Increasing Ion Dose Research Articles

Modifications in surface, structural and mechanical properties of brass using laser induced Ni plasma as an ion source

Laser induced Ni plasma has been employed as source of ion implantation for surface, structural and mechanical properties of brass. Excimer laser (248 nm, 20 ns, 120mJ and 30 Hz) was used for the generation of Ni plasma. Thomson parabola technique was employed to estimate the energy of generated ions using CR39 as a detector. In response to stepwise increase in number of laser pulses from 3000 to 12000, the ion dose varies from 60 × 1013 to 84 × 1016 ions/cm2 with constant energy of 138 KeV. SEM analysis reveals the growth of nano/micro sized cavities, pores, pits, voids and cracks for the ion dose ranging from 60 × 1013 to 70 × 1015 ions/cm2. However, at maximum ion dose of 84 × 1016 ions/cm2 the granular morphology is observed. XRD analysis reveals that new phase of CuZnNi (200) is formed in the brass substrate after ion implantation. However, an anomalous trend in peak intensity, crystallite size, dislocation line density and induced stresses is observed in response to the implantation with various doses. The increase in ion dose causes to decrease the Yield Stress (YS), Ultimate Tensile Strength (UTS) and hardness. However, for the maximum ion dose the highest values of these mechanical properties are achieved. The variations in the mechanical properties are correlated with surface and crystallographical changes of ion implanted brass.

Enhancement of Curie Temperature (T c) and Magnetization of Fe-Ni Invar alloy Through Cu Substitution and with He+2 Ion Irradiation

The magnetic properties of ternary Fe-Ni-Cu invar alloys are affected by ion irradiation, which goes on increasing with increasing ion fluence (Φ), and by increasing Cu content. In the present study, the ions used are He+2 with 2 MeV energy and with 1 × 1013 cm−2, 1 × 1014 cm−2, 5 × 1014 cm−2, 1 × 1015 cm−2 and 5 × 1015 cm−2 fluence (dose) for irradiation purpose. The face centered cubic structure of the alloy was investigated after ion irradiation using x-ray diffraction (XRD) and found unchanged. However, the peaks become broader with increasing ion dose. Additionally, the lattice fluctuations were observed in XRD study. Curie temperature (Tc) is also increased after irradiation. Many factors are considered here for the reason for increasing Tc, such as the stopping of incident ions, atomic mixing effect at micro scale level owing to ion irradiation, which might change local concentration and ordering already reported in diffuse scattering, and as a result the Fe-Fe interatomic distance and the Fe-Fe coupling are changed. A comparative study shows that the effect of irradiation on Tc and magnetization with increasing ion fluence is more distinctive than the addition of Cu.

Improved cellular response of ion modified poly(lactic acid-co-glycolic acid) substrates for mouse fibroblast cells

In this report, the effects of argon (Ar) ion irradiation on poly(lactic acid-co-glycolic acid) (PLGA) substrates on biocompatibility were studied. PLGA scaffold substrates were prepared by spin coating glass surfaces with PLGA dissolved in anhydrous chloroform. Previously, we showed that surface modifications of PLGA films using ion irradiation modulate the inherent hydrophobicity of PLGA surface. Here we show that with increasing ion dose (1×1012 to 1×1014ions/cm2), hydrophobicity and surface roughness decreased. Biocompatibility for NIH3T3 mouse fibroblast cells was increased by argon irradiation of PLGA substrates. On unirradiated PLGA films, fibroblasts had a longer doubling time and cell densities were 52% lower than controls after 48h in vitro. Argon irradiated PLGA substrates supported growth rates similar to control. Despite differences in cell cycle kinetics, there was no detectible cytotoxicity observed on any substrate. This demonstrates that argon ion irradiation can be used to tune the surface microstructure and generate substrates that are more compatible for the cell growth and proliferation.

Kinetics modeling of precipitation with characteristic shape during post-implantation annealing

In this study, we investigated the precipitation with characteristic shape in the microstructure during post-implantation annealing via a theoretical modeling approach. The processes of precipitates formation and evolution during phase separation were based on a nucleation and growth mechanism of atomic diffusion. Different stages of the precipitation, including the nucleation, growth and coalescence, were distinctly revealed in the numerical simulations. In addition, the influences of ion dose, temperature and crystallographic symmetry on the processes of faceted precipitation were also demonstrated. To comprehend the kinetic mechanism, the simulation results were further analyzed quantitatively by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The Avrami exponents obtained from the regression curves varied from 1.47 to 0.52 for different conditions. With the increase of ion dose and temperature, the nucleation and growth of precipitations were expedited in accordance with the shortened incubation time and the raised coefficient of growth rate. A miscellaneous shape of precipitates in various crystallographic symmetry systems could be simulated through this anisotropic model. From the analyses of the kinetics, more fundamental information about the nucleation and growth mechanism of faceted precipitation during post-implantation annealing was acquired for future application.

