Low Energy Ne Ions Research Articles

Deuterium retention in tungsten co-deposits with neon and argon inclusions

Deuterium (D) retention in tungsten (W) co-deposited layers, in the presence of neon (Ne) and argon (Ar), was investigated using the bipolar High Power Impulse Magnetron Sputtering (BP-HiPIMS) technique. The deposited layers have a polycrystalline structure, with a preferential growth of W(110) phase. The concentration of D and noble gases (Ne and Ar) is almost constant throughout the depth of the layers. In a D2-Ar discharge, the deposited layers exhibit compressive stress, indicating that Ar is mostly incorporated into the interstitial sites of the W crystal lattice. D retention increases when Ne is added in the discharge, especially when the deposited layer is bombarded with highly energetic ions. Low energy Ne ions (below the W damaging threshold) induce compressive stress, indicating that Ne atoms occupy interstitial sites in the W crystal lattice. High energy Ne ions induce tensile stress, a sign that Ne is trapped in the grain boundaries as inert-gas-vacancy defects, leading to a grain-boundary relaxation. In the presence of Ne, the ion acceleration towards the layer from 0 V to 300 V results in an increase of the D content of about three times, from 3.2 at.% to 8.6 at.%.

Neon ion beam induced pattern formation on amorphous carbon surfaces

We investigate the ripple pattern formation on amorphous carbon surfaces at room temperature during low energy Ne ion irradiation as a function of the ion incidence angle. Monte Carlo simulations of the curvature coefficients applied to the Bradley-Harper and Cater-Vishnyakov models, including the recent extensions by Harrison-Bradley and Hofsäss predict that pattern formation on amorphous carbon thin films should be possible for low energy Ne ions from 250 eV up to 1500 eV. Moreover, simulations are able to explain the absence of pattern formation in certain cases. Our experimental results are compared with prediction using current linear theoretical models and applying the crater function formalism, as well as Monte Carlo simulations to calculate curvature coefficients using the SDTrimSP program. Calculations indicate that no patterns should be generated up to 45° incidence angle if the dynamic behavior of the thickness of the ion irradiated layer introduced by Hofsäss is taken into account, while pattern formation most pronounced from 50° for ion energy between 250 eV and 1500 eV, which are in good agreement with our experimental data.

Low energy Ne ion beam induced-modifications of magnetic properties in MnAs thin films

Investigations of the complex behavior of the magnetization of manganese arsenide thin films due to defects induced by irradiation of slow heavy ions are presented. In addition to the thermal hysteresis suppression already highlighted in Trassinelli et al (2014 Appl. Phys. Lett. 104 081906), we report here on new local magnetic features recorded by a magnetic force microscope at different temperatures close to the characteristic sample phase transition. Complementary measurements of the global magnetization in different conditions (applied magnetic field and temperatures) enable the film characterization to be completed. The obtained results suggest that the ion bombardment produces regions where the local mechanical constraints are significantly different from the average, promoting the local presence of magneto-structural phases far from the equilibrium. These regions could be responsible for the thermal hysteresis suppression previously reported, irradiation-induced defects acting as seeds in the phase transition.

Modification of Barium Cerate by Heavy Ion Irradiation

The effect of irradiation with heavy ions Ne, Ar, and Kr of various energies on the structure and properties of ceramic barium cerate doped with neodymium and annealed in air at 650°C for 7 hours is studied. It is noted that blistering was observed on cerate surface during its irradiation by low energy Ne ions, whereas it was not observed under low-energy Ar and Kr ions irradiation. Irradiation of the cerate with high energy ions caused partial amorphization of the irradiated surface of the material, while the structure of the non-irradiated surface did not change. In addition, the irradiated surface of the cerate endured solid-phase structural changes. Thus, upon high-energy ions irradiation in the range of Ne, Ar, Kr the cerate surface resembled the stages of spherulite formation - nucleation, growth (view of cauliflower), formation of spherulitic crust, respectively. The increase in water molecules release and reduction of molecular oxygen release from the barium cerate, irradiated by high-energy ions is found during vacuum constant rate heating. It is concluded that cerates undergo changes to the distances significantly exceeding the ion ranges in these materials. Features of high-energy ions influence on thermal desorption of carbon dioxide from cerates show, apparently, the formation of weakly bound carbonate compounds on the cerate surface in the irradiation process.

