Structural characterizations and the third-order nonlinear optical properties of poly(2,5-didecyloxy)phenylene films modified by N ions implantation

Poly(2,5-didecyloxy)phenylene (PDDOP) films implanted by 30 keV nitrogen ions (N⁺) with the dose rang of 10¹⁵-10¹⁷ ions/cm² were characterized by FTIR-ATR spectra, UV-VIS spectra and X-ray photoelectron spectroscopy, which showed that the C-H bonds of the PDDOP films were largely broken and new bonds like CC, CN and CN were formed as the increasing ion fluence. The third-order nonlinear optical susceptibilities (χ⁽³⁾) were measured by degenerate four-wave mixing (DFWM) technique at 532 nm. The results demonstrated that the (χ⁽³⁾) value of PDDOP films was maximized to 4.19 × 10⁻¹¹ esu at an ion dose of 1.15 × 10¹⁷ ions/cm², which was 4.4 times larger than that of the pristine film. The enhanced third-order nonlinear properties may attribute to the enlarged expansion coefficient and the enhanced absorption coefficient of the bombarded films at proper N⁺ ions dose.     

Surface analytical studies of ion-implanted uni-directionally aligned silicon nitride for tribological applications

Uni-directionally aligned silicon nitride, which exhibits both high strength and high toughness, was implanted with B⁺, N⁺, Si⁺ and Ti⁺ ions at a fluence of 2 × 10¹⁷ ions/cm² and an energy of 200 keV. The effect of ion implantation on the surface structure of the uni-directionally aligned silicon nitride has been studied, in terms of surface analyses such as atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray absorption near edge structure (XANES). It was clarified that the ion-implanted layer was amorphized and the implantation profile showed good agreement with that estimated from a TRIM simulation. It was found that BN and TiN were formed in B⁺- and Ti⁺-implanted Si₃N₄, respectively. There was a slight difference in ion implantation depth among different structures of Si₃N₄, considered to be due to differences in ion channeling.     

The solid film lubrication by carbon ion implantation into α-Al2O3

Improvement in tribological performance by C⁺110 keV implantation can be achieved by having a more graphite-like carbon structure on Al₂O₃. It was shown that fracture toughness and critical peeling load increased for a fluence of 5 × 10¹⁷C⁺/cm² because of residual compression stress and amorphism of surface. The testing in a different implantation dose indicated that the friction and wear mechanism in Optimol fretting wear machine (SRV) was a combination of surface structure and its abrasive wear. Raman shift shows that the amorphous graphite with 5 × 10¹⁷–1 × 10¹⁸ C⁺/cm² implantation dose was formed on Al₂O₃ surface, so that it reduced friction coefficient and wear of Al₂O₃, also it is noticed that the failure of lubrication due to graphite-like film wear is much earlier in the implantation sample with 1 × 10¹⁷C⁺/cm² dose.     

Raman scattering and SEM studies of graphite and silicon carbide surfaces bombarded with energetic protons,deuterons and helium ions

Experimental investigations on the chemical and physical effects of 10–15 keV H₁⁺, D₁⁺ and He⁺ ion bombardments to fluences up to 10¹⁹ ions/cm² on graphite and SiC have been conducted using the techniques of Raman scattering and scanning electron microscopy (SEM). Raman scattering data for ion bombarded graphite reveal the formation of an amorphous surface layer as indicated by the appearance of a broad band in the spectrum centered at 1525 cm which replaces the bands due to microcrystalline carbon at 1585 cm^?1 and 1360 cm^?1. The microcrystalline structure could be partially restored upon vacuum annealing at 1040°C for several hours. A weak, broad band centered at 2150 cm also appears after bombardment which is indicative of the formation of ?C = C? bonds. Surfaces of “KT” SiC were also amorphized on ion bombardment as indicated by changes in the Raman spectra. Chemical trapping of the incident h₁⁺ and D₁⁺ ions to form bulk C-H, C-D and Si-H species was observed. Preferential sputtering of Si leaving a carbon rich surface region also occurred. Blister formation was observed in the SEM studies.     

