Kr Bombardment Research Articles

Characteristics of Ag thin films sputter deposited using Ar or Kr gas under different pressure

Recently, we found that Ag thin films with low electrical resistivity could be produced by DC sputtering using Kr gas, whose atomic mass is closer to that of Ag than Ar gas is. In contrast, sputtering using Ar caused trapping of Ar atoms in the film, leading to higher resistivity. In addition, the films sputtered using Kr gas had a much larger crystallite size than those sputtered using Ar gas. In the present study, we clarified the relation between the resistivity and crystallite size by data fitting using an equation proposed in the literature. Ag thin films with a thickness of 150 nm were deposited on glass substrates via DC magnetron sputtering in Ar or Kr gas at a pressure of 2 mTorr. The sputtering voltage was varied from 300 to 1000 V. By fitting the experimental data, we found that the model curves reproduced the experimental results for films sputtered in either Ar or Kr gas, and the electron reflection coefficient at the grain boundaries was the same for both types of film. Thus, the resistivity depends on the crystallite size, and the electron scattering behavior is basically the same for both films. Therefore, it is considered that the main reason for the lower resistivity of the film produced by sputtering in Kr is enhanced grain growth due to suppression of energetic neutral Kr bombardment of the film surface. Although it is known that the Ar gas pressure affects the characteristics of thin films, the effects of pressure have not been well investigated for Kr gas. In the present study, we examined the effect of the Kr gas pressure on the resistivity and crystallite size for sputtered Ag films. The results indicated that there was no significant effect.

Surface modification of RuO2 electrodes by laser irradiation and ion implantation: Evidence of electrocatalytic effects

RuO2 thin layers were deposited on Ti supports by thermal decomposition of RuCl3 at 400°C. Some of the samples were subjected to laser irradiation between 0·5 and 1·5 J cm−2. Some others to Kr bombardment with doses between 1015 and 1016 cm−2. Modifications introduced by the surface treatments were monitored by cyclic voltammetry and O2 evolution in H2SO4 solution. The voltammetric charge increased with surface treatment almost to the same extent for irradiation and bombardment. The electrocatalytic activity turned out much higher for Kr bombarded samples. Raw experimental data were scrutinized in an attempt to separate geometric from electronic factors. True electrocatalytic effects are clearly seen to prevail over purely surface area effects.

Modification of the thermal behavior of iron-carbonitrides induced by Kr bombardment on nitrogen-implanted low carbon steel

The effects of Kr post-bombardment on iron-carbonitrides produced by N-implantation in a low carbon steel are studied by means of conversion electron Mössbauer spectroscopy, nuclear reaction analysis and Rutherford backscattering techniques. The results show that the Kr bombardment strongly affects the thermal behavior of the precipitates, raising their temperature of dissolution. It is suggested that Kr-vacancy complexes are responsible for a nitrogen inhibited diffusion, which turns out in a retention of the iron-carbonitrides at higher temperature.

Displacement damage efficiency in sapphire

The efficiency of point defect production in sapphire by a variety of ion beams has been estimated by monitoring the oxygen vacancy colour centre concentration. Results are presented for H, D, He, B, N, Ne, Ar and Kr bombardment at both room temperature and 77 K. Experimentally determined values of the mean number of oxygen vacancies produced per incident ion are compared with theoretical values. The latter have been computed by solving the Lindhard integral equations to determine the partitioning of damage between the oxygen and aluminium sublattices. The stopping powers and cross sections of Ziegler, Biersack and Littmark have been used in these calculations and give significantly improved estimates of the damage energy. A significant Z1 variation in the damage efficiency is noted for low mass ions. The variation of damage efficiency with incident ion mass is discussed in terms of the primary knock-on spectrum.

Phase separation in ion bombarded FeNi Invar alloys

Studies of the effects of ion bombardment on the phase equilibria and ordering of FeNi alloys with 30.6 and 39.5 at. % Ni were performed. The FeNi samples were bombarded with Ne, Ar, and Kr at different doses and temperatures, and analyzed using the conversion electron Mössbauer spectroscopy (CEMS) technique with 57Fe. The changes in the CEMS spectra of Fe69.4Ni30.6 and Fe60.5Ni39.5 alloys, bombarded with Ne and Ar, indicate a phase separation, but no evidence of ordering. The Kr bombardment does not produce any change, however samples of 39.5 at. % Ni already showing phase separation returned to the single phase state after Kr irradiation. Our results give strong evidences of a prevalence of displacement mixing for bombardment with heavier ions, and of radiation enhanced diffusion for bombardment with lighter ions.

