Increasing Ion Dose Research Articles

Control of superconductivity in MgB2 by ion bombardment

The superconducting properties of MgB2 can be modified via controlled introduction of lattice defects by ion bombardment. Here, magnetometry and Raman spectroscopy are used to study ∼160 nm-thick MgB2 films bombarded at room temperature with megaelectronvolt-energy He, Ar, or Xe ions. Ion bombardment leads to a monotonic reduction in the critical superconducting transition temperature, transition width, and critical current density. There is a clear collision cascade density effect, whereby radiation-induced changes, once normalized to the number of atomic displacements generated, are greater for heavier ions. The sharpening of the superconducting transition with increasing ion dose suggests improved homogeneity of irradiated films. The suppression of superconducting properties correlates with the growth of defect signatures revealed by Raman spectroscopy. Superconducting properties can be recovered by annealing at relatively low temperatures of 500 °C, even for films exposed to high doses of heavy ions. These results have direct implications for the performance of MgB2 in radiation environments and understanding its defect-mediated superconductivity.

Copper ion implantation effects in ZnO film deposited on flexible polymer by DC magnetron sputtering

Zinc oxide (ZnO) films were deposited on flexible polyethylene terephthalate (PET) substrates by direct current (DC) magnetron sputtering in ArO2 environment. Singly charged copper ions (Cu+1) of doses 1 × 1011, 1 × 1012, 1 × 1013, and 1 × 1014 ions/cm2 were implanted in ZnO films using Pelletron Accelerator at room temperature. X-ray diffraction revealed c-axis oriented ZnO film having hexagonal wurtzite structure. The crystallite size of ZnO film was decreased with increasing Cu+1 dose up to 1 × 1012 ions/cm2, and then it started increasing with further increase of ion dose. The decrease in crystallite size was attributed to ion-induced lattice disorder in the film whereas the increase in crystallite size at higher doses (>1 × 1012 ions/cm2) was associated with the thermally induced annihilation of defects. The lattice parameter of ZnO was decreased after Cu+1 implantation at different doses that was ascribed to the lower ionic radius of Cu+1 as compared to the Zn+2. The UV–Vis spectroscopic analysis revealed a decrease in band gap of ZnO film after Cu+1 implantation up to 1 × 1013 ions/cm2. However, by increasing ions dose to 1 × 1014 ions/cm2, the band gap was increased. The electrical resistivity of ZnO film was increased at 1 × 1011 ions/cm2 and then decreased with further increase of the dose value.

Reduction and Increase in Thermal Conductivity of Si Irradiated with Ga+ via Focused Ion Beam.

Focused ion beam (FIB) technology has become a valuable tool for the microelectronics industry and for the fabrication and preparation of samples at the micro/nanoscale. Its effects on the thermal transport properties of Si, however, are not well understood nor do experimental data exist. This paper presents a carefully designed set of experiments for the determination of the thermal conductivity of Si samples irradiated by Ga+ FIB. Generally, the thermal conductivity decreases with increasing ion dose. For doses of >1016 (Ga+/cm2), a reversal of the trend was observed due to recrystallization of Si. This report provides insight on the thermal transport considerations relevant to engineering of Si nanostructures and interfaces fabricated or prepared by FIB.

Swift heavy-ion irradiation of graphene oxide: Localized reduction and formation of sp-hybridized carbon chains

Herein, we report the fabrication of nanometer-sized reduced graphene oxide (rGO) spots by swift heavy-ion (SHI) bombardment. Such structures can be considered graphene quantum dots (QDs) embedded in a non-conducting matrix. Both the number density and the diameter of the rGO spots can be tailored by a suitable choice of irradiation parameters (i.e., ion type, fluence, and energy). The degree of graphene oxide defunctionalization by SHIs with different energies scaled well with the deposited electronic energy density. The resistance of the samples decreased nonlinearly with increasing ion dose and, at fluences above 1013 ions/cm2, was orders of magnitude lower than the initial value. An increase in the electronic stopping power of the ion resulted (i) in suppression of the structural ordering at low fluences and (ii) in increased amorphization efficiency and formation of sp-hybridized carbon chains of both polyynes and polycumulenes at high fluences. A hypothesis suggesting that the sp-C chains are bridges joining opposite sides of nanoholes created inside the track core and thus assuming the formation of a coupled QD-antidot system is presented. These phenomena were found to be absent in comparative experiments with 200 keV Xe ion irradiation, i.e., in the nuclear stopping regime.

