Several features of the Ar<Superscript>+</Superscript>-ion irradiation of vanadium and its alloys

Changes in the surface properties of vanadium and its alloys irradiated by Ar⁺ ions with the energy 20 keV, to a dose of 10²² m⁻² at T _irr ≈ 700K have been studied. The radiation effect consists of material surface hardening, increasing the lattice parameters of the irradiated samples, and radiation erosion of the surface layers in the form of flaking. Features of radiation damage to the material’s surface irradiated by gas ions with high sputtering coefficients are discussed.     

Effect of high doses of N<Superscript>+</Superscript>, N<Superscript>+</Superscript> + Ni<Superscript>+</Superscript>, and Mo<Superscript>+</Superscript> + W<Superscript>+</Superscript> ions on the physicomechanical properties of TiNi

The surface layer of an equiatomic TiNi alloy, which exhibits the shape memory effect in the martensitic state, is modified with high-dose implantation of 65-keV N⁺ ions (the implantation dose is varied from 10¹⁷ to 10¹⁸ ions/cm²). TiNi samples are implanted by N⁺, Ni⁺-N⁺, and Mo⁺-W⁺ ions at a dose of 10¹⁷–10¹⁸ cm⁻² and studied by Rutherford backscattering, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction (glancing geometry), and by measuring the nanohardness and the elastic modulus. A Ni⁺ concentration peak is detected between two maxima in the depth profile of the N⁺ ion concentration. X-ray diffraction (glancing geometry) of TiNi samples implanted by Ni⁺ and N⁺ ions shows the formation of the TiNi (B2), TiN, and Ni₃N phases. In the initial state, the elastic modulus of the samples is E = 56 GPa at a hardness of H = 2.13 ± 0.30 GPa (at a depth of 150 nm). After double implantation by Ni⁺-N⁺ and W⁺-Mo⁺ ions, the hardness of the TiNi samples is ∼2.78 ± 0.95 GPa at a depth of 150 nm and 4.95 ± 2.25 GPa at a depth of 50 nm; the elastic modulus is 59 GPa. Annealing of the samples at 550°C leads to an increase in the hardness to 4.44 ± 1.45 GPa and a sharp increase in the elastic modulus to 236 ± 39 GPa. A correlation between the elemental composition, microstructure, shape memory effect, and mechanical properties of the near-surface layer in TiNi is found.     

Surface composition modification of tungsten higher oxide under He<Superscript>+</Superscript> ion bombardment

The surface reduction of higher oxide WO₃ under irradiation by He⁺ ions with the energies 1 and 3 keV in a high vacuum is investigated by X-ray photoelectron spectroscopy. It is found that lower WO₂ and intermediate WO _x (2 < x < 3) oxides form first in WO₃ surface layers under He⁺ ion bombardment, and with an increase in the irradiation dose metallic tungsten forms. It is shown that the degree of irradiated oxide surface metallization increases with an increase in the energy of the bombarding He⁺ ions. A comparison of WO₃ oxide surface composition modification under He⁺ and Ar⁺ ion irradiation is presented.     

Investigating <Superscript>64</Superscript>Zn<Superscript>+</Superscript> ion-doped silicon under conditions of hot implantation

The results from visualizing the structure and identifying the composition of surface and the nearsurface layers of CZ n-Si (100) implanted by ⁶⁴Zn⁺ ions with dose of 5 × 10¹⁶ cm^–2 and energy of 50 keV under conditions of a substrate heated to 350°C are presented. It is found that there is no Si amorphization after Zn implantation, and only one layer 200 nm thick forms and is damaged because of radiation-induced defects. Zn nanoparticles 10–100 nm in size are found on a sample’s surface and in its near-surface layer. Computer analysis and mapping of the elemental and phase composition of FIB crater walls and the surface show that the main elements (54%) in the sample near-surface layer are Si, O, and Zn. The presence of ZnO phase is recorded to a depth of 20 nm in the sample.     

