion that they originated from inert gas atoms trapped in the surface layers.