Nanoporous structure formation on the surface of Ge by ion beam irradiation

The ion beam induced formation of nanoporous structures on the surface of Ge under controlled conditions of ion dose, flux, and irradiation angle using a focused ion beam was investigated by electron microscopy. The formation of large-scale nanoporous structures on the surface of the Ge specimens with increasing ion dose and increasing flux was observed via nanostructural characterization using scanning electron microscopy and transmission electron microscopy (TEM). Compared with the structure formed under irradiation at 0°, that formed under irradiation at 45° was tilted and large-scale. These results suggest that the number of point defects per unit volume of surface is important for the formation of a nanoporous structure. TEM observations revealed that the nanoporous structural features formed during the initial process were not voids but surface roughness. This mechanism differs from the nanoporous structure formation mechanism of GaSb and InSb. The growth of the nanoporous structure in the vertical direction was promoted until the ion dose was 1 × 1021 ions/m2 or greater. At ion doses greater than 1 × 1021 ions/m2, the growth was saturated. The wall thickness remained almost constant with increasing ion dose.

3 MeV proton irradiation effects on surface, structural, field emission and electrical properties of brass

Abstract Ion-induced modifications of brass in terms of surface morphology, elemental composition, phase changes, field emission properties and electrical conductivity have been investigated. Brass targets were irradiated by proton beam at constant energy of 3 MeV for various doses ranges from 1 × 1012 ions/cm2 to 1.5 × 1014 ions/cm2 using Pelletron Linear Accelerator. Field Emission Scanning Electron Microscope (FESEM) analysis reveals the formation of randomly distributed clusters, particulates, droplets and agglomers for lower ion doses which are explainable on the basis of cascade collisional process and thermal spike model. Whereas, at moderate ion doses, fiber like structures are formed due to incomplete melting. The formation of cellular like structure is observed at the maximum ion dose and is attributed to intense heating, melting and re-solidification. SRIM software analysis reveals that the penetration depth of 3 MeV protons in brass comes out to be 38 µm, whereas electronic and nuclear energy losses come out to be 5 × 10−1 and 3.1 × 10−4 eV/A respectively. The evaluated values of energy deposited per atom vary from 0.01 to 1.5 eV with the variation of ion doses from 1 × 1012 ions/cm2 to 1.5 × 1014 ions/cm2. Both elemental analysis i.e. Energy Dispersive X-ray spectroscopy (EDX) and X-ray Diffraction (XRD) supports each other and no new element or phase is identified. However, slight change in peak intensity and angle shifting is observed. Field emission properties of ion-structured brass are explored by measuring I-V characteristics of targets under UHV condition in diode-configuration using self designed and fabricated setup. Improvement in field enhancement factor (β) is estimated from the slope of Fowler-Nordheim (F-N) plots and it shows significant increase from 5 to 1911, whereas a reduction in turn on field (Eo) from 65 V/µm to 30 V/µm and increment in maximum current density (Jmax) from 12 µA/cm2 to 3821 µA/cm2 is observed. These enhancements in field emission characteristics are correlated with the growth of surface structures, specifically agglomers which are responsible for electric field convergence. Electrical by four probe method has been correlated with maximum current density and decreasing trend is observed with increasing ion doses.

