keV Ne Ions Research Articles

A round robin experiment of elemental sensitivity factors in low-energy ion scattering

In a round robin experiment a set of five polycrystalline, metallic samples is studied by low-energy ion scattering (LEIS) in five different laboratories. The energy range is 0.6–3.5 keV and He and Ne ions are used. Even though different experimental setups are used the evaluated elemental sensitivity factors agree within ±20%. Reproducibility within single laboratories is better than 10%. In an additional study carried out in three laboratories the surface composition of an alloy, Cu 55Pd 45, was determined, using in situ calibration standards. These surface composition measurements agreed within ±3 at% demonstrating that quantitative composition determination is possible using this procedure.

Reduction of freely migrating defect concentrations by cascade remnants in Ni-Si alloys

Interactions of cascade remanants with freely migrating defects in Ni-12.7% Si were investigated using in-situ Rutherford backscattering spectrometry during simultaneous irradiation with 1.5 MeV He and 400 keV Ne ions at elevated temperatures. Radiation induced segregation of Si atoms toward the specimen surface caused γ′-Ni3Si layers to grow on the surface during irradiation. The γ′-Ni3Si growth rate during He bombardment was strongly suppressed by simultaneous irradiation with Ne ions, even when the calculated defect production rate for the Ne ions was only a few percent of that for the He ions. This results shows that the cascade remnants generated by the Ne ions act as additional recombination sites for freely migrating defects, reducing their steady state concentration. Despite a large difference in defect properties and in the kinetics of radiation induced segregation between the two alloys, the effects of cascade remnants on freely migrating defects in Ni-12.7% Si are remarkably similar to those found previously in Cu-1% Au.

Thermal regrowth of Si(100) damaged by Ne, Ar, and Xe ion bombardment

Thermally induced regrowth of Si(100) after ion sputtering with 3 keV Ne, Ar, and Xe ions has been studied with angle resolved photoemission. Significant differences are found in the regrowth, depending on the kind of ions used for the sputtering. While the Ne sputtered surface was fully recovered after annealing at 750°C, the Ar and Xe treated surfaces remained disordered after such treatment. It is concluded that Ne ion bombardment induces a different defect system than that obtained after bombardment with Ar or Xe ions at the same energy.

Order-disorder phase transition of the Cu 3Au(100) surface studied by ToF-ion scattering

Cu 3Au(100) surface has been investigated with ToF-ISS at different temperatures below and above the bulk order-disorder transition temperature ( T c = 663 K). Grazing angle azimuthal scans on the surface reveal the crystallinity of the first monolayer. The polar scans measured by 2 keV Ne ion scattering aligned along the major orientations, i.e. 〈100〉 and 〈110〉, show that the surface is terminated at room temperature by an ordered and rippled CuAu layer. The 〈100〉 rows are alternatively pure Cu rows and pure Au rows while the 〈110〉 rows are made by an alternated sequence of Cu and Au atoms. When increasing the temperature close to T c, the Au focusing peak at low incidence, along the 〈110〉 rows, broadens in a first time owing to thermal vibrations, then shifts rapidly to higher incident angles when we approach the transition. This effect is interpreted as the result of the order-disorder transition at the surface, which modifies the ordered atomic sequence constituting the rows. By plotting the Au scattering yield vs. temperature at fixed azimuthal and incident angles, a strong decrease of the signal near the transition is observed. However, the transition is not abrupt, indicating possibly a second-order phase transition at the first monolayer, in opposition to the first-order'bulk transition.

A new computer code for quantitative analysis of low-energy ion scattering data

We have developed a computer program for the full analysis of low-energy ion scattering (LEIS) data, i.e. an analysis that is equivalent to the full calculation of the three-dimensional trajectories of beam particles through a number of layers in the solid, and ending in the detector. A dedicated algorithm for this purpose is described, in which part of a trajectory is calculated backwards in time, i.e. starting from the detector. The program gives reliable results, as is proven by the application of the program in the analysis of spectra and azimuthal scans measured for the scattering of 5 keV Ne ions from the (110) face of a Au segregated Ni 0.08at.% Au alloy.

Quantitative determination of the imperfectness of a cleaved MoS2(001) surface by coaxial impact-collision ion scattering

Polar angle dependence of the Mo signal intensity in the case of CAICISS type scattering of 3 keV He and Ne ion beams from a cleaved (001) molybdenite surface has been obtained. The experimental results analyzed with the use of a recently developed computer simulation method allowed to determine quantitatively the incompleteness of the top, sulphur layer. A general method of CAICISS angular data fitting by normalization of the calculated second layer intensity contribution, to the background level at normal incidence is proposed. In addition, an approximate data treatment is suggested, which allows one to obtain an estimate of the surface roughness from the polar angle spectra.

