Ar Ion Impact Research Articles

Ion beam figuring with focused anode layer thruster.

This work presents the peculiarities of cone ion beam formation with a focused thruster with anode layer (TAL) and its application to silicon carbide (SiC) ion beam figuring. Modeling results of Lorentz E × B force distribution in the discharge gap are presented. 3D particle tracing for keV Ar ions is carried out for the first time in the beam drift region of TAL with magnetic lens. Extracted ion beam full width at half maxima is about 2mm in the focal plane, where the SiC etching rate reaches 0.5 µm/min. The SiC sputter yields are measured as a function of the Ar ion impact energy and beam incidence angle. The maximum sputter yield of 2.8 atom/ion is observed at 45° of the beam-sample angle for the Si targets. Furthermore, the maximum sputter yield value of 1.7 atom/ion is measured at 30° of the beam-sample angle for the SiC targets. The novelty of present research is in the application of focused TAL keV Ar ion beam to the SiC ion beam figuring.

Influence of Surface Curvature on Silicon Sputtering by Low-Energy Ar Ions

Molecular dynamics (MD) method was used to study 200 eV Ar ion impact on silicon nanoparticles of various sizes . Based on the MD simulations, the analysis of sputtering mechanisms and differences in the ion energy deposition which are determined by the curvature of the target surface, is performed in the paper.

Sputter yield of curved surfaces

The mean sputter yield produced by the impact of a single ion depends on the radii of curvature of the target surface at the point of impact. Using the Sigmund model of ion sputtering, we develop analytical formulas for this dependence for the case in which the radii of curvature are large compared to the size of the ion-induced collision cascade; both locally perpendicular and oblique ion impact are considered. The sputter yield is increased for impact on convex surfaces. The influence of surface curvature along the incident-ion azimuth and perpendicular to it are discussed separately. Our analytical results are in good agreement with Monte Carlo simulations for the specific case of 20 keV Ar ion impact on a cylindrical nanowire consisting of amorphous silicon. We also extend the results for this case to small radii of curvature using both Monte Carlo and molecular dynamics simulations.

Modification of transparent conductive ZnO and Ga-doped ZnO films by irradiation with electron cyclotron resonance argon plasma

By irradiating undoped ZnO and Ga-doped ZnO (GZO) films with electron cyclotron resonance Ar plasma, their electrical and optical properties have been modified. Both the carrier concentration and the Hall mobility increased with continuous irradiation in conductive ZnO films with a defect-rich crystalline lattice. Improved crystallinity was verified by intensifying the ZnO(002) x-ray diffraction peak and increasing the optical transmission level in the visible wavelength. This observation suggests network rearrangement through Zn atoms at interstitials or grain boundaries being oxidized or accommodated into the crystalline network. For insulating ZnO films that contain a sufficient number of oxygen atoms, the changes were better scaled with sheet resistance rather than resistivity. The interference fringes redshifted without lowering the transmittance level. Here, Ar ion impact will create oxygen vacancy donors in the near-surface region or desorb interstitial oxygen atoms that act as donor killers. In contrast, GZO films with resistivities in the 10−4 Ω cm range revealed little changes because there were very few imperfections in the crystalline lattice. The reduced amount of resistivity corresponded to the creation of oxygen vacancies in more resistive GZO films in the 10−3 Ω cm range.

Surface deformation of Ar+ ion collision process via molecular dynamics simulation with comparison to experiment

Molecular dynamics simulations of Ar ion collision on a Si surface using an optimized potential function were carried out in the case of the acceleration voltages of 50keV for Ar ions. A hillock structure was formed by the Ar ion impact on the Si surface. The height of the structure calculated by the simulations corresponded to those of the experiments. The height of the structure was found to be proportional to the fluence of Ar ions. The amorphous structural region was expanded by the progress of the interface region between the amorphous structure and the crystalline structure with increasing the fluence in the depth direction.