Modification of GaAs by medium-energy N<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> ions

The modification of GaAs with a 2500-eV beam containing N ₂ ⁺ and Ar⁺ ions is examined with Auger electron spectroscopy. Most implanted nitrogen atoms are found to react with the matrix, substituting arsenic atoms to produce a several-nanometer-thick layer of the single-phase GaAs_1−x N_x (x=6%) solid solution. The GaN phase is absent. Displaced arsenic atoms and nitrogen atoms unreacted with the matrix are present in the layer and on its surface. The former segregate, whereas the latter form molecules.     

Resonator effects of Ar<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> ionic excimer pumped by electron beam

The third continuum of argon from 200 to 270 nm is obtained by electron beam pumping argon. With the front mirror and the rear mirror, the resonator effects are observed at 240 and 220 nm. Compared with the intensity of fluorescence, the intensity near 240 nm increases more than 10 times when the resonator is formed. In order to explain the origin of the continuum, the kinetic model on Ar₂⁺ and Ar₂²⁺ ionic excimers pumped by electron beam is built and calculated. Based on the theoretical results, the Ar₂⁺ ionic excimer should be responsible for the continuum around 240 nm.     

Kinetics of radiation-induced segregation in 12Cr-MoWSiVNbB steel after Ni<Superscript>++</Superscript> and He<Superscript>+</Superscript> ion irradiation

Ferritic-martensitic 12Cr-MoWSiVNbB (EP-823) steel was irradiated with 7 MeV Ni⁺⁺ ions within fluence interval 5 × 10¹⁸−5.4 × 10¹⁹ ions/m² and with 30 and 70 keV He⁺ ions within fluence interval 10²⁰–10²¹ ions/m² at 500°C. Results from a comparative analysis of Cr and Si radiation-induced segregation profiles near the surface are presented. Dependence of the amount of surface segregation on damage dose, displacement generation rate, and radiation-induced point defects concentration is established.     

The characteristic spectral lines of target atoms in the impact of<Superscript>40</Superscript>Ar<Superscript><Emphasis Type="Italic">q</Emphasis>+</Superscript> ions on metal surfaces

We report the measured results of the 200 nm—1000 nm characteristic spectral lines of target atoms when highly charged ions⁴⁰Ar ^q+(6≤q≤14) with the same kinetic energy and⁴⁰Ar⁶⁺ with different kinetic energies are incident upon Al, Ti, Ni, Ta and Au surfaces, respectively. The results for¹²⁹Xe⁶⁺,¹²⁹Xe¹⁰⁺ and¹²⁹Xe¹⁵⁺ with the same kinetic energy (150 keV) incident upon a Ta surface are also reported. These results show that when the projectile and target are properly selected (⁴⁰Ar¹²⁺ impinges on Al,¹²⁹Xe⁶⁺ impinges on Ta), the spectral intensity of characteristic spectral lines of the target atom is effectively enhanced, and is not strongly dependent on the kinetic energy of the incident ions.     

Polymerization of solid C<Subscript>60</Subscript> under C<Stack><Subscript>60</Subscript><Superscript>+</Superscript></Stack> cluster ion bombardment

The structure transformation occurring in fullerene film under bombardment by 50 keV C₆₀⁺ cluster ions is reported. The Raman spectra of the irradiated C₆₀ films reveal a new peak rising at 1458 cm⁻¹ with an increase in the ion fluence. This feature of the Raman spectra suggests linear polymerization of solid C₆₀ induced by the cluster ion impacts. The aligned C₆₀ polymeric chains composing about 5–10 fullerene molecules have been distinguished on the film surface after the high-fluence irradiation using atomic force microscopy (AFM). The surface profiling analysis of the irradiated films has revealed pronounced sputtering during the treatment. The obtained results indicate that the C₆₀ polymerization occurs in a deep layer situated more than 40 nm below the film surface. The deep location of the C₆₀ polymeric phase indirectly confirms the dominant role of shock waves in the detected C₆₀ phase transformation.     

Theoretical study of charge-exchange and excitation processes in collisions of He<Superscript>+</Superscript> ions with C<Superscript>5+</Superscript>, N<Superscript>6+</Superscript>, and O<Superscript>7+</Superscript> hydrogen-like ions

Data on the cross sections for single-electron charge exchange and excitation in collisions of He⁺ ions with C⁵⁺, N⁶⁺, and O⁷⁺ ions in the He⁺ ion energy range of 0.2–3.0 MeV are obtained for the first time. The cross sections for the single-electron charge transfer into the singlet and triplet 1snl states of C⁴⁺, N⁵⁺, and O⁶⁺ (2≤n≤5) ions and for the 1s → 2p _{0, ±1} electronic excitation of He⁺(1s) ions are calculated. The calculations were performed by solving close-coupling equations on the basis of ten two-electron quasi-molecular states.     