Study of wettability and cell viability of H implanted stainless steel

In the present work, the effect of hydrogen ion implantation on surface wettability and biocompatibility of stainless steel is investigated. Hydrogen ions are implanted in the near-surface of stainless steel to facilitate hydrogen bonding at different doses with constant energy of 500 KeV, which consequently improve the surface wettability. Treated and untreated sample are characterized for surface wettability, incubation of hydroxyapatite and cell viability. Contact angle (CA) study reveals that surface wettability increases with increasing H-ion dose. Raman spectroscopy shows that precipitation of hydroxyapatite over the surface increase with increasing dose of H-ions. Cell viability study using MTT assay describes improved cell viability in treated samples as compared to the untreated sample. It is found that low dose of H-ions is more effective for cell proliferation and the cell count decreases with increasing ion dose. Our study demonstrates that H ion implantation improves the surface wettability and biocompatibility of stainless steel.

Evolution of ion damage at 773K in Ni- containing concentrated solid-solution alloys

Quantitative analysis of the impact of the compositional complexity in a series of Ni-containing concentrated solid-solution alloys, Ni, NiCo, NiFe, NiCoCr, NiCoFeCr, NiCoFeCrMn and NiCoFeCrPd, on the evolution of defects produced by 1 MeV Kr ion irradiation at 773 K is reported. The dynamics of the evolution of the damage structure during irradiation to a dose of 2 displacements per atom were observed directly by performing the ion irradiations in electron transparent foils in a transmission electron microscope coupled to an ion accelerator. The defect evolution was assessed through measurement of the defect density, defect size and fraction of perfect and Frank loops. These three parameters were dependent on the alloying element as well as the number of elements. The population of loops was sensitive to the ion dose and alloy composition as faulted Frank loops were observed to unfault to perfect loops with increasing ion dose. These dependences are explained in terms of the influence of each element on the lifetime of the displacement cascade as well as on defect formation and migration energies.

The Effects of Nitrogen on Structure, Morphology and Electrical Resistance of Tantalum by Ion Implantation Method

In this paper, samples of tantalum with purities of 99.99% (0.58 mm thickness) were implanted by Nitrogen ions. The ions’ implantation process was performed at 30 keV and also at different portions which were in the range between 1 × 1017 and 1 × 1018 ions/cm2. The electrical characteristics were investigated on tantalum nitrides and Ta structures by current–voltage. The samples’ surface morphology was also studied through the atomic force microscopy. Through the application of the X-ray diffraction technique, the microstructure of the modified surfaces was obtained after ion implantation. Results of the experiments show the formation of hexagonal tantalum nitride (TaN0.43), as well as the fact that ion dose increases, more interstitial spaces are occupied by nitrogen atoms in the target crystal. The electrical resistivity of the tantalum after nitrogen implantation is found to increase with ion doses. Experimental data demonstrated that different nitrogen dose in ion beam powerfully affects microstructure, phase formation, surface morphology and resistivity of the tantalum. The changes in nitrogen ions were found to be responsible for variation in the resistivity values.

Characterization of the Surface of Silver Ion-Implanted Silicon by Optical Reflectance

The optical reflection of the surface of silicon implanted with Ag+ ions at low energy of 30 keV in a wide dosage range of 5.0·1014–1.5·1017 ion/cm2 was studied in parallel with electron microscopy observation of the samples. It was found that with increasing ion dose of irradiation, the reflection intensity in the UV range of the Si spectrum decreases monotonically due to amorphization and macrostructuring of Si near-surface layer. In the long-wavelength region of the reflection spectra, a selective band with a maximum near 830 nm is recorded due to the plasmon resonance of ion-synthesized Ag nanoparticles.

Photoluminescence and reflectivity studies of high energy light ions irradiated polymethyl methacrylate films