A quartz-crystal-microbalance technique to investigate ion-induced erosion of fusion relevant surfaces

We describe a highly sensitive quartz-crystal-microbalance technique capable of determining erosion as well as implantation and retention rates for fusion relevant surfaces under ion bombardment. Total sputtering yields obtained with this technique for Ar ion impact on polycrystalline gold and tungsten surfaces are presented. The results compare well with existing experimental data as well as theoretical predictions and thus demonstrate the feasibility of the developed technique. Our setup is capable of detecting mass-changes as small as 10−5μg/s, which corresponds to a removal of only 10−4W monolayers/s.

Ion beam induced mixing of co-sputtered Au–Ni films analyzed by Rutherford backscattering spectrometry

Co-sputtered Au–Ni thin films having thickness of 30 nm were deposited on Si(1 0 0) substrates and irradiated with 160 keV Ar 40 + under ambient condition at a number of fluences and analyzed using Rutherford backscattering spectrometry (RBS). The variation of Au signal counts in the RBS spectra with ion fluence has been investigated. The distribution of Au, Ni and Si atoms over various depths within the as deposited and irradiated samples have been computed using the backscattering data by means of a direct analytical method. Au and Si profiles have been fitted with error function and the relative changes in variance for various ion fluences compared to that of as deposited profiles have been studied. The spreading rates of different constituents across the interface due to Ar ion impact have also been discussed.

Electron Emission in Grazing HCl–LiF(001) Collisions

We have measured the number statistics of emitted electrons for multiply charged Ar-ion impact on a clean LiF(001) surface under grazing incidence conditions. For projectiles reflected from the surface we have also recorded the scattering distribution on a two dimensional detector in coincidence with the number of emitted electrons. In this way it was possible to distinguish electron emission for three different types of trajectories: non-penetrating projectiles specularly reflected from the topmost surface plane, projectiles entering the target and being reflected from subsurface layers and projectiles penetrating deeply into the target. The results support existing concepts on the charge state dependence of potential- and kinetic electron emission from poly- and monocrystalline LiF gained in normal incidence experiments.

Rapid back-segregation effects on recoil implantation of monolayer Pb adsorbates at Si(1 1 1) surfaces by keV Ar ion impact

The decay curves of Pb coverage at the Si(111)-1×1-Pb surface by 5 keV Ar+ ion impact have been measured, by means of the Rutherford backscattering (RBS) technique, with successive irradiation for the short period at low ion fluxes at temperatures of 300 K and 200 K and with a continuous irradiation for the long period of 600 s at different ion fluxes at 300 K. For the successive short period irradiation it is found that the decay curves of Pb coverage measured under different conditions correspond with each other and with the previous one. The result is reasonably explained in terms of complete recovery (back-segregation) of Pb adsorbates recoil-implanted once by one Ar+ ion impact before the next Ar+ ion impacts on the same local position. For the continuous long period irradiation at high ion fluxes it is found that the decay fractions of Pb coverage increase with increasing the ion flux. The result is also reasonably and quantitatively explained in terms of back-segregation and additional radiation-induced segregation of recoil-implanted Pb adsorbates.

Multiple K- and L-shell ionizations of target atoms by collisions with high-energy heavy ions

The inner-shell ionization processes of atoms by bombardment of fast heavy ions are studied systematically through high-resolution measurements of K x rays. The K α satellite and K α hypersatellite x rays from target K-shell ionization were measured for He, C, N, O, and Ar-ion impact at energies between 0.56 and 92 MeV/u for satellite x rays and between 4.7 and 92 MeV/u for hypersatellite x rays. From the intensity distribution of the K α satellite x rays with a different number of L-shell vacancies, the L-shell ionization probability at small impact parameters (close collisions) have been obtained and the results are discussed in the framework of simple first-order theories like binary-encounter approximation (BEA), and semiclassical approximation (SCA). The results qualitatively agree with the BEA and SCA scalings at higher collision velocities than the orbital velocity of the L electrons. The intensity ratio between K α hypersatellite x rays and K α satellite x rays has been compared with results calculated by BEA and SCA.