Effect of Nitrogen Ion Implantation in Copper

In this study, copper samples with 99% purity implanted by N⁺ and N₂ ⁺ ions. Implantation of ions performed at 50 keV and various doses ranging from 1 × 10¹⁷ to 1 × 10¹⁸ ions/cm². Morphology of samples’ surface studied by atomic force microscopy. Microstructure of modified surfaces after ion implantation obtained using grazing incidence X-ray diffraction technique (GIXRD). Formation of both copper nitride and copper trinities confirmed by GIXRD results. Microhardness properties and corrosion behavior of implanted samples measured by Vickers and corrosion test, respectively. The maximum hardness of copper surface observed after nitrogen ion implantation at the dose of 3 × 10¹⁷ ions/cm². Moreover, the results showed that corrosion resistivity significantly increase.     

Rapid-relocation model for describing high-fluence retention of rare gases implanted in solids

It has been known for a long time that the maximum areal density of inert gases that can be retained in solids after ion implantation is significantly lower than expected if sputter erosion were the only limiting factor. The difference can be explained in terms of the idea that the trapped gas atoms migrate towards the surface in a series of detrapping–trapping events so that reemission takes place well before the receding surface has advanced to the original depth of implantation. Here it is shown that the fluence dependent shift and shape of implantation profiles, previously determined by Rutherford backscattering spectrometry (RBS), can be reproduced surprisingly well by extending a simple retention model originally developed to account only for the effect of surface recession by sputtering (‘sputter approximation’). The additional migration of inert gas atoms is formally included by introducing an effective shift parameter Y_eff as the sum of the sputtering yield Y and a relocation efficiency Ψ_rel. The approach is discussed in detail for 145 keV Xe⁺ implanted in Si at normal incidence. Y_eff was found to increase with increasing fluence, to arrive at a maximum equivalent to about twice the sputtering yield. At the surface one needs to account for Xe depletion and the limited depth resolution of RBS. The (high-fluence) effect of implanted Xe on the range distributions is discussed on the basis of SRIM calculations for different definitions of the mean target density, including the case of volume expansion (swelling). To identify a ‘range shortening’ effect, the implanted gas atoms must be excluded from the definition of the depth scale. The impact-energy dependence of the relocation efficiency was derived from measured stationary Xe concentrations. Above some characteristic energy (20 keV for Ar, 200 keV for Xe), Y exceeds Ψ_rel. With decreasing energy, however, Ψ_rel increases rapidly. Below 2–3 keV more than 90% of the reemission of Ar and Xe is estimated to be due to bombardment induced relocation and reemission, only the remaining 10% (or less) can be attributed to sputter erosion. The relocation efficiency is interpreted as the ‘speed’ of radiation enhanced diffusion towards the surface. The directionality of diffusion is attributed to the gradient of the defect density on the large-depth side of the damage distribution where most of the implanted rare gas atoms come to rest. Based on SRIM calculations, two representative parameters are defined, the peak number of lattice displacements, N_d,m, and the spacing, z_r,d, between the peaks of the range and the damage distributions. Support in favour of rapid rare gas relocation by radiation enhanced diffusion is provided by the finding that the relocation efficiencies for Ar and Xe, which vary by up to one order of magnitude, scale as Ψ_rel=kN_d,m/Δz_r,d, independent to the implantation energy (10–80 keV Ar, 10–500 keV Xe), within an error margin of only ± 15%. The parameter k contains the properties of the implanted rare gas atoms. A recently described computer simulation model, which assumed that the pressure established by the implanted gas drives reemission, is shown to reproduce measured Xe profiles quite well, but only at that energy at which the fitting parameter of the model was determined (140 keV). Using the same parameter at other energies, deviations by up to a factor of four are observed.     

Characterization of high energy ion implantation into Ti-6Al-4V

Ion implantation is a surface modification process that can improve the wear, fatigue, and corrosion resistance for several metals and alloys. Much of the research to date has focused on ion energies less than 1 MeV. With this in mind, Ti-6Al-4V was implanted with Al²⁺, Au³⁺, and N⁺ ions at energies of 1.5 and 5 MeV and various doses to determine the effects on strengthening of a high energy beam. A post heat treatment on the specimens implanted with Al²⁺ samples was conducted to precipitate Ti_xAl type intermetallics near the surface. Novel techniques, such as nanoindentation, are available now to determine structure-mechanical property relationships in near-surface regions of the implanted samples. Thus, nanoindentation was performed on pre-implanted, as-implanted, and post heat treated samples to detect differences in elastic modulus and hardness at the sub-micron scale. In addition, sliding wear tests were performed to qualitatively determine the changes in wear performance. The effect of this processing was significant for samples implanted with Al²⁺ ions at 1.5 MeV with a dose higher than 1 × 10¹⁶ ions/cm² where precipitation hardening likely occurs and with N⁺ ions.     