Ion-beam-induced epitaxial crystallization of amorphous GaAs on GaAs(100)

Epitaxial crystallization of deposited amorphous GaAs layers on GaAs(100) up to the surface by bombardments with 400 keV Ar and 400 keV Kr has been successfully performed at a temperature range between 125 and 200°C. Properties of crystal growth were investigated as a function of ion species (Ar and Kr), energy (400 and 800 keV), ion dose, dose rate and substrate temperature by RBS channeling experiments. The growth rate has shown a nearly linear dependence on ion fluence. Ion bombardments below 100°C have induced further amorphization beyond the initial crystal/amorphous interface. On the scale of nuclear energy deposition density, bombardments with higher electronic excitation efficiency give a small increase of the growth rate. Ar bombardments have shown a strong dependence of the growth rate on dose rate, whereas Kr bombardments have revealed a weak dependence. An apparent activation energy of 0.13 ± 0.06 eV for the crystal growth was observed.

Low-energy ion impact desorption cross sections of carbon monoxide from Ni(111)

Abstract We report on the determination of cross sections for desorption (σD) of CO/Ni(111) induced by rare-gas ion (He, Ne, Ar and Kr) bombardment at very low impact energy (10–500 eV). When bombarding the initially fully covered surface, mainly neutral CO was desorbed as was measured by the means of a quadrupole mass spectrometer. The desorption cross section was determined from the exponential decay of the signal of desorbed CO. The experiment was simulated with the dynamic Monte Carlo code TRIDYN [W. Moller, W. Eckstein and J.P. Biersack, Comput. Phys. Commun. 51 (1988) 355], and a very good agreement with σD obtained in the experiment was found. By comparing the calculated values of sputtering yields with σD, the role of recoil implantation and dissociation is discussed.

Conductivity of irradiated Kapton in relation to energy loss of ions and electrons

Abstract We have studied the effects of 2.5 MeV electron irradiation and ion (C, N, F, Si and Kr) bombardment on the electrical conductivity of a polyimide (Kapton-H) with ion energies ranging between 320 keV (N) and 1.25 GeV (Kr). In this wide range of situations we have tried to sort out the respective effects of nuclear and electronic excitation energy losses. For all ion irradiation the conductivity is found to scale with the electronic excitation absorbed dose: i.e. a power law of conductivity versus absorbed dose with an exponent around 9 is observed. At a given absorbed dose (in Gray units) the efficiency of each ion to enhance conductivity is found to be proportional to the electronic energy loss; electrons are much less efficient than ions and thus collective excitations are required to achieve this process. The nuclear energy loss can perhaps play some role at conductivities higher than 100 Ω−1 m−1, but its effects are negligible in the range explored here.

Evidence for diffusive relaxation along the mass asymmetry coordinate in the reaction 197Au + 620 MeV 86Kr

Nuclei have been identified by atomic number up to Z = 50 using ΔE- E telescopes. Kinetic energy spectra, charge and angular distributions have been measured from θ lab = 10–80° . At angles removed from the grazing, a single peak with a mean energy somewhat below the calculated Coulomb energy is observed for all elements. Near the grazing angle, a much broader peak appears, which extends from near elastic energies down to the Coulomb barrier. The charge distributions are peaked near the projectile Z and demonstrate a strong shape dependence on the angle of observation. The angular distributions for elements near the projectile are strongly side peaked; however, as Z is increased or decreased from Z = 36, they gradually become forward peaked. The dependence of the charge and angular distributions on energy dissipation is discussed as well as the patterns observed in the two-dimensional Wilczynski plots. Diffusion model calculations reproduce the experimental data both qualitatively and quantitatively. This successful application of the diffusion model, which was originally developed to explain N, Ne and Ar induced reactions, to the present system is strong evidence that no essential differences exist between the “quasi-fission” process observed in Kr bombardments of heavy targets and the deep-inelastic phenomena seen with lighter ions.

Charge and angular distributions and secondary fission of deep inelastic products from the reaction 197Au + 979 MeV 136Xe 1443 08

Kinetic energy spectra, charge and angular distributions are presented for over 40 elements ( Z = 27−68). The kinetic energy spectra show two distinct components: a deep inelastic one and another from secondary fission of the target-like product. The charge distribution widths are comparable to those observed in Kr bombardments, the angular distributions, however, are more extensively side peaked.