The self-standing films of non-conducting polymethyl methacrylate (PMMA) were irradiated in vacuum using high energy light ions (HELIs) of 50 MeV Lithium (Li+3) and 80 MeV Carbon (C+5) at various ion dose to induce the optical changes in the films. Upon HELI irradiation, films exhibit a significant enhancement in optical reflectivity at the highest dose. Interestingly, the photoluminescence (PL) emission band with green light at (514.5 nm) shows a noticeable increase in the intensity with increasing ion dose for both ions. However, the rate of increase in PL intensity is different for both HELI and can be correlated with the linear energy transfer by these ions in the films. Origin of PL is attributed to the formation of carbon cluster and hydrogenated amorphous carbon in the polymer films. HAC clusters act as PL active centres with optical reflectivity. Most of the harmful radiation like UV are absorbed by the material and is becoming opaque after irradiation and this PL active material are useful in fabrication of optoelectronic devices, UV-filter, back-lit components in liquid crystal display systems, micro-components for integrate optical circuits, diffractive elements, advanced materials and are also applicable to the post irradiation laser treatment by means of ion irradiation.

Ion-beam-induced planarization, densification, and exfoliation of low-density nanoporous silica

Planarization of low-density nanoporous solids is challenging. Here, we demonstrate that ion bombardment to doses of ∼1015 cm−2 results in significant smoothing of silica aerogels, yielding mirror-like surfaces after metallization. The surface smoothing efficiency scales with the ion energy loss component leading to local lattice heating. Planarization is accompanied by sub-surface monolith densification, resulting in surface exfoliation with increasing ion dose. These findings have implications for the fabrication of graded-density nanofoams, aerogel-based lightweight optical components, and meso-origami.

SURFACE MODIFICATION OF CHEMICAL VAPOR DEPOSITION (CVD) DIAMOND FILM/SI(111) BY IMPLANTATION WITH Fe + B IONS IN CONJUNCTION WITH THEIR MAGNETIC PROPERTIES

Surface Modification of Chemical Vapor Deposition (CVD) Diamond Film/Si(111) by Implantation with Fe+B ions In Conjunction with their Magnetic Properties. Surfcace modification of CVD manufactured diamond films on Si(111) substrate has been performed by means of Fe+B ion implantation followed by Argon ion gas sputtering with acceleration energy 20 keV and ion dose 1x1015 and 1x1016 ions cm-2. Scanning Transmission Electron Microscope (STEM) imaging shows the formation of amorphous carbon layer on top of the diamond film with thickness ca. 100 nm on the implanted sample and ca. 20 nm on the sample without implantion. The morphology and magnetic property of the films surface were characterized by Atomic and Magnetic Force Microscopy (AFM/MFM). The Electron Energy Loss Spectroscopy EELS analysis has revealed amount of Boron atoms distributed homogenously inside the carbon amorphous layer on both samples which is in close agreement to the result of Raman Spectroscopy showing the changes of the Raman spectrum due to implantation. The magnetic properties of the samples after Fe+B ion implantion were additionally investigated by means of Vibrating Sample Magnetometer (VSM). By increasing ion doses at constant energy 20 keV, the magnetoresistance property decreased from +45% on the sample implanted with dose 1x1015 to +8% on the sample implanted with dose 1x1016 ions cm-2.

Irradiation of zinc single crystal with 500 keV singly-charged carbon ions: surface morphology, structure, hardness, and chemical modifications

Cylindrical specimens of (1 0 4) oriented zinc single crystal (diameter = 6 mm and length = 5 mm) were irradiated with 500 keV C+1 ions with the help of a Pelletron accelerator. Six specimens were irradiated in an ultra-high vacuum (~10‒8 Torr) with different ion doses, namely 3.94 × 1014, 3.24 × 1015, 5.33 × 1015, 7.52 × 1015, 1.06 × 1016, and 1.30 × 1016 ions cm−2. A field emission scanning electron microscope (FESEM) was utilized for the morphological study of the irradiated specimens. Formation of nano- and sub-micron size rods, clusters, flower- and fork-like structures, etc, was observed. Surface roughness of the irradiated specimens showed an increasing trend with the ions dose. Energy dispersive x-ray spectroscopy (EDX) helped to determine chemical modifications in the specimens. It was found that carbon content varied in the range 22.86–31.20 wt.% and that oxygen content was almost constant, with an average value of 10.16 wt.%. The balance content was zinc. Structural parameters, i.e. crystallite size and lattice strain, were determined by Williamson–Hall analysis using x-ray diffraction (XRD) patterns of the irradiated specimens. Both crystallite size and lattice strain showed a decreasing trend with the increasing ions dose. A good linear relationship between crystallite size and lattice strain was observed. Surface hardness depicted a decreasing trend with the ions dose and followed an inverse Hall–Petch relation. FTIR spectra of the specimens revealed that absorption bands gradually diminish as the dose of singly-charged carbon ions is increased from 3.94 × 1014 ions cm−1 to 1.30 × 1016 ions cm−1. This indicates progressive deterioration of chemical bonds with the increase in ion dose.