Ion irradiation effects on surface mechanical behavior and shrinkage of hybrid sol-gel derived silicate thin films

A study of the effects of ion irradiation on the surface mechanical behavior and shrinkage of organic/inorganic modified silicate thin films was performed. The films were synthesized by sol-gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. The sol viscosity and the spin velocity were adjusted so that the films produced had a final thickness ranging from 580 to 710 nm after heat treatment. The ion species and incident energies used were selected such that the projected ion range was greater than the film thickness, resulting in fully irradiated films. After heat treatment at 300 °C for 10 min, the films were irradiated with 125 keV H⁺, 250 keV N²⁺ and 2 MeV Cu⁺ ions with fluences ranging from 1 × 10¹⁴ to 1 × 10¹⁶ ions/cm². Both hardness and reduced elastic modulus were seen to exhibit a monotonic increase with fluence for all three ion species. Also, H loss was found to increase monotonically with increase in fluence, while the film thickness was found to decrease with increase in fluence.     

Irradiation effect of carbon negative-ion implantation on polytetrafluoroethylene for controlling cell-adhesion property

We have investigated the irradiation effect of negative-ion implantation on the changes of physical surface property of polytetrafluoroethylene (PTFE) for controlling the adhesion property of stem cells. Carbon negative ions were implanted into PTFE sheets at fluences of 1 × 10¹⁴-1 × 10¹⁶ ions/cm² and energies of 5-20 keV. Wettability and atomic bonding state including the ion-induced functional groups on the modified surfaces were investigated by water contact angle measurement and XPS analysis, respectively. An initial value of water contact angles on PTFE decreased from 104° to 88° with an increase in ion influence to 1 × 10¹⁶ ions/cm², corresponding to the peak shifting of XPS C1s spectra from 292.5 eV to 285 eV with long tail on the left peak-side. The change of peak position was due to decrease of C-F₂ bonds and increase of C-C bonds with the formation of hydrophilic oxygen functional groups of OH and CO bonds after the ion implantation. After culturing rat mesenchymal stem cells (MSC) for 4 days, the cell-adhesion properties on the C⁻-patterned PTFE were observed by fluorescent microscopy with staining the cell nuclei and their actin filament (F-actin). The clear adhesion patterning of MSCs on the PTFE was obtained at energies of 5-10 keV and a fluence of 1 × 10¹⁵ ions/cm². While the sparse patterns and the uncontrollable patterns were found at a low fluence of 3 × 10¹⁴ ions/cm² and a high fluence of 3 × 10¹⁵ ions/cm², respectively. As a result, we could improve the surface wettability of PTFE to control the cell-adhesion property by carbon negative-ion implantation.     

Interaction of fast H1 + ions with metal surfaces in very high vacuum

The results of experiments on the interaction of fast hydrogen ions (H₁ ⁺) with metals forming weak chemical bonds (nickel, stainless steel) and metals forming strong chemical bonds (tantalum and titanium) with hydrogen are presented. The weighing method was used under very-high vacuum conditions to determine the sputtering coefficient of stainless steel bombarded by 35-keV H ₁ ⁺ ions and the penetration coefficient of H ₁ ⁺ ions entering the stainless steel (=9.10^–3, =0.5 for hydrogen concentrations greatly exceeding 10¹⁹ atoms/cm²). The variation of with the density of the hydrogen introduced and the temperature of the metals was determined by the pressure-variation method. The results indicate that metals of the titanium type are suitable for use in capturing fast hydrogen atoms in magnetic traps.Translated from Atomnaya Énergiya, Vol. 21, No. 5, pp. 339–345, November, 1966.     

Effect of H+ and O+ implantation on electrical properties of SrBi2Ta2O9 ferroelectric thin films

The effect on the crystalline structure and ferroelectric properties of ion implantation in SrBi₂Ta₂O₉(SBT) ferroelectric thin films has been investigated. 25 keV H⁺, 140 keV O⁺ with doses from 1 × 10¹⁴/cm² to 3 × 10¹⁵/cm² were implanted into the Sol–Gel prepared SBT ferroelectric thin films. The X-ray diffraction patterns of SBT films show that no difference appears in the crystalline structure of as-H⁺-implanted SBT films compared with as-grown films, H⁺ and O⁺ co-implanted SBT films show an obvious degradation of crystalline structure. Ferroelectric properties measurements indicate that both remnant polarization and coercive electric field of H⁺ implanted SBT films decrease with increasing the implantation dose. The disappearance of ferroelectricity was found in the H⁺, O⁺ co-implanted SBT films at room temperature. The great recovery of hydrogen-induced degradation in SBT films was obtained with O⁺ implantation using a heat-target-implantation technique.     