Structures and optical properties of -implanted GaN epi-layers

The implantation damage build-up and optical properties of GaN epitaxial films under ion implantation have been investigated by a combination of Rutherford backscattering in channeling geometry, Raman spectroscopy, UV–visible spectroscopy and transmission electron microscopy. GaN epitaxial films were implanted with 134 keV ions to doses ranging from 3.75 × 1016 to 1.75 × 1017 cm−2 at room temperature or the same dose of 1.5 × 1017 cm−2 at room temperature, 573 and 723 K. The dependence of lattice disorder induced by -implantation on the ion dose can be divided into a three-step damage process. A strong influence of the H concentration on the defect accumulation is discussed. The decrease in relative Ga disorder induced by -implantation is linear with increasing implantation temperature. The absorption coefficient of GaN epitaxial films increases with increasing ion dose, leading to the decrease in Raman scattering spectra of Ga–N vibration. With increasing implantation doses up to 5 × 1016 cm−2, nanoscale hydrogen bubbles are observed in the H deposition peak region. Interstitial-type dislocation loops are observed in the damaged layer located near the damage peak region, and the geometry of the dislocation loops produced by H implantation is analyzed. The surface layer is almost free of lattice disorder induced by -implantation.

Surface hardening in N+ implanted polycarbonate

The influence of low energy nitrogen ions on the surface hardness of polycarbonate has been studied by implanting some of these specimens with 100 keV N+ ions at a beam current of 1 μA/cm2 in the dose range of 1 × 1015 to 1 × 1017 ions cm−2. Knoop microhardness has been found to be increased nearly 24 times at a load of 9.8 mN, for the dose of 1 × 1017 ions cm−2. The structural changes occurred in implanted specimens were studied by Raman analysis, UV–Visible spectroscopy, and X-ray diffraction techniques. Raman studies point toward the formation of a structure resembling hydrogenated amorphous carbon. Disordering in the surface structure (ID/IG ratio) has also been found to increase with ion fluence using Raman technique. UV–Visible spectroscopic analysis shows a clear enhancement in Urbach energy (disorder parameter) from a value of 0.61 eV (virgin sample) to 1.72 eV (at a fluence of 1 × 1017 N+ cm−2) with increasing ion dose. The increase in Urbach energy has been found to be correlated linearly with the increase in Knoop microhardness number. Results of X-ray diffraction analysis also indicate disordering in implanted layers as a result of implantation. In the present work, the possible mechanism behind the formation of harder surfaces due to implantation has been discussed in detail.

Structural Changes of Makrofol Polymer due to Argon Ion Beam Irradiation

Structural Changes of Makrofol Polymer due to Argon Ion Beam Irradiation Argon ion beam extracted from cold conical cathode ion source has been used to induce changes in the structural properties of makrofol polycarbonate specimens. The feasibility of enhancing the physical properties of Makrofol polycarbonate detector using argon ion beam irradiation has been investigated, along with, the effects of irradiation on the structural properties. Samples from Makrofol Polycarbonate sheet of 300 μm thickness were exposed to an argon ions beam in the fluence range 0.5×1017 – 0.5×1019 ions/cm2. Fourier Transform Infrared (FTIR) Spectroscopy was used to study the modifications in the chemical and physical structure of Makrofol polycarbonate specimens. It has been found that the intensities of the characteristic absorption bands were affected predominantly with the increasing ion dose and indicating degradation followed by cross linking of this polymer by argon ions.