2 keV He and Ne ion scattering on a Cu(110) surface: Experiment vs simulation

Scattering experiments performed at 143° with a TOF-ISS system on a Cu(110) single crystal indicate the very different sampling depth of He ions as compared with Ne ions. The ISS polar scans measured with He ions show a high sensitivity to the bulk atomic rows of the single crystal, whereas the scans measured with Ne ions indicate a sensitivity to only a couple of atoms in the first atomic layers. In order to evaluate the depth sampled by the backscattered particles, ion trajectories have been calculated with the MARLOWE simulation code. With Ne, the simulation shows that backscattered particles arise only from the 4 first layers (5 Å), but with He ions, they come from at least 80 layers (100 Å). A detailed analysis of escaping trajectories indicates that the Ne projectiles are scattered from the first layers after short trajectories. On the other hand, helium trajectories are usually quite complex, due to the possibility to follow privileged directions (channels), so that the projectiles can scatter from deep layers. We see that, even at low energy, channeling may be the major contributor to the variations of the backscattered intensity.

Dislocation Loops in Spinel Crystals Irradiated Successively with Deep and Shallow Ion Implants

ABSTRACTThis study examines the influence of microstructural defects on irradiation damage accumulation in the oxide spinel. Single crystals of the compound MgAl2O4 with surface normal [111] were irradiated under cryogenic temperature (100°K) either with 50 keV Ne ions (fluence 5.0 × 1012/cm2), 400 keV Ne ions (fluence 6.7 × 1013cm2) or successively with 400 keV Ne ions followed by 50 keV Ne ions. The projected range of 50 keV Ne ions in spinel is ~50 nm (“shallow”) while the projected range of 400 keV Ne ions is ~ 500 nm (“deep”). Transmission electron microscopy (TEM) was used to examine dislocation loops/ defect clusters formed by the implantation process. Measurements of the dislocation loop size were made using weak-beam imaging technique on cross-sectional TEM ion-implanted specimens. Defect clusters were observed in both deep and shallow implanted specimens, while dislocation loops were observed in the shallow implanted sample that was previously irradiated by 400 keV Ne ions. Cluster size was seen to increase for shallow implants in crystals irradiated with a deep implant (size ~8.5 nm) as compared to crystals treated only to a shallow implant (size ~3.1 nm).

Ion-beam induced generation of Cu adatoms on Cu(100)

Low-energy ion scattering was used to study on-beam induced adatom generation during irradiation of a Cu(100) surface with 6 keV Ne ions at a sample temperature of 60 K. It was found that the number of adatoms produced per incoming ion decreases from an average of 3.5 to a saturation level of 1.8 after prolonged irradiation. Two mechanisms are believed to contribute to the adatom generation: ion-beam induced atom-replacement sequences and diffusion of self-interstitial atoms to the surface. From the adatom production as a function of irradiation dose the relative contributions of the two mechanisms were determined.

Ion-beam induced generation of Cu adatoms on Cu(100)

Low-energy ion scattering was used to study on-beam induced adatom generation during irradiation of a Cu(100) surface with 6 keV Ne ions at a sample temperature of 60 K. It was found that the number of adatoms produced per incoming ion decreases from an average of 3.5 to a saturation level of 1.8 after prolonged irradiation. Two mechanisms are believed to contribute to the adatom generation: ion-beam induced atom-replacement sequences and diffusion of self-interstitial atoms to the surface. From the adatom production as a function of irradiation dose the relative contributions of the two mechanisms were determined.

Surface sites and mobilities of In atoms on a stepped Cu( 100) surface studied at low coverage

The various surface sites of In atoms deposited to a coverage of 0.013 monolayer (ML) onto a stepped Cu(100) surface were determined with low-energy ion scattering (LEIS) as a function of deposition temperature. From the fractions of In atoms occupying different sites, observed in the temperature range 63–300 K, the mobilities of In atoms on the terraces and along the steps were deduced. It was found that during the LEIS measurements with 6 keV Ne ions at temperatures below 120 K Cu adatoms were accumulating at the surface. This is explained by diffusion to the surface of interstitial Cu atoms created in the damage cascades. For temperatures above 120 K these Cu adatoms were found to be mobile on the Cu(100) terraces.

Detailed Model for Ion-Beam Induced Adatom Generation

ABSTRACTIn earlier low-energy ion scattering experiments of 6 keV Ne ions on Cu(100), Cu adatoms were observed to appear on the surface. The number of produced adatoms per incoming ion was found to decrease to 50% of its initial value of 3.5 after prolonged irradiation. In this paper we present calculations of the adatom production as a function of irradiation dose. From a comparison with the experimental data, the trapping radius of a vacancy was determined to be 5.4 ± 0.9 Å, in agreement with values reported in the literature.

Modification of the structure and composition of tin oxide by ion implantation

2 μm thick tin oxide films, formed on silicon by plasma-assisted vapour deposition and originally of columnar structure and composition SnO x ( x ∽ 2), were irradiated at room temperature by 80 keV Ne, Ar and Xe ions to fluences in the range 0.5–4 × 10 16 ions/cm 2. The samples were then analysed using RBS, to check their composition and to evaluate the amount sputtered, and by SEM, to examine changes in surface morphology and compaction caused by the ion bombardment. Quantitative values of compaction were obtained by talysurfacing across the implanted/unimplanted boundary in each of the samples. It was found that the irradiation resulted in a compaction of the films which increased in magnitude with ion mass and dose. Preferential sputtering of oxygen from near the surface also occurred leading to an oxygen-deficient region (SnO x , x ∽ 1.3–1.7), the depth of which scales with the projected range of the ions. The reduction in film thickness was considerably greater, in the majority of cases, than that which could be explained by sputtering and appears to scale with the elastic component of the deposited energy.