Investigations of the Scattering of UF5+ Ions by N2 Molecules

The orientation-averaged classical deflection function for scattering of UF₅ ⁺ ions by N₂ molecules is calculated in the collision energy range 2–10 keV, using additive interatomic potentials to calculate the anisotropic interaction of the molecular particles. The elastic scattering cross sections are calculated for ions and the interaction potential of the colliding particles is reconstructed using the Firsov method based on classical mechanics.The results obtained are recommended for determining the isotopic sensitivity of mass spectrometers to be used for analysis of uranium compounds.     

AFM surface investigation of polyethylene modified by ion bombardment

Polyethylene (PE) was irradiated with 63 keV Ar⁺ and 155 keV Xe⁺ ions to fluences of 1 × 10¹³ to 3 × 10¹⁵ cm⁻² with ion energies being chosen in order to achieve approximately the same penetration depth for both species. The PE surface morphology was examined by means of atomic force microscopy (AFM), whereas the concentration of free radicals and conjugated double bonds, both created by the ion irradiation, were determined using electron paramagnetic resonance (EPR) and UV–VIS spectroscopy, respectively. As expected, the degradation of PE was higher after irradiation with heavier Xe⁺ ions but the changes in the PE surface morphology were more pronounced for Ar⁺ ions. This newly observed effect can be explained by stronger compaction of the PE surface layer in the case of the Xe⁺ irradiation, connected with a reduction of free volume available.     

Bombardment of SiC by 10 keV H+: Carbon deposition,surface swelling and changes in surface morphology

SiC surfaces were bombarded by H⁺ at 10 keV to total doses ranging from 0.7 to 25 C/cm² in both high and ultra high vacuum environments. In the former, carbonaceous deposits were observed optically and with AES and electron microprobe analysis. The thickness of these deposits (determined by surface profilometry) increased up to a dose of 3 C/cm² then remained constant. Surface features were observed on these deposits using SEM. In UHV, no deposit was formed, however surface swelling was observed. Surface features were again observed but were qualitatively different than those observed on the carbonaceous deposits. Several possible explanations for these observations are discussed including, in the case of the carbonaceous deposits, a possible phase change from amorphous to ordered occurring in the vicinity of a 3 C/cm² dose.     

Effects of He ion implantation on surface properties of UV-cured Bis-GMA/TEGDMA bio-compatible resins

This work reports on the surface characterisation of 2,2-bis[4-(2-hydroxy-3-methacryloxyl-oxypropoxy)phenyl]propane/triethylene glycol dimethacrylate bio-compatible resins after high energy He⁺ ion implantation treatments. The samples have been characterised by diffuse reflectance FT-IR, X-ray photo-electron spectroscopy, ultramicro-hardness and nano-scratch wear tests. In addition, osteblast cell assays MG-63 have been used to test the bio-compatibility of the resin surfaces after the ion implantation treatments.It has been observed that the maximum surface hardening of the resin surfaces is achieved at He-ion implantation energies of around 50 keV and fluences of 1 × 10¹⁶ cm⁻². At 50 keV of He-ion bombardment, the wear rate of the resin surface decreases by a factor 2 with respect to the pristine resin. Finally, in vitro tests indicate that the He-ion implantation does not affect to the cell-proliferation behaviour of the UV-cured resins.The enhancement of the surface mechanical properties of these materials can have beneficial consequences, for instance in preventing wear and surface fatigue of bone-fixation prostheses, whose surfaces are continuously held to sliding and shearing contacts of sub-millimetre scale lengths.     

Dynamic annealing study of SiC epilayers implanted with Ni ions at different temperatures

SiC epilayers grown on 4H-SiC single crystals were implanted with 850 keV Ni⁺ ions with fluences in the 0.5-9 × 10¹⁶ Ni⁺/cm² range. Most of the samples were implanted at 450 °C, but for comparison some implantations were performed at room temperature (RT). In addition, a post-implantation annealing was performed in N₂ at 1100 °C in order to recover the implantation-induced structural damage. The disorder produced by the implantation at 450 °C and the effect of the post-implantation annealing on the recrystallization of the substrates have been studied as a function of the fluence by Backscattering Spectrometry in channeling geometry (BS/C) with a 3.45 MeV He²⁺ beam. RT as-implanted samples showed a completely amorphous region which extends until the surface when irradiated with the highest dose, whereas in the case of 450 °C implantation amorphization does not occur. In general, partial recovery of the crystal lattice quality was found for the less damaged samples, and the dynamic recovery of the crystalline structure increases with the irradiation temperature.     