Modeling the effects of ion dose and crystallographic symmetry on the morphological evolution of embedded precipitates under thermal annealing

Thermal annealing is one of the most common techniques to synthesize embedded precipitates by ion implantation process. In this study, an anisotropic phase field model is presented to investigate the effects of ion dose and crystallographic symmetry on the morphological formation and evolution of embedded precipitates during post-implantation thermal annealing process. This theoretical model provides an efficient numerical approach to understand the phenomenon of faceted precipitates formation by ion implantation. As a theoretical analysis, the interfacial energy and diffusion kinetics play prominent roles in the mechanism of atomic diffusion for the precipitates formation. With a low ion dose, faceted precipitates are developed by virtue of the anisotropic interfacial energy. As an increase of ion dose, connected precipitates with crystallographic characters on the edge are appeared. For a high ion dose, labyrinth-like nanostructures of precipitates are produced and the characteristic morphology of crystallographic symmetry becomes faint. These simulation results for the morphological evolutions of embedded precipitates by ion implantation are corresponded with many experimental observations in the literatures. The quantitative analyses of the simulations are also well described the consequence of precipitates formation under different conditions.

Local control of magnetic damping in ferromagnetic/non-magnetic bilayers by interfacial intermixing induced by focused ion-beam irradiation

The influence of interfacial intermixing on the picosecond magnetization dynamics of ferromagnetic/non-magnetic thin-film bilayers was studied. Low-dose focused-ion-beam irradiation was used to induce intermixing across the interface between a 10 nm Ni81Fe19 layer and a 2–3 nm capping layer of either Au or Cr. Time-resolved magneto-optical Kerr effect was used to study magnetization dynamics as a function of ion-beam dose. With an Au cap, the damping of the un-irradiated bilayer was comparable with native Ni81Fe19 and increased with increasing ion dose. In contrast, for Ni81Fe19/Cr the damping was higher than that for native Ni81Fe19, but the damping decreased with increasing dose.

Effects of high-energy Si ion-irradiations on optical responses of Ag metal nanoparticles in a SiO2 matrix

Optical responses of pristine Ag metal nanoparticles in a SiO2 matrix have changed drastically upon high-energy Si ion-irradiations. Systematic blueshifts of the quantum surface plasmon resonances and concomitant decrease in the optical absorption resonance intensities with increase of ion dose of Si ions are thought to be due to decrease in size of Ag nanoparticles. Observed shrinking of sizes of Ag metal nanoparticles due to irradiation effects of high-energy Si ions has been elucidated using model calculations. Transmission electron microscopy as well as Raman scattering spectroscopy confirms decrease in size of Ag nanoparticles caused by the Si ion-irradiations.

Helium ion microscope generated nitrogen-vacancy centres in type Ib diamond

We report on position and density control of nitrogen-vacancy (NV) centres created in type Ib diamond using localised exposure from a helium ion microscope and subsequent annealing. Spatial control to <380 nm has been achieved. We show that the fluorescence lifetime of the created centres decreases with increasing ion dose. Furthermore, we show that for doses >1 × 1017 ion/cm2, significant damage of the diamond lattice occurs resulting in fluorescence quenching and amorphization. This places an upper limit on the density of NV centres that can be created using this method.

Nanostructure Variations and Their Effects on Mechanical Strength of Ni-17Mo-7Cr Alloy under Xenon Ion Irradiation

A nickel-base high-temperature alloy (Ni-17Mo-7Cr) has been characterized by nanoindentation and transmission electron microscopy to determine the changes of nanoindentation hardness and microstructural evolution under ion irradiation. Ion irradiation experiments for bulk and thin-foil specimens of Ni-17Mo-7Cr alloy were carried out at room temperature, up to 6.6 dpa, by 7 MeV Xe26+ and 1 MeV Xe20+ ions, respectively. The continuous stiffness measurement (CSM) with a diamond Berkovich indent was used to measure the depth profile of hardness. Nanoindentation results for bulk specimens showed an evident ion irradiation induced hardening phenomenon, and the nanoindentation hardness increases with increasing ion dose. High number density of nano-scale black spots and linear-like defects were observed in thin-foil specimens irradiated at 0.33 and 6.6 dpa, respectively. High-resolution transmission electron microscopy images revealed that the black spots were nano-scale solute clusters and dislocation loops, while the linear-like defects were found to be Ni, Mo and Cr-enrichment regions by using the high-angle annular dark field-scanning transmission electron microscope. The ion irradiation induced defects can be responsible for the hardening of Ni-17Mo-7Cr alloys.