Characteristic velocity for inner-shell charge exchange of low energy Ne ions scattered from a polycrystalline Ni surface

The threshold energy of charge exchange processes involving inner-shell electron promotion is investigated in the case of low collision energy Ne ions scattered from a polycrystalline nickel surface. Two distributions of charge fractions are measured from time-of-flight spectra at constant perpendicular velocity in the outgoing path. The energy distribution (energy=2–12keV, constant scattering angle=12°) and the angular distribution (scattering angle=7–50°, constant energy E=4keV) allow the crossing distance RC for electronic transitions during the close-encounter to be determined. Using the value of RC in statistical distributions of close collisions coupled with the Landau–Zener model, we obtain the characteristic velocity VC of the crossing point in the Ne/Ni system.

The structure of the Cu 3Au(0 0 1) surface studied by impact collision of low energy Ne ions

The structure of the Cu 3Au(0 0 1) surface has been studied by Ne + scattering spectroscopy under impact collision conditions (ICISS) at room temperature. Scattering of low energy ions (Ne +, 0–3 keV) provides scarce structural information due to the high neutralization probability. Using a Ne ++ beam with energy up to 6 keV and profiting also of the relatively high cross-section for Ne + production in violent collisions with Cu atoms well-defined focusing peaks were detected in ICISS polar scans. The ICISS patterns clearly reflect meaningful structural information, consistent with the 50% Cu–50% Au surface truncation proposed by theoretical investigation and supported by previous ISS works. A comparison of experimental scans with Monte Carlo simulations of ion trajectories, taking into account the Ne–Cu and Ne–Au interaction potentials, thermal disorder, neutralization and reionization processes, is presented and the theoretically predicted rippling between Cu and Au atoms in the first layer is discussed.

Inelastic energy loss and inner-shell electron promotion in low energy Ne ions scattered from Fe and Ni surfaces

Inelastic energy loss and inner-shell electron promotion of Ne + ions scattered from Fe(110) and Ni(100) surfaces have been studied systematically in the energy range from 1 to 7 keV at large scattering angles. The inelastic energy loss shows a threshold-type greater increase with incident energy in both scattering systems. Similar threshold-type behaviour is also observed in the scattered Ne + ion yield, the scattered Ne ++ ion yield and the peak fwhm. The threshold incident energy for such phenomena is found to increase with the atomic number Z of the target. It is suggested that excitations of the Ne 2s electrons occur during the close collision of the Ne with Fe or Ni atoms, resulting in a sudden increase in the inelastic energy loss. The excitation probability is found to depend on the atom position of the target relative to the swapping points of the Ne inner-shell energy levels. The ionization of the doubly excited Ne∗∗ particles alters the charge exchange behaviour of the Ne projectiles on their outgoing trajectories, leading to a remarkable increase in the scattered ion yield. The results show that inner-shell electron excitations could be significant in low energy ion surface scattering and may play an important role in the charge exchange process.

Pinned and chaotic electron trajectories in an antidot lattice

Antidot superlattices are fabricated on GaAs/AlGaAs heterostructures via holographic lithography and subsequent low energy Ne ion irradiation. The low-field magnetoresistance reveals maxima that are related to physical situations where a fraction of the electrons follows pinned trajectories that encircle an integer number of antidots. We suggest that the plateau-like structures in the Hall effect that arise where the magnetoresistance displays maxima allow for an estimation of the number of carriers that do no participate in the transport process.