Low Energy Helium Ions Research Articles

Structure of molybdenum bombarded with low-energy hydrogen and helium ions during creep tests

To find the causes of the increase in the creep resistance as a result of ion bombardment, methods of high-voltage and analytic transmission electronmicroscopy were used to make a detailed study of the three-dimensional structure of specimens of single-crystal molybdenum, deformed without irradiation and under bombardment with low-energy ions from a glow discharge. Foils for transmission electron microscopy (TEM) were prepared from the axial testsections of the molybdenum specimens, which had been earlier subjected to creep tests [2]. Since bombardment with ions from a glow discharge causes bulk changes in the structure of the metal by acting on its surface, it seemed natural to expect the most significant and informative (in relation to an understanding of the phenomenon as a whole) structural changes near the surface. Accordingly, we first made a detailed study of the defect structure of the surface layers in the specimens subjected to bombardment without a mechanical load. For this purpose a series of disk-shaped (diameter 3 mm) single-crystal specimens of molybdenum were prepared [3] and were bombarded with helium and hydrogen ions from a glow discharge (T = 1500~ T = 1 h), after which the well-known methods of [4, 5] were used to prepare foils for TEM and their surface structure was studied with the aid of tomography. Most of the foils were examined in JEM-1000 and EM-301 G microscopes at an accelerating voltage of 1 }fV and i00 kV, respectively. The three-dimensional dislocation structures of the specimens bombarded in a.discharge of H2 or a mixture of He + H2 under strain differ considerably from the structures Of specimens tested in a vacuum. Figure 1 presents photomicrographs of low-angle boundaries in molybdenum specimens after creep testing without (a, b) and with (c, d) irradiation from a mediumof pure hydrogen. Even though the average size (~i00 ~m) and shape of the blocks in both specimens are roughly the same, the dislocation structures of the interblock boundaries and the form of the dislocations themselves differ markedly, as can be seen well from the photomicrographs. In the specimen tested under bombardment the dislocations are highly curved, while in block boundaries they are intertwined, often forming pileups that cannot be resolved by TEM. Near block boundaries are dislocation loops of a size of 30-80 n m, whose density varies within wide limits. Extremely diverse dislocation configurations are formed in specimens that have been bombarded under strain with ions from a glow discharge in an He + H~ mixture (Fig. 2). The photomicrographs in Fig. 2a, b show a large-cell hexagonal dislocation wall and a wall with elements of tetragonal cells formed in the bombarded specimen under strain. In practically all of the dislocation lines of such walls, including purely screw dislocation lines, a fine serrated structure was detected at higher magnifications. Even larger-celled dislocation walls with a less regular structure are encountered (Fig. 2c) and so are individual phase precipitates of

Ion channeling study of radiation induced defects in a bent silicon crystal

High energy proton channeling (12–120 GeV) and low energy helium ion channeling (1.5–4 MeV) have been used to study the effects of radiation damage induced in silicon by high energy (400 GeV) proton irradiation. It is shown that radiation fluence up to 10 17/cm 2 does not preclude deflection of high energy charged particle beams in elastically bent silicon crystals. Evidence of macroscopic segregation of residual defects in the strain field of a deformed crystal is demonstrated.

The damage induced on the (111) silicon surface by low energy helium ions investigated by ion scattering spectroscopy (ISS)

Low energy scn scattering spectroscopy (ISS) is used to investigate the damage creation on a (111) surface bombarded by low energy helium ions. The influence of the total ion dose relahe relative contribution of single and multiple scattering is investigated at different temperatures. It is concluded that under ion bombardment (⊃ 10 −5 A cm-5 A/cm 2 a saturation in the amount of damage is directly obtained at room temperature, at 1000 K onnealing occurs and a 750 K the damage creation is observable.

Helium trapping in nickel and the use of the helium probe as a technique for defect and gas agglomeration studies

Abstract Very low energy helium ions have been injected into Ni (100) single crystal substrates previously implanted with argon ions of higher controlled energy and fluence, and the subsequent evolution of the atoms during thermal annealing have been observed mass spectrometrically. Studies of the helium evolution spectra were obtained for different argon ion energies and fluences and nickel substrate temperatures in the range 350 to 900 K during argon implantation. This temperature range includes that for rapid thermal migration of radiation generated vacancies and the defect and defect-argon agglomerate states change substantially with argon implant temperature. Comparison of the helium evolution spectra without argon pre-bombardment and with pre-bombardment at different temperatures has confirmed the occurrence of a number of different helium defect-argon interaction processes and indicated important changes in the helium trapping efficiency of different defect structures.