High resolution electron microscopy of ion-irradiated GdBa2Cu3O7

GdBa2Cu3O7 crystals were irradiated at room temperature with 200 keV Ne ions and 300 keV Xe ions. In situ standard TEM and further HREM studies show two types of extended defects: (i) mobile extended defects, which account for the preferential defect pinning to twin boundaries reported earlier. These defects are rapidly recovered and difficult to observe by HREM investigations; (ii) stable amorphous areas which are clearly identified by HREM observations. Their overlapping and aggregation conceivably lead to amorphization of the sample.

Ion beam induced modification of energy of adhesion for copper films on Al 2O 3 substrates

Thin films deposited on inert substrates can break up into an array of beads or islands after prolonged heating at temperatures well below the melting point. The energy of adhesion can be readily determined from the shape of equilibrated beads. We have established the feasibility of using this beading technique for direct and quantitative determination of the changes in the energy of adhesion produced by ion bombardment of Cu/ Al2O3 system. Copper films 10 and 20 nm thick were e-beam deposited on prepared substrates of alumina, a and c axis sapphire. After bombardment with 200 keV He or Ne ions, samples were heat treated at 450°C, up to 100 h or at 850°C for 30 h. Beading was studied using scanning electron microscopy. He bombardment had a minor effect on the beading while Ne ions suppressed it dramatically at 450°C, showing complete wetting. The morphology of beads depended on substrate orientation and at higher temperature, it approached the shape of a sessile liquid drop, except for α-axis substrates. The Ne induced adhesion enhancement was reduced at 850°C.

Soft X-rays from neon implanted in aluminium under MeV helium bombardment

Neon gas samples and aluminium samples implanted with 25 keV Ne ions have been irradiated with 2.8 MeV 4He ions. Neon K α 1,2 X-rays spectra from ionization show the presence of wide band structures in implanted metals. Two components are present, a 2 eV wide band attributed to the valence band of overpressurized liquid (or solid) neon and a peak attributed to the presence of gas bubbles. Measurements show the effect of radiation damage. Soft X-ray spectroscopy is presented as a new tool for the study of the physical state of rare gases implanted into metals.

Subsurface compositional modification of Au-Cu alloys sputtered with Ar, Xe, Ne and Kr ions

Surface and subsurface compositional changes in Au-Cu alloys and thin films sputtered with 2 keV Ar, Xe, Ne and Kr ions were observed with low energy (60 eV for Cu and 69 eV for Au) and high energy (239 eV for Au and 920 eV for Cu) Auger peaks at temperatures between liquid nitrogen and room temperature. For a Au 0.56Cu 0.44 alloy, Au enrichment at the surface and depletion beneath the surface was observed with high energy as well as low energy Auger peaks. But the compositional change assessed with low energy Auger peaks is greater than that assessed with high energy peaks. This was also calculated with the simulation of sputtering including ion radiation-enhanced segregation and diffusion. This shows clearly that the Gibbsian segregation plays an important role in composition changes at the surface and subsurface of the ion-sputtered alloy. Compositional changes of Au-Cu thin film alloys prepared by the co-evaporation technique were also observed following sputtering with Ar, Xe, Ne and Kr. Except in the case of Xe, the coevaporated composition was preserved during sputtering at low temperatures (<-120°C).

Kinetic energy versus total scattering angle diagrams for large-angle surface ion scattering

Based on the chain model, the relation between kinetic energies of reflected ions and total scattering angles has been studied for near 180° surface scattering in a non-vibrating system. The calculations are performed for 5 keV Ne ions incident on a Ti atomic row of a TiC(111) surface. For a large angle of incidence, two interesting features are found: (1) The upper limit of the total scattering angle exceeds 180°. (2) The peaks of the triple collisions besides the quasi-single (QS) and quasi-double (QD) peaks are observed at energies lower than the QS peaks in the energy spectra of large-angle backscattered ions.

Kinetic energy versus total scattering angle diagrams for large-angle surface ion scattering

Abstract Based on the chain model, the relation between kinetic energies of reflected ions and total scattering angles has been studied for near 180° surface scattering in a non-vibrating system. The calculations are performed for 5 keV Ne ions incident on a Ti atomic row of a TiC(111) surface. For a large angle of incidence, two interesting features are found: (1) The upper limit of the total scattering angle exceeds 180°. (2) The peaks of the triple collisions besides the quasi-single (QS) and quasi-double (QD) peaks are observed at energies lower than the QS peaks in the energy spectra of large-angle backscattered ions.

Application of the transparency model to the description of single-crystal sputtering at small sliding angles of incident ions

Abstract A model for crystal transparency is used to calculate the single-crystal sputtering yields at small sliding angles of ion incidence onto a target. The results of calculating the angular dependences of the (100) copper crystal face sputtering yield under 30 and 15 keV Ar and Ne ion bombardment prove to be in a satisfactory agreement with the available experimental data.