Temperature dependence of nickel ion irradiation damage in GH3535 alloy weld metal

Bulk samples of the GH3535 alloy weld metal have been characterized by transmission electron microscopy, X-ray diffraction and nanoindentation to determine their microstructural evolution and mechanical property changes after 8 MeV Ni3+ ions irradiation. The irradiation experiments were carried out at room temperature and 600 °C, and the ion fluences correspond to a calculated peak damage dose of 0.5, 2 and 12 dpa, respectively. TEM results show the formation of solute clusters or dislocation loops with a number density of approximately 5–14 × 1022 m−3 and sizes between 3 and 10 nm at room temperature due to irradiation induced defects and their evolution. Moreover, the peak shift with increasing ion dose observed in XRD diffraction patterns reveals the lattice distortion induced by ion irradiation. As far as the case of high temperature irradiation, several solute clusters with the same size were observed, whereas the number density was smaller than that of the former case. The calculated indentation values in irradiated samples were found to be much higher in comparison to the unirradiated one, indicating the dose dependent effect of irradiation on hardness. However, in the case of the ion irradiation at 600 °C, the hardness value of samples was significantly decreased. The relationship between ion irradiation induced microstructural evolution and the changes in the mechanical properties of this weld metal is discussed in the context of ion dose and irradiation temperature.

Microstructure analysis of Kr+ irradiation and post-irradiation corrosion of modified N36 zirconium alloy

The irradiation behaviors and corrosion properties of a modified N36 zirconium alloy with the composition of Zr-0.8Sn-1Nb-0.3Fe, developed by Nuclear Power Institute of China, were investigated by transmission electron microscopy and focused ion beam. The polished samples were irradiated by 400keV Kr+ ions up to 25dpa at 360°C using a NEC 400kV ion implanter. The as-received and irradiated samples were corroded for 14days at the water-vapor environment with 10.3MPa and 400°C. The krypton gas bubbles were formed in zirconium matrix and their size was increased with increasing ion dose. Meanwhile, a model that related with gas bubble size and displacement damage had been established. After the corrosion, a layer composed of zircona with different stoichiometric composition was formed on the sample surface. The higher the displacement damage was, the thicker the corrosion layer would be. An empirical equation between oxide thickness and displacement damage was provided. From sample surface to matrix inner, the oxygen content was decreased with increasing corrosion depth. Correspondingly, the zircona was changed from ZrO2 with monoclinic structure on the sample surface to the mixtures of ZrO2 with tetragonal structure and ZrO2 with monoclinic structure in the middle of corrosion layer, and then to ZrO2 with tetragonal structure near alloy matrix.

Modification of the saturation magnetization of exchange bias thin film systems upon light-ion bombardment

The magnetic modification of exchange bias materials by ‘ion bombardment induced magnetic patterning’ has been established more than a decade ago. To understand these experimental findings several theoretical models were introduced. Few investigations, however, did focus on magnetic property modifications caused by effects of ion bombardment in the ferromagnetic layer. In the present study, the structural changes occurring under ion bombardment were investigated by Monte-Carlo simulations and in experiments. A strong reduction of the saturation magnetization scaling linearly with increasing ion doses is observed and our findings suggest that it is correlated to the swelling of the layer material based on helium implantation and vacancy creation.