Composition and properties of nanoscale Si structures formed on the CoSi<Subscript>2</Subscript>/Si(111) surface by Ar<Superscript>+</Superscript> ion bombardment

The variations in the composition and structure of CoSi₂/Si(111) surface layers under Ar⁺ ion bombardment with subsequent annealing has been studied. It has been demonstrated that nanocluster phases enriched with Si atoms form on the CoSi₂ surface at low doses D ≤ 10¹⁵ cm^–2, and a pure Si nanofilm forms at high doses.     

Secondary Electron and Negative-Ion Emission from Metal Surface under the Bombardment by Positive Ions (H<Superscript>+</Superscript>, Cl<Superscript>+</Superscript>, HCl<Superscript>+</Superscript>)

A trap for positive ions (H⁺, Cl⁺, HCl⁺) is created within a time-of-flight mass spectrometer. The yields of secondary electrons and negative ions (HCl^?, H^?) formed due to forward and backward scattering of positive ions by steel wire at different kinetic energies (200–750 eV) are measured.     

Electron impact dissociation of ND<Superscript>+</Superscript>: formation of D<Superscript>+</Superscript>

Absolute cross sections for electron impact dissociation of ND⁺ leading to the formation of D⁺ have been measured by applying the animated electron-ion beam method in the energy range from the reaction threshold up to 2.5 keV. The maximum inclusive cross section is observed to be (16.8 ± 0.8) × 10⁻¹⁷ cm² at the electron energy of 65.1 eV. The appearance energy for the D⁺ production is measured to be (4.0 ± 0.5) eV. Collected data are analyzed in details by means of an original procedure in order to determine separately the contributions of dissociative channels. A specific Monte Carlo modeling has been developed, which is proven to reconstruct adequately the dissociative ionization cross section. The present energy thresholds provide information about the ground and excited states of the molecular ion, as well as about the possible population of the vibrational levels. The reaction D₂(v) + N⁺ (or H₂(v) + N⁺) is a probable source for that population and it constitutes the first step of the molecular activated processes, so the corresponding chain of reactions has to be considered to study the chemistry of plasma sources.     

Study of interface mixing induced by Ar<Superscript>+</Superscript> ion irradiation on Ag–Ge bilayer system

A 400 keV ⁴⁰Ar⁺ ion beam was utilized to induce mixing between two thin layers of Ag and Ge. Rutherford Backscattering Spectrometry and Electrical Resistivity Measurements were employed as probes to investigate the kinetics of ion mixing. The intermixed region was studied at several fluences up to 1.7×10¹⁷ ions/cm² at a constant flux of 0.25 μA/cm². The “RUMP” simulation computer code was used to assist in the evaluation of the experimental results from the spectra. The analysis of the Rutherford Backscattering Spectrometry spectra shows that increasing the Ar⁺ fluence enhances the Ag–Ge intermixing. To describe the mixing process, mixing rate parameters were calculated and compared with the theoretical models’ predictions. Børgesen’s local thermal spike model was found to accurately predict the diffusion in the Ag–Ge interface. An increase in the electrical resistivity of the film was detected during irradiation.     

Thermally stimulated desorption of Na<Superscript>+</Superscript> and Cs<Superscript>+</Superscript> ions from a NaAu alloy film grown on Au

The formation of Na⁺ and Cs⁺ ions on and their thermal desorption from the surface of a NaAu alloy film grown on metallic gold are studied. It is shown that thermionic emission from insulator-coated metallic substrates is governed by a sequence of processes, such as diffusion of Na and Cs adatoms into the film, ionization of these atoms at the insulator-metal interface, diffusion of the resulting ions toward the surface, and desorption of the ions. The effect of weak electric fields on ion diffusion and desorption is investigated.     