Energy and Angular Dependence of the Inelastic Energy Loss in the Scattering of Low Energy He Ions from a Silicon Surface

The energy distribution of low energy helium ions (∼ 500 eV to 1500 eV), scattered by (111) silicon surface, has been measured in different experimental conditions. The energy at the maximum of the single scattering peak was found lower than that calculated from the binary elastic collision model. This is interpreted as the result of the electronic interaction causing an additional inelastic contribution in the energy loss.From the angular measurements, it is concluded that this electronic process is mainly a local interaction between the ion and the target surface atom rather than a continuous process between the ion and the surface. This inelastic energy loss is found to be proportional to the primary ion energy and to depend weakly on the scattering angle. Comparison is made with theoretical models.

Preferential neutralization in low energy helium ion scattering from the second layer of MoS 2 basal plane surfaces

Low energy 3He + and 4He + scattering along the [100] direction of single crystal MoS 2 basal plane surfaces has been investigated. The layered atomic structure of this compound was used to demonstrate that preferential neutralization accompanies scattering from the second surface layer. Preferential neutralization that takes place upon scattering at molybdenum atomic sites leads to a marked increase in the Mo/S LEISS intensity ratio with increasing primary ion energy (0.38–2 keV).

Preferential neutralization in low energy helium ion scattering from the second layer of MoS 2 basal plane surfaces

Low energy 3He + and 4He + scattering along the [100] direction of single crystal MoS 2 basal plane surfaces has been investigated. The layered atomic structure of this compound was used to demonstrate that preferential neutralization accompanies scattering from the second surface layer. Preferential neutralization that takes place upon scattering at molybdenum atomic sites leads to a marked increase in the Mo/S LEISS intensity ratio with increasing primary ion energy (0.38-2 keV).

Spectral and compositional variations of low energy ions during an energetic storm particle event

view Abstract Citations (53) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral and compositional variations of low energy ions during an energetic storm particle event Klecker, B. ; Scholer, M. ; Hovestadt, D. ; Gloeckler, G. ; Ipavich, F. M. Abstract Attention is given to variations in the intensity, energy spectra, and composition of low-energy protons, helium, and heavy ions (C, O, and Fe) in the energy range 0.3-20 MeV per nucleon during an energetic storm particle event on September 28-29, 1978. The intensities of low enery (less than or equal to 0.6 MeV per nucleon) particles are found to increase exponentially with time before the arrival of the moving interplanetary shock front. The increase is largest for the particles of lowest energy. The spectral steepening, expressed in terms of differences in the spectral index, increases for particles of increasing mass per charge ratio from a difference of approximately 1 for protons to approximately 3 for iron. As a consequence, the He/O and C/O ratios at equal energy per nucleon are constant, whereas the He/p, Fe/He, and Fe/O ratios decrease by as much as one order of magnitude before passage of the shock. The observations are analyzed in terms of a first-order Fermi acceleration model with a rigidity dependent interplanetary mean free path. Publication: The Astrophysical Journal Pub Date: December 1981 DOI: 10.1086/159474 Bibcode: 1981ApJ...251..393K Keywords: Cosmic Rays; Energetic Particles; Energy Spectra; Interplanetary Medium; Ion Temperature; Particle Acceleration; Abundance; Helium Ions; Hydrogen Ions; Proton Energy; Shock Wave Propagation; Space Radiation full text sources ADS |

Sputtering of molybdenum by low energy He + bombardment

A high density and low energy helium ion beam is used to study the sputtering of molybdenum by a collector method. Sputtered and deposited amount of molybdenum on a silver collector was measured by Auger electron spectroscopy, which can sensitively detect a surface composition. From the results of this analysis, an angular distribution of sputtered molybdenum and the relative sputtering yield are estimated. The angular distribution is almost close to a cosine distribution, except that small deviations from the cosine law are observed at target normal direction.