Optical, structural, and chemical properties of CR-39 implanted with 5.2 MeV doubly charged carbon ions

Poly-allyl-diglycol-carbonate (CR-39) specimens were irradiated with 5.2 MeV doubly charged carbon ions using Pelletron accelerator. Ion dose was varied from 5 × 1013 to 5 × 1015 ions cm−2. Optical, structural, and chemical properties were investigated by UV–vis spectroscopy, x-ray diffractometer, and FTIR/Raman spectroscopy, respectively. It was found that optical absorption increases with increasing ion dose. Absorption edge shifts from UV region to visible region. The measured opacity values of pristine and ion implanted CR-39 range from 0.0519 to 4.7959 mm−1 following an exponential growth (9141%) with the increase in ion dose. The values of direct and indirect band gap energy decrease exponentially with an increase in ion dose by 59% and 71%, respectively. However, average refractive index in the visible region increases from 1.443 to 2.864 with an increase in ion dose, by 98%. A linear relation between band gap energy and crystallite size was observed. Both the number of carbon atoms in conjugation length and the number of carbon atoms per cluster increase linearly with the increase in ion dose. FTIR spectra showed that on C+2 ions irradiation, the intensity of all bands decreases gradually without appearance of any new band, indicating degradation of polymer after irradiation. Raman spectra revealed that the density of −CH2− group decreases on C+2 ions irradiation. However, the structure of CR-39 is completely destroyed on irradiation with ion dose 1 × 1015 and 5 × 1015 ions cm−2.

Nature of gallium focused ion beam induced phase transformation in 316L austenitic stainless steel

The microstructural evolution and chemistry of the ferrite phase (α), which transforms from the parent austenite phase (γ) of 316L stainless steel during gallium (Ga) ion beam implantation in Focused Ion Beam (FIB) instrument was systematically studied as a function of Ga+ ion dose and γ grain orientations. The propensity for initiation of γ → α phase transformation was observed to be strongly dependent on the orientation of the γ grain with respect to the ion beam direction and correlates well with the ion channelling differences in the γ orientations studied. Several α variants formed within a single γ orientation and the sputtering rate of the material, after the γ → α transformation, is governed by the orientation of α variants. With increased ion dose, there is an evolution of orientation of the α variants towards a variant of higher Ga+ channelling. Unique topographical features were observed within each specific γ orientation that can be attributed to the orientation of defects formed during the ion implantation. In most cases, γ and α were related by either Kurdjumov-Sachs (KS) or Nishiyama-Wassermann (NW) orientation relationship (OR) while in few, no known OR's were identified. While our results are consistent with gallium enrichment being the cause for the γ → α phase transformation, some observations also suggest that the strain associated with the presence of gallium atoms in the lattice has a far field stress effect that promotes the phase transformation ahead of gallium penetration.

Ion Irradiation-Induced Magnetic Transition of MnGa Alloy Films Studied by X-Ray Magnetic Circular Dichroism and Low-Temperature Hysteresis Loops

The ion irradiation-induced magnetic transition of $L1_{0}$ -MnGa alloy films was studied in detail by measuring X-ray magnetic circular dichroism (XMCD) and the temperature dependence of their hysteresis loops. The XMCD of (001)-oriented MnGa films exhibited different spectral shapes depending on whether magnetization was parallel or perpendicular to the film plane; that is considered to be the origin of the large perpendicular magnetic anisotropy of the $L1_{0}$ -MnGa. The anisotropy of XMCD spectra was not influenced by the ion irradiation to the MnGa, while the intensity of the XMCD signal decreased with increasing ion dose. From the measurement of hysteresis loops at low temperature, the significant increase of coercivity ${H}_{c}$ in the ion-irradiated MnGa was found by lowering the temperature, while only a slight increase of ${H}_{c}$ was observed in the as-prepared MnGa. These results suggest that the ion-irradiated MnGa film has a composite structure of $L1_{0}$ -ordered MnGa nanocrystals separated by an $A1$ -disordered MnGa matrix, and that increasing the ion dose results in an increase in the volume ratio of $A1$ -MnGa to $L1_{0}$ -MnGa in the film.