Reaction kinetics and the equilibrium state in the system CO2-CO-C under the action of fast electrons

The kinetics of reactions occurring in the system CO₂–CO–C under the action of fast electrons (200 keV) were studied under standard conditions. The temperature was varied within the range 25–400° C; pressure 200–600 mm Hg. The absorbed energy was equal to 3.0·10¹⁵ eV/(cm³· sec) at a current strength of 100 A. The decomposition of CO₂ in the presence of carbon is a zero order reaction, while the decomposition of CO is a first order reaction. The activation energies of both reactions are close to zero. The rate of decomposition of CO₂ and CO is a linear function of the radiation intensity. The steady-state concentration of CO, established in the system after prolonged irradiation, is independent of the radiation intensity, temperature of the reaction zone, and depends on the magnitude of the carbon surface.Translated from Atomnaya Énergiya, Vol. 18, No. 5, pp. 492–496, May, 1965     

A study of the systematic adsorption of radioactive strontium by montmorillonite and its fixation by roasting

The conditions of adsorbing Sr^89,90 by montmorillonite have been studied in detail. Various cations may be arranged in the following order according to their capacity to lower the adsorption of radioactive strontium: Al⁺³ > Fe⁺³ Ba⁺² Ca⁺² > Mg⁺² H⁺ > NH ₄ ⁺ > K⁺ > Na⁺.It has been shown that the adsorption of radioactive strontium by montmorillonite is an ionic exchange process and obeys the law of mass action. The presence of the anions CO₃ ^–2, SO₄ ^–2, and C₂O₄ ^–2 in a solution, which form relatively insoluble salts with strontium, does not change the mechanism of the adsorption, but decreases the quantity of radioactive strontium adsorbed, apparently by forming radioactive colloids.The process of fixing radioactive strontium on montmorillonitic clays during roasting has been studied. Roasting at temperatures above 850–900 ° and extending the roasting time over 1–2 hours do not affect the degree of fixation of radioactive strontium. In these experiments, the activity lost by washing in stream and sea water amounted to about 2%.It is suggested that, up to the beginning of alteration in the crystal lattice (T = 800 °C), the fixation is controlled by the formation of slightly soluble chemical combinations of strontium and the adsorbent. Above 800 °C the process is determined by changes in the crystal lattice and by a gradual vitrification of the mineral.     

The Effect of High Temperature He+ Implantation on Polycrystalline Tungsten in IR-IECF

High temperature (1,100–1,200°C) implantation impact of helium ions in PC Tungsten as a candidate fusion first wall material was studied in the Iranian Inertial Electrostatic Confinement device (IR-IECF). High energetic (100–120?keV) helium ions were applied to produce fluences up to 5?×?10²⁰ He⁺/cm² on the surface of Tungsten. Scanning electron microscopy (SEM) was used to investigate surface morphology changes for various ion fluences. The results showed formation of ‘coral-like’ surface structure and exfoliation and intensive increment in pore formation at high fluence. Microhardness measurements were used to evaluate mechanical properties of implanted tungsten. These investigations revealed that hardness increased with greater He⁺ dose. The phase formation and structural evolution were studied by X-ray diffractometry method.     

Electron-beam radial distribution analysis of irradiation-induced amorphous SiC

Advanced electron microscopy techniques have been employed to examine atomistic structures of ion-beam-induced amorphous silicon carbide (SiC). Single crystals of 4H-SiC were irradiated at a cryogenic temperature (120 K) with 300 keV Xe ions to a fluence of 10¹⁵ cm⁻². A continuous amorphous layer formed on the topmost layer of the SiC substrate was characterized by energy-filtering transmission electron microscopy in combination with imaging plate techniques. Atomic pair-distribution functions obtained by a quantitative analysis of energy-filtered electron diffraction patterns revealed that amorphous SiC networks contain heteronuclear Si–C bonds, as well as homonuclear Si–Si and C–C bonds, within the first coordination shell. The effects of inelastically-scattered electrons on atomic pair-distribution functions were discussed.