Nuclear relaxation phenomena, diffusion and orbiting in the reaction 107, 109Ag+ 84, 86Kr at 7.2 MeV/nucleon

Charged particles produced from the interaction of a 7.2 MeV/nucleon Kr beam and a natural Ag target have been studied. Fragments up to Z = 50 have been identified by means of a ΔE, E telescope. Kinetic energy distributions, charge distributions and angular distributions have been measured for the individual atomic numbers. The kinetic energy distributions show two components: a high energy “quasi-elastic” component, and a low energy or “relaxed” component close to the Coulomb energy for touching spheres. The charge distribution for this system is very broad and appears to peak at symmetry rather than at the Z of the projectile. The angular distributions for the relaxed component increase monotonically with decreasing angle and are all forward peaked in excess of 1/sinθ. These results are dramatically different from those obtained in Kr bombardments of heavier targets where rather narrow charge distributions and side peaked angular distributions have been observed. The behavior of the reaction Ag+Kr is strongly reminiscent of reactions induced by lighter projectiles. An interpretation of these data in terms of a diffusion process along the mass asymmetry coordinate is presented.

DAMAGE DEPTH DISTRIBUTION OF 15-keV Kr IMPLANTED IN RbCl AS OBTAINED FROM DIFFUSION MEASUREMENTS

The steady-state trapping model for inert-gas diffusion in alkali halides is used to obtain direct experimental information on the damage depth distribution resulting from 15-keV Kr bombardment of RbCl. The average damage concentration falls to 5% at about 350 Å (in rough agreement with random stopping theory) but does not reach 1% until about 650 Å (suggesting that channeled stopping also plays a role). Beyond 1200 Å the implanted damage merges with the background concentration of traps. The traps are shown to be single vacancies by comparing diffusion and conductivity measurements for pure and doped specimens.

Phénomènes de pulvérisation et de distribution en profondeur. Partie IV. Pulvérisation cathodique des oxydes Nb2O5, Ta2O5 et WO3

Three different methods have been used to determine the sputtering yield (S) for 2–30 keV Kr ions on the amorphous anodic oxides Nb2O5, Ta2O5, and WO3. The methods were based on (a) the change of interference colors due to ion bombardment, (b) the perforation of a film of free oxide by an intense ion beam, and (c) the loss of weight of the target. Although S for Kr–WO3 was larger than expected, S for Kr–Nb2O5 and Kr–Ta2O5 was similar to what has been found for other oxides. For example, at 4 keV, S lies between 1.1 and 2.4 atoms/ion for Ar or Kr bombardment of Al2O3, Nb2O5, SiO2, Ta2O5, TiO2, and UO2, whereas it is 6.2 atoms/ion for WO3. The results were interpreted first with a modified form of the theory of Rol et al., in which S is equated to K′E/Rm, where K′ is a constant in Å/keV and Rm is the experimental median range. A good fit between experiment and theory was obtained for K′ equal to 25 for Nb2O5, 13 for Ta2O5, and 51 for WO3. The recently formulated theory of Sigmund, which is in principle completely analytical, was also considered. The observed values of S could be made compatible with the predictions of the theory by taking the following values for Eb, the surface binding energy (units of kcal/gram atom): 100–150 for Nb2O5, 200–250 for Ta2O5, and 45–60 for WO3, We would point out that these latter values are similar to the heats of atomization.

A model for interpreting measurements of the formation of bombardment-induced disorder (Studies on Bombardment-Induced Disorder, IV)

Abstract It is well established that ion bombardment of certain solids leads to the formation of a disordered, often amorphous, phase. Though it is not difficult to describe the fractional disordering (F d) as a function of the depth and of the volume disordered per ion impact, there is still no adequate model which relates F d, to the fraction of inert gas (F IB) that would be released during the thermal annealing or chemical dissolution of the disorder. It is shown that an analytically manageable relation between F d and F IB can be obtained on the basis of four assumptions, the most critical of which is that each ion impact gives rise to a compact, rather than fragmented, disordered region. This relation is shown to be reasonably well obeyed with Al2O3, diamond, and ZrSiO4, making it possible to estimate both the effective depth of disordering (R d) and the size of the disordered regions (V d 1/3). R d for 10-keV Kr bombardment is with all three substances roughly 140 A. Likewise, V d 1/3 is 14–20 A wi...

Low-Energy-Ion-Bombardment Damage in Germanium

The depth of damage induced in Ge films by ions of energies of 200–1000 eV has been measured for He, Ne, Ar, and Kr bombardment, the depth decreasing for heavier ions. The effects exhibit saturation at critical ion dosages. From the results the damaged layer is deduced to consist of two main regions. The one nearer the surface consists mainly of lattice disorder plus trapped gas, which extends to a depth of approximately 10 atomic layers at 1000-eV ion energy. The second, lower region consists mainly of gas atoms trapped in the relatively ordered lattice, the depth of this region increasing with decreasing ion mass. It is concluded that focused atom emission observed in diamond-type lattices is due to the undisturbed surface region structure and focusing is weakened by the damage induced by ion bombardment.