Evolution of Phase Composition and Structure in Sapphire Implanted with <Superscript>64</Superscript>Zn<Superscript>+</Superscript> Ions and Heat-Treated in Oxygen

Single-crystal Al₂O₃ substrates are implanted with ⁶⁴Zn⁺ ions using doses of 5 × 10¹⁶ cm^–2 and an energy of 100 keV. The samples are annealed in oxygen with a stepwise increase in temperature from 400 to 1000°C. The changes on the surface and in the bulk of the sample are analyzed via scanning electron microscopy, energy-dispersive analysis, transmission electron microscopy, and Auger electron spectroscopy.     

Kinetics of Rb<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and Rb<Superscript>+</Superscript> formation in laser-excited rubidium vapor

We have studied the formation of the molecular ion Rb₂⁺ and the atomic ion Rb⁺. These are created in laser excited rubidium vapor at the first resonance, 5s–5p and 5p-nl transitions. A theoretical model is applied to this interaction to explain the time evolution and the laser-power dependence of the population density of Rb⁺ and Rb₂⁺. A set of rate equations which describe: the temporal variation of the population density of the excited states; the atomic ion density; and the electron density, were solved numerically under the experimental conditions of Barbier and Cheret. In their experiment the Rb concentration was 1×10¹³cm⁻³ and the laser power was taken to be 50–500 mW at vapor temperature = 450 K. The results showed that the main processes for producing Rb₂⁺ are associative ionization and Hornbeck-Molnar ionization. The calculations have also showed that, the atomic ions Rb⁺ are formed through the Penning Ionization (PI) and photoionization processes. Moreover, a reasonable agreement between the experimental results and our calculations for the ion currents of the Rb⁺ and Rb₂⁺ is obtained.      

Effect of the dose and energy of Ar+ ions on the surface properties of vanadium and its alloys

The features of processes occurring on the surface of vanadium and its alloys irradiated using the ILU ion-beam accelerator with Ar⁺ ions at an energy of 20 and 40 keV up to doses of 5.0 × 10²¹ m^?2 and 1.0 × 10²² m^?2 at T _irr ≈ 700 K are studied. The effect of the dose and energy of implanted ions on the surface hardness is obtained. The thickness of the hardened layer is more than two orders of magnitude higher than the theoretical and experimental projected range of Ar⁺ ions at an energy of 20 and 40 keV in vanadium. Structural changes in the surface layers, which are expressed in a change in the intensity of reflections from a number of planes and an increase in the crystal-lattice parameter of the irradiated materials, are also observed.     

Re-dispersible Li<Superscript>+</Superscript> and Eu<Superscript>3+</Superscript> co-doped CdS nanoparticles: Luminescence studies

Re-dispersible CdS, 5 at.% Eu³⁺-doped CdS, 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS nanoparticles in organic solvent are prepared by urea hydrolysis in ethylene glycol medium at a low temperature of 170°C. CdS nanoparticles have spherical shape with a diameter of ∼80 nm. The asymmetric ratio (A ₂₁) of the integrated intensities of the electrical dipole transition to the magnetic dipole transition for 5 at.% Eu³⁺-doped CdS is found to be 3.8 and this ratio is significantly decreased for 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS (A ₂₁ = 2.6). It establishes that the symmetry environment of Eu³⁺ ion is more favored by Li-doping. Extra peak at 550 nm (green emission) could be seen for 2 and 5 at.% Eu³⁺ co-doped CdS. Also, the significant energy transfer from host CdS to Eu³⁺ is found for 5 at.% Eu³⁺-doped CdS compared to that for 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS.      

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript> selectivity in the formation of ion pairs in aqueous solutions

The integral equations of liquids (RISM) and molecular dynamics method were used to calculate the mean force potential for the SO₃ and COO hydrophilic groups and the CH₃ hydrophobic group in the acetate, methyl sulfonate, and hydrosulfate anions, which form ion pairs with sodium and potassium cations in water. The carboxyl group selectively binds sodium ions from solutions containing Na⁺ and K⁺ ions, in spite of their equal charges, because the potassium ion experiences stronger steric hindrances near this group compared with sodium. The biophysical consequences of the revealed selectivity are discussed.