Effect of ion bombardment on the phase composition and mechanical properties of diamond-like carbon films

It is established that the addition of hydrogen to methane in the reaction mixture upon the fabrication of diamond-like carbon films via the plasma-enhanced chemical vapor deposition method decreases residual stresses in the obtained films and significantly reduces their growth rate. The films were investigated via atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Irradiation of the prepared films with P+ and PF 4 + ions results in strong sample swelling with increasing dose, as well as in a decrease in the compressive stress up to transition to tensile one reaching saturation. Moreover, the fraction of sp 3 bonds increases with increasing ion dose while the fraction of sp 2 bonds decreases symmetrically with the processes proceeding faster upon irradiation with molecular ions. Qualitative mechanisms explaining the experimental results are proposed.

In-situ positron lifetime spectroscopy of radiation damage by simultaneous irradiation of slow-positron and ion beams

An in-situ positron analysis system has been developed for positron annihilation lifetime spectroscopy during ion beam irradiation. An electron linear accelerator was used to produce a slow positron beam for this system. Positron lifetime spectroscopy of SiO2/Si and annealed pure Fe samples was successfully demonstrated during simultaneous irradiation with a 150 keV Ar+ beam. The lifetime spectra changed with increasing ion dose, indicating a decrease in ortho-positronium intensity (SiO2) and the decrease in positron diffusion length (Fe).

Tailoring Structural Properties of Polyethylene Terephthalate (PET) by 200 keV Ar<sup>+</sup> Implantation

In the present work, our aim is to reveal the effect of Ar+implantation on the structural behaviour of Polyethylene terephthalate (PET) using Fourier Transform Infrared and UV-Visible Spectroscopic techniques. PET specimens were implanted with 200 keV Ar+ions in the fluence range of 1x1015to 1x1017ions cm-2. The structural changes have been observed due to change in the position and intensity of the bands in the FTIR spectra of both implanted and unimplanted specimens. A continuous decrease in optical energy gap (from 3.63 eV to 1.48 eV) and enhancement in Urbach energy (from 0.29 eV to 3.70 eV) with increasing ion dose have been observed. The structural changes have been correlated with the optical parameters observed in PET specimens as a result of implantation.

A close to unity and all-solar-spectrum absorption by ion-sputtering induced Si nanocone arrays

Si nanocone arrays are formed on Si(100) by Ar(+) ion sputtering combined with metal ion co-deposition. The aspect ratio of Si cone is found to increases steadily with increasing sample temperature, but decreases slowly with increasing ion dose. Furthermore, the height and base diameter of Si cone increase monotonously with increasing dose at a constant temperature. The absorptivity increases in general with increasing aspect ratio and height. A close to unity and all-solar-spectrum absorption by the nanostructured Si is finally achieved, with the absorbance for λ = 350 to 1100 nm being higher than 96%, and that for λ = 1100 to 2000 nm higher than 92%. Photocurrents for different Si samples are also investigated.

RIMS analysis of ion induced fragmentation of molecules sputtered from an enriched U3O8 matrix

Resonance ionization mass spectrometry was used to measure the composition of the sputtered flux from 15 keV Ga+, Au+, Au2 + and Au3 + primary ions impacting a 235U enriched U3O8 standard. We demonstrate that molecular fragmentation decreases as the primary ion mass and nuclearity increases. Stopping and range of ions in matter calculations show that cluster ions (Au2 + and Au3 +) deposit more of their energy via direct knock-ons with near-surface target atoms, whereas monatomic ions (Ga+ and Au+) penetrate much deeper into the target sub-surface region. We correlate these results to the experimental observations by showing that increased cluster ion sputter yields partition the projectile energy over a larger number of sputtered molecules. Therefore, while cluster ions deposit more total energy into the near surface region of the target compared to monatomic ions, the energy per molecule decreases with projectile mass and nuclearity. Less energy per molecule decreases the number of U–O bond breaks and, consequently, leads to a decrease in molecular fragmentation. Additionally, the extent of molecular fragmentation as a function of ion dose was evaluated. We show that molecular fragmentation increases with increased ion dose; primarily as a result of sub-surface chemical damage accumulation. The relative intensity of this effect appears to be projectile independent.