Adsorption and desorption of oxygen and carbon monoxide on the Si(111) surface studied by ion scattering spectroscopy

Abstract The adsorption of O 2 and CO on the Si(111) surface was studied by low-energy helium ion scattering. The adsorption consists of a fast adsorption stage followed by a much slower Sorption process. In the final uptake region CO has a faster rate of increase than O. There is no evidence of He + scattering from C atoms. This fact excludes the CO molecule having its axis parallel to the surface. A comparison of the intensities of the substrate (Si) signals, for the same recorded oxygen content on the surface, shows that carbon monoxide shadows the Si atoms more than oxygen does. An increase in the oxygen signal was observed even after exposures in the range of 10 14 –10 15 molecules cm −2 . No substantial diffusion of CO into the bulk can be deduced from these results. Desorption of oxygen by He + ions was observed by following the adsorbate and substrate signals as a function of time. The sputtering cross-section has a maximum for an impact angle of 25° relative to the surface.

Inelastic effects in the scattering of low energy helium ions from monocrystalline silicon

High resolution energy spectra of He ions scattered from monocrystalline silicon have been measured at various scattering, azimuthal and incident angles for primary energies in the range 450–1600 eV. In these experiments, it is observed that the maximum of the peak corresponds to an energy significantly lower than predicted by the binary elastic collision model. The dependence of this inelastic loss is investigated as a function of the experimental parameters. Emphasis is placed on the energy dependence at a scattering angle of 30° for four (111) surface planes of differently doped silicon samples. With increasing primary energy, a broadening of the peak is observed and a second peak appears, which is well defined only in a restricted energy range. The relative intensity of both peaks is strongly dependent on the energy and on the incident angle. The experimental results are compared with models of inelastic energy loss by electronic excitation and multiple collisions.

Trapping of low-energy helium ions in polycrystalline al and Pt and in BeO and anodic Al2O3films at room temperature

Abstract The trapping of 3He and 4He ions with energies between 10 eV and 40 keV in polycrystalline Al and Pt and in BeO and anodic Al2O3 films has been studied. The measured collecting efficiencies vary from a few times at 10−4 at eV to ∼ 1 at energies above 10 keV. Except for very low implantation energies (less than ∼ 1 keV), where initially trapped particles are probably released by diffusion, we derive reflection coefficients and compare with current theoretical calculations. Our reflection coefficients obtained for implantation energies larger than 1 keV in Al and Pt are in excellent agreement with calculated values. We have also measured the dependence of the trapping probability on the angle of incidence for 3 keV He ions in Al and Pt.

Automatic tracking NMR system for use in measurement of low energy ion beams with a magnetic spectrometer

An automatic tracking NMR (nuclear magnetic resonance) system is described for use in measurement of low energy (0.2–2.0 MeV) helium ion beams with a magnetic spectrometer. With this instrument, accurate automatic magnetic field measurements can be made with fields of less than 500 G. In addition, the design is oriented toward usage with frequently changing magnetic fields and ease of practical usage. General circuit principles are also discussed, particularly those related to reduction of extraneous noise.

Computer simulation of low energy hydrogen and helium ion reflection from monocrystalline surfaces

physica status solidi (a)Volume 55, Issue 1 p. K53-K58 Short Note Computer simulation of low energy hydrogen and helium ion reflection from monocrystalline surfaces M. A. Chubisov, M. A. Chubisov Institute of High Energy Physics, Academy of Sciences of the Kazakh SSR, Alma-Ata Search for more papers by this authorA. F. Akkerman, A. F. Akkerman Institute of High Energy Physics, Academy of Sciences of the Kazakh SSR, Alma-Ata Search for more papers by this author M. A. Chubisov, M. A. Chubisov Institute of High Energy Physics, Academy of Sciences of the Kazakh SSR, Alma-Ata Search for more papers by this authorA. F. Akkerman, A. F. Akkerman Institute of High Energy Physics, Academy of Sciences of the Kazakh SSR, Alma-Ata Search for more papers by this author First published: 16 September 1979 https://doi.org/10.1002/pssa.2210550152Citations: 3 480082 Alma-Ata, USSR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume55, Issue116 September 1979Pages K53-K58 RelatedInformation

FIM studies of the lattice damage in tungsten following low-energy helium ion bombardment

FIM studies of the lattice damage in tungsten following low-energy helium ion bombardment

Neutralization and ionization of low energy helium ions scattering from a copper surface

Abstract Ion yield measurements are presented |of 2–10 keV helium ions scattered from a copper (100) face. The scattering angle is 30°. The results are explained using a charge transfer model originally proposed by the authors. The model takes into account Auger neutralization as well as ionization and neutralization resulting from a violent collision. The present results are compared with previous] experiments in which a primary atom beam was used. Within the experimental errors the results |of both experiments can be explained using the same charge exchange parameters. A second result of the present investigation is that more convincing evidence is given for the occurrence of neutralization during the violent collision by a non-Auger process. It is probable that this process, as well as the ionization process, results from an interaction between the helium particle and the copper L shell electrons.