Scanning Tunneling Microscope Studies on Recovery Processes of Sputter-Induced Surface Defects on Si(111)-7×7

Vacant regions have been introduced onto the Si(111)-7×7 surface by 1 keV Ar ion bombardment and studied by scanning tunneling microscopy. The vacant regions are defect regions where adatoms have been removed by Ar ion impact. When annealed at temperatures from 500°C to 730°C, the vacant regions recover the initial 7×7 structure via the new metastable 7×7 structure found in the present study. Both rate-controlling steps are described by single activation free energies with dominant -TΔS and minor ΔE terms. The activation entropies ΔS/(eV K-1) are found to be - 1.9 ×10-3 for the metastable 7×7 formation and -2.6×10-3 for the stable 7×7 formation.

Secondary ions produced from gaseous and frozen H2O under energetic (MeV/amu) Ar ion impact

Mass/charge spectra of secondary ions produced under energetic (∼MeV/amu) Ar ion impact on gaseous and frozen H2O targets are measured using a magnet-type mass spectrometer. The ion spectra are found to be quite different between these target phases. Multiply charged Oi+ ions with charge states i=2–6, as well as fragmented H+, O+, and OH+ ions, are clearly observed in the gas target, whereas the production of multiply charged ions is strongly suppressed in the frozen target. The most intense ion species is the parent H2O+ ion in the gas target; the H3O+ ion in the frozen target. The most outstanding feature in the frozen target is that the production of cluster ions of the type (H2O)nH+ (n=1–31), and their intensities, decreasing as the cluster size n increases, show anomalies between n=4 and n=5 and also around n=20, 21, and 22. Negatively charged cluster ions with formula (H2O)nO− and (H2O)nOH− are also efficiently produced in the frozen target.

Dissociation of multicharged CO molecular ions produced in collisions with 97-MeV Ar14+: Total-kinetic-energy distributions.

Transient molecular ions of CO{sup {ital q}+} (where {ital q}=2--7) were produced in single collisions of 97-MeV Ar{sup 14+} projectiles with neutral CO molecules. The resulting dissociation products were identified by coincidence time-of-flight spectroscopy in which the time of flight of the first ion to reach the detector and the time difference between the first ion and its partner were recorded event by event. An iterative matrix-transformation procedure was employed to convert the time-difference spectra for the prominent dissociation channels into total-kinetic-energy distributions. Analysis of the total-kinetic-energy distributions and comparisons with the available data for CO{sup 2+} and CO{sup 3+} from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization.

Alignment of He- and H-like P states of heavy ions produced by ion-atom collisions

The alignment of the 2P states of He- and H-like 48 MeV Mg and He-like 32 and 105 MeV S ions excited by thin carbon foils and the alignment of the 2P states of He-like Ne recoil ions produced by 1.35 MeV/amu Ar ion impact is discussed. The alignment of the Mg ions is deduced from the angular distributions of the He- and H-like X-ray lines measured with a pivoted plane-crystal Bragg spectrometer. The alignment of the S ions has been determined from the I( 3 P) I( 1 P) ratio in the He-like X-ray spectrum measured with a curved crystal spectrometer. The experimental results are compared with the Oppenheimer-Brinkman-Kramers (OBK) approximation, the first Born-approximation (BA) and the coupled states calculation (OHCE) of Reading et al. The OHCE generally gives good agreement with the experimental data, while the OBK grossly disagrees with them. The alignments and the relative population of the 2 3P and 2 1P states of He-like Ne recoil ions have been deduced from the relative intensity and polarizations of the 3P and 1P X-ray lines measured with a curved crystal polarimeter. By comparing the alignments and the relative populations of these states, the relative contributions of 1s–2p excitation and multielectron ionization to the production of 1s2p He-like states have been determined to be 37% and 63%, respectively.