Effect of Cr implantation on structural and optical properties of AlN thin films

Molecular beam epitaxy (MBE) grown AlN thin layer on sapphire substrates have been implanted with Cr+ ions for various dose from 1013 to 1015 cm−2. The analyses were carried out by an X-ray diffractometer (XRD), Raman spectroscopy, a spectrophotometer and spectroscopic ellipsometry (SE) for structural and optical analyses. E2(high) and A1(LO) Raman modes of AlN layer have been observed and analyzed. The behavior of Raman shift and the variation in intensity and in peak width of Raman modes as a function of ions flux are explained on the basis of chromium substituting aluminum atom and implantation-induced lattice damage. Both Raman and X-ray analyses reveal that the incorporation of chromium atoms increases in the host lattice with the increasing of Cr ions fluence. The band gap energy was determined by using transmission spectra. It was found that the band gap energy decreases as the ion dose increases. The band gap of the unimplanted AlN is 6.02 eV and it decreases down to 5.92 eV for the Cr+-implanted AlN with a ion dose of 1×1015 cm−2. Optical properties such as optical constants of the samples were examined by using a spectroscopic ellipsometer. It was observed that the refractive index (n) decreases with the increasing of ion dose.

Duoplasmatron Ion Source를 이용한 Parylene과 Al의 접착력 향상에 관한 연구

Poly-Monochloro-Para-Xylylene (Parylene-C)과 알루미늄 박막과의 접착력을 향상시키기 위하여 Duoplasmatron 이온원을 이용하여 발생시킨 아르곤 이온과 산소 이온을 Parylene-C 표면에 각각 조사하였다. 이온조사 시 이온에너지는 1 kV로 고정하였고 이온조사량은 <TEX>$5{\times}10^{14}$</TEX>에서 <TEX>$1{\times}10^{17}/cm^2$</TEX>까지 변화시켰다. 아르곤 이온과 산소 이온을 조사한 Parylene-C 박막의 물과의 접촉각은 초기 <TEX>$78^{\circ}$</TEX>에서 각각 <TEX>$17^{\circ}$</TEX>와 <TEX>$9^{\circ}$</TEX>까지 감소하였다. X선 광전자 스펙트럼을 이용하여 Parylene-C 표면에 이온빔 조사에 의하여 친수성 그룹이 형성되었음을 알 수 있었으며, 이 친수성 그룹들은 C-O 결합, C=O 결합 그리고 (C=O)-O 결합에 의한 것임을 알 수 있었다. Al 박막과 <TEX>${O_2}^+$</TEX> 이온에 의해 표면 개질된 Parylene-C 박막과의 접착력을 평가하기 위하여 cross cut tape test를 실시한 결과 접착력은 이온조사량이 증가할수록 향상됨을 알 수 있었다. In order to improve the adhesion between poly-monochloro-para-xylylene (Parylene-C) film and Aluminum thin film, the surface of Parylene-C film was irradiated by <TEX>${O_2}^+$</TEX> and <TEX>$Ar^+$</TEX> ion beam generated by duoplamatron ion source. The ion dose of <TEX>$Ar^+$</TEX> and <TEX>${O_2}^+$</TEX> was changed from <TEX>$5{\times}10^{14}$</TEX> to <TEX>$1{\times}10^{17}/cm^2$</TEX> and the ion beam energy was 1 kV. Contact angles of water on Parylene-C modified by <TEX>$Ar^+$</TEX> and <TEX>${O_2}^+$</TEX> ion irradiation decreased from <TEX>$78^{\circ}$</TEX> to around <TEX>$17^{\circ}$</TEX>, and <TEX>$9^{\circ}$</TEX>, respectively. X-ray photoelectron spectroscopy analysis shows that the hydrophilic groups were formed on the surface of Parylene-C by chemical reaction between the unstable chains induced by the ion irradiation and oxygen ions or residual oxygen gas. The hydrophilic groups were identified as C-O bond, C=O bond and (C=O)-O bond. The cross cut tape test which was applied to characterize the adhesion between Al thin film and Parylene-C film modified by <TEX>${O_2}^+$</TEX> ions irradiation shows that the adhesion strength was improved as increasing ion dose.

Ripple rotation on ion sputtered Si (100)

Controllable process of ion sputtered rippling is of significance for the generation of nanostructures on technologically important Si surface. Si(100) was irradiated with 30kV focused Ga+ ions at various incidence angles. It was found that ripple only formed at 30° incidence angle. At low ion dose, ripple with wavelength of 400nm was oriented perpendicular to the ion beam direction. However ripple with larger wavelength of 1μm was rotated with increasing ion dose. The orientation of rotated ripple was observed to be still dependent on the ion beam direction. Such rotated ripple structures can be explained by the nonlinear sputter patterning model.