Field-ion microscope observations of helium ion bombardment damage in tungsten

The field-ion microscope has been used in a pilot investigation of the damage caused to tungsten surfaces following bombardment with low-energy helium ions. Such effects could be important because the first wall of a fusion reactor will have to withstand high doses of these particles. The damage observed following bombardment with total doses in the range 10 13 to 5 × 10 18 ions cm −2 has been found to be dose dependent. These results have then been related to those derived from studies using more conventional techniques and this has led to the conclusion that the origin of the observed damage lies in the formation of near-surface gas bubbles and surface blisters.

The scattering of low energy helium ions and atoms from a copper single crystal. Elastic and inelastic effects

Abstract The scattering of 4–10 keV Helium ions from a copper surface can be described reasonably well with elastic, single collisions, even for fairly small scattering angles. However, in a more refined analysis of the experimental results, deviations from this behaviour are observed. Measurements of the energy and the width (FWHM) of the surface peak have been performed. The general behaviour can be explained by differences in inelastic energy losses for scattering from an ideal surface and from surface structures (surface damage). By comparing measurements in which the target is bombarded along different directions, it is shown that multiple scattering effects have only a minor influence. Additional information about the inelastic processes is obtained by performing scattering experiments with a primary atom beam. It appears that, for large angles of incidence, the energy of the reflected ions is reduced about 20 eV if the primary beam consists of atoms instead of ions. This difference is almost indepe...

Oxygen adsorption on (110) silver

The adsorption of oxygen on a (110)Ag surface is investigated by means of Auger electron spectroscopy, LEED and low energy helium ion scattering (IS). With LEED two ordered structures, i.e. (3×1) and (2×1) were observed at oxygen exposures of 1700 L and 7000 L respectively. The oxygen signal observed by AES and IS increases monotonically with oxygen exposure. The signals can be related to absolute coverage by comparison with Δφ measurements and by the use of the LEED data. With this calibration and with theoretical scattering cross-sections the IS measurements allow the position of the adsorbed oxygen to be estimated. The observation of a strong azimuthal anisotropy of the IS signal, e.g. a large oxygen signal if the plane of scattering is parallel to the [110] direction and a relatively small oxygen signal in the [100] direction, leads to the conclusion that the oxygen is adsorbed in a bridge position between two Ag atoms of the [110] surface channels, its centre being slightly below the centres of the Ag atoms.

Displacements of electron ejection energies in near-threshold excitation of autoionizing levels of helium by electron impact

The four lowest autoionizing levels in helium, namely (2s 2 ) 1 S, (2s2p) 3 P, (2p 2 ) 1 D and (2s2p) 1 P, have been studied near their thresholds for excitation by electron impact. Features in the spectra of electrons ejected from these states were seen to shift to steadily higher energies as the impact energy was lowered to within a few electron volts above threshold. This phenomenon is compared with a similar one which has been observed in the scattering of low energy helium ions from helium atoms. A qualitative explanation of these observations can be provided by considering a “post-collision interaction” between the scattered particle and the ejected electron. The limitations of this model are discussed. Structure in the spectra suggest that the situation is complicated by an interference phenomenon which cannot be explained in a classical treatment of the problem. The threshold electron excitation spectrum of these autoionizing levels has also been obtained, using an apparatus designed to detect very low energy electrons. As well as confirming the observations described above, this revealed the presence of one of the two negative ion states known to exist in this region. In an effort to obtain a complete picture of the processes taking place in helium at these energies, the negative ion states were also studied in direct ionization and in elastic scattering at various angles. The latter measurements confirmed the classifications of these states as (2s 2 2p) 2 P and (2s2p 2 ) 2 D, and we have obtained values for their energies of 57.22 ± 0.04 eV and 58.30 ± 0.04 eV respectively.